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  • 1.
    Alsrup, Tom
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Gherghetta, Alex
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Utveckling av förvaringslösning till byxväskor2021Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Dagens hantverkare har fler verktyg och redskap till sitt förfogande än någonsin förr. För att utföra sitt arbete är hantverkare beroende av sina verktyg och materiel och måste därför alltid ha tillgång till dem. Byxväskor till hantverkare finns i olika slag som ett komplement till fickor på arbetskläder. En variant producerats av Cirk-L men dessa saknar en förvaringslösning för smidig transport. Deras byxväskor är ämnade till att bytas vid behov av olika verktyg och material. Problemet är att det inte finns ett system att förvara byxväskorna och dess innehåll när de inte brukas på arbetsplatser. Syftet med arbetet är att utveckla en lösning som gör det möjligt att smidigt transportera Cirk-Ls byxväskor. Målet är att utveckla en prototyp av en förvaringslösning genom en konceptutvecklingsprocess, materialval, CAD-modellering med detaljritningar samt finita element-analys för hållfasthetsberäkningar.Förvaringslösningen kan bära sex stycken byxväskor utvändigt och diverse verktyg invändigt. Beräkningar utförs med hjälp av MATLAB tillägget CALFEM och simuleras i Creo för att dimensioneras. Materialval för samtliga komponenter utförs med hänsyn till hållbarhet ur ett miljöperspektiv. Processen resulterar i en prototyp som uppfyller de krav och önskemål som formulerats. Förvaringslösningen kan bära sex stycken byxväskor utvändigt och diverse verktyg invändigt.

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  • 2.
    Areitioaurtena, Maialen
    et al.
    Ikerlan Technology Research Centre, Basque Research and Technology Alliance (BRTA). Paseo J.M. Arizmendiarrieta 2, 20500 Arrasate-Mondragon, Spain.
    Segurajauregi, Unai
    Ikerlan Technology Research Centre, Basque Research and Technology Alliance (BRTA). Paseo J.M. Arizmendiarrieta 2, 20500 Arrasate-Mondragon, Spain.
    Fisk, Martin
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Division of Solid Mechanics, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden.
    Cabello, Mario J.
    Ikerlan Technology Research Centre, Basque Research and Technology Alliance (BRTA). Paseo J.M. Arizmendiarrieta 2, 20500 Arrasate-Mondragon, Spain.
    Ukar, Eneko
    Department of Mechanical Engineering, University of the Basque Country, Alameda Urquijo s/n, 48013 Bilbao, Spain.
    Numerical and experimental investigation on the residual stresses generated by scanning induction hardening2022Ingår i: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 108, s. 827-832Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Induction hardening is widely used in the industry as a surface heat treatment that improves the surface and the subsurface hardness of components greatly. The hardened case, which usually is a few mm, highly impacts the surface and structural integrity of the component. In this work, we simulate the scanning induction hardening process by means of finite element modeling. The computed hardness, microstructure, and residual stress profile are compared with experimentally measured data using several surface and subsurface characterization techniques. A very good agreement is found between the simulated and experimentally measured residual stresses, which were characterized by the incremental hole drilling technique.

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  • 3.
    Argatov, Ivan
    Malmö universitet, Biofilms Research Center for Biointerfaces. Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Chongqing University, People’s Republic of China.
    Controlling the adhesive pull-off force via the change of contact geometry2021Ingår i: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 379, nr 2203, artikel-id 20200392Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A first-order asymptotic analysis of the Griffith energy balance in the Johnson-Kendall-Roberts model of adhesive contact under non-symmetric perturbation of the contact geometry is presented. The pull-off force is evaluated in explicit form. A particular case of adhesive contact between a relatively stiff sphere and an elastic half-space is considered under the assumption that the sphere geometry is changed by the application of an arbitrary lateral normal surface loading. The effect of the sphere Poisson's ratio on controlling the adhesive pull-off force is considered.

    This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

  • 4.
    Argatov, Ivan
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    On the Size Effects in Indentation Testing of Elastic Functionally-graded Materials2019Ingår i: New Achievements in Continuum Mechanics and Thermodynamics: A Tribute to Wolfgang H. Müller / [ed] Bilen Emek Abali, Holm Altenbach, Francesco dell'Isola, Victor A. Eremeyev, Andreas Öchsner, Springer, 2019, s. 17-28Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The size effect in the small-scale indentation testing is studied for a functionally-graded material (FGM) whose shear elastic modulus varies according to the exponential law. Under the simplifying assumption of zero Poisson’s ratio, the asymptotic model of the indentation stiffness for an axisymmetric frictionless indenter is developed in the case when the contact radius is small compared to the inhomogeneity characteristic size. The so-called sample size effect is considered on the example of a simply supported FGM plate indented at the center of its top surface. A certain range of applicability of the first-order asymptotic models has been established by comparison with the approximate analytical solution available in the literature.

  • 5.
    Argatov, Ivan I
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Malmö universitet, Biofilms Research Center for Biointerfaces. Technische Universität Berlin.
    Indentation mapping of stretched adhesive membranes2021Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 477, nr 2251, artikel-id 20210349Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Unilateral adhesive contact between a rigid indenter and a uniformly stretched membrane of arbitrary shape is considered. The generalized Johnson-Kendall-Roberts (JKR)-type and Derjaguin- Muller-Toporov (DMT)-type models of non-axisymmetric adhesive contact are presented for short- and long-range adhesion, respectively, and the JKR-DMT transition is established in the framework of the generalized Maugis-Dugdale model. A refined method of matched asymptotic expansions is applied to construct the leading-order asymptotic model for indentation mapping of freestanding two-dimensional materials with an axisymmetric probe, using the approximate analytical solution obtained in explicit form for an infinite membrane in the limit of short-range adhesive contact with an indenter in the form of an elliptic paraboloid. The cases of a spherical indenter and a rectangular membrane are studied in detail.

