Key Engineering Materials Vol. 1039

Abstract: This work analyzes a shape memory alloy Stirling heat engine through an integrated thermal, mechanical, and materials approach. It builds on our previously published framework by generalizing behavior of shape memory alloys (SMA) beyond the nanoscale and extends it to elastocaloric applications, where mechanical work can be used to induce the stress-induced phase transformation. Parallels between stress-strain and enthalpy-temperature behavior underline this extension. Heat engine performance is evaluated in terms of torque and speed, and consideration is given to fatigue service life. Heat transfer and transformation energetics are examined with implications for heat engine performance. The resulting work supports shape memory alloy based heat engines and refrigerators for thermal management in space applications.

Abstract: A semiconductor based hydrogen sensor system was optimized by various modifications, which allow an improved detection of very low concentrations of hydrogen in air. The foundation for new investigations on the sensor structure are modifications of substrate and gate structures. Establishment of reference structures is a major aim. A possible drift compensation could be the use of aluminum or alloys for sensor system in order to stabilize signal in Metal Oxide Semiconductor (MOS) respectively Metal Electrolyte Insulator Semiconductor (MEIS) structures. Gold is more likely not capable to function for drift compensation as a pure metal. Nafion^TM treatment for cover up the palladium gate seems not to be suitable as a reference, besides could be an option to stabilize sensor signal responses and protect sensors from environmental influences.

Abstract: In this study, we explored the potential of a compact acoustic control system using giant magnetostrictive actuators (GMAs) for application in ultracompact electric vehicles (EVs), which face significant challenges in maintaining interior acoustic comfort due to their structural limitations. A fundamental investigation was conducted to clarify how differences in the internal structure of GMAs affect their vibration and acoustic output performances. Two GMA prototypes with different internal configurations (Model A, featuring two shorter rods and multiple permanent magnets, and Model B, featuring a single long rod) were evaluated through driving experiments. The acoustic signals were measured using a wall panel setup simulating in-cabin conditions. Both models exhibited an increase in sound pressure level with an increase in the applied voltage. However, the frequency response characteristics differed between the models. Model A performed better in the low-frequency range, whereas Model B maintained consistent performance across a broader frequency range. These findings provide essential insights into the design of space-saving and energy-efficient acoustic systems for next-generation mobility solutions.

Abstract: Conventionally, the sin²ψ method has been used as X-ray stress measurement. However, in recent years, the XRD² method and the cos α method have been put into practical use and spreading. In addition, the Fourier analysis method that shares the same measurement principle of the cos α method has been developed and is attracting attention. Therefore, in this paper, the Fourier analysis method is examined from the measurement theory and the measurement accuracy is investigated. It is reviewed that the basic equation is a finite Fourier series, and that stress can be determined from the Fourier coefficients by using coordinate transformations. Then, while comparing it with the multiple regression analysis, the accuracy of the Fourier analysis method is discussed by using numerical calculations.

Abstract: Novel injection moulding tools have been developed using metal additive manufacturing, particularly Selective Laser Melting (SLM). These technique enables the fabrication of new complex geometries, including the integration of lattice structures within components. These structures are renowned for their lightweight and high-strength characteristics. When designed with enhanced thermal properties, lattice structures have the potential to significantly improve the performance of injection moulding tools, where efficient thermal management is of importance. To realise these innovative thermal capabilities, a comprehensive investigation of the thermal behaviour and conductivity of the structures is essential. To this end, a cost-effective experimental setup has been designed and constructed. The system employs a comparative method, whereby heat flow through a 3D-printed sample is measured in series with a reference material. By analysing the temperature gradients across both bodies, the thermal conductivity of the printed structure can be accurately determined. BK7 glass is utilised as the reference material, due to its well-characterised and stable thermal conductivity. A key factor affecting measurement accuracy is interfacial thermal resistance, which arises at the contact interface between two materials and can hinder heat transfer. This resistance is influenced b the material properties, surface finish and contact pressure. To minimize the effect of interfacial resistance and ensure more reliable conductivity measurements, multiple tests are conducted on the same structure under varying temperature conditions. This approach facilitates the identification and compensation of thermal contact resistances.

