Influence of stress state on the creep property evaluation of three-point bending test
According to the lack of standards for most of small specimen creep test techniques and the problem that changes on the specimen size tend to cause changes on the stress state,which in turn affects the accuracy of creep parameter inversion,this research used finite element method to analyze the stress state of specimens with different cross-sectional width-thickness ratios and its influence on creep properties of three-point bending test based on the constitutive model of beam bending and Norton power law.The results show that when the cross-sectional width-thickness ratio b:2h is less than 1:2,the specimen tends to be in a plane stress state;When the ratio b:2h is larger than 2:1,the specimen tends to be in a plane strain state;When the ratio b:2h is between 1:2 and 2:1,the specimen falls in between the two states.For the load-point steady-state displacement rate,creep stress,conversion coefficient and creep parameter inversion,the influence of plane stress state is significantly greater than that of plane strain state.The comparison with uniaxial creep test data shows that the width-thickness ratio b:2h should be controlled within the range of 1:1 to 2:1,which can improve the accuracy of creep parameter inversion.The results provide basis for the rational application of three-point bending test technique.
small three-point bending specimencreepstress statefinite element
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