Correlations between damage initiation thresholds in textile composites and fatigue life limits

The paper explores the interrelations between damage initiation thresholds in quasi static tensile loading and tension-tension fatigue life limits. The damage initiation thresholds are determined using acoustic emission registration during a tensile test and are confirmed by X-ray observations of cracks and micrography. The paper systematise results of experiments with measurements of the static damage initiation thresholds and tension-tension fatigue S-N curves on a variety of textile composites. The following materials were studied: (1) glass/epoxy: plain weave laminates and 3D woven; (2) carbon/epoxy: twill weave laminates, 3D woven, 3D braided, NCF, NCF structurally stitched. Glass reinforced composites have the fatigue limit stress level (more then few millions cycles) close to the AE threshold strain (appearance of the first micro damage). Carbon reinforced composites, on the contrary, have the “infinite” fatigue load between the first and the second damage thresholds loads.