Papers by Keyword: Cyclic Torsion

Abstract: Thanks to their oxide layer, aluminium alloys are remarkable for their ability to resist corrosion. However, in welding, this protective layer acts as a barrier which must be broken in order to succeed in the thermomechanical joining of aluminium. The chosen alloy (6082-T6 or AlSi1MgMn) has been subjected to various deformation path. The first of them consists in the channel-die (plane strain) compression of two cuboids, one above the other. Considering the configuration of the test, the surface size between the two samples rises, so that the fragmentation of the oxide layer creates welding bonds. However, the friction effects in the channel lead to a heterogeneous deformation, so that the contact surface undergoes different behaviors: a microscopic study then shows that the welds appear in areas with significant shear. Channel-die and uniaxial compressions of beveled samples confirm that more significantly than the global deformation, the shear strain is the most active phenomenon for achieving an effective thermomechanical joining. Another approach is the cumulative deformation as a result of a cyclic load: a tube is cut through its section and undergoes both a compression and cyclic torsion load. The contact surface between the two semi-tubes is under a shear behavior and the combination between plastic deformation and local heating leads to a fragmentation of the oxide layer: all this factors allow the thermomechanical joining of aluminium alloys.

Abstract: Fatigue properties of mild steel are investigated under cyclic tension-compression and cyclic torsion loading using ultrasonic fatigue testing equipment and cycling frequency of approx. 20 kHz. Both S-N curves show a distinct change of slope at about 107 cycles, and endurance limits determined at 107 and 109 cycles differ by less than their respective standard deviations. Endurance limit shear stress determined for cyclic torsion loading is about 60% of the tension-compression endurance limit stress, and the slopes of the S-N curves are comparable. Non-propagating cracks could be found in specimens, which did not fail within 109 cycles in torsion loading endurance tests. The endurance limit can be understood as maximum stress amplitude, where possibly formed small cracks do not propagate to failure.