Solid State Phenomena Vol. 311

Abstract: Knee osteoarthritis is one of the major causes of musculoskeletal impairment in adults. This disease is mainly characterised by progressive degeneration of the articular cartilage, and to date, there is no known cure for it. Initiation and progression of the osteoarthritis pathology is associated with knee loading conditions. For younger, active patients with knee osteoarthritis, common treatments include non-invasive options in order to manage symptoms before considering, as a last resort, the surgical options, in particular the gold standard treatment: knee replacement. The advent of orthopedic prostheses for knee replacement and their widespread applications have helped millions of patients worldwide to be relieved from pain and gain their mobility. However, they are still not suitable for young or middle-aged patients suffering from localised cartilage damage, due to the limited life span of these load-bearing devices. All available remedies for those patients are temporary and some of them might result in regeneration of tissues with different properties to the existing one, and hence limited functionality and durability. In this paper, different types of implants developed and tested at Auckland University of Technology for younger patients with osteoarthritis will be presented and discussed. Recently developed load-sharing implants could be considered as suitable options lying between the symptom management and invasive treatments. One such implant is comprised of femoral and tibial components, and removes excessive load through the knee joint by attachment to the medial side. Another developed implant prevents further tissue degeneration through replacing damaged regions of the tissue and preserving the remaining healthy portion. This results in prolonging the tissue functionality, and further postponing the total joint replacement. These patient-specific implants would be suitable for early-onset knee osteoarthritis and can be used for younger active patients, as no major modification in the knee joint is required.

Abstract: In order to make micro composite drills (Fig. 1), cemented tungsten carbide (WC-10Co) and high strength (AISI 4340) steel were successfully bonded by hot compaction diffusion bonding at a low temperature. The effects of holding time, pressure and temperature on microstructure and mechanical properties of the sintered carbides and bonding strengths of the bimetallic composites were examined, and a transitional layer was found at the interface as a result of elemental inter-diffusion. The optimal bonding parameters were determined to achieve the maximum bonding strength of 226 MPa of the WC-10Co/AISI 4340 steel joints, which is helpful in producing micro composite drills. Microforming is introduced to produce lighter and more energy effective products. In this study, Magnesium-Lithium (Mg-Li) alloy, new material in microscale, was chosen to superior formed micro-cup due to its ultralight weight with outstanding ductility. The dry and oil lubrication conditions were chosen as benchmarks to investigate effects of a novel oil-based nanoparticle lubricant in micro deep drawing (MDD) process of Mg-Li alloy. Finite Element (FE) modelling was conducted and the simulation results of the drawing force were in a good agreement with the experimental results. The formed cup quality with consideration on the surface roughness has been extensively evaluated and the results illustrated the quality improvement was substantial.

Abstract: Vat photopolymerization is one of additive manufacturing and also known as photo-curable three-dimensional printing technology. It uses light energy with the proper wavelength to expose on the liquid photo-curable resin inducing the photopolymerization process and resulting in solidification layer-by-layer. The building method is classified into two ways: free-surface and constrained-surface. The advantage and disadvantage of both methods are described and analysed according to the different material property and requirement. The basic composition for photo-curable resin consists of photo-initiator and monomer. Adding powder into photo-curable resin makes the photo-curable slurry. Literatures report that high density powder such as zirconia oxide or Inconel 718 is suitable for free-surface building method because of poor suspension. However, the volume percentage in the slurry is less than 50% causing the higher shrinkage ratio and inaccuracy after sintering process. The coupling agent may increase the suspension of powder in slurry but experimental result shows that it still cannot improve the success rate in the constrained-surface building method. Therefore, this study proposes a combination method to overcome the difficulty of making high density ceramic or metal part. In addition, the sintering process is a key factor to obtain the high dense part with no crack occurrence and desirable microstructure. The optimized sintering parameters for zirconia oxide and Inconel 718 are also introduced.

Abstract: This study aims to plan the no-tail, i.e. zero waste, automatic cold forging model through the innovative development of a die to directly produce finished nail tails without second processing. It could enhance production efficiency, reduce production costs, and conform to the new model of zero waste under “circular economy”.

