Abstract This work studies the relation of the strain fields, final failure patterns and the apparent flexural modulus in CFRP laminates subjected to quasi-static indentation (QSI) with the in-plane mutiaxial loading state produced. QSI tests could be utilised for evaluating the degradation process in composites under low-velocity impacts (LVI) whenever analogous damage initiation and propagation are expected. Then, the research is focused on the LVI and QSI response of [±45]4S squared-plates simply-supported in a circular steel window. Similar levels of internal energy are found in the most notable events during the loading process, what supports the comparable final failure patterns observed. Nevertheless angle-ply laminates under LVI present non-negligible higher levels of apparent rigidity, opening the possibility of a certain efferct of the strain rate on the impact response. Besides, [0 90]4S configurations are taken into consideration for reviewing the effect on the results of the stacking sequence out of the simply-supported region. A strong influence on the internal energy is found, being 41.7% higher in angle-ply than in cross-ply laminates. The analytical estimation of the multiaxial apparent linear response of the laminate combined with the measured strains are utilised for the qualitative description of the experimental final failure modes. The deformation fields in QSI testing are acquired by Digital Image Correlation techniques and strain gauges, completing the analysis with the results of a finite element approach. The variation of the apparent flexural modulus with the in-plane loading direction leads to non-simetrical strain fields and lower out-of-plane displacements in the stiffer direction.

中文翻译：

---

±45° 角层 CFRP 板在低速冲击和准静态压痕下的机械响应：多向应变状态的影响

摘要 本工作研究了 CFRP 层压板在产生面内多轴加载状态下，在准静态压痕 (QSI) 下的应变场、最终破坏模式和表观弯曲模量之间的关系。QSI 测试可用于评估复合材料在低速冲击 (LVI) 下的降解过程，只要预计会发生类似的损伤。然后，研究重点是在圆形钢窗中简支[±45]4S方板的LVI和QSI响应。在加载过程中最显着的事件中发现了类似的内部能量水平，这支持观察到的可比较的最终故障模式。然而，LVI 下的角层层压板具有不可忽略的更高水平的表观刚度，开启了应变率对冲击响应产生一定影响的可能性。此外，还考虑了[0 90] 4S构型，以考察简支区域外堆叠序列对结果的影响。发现对内能的影响很大，角层比交叉层高 41.7%。层压板的多轴表观线性响应的分析估计与测量的应变相结合，用于对实验最终失效模式进行定性描述。QSI 测试中的变形场是通过数字图像相关技术和应变仪获取的，并通过有限元方法的结果完成分析。