FATIGUE PROPERTIES OF THREE DIMENSIONAL BRAIDING COMPOSITES

The dynamic mechanical properties ———fatigue properties and the effect of braiding st ructures on the fatigue properties of three dimensional braiding composites were studied. Tensile-tensile fatigue test s were carried outat different maximum stress ratios . All the tests were run at a stress ratio R(σ_min /σ_max ) = 0.1. The fatigue f requency was 10 Hz. The result s show that the fatigue st rength of three dimensional braiding composites is 60 %～80 % ofit s static strength , which is higher than that of metal material. The braiding angles have a great influence on the fatigue properties of 3-D braiding composites. The fatigue damage will be easy and the hysteresis heat will occur forthe large braiding angle composites. The st rain-st ress curves of the specimens with large braiding angles are non-linear , and the modulus is increasing with the testing time increasing. The variational rule of fatigue properties of threedimensional composites cont rasted with the metal’s rules. After one million times of fatigue test s , the residualst rength of the specimens is higher than the static test st rength , which is due to fiber bundles being reoriented to alower angle toward the tensile loading direction af ter the fatigue test .