Abstract: High strength can be achieved by severe plastic deformation but at the cost of ductility. A novel strategy, which named multiple surface rolling was applied on a homogeneous annealed pure copper to break the strength and ductility trade-off. A combination of high strength and acceptable ductility was achieved in copper strips after submitted to multiple surface rolling. The detail microstructure evolution rolled samples were characterized by EBSD observation and compared with the initially annealed ones. The average grain size does not show significant deviation in both initially annealed and multiple surfaces rolled copper. Detailed observations show a heterogeneous distribution of low angle grain boundaries through thickness direction. The low angle grain boundaries and misorientations revealed the potential strengthening mechanisms in the material. Both microstructural characterization and numerical simulations indicate that multiple surface rolling contributes to strain hardening at the sample surface, while the interior layer was undergoing elastic deformation or partial plastic deformation. This heterogeneous deformation renders copper sheet with a combination of high strength and ductility.

Abstract: The blank development of sheet metal for the stamping and the roll forming processes is crucial for the dimensional accuracy of the products. The neutral line parameter is the indicator to present the thinning phenomenon at the bending corners of the products. The basic assumption of the neutral line position is the surface that the sheet metal remains un-deformed after the stamping or the roll forming process. The conventional determination method of the neutral line position is based on the zero strain position through the thickness direction of the blank. In this paper, a different neutral line factor calculation method based on the mean profile length was proposed to find the neutral line factor, which is directly related to the profile length and more precise for the bland development calculation. A cross sectional profile was obtained after the forming process and the mean profile length of the upper and the lower surface was obtained. The ratios of the bending radius to the sheet thickness were calculated using the FEM simulation. A neutral line equation was proposed considering the material mechanical properties and the bending tool parameters. The initial blank width was compared to the forming result of the CAE simulation to validate the neutral line model. This model is able to take into consideration of the thinning effect at the entire bending zone of the metal forming without the assumption of the uniform thinning and is more accuracy for the blank width calculation.

Abstract: A forward open cold extrusion process is evaluated to reveal the sensitivity of forming load to numerical factors including number of total degrees of freedom, time step size and mesh size. The allowable reduction of area was examined by varying number of finite elements and the total solution steps to determine the reliability, in which the results are affected significantly by the positions of the lowest and highest nodal points in contact with the die. An investigation of the oscillations of the forming load in forward open extrusion revealed a set of critical numerical conditions that minimize unwanted oscillatory behavior. The limits of the material initial radii were obtained, suggesting that rigid plasticity with rigid dies is inappropriate for simulations of forward open cold extrusion with extreme reduction of area. Due to artificial numerical deformation of the rigid zone and die elastic deformation thus each of which has a non-negligible influence on the maximum reduction of area.

Abstract: There is a significant effect for the performance of proton exchange membrane fuel cell with the liquid water generated in cathode channel during the operation process In this paper, based on the numerical simulation of three-dimensional and VOF model of multiphase flow, according to the different flow channel design and the change of different inlet temperature, the transport phenomena of multiphase flow in PEMFC is discussed at temperature effect. In U-shaped cathode channel with bump scale (h/H=1/4), a long water film is assumed to cover the surface of the gas diffusion layer at the entrance. Under the simulated oxygen flow conditions of inlet 200 Reynolds number, 4.4 Weber number and inlet temperature 333K, the water film heated is not obviously affected by oxygen flow from inlet channel to bend channel. Subsequently, the shape of water film is elongated and broken from outflow of bend channel to outlet channel. The computational results are obtained that the residual broken water film can be existed in the outlet channel. The flow field temperature can affect the residual flow rate of water film in the channel. The residual rate of water film in the hot flow field is lower than that in the cold flow field.

Abstract: With the advancement of technology, plastic products are inseparable in our environment, and the impact of the plastics industry on us is gradually increasing. Although Taiwan's plastics industry has been progressively added to mold flow analysis and automation, there are still some areas in the manufacturing process that can be optimized. In the process of slit-shaped materials, bending and deformation have a very large impact on the finished product, which is a major issue at the technical level. In this study, a toothbrush was taken as an example to find the best combination of injection molding parameters. The research process was studied from CAD mold design, CAE mold flow analysis, injection molding parameter analysis, mold opening, product injection and measurement, and the results were verified. Among them, the injection pressure, dwell time and holding pressure are used as the Taguchi factor, and the CAE mold flow analysis is performed by the direct cross table L₁₆ (4⁵) combination to find a small amount of warpage, and the Taguchi method and the reaction surface method are used to find out the best combination of parameters. After the final product was shot and the dimensions and simulation were compared with each other, the data showed that the amount of warpage of the finished product was 0.0892 mm, and the error with the analog value was 0.0212 mm, which confirmed that the injection molding parameters were reliable.