《机械设计》

§3-3影响强度因素一、应力集中的影响由于实际零件与 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 试件有很大区别，影响机械零件疲劳强度的因素有应力集中、尺寸效应、表面状态、腐蚀介质、加载顺序和频率等等，其中以前三项较为重要。理论应力集中系数：在应力集中处，最大局部应力σmax与名义应力σ的比值。引起应力集中的现象：截面形状的突然变化处，如凹槽、孔、圆角、缺口等。材料不同，应力集中的敏感性不同。强度极限愈高的钢材，应力集中越敏感，铸铁则迟钝很多。常用有效应力集中系数kσ、kτ来考虑应力集中对疲劳强度的影响。理论应力集中系数材料的敏感系数附表3-1附表3-2附表3-3附图3-1注意：若在同一截面上同时有几个应力集中源时，应采用其中最大有效应力集中系数进行计算。附表3-4、3-5附表3-6、3-7其它应力集中系数见二、尺寸效应零件尺寸越大，疲劳强度越低，称为尺寸效应。其原因是因为尺寸大时，材料晶粒粗，出现缺陷的概率多，机加工后表面冷作硬化层相对较薄，疲劳裂纹容易形成。对于受弯曲和转矩的零件，疲劳强度随尺寸增大而降低的现象还与零件截面上承受非均匀分布的应力剃度有关，如右图所示。显然，直径较大的试件更容易发生破坏。尺寸系数愈小表示疲劳强度降低愈大。附图3-3附图3-2螺纹联接件的尺寸系数（因截面为圆形，故只有尺寸影响）见下表：对于轮毂或滚动轴承与轴以过盈配合相联接时，可按求出其有效应力集中系数与尺寸系数的比值。如缺乏试验数据，设计时可取。附表3-8三、表面状态的影响零件表面质量（主要指表面粗糙度，表面粗糙度参数值越小疲劳强度越高）对疲劳强度的影响，通常用、表示表面状态的影响程度。1、表面质量附图3-42、表面处理表面处理对疲劳强度影响用强化系数表示。附表3-9附表3-10附表3-11则零件的极限应力图为：综合考虑上述三个主要方面，则可获得综合影响系数Kσ：附表3-1轴上环槽处的理论应力集中系数返回下一页简图应力公称应力公式（拉伸、弯曲）或（扭转剪切）拉伸r/dD/d∞2.001.501.301.201.101.051.031.021.010.042.702.372.151.941.700.102.452.392.332.272.182.011.811.681.581.420.152.082.041.991.951.901.781.641.551.471.330.201.861.831.801.771.731.651.541.461.401.280.251.721.691.671.651.621.551.461.401.341.240.301.611.591.581.551.531.471.401.361.311.22附表3-1轴上环槽处的理论应力集中系数返回下一页上一页简图应力公称应力公式（拉伸、弯曲）或（扭转剪切）弯曲r/dD/d∞2.001.501.301.201.101.051.031.021.010.042.832.792.742.702.612.452.222.021.881.660.101.991.981.961.921.891.811.701.611.531.410.151.751.741.721.701.691.631.561.491.421.330.201.611.591.581.571.561.511.461.401.341.270.251.491.481.471.461.451.421.381.341.291.230.301.411.411.401.391.381.361.331.291.241.21附表3-1轴上环槽处的理论应力集中系数返回上一页简图应力公称应力公式（拉伸、弯曲）或（扭转剪切）扭转剪切r/dD/d∞2.001.301.201.101.051.021.010.041.971.931.891.851.741.611.451.330.101.521.511.481.461.411.351.271.200.151.391.381.371.351.321.271.211.160.201.321.311.301.281.261.221.181.140.251.271.261.251.241.221.191.161.130.301.221.221.211.201.191.171.151.12附表3-2轴肩圆角处的理论应力集中系数返回下一页简图应力公称应力公式（拉伸、弯曲）或（扭转剪切）拉伸r/dD/d2.001.501.301.201.151.101.071.051.021.010.042.802.572.392.282.141.991.921.821.561.420.101.991.891.791.691.631.561.521.461.331.230.151.771.681.591.531.481.441.401.361.261.180.201.631.561.491.441.401.371.331.311.221.150.251.541.491.431.371.341.311.291.271.201.130.301.471.431.391.331.