Failure of composite laminates, in load cases where transverse shear prevail, involves shear cracks and delaminations, and yet it is unclear which damage mechanism triggers the other or how it depends on ply-thickness. Combining interrupted interlaminar shear strength tests with X-ray tomography inspections, we compared the damage sequence of ${[45°/0°/-45°/90°]}_{\mathit{ns}}$ short-beam specimens manufactured with standard- ($n=2$) or thin-ply ($n=4$) non-crimp fabrics (fibre areal weights of 134 and 67 gsm per ply). Failure manifested as a load drop in the force-displacement curve. In both materials, we associated the onset of instability to a shear crack tunnelling across the central ${90}_2°$ ply-cluster. The intersection of this crack with the ones developing in the adjacent layers induced a delamination which, in turn, activated the load drop. A 3D elasto-plastic model predicted that, for the same applied load, the ply-cluster of both laminates would display a similar maximum principal stress distribution. However, the thin-ply samples improved the interlaminar shear strength by 34%, evidencing the so called in-situ effect: the resistance to matrix cracking under transverse shear (${\tau }_{23}$ in the local coordinates of the $90°$ plies) increases when ply-thickness is reduced.

在发生横向剪切的载荷情况下，复合材料层压板的失效会引起剪切裂纹和分层，但尚不清楚哪种破坏机制会触发另一种破坏机制或它如何取决于层厚。将间断的层间剪切强度测试与X射线断层扫描检查相结合，我们比较了损伤的顺序${[45°/0°/--45°/90°]}_{\mathit{ns}}$ 标准制造的短光束试样-（$ñ=2$）或薄（$ñ=4$）非卷曲织物（每层纤维的单位面积重量为134和67 gsm）。失效表现为力-位移曲线中的载荷下降。在这两种材料中，我们都将不稳定的发生与横穿中心的剪切裂缝隧道联系起来。${90}_2°$层簇。该裂纹与在相邻层中形成的裂纹的相交处引起分层，从而激活了载荷下降。3D弹塑性模型预测，对于相同的施加载荷，两个层压板的层状簇都将显示相似的最大主应力分布。然而，薄层样品将层间剪切强度提高了34％，证明了所谓的原位效应：在横向剪切作用下对基体开裂的抵抗力（${\tau }_{23}$ 在本地坐标 $90°$ 当厚度减小时，厚度增加。