Abstract:A new elastoplastic J 2 -flow models with thermal effects is proposed toward simulating thermo-coupled finite deformation behaviors of shape memory polymers. In this new model, an elastic potential evolving with development of plastic flow is incorporated to characterize the stress-softening effect at unloading and, moreover, thermo-induced plastic flow is introduced to represent the strain recovery effect at heating. It is shown that any given test data for both effects may be accurately simulated by means of direct and explicit procedures. Numerical examples for model predictions compare well with test data in literature.Keywords: shape memory polymers; thermo-coupled effects; finite deformations; stress softening; elastoplasticity models; explicit simulation
Motivation and IntroductionIn recent years, much attention has been directed to smart materials such as shape memory alloys (SMAs) and shape memory polymers (SMPs) (cf., e.g., [1,2]). It is of great interest to simulate thermo-coupled deformation behaviors of such materials under both loading and heating. Unlike deformation behavior of SMAs with very small elastic deformations, however, SMPs exhibit complicated thermo-mechanical deformation effects coupled with both temperature and large recoverable deformations. Typical representatives of such effects are the stress softening effect at unloading in the isothermal case and the strain recovery effect at pure heating. The former is characteristic of all kinds of polymers and associated with a number of unloading stress-strain curves of complex shapes that differ from one another and result in different permanent sets, while the latter is unique to SMPs and related to the recovery of a large pre-strain at heating. Usually, recoverable strains of SMPs both at unloading and at heating may be several hundred percents. As such, large thermo-coupled inelastic deformations incorporating large recoverable deformations should be treated toward modeling thermo-mechanical behavior of SMPs, in particular, in simulating both the stress-softening effect at unloading and the large strain recovery effect at heating (i.e., the shape memory effect).Many efforts have been made to establish constitutive models for the purpose of incorporating the above two effects. As a typical isothermal deformation feature for various kinds of polymers, the stress softening effect at unloading was observed earlier and has been simulated for some time. Results in this respect have been given based either on phenomenological models with damage-like variables or micro-mechanical models with macromolecular mechanisms. Representatives in these respects may be found, e.g., earlier in [3] and later in [4][5][6][7][8][9][10][11][12][13][14] for phenomenological models, and in [15][16][17][18][19][20][21][22][23][24][25] for micro-mechanical models. On the other side, the modeling of the shape memory effect for SMPs is relatively recent. Results in this respect and, generally, in the thermo-mechanical behavior of SMPs may be found, e.g., in ...