An experimental and numerical study on mechanical properties and damage behavior of 3D multi-layer wrapping braided composite under axial tensile load is presented. The braiding process of this material is introduced and its tensile properties are obtained in tensile tests. Numerical simulations employ periodical boundary conditions, with interface elements between yarns and matrix added to improve the accuracy of prediction. 3D Hashin-type criteria and Von-Mises stress criterion are employed as damage initiation criteria for yarns and matrix, respectively. The obtained numerical results show a good agreement with the experimental data. The load-bearing capacity and failure mechanisms of 3D multi-layer wrapping braided composites under axial tensile loading are also discussed. A stress distribution shows that the axial yarns are the main load-bearing component of the composite. The main failure mode of the yarns is the yarn-matrix tensile cracking in the width direction, followed by the yarn-matrix tensile cracking in the thickness direction and fibre tensile failure. When the fibres in axial yarns begin to break, the material loses its load-bearing capacity.

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The mechanical properties and corrosion resistance of the stainless steel (SS) corbel decline sharply after the welding process, which may cause serious accidents. Combining with microcharacteristics, mechanical properties, and corrosion properties, mathematic theories were used and an accurate prediction model of the corrosion fatigue life of SS butt joints produced by laser-metal active gas hybrid welding (LMHW) was established. The joints produced by LMHW have good mechanical properties, with the joint strength coefficient a remarkable 89%. In corrosion fatigue testing, corrosion pits will first appear in the weld seam as a result of the microstructural difference, then cracks initiate. Meanwhile, both the higher NaCl concentration and lower stress ratio will promote the anodic dissolution of metal, leading to the reduction and obscuring of fatigue striation features on the fracture surface. This high-accuracy mathematical modeling can help validate the advanced LMHW method and, in turn, facilitates the manufacture of stainless steel corbels in rail vehicles.

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