Intrinsic strain softening appears to be the main cause for the occurrence of plastic localization phenomena in deformation of glassy polymers. This is supported by the homogeneous plastic deformation behavior that is observed in polycarbonate samples that have been mechanically pretreated to remove (saturate) the strain softening effect. In this study, some experimental results are presented and a numerical analysis is performed simulating the effect of mechanical conditioning by cyclic torsion on the subsequent deformation of polycarbonate. To facilitate the numerical analysis of the “mechanical rejuvenation” effect, a previously developed model, the “compressible Leonov model,” is extended to describe the phenomenological aspects of the large strain mechanical behavior of glassy polymers. The model covers common observable features, like strain rate, temperature and pressure dependent yield, and the subsequent strain softening and strain-hardening phenomena. The model, as presented in this study, is purely “single mode” (i.e., only one relaxation time is involved), and therefore it is not possible to capture the nonlinear viscoelastic pre-yield behavior accurately. The attention is particularly focused on the large strain phenomena. From the simulations it becomes clear that the preconditioning treatment removes the intrinsic softening effect, which leads to a more stable mode of deformation. [S0094-4289(00)01002-1]

Abstract. Stretchable electronics offer increased design freedom of electronic products. Typically, small rigid semiconductor islands are interconnected with thin metal conductor lines on top of, or encapsulated in, a highly compliant substrate, such as a rubber material. A key requirement is large stretchability, i.e. the ability to withstand large deformations during usage without any loss of functionality. Stretching induced delamination is one of the major failure modes that determines the amount of stretchability that can be achieved for a given interconnect design. During peel testing, performed to characterize the interface behaviour, the rubber is severely lifted at the delamination front while at the same time fibrillation of the rubber at the peel front is observed by ESEM analyses. The interface properties are established by combining the results of numerical simulations and peeling experiments at two distinct scales: the global force-displacement curves and local rubber lift geometries. The thus quantified parameters are used to predict the delamination behaviour of zigzag and horseshoe patterned interconnect structures. The accuracy of these finite element simulations is assessed by a comparison of the calculated evolution of the shape of the interconnect structures and the fibrillation areas during stretching with experimental results obtained by detailed in-situ analyses.

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