Control and qualification of titanium welds

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The study was aimed at controlling the weld geometry of thin-plate titanium and one of its alloys (Ti-6Al-4V) by ultrasonic means and qualiFying the metals in the as-welded condition in terms of their grain sizes and mechanical properties. The alignment and symmetry of the weld pools were successfully tested by using ultrasonic shear waves. The grain sizes at the weld fusion zone were found to be related to their ultrasonic attenuation by a mathematical relationship. The temperature effect in locating weld pool radii in titanium was found at temperatures up to 600 °C. The ultrasonic velocity decreased as the temperature increased and the square of temperature affected the rate of change of the ultrasonic velocity. After compensation for the temperature effect, the maximum location error of the weld pool radius was 17 % which was comparable to previous measurement using different techniques.A positive relationship was seen between weld geometry (penetration depth and weld width) and heat input. A welding spectrum for titanium and its alloys of different thicknesses was obtained. Back shielding gas was beneficial in obtaining good welds. Both heat input rate and cooling rate were found to affect the grain size of the weld, with the cooling rate being the dominant factor. The grain size exhibited a Hall-Petch effect on mechanical properties, such as the tensile properties and fracture toughness of the weld. The phase transformation positively contributed to better mechanical properties in most cases, whilst the presence of interstitials worsened tensile properties. A system was developed in this study to utilise the above information and data for possible real-time and closed-loop control of the TIG welding process to give a desirable weld. Specifically, a process control data base was built up using software and a knowledge-based system for acceptable welding parameters, which were determined by acceptable penetration depth, grain size and mechanical properties. An algorithm was successfully written which relates the ultrasonic signal to the penetration depth of the weld. A hardware control circuit was built which took in the ultrasonic signal and converted it to a driving signal to change the welding speed and thereby change cooling rate

Knee kinematics of ACL-deficient patients: A development of a portable motion analysis system

This study is to compare the knee kinematic measurements between the novel portable skin marker-based motion analysis system (Opti-Knee®) and a conventional system (Vicon®). Nineteen subjects were recruited and asked to perform stair descent with lower limb placed with skin markers. Knee kinematic data was computed from the trajectories of the skin markers. Pearson’s correlation coefficient and Root-mean-square deviation (RMSD) were used to analyze the data. For the waveform, sagittal plane rotation is strongly positive correlated between systems, while for axial and coronal plane rotation, it was moderately to strongly positive correlated in both normal (ACLN) and ACL-deficient (ACLD) group. Substantial difference between two groups was found in correlation of abduction/adduction in both stance and swing phase, as well as in external/internal rotation in all selected regions of interest. Moreover, the RMSD was larger in ACLN than in ACLD in three planes of rotation. The capability of Opti-Knee® in tracking lower limb sagittal plane rotation was comparable to Vicon®. However, for coronal and axial plane rotation, although the correlation to Vicon® in kinematic waveforms was moderately high, their ROM and peak values substantially deviated from the values in Vicon®.This study is supported by the Innovation and Technology Support Program, Hong Kong (Ref. No.: ITS/289/14FX)

How students cope with part-time study

This study provides a qualitative test and illustration of a model of how students cope with the demands of part-time study. The model shows that students who are successful in finding the time to complete the requirements of part-time courses do so by adopting three mechanisms; sacrifice, support and the negotiation of arrangements. All three mechanisms operate in four domains, namely work, family, social lives and the self. The mechanisms and domains were related together in a three by four matrix. Data to verify and illuminate the model were gathered by the researchers through an on-line forum discussion on the topic of coping with part-time study. The researchers themselves were studying part-time in a course called Adult Education and Professional Development. Analysis of the data showed that the work domain was very important but little adaptation was possible. The family was seen as the most important domain and all three mechanisms were used. Time was commonly found for part-time study by sacrificing social lives. The self-domain was interpreted as important in establishing motivation and self-determination

A Green Approach to Synthesis of Nanoparticles of Sn–3.0Ag–0.5Cu Lead-Free Solder Alloy

Sn-3.0Ag-0.5Cu nanoparticles can provide a potential solution to the high soldering temperature problem of lead-free solder alloy because the nanosize effect can depress the melting temperature. In this paper, a green approach to the synthesis of Sn-3.0Ag-0.5Cu nanoparticles by chemical reduction at room temperature is reported. A safe organic solvent, ethanol, was used to prevent the formation of tin oxide during synthesis without the help of capping agents and N-2 purging. Vigorous stirring instead of the use of capping agents was applied to the reaction mixture to reduce agglomeration of particles during the reaction time. Owing to not having capping agents on the nanoparticles and no detection of tin oxide, the subsequent steps for eliminating them are not necessary. Ag3Sn revealed by the XRD pattern and the electron diffraction pattern confirmed the successful alloying of Sn and Ag during synthesis. The TEM image showed that the nanoparticles were composed of a crystalline core embedded by an amorphous matrix. The average particle diameter was 53.3 nm with a standard deviation of 8.9 nm. An onset melting temperature of 187.3 degrees C and a peak melting temperature of 212.7 degrees C were achieved. This simple, safe and environmentally friendly method can reduce the production cost of nanosolder and may be applicable to the synthesis of other metal nanoparticles.Department of Industrial and Systems Engineerin