1,721,329 research outputs found
Dynamic nonlinear crack growth at interfaces in multi-layered materials
No full textFinite thickness interfaces, such as structural adhesives, are often simplified from the modelling point of view by introducing ideal cohesive zone models that do not take into account the finite thickness properties in the evaluation of the interface stiffness and inertia. In the present work, the nonlinear dynamic response of those layered systems is numerically investigated according to the finite element method. The weak form of the dynamic equilibrium is written by including not only the contribution of cohesive interfaces related to the virtual work exerted by the cohesive tractions for the corresponding relative displacements, but also considering the work done by the dynamic forces of the finite thickness interfaces resulting from their inertia properties. A fully implicit solution scheme both in space and in time is exploited and the numerical results for the double cantilever beam test show that the role of finite thickness properties is remarkable as far as the crack growth kinetics and the dynamic strength increase factor are concerned
Image analysis of polycrystalline solar cells and modeling of intergranular and transgranular cracking
No full textAn innovative image analysis technique is proposed to process real solar cell pictures, identify grains and grain boundaries in polycrystalline silicon, and finally generate finite element meshes. Using a modified intrinsic cohesive zone model approach to avoid mesh dependency, nonlinear finite element simulations show how grain boundaries and silicon bulk properties influence the crack pattern. Numerical results demonstrate a prevalence of transgranular over intergranular cracking for similar interface fracture properties of grains and grain boundaries, in general agreement with the experimental observatio
A multi-scale numerical method for the study of size-scale effects in ductile fracture
No full textThe use of a stress-strain constitutive relation for the undamaged material and a traction-separation cohesive crack model with softening for cracking has been demonstrated to be an effective strategy to predict and explain the size-scale effects on the mechanical response of quasi-brittle materials. In metals, where ductile fracture takes place, the situation is more complex due to the interplay between plasticity and fracture. In the present study, we propose a multi-scale numerical method where the shape of a global constitutive relation used at the macro-scale, the so-called hardening cohesive zone model, can be deduced from meso-scale numerical simulations of polycrystalline metals in tension. The shape of this constitutive relation, characterized by an almost linear initial branch followed by a plastic plateau with hardening and finally by softening, is in fact the result of the interplay between two basic forms of nonlinearities: elasto-plasticity inside the grains and classic cohesive cracking for the grain boundaries
Who is the boss in the Retinoblastoma family? The point of view of Rb2/p130, the little brother
No full textThis review portrays an updated overview about the possible tumor suppressive properties of the Rb2/p130 gene, the third member of the retinoblastoma (RB) family of genes, including RB itself and p107. After a brief analysis of the established structural and functional similarities among the three genes, the main purpose is to critically analyze present evidence whether Rb2/p130 shares the role of a tumor suppressor. Taking into account the well-proven growth suppressive properties of Rb2/p130 and p107, we discuss the analysis of mutated or deleted forms of Rb2/p130 found in a number of human cancers. Finally, we take into consideration the data provided by the targeted disruption of each RB family gene, alone or in combination, in the mouse model
A global/local approach for the prediction of the electric response of cracked solar cells in photovoltaic modules under the action of mechanical loads
No full textAbstractA numerical approach based on the finite element method to assess the impact of cracks in Silicon solar cells on the electric response of photovoltaic modules is proposed. A global coarse-scale finite element model of the composite laminate is used for carrying out the structural analysis. The computed displacements at the edges of each solar cell are passed via a projection scheme as boundary conditions to a 3D local fine-scale finite element model of the cells which accounts for cohesive cracks. The evaluated crack opening displacements along the crack faces are finally used as input to an electric model characterizing the grid line/solar cell ensemble. The identification of the relation between the localized electric resistance due to cracks and the crack opening, to be used as a constitutive model of cracks, is finally discussed in reference to experimental tests performed in the laboratory
Genetic and epigenetic alterations as hallmarks of the intricate road to cancer
No full textDespite the clonal origin of most tumors, their tremendous heterogeneity suggests that cancer progression springs from the combined forces of both genetic and epigenetic events, which produce variant clonal populations, together with the selective pressures of the microenvironment, which promote growth and, perhaps, dissemination of variants with a specific set of characteristics. Although the importance of genetic mutations in cancer has long been recognized, the role of epigenetic events has been suggested more recently. This review focuses on the genetic and epigenetic molecular mechanisms involved in cancer onset and progression, and discusses the possibility of new strategies in the development of anticancer treatments
Inclusion of "interaction" in the Greenwood & Williamson contact theory
No full textRecent direct implementation of asperity theories is reinterpreted here to formulate an improved version of the Greenwood and Williamson (GW) theory with the inclusion of interaction between asperities. This is achieved by treating the contact pressures as uniformly distributed over the apparent contact area and the resulting deformation as uniform. The correction is equivalent to an increase of the effective separation of the mean planes by a quantity proportional to the nominal pressure, resulting in a reduction of the "real" area of contact and of total load for a given separation. However, the area-load relationship is unchanged. The correction effectively depends on the ratio between the nominal pressure and the elastic modulus multiplied by the ratio between the size of the nominal contact area and standard deviation of the asperity heights. For contacts much larger than the size of roughness, uniform interaction effectswould be dominant at relatively modest pressures (particularly for soft materials). This also means that the effect of interaction is unlimited. However, the only significant change is in the prediction of gas-tightness, it is harder to seal a large area than a small one. The modification of the theory has a significant effect on stiffness and conductance. Indeed, a parallel is drawn between this correction and the "clustering" terms of resistance in the Holm-Greenwood formulae for a cluster of circular spots. Finally, numerical contact simulations using Weierstrass-Mandelbrot (WM) surfaces show a general agreement with the improved theory but also significant scatter for low load levels. Taking into account the effect of asperity interaction, the improved GWtheory is now able to predict the numerically obtained contact response for intermediate load level
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