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本文基于超声疲劳振动技术,设计了三种焊接接头试样(圆形对接焊接试样及其喷丸处理试样和板状十字焊接试样),并利用超声疲劳试验系统测定了其超高周疲劳性能,实验应力比为-1,频率20kHz,实验在室温条件下进行。实验结果表明,圆形对接焊接接头的疲劳性能高于板状十字焊接接头,喷丸处理能提高焊接接头的疲劳强度。将焊接接头的疲劳性能与对应形状的母材进行对比分析,发现焊接接头的疲劳性能远低于母材。在相同疲劳寿命的条件下,圆形焊接接头试件的疲劳强度仅为母材的45%,十字焊接接头试件仅为母材的29%;圆形对接接头在5×106周次以后,试件仍然发生疲劳断裂,而板状十字焊接接头在超高周区域(107～109周次)存在疲劳极限。超声疲劳断口的扫描电子显微镜分析结果显示,圆形焊接接头试件断口位置主要位于熔合区的焊趾处或焊接接头表面几何非连续处,十字接头试件断口位于焊趾处;焊接接头试件裂纹萌生于焊接缺陷、试样表面夹杂或熔合区的不连续处;喷丸处理对焊接接头的裂纹萌生机制没有显著影响。
In this paper, based on the ultrasonic fatigue vibration technology, three kinds of welded joint samples (circular butt welded specimens and shot peening specimens and plate cross welded specimens) were designed and their ultrahigh-frequency Fatigue performance, experimental stress ratio of -1, frequency of 20kHz, experiments were conducted at room temperature. The experimental results show that the fatigue performance of circular butt welded joints is higher than that of flat cross welded joints, and the shot peening can improve the fatigue strength of welded joints. The fatigue performance of welded joints and the corresponding shape of the parent material for comparative analysis and found that the fatigue performance of welded joints is much lower than the base metal. Under the same fatigue life, the fatigue strength of the circular welded joint specimen is only 45% of that of the base metal, and the cross welded joint specimen is only 29% of the base metal. After the circular butt joint is 5 × 106 cycles, The fatigue fracture of the specimen still occurs, while the flat cross-welded joints in the ultra-high frequency region (107-109 weeks) fatigue limit. Scanning electron microscopic analysis of the ultrasonic fatigue fracture shows that the fracture location of the round welded joint specimen is mainly located at the welding toe of the welding zone or the geometric discontinuity of the welding joint surface, and the fracture of the cross joint specimen is located at the welding toe. The crack initiation was caused by the welding defects, the discontinuities at the surface of the sample inclusions or the fusion zone. The shot peening had no significant effect on the crack initiation mechanism of the welded joints.