Lifetime and young's modulus changes of glass/phenolic and glass/polyester composites under fatigue

Abstract

Fatigue of composites causes a loss of stiffness and development of damage before ultimate failure. These effects were compared for phenolic and polyester resins reinforced by five layers of woven roving/chopped strand combination glass mat. Such polyester laminates are widely used, e.g. in marine applications such as high speed craft. The phenolic laminates are promising candidates for applications where fire resistance is important. S-N and ε-N curves were obtained. In addition, stress versus strain curves were measured continuously under reverse loading ( R = -1) up to 10 6 cycles. Analysis of these curves allows further insight into the fatigue process. Tensile moduli drop dramatically (25%) with increasing number of cycles, but remain fairly constant in the compressive region. This behaviour can be explained by effects of matrix cracking. It also indicates the need to define different moduli for non-linear stress-strain curves. Absorbed energy (damping) can also be determined from the stress-strain curve and can be used as an indicator of the onset of rapid degradation of the material leading to ultimate failure. All data are compared for polyester and phenolic matrix laminates.