Key Engineering Materials Vol. 957

Abstract: Traditional manufacturing and finishing operations of crystal products use intensive specialized labour resulting in high cycle times and production costs. It is intended to investigate the applicability of automated finishing technology, namely grinding in a CNC machining centre, with consideration of material’s characteristics and geometric variability to crystal processing. A case study will be presented, involving cutting tools development, cutting parameters optimization, CAM programming of machining strategies and toolpaths, product clamping systems and finally product machining and quality control that is being implemented at Vista Alegre Atlantis company.

Abstract: Ceramic Matrix Composites (CMC) are becoming increasingly important in aeronautical and space applications due to their excellent mechanical properties and wear resistance at high temperatures. Abrasive processes are commonly used for CMC machining due to its high hardness. In this work, an experimental analysis of the influence of grinding parameters has been carried out. Namely, the effect of the variation of cutting speed and feed speed have been studied when grinding a Cf/SiC composite with diamond wheels. Forces were registered during the tests and workpiece quality was analyzed by means of optical techniques. Results show that higher feed rates increase normal force values, while higher cutting speeds lead to lower normal machining forces. Moreover, a relationship between grain aggressiveness and specific grinding energy was observed. Decreasing machining forces also helped to preserve surface integrity of the machined parts.

Abstract: This work reports on the development of thermoplastic starch materials based on mango kernel flour. Mango kernel has a high starch content, which is why the flour obtained after grinding can be used as raw material to obtain thermoplastic starch (TPS) or rather starch rich thermoplastic materials. For this purpose, a plasticization process is carried out in a twin-screw extruder using different plasticizers, namely glycerol, sorbitol and urea, which are thereafter subjected to an injection-moulding process to obtain tensile test samples. In order to assess the difference in properties depending on the plasticizer used, the rheological, mechanical and morphological properties were characterized and evaluated. Sorbitol and urea plasticized thermoplastic starch showed superior mechanical properties to those of the sample with glycerol, achieving tensile strengths close to 3 MPa and an elongation at break of 50%. This was ascribed to the higher molecular weight of sorbitol and the higher amount of active functionalities in urea and sorbitol, which allow to form stronger bonds with starch during thermoplastification. Morphological images confirmed this fact and showed that MKF particles were also present in the TPS matrix, probably acting as reinforcing agents that enhance the mechanical performance of the materials.

Abstract: Shear thickening fluids (STF) viscosity significantly increases when subjected to an external dynamic load. Recent advances show their potential for engineering applications, such as developing shock absorbers and impact energy-absorbing structures. There is a search for sustainable materials for several applications due to the critical need to replace nonrenewable raw materials. Cork is a sustainable material reported to be an excellent alternative to synthetic energy absorbers thanks to its cellular microstructure and cell wall composition. This work explores the development of cork-STF composites designed for impact energy mitigation. The cork-STF composites were manufactured by compression moulding, exploring different compositions of both materials. Additionally, the manufactured compounds were characterized by submitting samples to impacts. The results made it possible to conclude that deagglomeration occurs for STF concentrations higher than 20%. On the other hand, good results were achieved with compounds that have less than 20% of STF in their composition and can withstand impact loading. Therefore, the energy absorption of white cork agglomerates decreases with STF. Nevertheless, the agglomeration was successful, and this design can be adapted for other specific purposes, applications, or even strain rates than the ones explored in this work.

Abstract: Wood-plastic composites were manufactured with Posidonia oceanica (PO) waste and poly(lactic acid) (PLA) by injection molding. To increase the interaction between PO/PLA, DCP was added during extrusion (pre-injection process), and different amounts of methyl trans-cinnamate were added to increase the flexibility of the composites. The results showed that the incorporation of PO fibers generated a stress concentration phenomenon that caused a decrease in the impact properties of the composites. Incorporating DCP improved the interaction between the fibers and the matrix and enhanced the plasticizing effect of methyl trans-cinnamate, as FESEM images shown.

Abstract: This article presents an experimental research carried out on polymer sheet deformed by conventional forming, i.e. tensile and Nakajima tests, as well as by single point incremental forming (SPIF). The analysis is performed for polycarbonate (PC) polymer sheet material within the framework developed in previous recent papers of the authors, which the aim of defining a complete testing methodology for assessing formability and failure by necking and fracture of polymeric sheets. In the case of SPIF, truncated pyramid and cone test geometries are selected, enabling a variety of strain states from plane to biaxial strains. The results obtained allow an accurate evaluation and assessment of the forming limits by necking and fracture within the material forming limit diagram (FLD), and also include an analysis of the influence of the process parameters on the formability and failure modes attained in the case of incremental forming.

Abstract: Riveting is the most important method for joining two sheets of different materials. In order to promote electromagnetic pulse riveting (EMR), the influence of the impact velocity will be studied in this paper in order to correctly model the electromagnetic field of the riveting process. There are many parameters associated to the riveting process, however, the interference fit is considered as the most important criterion to measure the riveting quality, which consequently will be associated to the impact velocity, being this the most important parameter. The use of the washer will be studied to guarantee the optimal flow of the material and to restrict the expansion of the rivet shaft, thus minimizing damage to the composite material. The interference generated between the rivet shaft and the hole of the sheets and the flow of the material will be developed by finite elements which will later be validated by means of experimental tests analyzing its final microstructure. Finally, the relationship between the impact velocity on the rivet head will be directly related to the distribution of the interference generated in the deformation, verifying that the impact velocity.

Abstract: This article presents an experimental investigation of biocompatible Polyether ether ketone (PEEK) polymeric sheet deformed using Single Point Incremental Forming (SPIF) at room temperature, with the objective of manufacturing a cranial medical implant. The investigation was performed in terms of formability and failure within the principal strains space, being the material Forming Limit Diagram (FLD) assessed by means of Nakajima tests. This material characterization allowed to obtain the formability limits at necking and at fracture of PEEK polymeric material. In addition, an experimental work plan in SPIF was performed in terms of spifability (or formability in SPIF) with the aim of determining the effect of the main process parameters on the spifability, modes of failure, and temperature, among others. As a result, an optimum set of parameters along with the established methodology were used for manufacturing a cranial medical implant made of this high-performance and biocompatible polymeric material. The work primarily shows the feasibility of manufacturing PEEK medical prostheses and implants using SPIF.

Abstract: Global plastic production and consumption have increased due to its outstanding properties. Their widespread use is cause for concern, as most plastics deteriorate but never fully decompose, posing a risk to ecosystems. A large source of ocean plastic waste is "ghost gear", a result of intentional or accidental abandonment of fishing gear at sea. To reduce their impact, mechanical recycling is considered a viable option as it is an efficient recycling method in terms of time, cost-effectiveness, and environmental impact. This study aims to investigate the feasibility of producing injection moulded components from recycled fishing nets composed of polyamide 6 (PA6). The degradation in a marine environment allied with the mechanical recycling process was evaluated by comparing the physical and mechanical properties of injection moulded specimens of both recycled fishing nets and commercially available extruded PA6 plates. In addition, both materials were subjected to an additional mechanical recycling step (after the injection) to determine the impact on the properties of additional recycling cycles. Finally, the feasibility of injection moulding of cardholders was also studied. The physical and mechanical characterization concluded that the property values obtained in the tensile test and the density measurements of the recycled fishing nets are within the range of values established for the properties of an extruded, non-recycled PA 6, and that the effect of the second recycling on its properties was negligible. The marine degradation had a more significant impact on the tensile properties and Charpy notched impact strength than on the hardness and density values.