新型低应力弯曲下料外力加载模式的研究
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摘要
针对新型低应力弯曲下料中棒料V型槽尖端形状的特殊性,提出对V型槽尖端起裂和裂纹扩展分别处理,采用应力集中系数计算V型槽尖端起裂所需的初始外力,采用裂纹扩展门槛值计算V型槽尖端裂纹扩展所需的外力。利用曲线拟合方法,耦合出外力与裂纹起裂扩展长度间呈近似1/4凹圆弧递减关系。基于低应力下料特点,设计4种形式的外力控制曲线。下料实验结果表明,所提出的凹圆弧递减外力控制曲线能使下料时间最短、断面质量最好。
According to particularity of shape of V-shaped notch tip in a new-type of low stress precise cropping,it is proposed that the initial external load is obtained by means of stress concentration coefficient method when the tip of V-shaped notch is checking,and the variable external load is obtained by using the fracture mechanics when the macroscopic crack of V-shaped notch tip appears.Based on it,the relationship of the external force and crack propagation length is coupled out.Based on the characteristics of the low stress precise cropping,four types of external load control curves are designed in detail.The experimental results show that the cropping time is the shortest,and the section quality is best for LY8 bar by the approximate concave arc decreasing external control curve,which is also proposed.
According to particularity of shape of V-shaped notch tip in a new-type of low stress precise cropping,it is proposed that the initial external load is obtained by means of stress concentration coefficient method when the tip of V-shaped notch is checking,and the variable external load is obtained by using the fracture mechanics when the macroscopic crack of V-shaped notch tip appears.Based on it,the relationship of the external force and crack propagation length is coupled out.Based on the characteristics of the low stress precise cropping,four types of external load control curves are designed in detail.The experimental results show that the cropping time is the shortest,and the section quality is best for LY8 bar by the approximate concave arc decreasing external control curve,which is also proposed.
引文
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[7]Zhang LiJun,Xue JieQiong,Zhao YongRui,Xiang HengFu.Computation of theoretical stress concentration factor of V-shapednotch tip[J].Applied Mechanics and Materials,2012,152-154:765-769.
[2]赵升吨,雷净,郝永江.现代数控板材成形设备的现状[J].机械工人,2006(6):10-14.ZHAO ShengDun,LEI Jing,HAO YongJiang.Status of modernCNC sheet metal forming equipment[J].Machinist MetalForming,2006(6):10-14(In Chinese).
[3]洪深泽.冷挤压工艺及模具设计[M].合肥:安徽科学技术出版社,1985:101-103.HONG ShenZe.Cold extrusion process and die design[M].Hefei:Anhui science and Technology Press,1985:101-103(InChinese).
[4]肖景容.精密模锻[M].北京:机械工业出版社,1985:1-25.XIAO JingRong.Precision forging[M].Beijing:MachineryIndustry Press,1985:1-25(In Chinese).
[5]张立军,相恒富,王世敬.变速周向低应力弯曲断裂下料初始工艺参数的确定[J].机床与液压,2011,39(7):69-70;2011,39(7):123.ZHANG LiJun,XIANG HengFu,WANG ShiJing.Research on thecropping technology key parameters with variable-speedcircumferential low-stress bend fracture[J].Machine Tool&Hydraulics,2011,39(7):69-70;2011,39(7):123(InChinese).
[6]郑修麟.金属疲劳的定量理论[M].西安:西北工业大学出版社,1994:80-85.ZHENG XiuLin.Metal fatigue quantitative theory[M].Xi'an:Northwestern Polytechnical University Press,1994:80-85(InChinese).
[7]Zhang LiJun,Xue JieQiong,Zhao YongRui,Xiang HengFu.Computation of theoretical stress concentration factor of V-shapednotch tip[J].Applied Mechanics and Materials,2012,152-154:765-769.