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9A micromechanics based constitutive model is developed that focuses on the effect 10 of distributed crazing in the overall inelastic deformation behavior of rubber-toughened 11 ABS (acrylonitrile-butadiene-styrene) materials. While ABS is known to exhibit craz-12 ing and shear yielding as inelastic deformation mechanisms, the present work is meant 13 to complement earlier studies where solely shear yielding was considered. In order to 14 analyse the role of either mechanism separately, we here look at the other extreme and 15 assume that the formation and growth of multiple crazes in the glassy matrix between 16 dispersed rubber particles is the major source of overall inelastic strain. This notion is 17 cast into a homogenized material model that explicitly accounts for the specific (cohesive

This paper is concerned with a comparative study of different, partly complementary micromechanical models for crack tip plasticity in polymer-rubber blends. It is experimentally well established that interspersion of micron-scale rubber particles into a polymer matrix can lead to a significantly enhanced toughness of the material. The last two decades have witnessed growing consensus about the underlying mechanisms: particle cavitation, void growth, crazing, and shear yielding. Cavitation of the particles followed by massive shear yielding of the matrix and the resulting dissipation of energy is believed to give blends their improved toughness. At the very microlevel, i.e. at length scales of the order of the micron-sized rubber particles, the key damage processes are well identified and largely understood. Their effect on the macroscopic scale may well be captured in a homogenized sense by continuum models, e.g. of the Gurson-type when focusing on void growth. However, at the scale of a crack, a complete and tractable model incorporating all relevant deformation mechanisms is not yet available. On the one hand, strong gradients of the stress fields violate the assumption of a sufficiently homogeneous material for a continuum representation to be valid, while on the other hand the length scale involved is too large in practice to model all particles individually. Therefore, in this paper several models for crack- tip plasticity in blends are combined and compared. Although none of the models introduced pretends to be the final answer, they all shed some light on parts of the solution

A cell model study of crazing and matrix plasticity in rubber-toughened glassy polymers Seelig, Th.; van der Giessen, Erik a b s t r a c tThe competition between crazing and matrix shear yielding in rubber-toughened glassy polymers is investigated by detailed finite element simulations. To this end the microstructure is represented by an axisymmetric unit cell of glassy matrix containing a single cavitated rubber particle which is modeled as a void. The behavior of the matrix material is described in the framework of finite strain viscoplasticity while a cohesive surface model is employed for crazing. The influence of the matrix yield behavior, the craze response, the rubber content, and the overall loading state are analyzed.

To cite this version:Th. Seelig. Computational modeling of deformation mechanisms and failure in thermoplastic multilayer composites. Composites Science and Technology, Elsevier, 2009, 68 (5), pp.1198. <10.1016/j.compscitech.2007.07.017>. C o m p u t a t i o n a l m o d e l i n g o f d e f o r m a t i o n m e c h a n i s m s a n d f a i l u r e i n t h e r m o -p l a s t i c m u l t i l a y e r c o m p o s i t e s T h . S e e l i g P I I : S 0 2 6 6 -3 5 3 8 ( 0 7 ) Accepted Manuscript AbstractThe deformation and failure behavior of composites consisting of multiple alternating layers of a brittle and a ductile amorphous thermoplastic polymer is controlled by the interaction between crazing and shear banding and displays a brittle-to-ductile transition depending on the composition. In order to gain a better understanding of these interrelations in PC/SAN multilayer composites numerical simulations are performed and compared with experimental observations. The set-up of the computational problem utilizes constitutive models for the large strain viscoplastic behavior of glassy polymers as well as a cohesive surface methodology describing the localized formation, growth and breakdown of crazes. The simulations well reproduce the strong dependence of the mode of failure on the relative layer thickness and help to explain how the latter determines whether the composites display a ductile overall response or undergo localized brittle failure by the coalescence of microcracks.