  • 6.
    Argatov, Ivan I
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Borodich, Feodor M.
    A Macro Model for Electroadhesive Contact of a Soft Finger With a Touchscreen2020Ingår i: IEEE Transactions on Haptics, ISSN 1939-1412, E-ISSN 2329-4051, Vol. 13, nr 3, s. 504-510Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A contact problem of electroadhesion for a conductive elastic body pressed against a rigid plane surface of a dielectric coating covering a conductive substrate is formulated applying the Johnsen-Rahbek approximation for the attractive surface stresses and the Derjaguin-Muller-Toporov (DMT) hypothesis about the influence of the adhesive stresses on the deformable shape of the elastic body. An approximate solution is obtained using the Winkler-Fuss deformation model with the equivalent (contact load dependent) stiffness coefficient evaluated according to the Xydas-Kao soft finger model. The friction force under applied voltage is evaluated as the product of the coefficient of friction and the integral of the macro contact pressure over the apparent contact area. The upper and lower estimates for the friction force are discussed in the case of absence of any external normal load.

  • 7.
    Argatov, Ivan
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Papangelo, A.
    Department of, Mechanical Engineering, University of Technology, Hamburg, Germany; Department of Mechanics, Mathematics and Management, Politecnico di Bari, Bari, Italy.
    Axisymmetric JKR-type adhesive contact under equibiaxial stretching2021Ingår i: The journal of adhesion, ISSN 0021-8464, E-ISSN 1563-518X, Vol. 97, nr 2, s. 140-154Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An axisymmetric frictionless adhesive contact problem for a spherical indenter pressed against an isotropic elastic incompressible half-space under equibiaxial stretching is studied in the framework of the generalized Johnson-Kendall-Roberts (JKR) theory, which accounts for the effect of weak coupling between fracture modes I and II by means of a phenomenological mode-mixity function. The model predicts that contact area can withstand a larger level of the substrate stretch under moderate pre-pulling force. We have provided simple formulas to evaluate the pull-off force and the critical contact radius at the detachment point.

  • 8.
    Argatov, Ivan
    et al.
    Malmö universitet, Biofilms Research Center for Biointerfaces. Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Papangelo, A.
    Ciavarella, M.
    Elliptical adhesive contact under biaxial stretching2020Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 476, nr 2233, artikel-id 20190507Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adhesive contact of the Hertzian indenter with an incompressible elastic substrate bi-directionally stretched along the indenter principal planes of curvature is considered in the Johnson-Kendall-Roberts theoretical framework. An approximate model is constructed by examining energy release rate conditions only on the edges of the minor and major axes of the contact ellipse. The effect of weak coupling between fracture modes I and II is introduced using a phenomenological mode-mixity function. This study was motivated by the need to model a passive-adhesive mechanism in cell mechanics on stretchable substrates.

  • 9. Banks-Sills, Leslie
    et al.
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Svensson, Ingrid
    Eliaz, Noam
    Strain Driven Transport for Bone Modeling at the Periosteal Surface2011Ingår i: Mathematical Biosciences, ISSN 0025-5564, E-ISSN 1879-3134, Vol. 230, nr 1, s. 37-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bone modeling and remodeling has been the subject of extensive experimental studies. There have been several mathematical models proposed to explain the observed behavior, as well. A different approach is taken here in which the bone is treated from a macroscopic view point. In this investigation, a one-dimensional analytical model is used to shed light on the factors which play the greatest role in modeling or growth of cortical bone at the periosteal surface. It is presumed that bone growth is promoted when increased amounts of bone nutrients, such as nitric oxide synthase (NOS) or messenger molecules, such as prostaglandin E2 (PGE2), seep out to the periosteal surface of cortical bone and are absorbed by osteoblasts. The transport of the bone nutrients is assumed to be a strain controlled process. Equations for the flux of these nutrients are written for a one-dimensional model of a long bone. The obtained partial differential equation is linearized and solved analytically. Based upon the seepage of nutrients out of the bone, the effect of loading frequency, number of cycles and strain level is examined for several experiments that were found in the literature. It is seen that bone nutrient seepage is greatest on the tensile side of the bone; this location coincides with the greatest amount of bone modeling

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  • 10.
    Bjerkén, Christina
    Malmö högskola, Teknik och samhälle (TS).
    Branching of a dissolution driven stress corrosion crack2009Ingår i: Proceedings of the International Conference on Crack Paths 2009, European Structural Integrity Society , 2009Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Stress corrosion cracking occurs due to the synergistic interaction between mechanical load and corrosion reactions. Some types of stress corrosion crack branch heavily. Here, branching during dissolution driven crack growth is studied using an adaptive FE method. A strain-assisted evolution law is used for the inherently blunted crack. No criterion for crack growth is needed as for a sharp crack, neither for the growth direction. Several simulations are performed with different degrees of load biaxiality. It is found that large biaxiality promotes branching, but no conditions for when branching takes place is found. Instead, branching seems to occur rather randomly due to the perturbation sensitivity of a dissolution driven crack. Also crack growth rates for branched cracks are investigated, and it is found that both constant growth rates can be reached, as well as decreasing rates and eventual arrest. The cracks follow a mode I crack path, however local changes may occur due to the perturbation sensitivity.

  • 11.
    Bjerkén, Christina
    Malmö högskola, Teknik och samhälle (TS).
    Spänningskorrosion - modellering av utveckling från ytojämnheter via gropar till sprickor2007Ingår i: Abstracts Svenska mekanikdagarna, Luleå, Sweden, 2007Konferensbidrag (Övrigt vetenskapligt)
    Abstract [sv]

    Den kombinerade effekten av mekanisk belastning och en korrosiv miljö kan leda till spänningskorrosion. Vid anodisk spänningskorrosion löses materialet upp och bildar korrosionsprodukter. I vissa fall bildas en ytbeläggning, t ex en oxidfilm, som verkar skyddande och därmed bromsar korrosionsprocessen. Om en dylik film inte skapas, eller om den kontinuerligt bryts ned, kan korrosionsprocessen fortgå. I en plan yta kan gropar bildas, och någon eller några av dessa kan i sin tur utvecklas till en kritisk spricka. I denna studie undersöks utvecklingen av korrosionssprickor med hjälp av en modell där korrosionshastigheten är proportionell mot den elastiska töjningsenergin och kurvaturen i varje punkt på ytan. Det är känt sedan tidigare att kurvaturen påverkar benägenheten för atomer att lossna från eller binda vid en yta, vilket leder till att en obelastad yta planar ut vid t ex etsning. Om ytan däremot är belastad kommer en ytojämnhet med ett specifikt frekvensinnehåll att utvecklas. Vågor med längder kortare än en viss kritisk våglängd kommer att avklinga. På detta sätt leder korrosionen till att gropar bildas i ytan och vissa av dessa fördjupas allt mer tills de blir sprickliknande. Dessa spänningskorrosionssprickor kommer dock att ha en finit radie i spetsen som är given av det lokala spänningstillståndet. Simuleringar är gjorda med en adaptiv metod. För varje tidsinkrement beräknas töjningarna i ytan i en finita element-analys, därefter bestäms ytevolutionen och sedan genereras ett nytt elementnät för den uppdaterade geometrin. Resultat från simuleringarna visar utvecklingen från en plan yta, med en initiell pertubation, via gropbildning till sprickor.

