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

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

Experimental and finite element study of the behaviour of structural members to combined tension and torsion loadings

This research work is concerned with the determination of elastic-plastic deformation behaviour of structural members to combined tension-torsion loadings. Three aspects of the work were examined. In the first, an adaptive control system is developed for performing combined tension and torsion tests on solid and thin-walled tubular specimens by using systems supplied by National Instruments to control the axial and torsion loads on the specimen through data acquisition boards. The LabView software in conjunction with data acquisition board, servo-controllers and servomotors form the adaptive control system for the torque-tension machine. The second aspect was to carry out experimental investigations, where solid steel rods (structural steel) were subjected to non-proportional combined tension-torsion loading paths. In these loading paths, initial elastic tension followed by torsion, holding corresponding axial displacement constant and initial elastic torsion followed by tension, keeping the corresponding angle of twist constant, were examined The experimental programme also considered the non-proportional combined tension-torsion loading of thin walled steel tubes. It has been observed experimentally that, when the rod is initially subjected to an axial load keeping the corresponding axial displacement constant and then followed by subsequently application of the torque the rod behaves as if its axial load carrying capacity decreases without affecting its torque carrying ability. Similarly when the rod is initially subjected to a torque, keeping its corresponding angle of twist constant, and then followed by subsequently application of the axial load the rod behaves as if its torque carrying capacity is reduced without affecting its axial load carrying ability. The third aspect was devoted to the finite element analysis. The finite element analysis package ANSYS (version 5.7) was used for the analysis of the combined tension-torsion loadings of the steel rods. The geometry of the steel rod was supplied to the Ansys package and meshed .The preconditioning conjugate gradient (PCG) and the spare direct solver were used to solve all the combination of loads. Experimental results obtained were compared with computed values from the finite element analysis and are presented. Reasonably good agreement is obtained between the experimental and computed stresses and displacements. This work has direct bearing on the relaxation of tightening torques or axial loads as experienced by critical engineering components, such as couplings, bolted joints, rotating shafts, and steel structures that are subjected to similar types of combined loadings. It is also hoped that the information generated in this research work will guide the designer towards the use of more realistic materials and achieve better design