Laser beam oscillation has been recognized as an effective means to modify temperature gradients and relieve stress concentration in welded joints, yet its role in dissimilar titanium alloy bottom-locking configurations—where asymmetric thermo-mechanical responses arise from both material mismatch and structural constraints—remains unclear. This study investigates the influence of circular oscillation amplitude (0, 0.5, 1.0, and 1.5 mm) on residual stress distribution in laser-welded TC4/TA18 bottom-locking tube joints at a constant power of 1000 W. Unlike the monotonic effect of laser power, oscillation amplitude redistributes the heat source spatially. A three-dimensional thermo-elastic–plastic finite element model incorporating a moving oscillating Gaussian conical heat source was developed in ABAQUS and validated against weld macrographs, thermal cycles, and blind-hole residual stress measurements. The results reveal a non-monotonic dependence of residual stress on oscillation amplitude: as amplitude increases from 0 to 0.5 mm, the peak hoop residual stress rises, but further increasing amplitude to 1.5 mm substantially reduces both hoop and axial residual stresses while promoting a more uniform stress field. At 1.5 mm, the molten pool covers the entire bottom-locking step geometry, the region of high hoop tensile stress (>700 MPa) is minimized, and the peak axial tensile stress at the bottom-locking gap end (BLG End) is reduced by 41% (from 415 MPa to 243 MPa) compared with non-oscillation welding. An amplitude of 1.5 mm is therefore recommended as the optimal parameter for residual stress control of these joints at 1000 W within the investigated parameter range. This finding provides a practical guideline for mitigating residual stress-induced failure risks in aerospace hydraulic and fuel delivery systems.

Conventional fabrication processes for fiber-reinforced composites are complex and stepwise, limiting their application in blast protection engineering. In this study, KH550 surface-modified glass fiber powder (1.5 wt%) was incorporated into a polyurea matrix, and a homogeneous glass fiber-reinforced polyurea (GFRPU) composite was successfully synthesized via an optimized one-step spray process. The strain-rate-dependent mechanical behavior (0.01–100 s⁻¹), fracture mechanisms, molecular structure, and blast mitigation performance of GFRPU were systematically investigated through mechanical testing, SEM, FTIR, 75 g TNT contact explosion tests, and calibrated and partially verified finite element simulations. Results show that the surface-modified fibers form chemical crosslinks with the matrix, shortening the N–H hydrogen bond length from 3.023 Å to 2.983 Å and increasing the hydrogen bonding degree of the urea carbonyl region from 80.0% to 84.1%, thereby enhancing structural ordering and strength. At a strain rate of 100 s⁻¹, the tensile strength of GFRPU reaches 50.27 MPa, 26% higher than that of the polyurea matrix. Under contact explosion, a 4 mm back-face GFRPU coating reduced the center-point deflection of the steel plate by 31.6% and suppressed brittle cracking, with interfacial debonding and coating tensile failure as the dominant failure modes. Considering protective efficiency and structural safety, 4 mm is recommended as the optimal coating thickness.

In response to the challenge of achieving highly reliable interface fabrication in the fields of microelectronics and micro-electromechanical system (MEMS) packaging, this study harnesses the superior characteristics of solid-state bonding inherent in explosive welding (EXW) technology. This study investigates the precise EXW of milligram-scale metallic foils by employing focused laser energy to control the explosion behavior of liquid energetic materials, thereby generating shockwaves that induce high-velocity oblique collisions between metallic foils and base plates. Laser-focused energy was utilized to regulate energetic materials for conducting precision EXW experiments on Al/Cu couples. The technical feasibility and interfacial quality of this method for fabricating Al/Cu bonding interfaces were systematically evaluated through in situ observation of the dynamic welding process, comprehensive analysis of interfacial microstructures, and numerical simulations. The results reveal distinct Al/Cu elemental diffusion at the bonding interface, confirming the technical viability of the approach. However, an unloading rebound phenomenon is observed at the interface, which is inherently associated with the dynamic impact process, indicating the need for further optimization in the precise control of impact loading.