Volume 37, Issue 2

In this research paper, the effects of the combined compacting and back-injection process to produce back-injected self-reinforced composites on the mechanical properties of the self-reinforced composites (SRCs) are investigated. For this purpose, the parameters barrel temperature, time of injection and holding pressure were varied for the back injection. Tensile and bending tests were carried out on the SRCs. The results show that the mechanical properties depend to a large extent on the process parameters. The measured tensile strength varies between approx. 186 and 86 MPa, the stiffness between approx. 3500 and 2000 MPa. The flexural strength is measured between approx. 75 and 5 MPa, the flexural modulus between approx. 5480 and 650 MPa. Flexural tests are more suitable for evaluation of the consolidation, as tensile tests cannot evaluate the adhesion of the fabric layers to each other in the SRCs. Microscopic examinations show that consolidation by the back-injected melt can lead to smaller cross-sections in the SRCs compared to an area that was not back-injected. At high barrel temperatures, melting of individual fabric layers can occur, which explains, among other things, the drop in the mechanical properties of the SRCs.

There is a possibility that hip joints may become dysfunctional due to age, wear or some accidents, and in this case they need to be replaced with hip implants. However, after conventional hip stem implantation, the load transferred to the bone usually decreases due to the high stiffness of the metallic (most commonly Ti6Al4V, CoCr or stainless steel) hip stem implant, and as a result, mineral loss occurs in the bone which weakens. On the other hand, PEEK is an advantageous material with its low cost, ease of production, corrosion resistance and biocompatibility. More importantly, it has the potential to be a good alternative to metallic materials in load-bearing bone replacements, thanks to its mechanical properties and density close to that of the bone. In this study, hip stem implants having three different commercial PEEK materials and four different metallic main spar designs were modeled. Their behavior under static and dynamic loading conditions was analyzed according to ASTM-F2996-20 and ISO-7206-4:2010 standard test methods, and the stress-shielding effect of hip stems modeled as implanted into the femur was simulated using ANSYS commercial finite element analysis software. According to the results, it was observed that CFP based hip stem models meet the five million life time criteria and increase the stress on the femur bone by up to 57%.

Injection compression molding (ICM) is a nontraditional hybrid injection molding (IM) process that has been utilized to mold a wide range of the latest and difficult-to-manufacture precision parts that require high dimensional accuracy and no residual stresses. This paper introduces the accurate calculation of warpage for ICM by numerical simulation via Moldflow software, and a comparison of results with products produced experimentally by ICM. To begin with, the process parameters of ICM were discussed based on the numerical simulations. The effects of process parameters, namely melt temperature, mold temperature, compression pressure, and compression distance, on warpage behavior of a molded 3D BJ356MO polypropylene (PP) (100MFI) part were investigated using Taguchi analysis. The obtained warpage results with optimum process parameters were compared with experimental measurements to test the validity of the simulation model of ICM. It was found that the numerical simulations of the ICM show good agreement with experimental measurements.

In this paper, the mechanical behavior of epoxy polymer nanocomposite with continuous single-walled carbon nanotubes (SWCNT) with and without vacancy defects has been investigated based on two approaches of deformation, molecular mechanics (static) and molecular dynamics. In this regard, molecular simulation has been performed on the basis of the compass force field. In order to validate the research steps, the results obtained for pure epoxy polymer were compared with similar molecular dynamic simulations, which confirmed the simulation process. The research process proposed a method for controlling the symmetry of the system during equilibration with an asymmetric barostat. The Souza-Martins barostat was also used to apply loading and deformation control over a constant strain rate range. The results showed that in both deformation approaches (with and without calculating the contribution of kinetic energy), the presence of defects improved the transverse tensile and shear moduli, while the longitudinal tensile modulus decreased. Also, the improvement and decrease of the longitudinal tensile modulus and longitudinal shear modulus of the nanocomposite in comparison with the net polymer have been observed in both approaches, respectively. As a general result, it was observed that the contribution of kinetic energy has a major effect on the mechanical properties of pristine and defective nanocomposites.

