形状记忆聚合物热力学本构方程

THERMOMECHANICAL CONSTITUTIVE EQUATIONS OF SHAPE MEMORY POLYMERS

借鉴聚合物结晶学相关理论,建立了一个针对该类材料的新的热力学本构关系,通过与已有实验结果相比较,发现理论预测值与实验吻合较好.

Since the shape memory and recovery characteristics of shape memory polymers （SMPs） are realized by a certain thermalmeehanical cycling process, the thermomechanical constitutive equations are critical for predicting the deformation and recovery of this class of materials at different constraint conditions. In this study, a new physicalbased, temperature and time-dependent constitutive model was proposed. The crystallization theory was used for reference to describe the frozen fraction of SMPs, and the frozen retardant time at the cooling/heating cycle was considered in the constitutive equations. In order to consider both matrix/reinforcement and reinforcement/ reinforcement actions during the shape changing process, Moil-Tanaka approach was used to predict the effective elastic modulus. Moreover, the thermal- and mechanical-frozen fractions as a function of the temperature were compared. The mechanical strain determines the shape storage characteristics of SMPs and will be frozen mostly at the temperature to be lower than the shape changing temperatures （ Ttran= ） of SMPs. The thermal strain, however, mainly determines the instant recovery stress of SMPs during the shape recovery stage, and the part accumulated at T 〈 Tran can hardly be frozen. Hence, the values of the mechanical and thermal frozen fractions at the same temperature are different. Finally, the stress responses at different strain conditions during the cooling process were predicted by the new model, and the results exhibited to be much agreeable with the testing values.