Welded joint is a mechanical heterogeneous body, and mechanical heterogeneity has great effect on dynamic fracture behaviour of welded joints. In the present investigation, dynamic response curve and dynamic J-integra...Welded joint is a mechanical heterogeneous body, and mechanical heterogeneity has great effect on dynamic fracture behaviour of welded joints. In the present investigation, dynamic response curve and dynamic J-integral of practical undermatched welded joint and whole base and whole weld three-point-bend (TPB) models containing longitudinal crack are com- puted. Dynamic J-integral is evaluated using virtual crack extension (VCE) method and the computation is performed using MARC finite element code. Because of the effect of inertia, dynamic load response curve of computed model waves periodically. Dynamic J-integral evaluated by VCE method is path independent. The effect of inertia has little influence on dynamic J-integral curve. The value of dynamic J-integral of undermatched welded joint is lower than that of whole base metal and higher than that of whole weld metal. The results establish the foundation of safety evaluation for dynamic loaded welded structures.展开更多
Due to poor metallurgical weldability of magnesium alloy,laser welding crack is still one of the main defects.The generations of welding crack seriously affected the weld quality and reduce the mechanical properties o...Due to poor metallurgical weldability of magnesium alloy,laser welding crack is still one of the main defects.The generations of welding crack seriously affected the weld quality and reduce the mechanical properties of welded joints which have become a bottleneck of the magnesium alloy products widely used in the structure materials.In this paper,AZ31B magnesium alloy sheet with 2mm thickness was used for this investigation.The forming reason and extending characteristics of the welding cracks were investigated during the Nd:YAG pulsed laser welding.The results show that welding cracks are mainly solidification crack which were always present in the weld centers.Few welding hot cracks appear multiple furcation phenomenons,and main and branch cracks were intercrystalline crack.The partial branch crack was mixed intercrystalline and transgranular extension.In addition,few cracks in the weld were caused due to irregular shape porosity and inclusion.The delayed crack weren't observed in the weld after deposited 48 hours.In the pre-process on the basis,the characteristics and generation mechanism of YAG pulsed laser welding cracks of magnesium alloy were analyzed further.展开更多
The distribution law of the lateral residualstress at the welding seam is determinated by meansofcuttingthespecimen. Becausetocutthespecimencansimulateapproximatelytheex tension ofthe fatiguecrack,through measuring ...The distribution law of the lateral residualstress at the welding seam is determinated by meansofcuttingthespecimen. Becausetocutthespecimencansimulateapproximatelytheex tension ofthe fatiguecrack,through measuring thestressreleased and calculating the distri bution oftheresidualstressthelaw isfound thattherateofthefatiguecrackextensionisaf fected bytheresidualstress.展开更多
刀座焊接处是全断面岩石隧道掘进机(Full face rock tunnel boring machine,TBM)刀盘上最易发生疲劳破坏的部分。基于线弹性断裂力学,以裂纹疲劳寿命为基本变量,建立裂纹扩展可靠性模型,通过JC法计算刀座正面焊缝在不同滚刀实验载荷下...刀座焊接处是全断面岩石隧道掘进机(Full face rock tunnel boring machine,TBM)刀盘上最易发生疲劳破坏的部分。基于线弹性断裂力学,以裂纹疲劳寿命为基本变量,建立裂纹扩展可靠性模型,通过JC法计算刀座正面焊缝在不同滚刀实验载荷下的疲劳可靠性,并分析了不同因素对失效概率的影响。结果显示:中心滚刀刀座焊缝的失效概率比正滚刀小,正滚刀的失效概率随着安装半径的增大而减小;刀座焊缝失效概率随着初始裂纹深度的增大而显著增大,而临界裂纹深度的变化对失效概率的影响不大;裂纹形状比越大,刀座焊缝的失效概率越小。展开更多
基金National Natural Science Foundation of China(No.59501011)Science and Technology New Star Project of Beijing.
文摘Welded joint is a mechanical heterogeneous body, and mechanical heterogeneity has great effect on dynamic fracture behaviour of welded joints. In the present investigation, dynamic response curve and dynamic J-integral of practical undermatched welded joint and whole base and whole weld three-point-bend (TPB) models containing longitudinal crack are com- puted. Dynamic J-integral is evaluated using virtual crack extension (VCE) method and the computation is performed using MARC finite element code. Because of the effect of inertia, dynamic load response curve of computed model waves periodically. Dynamic J-integral evaluated by VCE method is path independent. The effect of inertia has little influence on dynamic J-integral curve. The value of dynamic J-integral of undermatched welded joint is lower than that of whole base metal and higher than that of whole weld metal. The results establish the foundation of safety evaluation for dynamic loaded welded structures.
文摘Due to poor metallurgical weldability of magnesium alloy,laser welding crack is still one of the main defects.The generations of welding crack seriously affected the weld quality and reduce the mechanical properties of welded joints which have become a bottleneck of the magnesium alloy products widely used in the structure materials.In this paper,AZ31B magnesium alloy sheet with 2mm thickness was used for this investigation.The forming reason and extending characteristics of the welding cracks were investigated during the Nd:YAG pulsed laser welding.The results show that welding cracks are mainly solidification crack which were always present in the weld centers.Few welding hot cracks appear multiple furcation phenomenons,and main and branch cracks were intercrystalline crack.The partial branch crack was mixed intercrystalline and transgranular extension.In addition,few cracks in the weld were caused due to irregular shape porosity and inclusion.The delayed crack weren't observed in the weld after deposited 48 hours.In the pre-process on the basis,the characteristics and generation mechanism of YAG pulsed laser welding cracks of magnesium alloy were analyzed further.
文摘The distribution law of the lateral residualstress at the welding seam is determinated by meansofcuttingthespecimen. Becausetocutthespecimencansimulateapproximatelytheex tension ofthe fatiguecrack,through measuring thestressreleased and calculating the distri bution oftheresidualstressthelaw isfound thattherateofthefatiguecrackextensionisaf fected bytheresidualstress.
文摘刀座焊接处是全断面岩石隧道掘进机(Full face rock tunnel boring machine,TBM)刀盘上最易发生疲劳破坏的部分。基于线弹性断裂力学,以裂纹疲劳寿命为基本变量,建立裂纹扩展可靠性模型,通过JC法计算刀座正面焊缝在不同滚刀实验载荷下的疲劳可靠性,并分析了不同因素对失效概率的影响。结果显示:中心滚刀刀座焊缝的失效概率比正滚刀小,正滚刀的失效概率随着安装半径的增大而减小;刀座焊缝失效概率随着初始裂纹深度的增大而显著增大,而临界裂纹深度的变化对失效概率的影响不大;裂纹形状比越大,刀座焊缝的失效概率越小。
