Abstract Highly-curved laminates are prone to fail by delamination when they are loaded under a bending moment which tries to flatten the laminate. This failure, commonly called unfolding failure, has been traditionally associated with the tensile interlaminar stresses which appear in the laminate, due to its high curvature. However, some specimens failing by unfolding present a maximum interlaminar tensile stress, at the failure instant, much lower than other specimens with different thicknesses or stacking sequences. This fact has been commonly associated with a thickness dependence of the interlaminar tensile strength for which no physical explanation can be found in the literature, although sometimes it has been attributed to manufacturing defects, which are assumed to be higher in thinner laminates. The present work considers the idea of a second failure mechanism named induced unfolding, which assumes that an intralaminar failure is responsible for the failure onset. Therefore, in some cases, the unfolding failure starts as an intralaminar crack which, under a high enough interlaminar tensile stress, propagates instantaneously, causing the delamination and the final failure. Analysing the results of a test campaign, proofs of the occurrence of this kind of failure on L-shape CFRP laminates of UD plies are reported.

中文翻译：

---

复合材料层合板展开失效的竞争机制

摘要 高度弯曲的层压板在试图压平层压板的弯矩下加载时容易因分层而失效。这种失效通常称为展开失效，传统上与​​层压板中出现的层间拉伸应力有关，因为它的曲率很高。然而，一些因展开而失效的试样在破坏瞬间呈现最大层间拉伸应力，远低于具有不同厚度或堆叠顺序的其他试样。这一事实通常与层间拉伸强度的厚度依赖性有关，在文献中找不到物理解释，尽管有时它被归因于制造缺陷，假设在较薄的层压板中这种缺陷更高。目前的工作考虑了称为诱导展开的第二种失效机制的想法，它假设层内失效是失效发生的原因。因此，在某些情况下，展开破坏以层内裂纹开始，在足够高的层间拉伸应力下，该裂纹会瞬间传播，导致分层和最终破坏。分析测试活动的结果，报告了在 UD 层的 L 形 CFRP 层压板上发生这种故障的证据。导致分层和最终失败。分析测试活动的结果，报告了在 UD 层的 L 形 CFRP 层压板上发生这种故障的证据。导致分层和最终失败。分析测试活动的结果，报告了在 UD 层的 L 形 CFRP 层压板上发生这种故障的证据。