压差载荷对蜂窝夹层结构分层扩展影响研究

复合材料蜂窝夹层结构随飞机起飞-巡航-降落过程中,反复经受内外压差载荷。为研究地空地压差载荷对复合材料蜂窝夹层结构中蒙皮和蜂窝之间胶接面分层扩展行为的影响,设计了可叠加压差疲劳载荷谱和压缩疲劳载荷谱的试验装置,对含预埋分层的复合材料蜂窝夹层平板开展了重复载荷试验研究,一组试验施加压缩疲劳载荷谱,另一组试验施加压缩疲劳载荷谱叠加地空地压差载荷谱。破坏试验件的剖切检查表明预埋分层沿垂直于压缩载荷方向在胶接层内扩展。在约80%极限载荷水平的压缩疲劳载荷谱下,分层初始经历一段缓慢扩展,达到一定程度后开始加速扩展直至破坏。叠加的压差载荷谱使分层扩展速率显著加快。基于试验构型的有限元仿真分析表明压差载荷作用下蒙皮与蜂窝之间的面外剥离应力是导致损伤扩展加快的主要原因。

The influence of pressure differential loads on the delamination propagation of honeycomb sandwich structure

With the repeated cycles of aircraft take-off-cruise-landing, the composite honeycomb sandwich structures undertakes pressure differential loads. To research the influence of the repeated ground-air-ground pressure differential loads on the delamination propagation behavior, a test fixture was designed to apply compression loads while applying pressure differential loads simultaneously. Cyclic load tests were performed with composite honeycomb sandwich panel specimen, within which a delamination of diameter 30 millimeters was embedded. One set specimen were tested by compression fatigue loads, as contrast, another set specimen were tested under compression fatigue loads combined with repeated pressure differential loads. The teardown inspection of failed specimen shows that the delamination grows in the bondline in the direction vertical to the loading direction. Under the compression fatigue loads level of about 80% ultimate load, the delamination grows slowly in the initial stage and then accelerates when the delamination size becomes big enough. Compared with the specimen only tested by repeated compression load, the delamination growth rate is much higher in the specimen tested by the combination of repeated compression loads and pressure differential loads. Finite element analysis was then performed, and the results show that the out-of-plane peeling stress between the composite skin panel and the honeycomb caused by the pressure differential load is the main driving force for the accelerated delamination propagation.