  • 12.
    Bjerkén, Christina
    et al.
    Division of Materials Engineering, Department of Mechanical Engineering, Lund University.
    Melin, S
    Division of Solid Mechanics, Department of Mechanical Engineering, Lund University.
    A study of the influence of grain boundaries on short crack growth during varying load using a dislocation technique2004Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 71, nr 15, s. 2215-2227Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The propagation of short cracks in the neighbourhood of grain boundaries have been investigated using a technique were the crack is modelled by distributed dislocation dipoles and the plastic deformation is represented by discrete dislocations. Discrete dislocations are emitted from the crack tip as the crack grows. Dislocations can also nucleate at the grain boundaries. The influence on crack growth characteristics of the distance between the initial crack tip and the grain boundary has been studied. It was found that crack growth rate is strongly correlated to the dislocation pile-ups at the grain boundaries. (C) 2004 Elsevier Ltd. All rights reserved.

  • 13.
    Bjerkén, Christina
    et al.
    Department of Mechanical Engineering, Lund University.
    Melin, S
    Department of Mechanical Engineering, Lund University.
    A tool to model short crack fatigue growth using a discrete dislocation formulation2003Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 25, nr 6, s. 559-566Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method is presented that combines the modelling of cracks by distributed dislocation dipoles with developing plasticity represented by discrete dislocations moving along slip bands. Crack growth is due to the emission of dislocations from the crack tip along preferred slip planes. Eventual annihilation of dislocations occurs by reunion with the corresponding displacement steps of the crack surface. Crack surface overlap is not allowed. The equilibrium state for each load increment is solved iteratively, allowing various crack geometries. The method is applied to the problem of a short edge crack growing in mode I due to fatigue loading. It is shown that the development of a local plastic zone and the propagation of the crack can be monitored in detail. (C) 2003 Elsevier Science Ltd. All rights reserved.

  • 14.
    Bjerkén, Christina
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Melin, Solveig
    Growth of a short fatigue crack - A long term simulation using a dislocation technique2009Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 46, nr 5, s. 1196-1204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, the growth of a short edge crack during more than 14 000 cycles of fatigue loading is investigated in detail. An edge crack, in a semi-infinite body with no pre-existing obstacles present, is modelled in a boundary element approach by a distribution of dislocation dipoles. The fatigue cycles are fully reversed (R = -1), and the load range is well below the threshold for long fatigue cracks. The developing local plasticity consists of discrete edge dislocations that are emitted from the crack tip. The movements of discrete dislocations are restricted to slip along preferred slip planes. The present model is restricted to a 2D plane strain problem with a through-thickness crack, assuming no 3D irregularities. A remote load is applied perpendicular to the crack extension line, and the material parameters are those of a BCC crystal structure. The competition between influence of the global loading on and local shielding of the crack tip governs the crack growth. The growth rate increases in discrete steps with short periods of retardation, from approximately the size of Burgers vector, b, up to 25 b per cycle as the length of the crack is tripled. The plastic zone changes from having an elongated, slender form to include a low angle grain boundary, which, eventually, divides into two parts. The crack growth is found to change from constant acceleration to constant growth rate as the event of the low-angle grain boundary split is approached. ; The results are compared to long crack characteristics, for which linear elastic fracture mechanics and Paris law can be used to predict fatigue crack growth. The exponent in Paris law varies between 1 and 0 in the present study, i.e. smaller than typical values for ductile BCC materials. The ratio between static and cyclic plastic zone sizes is found to increase during crack growth, and the angle of the general plastic zone direction increases, showing a tendency towards long crack values. The characteristics of the simulated crack growth, found in the present study, are typical for below-threshold growth, with slow acceleration, constant growth rate. and, eventually, either arrest or transition to long crack growth behaviour, as reported in the literature.

  • 15.
    Bjerkén, Christina
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Ortiz, Michael
    Evolution of anodic stress corrosion cracking in a coated material2010Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 165, nr 2, s. 211-221Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present paper, we investigate the influence of corrosion driving forces and interfacial toughness for a coated material subjected to mechanical loading. If the protective coating is cracked, the substrate material may become exposed to a corrosive media. For a stress corrosion sensitive substrate material, this may lead to detrimental crack growth. A crack is assumed to grow by anodic dissolution, inherently leading to a blunt crack tip. The evolution of the crack surface is modelled as a moving boundary problem using an adaptive finite element method. The rate of dissolution along the crack surface in the substrate is assumed to be proportional to the chemical potential, which is function of the local surface energy density and elastic strain energy density. The surface energy tends to flatten the surface, whereas the strain energy due to stress concentration promotes material dissolution. The influence of the interface energy density parameter for the solid-fluid combination, interface corrosion resistance and stiffness ratios between coating and substrate is investigated. Three characteristic crack shapes are obtained; deepening and narrowing single cracks, branched cracks and sharp interface cracks. The crack shapes obtained by our simulations are similar to real sub-coating cracks reported in the literature.

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  • 16.
    Bjerkén, Christina
    et al.
    Department of Mechanics and Materials, Lund University.
    Persson, Christer
    Department of Mechanics and Materials, Lund University.
    A numerical method for calculating stress intensity factors for interface cracks in bimaterials2001Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 68, nr 2, s. 235-246Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a method For obtaining the complex stress intensity factor (or alternatively the corresponding energy release rate and mode mixity) for an interface crack in a bimaterial using a minimum number of computations. A crack closure integral method for homogeneous materials developed by Rybicki and Kanninen has been modified to include mismatch in material properties. This was achieved directly from the nodal forces at the crack tip and the displacements near the tip as obtained from a finite element analysis using only four-node constant strain elements. Numerical calculations for tensile and mixed mode loading showed good agreement with results from corresponding analytical solutions. The main advantages of this method are that it is straightforward and easy to use and that the number of calculations needed to obtain the stress intensity Factors can be held to a minimum. (C) 2000 Elsevier Science Ltd. All rights reserved.

