表面质量对疲劳强度的影响英语精选文档.ppt

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1、表面表面质质量量对对疲疲劳劳强强度的影响英度的影响英语语本讲稿第一页，共十二页The fatigue life of a machined part depends strongly on its surface condition.And the effect of residual stress on fatigue life is more pronounced than that of surface roughness.Some defects of surface quality have a considerable effect on fatigue strength,such

2、 as strain hardening and residual compressive stresses.Stress concentration occurs easily at the troughs of surface roughness,especially the groove and fillet corner,which can lead to fatigue crack and accelerate the fatigue failure.A brief introduction本讲稿第二页，共十二页Material and experimental set-upThe

3、test specimens were machined by turning in wetcondition.Residual stresses were measured by means of the blind hole drilling method.本讲稿第三页，共十二页Surface roughnessThe surface roughness of the machined part is largely determined by the feed and tool nose radius.A large feed will give shorter cutting time

4、s but a poor surface quality.A large nose radius will generate a better surface quality.But an excessively large nose radius can lead to vibration tendencies,unsatisfactory chip breaking and shorter tool-life.A theoretical model for surface roughness is approximated by the following equation:where f

5、 is feed rate(mm/r)and r is the tool nose radius(mm).本讲稿第四页，共十二页The Figure illustrates the effect of the nose radius on the surface roughness for the cutting condition employed for the fatigue test(f=0.2,r=0.2,0.4,0.8).The results present that the value of Rmax parameter increases with the decreasin

6、g of nose radius.本讲稿第五页，共十二页Residual stressAfter the turning operation,the residual stresses were measured using the blind hole drilling method.The machining of round samples was carried out with different feed rates and nose radius.These data are measured by the blind hole drilling method.It shows

7、residual stress increases with the depth.本讲稿第六页，共十二页We can see that an increase of feed rate causes anincrease of compressive stresses in both directions.On the other hand,an increase of the nose radius of the insert causes a decrease of the compressive residual stresses.本讲稿第七页，共十二页In the rotating b

8、ending fatigue tests,residual rotation speed was 3800 rev/min.When the number of rotation exceeded 107,the test was stopped,with the test specimen not break under that condition.Although the surface roughness of specimens with re=0.2 is higher than that with r=0.4 and 0.8,which shows the former has

9、a higher fatigue life than others.That means a higher compressive residual stress causes a higher fatigue life and the effect of residual stress on fatigue life is more than the effect of surface roughness.本讲稿第八页，共十二页Finite element analysisA 2*2 cm2 model of a forged Aluminum component本讲稿第九页，共十二页Thi

10、s is just a model we abstract from the real component,and may not represent the actual surface.However,we still believe finite element analysis can be a valuable tool when studying the cause and effect of surface quality and fatigue strength.Common methods employing reduction factors and roughness p

11、arameters are inaccurate,leading to large safety factors and overly conservative designs.So with the new method proposed,we can solve these problems easily.本讲稿第十页，共十二页Summary Fatigue cracks usually initiate at the surface in materials,thus the surface state has a high influence on fatigue life.The m

12、ost important surface parameters are surface roughness,residual stress,and microstructure.The residual stress become more compressive as the feed rate increases.On the other hand,an increase of the nose radius of the insert causes a decrease of the compressive residual stresses.An increase of compressive residual stress causes an increase of fatigue life.And the effect of residual stress on fatigue life is more pronounced than that of surface roughness.本讲稿第十一页，共十二页Thanks for you listening！本讲稿第十二页，共十二页