Lightweight design of leaf springs is a key approach to reducing the operating costs of commercial vehicles. In recent years, a variety of new materials and manufacturing processes have created opportunities for the performance improvement of traditional automotive leaf springs. Leaf springs have complex stress characteristics that involve typical mechanical behaviors, including nonlinearity, large deformation, and friction between spring leaves. In the design of leaf springs for light-duty vehicles, 50SiMnCr ultra-high-strength spring steel with a tensile strength over 2000 MPa was innovatively adopted, and response surface optimization was carried out. The thickness and width of the leaf springs were taken as design variables, while equivalent stress, deformation, and mass were set as optimization objectives and constraints. After optimization, the maximum equivalent stress of the leaf springs was 1335.2 MPa. This value was lower than the yield strength of the material (1855 MPa), yielding a safety factor of 1.39 that satisfied the design specifications for automotive leaf springs. The maximum deformation reached 42.462 mm, which was within the allowable full-load deflection range of the suspension system. A weight reduction of 14% was achieved. The optimized leaf springs exhibited excellent fatigue life and overall reliability, meeting the design requirements for high-cycle fatigue performance. This study proposes a new method for the lightweight design of automotive leaf springs.

Common distresses in bridge expansion joints, such as rutting and interface debonding, often result in premature failure and frequent replacement. To address these issues, this study evaluates a custom-synthesized polyurethane (PU) modified bitumen for use in asphalt plug joints (APJ) against a commercial high-viscosity elastic (HVE) modified bitumen. The rheological properties of the binders were characterized using temperature sweep, frequency sweep, and stress relaxation tests. To optimize the APJ mixtures, four joint mixtures (P-Ⅰ, P-Ⅱ, H-Ⅰ, and H-Ⅲ) were prepared using two binder types (PU and HVE), three combined gradations (Ⅰ, Ⅱ, and Ⅲ), and varying binder-to-aggregate ratios (1:6, 1:7, and 1:8). Their mechanical performance was investigated through rutting, low-temperature bending, freeze–thaw splitting, and fatigue tests. Experimental results indicated that the PU modified bitumen exhibited high-temperature mixture performance comparable to that of the HVE bitumen, while maintaining similar low-temperature properties. Furthermore, PU-based mixtures exhibited higher flexural strength and elastic modulus, along with superior water stability and fatigue resistance. This study provides a reference for developing durable bridge joints that extend service life, thereby contributing to reduced maintenance needs and resource consumption.

A six-band polarization-insensitive terahertz metamaterial absorber based on a hybrid square-ring and circular-ring resonator is proposed for refractive-index sensing applications. Numerical simulations were carried out using the finite-difference time-domain method. The absorber consists of a patterned metallic resonator, a dielectric spacer, and a metallic ground plane. The results demonstrate six distinct absorption peaks within 0.4–4.5 THz, five of which exhibit absorption above 95%, while the sixth peak reaches 64.8%. The resonant frequencies can be effectively tuned by varying the structural parameters. Electric- and magnetic-field analyses indicate that the six absorption peaks arise from square-ring-dominated, circular-ring-dominated, and hybrid resonances with distinct field-localization characteristics. Refractive-index sensing analysis shows that the proposed absorber exhibits favorable sensing performance, with a maximum figure of merit of 5.71 at the f4 resonance peak. In addition, stable polarization-insensitive absorption behavior is achieved owing to the symmetric resonator geometry. Benefiting from its simple structure, stable polarization response under normal incidence, and favorable refractive-index sensing performance, the proposed absorber shows potential for terahertz refractive-index sensing and related integrated terahertz sensing devices.

