PLA-based blends were prepared with different ratios of PBS, PBAT and TPS additives to adjust their mechanical and processing properties in various temperatures ( − 20 °C, 0 °C, 20 °C, 40 °C). Biodegradable polymeric specimens were obtained by preliminary extrusion and subsequent injection molding. Tensile properties, e.g., tensile strength, elongation at break, Young’s modulus and yield strength were evaluated. Next, melt flow and melt volume ratios were established. Softening, glass transition, cold crystallization and crystallization temperatures were determined with the use of the DSC method. Heat Deflection Temperatures for 1.8 MPa (HDT A) and 8 MPa (HDT C), as well as Vicat Softening Temperatures at 10 N (VST A) and 50 N (VST B), were examined. The manufacturing method was intentionally simplified to eliminate the need for additional mixture’s modification with compatibilizers. Each of the ductile compounds enhanced the deformability of PLA—most significantly in the case of PBAT and TPS, while at the same time reducing its tensile strength. The effect of the test conditions (strain rate and temperature) on the specimens was evaluated in order to determine the stability of the manufactured blends in dependence on these parameters.
In the present paper, the finite element method is used to perform an exhaustive analysis of the thermal behavior of encapsulated phase change materials (EPCMs), which includes an assessment of several materials in order to identify the best combination of PCM and shell material in terms of thermal energy storage, heat transfer rate, cost of materials, limit of pressure that they can support and other criteria. It is possible to enhance the heat transfer rate without a considerable decrease of the thermal energy storage density, by increasing the thickness of the shell. In the first examination of thermomechanical coupling effects, the technical feasibility can be determined if the EPCM dimensions are designed considering the thermal expansion and the tensile strength limit of the materials. Moreover, when a proper EPCM shell material and PCM composition is used, and compared with the current storage methods of concentrated solar power (CSP) plants, the use of EPCM allows one to enhance significantly the thermal storage, reaching more than 1.25 GJ/m3 of energy density.
Phase change materials (PCMs) are applied in heat storage units, as they are able to accumulate the energy in the form of the latent heat of fusion. Thus, they can be used in recovering the excess of heat from various industrial processes. Their main weakness is their low thermal conductivity coefficient, which strongly limits their usage. In this paper, the benefits of the application of metallic inserts in heat storage PCM-based units were elaborated. Two kinds of Al–Si spatial elements (foams and honeycomb structures) were produced with the use of means of the investment casting method. Key factors influencing the technological process were established. The surface’s roughness was measured in order to compare the obtained structures with their patterns in terms of the casting’s accuracy. The compressive strength of the samples was tested, and their fatigue resistance was considered. The thermal performance of manufactured inserts in the PCM (paraffin)-based accumulator, supported by the calculation of heat fluxes, was analyzed and adjusted. Finally, further optimization was conducted in terms of the volume ratio of the metal insert to the PCM. Metallic inserts were found to significantly affect the performance of the entire energy storage system, as their use results in reduced charging time, a longer heat release time, increased maximum temperature, and a significant reduction in the temperature gradient in the heat storage unit.
In recent years, hybrid composite materials are of increasing interest during the search for new materials to be used as ballistic barriers (shields) and kinetic energy absorbers. The main objective of this study is to test the energy absorption capacity of Zn-Al alloys filled with various polymer materials (epoxy resin, polyurethane resin and silicone). The ballistic resistance of modern hybrid materials to direct firing of a 5.56 × 45 mm SS109 projectile and during quasi-static piercing test is examined. Next, a numerical simulation in the ABAQUS environment is performed. In order to accurately reproduce the foam structure, a computed microtomography (CT) system is used. In the simulation of deformations of viscoplastic bodies, the Lagrange and Smoothed Particle Hydrodynamic (SPH) methods are applied. The obtained results from numerical analyses are verified with experimental results. Metallic foams are proven to have only a remote influence on the impact load, while, when filled with polyurethane resin, they show resistance to the overshoot. Performed simulation supports the detailed analysis of the impact energy dissipation for each of the samples.
11 January 2023 in International Communications in Heat and Mass Transfer
Open-porous MAX phase skeletons from Ti3SiC2 were manufactured by Microwave-Assisted Self-propagating High-temperature Synthesis (MASHS) and subsequently subjected to squeeze casting infiltration with an Al-Si lightweight casting alloy (EN AC-44200). This alloy was chosen due to its high flowability, corrosion resistance and good machinability. The manufactured composites, together with a reference sample of the original alloy, underwent testing of thermal properties, including thermal conductivity and diffusivity, specific heat and thermal expansion in the temperature range 50-500 °C, which corresponds to the expected working temperatures of the material. The fabricated AlSi/Ti3SiC2 composites have significantly increased thermal stability, with coefficients of thermal expansion (approximately 10-11 × 10−6 °C−1) half that of the original alloy. As regards mechanical properties, the instrumental Young’s modulus and Vickers hardness of the composite materials are 170.8 and 8.5 GPa, respectively. Moreover, the microstructure and phase composition, structural defects and potential impacts between constituents of the manufactured composites were characterized using SEM, TEM and STEM microscopy and EDS and XRD analysis.