DP780双相钢电阻点焊接头动态载荷下失效行为研究

Failure Behavior Analysis of Resistance Spot Welding Joints of DP780 Dual-phase Steel under Dynamic Load

采用DP780双相钢电阻点焊接头,针对不同拉伸速度下接头的失效行为进行了研究。利用数字图像相关(Digital image correlation,DIC)技术分析接头的全场应变,同时对不同失效模式下的接头微观断口形貌进行分析。结果表明,准静态与动态拉伸下接头的失效模式主要有界面断裂与熔核拔出两种。随着拉伸速度的增加,接头的失效位置由界面断裂向母材撕裂变化,同时接头失效的峰值载荷与吸能值逐渐增大。2 mm/min测试速度下的峰值载荷为21.08 kN,相比2 mm/min,2 m/s、6 m/s、10 m/s的峰值载荷分别提升了26.57%、46.92%、63.99%。四种测试速度下的失效吸能值分别为10.16 J、31.37 J、52.83 J和63.77J。由于拉伸时搭接接头焊点会发生偏转,造成了焊点上方拉伸作用为主,下方压缩作用为主。焊点不同程度的偏转,将使接头发生不同的失效模式。随着拉伸速度的提升,接头断口韧窝的摩擦分层越发剧烈。

The resistance spot welding joints of DP780 dual-phase steel are used to study the failure behavior under different tensile speeds. The digital image correlation(Digital image correlation, DIC) technique is used to analyze the full-field strain of the joints. At the same time, the micro fracture morphology of the joints under different failure modes is analyzed. Results show that the failure modes of the joints are interface fracture and nugget pull-out under quasi-static and dynamic stretching. With the increase of tensile speed, the failure position of the joints changes from interface fracture to base metal tear. The peak load and energy absorption values of joint failure increase gradually. The peak load of 2 mm/min is 21.08 kN. Compared with 2 mm/min, the peak load of 2 m/s, 6 m/s and 10 m/s is increased by 26.57%, 46.92% and 63.99%, respectively. The energy absorption values at these four test speeds are 10.16 J, 31.37 J, 52.83 J, and 63.77 J, respectively. Due to the nugget deflection of the lap joints during stretching, the tensile action above the solder joint is dominant and the compression action is dominant below. Different degrees of the nugget deflection will cause different failure modes of the joints. The friction stratification of the joint fracture dimples becomes more and more severe with the increase of tensile speed.