Formation of resin matrix defects is common during composites manufacturing. The mechanisms behind these defects depend on the state of the resin at the time of their formation. Process-induced matrix defects are commonly studied in the form of porosity before gelation, or matrix cracking after vitrification. The present study investigates defect formation when the thermoset resin is between gelation and vitrification.

After gelation, the resin is in a rubbery state and does not flow. At this state, cure in a constrained geometry leads to internal stress development and potential formation of defects. An experimental setup was used which allowed direct visual observation of the resin behavior after gelation. It was found that post-gelation defect formation is driven by hydrostatic stress and the defect morphology is cure rate-dependent. An analytical approach to avoid post-gelation defects based on comprehensive material characterization and internal stress evolution calculations is proposed, and experimentally validated.

树脂基质缺陷的形成在复合材料制造过程中很常见。这些缺陷背后的机理取决于它们形成时树脂的状态。过程引起的基体缺陷通常以胶凝前的孔隙率或玻璃化后的基体开裂的形式进行研究。本研究调查了热固性树脂处于凝胶化和玻璃化之间时的缺陷形成。

胶凝后，树脂处于橡胶态并且不流动。在这种状态下，以受约束的几何形状进行固化会导致内部应力的发展和缺陷的潜在形成。使用实验设置，其允许在胶凝之后直接视觉观察树脂行为。发现胶凝后缺陷的形成是由静水应力驱动的，并且缺陷的形态与固化速率有关。提出了一种基于全面材料表征和内部应力演化计算的避免后胶凝缺陷的分析方法，并进行了实验验证。