Abdus Samad Mahmud

Gradient anneal of functionally graded NiTi

This paper reports on a novel heat treatment method for the creation of functionally graded near-equiatomic NiTi shape memory alloys. The method is an anneal within a temperature gradient after cold work, thus creating a structural gradient within the matrix of the alloy. It is based on the principle that the transformation behaviour and the thermomechanical properties of NiTi are sensitively dependent on the annealing temperature. For the Ti?50.2?at.%?Ni alloy used, it was found that the gradient-anneal resulted in varying thermal transformation behaviour along its length and a unique L?ders-type deformation behaviour with a positive stress gradient. Such behaviour provides improved controllability for actuation applications.

Experiments on deformation behaviour of functionally graded NiTi structures

Functionally graded NiTi structures benefit from the combination of the smart properties of NiTi and those of functionally graded structures. This article provides experimental data for thermomechanical deformation behaviour of microstructurally graded, compositionally graded and geometrically graded NiTi alloy components, related to the research article entitled “Functionally graded shape memory alloys: design, fabrication and experimental evaluation” (Shariat et al., 2017) [1]. Stress–strain variation of microstructurally graded NiTi wires is presented at different heat treatment conditions and testing temperatures. The complex 4-way shape memory behaviour of a compositionally graded NiTi strip during one complete thermal cycle is demonstrated. The effects of geometrical design on pseudoelastic behaviour of geometrically graded NiTi plates over tensile loading cycles are presented on the stress–strain diagrams.

Effect of Cold Work and Partial Annealing on Thermomechanical Behaviour of Ti-50.5at%Ni

This study investigated the effect of cold work and partial annealing on the thermal and mechanical behaviour of NiTi. It is well understood that the thermomechanical properties of near-equiatomic NiTi are highly dependent on the microstructure, and hence the history of thermomechanical treatments has undergone through. It has been generally accepted that a sufficiently high cold work is necessary prior to annealing but detailed knowledge of the influence of the level of prior cold work on annealing is unclear. This study determined the threshold effective levels of cold work required for annealing and demonstrated that the thermal and mechanical properties of Ti-50.5at%Ni are sensitive to the level of cold work as well as temperature of partial annealing.

Effect of ageing temperatures on pseudoelasticity of Ni-rich NiTi shape memory alloy

The shape memory behavior of NiTi alloy is very sensitive to alloy composition and heat treatments, particularly annealing and ageing. This paper analysed the effect of ageing towards the thermomechanical behaviour of Ti-51at%Ni wire. The analysis focused on the effect of ageing at the different temperature on thermal transformation sequence and tensile deformation behaviour with respect to the recoverability of the alloy. It was found that B2-R transformation peak appeared in the differential scanning calorimetry (DSC) measurement when the alloys were aged at the temperature between 400°C to 475°C for 30 minutes. Further ageing at 500°C to 550°C yielded two stage transformation, B2-R-B19’ in cooling. All aged wires exhibited good pseudoelastic behaviour when deformed at room temperature and yielded below 1% residual strain upon unloading. Ageing at 450°C resulted the smallest unrecovered strain of about 0.4%.The shape memory behavior of NiTi alloy is very sensitive to alloy composition and heat treatments, particularly annealing and ageing. This paper analysed the effect of ageing towards the thermomechanical behaviour of Ti-51at%Ni wire. The analysis focused on the effect of ageing at the different temperature on thermal transformation sequence and tensile deformation behaviour with respect to the recoverability of the alloy. It was found that B2-R transformation peak appeared in the differential scanning calorimetry (DSC) measurement when the alloys were aged at the temperature between 400°C to 475°C for 30 minutes. Further ageing at 500°C to 550°C yielded two stage transformation, B2-R-B19’ in cooling. All aged wires exhibited good pseudoelastic behaviour when deformed at room temperature and yielded below 1% residual strain upon unloading. Ageing at 450°C resulted the smallest unrecovered strain of about 0.4%.

