Papers by Timotius Pasang
Universal Journal of Mechanical Engineering, 2015
Ijmpb, 2010
The magnesium silicide precipitates in the 6XXX series alloy are the main components contributing... more The magnesium silicide precipitates in the 6XXX series alloy are the main components contributing to the heat treatable properties and T6 strength of the alloy, which is influenced by the size, morphology and distribution of this phase. During the extrusion process, the strength contributing phase, magnesium silicide is supposed to dissolve and form again in a controlled state during age hardening. Whereas the intermetallic AlFeSi phase has little if any influence on the strength, the β phase of this intermetallic is known to cause brittle fracture of this alloy, as opposed to the less detrimental, more equiaxed α phase formed during homogenisation. This study investigates the as-extruded 6060 and the more heavily alloyed 6261 aluminium alloys, as well as the subsequent heat treated forms to investigate the ageing conditions to optimise hardening and shorten age hardening times for higher cost effectiveness. The microstructure, texture and precipitate size and distributions were studied using optical microscopy, SEM, EBSD and DSC. SEM and EDAX results have indicated signs of evenly distributed α AlFeSi and β Magnesium Silicide precipitates. The phase responsible for hardening is believed to be the much smaller scaled β" magnesium silicide, requiring much higher resolution studies.
International Journal of the Society of Materials Engineering for Resources, 2014
International Journal of the Society of Materials Engineering for Resources, 2014
International Journal of Machine Tools and Manufacture, 2014
ABSTRACT In this paper, a sheet metal forming simulator (SMFS) is used for evaluation of the fric... more ABSTRACT In this paper, a sheet metal forming simulator (SMFS) is used for evaluation of the frictional behaviour of AZ80 and ZE10 magnesium alloys under lubricated contact conditions. The results showed that the friction coefficient increases by increasing the contact pressure and decreasing the sliding velocity. A friction model is further developed for lubricated contact taking into account the surface roughness characteristics and the viscosity of lubricant. The proposed model showed very good agreement with the results of experiments. Finite element (FE) simulations were also carried out to investigate the effect of key process parameters on the results of SMFS. Based on the results of the FE model, the coefficient of friction increases by increasing the bending angle and pin diameter; however, these increases are not significant.
International Journal of Modern Physics B, 2010
The magnesium silicide precipitates in the 6XXX series alloy are the main components contributing... more The magnesium silicide precipitates in the 6XXX series alloy are the main components contributing to the heat treatable properties and T6 strength of the alloy, which is influenced by the size, morphology and distribution of this phase. During the extrusion process, the strength contributing phase, magnesium silicide is supposed to dissolve and form again in a controlled state during age
Journal of Materials Research and Technology, 2014
ABSTRACT Although the cost of the heat treatment process is only a minor portion of the total pro... more ABSTRACT Although the cost of the heat treatment process is only a minor portion of the total production cost, it is arguably the most important and crucial stage on the determination of material quality. In the study of the carbon diffusion in H13 steel during austenitization, a series of heat treatment experiments had been conducted under different atmospheric conditions and length of treatment. Four austenitization atmospheric conditions were studied, i.e., heat treatment without atmospheric control, heat treatment with stainless steel foil wrapping, pack carburization heat treatment and vacuum heat treatment. The results showed that stainless steel foil wrapping could restrict decarburization process, resulting in a constant hardness profile as vacuum heat treatment does. However, the tempering characteristic between these two heat treatment methods is different. Results from the gas nitrided samples showed that the thickness and the hardness of the nitrided layer is independent of the carbon content in H13 steel.
