Paper number 972

EFFECTS OF SPECIMEN ORIENTATION ON THE FATIGUE CRACK GROWTH RESISTANCE OF CROSS-PLY TI-6AL-4V/SCS-6 METAL-MATRIX COMPOSITES

A. Yasmin, T. J. A. Doel and P. Bowen

School of Metallurgy and Materials/IRC in Materials for High Performance Applications
The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Summary

The fatigue crack growth resistance of cross-ply [0/90]2s laminate of Ti-6Al-4V reinforced with continuous SCS-6 fibres has been investigated at room temperature for three different mode-I crack growth directions relative to the axis of the fibres in the [0/90]2s laminate: 30, 45, and 60°. The tests were conducted under three point bending at initial applied stress intensity range ((Kini) from 8 to 14 MPa. When tested with the mode-I crack growth direction at 30 and 60° to the fibre axis, a CA/CF (Crack Arrest/Catastrophic Failure) transition of 10-12 MPa was found, whereas when the mode-I crack growth direction was at 45° to the fibre axis the transition was 8-10 MPa. Unlike crack propagation in unidirectional composites for crack growth perpendicular to the fibre axis, and for crack growth perpendicular (and parallel) to the fibre axis in [90/0]2s and [0/90]2s cross-ply laminates, the fatigue crack is found to grow at an angle to the mode-I direction. For the specimens where mode-I directions are at 60 and 30° to the fibre axis, single dominant fatigue cracks were found to grow. However in the case of 45°, multiple cracks have been found to grow under some of the conditions used.

Keywords

effects of crack orientation, cross-ply, fatigue crack growth, fibre orientation, silicon carbide fibre, fibre bridging, crack arrest and catastrophic failure.