The mechanical properties of tightly woven carbon-carbon composites

The mechanical properties of a tightly woven carbon-carbon composite were investigated. The flexural strength and fracture toughness of these composites were measured as a function of temperature and atmosphere. The average flexural strengths are 147.1 {dollar}pm{dollar} 6.4 MPa in air and 144.0 {dollar}pm{dollar} 5.9 MPa in argon at room temperature. The critical stress intensity factors, K{dollar}sb{lcub}rm Ic{rcub}{dollar}, of these composites are 4.4 {dollar}pm{dollar} 0.2 MPa.m{dollar}sp{lcub}-1/2{rcub}{dollar} in air and 4.5 {dollar}pm{dollar} 0.2 MPa.m{dollar}sp{lcub}-1/2{rcub}{dollar} in argon at room temperature.; The cyclic fatigue behavior of these composites was investigated as a function of stress levels. Fatigue tests were performed in tension-tension mode under ambient laboratory conditions. The applied stress levels versus number of fatigue cycles (S-N curves) are plotted to determine the effect of fatigue on these composites. Results of composite behavior are discussed in terms of the relationship of the stress-strain behavior to the fatigue life of these composites as well as the effects of applied stress levels. These composites exhibit excellent fatigue resistance to fluctuating stresses. Stress without failure after 10{dollar}sp6{dollar} cycles is 80% of the ultimate tensile strength.; Results of mechanical tests are correlated with Scanning Electron Microscopy (SEM) analysis to explain observed fatigue mechanisms. Evidence of textural changes related to fatigue was observed in the matrix region of these composites.