SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING The residual stress is generated in the surface layer after machining. The causes of the generation of the residual stress are (i) The material of the workpiece sur face expands while it is heated by the cutting or grinding heat, and it contracts when it is cooled The expansion and contraction are resisted by the internal material of the workpiece which results in the residual tensile stress in the surface layer after machining,(ii) The surface material plastically deforms under the extrusion and friction of the tool. while the 挤压 internal material close to the surface layer elastically deforms. After machining, the recovery of the elastic deformation of the interna material is restricted by the sur face material, which has deformed plastically. This results in the residual stress, usually compressive residual stress, in the surface layer;(iii The metallographical variation of the surface layer leads to its volume change, either expansion or contraction, which is restricted by the internal material and results in the residual stress(compressive or tensile)in the surface laver
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING The residual stress is generated in the surface layer after machining. The causes of the generation of the residual stress are: (i) The material of the workpiece surface expands while it is heated by the cutting or grinding heat, and it contracts when it is cooled. The expansion and contraction are resisted by the internal material of the workpiece which results in the residual tensile stress in the surface layer after machining; (ii) The surface material plastically deforms under the extrusion and friction of the tool, while the internal material close to the surface layer elastically deforms. After machining, the recovery of the elastic deformation of the internal material is restricted by the surface material, which has deformed plastically. This results in the residual stress, usually compressive residual stress, in the surface layer; (iii) The metallographical variation of the surface layer leads to its volume change, either expansion or contraction, which is restricted by the internal material and results in the residual stress (compressive or tensile) in the surface layer. 挤 压
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING Influence of Surface Quality on the Performance of Machined parts A field failure of a machined part caused by its wear, fatigue or corrosion, etc, starts from the part sur face in most cases. The sur face quality of a machine part greatly influences its performance, such as the fitting between parts, wear resistance, corrosion resistance, and fatigue strength Influence on Fitting between Parts 强度间隙配合 The surface roughness influences directly the fitting condition between parts. For the clearance fit, the existence of the micro-irregularities on part surfaces leads to a rapid initial wear. Thus the clearance increases between the mating parts which cause the deterioration of the fitting condition
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Influence of Surface Quality on the Performance of Machined Parts A field failure of a machined part caused by its wear, fatigue or corrosion, etc., starts from the part surface in most cases. The surface quality of a machine part greatly influences its performance, such as the fitting between parts, wear resistance, corrosion resistance, and fatigue strength. Influence on Fitting between Parts The surface roughness influences directly the fitting condition between parts. For the clearance fit, the existence of the micro-irregularities on part surfaces leads to a rapid initial wear. Thus the clearance increases between the mating parts, which cause the deterioration of the fitting condition. 强度 间隙配合
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING As to the interference fit, the strength of fit interference fit depends upon the surface roughness of the part过盈配合 When one part is press-fitted into another, the ridges of the micro-irregularities are extruded: ridge it uk This reduces the actual interference and thus the strength of fit. The actual interference can be calculated by the following equation e=(D-D)-1.2[(H max/s +(Hna6.4 where e-actual interference (Hma s(Hma maximum height of irregularities of shaft and hole, respectively, D-diameter of shaft D, -diameter of hole
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING As to the interference fit, the strength of fit depends upon the surface roughness of the parts. When one part is press-fitted into another, the ridges of the micro-irregularities are extruded: This reduces the actual interference and thus the strength of fit. The actual interference can be calculated by the following equation: e = (Ds - Dh ) - l.2[(Hmax) s + (Hmax) h ] 6.4 where e—actual interference, (Hmax) s , (Hmax) h—maximum height of irregularities of shaft and hole, respectively, Ds—diameter of shaft, Dh—diameter of hole. interference fit 过盈配合 ridge 波峰