On Mode I Fatigue Crack Growth in Foam Core Materials for Sandwich Structures

Abstract

This paper addresses the experimental study of mode-I fatigue crack propagation in polymeric cellular foam cores for sandwich structures. Measurements of fatigue crack growth (FCG) rates dald N are experimentally conducted under constant load amplitude tests, K-increasing technique and under manual shedding of load amplitude tests, K-de-creasing technique. The results are found to be reasonably repeatable and FCG rates are consistent with each other. The influence of various stress ratios R and mean stresses on the FCG rates is examined. The FCG rates dald N appear to be related to the numerically derived stress intensity factors AKby the conventional Paris' law, when plotted on a double logarithmic scale. Constants C and m are derived from a power function curve fit and the applicability of Paris' law to the investigated type of material is discussed. Near-threshold stress intensity factors AKth are derived from the dald N vs. AK curves by extrapolating curve fits down to the FCG rates of 10-8 mm/cycle assuming the continuous slope of dald N vs. AK curve.