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Thermal imaging and thermal stress analysis of the impact damage of composite materials

Composite structures, such as wind blade turbines, can be damaged due to the impact, or damaged during the transportation and montage. In the presented work the thermal imaging and the Thermal Stress Analysis (TSA) have been used to observe the impact on a composite material, and to evaluate the resulting damage. The 1st step included controlled impact and thermal imaging of the impact. The specimen was a four layered 490g/m2 fibreglass roving for polyester resin impacted with a 19, 61J impactor (1kg, 16mm diameter spherical tip, dropped from 2m). The 2nd step included the TSA of the damaged composite cyclically loaded (Fig.1). The TSA is based on the infrared camera (IR) and the Lockin [1, 2]. Every material in elastic tension cools for a short instant, while heats for the case of elastic compression. For the plastic/damage case, thermal energy is generated and heat can be observed for a while. Fig. 2I is the moment before impact. Fig. 2II shows cooled (elastic tension) zone under the impactor. Fig. 2III shows heated zone where the damage in material occurred and the cooled zone around. The last two figures show the generated heat in damaged area after the impact.Fig. 3 shows the stress distribution for damaged and intact specimens. For the damaged specimens, the 0MPa stress at the point of impact, and in damaged glass fibres, is clearly visible.

thermal imaging; Thermal Stress Analysis; impact; damage

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