The phase transformation behaviors of a Ni–Cr–Mn–Mo gear steel were systematically investigated by dilatometric analysis. Continuous-cooling-transformation and time-temperature-transformation diagrams were constructed. The results indicated that the austenite start temperature (Ac1) and finish temperature (Ac3) were 680 °C and 770 °C, respectively. Continuous cooling experiments confirmed that the studied gear steel exhibited excellent bainitic/martensitic hardenability. Bainite formed over the cooling rate range of 0.1–15 °C s−1, while the fully martensitic microstructure formed with a critical cooling rate of 8–15 °C s−1. Isothermal transformation experiments revealed that no phase transformation occurs after 2 h holding at 580 °C–620 °C, indicating a prolonged incubation period for ferrite. Within the temperature range of 320 °C–400 °C, the bainite fraction decreased with increasing temperature. When isothermally held above 360 °C and subsequently cooled to ambient temperature, martensite-austenite (M/A) islands formed. The volume fraction and size of M/A islands are proportional to the isothermal temperature. Kinetic equations for continuous cooling and isothermal transformations were established based on the Koistinen–Marburger (K–M) and Johnson–Mehl–Avrami–Kolmogorov models, respectively, with good agreement between calculated and experimental values. This study provided a theoretical basis for optimizing the heat treatment process of the studied gear steel, particularly for selecting critical process parameters including austenitizing temperature, quenching cooling rate, and austempering temperature, and so on.

High-performance transmission components such as shafts and axles are frequently subjected to cyclic torsional loading, where fatigue resistance is critical for service reliability. In this study, a modified austempering process was developed to produce a bainite-martensite mixed microstructure in SAE 8660 steel for enhancing torsional fatigue performance. Microstructural characteristics were systematically examined using optical microscopy, scanning electron microscopy, and quantitative electron backscatter diffraction analysis. Mechanical properties were evaluated through hardness, tensile strength, torsional strength, and torsional fatigue tests. In addition, finite element analysis (FEA) was employed to compare the macroscopic deformation responses of the different heat-treatment conditions using experimentally measured constitutive data. Compared with the conventional quenching and tempering condition, the modified microstructure exhibited improved torsional fatigue resistance while retaining a relatively high torsional strength, demonstrating an effective balance between strength and deformation capability. Microstructural characterization and fractographic observations were consistent with improved strain accommodation and more tortuous crack propagation in the bainite-martensite mixed microstructure. The FEA predictions reproduced the experimentally measured maximum shear stresses with deviations below 3.3%, while the calculated damage was primarily localized within the central gauge section. These results indicate that controlled bainite-martensite microstructure design via modified austempering represents a promising approach for improving torsional fatigue performance in high-strength steels used in torque-transmission components.

In this study, the mechanical and electrical properties of as-cast and thermomechanically treated Al–xCu–0.25Mg alloys (x = 0–1.25 wt%) were systematically investigated, with the Mg content fixed at 0.25 wt% to isolate the effect of Cu addition. In the as-cast state, increasing the Cu content from 0 to 1.25 wt% continuously increased the tensile strength from 69 MPa to 141 MPa and the hardness from 27 HV to 59 HV, while the electrical conductivity decreased from 60.0%IACS–53.5%IACS. Among the investigated compositions, the as-cast Al–0.75Cu–0.25Mg alloy exhibited the best overall balance of strength, conductivity, and ductility, with a tensile strength of 110 MPa, an electrical conductivity of 56.3%IACS, and an elongation of 29.2%. This alloy was therefore selected for further thermomechanical treatment involving solution treatment (515 °C/90 min), cold drawing, and subsequent aging at 260 °–340 °C. After aging at 260 °C for 12 h, the alloy achieved an improved combination of properties, with the electrical conductivity increasing to 60.2%IACS while retaining a tensile strength of 143 MPa. Microstructural characterization by x-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy, and electron backscatter diffraction indicates that the strengthening behavior is associated with solid-solution strengthening and the precipitation of θ-Al2Cu phases, whereas the conductivity evolution is closely related to the precipitation of Cu from the matrix, the resulting reduction in lattice distortion, and changes in precipitate morphology during aging. These results provide useful guidance for optimizing the strength-conductivity balance of Al–Cu–Mg alloys through compositional design and thermomechanical treatment.

