Cure shrinkage accumulated only after the gel point is known as effective cure shrinkage (ECS), which produces residual stresses inside molded components. The ECS of an epoxy-based molding compound (EMC) is measured by an embedded fiber Bragg grating (FBG) sensor. Under a typical molding condition, a high mold pressure inherently produces large friction between EMC and mold inner surfaces, which hinders EMC from contracting freely during curing. A two-stage curing process is developed to cope with the problem. In the first stage, an FBG sensor is embedded in EMC by a molding process, and the FBG-EMC assembly is separated from the mold at room temperature. The molded specimen is heated to a cure temperature rapidly in the second stage using a constraint-free curing fixture. Several technical issues have to be taken into considerations to ensure that (1) EMC does not pass the gel point before it reaches the cure temperature, and (2) EMC cures uniformly around the FBG during measurements. The ECS of an EMC with a filler content of 88 wt% is measured by the proposed method, and its value is 0.077%. The repeatability of the proposed method is corroborated by the results of a duplicate test.

中文翻译：

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基于光纤布拉格光栅传感器的两阶段固化过程测量环氧基模塑料的有效固化收缩率

仅在胶凝点之后累积的固化收缩称为有效固化收缩 (ECS)，它会在成型部件内部产生残余应力。环氧基模塑料 (EMC) 的 ECS 由嵌入式光纤布拉格光栅 (FBG) 传感器测量。在典型的成型条件下，高模具压力固有地在 EMC 和模具内表面之间产生很大的摩擦，这阻碍了 EMC 在固化过程中自由收缩。开发了一种两阶段固化工艺来解决这个问题。在第一阶段，FBG传感器通过成型工艺嵌入EMC中，FBG-EMC组件在室温下与模具分离。在第二阶段使用无约束固化夹具将模制样品快速加热到固化温度。必须考虑几个技术问题，以确保 (1) EMC 在达到固化温度之前不会超过凝胶点，以及 (2) EMC 在测量期间在 FBG 周围均匀固化。用所提出的方法测量填料含量为 88 wt% 的 EMC 的 ECS，其值为 0.077%。重复测试的结果证实了所提出方法的可重复性。