Abstract: Batteries are an important part of our everyday lives. They are used in many areas of life, such as watches, flashlights, fire alarms and other appliances, but also in infrastructure for storing energy in households or for emergency power. Metal-air batteries could be used in many of these energy storage scenarios. Magnesium (Mg)-air batteries, in particular, are a promising technology due to the large Mg deposits in the earth's crust and the relatively low extraction costs make them interesting as an alternative for other primary batteries. A weak point of Mg-air batteries is parasitic corrosion, in which hydrogen is released and additionally forms a passivation layer of Mg hydroxide which reduces the active surface. The parasitic corrosion depends on the type and concentration of the electrolyte. When using sodium chloride (NaCl) as an electrolyte, the concentration is decisive for the performance of the battery. During operation of the battery, the electrolyte is saturated with Mg hydroxide due to the discharge process and parasitic corrosion. The magnesium hydroxide (Mg (OH)₂) precipitates together with the NaCl and thus changes the concentration of the electrolyte, which leads to an uneven conduction of the ions. Thus, a new way of influencing the stabilisation of the electrolyte for Mg-air batteries was tested. For this purpose, anodes consisting of NaCl particles and Mg powder were produced by indirect extrusion. In order to investigate the functionality and application possibilities of this technology, the anodes were tested for their microstructure and performance compared to pure Mg and the conductivity of the electrolyte during the discharge of the battery. The influence of the salt particle size and the salt particle content was also investigated using different anodes and different electrolytes.

Abstract: SPPSU(2S) and SPPSU(4S) ionomers with two and four sulfonic acid groups per PPSU unit were synthesized and characterized. SPPSU(2S) ionomers were synthesized and characterized by varying the acid type, sulfonation temperature, and time. Mild sulfuric acid was suitable for sulfonation of PPSU(2S). The IEC, molecular weight, and viscosity of SPPSU(2S) ionomers were 3.42–5.15 meq/g, 150,000–430,000, and 50–80 mPa·s, respectively, depending on the synthesis conditions. The tensile strength of SPPSU(2S) ionomer membranes was higher than that of Nafion membrane, the tensile elongation was lower than that of Nafion membrane, and the elastic modulus was higher than that of Nafion membrane. The conductivity of SPPSU(2S) ionomer membranes was similar to that of Nafion212 membrane. On the other hand, SPPSU(4S) ionomer was synthesized by monomers. The IEC and molecular weight of SPPSU(4S) ionomer were 5.6 meq/g and 303,203. The viscosity of SPPSU(4S) ionomer was higher than that of SPPSU(2S) ionomer. The stress-strain properties of SPPSU(4S) ionomer membrane showed a slightly higher elastic modulus than Nafion membrane, but the tensile strength and tensile elongation were similar to those of Nafion membrane. In addition, the conductivity of SPPSU(4S) ionomer membrane was higher than that of SPPSU(2S) and Nafion membranes. The above characteristics of SPPSU(2S) and SPPSU(4S) ionomer membranes are expected to be used as ionomer electrolytes for energy devices.

Abstract: This study investigates the degradation of adhesion between aluminum alloy and epoxy resin under high-temperature and high-humidity conditions. As next-generation power modules increasingly demand enhanced reliability, understanding the factors that affect metal/resin adhesion has become crucial. In this work, fourier transform infrared spectroscopy and adhesion strength testing were employed to evaluate the chemical and mechanical changes occurring at the interface during accelerated aging. FT-IR analysis revealed that the peak intensity of the carbonyl C=O peak in the epoxy resin decreased with aging time, while the aromatic C=C peak remained largely unchanged. The degree of moisture absorption, calculated from the ratio of these peak intensities, increased with the progress of aging. In addition, moisture uptake was found to weaken hydrogen bonding at the A1050/epoxy resin interface, and this effect was more pronounced in specimens with thinner resin layers. Adhesion strength tests showed a significant reduction in adhesive strength with prolonged exposure to high humidity and temperature. Fracture surface observations further indicated a shift in failure mode from cohesive to interfacial with aging. These results suggest that moisture-induced chemical changes at the interface contribute to the degradation of adhesion.

Abstract: To improve the reliability of solder joint, Ni–Cu alloy plating films with three-dimensional structures were fabricated on Cu substrates via electroplating. By varying the plating potential, the morphology of the Ni–Cu alloy plating films was controlled, and their effect on solder joint microstructure and mechanical properties was investigated. Sn–5Sb lead-free solder was used to join the plated Cu substrates, followed by aging at 200°C for up to 100 h. Surface observations revealed that more negative plating potentials promoted the formation of larger and more numerous three-dimensional structures. Cross-sectional analysis showed that Cu–Ni–Sn and Cu–Sn reaction layers formed at the solder interface and thickened with aging. Shear test showed that the joint strength decreased after 25 h of aging and remained nearly constant thereafter. In addition, joints with Ni–Cu alloy plating exhibited lower shear strength than those without plating. Fractographic analysis showed that fracture initially occurred within the solder and Cu–Ni–Sn reaction layers, whereas prolonged aging induced fracture propagation through the solder, Cu–Ni–Sn, and Cu–Sn reaction layers.