Laser bending of commercially pure grade 2 titanium alloy plates: mechanisms analysis and characterisation of mechanical properties
- Authors: Mjali, Kadephi Vuyolwethu
- Date: 2014
- Subjects: Materials -- Mechanical properties , Bending , Titanium-aluminum alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9642 , http://hdl.handle.net/10948/d1021147
- Description: The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.
- Full Text:
- Date Issued: 2014
Mechanisms, analysis and characterisation of mechanical properties of laser formed commercially pure grade 2 titanium alloy plates
- Authors: Mjali, Kadephi Vuyolwethu
- Date: 2014
- Subjects: Materials -- Mechanical properties , Bending , Titanium-aluminum alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9641 , http://hdl.handle.net/10948/d1021083
- Description: The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.
- Full Text:
- Date Issued: 2014
Characterising the stress-life response of mechanical and laser formed titanium components
- Authors: Fidder, Herman
- Date: 2012
- Subjects: Titanium alloys -- Fatigue , Titanium --- Fatigue , Materials -- Mechanical properties
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9634 , http://hdl.handle.net/10948/d1018462
- Description: This dissertation involves the experimental investigation of commercially pure titanium (CP Ti) which was subjected to laser forming and mechanical forming processes. Commercially pure titanium grade 2 was formed to a radius of curvature of approximately 120 mm using three forming procedures, i.e. i) laser forming; ii) mechanical forming (stretched forming) and iii) a combined forming process (laser-mechanical forming). Fatigue testing revealed, for all the forming processes, that samples produced by laser forming performed the best at high load settings. However, mechanically formed specimens performed the best at low load settings, whereas the laser-mechanical process resulted in midway performance between laser and mechanical processing. Considering microstructure vs fatigue; impact vs fatigue; and residual stress vs fatigue; at high load settings it is evident that the microstructure is the dominant contributor to crack initiation and growth. Crack morphology of fatigue samples revealed that secondary cracks (parallel to main crack front) followed the grain boundaries of the Widmanstätten microstructure, whereas irregular secondary cracks grew parallel and through the twinning planes and along the grain boundaries of the equiaxed microstructure. Laser forming resulted in microstructural changes from equiaxed grains to a Widmanstätten structure due to fast cooling rates. Excessive twinning is developed within the equiaxed microstructure after the mechanical forming procedure. This is due to cold working / strain hardening. The combined process shows a combination of equiaxed grains and Widmanstätten microstructure. Residual stress relieved for all forming processes revealed an increase in the magnitude of the residual stress compared to the parent plate and that the maximum values were obtained at the inner radius of curvature (i.e. 118.4 mm). Laser forming revealed the highest values in residual stress whereas the other two processes i.e. mechanical and laser-mechanical forming exhibited an increase midway between the parent plate and laser forming. The second most influential factor with regards to fatigue was the magnitude of the residual stress, especially at medium to low load settings. When considering theoretical models to predict fatigue life it was found that the Goodman model showed the closest relation to the actual fatigue data when considering the entire theoretical curve. Vickers microhardness profiling was applied to the thickness of the samples for the parent plate and all forming processes. No significant hardening occurred due to the forming processes and differences in hardness were considered negligible. Charpy impact testing revealed that the laser formed specimens exhibited the most brittle behaviour when compared to the parent plate results. Mechanical formed specimens showed a slight increase in brittleness compared to parent plate whereas the combined process yielded results midway between the laser and mechanically formed specimens. Mathematical equations are formulated and presented for predicting the fatigue life of CP Ti grade 2 for the parent plate and the three forming processes. This study proved that the laser forming process can be successfully used as a production stage in the forming of CP Ti grade 2.
- Full Text:
- Date Issued: 2012
Shape memory Alloy Actuator for cross-feed in turning operation
- Authors: Otieno, Timothy
- Date: 2012
- Subjects: Shape memory alloys -- Mechanical properties , Shape memory alloys , Intermetallic compounds , Materials -- Mechanical properties
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:9650 , http://hdl.handle.net/10948/d1012590 , Shape memory alloys -- Mechanical properties , Shape memory alloys , Intermetallic compounds , Materials -- Mechanical properties
- Description: A shape memory alloy (SMA) is an intermetallic compound able to recover, in a continuous and reversible way, a predetermined shape during a thermal cycle while generating mechanical work. In this thesis, its use in developing an actuator for a machining process is investigated. The actuator is to drive the tool cross feed into an aluminium workpiece in a finishing lathe operation. The actuator structure was designed with an output shaft to transfer the movement and force of the SMA wire outside the device. The actuator was fabricated and the experimental setup was assembled which also included a power supply control circuit, displacement sensor, temperature sensor and current sensor for feedback, and data collection and monitoring within software. PID control was implemented within the software that regulated the power supplied to the SMA, thereby providing the position control. This study covers the mechatronics system design and development of the actuator, the experiments carried out to determine performance and the results. Open loop tests were conducted to determine the maximum stroke, the effect of cooling and response to radial forces. These tests revealed the expected non-linearity of the SMA. The actuator achieved the rated maximum stroke of 3-4 percent. The forced cooling test showed a general improvement of approximately 65 percent with fans. The radial force tests showed the value of the maximum stroke remained unaffected by force. The results from the closed loop tests responses with a tuned PID controller produced a stable system for various displacement setpoints. The actuator had a feed rate of 0.25 mm/s and an accuracy of 0.0153mm, which was within the acceptable accuracy for turning operations. The system was deemed accurate for a conventional lathe machine cross feed.
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- Date Issued: 2012