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The estimation of crack initiation for a bent sample with V-notch
Majer, Zdeněk ; Hutař, Pavel ; Náhlík, Luboš
The aim of this paper is to investigate the beginnings of crack propagation from sharp V-notches. Stress distribution around the tip of a V-notch is described on the basis of linear-elastic fracture mechanics. The V-notch is a singular stress concentrator with a singularity exponent dependent on the V-notch opening angle. The stability criteria are generalized for a stress singularity different from 0,5.
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Některé aspekty chování polymerních částicových kompozitů
Hutař, Pavel ; Knésl, Zdeněk ; Majer, Zdeněk ; Prod’homme, G. ; Náhlík, Luboš ; Nezbedová, E. ; Veselý, P.
Computation of the internal stress and strain fields in the microstructural level of the studied composite and understanding of microcracks behaviour in the interaction with particles is the first step to understanding the global behaviour of the composite based on microstructural morphology. Therefore, particle reinforced composite has been modelled as a three-phase material with homogenously distributed coated particles and numerically studied on the microscopic scale using finite element modelling. The FEM modelling and unit cell models provide an effective tools for parametric study of the three-phase composite mechanical properties.
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Efekt velikosti částic na lomové chování polypropylenového kompozitu
Nezbedová, E. ; Knésl, Zdeněk ; Hutař, Pavel ; Majer, Zdeněk ; Veselý, P.
The addition of mineral fillers to polypropylene (PP) can profoundly change the mechanical properties of polymer system. The properties of the particles themselves (size, shape, and material properties) can have significant effect on the global behaviour of composite, particularly on its toughness and stiffness. This contribution is focused on effects of particles size and their density on fracture toughness of polyprophylen particulate composite. The effect was studied from the experimental as well as from the theoretical point of view. The change of fracture toughness was estimated with utilisation of linear elastic fracture mechanics approach. The composite was modelled as a three-phase material with homogeneously distributed coated particles and numerically simulated using the finite element program ANSYS.
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Influence of particles shape on fracture toughness of PP-based particulate composite
Majer, Zdeněk ; Knésl, Zdeněk ; Hutař, Pavel
Polymeric particulate composites with thermoplastics are of great practical importance due to the possibility of modifying mechanical properties and reducing the price/volume ratio of resulting material. The properties of the particles themselves (size, shape, material properties) can have a significant effect on the global behaviour of the composite. Generally, the addition of rigid particles to a polymer matrix will have an embrittling effect on the composite. The presence of the particles significantly influences the cure reaction resulting in the formation of a third phase known as the interphase, which possesses a property distinct from those of the matrix and the particles. The particle-reinforced composite (PP-CaCO3) was modeled as a three-phase material with homogeneously distributed coated particles. The main aim of the article is estimate an effect of the interphase properties on microcrack behaviour.
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Stanovení kritické hodnoty pro šíření trhliny z ostrého v-vrubu
Majer, Zdeněk ; Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk
The aim of this paper is to investigate the beginnings of crack propagation from sharp V-notches. Stress distribution around the tip of a V-notch is described on the basis of linear-elastic fracture mechanics. The V-notch is a singular stress concentrator with a singularity exponent dependent on the V-notch opening angle. The stability criteria are generalized for a stress singularity different from 0,5. Using FEM analysis the critical stress for crack initiation was estimated as a function of the V-notch angle. The results of numerical calculations were compared with experiments taken from the literature.
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Vliv singularity způsobené volným povrchem na chování tenkých těles s v-vrubem
Majer, Zdeněk ; Hutař, Pavel ; Náhlík, Luboš
The influence of the singularity induced by the free surface on the behaviour of a body with a V-notch is investigated in this paper. Attention is focused mainly on the change of the singularity and the stress state through the thickness of a three-dimensional specimen. Numerical finite-element analysis of the tension loaded specimens with a V-notch were performed. The displacements and the stresses from the analysis were used to estimate the power of singularities using a log-log regression analysis along the crack front. It was found that in the middle of the specimen singularity of the V-notch is dominant this can be found using analytic equations describing two-dimensional stress distribution around the sharp V-notch. The thickness of boundary layer (region influenced by corner singularity) depends only on the Poisson's ratio of the material. The presented results can be used for a more reliable estimation of the free-surface effect on singular concentrator behaviour.
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Numerical analysis of a surface crack in protective layers
Šestáková, Lucie ; Majer, Zdeněk ; Náhlík, Luboš ; Knésl, Zdeněk
Two elastic plane strain problems relevant to the cracking of protective layers bonded to dissimilar semi-infinite substrate materials are solved. In the first case a crack initiated at the free surface of the layer and propagating within the film is considered and the influence of its original orientation on cracking mode of the layer is studied. The second problem is that of the crack in the layer oriented perpendicularly to the layer/substrate interface and its influence on a debonding of the layer/substrate system is analysed. In both cases the influence of elastic mismatch of both components on the crack behaviour is discussed. The results provide the details making it possible to solve practical problems connected with damage of bodies with protective layers.
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Numerical analysis of a surface crack propagation in protective layers
Majer, Zdeněk
The paper contains a numerical analysis of a surface crack propagation in an elastic surface layer. It was analysed an influence of elastic material parameters of both system components, initial length and orientation of crack on fatigue crack propagation direction. The typical behaviour of crack propagation in thin layers was described. The finite element method for determination of the direction of the farther crack propagation was used.
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