A crack growth rate model with load history effects for mode I fatigue-driven delamination under multi-level block loading

Load interaction effects in fatigue-driven delamination in fiber-reinforced polymer composites are neglected in state-of-the-art models although this assumption highly underestimates the delamination growth under variable amplitude (VA) loading. A new phenomenon called “transient delamination growth” has recently been observed in VA fatigue experiments by the authors. In the current work a new crack growth rate model with transient delamination growth capabilities is presented. The new model evaluates the crack growth rate by addition of a steady-state non-interaction term and a transient interaction term. The former term neglects load interaction effects and is characterized from constant amplitude loading tests, while the latter term includes load interaction effects and is characterized from two-level block loading tests. Fatigue tests are conducted on glass/epoxy DCB specimens by means of a new test fixture. The new crack growth rate model is able to accurately represent the crack growth rate at high-to-low load amplitude changes during multi-level block loading tests and reduces the error in delamination growth prediction by nearly 50% compared to non-interaction models.