均布外压下复合材料球壳脱层跳跃屈曲研究

Research on the delamination snap buckling of composite spherical shells under uniform external pressure

本文提出了一种研究均布外压下复合材料球壳内表面薄层脱层屈曲特性的理论方法,基于弹性相似性原理建立了复合材料球壳受压内表面脱层跳跃屈曲的模型,采用非线性大挠度理论建立了脱层屈曲的控制方程,分别研究了初始状态含脱层和不含脱层的复合材料球壳的脱层屈曲特性,得到了两种情况下脱层屈曲临界载荷的表达式,讨论了脱层厚度、脱层位置、脱层大小对脱层临界屈曲载荷的影响。结果表明:对于初始状态靠近内表面存在脱层的复合材料球壳,如果脱层厚度很薄,在压力达到一定值时,内表面的脱层区域将发生跳跃屈曲,其屈曲的挠度远远大于脱层的厚度,屈曲的临界载荷随脱层大小的增大而增大,且与脱层厚度几乎成正比;对于初始状态不含脱层的受压复合材料球壳,在靠近其内表面区域存在一个位置,其对应的脱层屈曲临界载荷为最小,最有可能脱离球壳整体,发生跳跃屈曲;如果层间强度不足,该脱层还有可能进一步地扩展,从而导致薄层大面积地脱离整体,降低结构刚度。

A theoretical approach for investigating the characteristics of buckling coupled with delamination(snap buckling)of composite spherical shells under uniform external pressure is presented in this paper.A delamination snap buckling model for a composite shell subjected to external hydrostatic pressure is developed by the principle of elastic similarity.The governing equation for such delamination buckling is derived from nonlinear large deflection theory.The delamination buckling characteristics of the composite spherical shell with and without initial delamination are respectively studied.With the corresponding critical loads in both these two cases obtained,the effects of delamination thickness,delamination location and delamination size on the critical loads of buckling coupled with delamination are finally investigated respectively.It is shown that,if there is an initial delamination near the inner surface of the composite shell,snap buckling of this thin delaminated ply will take place when the pressure reaches a critical value and deflection(of the concaved film going toward the sphere center)is far larger than the ply thickness.The critical load of buckling coupled with delamination increases very little with the delamination propogating to quite a no-small extent,and is approximately proportional to the thickness ratio of the delaminated and the whole.As far as a composite spherical shell without any initial delamination is concerned,there is a position near the inner surface,where the corresponding delamination buckling critical load is the smallest,the shell is most likely to detach from the whole spherical shell and snap buckling occurs.The delamination may be further progressing in case of insufficiency of interlaminar bond strength,resulting in a larger-scaled detachment of the thin film from the whole shell and reduction of structure stiffness.