SEDL / STP / STP1059-EB / STP24122S

Investigation of Damage in Composite Laminates Using the Incremental Strain Test

Swain, RE
Graduate research assistant and Reynolds Metals professor, Materials Response GroupVirginia Polytechnic Institute and State University, Blacksburg, VA

Reifsnider, KL
Graduate research assistant and Reynolds Metals professor, Materials Response GroupVirginia Polytechnic Institute and State University, Blacksburg, VA

Vittoser, J
Research engineer, Armament Development Authority, Haifa,

Pages: 14    Published: Jan 1990

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Abstract

A new test method, named the incremental strain test (IST), is introduced. In the IST a composite laminate is subjected to an “interrupted-ramp strain input,” allowing for load relaxation to occur at each increment of applied constant strain. The magnitude of this relaxation reflects the change of laminate compliance caused by the inception of time-dependent damage or viscoelastic creep. A variable quantifying the load relaxation, when plotted as a discrete function of applied strain, gives a unique indicationof damage onset, duration, and degree. Such plots are obtained for a quasi-isotropic graphite/epoxy laminate with and without interlayers. IST results are positively correlated with the results of X-ray radiography and acoustic emission. Ultimately, the IST is seen as a potential tool in the investigation of damage development in composite laminates.