  • 17.
    Bjerkén, Christina
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Rimoli, Julian
    Ortiz, Michael
    Stress corrosion crack growth beneath a stiff coating: influence of chemical potential and interface toughness2009Ingår i: Proceedings 12th International Conference on Fracture, Ottawa 2009, ICF12 , 2009Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In the present paper we investigate the influence of corrosion driving forces and interfacial toughness for a coated material subjected to mechanical loading. If the protecting coating is cracked, the substrate material may become exposed to a corrosive media. For a stress corrosion sensitive substrate material, this may lead to detrimental crack growth. A crack is assumed to grow by anodic dissolution, inherently leading to a blunted crack tip. The rate of dissolution along the crack surface is assumed to be proportional to the chemical potential, which is function of the local surface energy density and the elastic strain energy density. The surface energy tends to flatten the surface, whereas the strain energy due to stress concentration promotes material dissolution. The evolution of the crack surface is modelled as a moving boundary problem using an adaptive finite element method. The crack shapes obtained by our simulations are remarkably similar to real stress corrosion cracks reported in the literature.

  • 18.
    Bjerkén, Christina
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Branching of growing corrosion fatigue cracks2005Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Strain-driven corrosion of branching cracks, initiated from a virtually plane surface, has been studied using a moving boundary technique. The material is assumed linear elastic and is subjected to fatigue loading under plain strain conditions. The surface of the material is covered by a protective film. During loading this film can be damaged if it is strained above a threshold value, thus revealing an unprotected surface. Corrosion advances by material dissolution, eventually evolving into cracks. The rate of surface evolution is a function of the degree of protective film damage. During unloading the protective film is assumed to develop and heal the surface. A low frequency cyclic loading is applied to ensure that total healing is assumed. The moving boundary technique, simulating corrosion, results in arc-shaped crack tips, rather than singular crack tip points, thus no crack growth criterion is needed in the analysis. For each load step, the strain distribution is found using the finite element method, followed by required the movement the boundary and then remeshing. The crack growth has been investigated for at least 2000 cycles. A more or less pronounced branching of the cracks is found to develop. The crack branches can be classified in three groups; main cracks that grows with maximum rate and branches further, branch cracks that initially retards and then find a steady state growth rate that is a fraction of maximum speed, and finally, arresting cracks that after a period of retardation stop growing. The crack patterns are realistic, showing a sort of self-similarity with tree-like structure, cf. the picture below that shows a typical finite element result. The width of a crack branch together with the shielding from the applied stresses, caused by the other branches and main cracks, seem to govern the evolution of the crack branch. A steady-state growth rate is achieved during parts of the evolution as the crack width and the strain field surrounding the crack tip is in balance, i.e. the crack widens while the crack grows longer. As the bluntness of the tip reaches an upper limit, branching results.

  • 19.
    Bjerkén, Christina
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Simulation of corrosion fatigue crack growth under mixed-mode loading2008Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, nr 3-4, s. 440-451Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The kinking of a corrosion crack due to mixed-mode fatigue loading is studied using an adaptive finite element procedure. The rate of material dissolution is assumed to be proportional to the stretching of the corroding surface. The dissolution of material is governed by a corrosion law, where no criterion is needed for neither crack growth nor growth direction. The problem is treated as a general moving boundary problem. The kink angles are found to be in very good agreement with results for sharp cracks using criteria reported in the literature.

  • 20.
    Everbring, Adam
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Larsson, Robin
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Momentmätare för lossning av distansskruvar2023Självständigt arbete på grundnivå (kandidatexamen), 180 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Underhåll av tandimplantat är tidskrävande och kan vara smärtsamt för patienten. Av denna anledning är det önskvärt att maximera tiden mellan återbesök. En faktor som påverkar återbesökstiden är hur mycket distansskruven i ett tandimplantat har lossnat med tiden. För att forska vidare på detta så behövs en momentnyckel som kan mäta det maximala momentet som krävs för att lossa distansskruven. För att uppnå detta har en systematisk produktutvecklingsprocess genomförts. Hållfasthetsberäkningar och FEM-analyser har genomförts för att se till att prototypens mekaniska egenskaper uppfyller de krav som ställs. För att framställa prototypen har 3D-skrivning använts, där mätningar, kalibrering och programmering gjorts för att säkerställa så momentnyckeln kan mäta det maximala momentet. Arbetet resulterade i en prototyp av kolfiberkomposit och titan för att mäta det maximala momentet som krävs för att lossa en distansskruv.

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    A.Everbring, R.Larsson
  • 21.
    Friberg, Andreas
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS).
    Larsson, Filip
    Malmö universitet, Fakulteten för teknik och samhälle (TS).
    Vidareutveckling av Cirk-L ClickSlide-spänne2021Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Arbetskläder förekommer i olika yrken varav hantverkare är en av dem. Hantverkarnas arbetskläder är till för att skydda personen samt att för- vara utrustning. Då fickorna oftast är fastsydda måste användaren tömma fickorna för att byta utrustning ifall arbetssituationen ändras. Då det kan ta tid att byta fickornas innehåll har företaget Cirk-L utvecklat en kollektion arbetskläder med ett integrerat modulärt bärsystem som de kallar ClickSlide. ClickSlide ger användaren möjlighet att anpassa sin utrustning genom att ta av, ta på samt flytta runt utrustningsfickorna efter behov. Nästa steg i utvecklingen av Cirk-Ls ClickSlide är att göra det MOLLE-kompatibelt. Syftet med det här arbete är att möjliggöra sammankoppling av Cirk-Ls ClickSlide med MOLLE-kompatibla tillbehör. Målet är att designa ett spänne som kan sammankopplas med Cirk-Ls Slider och som är MOLLE-kompatibelt. En prototyp tas fram med hjälp av en prototyputvecklingsprocess. Processen delas upp i tre steg: konceptutveckling, utveck- ling av ingående delar och säkerställande av hållfasthet. I dessa delprocesser används bland annat: urvalsmatriser, 3D-modellering, beräkningar och materialval. Arbetet resulterar i en 3D-printad prototyp som svarar mot syfte, mål och krav. Vid vidare utveckling av spännet kan bl.a. haken modifieras, fasning av låsets utsida, tunnare material, hur spännet ska kunna anpassas för tillverkning samt finita elementberäkningar göras.

