Toughness of fiber-reinforced titanium as a function of temperature:: experimental results and micromechanical modeling

The fracture behavior of Ti-6Al-4V uniaxially reinforced with 35 vol% SiC Sigma 1140+ fibers was studied between 20 and 550 degreesC by three-point bend tests of notched beams. It was found that the fracture energy remained essentially constant in the whole temperature range while the initial toughness decreased linearly with temperature from 78 MPa,rootm at 20 degreesC to 44 MParootm at 550 degreesC. Fracture occurred by the development of a thin fracture process zone propagated from the notch root where the matrix plastic deformation was localized. The fracture of the composite panels was simulated by representing the fracture process zone by a cohesive crack. The corresponding cohesive law was described by a new micromechanical model. The critical parameters which determine the cohesive stresses as a function of temperature were measured independently or taken from well-established values in the literature. and the fracture behavior was simulated numerically using the finite element method. The numerical simulations were in good agreement with the experimental results and showed that the reduction of the initial fracture toughness with temperature was associated with the critical condition to reach the maximum load. Below 200 degreesC the critical condition was attained when the crack opening displacement at the notch tip reached the matrix critical crack opening displacement. Above 200 degreesC, the maximum load was dictated by the crack opening displacement at the notch tip which led to the fracture of all the fibers ahead of the notch tip. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.