The aim of this study is to utilise recycled aluminium, expanded polyethylene (EPE) and expanded polystyrene (EPS) to develop a ternary composite. The study was a preliminary investigation into the microstructural, functional groups and textural properties of the novel material. The material was characterised by Fourier Transform Infra-Red Spectroscopy (FTIR), Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX) and Branueur-Emmet-Teller analysis (BET). The shifts in the FTIR peaks for each of the polymer feedstock in comparison with the binary composite indicated chemical interactions between them. For the ternary composites, there were shifting of peaks as the proportion of the aluminium increased in the composites, suggesting the influence of aluminium on the curing process. Beyond 20% Al filler, there were no significant functional group changes in the composite. SEM revealed that an increase in aluminium filler percentage led to better interfacial adhesion and dispersion. BET revealed that the blend of polystyrene and powdered EPE reduces the surface area, while the introduction of the aluminium particles within the range observed increases the surface area of the hybrid composites formed. As the dispersion of aluminium increased, pore volume increased while pore size decreased.

This publication investigates the adhesion between an injection molded component and a self-reinforced composite (SRC) produced in a combined compaction and back-injection process to produce back-injected self-reinforced composites. To study the influence of the process, the parameters barrel temperature, time of injection, and tool temperature were varied. In addition, samples were taken at different positions along the flow path. In light of the orthotropic material behavior of SRCs, investigations were conducted to see whether different loading cases lead to different mechanical behavior. Shear-off and pull-off tests revealed a different strength as a function of the loading type. In the shear-off tests, a mean strength of 11.37 MPa was recorded over the entire test series, while the measured mean strength in the pull-off tests is considerably lower, 4.04 MPa. The type of failure is determined with the aid of SEM images, and the influence of the microstructure of the thermoplastic fibre materials on the adhesion is set out. It is shown that, as of a sufficiently high level of adhesion, failure occurs within the fibres.

Because of their appealing properties, such as biodegradability, high basic stiffness, low density, and low cost, natural fibers have begun to be used in a variety of applications. In comparison to synthetics, they are also reusable. The aim of this work is to develop new woven materials made of wool and Alfa fibers (Stipa-tenacissima). The extraction of Alfa fibers was achieved via alkaline treatment. The chemical composition, mechanical and physical properties of the extracted fibers were determined. Wovens were produced using the weaving of taffetas technique. This study presents a chemical, physical, morphological and mechanical characterization of Alfa/wool yarns and fabrics. The results show that the fabric made of fibers treated with 2 mol concentration of NaOH presents the greatest morphological structure and a higher degree of crystallinity due to the reorganization of the molecular chains that results in a better orientation of the fibers compared to other concentrations. On the other hand, the results of the tensile test show that the Young’s modulus of the Alfa/Alfa woven fabric is 8 ± 1.157 MPa in the weft direction, compared to the Alfa/wool woven fabric which has 6.06 ± 0.196 MPa and wool/wool woven fabric with 14.10 ± 1.369 MPa.

The extrusion process of silica rubber through a chemical reaction is unstable, and the flow mechanism in the extruder is still unclear. In this study, styrene-butadiene rubber (SBR) has been chosen as the matrix and the reinforcing effects of two different kinds of fillers, silica and titanium dioxide, have been investigated on SBR. Additionally, the effect of the properties of the SBR/filler composites on extrudate swelling has been examined. The reinforcing effect of the filler was confirmed by dynamic viscoelasticity, and the swell ratio was measured using a capillary rheometer. The results suggest that titanium dioxide has no reinforcing effect, as there is no interaction between titanium dioxide and the molecular structure of SBR. In contrast, there was a significant interaction between silica and SBR. It was found that the bound rubber, which is an SBR gel with restricted molecular chains, causes a reduction in the swell ratio, and this reduction effect is larger than that caused by filling the filler in the matrix. Furthermore, it was observed that this bound rubber deforms during flow and affects the extrudate swell phenomenon.