Papers by Author: Timotius Pasang

Abstract: Sandwich panels made of thin and stiff skins, connected by a thick and soft core are widely used in load-bearing components mainly due to their high strength to weight ratio. To improve the reliability in using sandwich beams, it is necessary to understand their responses under external mechanical and environmental stimuli. This paper investigates the construction of steel-polyurethane-steel sandwich panels and their mechanical properties. Key properties of a sandwich structure are the adhesion between the skins and the sandwich material, and the load transfer from the outer skin to the inner skin. Lap shear specimens were selected to give an indication of the bond strength of the polyurethane to steel, whilst three point bend test specimens were selected to indicate the degree of load transfer between the skins and the bending resistance provided by the sandwich structure.

Abstract: Formability of two magnesium alloys, namely, AZ80 and ZE10, has been investigated. Both alloys were supplied with a thickness of 0.8 mm. The grain structure of the as-received AZ80 alloy showed dislocations, twins and second-phase particles and-/or precipitates distributed uniformly within grains. These were not obvious on the ZE10 alloy. The investigations were carried out at room temperature for both alloys in the as-received and heat treated conditions (410^oC for 1 hour followed by water quench). The heat treatment significantly changed the grain structure of the AZ80 alloy, but did not affect the ZE10 alloy apart from grain enlargement. The formability was studied on the basis of plastic strain ratio (r) and strain hardening coefficient (n) by means of tensile testing. In the as-received condition, the ZE10 alloy had a slightly better formability () than AZ80 alloy. Following heat treatment, however, the formability of the AZ80 alloy was improved significantly (by about 26%), while the ZE10 alloy did not show any significant change.

Abstract: Butt welded joins were produced between commercially pure (CP) titanium and various titanium alloys using an electron beam welding technique. The materials used were CP Ti, Ti-6Al-4V (Ti64) and Ti-5Al-5V-5Mo-3Cr (Ti5553). Grain boundary structures, mechanical properties, compositional profiles across the welds and fracture modes are presented. CP Ti has always been known for its excellent weldability, Ti64 has good weldability and, preliminary results indicated that Ti5553 alloy is also weldable.

Abstract: Similar and dissimilar butt joint welds comprising combinations of commercially pure grade 4 titanium (CP-Ti), Ti-6Al-4V (Ti-64) and Ti-5Al-5V-5Mo-3Cr (Ti-5553) were created using the electron beam process. The resultant welds were studied by means of metallography, optical microscopy, mechanical testing and scanning electron microscopy. Mechanical testing was performed on welded samples to study the joint integrity and fracture characteristics. A scanning electron microscope investigation was performed on the fracture surface to reveal their fracture modes. While all weldments were crack free and most weldments exhibited mechanical properties comparable to the base metal, negligible ductility was exhibited during tensile testing joints of Ti-5553 welded to either Ti-64 or Ti-5553.

Abstract: Knowledge on the contact condition at the tool/workpiece interface is essential for understanding many aspects of FSW. In the present study, FSW experiments were conducted using aluminium alloys followed by metallographic examination focusing on the tool shoulder-workpiece interface region. It was observed that an interfacial intermetallic layer and hence metallurgical sticking/soldering readily formed. Temperature measurements have suggested the presence of interface liquid, hence suggesting a mechanical sliding contact condition dominant. This has been supported by the observation on material flow within the shear layer.