粘弹性夹心夹层结构卸载后的裂纹持续扩展现象研究

以聚氨酯弹性体钢夹层板为研究对象，对其进行了三点弯曲实验，对不同类型试件的实验结果进行了总结。实验发现，在加载过程中，在弯曲挠度超过一定程度时，夹层板结构的角点位置出现开裂，由于层间强度不足和夹心材料的粘弹性性质，卸载后裂纹会在一段时间内沿层间继续发生扩展，最后导致整个面板发生脱粘或夹心撕裂。针对这一现象，以弹性地基梁理论为基础，计算了上下面板的挠度差异，并使用层间粘结强度来分析试件的临界状态，获得了软夹芯试件和硬夹芯试件的临界破坏的裂纹长度。结果表明，使用层间粘结强度分析方法，获得的结果都能够描述聚氨酯弹性体钢夹层板的层间延迟破坏的特点。

Interfacial crack propagation study for sandwich composites with visco-elastic core after unloading

Sandwich plate with steel faceplates and polyurethane elastomer core (SPS) is a new type of composite which is wildly used in shipbuilding and civil engineering. Lightweight, high strength, excellent fatigue resistance and good workability make SPS have more application prospects. Debonding is one of main failure modes of SPS under bending loads and interface strength is the key factor to determine bending strength. In this paper, 3-points bending tests are carried out to investigate bending performance of SPS. Different failure modes are obtained and discussed with different manufacture ways. It can be observed from bending tests that when the deflection exceed a certain range, the crack will appear in loading process. And it will lead to debonding of whole interface between faceplates and polyurethane (PU) core in the following unloading process. The reason of this phenomenon is PU core has viscoelasticity characteristic and lower interface strength, so the debonding process does not happen immediately after tests, but take a period of time before upper faceplate debonds from the core. In case of cohesive interface manufactured by glue, the core will be tear out at location of 1/3 length of specimen. These phenomenon are illustrated by a series of analysis: Firstly, deflection difference between upper faceplate and under faceplate is calculated by introducing the theory of beam on elastic foundation. Secondly, plastic analysis of sandwich plate is carried out and cohesive strength analysis is utilized to evaluate the critical state of crack propagation. Finally, critical interface crack lengths are obtained for different core types and at same time, relationship between different bending angle and crack length is also given to address interactions between critical crack length and cohesive stress. The results show that the former analysis based on interface cohesive strength can illustrate the characteristics of interface delay debonding for sandwich plate with viscoelastic core.