Mechanical Properties of Resistance Spot Welded Components of High Strength Austenitic Stainless Steel

Tensile-shear fracture behaviour of resistance spot-welded hot stamping sheet steel with Al–Si coating

“…The fatigue fracture paths are illustrated by blue dashed lines, as shown in Figure 11(a and b). Similar failure modes have been reported by Wu et al in the DP780GI (UTS 780 MPa grade galvannealed dualphase steel) [18] and by Liu et al in the austenitic stainless steel (301L) [5] RSW joints. Generally, the fatigue cracks always initiated from the edge of nugget tongue and fractured along the soft BM/HAZ intercritical layers, which was different from the present work.…”

“…In the case of pull-out failure, the crack propagation within the nugget is largely restricted and ductile failure always happens through thickness necking, and high strength/toughness can be expected for the RSW joints. It is generally accepted that the static failure mode of RSW joints depends on the nugget diameter, and there exists a minimum threshold value for the occurrence of the pull-out failure, termed as ‘critical nugget diameter’ [5, 6]. Several empirical models for estimation of the critical nugget diameter ( D ), including SAE standards [7], Chao's model [8] and Zhao's model [9], have been proposed, where t is the thickness of the spot-welded sheets.…”

Overview of Fatigue Research of Spot Welded Joints

“…在断裂力学方面，TADA 等 [39] 提出了焊核边缘 母材区的应力强度因子公式。BROEK [40] 基于 TADA 公式推导出了一般载荷作用下的点焊接头的等效应 力强度因子。SWELLAM 等 [41][42] 引入经验几何修正 因子 G 对 BROEK 等效应力强度因子进行了修正。 后来，为了考虑载荷比的影响，SWELLAM 等 [43] 又通过引入平均应力修正因子，提出了一种混合型 应力强度因子 K i 。此外，SHEPPARD [31,44] 通过线 弹性断裂力学建立了点焊接头疲劳裂纹扩展模型。 RADAJ 等 [45][46][47] [54][55] 。 拉剪和剥离疲劳试验主要研究点焊接头的疲劳 极限、疲劳裂纹扩展和疲劳失效机理等。BARKEY 等 [56] 提出了一种在拉力和剪切力共同作用下开展 点焊强度和疲劳试验的夹具和方法。LONG 等 [57][58] 对图 5 所示的三种高强度钢点焊试件进行了拉剪和 剥离疲劳试验，发现在低幅值高循环载荷下，材料 的疲劳强度基本一致，但是拉剪载荷下不同材料的 点焊试件表现出不同的疲劳裂纹路径。WU 等 [11] 对 DP780GI 点焊接头进行拉剪和剥离试验之后发现 TS 接头有热影响区眉毛状裂纹失效和焊核拔出失 效两种失效模式，而 CP 接头仅存在界面破坏失效。 LIN 等 [59] 基于拉剪和剥离疲劳试验得到裂纹的局部 应力强度因子，建立了点焊疲劳裂纹扩展模型。 WANG 等 [60] 双焊点疲劳寿命的关联性，其中等效应力强度因子 关联单、双焊点疲劳寿命的性能最好。杨轶宁 [64] 对 ST12 和 BGXH50 两种低碳钢板的点焊拉剪试件进 行恒幅与两级加载试验，并通过 BP 神经网络法对 试件进行了疲劳寿命预测。LIU 等 [65] 通过对 301L 不锈钢多点焊试件开展疲劳试验得到多点焊的疲劳 极限随焊点数增加而非线性增加，焊点的布置方式 对多点焊的平均疲劳极限影响很大 [65][66] 。 此外， PAN 等 [67] 通过开展缺口试验研究了不同板 厚下点焊熔核缺口处的应力应变，发现最大循环主应 变出现在缺口根部，即使在小载荷下点焊接头也会发 生明显的屈服，并将最大主应变与疲劳寿命相关联提 出了一种基于应变的疲劳寿命预测方法。UWABA 等 [68] 通过对点焊缺口试件进行夏比冲击试验测量出 了点焊接头韧性至脆性的转变温度。韩长录 [ [76] 。起初，POLLARD 等 [77] 对点焊试件 开展了拉剪和横向拉伸疲劳试验，建立了疲劳寿命 N 与板厚、焊核直径、载荷幅 ΔF 和载荷比关系的 经验公式，且寿命预测结果与试验结果一致。LIN 等 [78] 通过试验得到了双相钢、低碳钢和高强度钢点 焊接头的 F-N 曲线，并验证了点焊疲劳裂纹扩展模 型。后来，王瑞杰等 [16] 通过对比几种不同的点焊疲 劳试验方法得出载荷-寿命法的估计公式必须基于 大量试验统计得出，不能将不同形状焊点的疲劳寿 命相联系，是一种粗略的估计方法。 目前，工程上多采用载荷-寿命(F-N)曲线来预 测点焊结构寿命 [9] 。作为基础性工作，针对点焊 接头疲劳强度的研究都是在疲劳试验的基础上进…”

Fatigue resistance and failure behavior of penetration and non-penetration laser welded lap joints

“…Cold rolled 301L plate is a metastable austenitic stainless steel containing less chromium and nickel and adding austenitizing element nitrogen, which is the main material used in the manufacture of railway light stainless steel passenger cars. Due to the different amount of strain-induced martensite transformed in the cold rolling process, the yield strength of cold-rolled plates ranges from 200 MPa to 700 MPa, which determines that the welding methods used in the vehicle manufacture are resistance spot welding and laser welding with concentrated heat input to reduce the deterioration of the mechanical properties of cold-rolled plates caused by welding heat [1][2][3][4]. The penetration and non-penetration laser welded lap joints are common joining method in rail passenger cars, and the non-penetration laser lap welding is an assembling method for side facade panels of passenger cars, which can not only improve corrosion resistances but also provide vehicle body with a weld-free appearance [5].…”