加工硬化对焊接接头缺陷裂纹力学性能的影响

Effect of work hardening on mechanical properties of welded joints with defective cracks

【目的】为了分析核电一水回路安全端焊接接头熔合线处加工硬化分布,并为其缺陷裂纹尖端力学性能的分布及裂纹扩展驱动力提供分析依据。【方法】通过试验获得不同加工硬化程度316L不锈钢的维氏硬度和屈服强度的关系,并通过焊接接头不均匀硬化规律获得焊接接头熔合线附近材料的屈服强度。在此基础上,采用有限元模拟的方法获得熔合线处缺陷裂纹尖端力学性能的分布规律。【结果】结果表明,焊接接头熔合线两侧维氏硬度不同,材料出现了不同程度的加工硬化,沿着熔合线两侧维氏硬度逐渐减小。焊接接头不均匀的加工硬化规律会影响裂尖的Mises应力、裂纹的张开应力、裂尖的等效塑性应变和张开应变,加工硬化会增大裂尖Mises应力和张开应力,使Mises应力和张开应力偏向加工硬化程度较高的金属;加工硬化会抑制等效塑性应变和裂纹的张开应变,等效塑性应变和张开应变偏向硬化程度较低的金属。加工硬化也会影响裂尖应力三轴度,增大裂尖应变率和裂纹扩展速率。【结论】焊接接头熔合线附近材料的加工硬化会增大裂纹扩展驱动力,增加缺陷裂纹的扩展速率,加剧焊接接头失效。

[Objective]The purpose was to analyze distribution of work hardening at fusion line of welded joints at safe end of nuclear power one-water circuit,and to provide an analytical basis for distribution of mechanical properties of crack tip and driving force of crack extension.[Methods]Relationship between Vickers hardness and yield strength of 316L stainless steel under different work hardening degrees was obtained by experiments.The yield strength of fusion line attachment material of welded joints was obtained by non-uniform hardening law of welded joints.On this basis,the distribution of mechanical properties at crack tip on the fusion line were obtained by finite element simulation.[Results]The results showed that Vickers hardness was different on both sides of fusion line of welded joints,and material showed different degrees of work hardening,the Vickers hardness gradually decreases along both sides of the fusion line.Uneven work hardening law of welded joints could affect Mises stress,opening stress,equivalent plastic strain and opening strain of crack tip.Work hardening could increase the Mises stress and opening stress at the crack tip,and make the Mises stress and opening stress incline to the metal with higher work hardening degree.However,work hardening could inhibit the equivalent plastic strain and crack opening strain,the equivalent plastic strain and opening strain were biased towards the metal with lower degree of work hardening.Work hardening also affected stress triaxiality of crack tip,and increased crack tip strain rate and crack growth rate.[Conclusion]The work hardening of materials near fusion line of welded joints increased driving force of crack growth,accelerated the crack growth rate of defective cracks,and exacerbated failure of welded joints.