表面质量对疲劳强度的影响英语精选PPT.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第1页，此课件共12页哦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,suc

2、h 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第2页，此课件共12页哦Material and experimental set-upTh

3、e test specimens were machined by turning in wetcondition.Residual stresses were measured by means of the blind hole drilling method.第3页，此课件共12页哦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 t

4、imes 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:wher

5、e f is feed rate(mm/r)and r is the tool nose radius(mm).第4页，此课件共12页哦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 decre

6、asing of nose radius.第5页，此课件共12页哦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 s

7、hows residual stress increases with the depth.第6页，此课件共12页哦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.第7页，此课件共12页哦In the rot

8、ating bending 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 form

9、er has 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.第8页，此课件共12页哦Finite element analysisA 2*2 cm2 model of a forged Aluminum component第9页，此课

10、件共12页哦This 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 ro

11、ughness parameters are inaccurate,leading to large safety factors and overly conservative designs.So with the new method proposed,we can solve these problems easily.第10页，此课件共12页哦Summary Fatigue cracks usually initiate at the surface in materials,thus the surface state has a high influence on fatigue

12、 life.The most 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.第11页，此课件共12页哦Thanks for you listening！第12页，此课件共12页哦