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| Interfacial crack propagation study for sandwich composites with visco-elastic core after unloading |
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Abstract 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.
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Received: 06 September 2016
Published: 28 August 2017
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2017, Vol. 38 