301.281.261.241.191.12附表3-2轴肩圆角处的理论应力集中系数下一页上一页返回简图应力公称应力公式（拉伸、弯曲）或（扭转剪切）弯曲r/dD/d6.03.02.01.501.201.101.051.031.021.010.042.592.402.332.212.092.001.881.801.721.610.101.881.801.731.681.621.591.531.491.441.360.151.641.591.551.521.481.461.421.381.341.260.201.491.461.441.421.391.381.341.311.271.200.251.391.371.351.341.331.311.291.271.221.170.301.321.311.301.291.271.261.251.231.201.14附表3-2轴肩圆角处的理论应力集中系数返回上一页简图应力公称应力公式（拉伸、弯曲）或（扭转剪切）扭转剪切r/dD/d2.01.331.201.090.041.841.791.661.320.101.461.411.331.170.151.341.291.231.130.201.261.231.171.110.251.211.181.141.090.301.181.161.121.09附表3-3轴上横向孔处的理论集中系数公称扭转应力公称弯曲应力返回d/D0.00.050.100.150.200.250.30d/D0.00.050.100.150.200.250.303.02.462.252.132.031.961.892.01.781.661.571.501.461.42●●0.88查表过程返回返回返回返回注：⑴滚动轴承与轴配合处的值与表内所列H7/r6配合的值相同；⑵表中无相应的数值时，可按插入法计算。附表3-8零件与轴过盈配合处的值返回直径/mm配合σB/MPa4005006007008009001000120030H7/r62.252.502.753.003.253.503.754.25H7/k61.691.882.062.252.442.632.823.19H7/h61.461.631.791.952.112.282.442.7650H7/r62.753.053.363.663.964.284.605.20H7/k62.062.282.522.762.973.203.453.90H7/h61.801.982.182.382.572.783.003.40>100H7/r62.953.283.603.944.254.604.905.60H7/k62.222.462.702.963.203.463.984.20H7/h61.922.132.342.562.763.003.183.46附表3－9表面高频淬火的强化系数βq注：表中系数值用于旋转弯曲，淬硬层厚度为0.9～1.5。应力集中时，强化系数较高。返回试件种类试件直径/mmβq无应力集中7～201.3～1.630～401.2～1.5有应力集中7～201.6～2.830～401.5～2.5附表3－10化学热处理的强化系数βq返回化学热处理 方法 快递客服问题件处理详细方法山木方法pdf计算方法pdf华与华方法下载八字理论方法下载 试件种类试件直径/mmβq氮化，氧化层厚度0.1~0.4mm表面硬度64HRC以上无应力集中8～151.15～1.2530～401.10～1.15有应力集中8～151.9～3.030～401.3～2.0渗碳，渗碳层厚度0.2~0.6mm无应力集中8～151.2～2.130～401.1～1.2有应力集中8～151.5～2.530～401.2～2.0氧化，氰化层厚度0.2mm无应力集中101.8附表3－11表面硬化加工的强化系数βq返回加工方法试件种类试件直径/mmβq滚子滚压无应力集中7～101.2～1.430～401.1～1.25有应力集中7～201.5～2..230～401.3～1.8喷丸无应力集中7～201.1～1.330～401.1～1.2有应力集中7～201.4～2.530～401.1～1.5附表3-4轴上键槽处的有效应力集中系数注：公称应力按照扣除键槽的净截面面积来求。附表3-5外花键的有效应力集中系数返回轴材料的σB/MPa5006007007508009001000kσ1.5－－1.75－－2.0kτ－1.51.6－1.71.81.9轴材料的σB40050060070080090010001200kσ1.351.451.551.601.651.701.721.75kτ矩形齿2.102.252.362.452.552.652.702.80渐开线形齿1.401.431.461.491.521.551.581.60附表3-6公称直径12mm的普通螺纹的拉压力集中系数附表3-7螺纹联接件的尺寸系数εσ返回材料的σB/MPa4006008001000kτ3.03.94.85.2直径d/mm≤1620242832404856647280εσ10.810.760.710.680.630.600.570.540.520.50