WAVE PROPAGATION IN GRAPHITE/EPOXY LAMINATE DUE TO IMPACT
Abstract
Harmonic wave in a graphite/epoxy laminate was studied using a plate theory that includes transverse shear deformation. Propagation of stress wave front in the laminate was also investigated. The velocity with which the wave front propagates was discussed and the position of wave front as function of time was constructed using ray theory. Contact behavior between spherical steel indenters and graphite/epoxy laminates was determined by performing statical indentation tests. Identation was measured using a Linear Differential Variable Transformer which allowed more accurate estimations of permanent deformations in the laminate. Relation between permanent identation and maximum identation at unloading was found to be approximately linear from the test data. It was shown that the loading and reloading curves follow the power laws with n = 1.5 very well while the power index for the unloading curves exhibited wider scatter. The experimental contact laws were incorporated into a 9-node isoparametric plate finite element program for impact analysis. An impact experiment on graphite/epoxy laminated plate was conducted to verify the validity of the statically determined contact laws in the application of impact analysis. The strain histories at several locations on the plate and the impact loading were measured using surface strain gages and an impact-force transducer, respectively. Excellent agreements were found for both strain history and impact loading on comparing the experimental results with finite element solutions. This indicates that the statical contact laws are adequate in describing the contact behavior under low velocity impact conditions.
Degree
Ph.D.
Subject Area
Aerospace materials
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