Cavity Expansion in Cohesive-Frictional Soils with Limited Dilation

The problem of cavity expansion from zero radius has no characteristic length and therefore possesses a similarity solution, in which the cavity pressure remains constant and the continuing deformation is geometrically self-similar. In this case, the incremental velocity approach first used by Hill (1950) to analyze cavity expansion in Tresca materials can be extended to derive a solution for limiting pressure of cavity expansion in other types of material. In this article, a rigorous semi-analytical solution is derived, following Hill's incremental velocity method, for the expansion of cavities from zero initial radius in cohesive-frictional soils with limited dilation. In particular, the radius of the elastic-plastic interface c is used in this article as the time scale and the solution for the limit pressure has been presented. Solutions are evaluated for a number of cases representative of a range of cohesive-frictional and dilatant soils. A comparison is also made between the solutions presented here and previous solutions for cohesive-frictional soils that have unlimited (on-going) plastic dilation. In particular, the influence of limited plastic dilation on the cavity limit pressure is identified and discussed.

Numerical and Experimental Investigations on the Effects of Variable Cavity Pressure on the Formability of GLARE Using Hydromechanical Deep Drawing

Excellent physical and mechanical properties of fiber metal laminates (FMLs) have made them a very popular and most suitable material to make high strength and lightweight products in different industries for example automobile, military, and aerospace. Glass fiber aluminum reinforced epoxy (GLARE) is one of the most used fiber metal laminate among the family of fiber metal laminates, but there are some challenges in its formability. Our study mainly focuses on the formability of the GLARE cup parts by using hydromechanical deep drawing. Forming depth with good quality (without any wrinkling, delamination, or fracture), failure mode analysis and wall thinning rate (%) distribution of the parts are the main criteria in the formability. The influence of variable cavity pressure (VCP) with respect to punch strokes had been investigated by using numerical simulations and experiments. Results showed that the variable cavity pressure in case of increasing or decreasing the cavity pressure had very much effect on the formability. Stepwise increasing the VCP with respect to punch strokes resulted in a maximum forming depth of 29.00mm as well as good quality whereas in the case of stepwise decreasing the variable cavity pressure, results were not encouraging. Commercially available code ABAQUS explicit was used for finite element analysis simulation which had shown close agreement with the experimental results.

Number of Times Recycled and Its Effect on the Recyclability, Fluidity and Tensile Properties of Polypropylene Injection Molded Parts

The ease with which modern plastics can be injection molded makes them very suitable for the production of many different products and, today, plastics are often used as substitutes for metal. Polypropylene (PP) is one of the most widely used thermoplastics globally since it is very useful, cost-effective and flexible for molding. However, the amount of harm to the environment caused by plastic waste has become phenomenal and the recycling of plastics has become a serious aspect of environmental protection. PP, as the most commonly used plastic material, was selected for use in this study. It has a melt flow index of 15 g/min and its recyclability, fluidity, and physical properties, as well as manufacturing conditions, were explored in relation to the number of times the material could be recycled (TR). A cavity pressure sensor was used to measure the viscosity index of the recycled plastic after multiple cycles of plasticizing and injection, part molding, scrap-recycling, and crushing. A paperclip-shaped test specimen was used to determine PP fluidity and crystallinity of specimens with different TRs. Tensile tests were used to detect differences in the tensile strength between specimens made from Raw-PP and recycled PP. The results showed that PP that had been recycled several times had a higher melt flow index, material fluidity, melting peak area, crystallinity, crystallization rate, and crystallization temperature. Repeated injection and recycling of the material had reduced the length of the molecular chains and broadened the molecular weight distribution. This improved the fluidity and increased crystallinity. The increase in fluidity made cavity filling easier, reducing the cavity pressure as well as the viscosity index. The results of this study showed that the recycling of the PP could improve the physical properties of the products to a degree and also went some way to further the benefits of a circular economy. The recycling of injection-molded PP material can be added to renewable energy technologies and used in environmental impact assessment.

Novel Analysis Methodology of Cavity Pressure Profiles in Injection-Molding Processes Using Interpretation of Machine Learning Model

The cavity pressure profile representing the effective molding condition in a cavity is closely related to part quality. Analysis of the effect of the cavity pressure profile on quality requires prior knowledge and understanding of the injection-molding process and polymer materials. In this work, an analysis methodology to examine the effect of the cavity pressure profile on part quality is proposed. The methodology uses the interpretation of a neural network as a metamodel representing the relationship between the cavity pressure profile and the part weight as a quality index. The process state points (PSPs) extracted from the cavity pressure profile were used as the input features of the model. The overall impact of the features on the part weight and the contribution of them on a specific sample clarify the influence of the cavity pressure profile on the part weight. The effect of the process parameters on the part weight and the PSPs supported the validity of the methodology. The influential features and impacts analyzed using this methodology can be employed to set the target points and bounds of the monitoring window, and the contribution of each feature can be used to optimize the injection-molding process.

OPTIMIZATION OF INJECTION PROCESS PARAMETERS OF PLASTIC REINFORCED COMPOSITES USING RESPONSE SURFACE METHODOLOGY AND CENTRAL COMPOSITE DESIGN

The injection molding process is among the most efficient processes for mass production of polymer products with complex geometry at optimal cost. This study investigates the effect of the injection parameters on the cavity pressure, tensile and microstructural properties of plastic-reinforced composites and optimized the process to determine the optimum injection parameters using the Response Surface Methodology and central composite design. The two polymer composite materials used for this work are low-density polyethylene reinforced with aluminium powder (LDPE/Al) and low-density polyethylene reinforced with carbon black (LDPE/CB) at 250 and 200oC injection temperature respectively. The analysis of the results obtained from both the numerical and physical experimentations were used to obtain two predictive models which correlate cavity pressure and tensile strength as a function of the independent process parameters namely, injection pressure and time. An injection pressure of 70 MPa and time of 1.00 sec was found to be optimum producing a cavity pressure of 37.658 MPa while an injection pressure of 70 MPa and time of 1.75 sec was found to be optimum producing a material with tensile strength of 7.41 MPa. The results indicate that the cavity pressure increases with an increase in the injection pressure but decreases with an increase in the injection time for the two analyzed polymer composites. The study shows that process parameters have significant effects on the cavity pressure, mechanical and microstructural properties of LDPE/Al and LDPE/CB.

Research on Quality Characterization Method of Micro-Injection Products Based on Cavity Pressure

The cavity pressure in the injection molding process is closely related to the quality of the molded products, and is used for process monitoring and control, to upgrade the quality of the molded products. The experimental platform was built to carry out the cavity pressure experiment with a micro spline injection mold in the paper. The process parameters were changed, such as V/P switchover, mold temperature, melt temperature, packing pressure, and injection rate, in order to analyze the influence of the process parameters on the product weight. The peak cavity pressure and area under the pressure curve were the two attributes utilized in investigating the correlation between cavity pressure and part weight. The experimental results show that the later switchover allowed the injection to proceed longer and produce a heavier tensile specimen. By comparing different cavity pressure curves, the general shapes of the curves were able to indicate different types of shortage produced. When the V/P switchover position is 10 mm, the coefficient of determination (R2 value) of part weight, for the peak cavity pressure and area under the curve, were 0.7706 and 0.8565, respectively. This showed that the area under the curve appeared to be a better process and quality indicator than the peak cavity pressure.