An investigation of the effect of the manufacturing process on the performance of conveyor pulleys
- Authors: Styger, Gary
- Date: 2012-08-01
- Subjects: Pulleys , Belt conveyors - Standards , Conveying machinery , Conveying machinery - Design and construction
- Type: Thesis
- Identifier: uj:8920 , http://hdl.handle.net/10210/5390
- Description: M.Phil. , Pulleys are critical items in belt conveyors. Their primary role is to drive large mining conveyor systems, facilitating the transportation of ore over extensive distances, both in South Africa and abroad. The effect of the manufacturing process (with specific emphasis on the induced residual stresses) on the fatigue performance of conveyor pulleys is herein investigated and reported. A pre-selected pulley was chosen based on size, suitable for experimental work as well as practical specifications. The static and fatigue performance of the pulley were investigated both with the current design criteria as well as Finite Element Analysis, with comparisons drawn. The material data for the Finite Element Models was obtained experimentally with tensile tests of the SANS 1431 350 WA plate. The magnitude of the residual stresses were obtained experimentally by using the incremental hole-drilling technique for non-uniform residual stresses. The method was verified by comparison with the Finite Element Analysis results for the non-linear material analysis of the roll-bending of the shell. The fatigue analysis revealed that the stress ranges of interest for the pulley were below the non-propagating stress range, and hence theoretically infinite fatigue life would be possible under constant amplitude conditions. The operational fatigue life required for the pulley would be possible, when considering the latest S-N curve for "very high cycle fatigue". The stress intensity factors for the weld details were also below the threshold value and hence crack growth should not occur, upon crack initiation. A new design criteria was proposed for the fatigue analysis considering either fatigue assessment standards or fracture mechanics for the assessment of the butt-welds. This investigation showed that the manufacturing-induced residual stresses may play a significant role in the fatigue life of a pulley. The fatigue strength of a machined stressrelieved joint is higher if the stress range is partly compressive. The fatigue strength of a machined as-welded joint is higher than estimated by the fatigue classifications. This is due to residual stress relaxation that occurs at the weld toe because of yielding and hence a subsequent reduction and redistribution of the residual stresses. This reduction in the mean stress level, with a stress range that is partly compressive, would mean an increase in the fatigue strength of the joint. This would in conclusion result in similar fatigue strengths for a stress-relieved and an aswelded joint. This would additionally depend on the extent of the reduction of the residual stress in the as-welded joint. Recommendations were suggested for further experimental and numerical work for both the T-bottom and Turbine-type pulleys.
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Effect of constitutive modeling during finite element analysis of machining-induced residual stresses in Ti6Al4V
- Authors: Oosthuizen, Gert A. , Laubscher, Rudolph F. , Styger, Gary
- Date: 2014
- Subjects: Residual stresses , Titanium alloys , Finite element method , Machining
- Type: Article
- Identifier: uj:5028 , http://hdl.handle.net/10210/13547
- Description: Residual stress is an important surface integrity descriptor that may have a marked effect on the functional performance of machined alloy parts. This paper describes a finite element evaluation of the effect of different constitutive models on machining induced residual stresses for Ti6Al4V titanium alloy. A two dimensional orthogonal turning process is modelled and the results compared to experimental data. Residual stress is evaluated with respect to different elastic-viscoplastic constitutive models at certain cutting speeds and feeds. The general-purpose finite element code MSC Marc@ was used with comparisons with experimental data made relative to residual stress, cutting force and temperature. The magnitude and extent (depth) of the residual stress field is evaluated with regards to the different material models and compared with experimental data.
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