Tribology International, 2015
ABSTRACT Frictional behaviour of ZE10 and AZ80 magnesium alloys was investigated using a sheet me... more ABSTRACT Frictional behaviour of ZE10 and AZ80 magnesium alloys was investigated using a sheet metal forming simulator (SMFS) with a steel pin as counterpart on dry sliding conditions. Friction coefficients were measured within a sliding velocity range of 5–35 mm/s and contact pressure range of 2–15 MPa. The results showed that increasing contact pressure lead to an increase in coefficient of friction for both alloys; while the effect of sliding speed was negligible. A theoretical model is also developed to predict the coefficient of friction as a function of contact pressure. The model takes into account the surface characteristics as well as mechanical properties of alloys. The results of the theoretical model were compared with the results obtained from experiments and showed very good correlation. To further investigate the effect of process parameters on SMFS outputs, a finite element (FE) model was developed in ABAQUS software and the effects of bending angle and pin diameter on the friction tests results were studied. The FE model showed that the friction coefficient increases by increasing the bending angle and pin diameter.
Procedia Engineering, 2014
The frictional properties of two types of magnesium alloys, i.e. AZ80 and ZE10 were investigated.... more The frictional properties of two types of magnesium alloys, i.e. AZ80 and ZE10 were investigated. A purpose-developed sheet metal forming simulator was used to conduct the experiments under constant plastic deformation. Both lubricated and dry sliding contact conditions were simulated and the effect of key process parameters such as contact pressure and sliding velocity on the frictional properties of these alloys were investigated. Due to the different sliding velocities, the contact pressure rose during each experiment which enables the measurement of the coefficient of friction for a wide range of contact pressures. The results showed an increase in the friction coefficients of both alloys with increasing contact pressure. Furthermore, a decrease of the friction coefficient was observed for higher sliding velocities.
ASME 2010 International Manufacturing Science and Engineering Conference, Volume 1, 2010
This work is an experimental study on effect of microstructural change due to Strain Induced Tran... more This work is an experimental study on effect of microstructural change due to Strain Induced Transformation (SIT) of Austempered Ductile Iron (ADI) by heat tinting and corroborates the result with SIT related to machining of ADI. On machining ADI, the microstructure changes rapidly from austenite to martensite due to SIT. The analogy between SIT and machining is addressed in this paper. Evaluation to quantify the likely extent of SIT during machining of grades 900, 1050, 1200 and 1400 via heat tinting of plastically deformed samples has been conducted. Heat tinting causes coloration of the etched specimen, distinguishing each microstructural phase. The initial results appear to indicate the occurrence of SIT on all grades of ADI. SIT can be excessively seen on Grade 1400.
Materials Science Forum, 2012
ABSTRACT Butt welded joins were produced between commercially pure (CP) titanium and various tita... more 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.
International Journal of the Society of Materials Engineering for Resources, 2006
Journal of Materials Science and Chemical Engineering, 2013
Key Engineering Materials, 2014
ABSTRACT Formability of two magnesium alloys, namely, AZ80 and ZE10, has been investigated. Both ... more 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 (410oC 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.
Advanced Materials Research, 2011
Abstract Similar and dissimilar butt joint welds comprising combinations of commercially pure gra... more 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 ...
Journal of Materials Science: Materials in Medicine, 2011
A new method of bone fracture fixation is considered in which small pins/darts are dynamically in... more A new method of bone fracture fixation is considered in which small pins/darts are dynamically inserted into bone to prevent translation and rotation at the fracture site. An ABAQUS model was developed to analyze dart penetration in cortical and cancellous bone for varying dart diameter, material, and velocity, and cortical thickness. The method is advocated for bioresorbable darts, so polylactide (PLA) and magnesium are the materials examined in this study. Numerical results showed that magnesium darts can achieve full penetration in bone while suffering little damage. The PLA darts penetrated thin bone well, but substantial deformation was seen as the cortical thickness increased, especially for small diameter darts. As partial validation, prototype PLA fixation darts were fired into cadaveric bone with a custom nailer. As in the model, the PLA darts could penetrate thin cortices but saw gross deformation when impacted against thicker bone.
