Dhaliwal Gurpinder Singh, Newaz Golam M
Department of Mechanical Engineering, Wayne State University, Detroit, MI 48201, USA.
Materials (Basel). 2020 Nov 27;13(23):5399. doi: 10.3390/ma13235399.
Structural systems developed from novel materials that are more durable and less prone to maintenance during the service lifetime are in great demand. Due to many advantages such as being lightweight as well as having high strength, corrosion resistance, and durability, the sandwich composites structures, in particular, have attracted attention as favorable materials for speedy and durable structural constructions. In the present research, an experimental investigation is carried out to investigate the flexural response of sandwich beams with a pre-cracked core-upper facesheet interface located at one end of the beam. During the development of the sandwich beams, an initial pre-cracked debond was created between the core and facesheet by placing a Teflon sheet at the interface. Both three-point and four-point flexural tests were conducted to characterize the flexural behavior of the sandwich beams. The effects of the loading rate, core thickness, and placement of the initial interfacial crack under a compressive or tensile stress state on the response and failure mechanism of Carbon Fiber-Reinforced Polymer (CFRP)/Polyurethane (PU) foam sandwich beams were investigated. It was found that the crack tip of the initial debonding between the upper facesheet and the core served as a damage initiation trigger followed by the fracture failure of the core due to the growth of the initial crack into the core in an out-of-plane mode. Finally, this leads to facesheet damage and rupture under flexural loadings. An increase in the core thickness resulted in a higher peak load, but the failure of the sandwich beam was observed to occur at significantly lower displacement values. It was found that the behavior of sandwich beams with higher core thickness was loading rate-sensitive, resulting in stiffer response as the loading rate was increased from 0.05 to 1.5 mm/s. This change in stiffness (10-15%) could be related to the squeezing of all pore space, resulting in the collapse of cell walls and thereby making the cell behave as a solid material. As a result, the occurrence of the densification phase in thick core beams occurs at a faster rate, which in turn makes the thick cored sandwich beams exhibit loading rate-sensitive behavior.
人们对由新型材料开发的结构系统有很大需求，这些材料在使用寿命期间更耐用且维护需求更少。特别是夹层复合材料结构，由于具有轻质、高强度、耐腐蚀和耐用等诸多优点，已作为快速且耐用的结构建造的理想材料而受到关注。在本研究中，进行了一项实验研究，以探究位于梁一端的具有预裂核心 - 上层面板界面的夹层梁的弯曲响应。在夹层梁的制作过程中，通过在界面处放置一块特氟龙片，在核心与面板之间创建了一个初始预裂脱粘。进行了三点和四点弯曲试验，以表征夹层梁的弯曲行为。研究了加载速率、核心厚度以及初始界面裂纹在压缩或拉伸应力状态下的位置对碳纤维增强聚合物（CFRP）/聚氨酯（PU）泡沫夹层梁的响应和破坏机制的影响。研究发现，上层面板与核心之间初始脱粘的裂纹尖端作为损伤起始触发点，随后由于初始裂纹以平面外模式向核心扩展，导致核心发生断裂破坏。最后，这导致在弯曲载荷作用下面板损坏和破裂。核心厚度的增加导致峰值载荷更高，但观察到夹层梁在显著更低的位移值时发生破坏。研究发现，具有较高核心厚度的夹层梁的行为对加载速率敏感，当加载速率从0.05毫米/秒增加到1.5毫米/秒时，响应变得更硬。这种刚度变化（10 - 15%）可能与所有孔隙空间的挤压有关，导致细胞壁坍塌，从而使单元表现为固体材料。因此，厚核心梁中致密化阶段的发生速率更快，这反过来使厚核心夹层梁表现出对加载速率敏感的行为。
