基于多级松弛机制的形状记忆聚氨酯循环热-力学本构模型

Multiple relaxation mechanism-based thermo-mechanical constitutive model describing cyclic shape memory effect of shape memory polyurethane

松弛作为形状记忆聚合物的固有特性,在其机械变形和形状记忆行为中起着至关重要的作用.在形状记忆过程中,松弛行为包含了短期、中期和长期机制,这些机制共同组成了多级松弛机制.基于多级松弛机制,结合热弹性行为和相转变模型,在有限变形框架下建立了热致形状记忆聚氨酯的循环热-力学本构模型。在此模型中,着重考虑黏度随温度的变化,优化了相转变模型框架中温度对机械变形的影响。为了进一步描述橡胶相和冻结相之间的循环转变行为,引入循环的储存应变比,表征了循环形状记忆过程中变形的储存和释放机制与相转变之间的关系。与不同应变幅值和应变速率下的循环形状记忆实验结果对比,验证了所建立的基于多级松弛机制的循环热-力学本构模型能合理地描述形状记忆聚氨酯的循环形状记忆行为.

As an inherent property of the shape memory polymers(SMPs),relaxation plays a crucial role in their mechanical deformation and shape memory effect(SME).During the shape memory processes,relaxation behavior can be divided into short-,medium-,and long-term mechanisms that collectively contribute to the multiple relaxation mechanisms.In this study,based on the multiple relaxation mechanisms,we establish a thermo-mechanical constitutive model for the thermo-induced shape memory polyurethane(TSMPU)within the finite deformation framework.Additionally,the effect of temperature on mechanical deformation is further optimized by considering the change of viscosity with temperature.To further characterize the cyclic transition behavior between the rubbery and the frozen phases,we employ the storage strain ratio to describe the storage and release of deformation during the cyclic SME.The proposed cyclic thermo-mechanical model effectively captures the cyclic SME of TSMPU as demonstrated through comparison with the experimental results at various strain amplitudes and strain rates.