  • 22.
    Hejman, Ulf
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Bjerkén, Christina
    Malmö högskola, Teknik och samhälle (TS).
    Dissolution driven crack branching in polycarbonate2011Ingår i: Fatigue and Fracture of Engineering Materials and Structures, Vol. 34, nr 4, s. 227-239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Stress corrosion, in the form of chemically assisted crack growth, in polycarbonate is examined with focus on crack branching characteristics. Cracks with finite width are observed; this is to be expected for dissolution driven cracking. The cracks branched repeatedly and crack widths before and after branching are measured. Both symmetric and asymmetric branching is found. The dissolution rate is assumed to be a linear function of the strain along the crack surface. In the literature, it is proposed that the crack width is proportional to the square of the mode I stress intensity factor. Energy considerations lead to that the sum of branch widths must equal the width of the unbranched crack. The results from the present study correspond fairly well with this assumption. The branching angle is found to be 32º ± 12º, which is in line with results for sharp cracks reported in the literature. The mean growth direction of the branches is found to deviate slightly from the expected straight. No significant correlation between angles and crack widths is found. The scatter in results is mainly addressed to the inherent perturbation sensitivity of stress corrosion cracking. Also numerically simulations of crack branching is performed. These results show promising agreement with the experiments.

  • 23.
    Hiremath, Praveenkumar
    et al.
    Division of Mechanics, Lund University.
    Melin, Solveig
    Division of Mechanics, Lund University.
    Bitzek, Erik
    Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany ; Computational Materials Design, Düsseldorf, Germany.
    Olsson, Pär A T
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Division of Mechanics, Lund University.
    Effects of interatomic potential on fracture behaviour in single- and bicrystalline tungsten2022Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 207, s. 1-18, artikel-id 111283Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, we have evaluated the performance of different embedded atom method (EAM) andsecond-nearest neighbour modified embedded atom method (2NN-MEAM) potentials based on their predictive capabilities for modelling fracture in single- and bicrystalline tungsten. As part of the study, a new 2NN-MEAM was fitted with emphasis on reproducing surface, unstable stacking fault and twinning energies as derived fromdensity functional theory (DFT) modelling. The investigation showed a systematic underestimation of surfaceenergies by most EAM potentials, and a significant variation in unstable stacking and twinning fault energies.Moreover, the EAM potentials in general lack the ability to reproduce the DFT traction–separation (TS) curves. The shorter interaction length and higher peak stress of the EAM TS curves compared to the 2NN-MEAM and DFT TS curves result in one order of magnitude higher lattice trapping than for cracks studied with 2NN-MEAM. These differences in lattice trapping can lead to significant qualitative differences in the fracture behaviour. Overall, the new 2NN-MEAM potential best reproduced fracture-relevant material properties and its results were consistent with fracture experiments. Finally, the results of fracture simulations were compared with analytical predictions based on Griffith and Rice theories, for which emerging discrepancies were discussed.

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    data set
  • 24. Isaksson, Per
    et al.
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Mode II crack paths under compression in brittle solids - a theory and experimental comparison2002Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 39, nr 8, s. 2281-2297Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A study of crack propagation paths in the situation where the crack is suppressed to open during growth due to high compressive forces has been performed. This problem was analyzed theoretically very recently by the authors and is here extended to involve a limited number of illustrative experimental results reported elsewhere in the literature. By analyzing the experimental crack growth patterns, the conclusion is that the model cannot describe the more realistic microscopic failure in detail. Since shear crack growth on the microscale strongly depend on inhomogenities in the material, like cavities, grains or inclusions; the closed crack growth patterns observed are not smooth or free of kinks. Nevertheless, the model show good agreement with the reported experimental observations of the paths of closed macroscopic mode II cracks on samples in brittle materials, induced under overall compression. Failure patterns experimentally observed supports the theory that the growth of mode II cracks under compression in brittle materials follow a propagation path described by a function y=k x^b, where b=3/2. This is strongly supported by the measured values obtained from various experiments. In all the studied experiments, the exponent b was found in the interval [1.43–1.58]. Further, an investigation of the curvature parameter k has been performed and the conclusion is that k does also agree with the simplified model, even though not as good as the exponent b. However, k differs in general <15% from the theoretical value predicted by the model. The process of crack growth is in the simplified model assumed to be controlled by the mode II stress intensity factor KII of the main crack and the difference between the compressive remote normal stress parallel with the crack plane (r11) and the compressive remote normal stress per- pendicular to the crack plane.

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  • 25.
    Jernkvist, Lars Olof
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Massih, Ali R
    Malmö högskola, Teknik och samhälle (TS).
    Multi-field modeling of hydrogen transport and fracture in group 4 transition metals2012Ingår i: Proceedings of the International Hydrogen Conference (IHC 2012): Hydrogen-Materials Interactions, ASME Press, 2012, s. 717-726Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This work deals with a computational model for hydrogen transport, hydrogen induced deformation, embrittlement and fracture in hydride forming metals, notably Ti and Zr. The model uses a continuum description of the two-phase (alpha-phase metal plus delta-phase hydride) material, and solves the multi-field partial differential equations for temperature- and stress-directed hydrogen diffusion together with mechanical equilibrium in a three-dimensional finite element setting. Point-kinetics models are used for metal-hydride phase transfor¬mation and stress-directed orientation of hydrides, while a cohesive zone fracture model caters for initiation and propagation of cracks. The model as a whole is versatile and can be used to study a wide range of problems and conditions involving transport of hydrogen by directed diffusion in combination with hydride precipitation and fracture. The applicability of the model is demon-strated by simulations of fracture tests on a hydrogen-charged Zr-Nb alloy.

