Abstract
Static tensile tests and their fracture process of the unidirectional Si-Ti-C-O/BMAS composite (V_f=0.5) and Si-Ti-C-O fiber-bonded composite (V_f=0.9) were studied at room temperature in order to clarify the fracture behavior of fiber reinforced ceramics. The observation revealed the following common features of the fracture behavior. (i) First, matrix cracking was initiated in both composites. (ii) Then, the number of matrix cracking increased with the strain increase. In spite of matrix cracking, the associated interfacial debonding was suppressed by the compressive residual stress of the matrix in the fiber axis direction. (iii) Fiber breakage occurred when the stress reached about 90% of the fracture strength of the composites. Once fiber breakage occurred, large scale debonding was enhanced due to the tensile residual stress of fiber. (iv) Finally, overall fracture of the composite occurred, accompanied by a large number of fiber breakage. The difference of fracture process between both composites was the macroscopic behavior. The slope of the stress-strain curve of the Si-Ti-C-O/BMAS composite decreased from the initial one owing to matrix cracking. On the other hand, that of the Si-Ti-C-O fiber-bonded composite was almost the same until the final fracture in spite of the matrix cracking accumulation. The higher fiber volume fraction of the Si-Ti-C-O fiber-bonded composite was responsible for more suppressed interfacial debonding. The observation results were realized in computer by means of the approximate simulation using the modified shear lag analysis combined with the Mote Carlo method which enables to describe the relationship of mesoscopic damage of interfacial debonding, matrix cracking and fiber breakage to the macroscopic fracture behavior of unidirectional fiber reinforced ceramics. The effect of the fiber volume fraction on the fracture behavior of unidirectional fiber reinforced ceramics was discussed on the basis of experiments and simulation.
