Stress-strain curve of a fibre-reinforced composite

Abstract

Careful measurements have been made of the stress-strain curves of tungsten wires of 10 μ and 20 μ. diameter and of aligned composites of the same wires in copper. At strains greater than the yield strain of the copper the apparent stresses in the matrix, evaluated from the law of mixtures, are very high. The effect appears to be due to the mutual constraint of the two phases caused by their different lateral contractions, since it disappears when the fibres yield and hence the transverse contractions become the same. The experimental results are compared with those predicted for a completely plastic matrix and the stresses are found to be higher than calculated. This is interpreted to mean that the yield of the copper is gradual, and that during stage II of the stress-strain curve of the composites an appreciable portion of the copper continues to deform elastically.