  • 26.
    Juzel, Odai
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS).
    Bui, Tommy
    Malmö universitet, Fakulteten för teknik och samhälle (TS).
    Konceptutveckling för ett naturlekhus2022Självständigt arbete på grundnivå (högskoleexamen), 180 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Several households today have access to digital tools, which increases children's screen time. This is considered a threat to their health, as studies show that sedentary activity increases while physical activity decreases. The purpose of this work is to create a stimulating environment for children through a nature playhouse that offers challenging physical play. The work is done in collaboration with the company Utform AB, where the goal is to develop construction foundation for a final concept solution for the playhouse, by systematically using established product development processes. These processes include information gathering, concept generation, material selection, strength calculations performed manually as well as the Finite Element Method (FEM), and finally 3D-CAD modeling of the concept.

    The result is a two-story building that combines different play equipment in a developed playhouse concept. The bottom floor offers ample space for play with the ability to store different loose materials from the nature and access to chair and table equipment. To get to the upper floor there is a ladder or a wooden log that serves as a climbing tool. Between the upper floor and the bottom floor there is a current panel tool that transports loose materials. The dimensioning of the playhouse and the play equipment is adapted to the SS-EN 1176 standard, existing solutions in the market and Utform's current range. For the basic construction, larch has been chosen as the most suitable material. Larch has particularly good strength properties and is resistant to the Swedish outdoor climate as well as being easy to process and environmentally friendly. Larch wood is also used advantageously since it is in line with Utform's current profile.

  • 27.
    Knudsen, J.
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS).
    Massih, Ali R
    Quantum Technologies AB, Uppsala, Sweden.
    Nonlinear dynamics of a loosely supported beam subject to harmonic excitation2002Ingår i: Proceedings of IMECE2002, ASME Press, 2002, s. 1305-1312Konferensbidrag (Refereegranskat)
    Abstract [en]

    The nonlinear dynamic behavior of damped beam oscillator with elastic two-sided amplitude constraints is analyzed. The structure is modeled by a Bernoulli-Euler beam supported by elastic springs. Finite element method is used for discretization in space and time integration is performed by Newmark’s method. Rayleigh damping is assumed for the structure. Symmetric and elastic double-impact motions, both harmonic and subharmonic, are studied by way of a Poincare´ mapping that relates the states at subsequent impacts. We have found that by increasing the forcing frequency (ω) for the beam at a certain frequency a stable period one motion (solution) turns into a stable period two motion and subsequently without bifurcation it transits to an infinite number of solutions characteristic of chaotic behavior. By further increasing ω a series of windows in the bifurcation diagram (impact velocity vs. ω) comprising periodic solutions within the chaotic domain appear.

  • 28.
    Knudsen, Jakob
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Massih, Ali R
    Luleå University of Technology, SE 971 87 Luleå, Sweden; ABB Atom AB, SE 721 63 Västerås Sweden.
    Vibro-impact dynamics of a periodically forced beam2000Ingår i: Journal of Pressure Vessel Technology-Transactions of the ASME, ISSN 0094-9930, E-ISSN 1528-8978, Vol. 122, nr 2, s. 210-221Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vibration and impact dynamics of a periodically forced loosely supported beam are analyzed. The wear work rates at impact points are evaluated. The considered beam is clamped at one end, and constrained against unilateral contact at contact sites, with or without friction, near the other end. In this work, the structure is modeled by a Bernoulli-type beam supported by springs using finite element method. Our model calculations are compared with measurements of contact forces and displacements made on a loosely supported rod that was subjected to harmonic loading. Furthermore, the dynamics of vibro-impacts are characterized by evaluating the impact velocity as a function of harmonic excitation frequency for two idealizations of the aforementioned structure. [S0094-9930(00)01002-7] 

  • 29.
    Li, Chong
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Espinosa, Rogelio
    Malmö högskola, Teknik och samhälle (TS).
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Fracture mechanics for membranes2004Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    During fracture of membranes loading often produces buckles above and below the crack surface. This changes the stress state surrounding the crack-tip and stresses in the neighbourhood of the crack-tip posses a weaker singularity than r-1/2. As a result, fracture occurs when the crack-tip stress distribution is different as compared with that when buckling is artificially prevented. Therefore the conditions for transfer of lab results to real structures are changed. The weaker singularity is here utilised to formulate an adopted fracture mechanical theory. An approximate application is made based on an assumption that the buckled area of the paper is incapable of carrying load. This region is approximated with the region that is under compressive load at plane stress conditions. The result is compared with experiments performed on paper. The importance of the linear extent of the process region has on the energy available for fracture is discussed.

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  • 30.
    Olsson, Pär A T
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Ab initio thermo-elasticity of δ-MHx (M=Zr, Ti)2023Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 218, artikel-id 111953Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, we report the results of a systematic ab initio study of the thermo-elastic properties of -MH1.5 (M=Zr, Ti). This investigation serves three purposes: (i) Elucidate the fully anisotropic temperature dependent elastic constants of hydrides, (ii) address discrepancies in thermal expansion data reported in the literature and (iii) provide input data for thermodynamic-based phase-transformation modelling. Due to a reduced contribution from the vibrational free energy to the strain energy, in agreement with experimental observations we find that the temperature  dependent stiffness of hydrides vary to a much lesser degree than the matrix. For -ZrH1.5, we further find that Zener’s anisotropy ratio varies with temperature. Regarding the linear thermal expansion, our results indicate that it is highly temperature dependent. With the exception of a few outliers, our DFT data concurs well with experimental data, if the temperature range over which it was measured is taken into account.

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  • 31.
    Olsson, Pär A T
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Materials Science and Applied Mathematics.
    Awala, Ibrahim
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Holmberg-Kasa, Jacob
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Division of Solid Mechanics, Lund University, Lund, Sweden.
    Krause, Andreas M.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Tidefelt, Mattias
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Vigstrand, Oscar
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Music, Denis
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Malmö universitet, Biofilms Research Center for Biointerfaces.
    Grain Size-Dependent Thermal Expansion of Nanocrystalline Metals2023Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 16, nr 14, artikel-id 5032Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, we have used classical molecular dynamics and quantum mechanical density functional theory modeling to investigate the grain size-dependent thermal expansion coefficient (CTE) of nanocrystalline Cu. We find that the CTE increases by up to 20% with a gradually decreasing grain size. This behavior emerges as a result of the increased population of occupied anti-bonding states and bond order variation in the grain boundary regions, which contribute to thereduced resistance against thermally-induced bond stretching and dictate the thermal expansion behavior in the small grain size limit. As a part of the present work, we have established a procedure to produce ab initio thermal expansion maps that can be used for the prediction of the grain size dependent CTE. This can serve as a modeling tool, e.g., to explore the impact of grain boundary impurity segregation on the CTE.

