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Bending fretting fatigue behavior of 17CrNiMo6 alloy structural steel at room temperature was investigated under different bending and contact loads; and the $S$–$N$ curve also was built up. The results showed that the $S$–$N$ curve had a “C” shape. The bending fretting fatigue life was mainly dependent on the bending fatigue stress and fretting displacement. The limit of the specimens and the fretting fatigue life were dramatically decreased by fretting actions. The bending fretting fatigue damage changed under varied bending fatigue stress levels. When the wear first occurred, there is a lower bending fatigue stress; and with a higher bending fatigue load, microcracks were generated. However, some serious wear and surface delamination were observed under the highest fatigue load.

Coated hot forming steels have the advantages of oxidation protection during hot stamping and improving the working environment. However, the commercial available AlSi coating cannot provide cathodic corrosion protection to the stamped parts. The development of Zn based coating potentially provides both oxidation resistance during hot stamping and corrosion resistance during subsequent usage. However, Zn coated hot forming steels are subjected to the generation of microcracks during hot stamping, which can potentially affect the mechanical properties of the parts. This paper focused on the effect of hot stamping parameters, such as austenization conditions, stamping temperature and deformation strain etc, on the phase evolution of the coating, and on the formation of microcracks. The optimum hot stamping conditions have been proposed.

The morphology of a hot press forming steel galvannealed by HDPS (hot dipping process simulator) and hot stamped with different re-austenization temperatures in laboratory was studied in the paper. The results showed that, coating thickness may have a great effect on morphology transformation after hot stamping. Two typical thicknesses of 23 and 42 μm galvannealed samples were chosen, with coating morphology of delta phase and zeta phase (only thicker coating) transformed to Zn-rich gamma phase (Γ-Fe₄Zn₉) and Fe-rich alpha phase (α-Fe (Zn)) after hot stamping. The coating morphologies of three areas of the omega-shaped samples were analyzed, mainly composed of Γ-Fe₄Zn₉, α-Fe (Zn) and ZnO, with none of the microcracks penetrated to the matrix. The corrosion property can be guaranteed by Zn content in the two phases (Γ-Fe₄Zn₉ and α-Fe (Zn)) in which both were greater than 30%. The external oxides were also observed and the alloying element Si promoted Mn₂SiO₄ formation along grain boundaries.

The plane problem for the Haversian cortical bone with a radial microcrack in the interstitial bone under biaxial tension loading is considered. A two-dimensional coated fiber composite model of the Haversian cortical bone is developed correspondingly. By using the solution for the edge dislocation as Green’s functions, the problem of a radial microcrack located in the interstitial bone in the vicinity of the osteon is formulated into a system of singular integral equations with Cauchy kernels. And the interaction effect of various material and geometric parameters of the Haversian cortical bone upon the microcrack tip’s stress intensity factors is studied. The numerical analysis indicates that the stress intensity factor of the microcrack is dominated by the shear modulus ratio among the Haversian canal, the osteon and the interstitial bone, the distance of the left tip of the microcrack from cement line, the length of the microcrack. The numerical results suggest that when the osteon is softer than the interstitial bone the osteon prompts the microcrack propagation while the osteon is stiffer than the interstitial bone the osteon repels microcrack propagation. However, this interaction effect is limited near the osteon. Some of the numerical results are in accordance with the results obtained. And additional predicted numerical results are given, which need to be confirmed via experiment or computer simulation.