Detection and monitoring of fatigue damage in SMCR26 specimens using spate, for a constant mean stress – a qualitative approach

Abstract

The primary aim of the work presented here was to establish the use of thermoelastic measurements in detecting the presence of damage and its subsequent accumulation in sheet moulding compound (SMCR26). To this end, several dog bone shaped specimens of SMCR26 were cycled at a constant mean stress of 38.87 MPa and at varying stress amplitudes, the latter in order to investigate any dependencies on stress amplitude. Surface scans were taken from each specimen at various stages in their load history using the Stress Pattern Analysis by Thermal Emission (SPATE) measurement equipment. The first scan obtained from each specimen was used to determine its initial state of damage, while subsequent scans were used to monitor the accumulation of damage. The thermoelastic signal in the initial and subsequent scans exhibited different magnitudes and distribution for the different specimens, which denoted heterogeneity of the SMCR26 specimens and of the occurrence and accumulation of damage. This was in sharp contrast to the uniform thermoelastic signal that is emitted from the surfaces of cycled, undamaged homogeneous materials. The absence of any apparent relationship between the stress amplitude and the accumulation of damage in the tested specimens was thought to be a result of the in-homogeneity inherent in SMCR26, and of the heterogeneous nature of the accumulation of damage, rather than a limitation of the thermoelastic equipment used. The results obtained in this work demonstrated SPATE to be a fast and useful means of detecting the presence of damage and of monitoring its accumulate Keywords : Sheet Moulding Compound (SMC), fatigue, damage Journal of Agriculture, Science and Technology Vol. 7(1) 2005: 91-121