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  • 32.
    Olsson, Pär A T
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Bergvall, Erik
    Atomistic investigation of functionalized polyethylene-alumina interfacial strength and tensile behaviour2021Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 187, artikel-id 110075Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the adhesion and tensile behaviour of bi-layer interfaces comprising polyethylene, doped with carbonyl and hydroxyl functional groups emanating from ozone treatment, and &#x3B1;" role="presentation">-Al2O3" role="presentation"> by means of density functional theory and classical atomistic modelling. The results show that the deformations are localized within the polymer and comprise chain slip, disentanglement and detachment from the substrate, where only the latter is notably affected by the doping. The binding energies and excess forces associated with the detachment of functional groups from the alumina substrate are of the order of 1.7 eV and 1 nN, respectively, for both types. Although such forces do not affect the maximum peak stress notably, they give rise to spikes in the traction-separation curves following the fibril formation and promote increased total work of fracture.

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  • 33.
    Olsson, Pär A T
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Division of Mechanics, Materials and Components, Lund University.
    Hiremath, Praveenkumar
    Division of Mechanics, Materials and Components, Lund University.
    Melin, Solveig
    Division of Mechanics, Materials and Components, Lund University.
    Atomistic investigation of the impact of phosphorus impurities on the tungsten grain boundary decohesion2023Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 219, artikel-id 112017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, we have generated a new second-nearest neighbour modified embedded atom method potential (2NN-MEAM) for the W-P system to investigate the impact of P impurity segregation on the strength of symmetric [110] tilt coincident site lattice grain boundaries (GBs) in tungsten. By incorporating the impurity-induced reduction of the work of separation in the fitting strategy, we have produced a  potential that predicts decohesion behaviour as found by ab initio density functional theory (DFT) modelling. Analysis of the GB work of separation and generalized stacking fault energy data derived from DFT and the 2NN-MEAM potential show that P-impurities reduce the resistance to both cleavage and slip. Mode I tensile simulations reveal that the most dominant mode of GB failure is cleavage and that pristine GBs, which are initially ductile, on most accounts change to brittle upon introduction of impurities. Such tendencies are in line with experimentally observed correlations between P-impurity content and reduced ductility.   

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  • 34.
    Perepelkin, Nikolay V.
    et al.
    School of Engineering, Cardiff University, Cardiff, United Kingdom; Department of Applied Mathematics, National Technical University Kharkiv Polytechnic Institute, Kharkiv, Ukraine.
    Argatov, Ivan I
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Borodich, Feodor M.
    School of Engineering, Cardiff University, Cardiff, United Kingdom.
    Evaluation of elastic and adhesive properties of solids by depth-sensing indentation2021Ingår i: The journal of adhesion, ISSN 0021-8464, E-ISSN 1563-518X, nr 6, s. 569-610Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To describe properly interactions between contacting solids at micro/nanometre scales, one needs to know both adhesive and mechanical properties of the solids. Borodich and Galanov have introduced an effective method (the BG method) for identifying both characteristics from a single experiment on depth-sensing indentation by a spherical indenter using optimal fitting of the experimental data. Unlike traditional indentation techniques involving sharp indenters, the Borodich-Galanov methodology intrinsically takes adhesion into account. It is essentially a non-destructive approach. These features extend the scope of the method to important applications beyond the capabilities of conventional indentation. The scope of the original BG method was limited to the classic JKR and DMT theories. Recently, this restriction has been overcome by introducing the extended BG (eBG) method, where a new objective functional based on the concept of orthogonal distance curve fitting has been introduced. In the present work, questions related to theoretical development of the eBG method are discussed. Using the data for elastic bulk samples, it is shown that the eBG method is at least as good as the original BG method. It is shown that the eBG can be applied to adhesive indentation of coated, multilayered, functionally graded media.

  • 35.
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Foreword of the KB Broberg symposium issue2010Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 165, nr 2, artikel-id 139Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    To honour the memory of Knut Bertram Broberg, and to promote continuing work on the many ideas which he shared so generously with students and colleagues throughout his lifetime, a symposium was arranged at University College of Dublin in 2007. The idea was to create an informal atmosphere, and to keep the num- ber of participants fairly low. This has now become a bi-annual symposium with the highlight being one or two lectures by outstanding world-class scientists. The second Broberg Memorial Symposium was arranged by the Lund Institute of Technology in Sweden (LTH) in May 2009. The venue of the conference was a renais- sance castle, Trolleholm, that was put to our disposal by the courtesy of the Rector of LTH. Trolleholm was once the home of Sophia Brahe whose careful obser- vations of planetary orbits later was used by Johannes Kepler to develop his laws of planetary motion. Kepler was at the time working as an assistant to Sophia’s brother Tycho Brahe.

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  • 36.
    Ståhle, Per
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Jivkov, Andrey P
    Selfsimilar solutions for stress driven material dissolution2004Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    During corrosive dissolution of metal ions from a body surface, an oxide compound is produced. This compound forms a protective film that reduces the dissolution rate. When a fraction of a millimetre depth is dissolved the dissolution rate become insignificant. However, repeated loading will damage the film with continued dissolution as a result. In connection with this a threshold strain is assumed to exist. This paper proposes a model where electro- chemical processes and the mechanical load work together in forming a corrosion pit. The ratio between the threshold strain and the remotely applied strain is shown to control the shape of the pit. For small applied strains cracks are formed. A crack evolving from a surface irregularity is studied. The growth rate of the crack is determined by the dissolution rate at the crack tip. No crack growth criterion is needed. The growing crack is itself creating conditions for strain concentration, which leads to a high crack growth rate. The model simulates how dissolution forms a pit that grows to become a crack in a single continuous process. For small loads the crack growth rate is independent of applied load.

