EXPERIMENTAL INVESTIGATION OF CYCLIC PLASTICITY CONTINUUM DAMAGE EVOLUTION IN AN ENGINEERING COMPONENT SUBJECTED TO THERMAL LOADING

A thermal shock test facility is designed and built to enable a copper model slag tap component to be tested under cyclic thermal loading conditions. Infra-red line heaters and pumped cooling water are used to impose temperature loading cycles on to the specimen. Accurate focussing of the line beaters using a two degree of freedom adjustment mechanism, enables a heating area of width 3 mm to be applied to the specimen. Both the heating and the cooling processes are controlled by a proportional, integral, and derivative feedback micro-processor controller. Specimen temperature fields are obtained using thermocouples, and specimen displacements and strains are measured using linear voltage displacement transducers and strain gauges. A cyclic thermal loading test is carried out for approximately 7150 cycles on a model slag tap component. The variations of specimen strains and displacements are recorded and compared with results obtained from a finite element viscoplastic damage analysis. Good agreement between the predicted and experimental results is obtained. Microstructural examination of the specimen reveals the development of persistent slip bands and micro-cracking at grain boundaries. This occurs at the regions of the specimen undergoing cyclic plasticity due to the imposed cyclic thermal loading. The experimental observations of cyclic plasticity damage formation in copper undergoing cyclic thermal loading indicates the suitability of the Continuum Damage Mechanics (CDM) theory to model the evolution of cyclic plasticity damage. The damage is characterized by the development of fields of micro-cracked grain boundaries due to the formation and interaction of persistent slip bands within the grains.