Elastic-plastic behaviour of AISiC metal matrix composite rod under combined tension and torsion loading

Abstract

Most machine components and structural members are subjected to complex loading conditions during service. Typical complex loading conditions can be observed in the case of a bolt When a bolt is tightened to bring machine components together, stresses such as tensile stress (clamp load/area), and torsional or shear stresses (proportional to applied torque) are developed in the shank and bolt threads. To simplify the complex relationship between tightening torque, friction co-efficient and the preload in the fastener, a circular rod is chosen to represent the problem. Investigations were carried out to determine 1) how the external tensile load affects the magnitude of the initially applied torque, and 11) how application of torque affects the initially applied axial load or preload in a specimen in elastic-plastic range. A preliminary study on copper specimens was undertaken to gain knowledge about elastic-plastic behaviour under combined tension and tors ion loading. Various combinations of combined tension and tors ion loading conditions were applied on the specimens to establish the proper functioning of a recommissioned tension- torsion machine and a dedicated Lab VIEW program. Experimental investigations on AlSiC MMC rod specimens reveal that the rod can sustain combined axial load and torque well beyond the combined initial yield curve When the specimen is subjected to an ini tial axial load or torque followed by torque or axial load respectively, the subsequent load or torque becomes dominant in describing the elastic-plastic behaviour of the specimen. The initial load or torque in the specimen does not af fect the subsequent torque or load car rying capaci ty of the specimen. A specimen subjected to a constant relative extension and angle of twist can sustain the combined axial load and torque well beyond the combined initial yield curve. It is apparent that the specimen carries relatively higher axial load when the load-torque path is closer to the axial load axis Similarly, the specimen carries relatively higher torque when the load- torque path is closer to the torque axis. In addition to the experimental investigation, a comprehensive finite element modelling of combined tension and torsion loading of a model was under taken that includes both geometric as well as large deformation effects for capturing axial and shear stresses. A methodology for the finite element analysis of solid rods under combined tension and torsion loads was developed. The numerical models have success fully captured the basic features of the elastic-plastic response of the AlSiC metal matrix composite and demonstrated the effect of particle inclusion in the overall flow properties of the composite, while demonstrating some limitations