Damage Threshold Characterization in Structural Composite Materials and Composite Joints

摘要

This program consisted of three tasks related to damage thresholds. Task A explored test methods for characterizing fatigue damage thresholds in resin infused laminates through a complex structured coupon containing ply drops, representative of large composite structures. The complex coupon provides a context for comparing different infusion resins which is economical, but representative of complex structure. Test results and simulations for damage growth and damage thresholds under reversed fatigue loading are given for several types of infusion resins. Task B explored the potential of qualifying new material damage thresholds with multi-axial testing, wherein the material constitutive response in multi-axial strain space is an empirical parameter instead of an assumed functional form. The onset of damage, plus damage progression was monitored for fiberglass/epoxy and carbon fiber/epoxy laminates. A damage metric, known as Dissipated Energy Density (DED) was developed, as well as nonlinear constitutive relationships for continuum based finite element modeling. In Task C a methodology for adhesive joint characterization using the geometry independent nonlinear constitutive behavior of the adhesives from joint tests was developed in conjunction with Boeing. This methodology enabled the use of dissipated strain energy density as the metric to evaluate onset of damage and growth in strain space, for FM300 adhesive with aluminum and carbon/epoxy joints.