Multiscale modeling of acoustic shielding materials

It is very important to protect high-tech systems from acoustic excitation when operating in a noisy environment. Some passive absorbing materials such as acoustic foams can improve the performance which depends on the interaction of the acoustic wave and the microstructure of the foam

An enriched cohesive zone model for delamination in brittle interfaces

Application of standard cohesive zone models in a finite element framework to simulate delamination in brittle interfaces may trigger non-smooth load-displacement responses that lead to the failure of iterative solution procedures. This non-smoothness is an artifact of the discretization; and hence it can be avoided by sufficiently refining the mesh leading to unacceptably high computational costs and a low efficiency and robustness. In this paper, a process-driven hierarchical extension is proposed to enrich the separation approximation in the process zone of a cohesive crack. Some numerical examples show that instead of mesh refinement, a more efficient enriched formulation can be used to prevent a non-smooth solution

Gradient crystal plasticity modelling of anelastic effects in particle strengthened metallic thin films

It is now a well known phenomenon that thin films are susceptible to size effects, which can be captured adequately by gradient plasticity theories. Besides the scale dependency, metal thin films also exhibit time dependent behavior: anelasticity (deformation recovery over time following elastic spring back upon load removal) and creep (permanent deformation developed over time at constant loads). This work focuses on the extension of a strain gradient crystal plasticity (SGCP) model (Int J Solids Struct 43:7268–7286, 2006; Phil Mag 87:1361–1378, 2007; J Mech Phys Solids 52:2379–2401, 2004; Int J Solids Struct 41:5209–5230, 2004), previously developed for the scale dependent behavior of pure fcc metals, so that it can be exploited for the description of the scale and time dependent mechanical behavior of thin films that are made of metal alloys with second phase particles. For this purpose, an extended physically based slip law is developed for crystallographic slip in fcc metals by considering the deformation mechanisms that are active within the grains. In doing so, the interaction of dislocations with other dislocations and with second phase particles is taken into account. Three types of dislocation–particle interactions are considered: (i) the Orowan mechanism, (ii) the Friedel mechanism, and (iii) dislocation climb. Finite element simulations of the bending of a single crystalline beam show that at low stress levels, the plastic slip rate is controlled by dislocation climb within the presented model. Provided that a considerable lattice diffusion occurs and sufficiently large back stresses exist in the material, the extended SGCP model predicts a noticeable time dependent recovery, reducing the residual deformation after unloading. The magnitude and the characteristic time scale of the anelastic recovery are controlled by dislocation glide limited by climb

Multiscale modeling of particle-modified polyethylene

A common practice in toughening of semicrystalline polymers is to blend them with second-phase rubber particles. A toughening mechanism has recently been suggested which considers a layer of transcrystallized material around well-dispersed particles. A multiscale numerical model is used to investigate the effect of such a specific microstructural morphology on the mechanical behavior of voided systems. A polycrystalline model is used for high density polyethylene (HDPE) matrix material. The basic structural element in this model is a layered two-phase composite inclusion, comprising both a crystalline and an amorphous domain. The averaged fields of an aggregate of composite inclusions, having either a random or a preferential orientation, form the constitutive behavior of the polymeric matrix material. The anisotropy of material with preferential orientations is determined. The particle-dispersed system is described by finite element RVE models, with in each integration point an aggregate of composite inclusions. Transcrystallzed orientations are found to have a limited effect on matrix shear yielding and alter the triaxial stress field. An hypothesized, flow-influenced, microstructure is shown to further improve material properties if loaded in the appropriate directionl