Hyperspectral technology can readily identify targets in vegetated environments by exploiting subtle spectral differences, imposing stringent requirements on camouflage materials. To mimic vegetation spectra with particle-embedded films, the optical properties of the embedded particles must first be determined, yet these properties are frequently unavailable and cannot be measured directly. In this study, an improved Kubelka–Munk (K–M) model that accounts for asymmetric forward and backward scattering is adopted as the forward solver, and its predictive accuracy is verified against physical samples. On this basis, two inversion methods are established to retrieve particle optical properties from measured reflectance and transmittance spectra. The first retrieves the optical constants of homogeneous particles, whereas the second characterizes inhomogeneous particles as a whole at unit volume fraction. Both methods are validated using representative titanium chromium yellow and microcapsule pigment particles. Furthermore, using the retrieved optical properties as design inputs, a yellow camouflage material closely mimicking the solar spectrum of natural yellow foliage is designed and fabricated. These methods can be applied not only in hyperspectral camouflage but also in areas such as radiative cooling.

This paper presents a case study of immersion ultrasonic C-scan inspection of a single fatigue-cracked laser powder bed fusion 316 L stainless steel double-hourglass specimen, relevant to the qualification of additively manufactured components for nuclear power plant applications. Ultrasonic testing of complex-shaped additively manufactured 316 L components presents particular challenges, especially for contact testing methods. Scans were performed from four lateral faces (0°, 90°, 180°, and 270°). The results show that the crack is successfully detected from the two flat-face views (0° and 180°), whereas the echo signals from the two curved-face views (90° and 270°) are dominated by geometric beam deflection, mode conversion, and amplitude loss, producing unreliable ultrasonic images. The crack detection is confirmed by Penetrant Testing.

To improve the service stability of carbon fiber reinforced SiBCN matrix composites (C/SiBCN) in high-temperature and oxidative environments, BN interphases with different thicknesses were fabricated on carbon fiber surfaces by chemical vapor deposition process. The effects of the BN interphase on the microstructure, mechanical properties, thermal stability, and oxidation resistance of the composites were systematically investigated. The results show that the BN interphase effectively prevented direct contact between the carbon fibers and the SiBCN matrix, thereby suppressing interfacial reactions and carbon fiber degradation at elevated temperatures and reducing thermal damage in the composites. With increasing BN coating thickness, the mass loss of the composites after heat treatment at 1500 °C–1900 °C generally decreased. However, an excessively thick BN coating hindered precursor infiltration and introduced additional porosity, resulting in degraded mechanical properties. After heat treatment at 1700 °C, the BN0.2 sample retained a flexural strength of 82.9 MPa, compared with 51.1 MPa for the sample without a BN interphase, indicating superior retention of high-temperature mechanical performance. In oxidative environments, the BN interphase also slowed oxygen diffusion toward the fibers and interfaces, reduced oxidative damage to the carbon fibers, and maintained the structural integrity of the composites. In particular, the BN0.2 sample retained a flexural strength of 114 MPa after static oxidation at 1400 °C for 30 min, with a strength retention rate markedly higher than that of the composite without a BN interphase. This study demonstrates that rational control of the BN interphase thickness is an effective strategy for enhancing the high-temperature thermal stability and oxidation resistance of C/SiBCN composites, providing guidance for the design of high-temperature thermal protection structural materials for aerospace applications.

The objective of this work is to investigate the effect of aqua-alcoholic solvents on the physical properties of zinc oxide (ZnO) thin films prepared using a simple and cost-effective atomization technique. X-ray diffraction analysis revealed that, regardless of the solvent type, the thin films are polycrystalline and crystallize in the hexagonal wurtzite structure. Fourier transform infrared analysis confirmed the presence of functional groups. Scanning electron microscopy observations showed that the film morphology is strongly influenced by the nature and proportion of the solvents, with the distilled water/ethanol (25/75) mixture promoting Volmer–Weber growth, characterized by fine, compact, and uniformly distributed grains. UV–visible measurements indicated that the variation of the distilled water/alcohol ratio significantly affects the optical properties: the maximum transmittance reaches 82% for distilled water/ethanol (25/75) and 80% for distilled water/methanol (25/75) in the visible range. The optical bandgap shows only slight variation (3.27–3.30 eV), indicating that the solvent mainly affects microstructure and defect distribution rather than the intrinsic electronic structure of ZnO. Based on the structural, morphological, and optical analyses, the distilled water/ethanol (25/75) composition provides the optimal balance between crystallinity and optical transparency in ZnO thin films, suggesting its potential suitability for optoelectronic applications.