Buckling and Postbuckling Behaviors of Composite Panels with a Delamination

复合材料板的层间断裂韧性较弱，在冲击载荷、疲劳等作用下，容易在层间区域产生层间分层。由于脱层导致的弯曲刚度降低，导致了屈曲载荷和抗压强度的显著下降。这个问题被称为CAI(冲击后压缩)。对于复合材料在飞机结构中的广泛应用来说，计算机辅助设计是一个迫切需要解决的问题，因为它往往成为飞机复合材料结构设计的关键。本研究的目的是为改善复合材料的抗计算机辅助教学性能提供数据。对单向增强复合材料方板和机织复合材料层合板的脱层尺寸和位置对屈曲和后屈曲行为的影响进行了理论分析和试验研究。正方形面板被夹紧在四边，并将其作为二维面板进行研究，以澄清分层对更逼真结构的影响。对分层引起的压缩性能退化的复杂机理进行了观察和研究。本文发展的基于Rayleigh-Ritz近似的分析不仅可以很好地解释屈曲行为，而且可以很好地解释包括二次屈曲在内的非常复杂的后屈曲行为。

Interlaminar delaminations are introduced easily in the interlaminar area of composite panels by the impact loadings, fatigue etc owing to its weak interlaminar fracture toughness. The decrease of the bending rigidity due to the delaminations causes significant drops of the buckling load and the compressive strength of the panel. This problem is called CAI (Compression After Impact)". CAI is an urgent issue for the wider application of the composite materials to the airplane structures, because it often becomes critical for the design of the composite structures of airplanes. The objective of the present research is to get the data to improve the properties of the composite materials against CAI. The effects of delamination size and position on the buckling and postbuckling behaviors are studied analytically and experimentally about unidirectionally reinforced composite square panels in the first year and woven composite laminates in the second year. The square panels are clamped on the four sides and studied as a two dimensional panel in order to clarify the effects of the delamination on the more realistic structure. The complex mechanisms of the compressive property degradation owing to the delamination are observed and investigated. The analysis developed in the present research based on the Rayleigh-Ritz approximation can explain well not only the buckling behaviors but also the very complex postbuckling behaviors including secondary buckling.