Holographic Interferometry Measurement and Theoretical Analysis of Deformations of Composite Laminates due to Interlaminar Stresses

研究了层合板在均布机械载荷和湿热载荷作用下层间应力引起的变形，以了解层合板最常见的破坏模式之一--分层的机理。采用准三维有限元方法，在假设应力沿自由边或横向裂纹方向不变的情况下，分析了自由边或横向裂纹尖端附近的变形。提出了一种叠加法，将自由边问题和横向裂纹尖端问题分别转化为均匀应力作用下无限大层合板和自由边面和横向裂纹面分别受外力作用的层合板的叠加问题。利用全息干涉法测量了石墨-环氧层压板试件在纯弯矩和均匀拉伸载荷作用下的变形。在自由边的循环拉伸载荷作用下产生了脱层。由弯矩引起的总变形与基于经典层合板理论的无限大层合板的理论预测相吻合。由于层间应力引起的自由边附近的变形与整体弯曲变形相比很小，因此无法检测到。对于含脱层的层合板，在拉伸载荷作用下，观察到层合板在自由边附近由于层间应力引起的变形，验证了有限元数值结果。

Deformations due to the interlaminar stresses in the composite laminates subjected to the uniform mechanical and hygrothermal loadings were investigated in order to understand the mechanism of the delamination which is one of the most frequently observed fallure modes of the laminates.By the quasi three-demensional finite element method, the deformations in the vicinity of the free edges or the transverse crack tips were analyzed assuming that the stresses do not vary along the direction of the free edge or the transverse crack. The superposition method was proposed where the free edge problem and the transverse crack tip problem are transformed to the superpositions of the infinite laminate under uniform stresses and the configurations with external loads applied on the free edge surface and the transverse crack surface, respectively. The superposition technique can eliminate the deformations not resulting from the interlaminar stresses.By the holographic interferometry, the deformations of the graphite-epoxy laminates coupons under the pure bending moment or the uniform tensile load were measured. The delaminations were introduced by the cyclic tensile loading at the free edges. The overall deformations by the bending moment coincided with the theoretical predictions for the deformations of the infinite laminates based on the classical lamination theory. The deformation near the free edges due to the interlaminar stresses could not be detected since they were small compared to the overall bending deformations. The deformation near the free edges due to the interlaminar stresses in the laminates under the tensile loads were observed for the coupons with delaminations, verifying the numerical results by the finite element method.