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The mechanical behaviours of a high-pressure die cast AM60B magnesium alloy were studied. Monotonic and cyclic tests (with a strain ratio R = −1) were carried out at ambient temperature. The results of the mechanical testing were discussed with respect to the crystallographic texture and the microstructure of the alloy in terms of clusters of pores, grain size, second phase strengthening as well as the orientation-dependent activation of different deformation mechanisms such as slip and twinning. [ABSTRACT FROM AUTHOR]

In-mold assembly can be used to create mesoscale articulating polymeric joints that enable the miniaturization of devices, reduction in production costs, and increase in throughput. One of the major challenges in miniaturizing devices using the in-mold assembly is to develop appropriate characterization techniques and modeling approaches for the interaction between polymer melt flow fronts and premolded components. When a high speed, high temperature second stage melt cones in contact with a premnolcied mesoscale component that has similar melting temperatures, the premnolded component can experience a significant plastic deformation due to the thermal softening and the force associated with impingement of the melt flow front. in our previous work, we developed methods to inhibit the plastic deformation by supporting the ends of the mmiesoscale premoldeci components. in this paper we present an alternative strategy for controlling premolded component deformations. This involves a mnesoscale in-mnold assembly strategy that has a mnultigate mnold design for bidirectional filling. This strategy permits in-mold assembly using polymners with comparable inciting points. This paper demonstrates the technical feasibility of manufacturing in-mold-assembled mesoscale revolute joints using this bidirectional filling strategy Au experimental technique was developed for characterizing the transient impact force of the melt flow fronts and premolded components inside of a mold. The experimental data were used to validate a new computational model for predicting the effects of tile melt flow front positiomi in order to minimize the plastic cleformatiomi of premolded component using time bidirectional filling strategy This paper also investigates the effects of the flow front position on the force applied on the premolded component and its corresponding plastic deformation. [ABSTRACT FROM AUTHOR]

Abstract  In micro injection molding, the melt flow behavior is important for the final product quality. However, the current process monitoring and measurement technology are not adequate enough to provide a direct analysis access. In the presented study, a glass insert mold designed for performing the direct visual analysis for melt flow phenomena in micro injection molding is introduced. The micro tensile specimen with 0.1 × 0.4 mm2 (depth × width) cross section dimension is chosen as the objective part. The correlation between processing parameters (injection pressure, injection speed, mold temperature) and flow behavior was investigated and analyzed. The results show that the injection pressure put an obvious effect on the filling speed through micro cavity. Injection speed can influence the filling time dramatically also. Higher mold temperature brings positive influence with the flowing speed, due to the lower viscosity of polymers in higher mold temperature. [ABSTRACT FROM AUTHOR]

The paper reports the mechanical behaviour of two polymers, poly(vinylidene fluoride) (PVDF) and polyamide 11 (PA11), under high-gas-pressure (carbon dioxide and argon atmospheres) media at 42°C by using a normal indentation test. The experimental technique, an indentation method, for the measurement of the indentation hardness is described and the corresponding data are reported as a function of the temperature and pressure. Argon interacts poorly with both polymers and the data are similar; the hardness increases with increase in the pressure. It is shown that with PVDF, which has a relatively low glass transition temperature (-100°C), the influence of the plasticization due to carbon dioxide upon the hardness is negligible; the hardness data for argon and carbon dioxide are comparable. Subsidiary studies indicate that in the carbon dioxide and indeed argon environments no increase in crystallinity is detected after exposure to the gas environment. However, with PA11, which has a glass transition temperature (20-50°C), closer to the ambient, the influence of the carbon dioxide plasticization is pronounced and a significant initial decrease in the hardness is reported. Subsequently, the hardness increases with increasing gas pressure, which is attributed to the action of an effective hydrostatic constraint. The data for the argon environment for PA11 show no evidence of plasticization and only an increase in the hardness with increasing hydrostatic pressure. Again, no evidence of enhanced gas-induced crystallinity is observed. [ABSTRACT FROM AUTHOR]

In this paper, the effects of pressure-sensitive yielding on the η factor and the J integral estimation for compact tension specimens are investigated. The analytical expressions for η and J for pressure-insensitive von Mises materials are generalized to pressure-sensitive Drucker-Prager materials using a lower bound approach. The η factor as a function of the pressure sensitivity and the normalized crack depth for compact tension specimens is derived under plane stress and plane strain conditions. The numerical results indicate that the η factor decreases as the pressure sensitivity increases. The effects are more pronounced under plane strain conditions than under plane stress conditions. However, the effects of the pressure sensitivity on η are found to be mild in general. For rigid perfectly-plastic materials, the J estimation for pressure-sensitive materials is also reduced to a simple expression of the tensile yield stress times the crack tip opening displacement as for the von Mises materials. [ABSTRACT FROM AUTHOR]