Journal of Manufacturing Processes, 2013
ABSTRACT As part of an aircraft fleet fatigue life improvement program, investigation has been ca... more ABSTRACT As part of an aircraft fleet fatigue life improvement program, investigation has been carried out into the effect pitting corrosion has on bare 7075-T651 which had undergone split sleeve cold hole expansion. Constant amplitude sinusoidal loading was applied to fatigue test coupons which had pitting corrosion induced upon them by a modified cyclic immersion process using a 3.5% NaCl solution. A pit depth of 39–58 μm was found to significantly reduce the increased fatigue life gains achieved by carrying out cold hole expansion. At 137.9 MPa fatigue life was reduced from achieving run out of ten million cycles to an average 371 × 103 cycles, while at 165.5 MPa average fatigue life was reduced from 810 × 103 to 65 × 103 cycles. The fracture surfaces were analysed under a scanning electron microscope where each displayed an individual crack initiation site located on the material surface within the zone of residual circumferential stress.
IOP Conference Series: Materials Science and Engineering, 2009
Over the past ten years, a novel cellular solid, Trabecular Metal TM , has been developed for use... more Over the past ten years, a novel cellular solid, Trabecular Metal TM , has been developed for use in the orthopaedics industry as an ingrowth scaffold. Manufactured using chemical vapour deposition (CVD) on top of a graphite foam substrate, this material has a regular matrix of interconnecting pores, high strength, and high porosity. Manufacturing difficulties encourage the application of bending, stamping and forming technologies to increase CVD reactor throughput and reduce material wastes. In this study, the bending and forming behaviour of Trabecular Metal TM was evaluated using a novel camera-based system for measuring surface strains, since the conventional approach of printing or etching gridded patterns was not feasible. A forming limit diagram was obtained using specially fabricated 1.65 mm thick sheets. A springback coefficient was measured and modeled using effective hexagonal cell arrangements.
Engineering Failure Analysis, 1995
An in-service failure of a thin-walled titanium bleed-air duct from a wide-bodied commercial airc... more An in-service failure of a thin-walled titanium bleed-air duct from a wide-bodied commercial aircraft has been investigated. Cracking had occurred in the heat-affected zone (HAZ) adjacent to a circumferential weld joining two sections of the duct which was manufactured from commercially pure (grade 3) titanium sheet. Specimens were cut from the duct to include an intact weld and tested under known conditions (overload, fatigue, sustained loading) for comparison with the failed duct. Metallographic observations showed that cracking occurred through an acicular tr HAZ, and fractographic observations revealed brittle, cleavage-like cracking with occasional areas of fatigue striations for both the failed duct and fatigued specimens. These observations, and the absence of sustained-load cracking in test specimens, suggested that the in-service failure had occurred primarily by fatigue. Observations also indicated that small, cleavage-like cracks had been present in the ducts prior to service, although whether these cracks were caused by overload tearing, stress-corrosion cracking, hot-salt cracking or fatigue was not clear. Other possible causes of cleavage-like cracking, e.g. the presence of hydrides as proposed for previous failures, contamination of HAZs by oxygen/nitrogen, are discussed. Possible ways of preventing further failures are then outlined.
Computational Materials Science, 2013
ABSTRACT Friction and heat transfer in metal forming simulations are usually restricted by softwa... more ABSTRACT Friction and heat transfer in metal forming simulations are usually restricted by software to be interface constants, a situation not reflected by the mechanics of real manufacturing processes. A better simulation approach is to use a micromechanics based method to estimate friction and heat transfer as evolutionary phenomenon. This paper presents a friction and heat transfer module for hot forging simulations. The friction model is based on a lubricant film thickness calculation using the Reynolds equation, and a calculation of the fractional contact area based on asperity flattening and roughening. Friction is then portioned between asperity and lubricant contacts. Heat transfer coefficients are calculated using a new model for heat conduction through asperity contact patches and lubricant that takes into account the restriction to heat flow at the contacts. The program is implemented as a user routine in a popular commercially available finite element code, DEFORM 2D. © 2013 Elsevier B.V. All rights reserved.
Uploads
Papers by Timotius Pasang