The Mehanical Properties Of Vacuum Thermal Cycling For T700/5224 Composite

In order to reveal the damage effects and mechanism of vacuum thermal cycling on carbon/epoxy composites,the changes in mass loss rate and mechanical properties of T700/5224 composites were investigated under vacuum thermal cycling at the interval of-140～140℃and 10-3 Pa.The surface morphology,fracture and changes in microscopic structure in the skin layer of specimen were characterized in terms of SEM,DMA and FTIR-ATR,respectively.The experimental results shows that with increasing the vacuum thermal cycling,the mass loss rate of T700/5224 composites increases,then this rate increases slowly after 29 cycles,and tends to level off after 157 cycles.Mass loss is due to the gradual evaporation of the water absorbed in the composites and the residue organic solvent retained during preparation in vacuum.90°tensile strength of the T700/5224 composites firstly decreases with increasing thermal cycles and improves after 48 cycles and then tends to level off 198 cycles.Bending strength does not exhibit increase until after 48 cycles,then decreases after 95 cycles and level off after 198 cycles.The interlaminar shear strength does not show significant change.E'and tans temperature spectroscopy analysis of T700/5224 composites suggest that the crosslink density of the resin matrix increase from 48 cycles to 198 cycles.SEM show that a certain amount of interfacial debonding zone is attributed to 48 vacuum thermal cyclings and the form and the volume of the debonding zone change litter with the further increase in vacuum thermal cycling(to 198 cycles).In other words,interfacial debond zone gradually tend to saturature.ANSYS 11.0 simulation demonstrates that there exist the different residual thermal stress in the different region of the composites.The minimum equivalent stress locates at the carbon fiber and the maximum value locates in the resin matrix.The equilvalent stress in the matrix-riched zone of composites is much larger than that in the matrix-starved zone. Stress concentration exists at the interface between the carbon fiber and resin matrix.With increasing the cycles of the vacuum thermal cycling,residual stress will gradually accumulate to such a certain vacuum that interfacial layer of the composites are damaged.