超声波塑料焊接粘弹性热的仿真计算

Simulation of viscoelastic heat during ultrasonic welding of thermoplastics

粘弹性热是超声波塑料焊接的主要热源之一.针对目前已有方法在计算粘弹性热时不能很好的体现聚合物材料的动态粘弹性而产生较大误差的缺点,首先利用静态松弛模量和"时温等效性原理"对材料的动态粘弹性进行表征,该方法把动态模量表示成温度和频率的函数,避免了动态模量这一复杂过程.提出了一种用于超声波焊接过程中粘弹性热计算的策略,并对周期载荷作用下PMMA二维模型的粘弹产热过程进行了有限元仿真.结果表明,所得的温度变化趋势与文献中的试验测量结果基本相符.

Viscoelastic heat is one of the main heat sources during ultrasonic welding of thermoplastics.Unfortunately the present works could not definitely take into account the dynamic viscoelasticity of thermoplastics.In this paper a simplified method was proposed to characterize dynamic viscoelasticity based on static relaxation modulus and TTEP(time-temperature equivalent principle).The method could represent dynamic modulus as the function of temperature and frequency,and avoids calculating dynamic modulus of high frequency by shifting and extrapolating the dynamic modulus of lower frequency from experiments.With the method mentioned above,a strategy was put forward to simulate the viscoelastic heat of PMMA(polymethyl methacrylate)under periodic load using FEM(finite element method).The calculated temperature shows a similar tendency as tested results in other literatures.