CONTACT BEHAVIOR, IMPACT RESPONSE AND DAMAGE IN GRAPHITE-EPOXY LAMINATES SUBJECTED TO INITIAL STRESSES
Abstract
Analytical methods have been developed to study the problem of indentation of a beam by a rigid cylinder. The contact coefficient is found to depend on the transverse Young's modulus. At smaller loads, initial stresses have no significant effect on the contact behavior. Numerical methods have been developed to compute the response due to low velocity impact. A higher order, rectangular, plane strain finite element was used to model laminated beams under initial stresses. A detailed analysis was conducted to study the effect of initial stresses on the impact response of a graphite-epoxy laminated beam. The effects of preload on the impact duration, coefficient of restitution, maximum impact force, and bending and shear stresses were studied. Low velocity impact tests were conducted to measure the contact force directly during impact. The measured impact response was found to be in good agreement with the finite element computations. Specimens were also impacted with velocities high enough to cause damage. Ultrasonic C-scanning was used to measure the area of delamination. It is found that the tensile initial stresses decrease the threshold velocity for damage, and also the residual tensile strength. But, the extent of delamination can be reduced by the initial stresses.
Degree
Ph.D.
Subject Area
Mechanics
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