Damage Evaluation in Composite Materials Using Thermographic Stress Analysis

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Abstract
Damage in composite materials initiates and propagates randomly at many sites, which makes both the monitoring and evaluation of its local and global effects difficult. The recently developed thermographic stress analysis method (TSA) provides unique opportunities for full-field damage investigation. To make quantitative analysis possible, a thermoelasticity theory for damage in anisotropic materials was developed. The TSA method associated with this theory opens new doors in investigating the microstructure-mechanics connection of multiphase materials, and in establishing quantitative prediction capabilities of microscopic behaviors and service lives.Experiments have been performed to measure the damage parameter D, the normalized effective mass density ρc/ρ, and the effective modulus Ec in glass/epoxy [0/90/0/90/0]sand [0/90]5 laminates by the TSA method. Good correlations between the effective moduli of the laminates measured by the TSA method and by an extensometer are found. A relationship between the effective modulus Ec, the undamaged material's modulus E, the number of damaging cyclic loads N, and the peak nominal stress σmax is used to describe the progressive reduction of the modulus. In light of the new thermoelasticity theory for damage, the normalized effective mass density is determined quite easily by the TSA method in comparison with conventional experimental techniques.

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