Failure Criteria for Low-Temperature Irradiated Organic Composite Insulation Systems
Composite insulation systems in fusion magnet applications are often subjected to conditions of combined through thickness compression and shear at varying stress ratios. Characterization of insulation system strength under these conditions requires unidirectional shear and compression tests, as well as biaxial shear/compression testing to define the systems’ failure envelope. An appropriate failure criteria would reduce the number of tests required to define this envelope, and would give designers a better estimate of material strengths at intermediate stress ratios. Biaxial shear/compression testing requires the use of metallic sandwich specimens, which are susceptible to activation during irradiation. A reliable failure criteria which eliminates the need for biaxial characterization would also reduce the difficulty and expense involved in radiation effects characterization while still providing a complete failure envelope.
Several generalized failure criteria, taken from classical composites analysis, were reformulated for application in the shear/compression quadrant. The maximum stress and Tsai-Hill criteria were found to be inadequate to represent the biaxial failure envelope. The generalized Tsai-Wu tensor quadratic failure criterion was also examined. Application of this criterion requires through thickness tensile strength data. Through thickness tensile strengths of insulation systems have not been routinely characterized, but limited data are available. Utilizing unidirectional through thickness tension, compression, and interlaminar shear strength data, the Tsai-Wu failure criteria was found to agree well with biaxial shear/compression test data.
KeywordsFailure Criterion Failure Envelope Insulation System Classical Laminate Plate Theory Short Beam Shear
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