焊接对热轧H型钢高应变低周疲劳行为的影响

Effect of welding on high strain and low cycle fatigue behavior of hot-rolled H-beam

对热轧H型钢热轧和焊接后的高应变低周疲劳循环应力响应曲线、循环应力-应变关系和应变-寿命关系进行了分析,通过Coffin-Manson公式得到疲劳寿命计算公式,计算出Nf=100周时的循环韧度值σa.Δεt。结果表明,H型钢焊接试样的循环韧度比热轧试样的循环韧度降低38%。热轧试样表现出明显的循环稳定特性,焊接试样表现出循环软化-直接断裂的应力响应特征。焊接试样的断口扫描电镜观察发现,疲劳裂纹在焊接接头的粗晶区表面处萌生,断口瞬断区具有明显的韧窝特征,表明材料焊接后保持较高的韧性。

Low cycle fatigue（LCF）properties of H-beam as hot-rolled and welded are studied, and the cyclic stress-strain relationship and cyclic response characterization are determined. Based on the Coffin-Manson formula, the strain-fatigue life relationship is obtained. Finally, the cyclic toughness, which is the product of strain range at LCF life of 100 cycles and the stress amplitude, are calculated. The test results show that the cyclic toughness as welded H-beam is 62~//oo of that as hot-rolled. Hot-rolled materials exhibit cyclic stability, and welded materials show cyclic softening followed by fracture. The scanning electron microscope（SEM） micrograph of fracture surfaces reveals that the fatigue crack initiates from the coarse grain area of welding joint, and the fine dimple is observed in the fracture surface, which indicates the welding joint remains a good ductility.