Burr Height as Quality Indicator in Single Shot Drilling of Stacked CFRP/Aluminium Composite

In drilling metallic parts, burr height is one of the quality indicators that is used for hole quality assessment, and burr height need to be minimized for best hole quality. This is important because the induced exit burr height usually causes serious problem for further assembly of the stack up during the riveting and fasteners installation. This paper aims to establish an appropriate choice of drill geometry and drilling parameters to achieve a minimum or eliminate the burr height formation when drilling stacked Carbon Fibre Reinforced Plastic (CFRP)/aluminium 7075 T-6 composite in a single shot drilling process. The two levels of fractional factorials method was used to determine the optimum setting that give minimum burr height and the percentage of significance for each parameter in drilling a stack up materials was further analysed. The results revealed that burr height formation for stack up materials can be minimized at 15° of helix angle, 8° of primary clearance angle, 130°of point angle, 30° of chisel edge angle at spindle speed 2600 RPM and 0.05 mm/rev. A minimum burr height of 133.62 µm was found at these optimized combinations of parameters.

Finite-element analysis of NiTi wire deflection during orthodontic levelling treatment

Finite-element analysis is an important product development tool in medical devices industry for design and failure analysis of devices. This tool helps device designers to quickly explore various design options, optimizing specific designs and providing a deeper insight how a device is actually performing. In this study, three-dimensional finite-element models of superelastic nickel-titanium arch wire engaged in a three brackets system were developed. The aim was to measure the effect of binding friction developed on wire-bracket interaction towards the remaining recovery force available for tooth movement. Uniaxial and three brackets bending test were modelled and validated against experimental works. The prediction made by the three brackets bending models shows good agreement with the experimental results.

Numerical Investigation on the Effect of Injection Pressure on Melt Front Pressure and Velocity Drop

Computational Fluid Dynamic (CFD) was used to simulate the injection molding process of a tray. The study focuses on pressure distribution and velocity drop during the injection process. CFD simulation software ANSYS FLUENT 14 was utilized in this study. The melt front pressure in the mold cavity shows that it was affected by the shape of mold cavity and filling stage. The melt front pressure will decrease as the flow move further than the sprue but it will increase rapidly when the mold was about to be fully filled. The slight pressure drop was detected when the molten flow meets the rib of the tray. The velocity of higher injection pressure was greater than the lower injection pressure but the velocity rapidly dropped when the melt front fully filled the cavity. The current predicted flow profile was validated by the experimental results, which demonstrates the excellent capability of the simulation tool in solving injection-molding problems.

Effect of Titanium Depletion of High Temperature Treated NiTi Shape Memory Alloy Wire

Shape memory behaviour of NiTi is very sensitive to the presence of inclusion in the matrix and oxide and the surface. This work studied the influence of high temperature treatment towards thermal martensitic transformation behaviour of NiTi. The alloy was subjected to heat treatment at 1223 K for various times in argon and air environment. It was found that treatment in air severely destroyed the shape memory property of the alloy due to the formation of multilayer of oxides. Treatment in argon also reduced the volume percentage of martensite phase transformation, even though no oxide layer was observed at the surface. This reduction is caused by the depletion of Ti element in the matrix due to the outward diffusion of Ti element. The outward diffusion of Ti is however stabilized at 15 hours exposure time of 1223 K heating temperature.

Transformation Cyclic Damage of Near-Equiatomic Ni-Ti

Near-equiatomic Ni-Ti alloys are known to exhibit shape memory effect associated with a B2↔B19’ martensitic transformation. These alloys are often used in various cyclic modes in application, typically as actuators and sensors. The B2↔B19’ martensitic transformation in Ni-Ti is accompanied with a large lattice distortion. Cycling through this transformation, induced thermally, mechanically or by the combination of the two, is found to cause structural damage to the alloys, hence changes their functional properties. This study investigates the effect of transformation cycling and heat treatment on the property stability of near-equiatomic Ti-Ni. It was found that in the case of thermally induced transformation cycling, incomplete transformation cycles caused less structural damage to the matrix than full transformation cycles whereas in the case of mechanically induced transformation cycling via pseudoelasticity in tension, partial or full transformation cycling caused similar property changes. The indifference of the case of pseudoelastic cycling is attributed to the localisation of the deformation, commonly known as the Lüders-type deformation.