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热固化树脂在成型过程中产生的残余应力,对其力学性能的影响相当严重。这种残余应力通常分为两类:一类是由单体固化反应中的收缩作用引起的,另一类是由冷却过程中温度分布的不均匀引起的。本文以上下两面都淬火了的热固化树脂矩形梁为例,对后一类残余应力的产生机制进行了理论和实验分析。首先,采用一个粘弹性模型对淬火后的梁的残余应力进行定性预测。其次,假定温度沿梁厚度方向的分布是不稳定的非均匀的,应用线性——粘弹性理论,推导粘弹性矩形梁的残余应力所服从的基本方程,并对两种具有不同粘弹性力学性质的树脂即环氧树脂和不饱和聚酯,在不同的淬火条件下,计算其矩形梁中的残余应力的理论值。两种树脂在每一种淬火条件下,其理论计算的和实验测定的残余应力分布都是非常一致的,这样就证实了定性预测的结果,即在淬火梁中,上表层和下表层附近是压应力,中间部分是拉应力。环氧树脂的松驰模数随时间和温度的变化要比不饱和聚酯大得多。理论和实验分析表明,前者的残余应力要比后者大。因此可引出结论,当树脂的松驰模数随时间和温度发生很大变化时,所形成的残余应力就比较显著了。
The residual stress produced by the thermosetting resin in the forming process has a serious impact on the mechanical properties. This residual stress is usually divided into two categories: one is caused by the contraction of the monomer curing reaction caused by the other is caused by the uneven temperature distribution during cooling. In this paper, a thermosetting resin rectangular beam quenched from the top and the bottom is taken as an example to theoretically and experimentally analyze the mechanism of the latter residual stress. First, a viscoelastic model is used to qualitatively predict the residual stress of quenched beams. Secondly, assuming that the distribution of temperature along the beam thickness is unstable and non-uniform, the basic equations obeyed by the linear-viscoelastic theory and the residual stress of the viscoelastic rectangular beam are deduced. Two different viscoelastic mechanical properties Of the resin that epoxy resin and unsaturated polyester under different quenching conditions, calculate the theoretical value of the residual stress in the rectangular beam. Under both quenching conditions, the theoretical and experimental residual stress distributions of the two resins are very consistent, thus confirming the qualitative predictions that in the quenched beams the upper and lower surface layers are Compressive stress, the middle part is the tensile stress. The relaxation modulus of epoxy resin changes with time and temperature much more than unsaturated polyester. Theoretical and experimental analysis shows that the former’s residual stress is greater than the latter. Therefore, it can be concluded that when the relaxation modulus of the resin changes greatly with time and temperature, the residual stress is more significant.