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Non-destructive testing method of PMI foam composite sandwich structure

Update:29-06-2021
Summary:

The simple PMI foam sandwich structure consists of thre […]

The simple PMI foam sandwich structure consists of three parts: the panel, the core material and the glued joint. The load is transferred between the first two components through the glued joint. The function of the sandwich structure is to allow the lightweight core material with a certain thickness to withstand shear stress, while at the same time separating two relatively tough and thin load-bearing panels.

 

For the panel, the main consideration is the strength and rigidity of the material, but for the core material, the main purpose is to reduce the weight the most. In aircraft structure, aluminum honeycomb, foam or NOMEX® honeycomb is usually used as the core material. Aluminum honeycomb or NOMEX® honeycomb has the advantages of high compressive modulus and light weight. It is a widely used sandwich material in the aerospace industry and is usually used with carbon/glass fiber prepreg. This article mainly discusses the non-destructive testing of the foam core sandwich structure.

In the field of composite materials, foam core sandwich structures are commonly used in wing leading edges and rudders, landing gear doors, wing body/wing tip fairings, etc. Similar to the honeycomb sandwich structure, the common defects of foam composite materials are: defects of composite material panels, such as scratches, cracks, pores, inclusions, etc. Bonding defects between the composite panel and the foam core, such as debonding. Damage to the PMI foam core.

 

In response to these defects, a variety of non-destructive testing methods have been developed accordingly. However, the foam sandwich structure generally has a large detection area, thin thickness, low thermal conductivity and electrical conductivity, and large sound attenuation of foam materials, so it is significantly different from the nondestructive testing of general composite materials. At present, the non-destructive testing methods suitable for PMI foam sandwich structure mainly include ultrasonic non-destructive testing and laser dislocation speckle interference non-destructive testing.