Computational modeling of deformation mechanisms and failure in thermoplastic multilayer composites

Abstract

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>. <hal-00545282> 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.

Identification of a cohesive zone model from digital images at the micron-scale

“…The traction-opening profile identified during craze thickening is found to decay slightly (as in Elices et al, 2002) while a profile with a constant traction is suggested in Döll (1983), Döll and Könczöl (1990) and Saad-Gouider et al (2006). There are also studies of fracture in PMMA that suggest some softening in the traction-separation profile (Murphy and Ivankovic, 2005) or a combination of softening followed by hardening (Seelig, 2008). Although no general agreement is found in the traction-separation profile, the order of magnitude of the traction during crazing is comparable, the slight differences in the profile still suggest that an approximately constant or decaying traction-opening is realistic.…”

Mechanical Behavior and Failure Mode of Unidirectional Fiber Composites at Low Strain Rate Level

“…As the strain rate is low, specimen yields, and due to the strain softening, matrix shear failure and/or interfacial failure will occur [29,34], resulting in interface de-bonding and permanent birefringence after unloading. The bonding lines a little away from the fiber break do not break but orient.…”

“…For a low tensile loading rate (2EÀ5 s À1 ), with further loading, the fiber fractures, and almost simultaneously, some lines near the fiber break are disconnected, as the so-called interface de-bonding (Figure 7(b)). As the strain rate is low, specimen yields, and due to the strain softening, matrix shear failure and/or interfacial failure will occur [29,34], resulting in interface de-bonding and permanent birefringence after unloading. The bonding lines a little away from the fiber break do not break but orient.…”

“…So, there is not much permanent deformation for matrix or interphase, resulting in the diminishing of birefringence in a short time (Figure 5(d)). However, for the case that the tensile strain rate is relative high (higher than 2EÀ3 s À1 ), a macro-crack fracture occurs prior to yielding, some of the fibers are pulled out from matrix (Figure 6(c) and (d)), and the fiber breaks on the remaining embedded fragments propagate into matrix (Figure 6(a,b) and Figure 7(d)), which are attributed to strain hardening [34]. The transient orientation of bonding lines relaxes after unloading, consequently leading to a totally disappeared birefringence (Figure 6(b)).…”

Micromechanics of toughening in ductile/brittle polymeric microlaminates: Effect of volume fraction

“…Seelig (2007) has performed 2D plane strain finite element studies on PC/SAN, where he used a cohesive zone framework to model crazes, as well as a finite deformation viscoplastic model to account for shear yielding. While Seelig's numerical studies qualitatively indicate higher toughness with increasing PC volume fraction, the three-dimensional synergistic interactions between crazing and shear yielding have not been investigated.5 Baer and co-workers have investigated microlayered laminates in which the outermost layers were constituted of PC.…”