The shift fork shaft is a key component in transmissions, connecting the shift fork in order to adjust the gear engagement. This study investigates the effects of different welding sequences on deformation and residual stress during plasma welding of the shift fork shaft. A temperature-displacement coupled finite element method, using ABAQUS simulation software and a double ellipsoid heat source model, was employed for the numerical analysis. The simulation results show that welding in the same and opposite directions leads to opposite deformation directions but similar deformation magnitudes. However, opposite-direction welding generates more significant stress concentration. After determining an optimal welding process, experimental welding was conducted. Microstructural observations of the weld seam and critical areas, along with mechanical property tests, revealed that the welds were well formed with no surface defects. The heat-affected zone (HAZ) exhibited a mixture of martensitic and non-martensitic phases, while the fusion zone (FZ) underwent phase transformation and recrystallization, forming fine-grained ferrite with martensite. Microhardness (HRC) in the weld seam ranged from 35 to 50, with the FZ and HAZ hardness higher than that of the base material (BM). The second weld pass showed significantly higher hardness in the FZ than the first pass. The tensile strength of the weld joint reached 94% of the base material strength, though plasticity and toughness were reduced. Fracture surface analysis indicated a combination of brittle cleavage and localized plastic deformation.

In this paper, a sensitivity sensor of dual-core photonic crystal fiber (DC-PCF) filled with magnetic liquid is introduced and investigated by the finite element method (FEM). To regulate the energy coupling involving the two cores, the magnetic fluid is filled into the pore between the two cores. To adjust the coupling between the supermodes in the DC-PCF, the refractive index of the magnetic fluid-filled air hole may change due to the external magnetic field. This specifically created a magnetic fluid-filled DC-PCF, the magnetic fluid-filled hole is not used as the core for energy transmission, thus avoiding transmission loss. The dip wavelength and the magnetic field displayed an excellent linear connection between 80 and 260 Oe, depending on the numerical data. The detection sensitivity of the magnetic field reached 515.75 pm/Oe at a short fiber length of 482 m. The designed magnetic fluid-filled DC-PCF has high sensitivity and small volume and has great application prospects in medical and industrial field magnetic field detection.