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  • 37.
    Tsompou, Andriani
    et al.
    Malmö universitet, Fakulteten för hälsa och samhälle (HS), Institutionen för biomedicinsk vetenskap (BMV). Malmö universitet, Biofilms Research Center for Biointerfaces. Malmö Univ, Dept Biomed Sci, Malmö, Sweden.;Malmö Univ, Biofilms Res Ctr Biointerfaces, Malmö, Sweden..
    Kocherbitov, Vitaly
    Malmö universitet, Fakulteten för hälsa och samhälle (HS), Institutionen för biomedicinsk vetenskap (BMV). Malmö universitet, Biofilms Research Center for Biointerfaces.
    Surface and bulk mechanisms in repeating treatment of solid surfaces by purified water2023Ingår i: Heliyon, E-ISSN 2405-8440, Vol. 9, nr 6, artikel-id e17163Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To decrease the negative impact of surfactants, the idea of using purified water in washing has been proposed. Previous studies showed that purified water facilitates the roll-up mechanism by promoting electrostatic interactions between the surface and the soil. However, washing mech-anisms can be dependent on the amount of remaining soil.In this work we studied the removal of thin Vaseline films and thicker oil films from hydro-philic surfaces using multiple washing cycles at different temperatures. The Quartz Crystal Mi-crobalance with Dissipation monitoring (QCM-D) and gravimetric analysis were used for thin and thick films respectively. In QCM-D experiments most of the thin film was removed during the first two cycles, while following cycles did not substantially affect washing efficiency; increased temperature facilitated the washing process. Gravimetric analysis showed that the washing of thicker films can be divided into two regimes. During the first, exponential, regime the amount of oil on the surface is high and surface mechanisms, such as roll-up, dominate. Oil droplets are kinetically stabilized in purified water by electrostatic interactions. As the amount of oil on the surface decreases, the second, linear, regime is introduced. The removal of oil occurs by equi-librium bulk mechanisms, where electrostatic interactions are less important.

  • 38.
    Vesti, Anders
    et al.
    Lund Institute of Technology.
    Hiremath, Praveenkumar
    Lund Institute of Technology.
    Melin, Solveig
    Lund Institute of Technology.
    Olsson, Pär A. T.
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Ab-initio investigation of mechanical and fracture-related properties of W-Re σ and χ precipitates2023Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 577, artikel-id 154261Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tungsten (W) is a leading candidate for plasma-facing materials in fusion reactors. Recently, experiments have shown that during neutron irradiation, W and its transmutation products, mainly rhenium (Re),will form precipitates of the σ and χ types. This study identifies close-packed planes of the σ - and χ-phases in the W-Re system and uses ab-initio methods to identify mechanical properties such as elasticconstants, generalized stacking fault energies (GSFE), and fracture toughness associated with brittle andductile mechanisms. By utilizing a sublattice model we demonstrate how these properties depend onthe Re content. For Re concentrations in the range where the σ - and χ-phases are stable, we find aweak dependency on the Re content, meaning that the elemental composition has little influence on the mechanical and fracture-related properties.

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  • 39.
    Vesti, Anders
    et al.
    Lund University.
    Music, Denis
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Malmö universitet, Biofilms Research Center for Biointerfaces.
    Olsson, Pär A T
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM). Lund University.
    First-principles study on thermal expansion of W-Re sigma and chi phases2024Ingår i: Nuclear Materials and Energy, ISSN 2352-1791, Vol. 39, artikel-id 101684Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate how the Re content affects the coefficient of thermal expansion (CTE) of the non-stoichiometric W-based  and  phases, forming upon neutron irradiation of W, to explore and quantify its mismatch between precipitates (W-Re) and matrix (W). To this end, we have conducted first-principles calculations using two approaches: the Debye-Grüneisen (DG) model and the quasi-harmonic approximation (QHA). The two approaches yield different results: the QHA, which is deemed to be the most accurate of the two, predicts substantial changes with Re content, while the acoustic-modes based DG model does not. The CTE of the σ and χ at stable Re contents is compared to experimental values for bcc-W and bcc-W-Re containing 25 at.% Re. Taking bcc-W as a reference, we find a significant mismatch in CTE of up to 37% and 62% for σ and χ, respectively, which may contribute to thermal stress buildup in the material at elevated temperatures. The mismatch is shown to increase with the temperature and Re content for both phases. The produced data are used to fit a temperature and Re concentration-dependent analytical function of the CTE for both phases, which can be employed as input for continuum mechanical modeling.Previous article in issue

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  • 40.
    Ward, Peter
    et al.
    Malmö universitet, Fakulteten för teknik och samhälle (TS).
    Engfalk, Linn
    Malmö universitet, Fakulteten för teknik och samhälle (TS).
    Markställning av trä för sollcellspark2022Självständigt arbete på grundnivå (högskoleexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Sveriges energiproduktion från solceller växer sig allt större, främst pågrund av att det är en förnybar energikälla. Företaget Eon bygger störresolcellsparker för kommersiellt bruk där solcellerna monteras på ställningari stål. Syftet med arbetet är att minska CO2-avtrycket från markställning-arna genom att undersöka om de istället kan byggas i trä utan att försäm-ra de ekonomiska aspekterna. När koncept är valt görs ett systematisktmaterialval till markställningen, materialvalet avgränsas inom Europa. Vi-dare byggs en 3D-modell i Computer aided design (CAD), 3D-modellenanvänds som underlag till analyser i finita elementmetoden (FEM) och rit-ningar. Enklare beräkningar på böjspänningen görs för att validera FEM-analyserna. Efter framtagning av markställning i trä görs en livscykelanalys (LCA) som visar att markställningen i trä bidrar till ett lägre CO2-avtryckän den befintliga i stål. Arbetet avgränsas och tar bland annat inte hänsyntill markförhållande och val av fästelement i ställningen. Markställningenkommer heller inte byggas upp som en prototyp vid färdigställd analys. Resultatet visar en markställning i tryckimpregnerat furu som placeras påstålpålar. På markställningen får tre liggande solcellspaneler i höjd platssom monteras med infästningsklämmor genom förborrade hål i ställningen.

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