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Abstract The stress field around the notch tip of a mode Ⅱ notched specimen was analyzed by means of finite element method and the stress intensity factor K_(?)was calculated by J-integral. The results indicate that the maximum shear stress is located at 0=80°and its direction is α=5°, the maximum principal stress σ_1 and the maximum hydrostatic stress are both atθ=-110° and the direction of σ_1 is α=10°. Hydrogen induced cracking (HIC)and stress corrosion cracking (SCC) of a high-strength steel 34CrNi3MoA(T. S=1500MPa)under Mode Ⅱ loading were investigated using notched specimens. The results show HIC and SCC under Mode Ⅱ loading initiated at the maximum hydrostatic stress site. However, cracking is oriented along the shear stress direction at the site, not normal to the direction of maximum principal stress component. On the contrary if the specimens are loaded to fracture in air under Mode Ⅱ loading, cracking oringinates at the maximum principal stress site around the notch tip and the cracking direction coincides with the direction of the maximum shear stress. The above mentioned facts indicate that hydrogen induced delayed plastic deformation is a necessary condition for HIC; and the nature of SCC for high-strength steel in 3.5% NaCl solution is HIC. The results show that HIC and SCC under Mode Ⅱ loading can occur during dynamic charging with hydrogen and in 3.5%NaCl solution respectively. The normalized threshold stress intensity factors under Mode Ⅱ loading during dynamic charging in 1N H_2SO:+0.25g As_2O_3/l solution and in 3.5% NaCl solution are K F/K_(?) X=0.1 and K_Ⅱ SCC/K_(?) X=0.45, respectively. The corresponding values under Mode Ⅰ loading are K_Ⅰ H/K_Ⅰ X=0.02 and K_(Ⅰ)SCC/K_(Ⅸ)=0.37, where K_(ⅡⅩ)and K_(Ⅸ)are critical values loaded to failure in air under Mode Ⅱ and Mode Ⅰ loading respectively. Thus, (K_Ⅱ H/K_(ⅡⅩ))/(K_(Ⅰ) B-/K_(Ⅸ))=5 and (K_Ⅱ SCC/K_(Ⅸ))/(K_Ⅰ SCC/K_(;Ⅸ))=1.2 A typical intergranular fracture was observed during HIC and SCC under Mode Ⅱ and Ⅰ loading. But the fracture surfaces of specimens failed in air are composed of dimples for both kinds of loading.
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Received: 25 April 1987
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[14] 白清溪,氢在铁中的应变场,北京钢铁学院金属物理专业硕士论文,(1986) |
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