飞机起落架用钢贝氏体组织的屈强比问题

本文根据强度设计规范要求和试验结果,指出飞机起落架用钢在满足屈强比σ_(0.2)/0_h>0.67的条件下,以适当降低该值更为行利。对40CrMnSiMoVA钢的研究证实,σ_(0.2)和σ_(0.2)/σ_h值在循环载荷作用下并非恒值。贝氏体组织较低的σ_(0.2)/σ_h值使其发生循环硬化,从而减轻钢的缺口敏感性并延长其疲劳裂纹形成寿命,同时具有更为明显的超载延寿效果。

ON YIELD TO ULTIMATE TENSILE STRENGTH RATIO OF BAINITIC MICROSTRUCTURE IN A STEEL FOR AIRCRAFT LANDING GEAR

According to the demand of strength design standard and experimental results, the present paper indicates that it is more favourable to properly reduce yield to ultimate tensile strength ratio σ0.2 / σh of ultra-high strength steel for aircraft landing gear under the conditions of σ0.2/σb >0.67. The study on 40CrMnSiMoVA steel verifies that σ0.2value and σ0.2/σb ratio of bainitic microstructure are lower than those of martensitic microstructure in monotonic tensile test. While after a small number of pre-cyclic loads, the σ0.2 and σ0.2 / σb the former become higher than those of the latter. That is , σ0.2 value and σ0.2/σb ratio determined by monotonic tensile test are unconstant, but ultimate tensile strength σb, fracture strength Sk, elongation percentage δ and reduction of cross-sectional area ψ are constant. The lower original σ0.2 / σb ratio of bainitic microstructure causes it cyclic hardening,which could homogenizemicro-deformation and lighten notch sensitivity. As a result, strain-controlled and impact fatigue crack initiation of the steel with bainitic microstructure is delayed in longer life range. Meanwhile, because of the lower σ0.2 / σb ratio, overload effect of the bainitic microstructure is more distinct to prolong fatigue life. So, the lower σ0.2 / σ0.2 ratio characteristic of bainitic microstructure in ultra-high strength steel is an advantage among mechanical properties.