Research On The Creep Deformation Behavior Of Three-Point Bending Specimen With Fixed Constraints

Small specimen creep test is widely used in the creep property evaluation of equipment in service.Three-point bending specimen with fixed constraints(TPBSF)has great advantages in engineering application because of its simple stress and being able to achieve rupture data.However,the study on creep deformation of TPBSF is not complete.In addition,as the small specimen is very small compared with the standard tensile specimen,and there is a lack of standardization research on the sample size.In this paper,the creep deformation and size effect of TPBSF is studied by theoretical analysis,numerical simulation and experimental verification.The main research contents and conclusions are as follows:(1)Based on the error function and small deformation assumption,a method for determining the critical displacement of TPBSF are presented.This method can reasonably define the small deformation and large deformation area of small sample creep and ensure the accurate application of deformation equation.Based on this method,the influencing factors of the time correction coefficient are analyzed.The results show that the time correction coefficient is only related to the thickness of the sample and the span between the lower dies.(2)The transient creep displacement data have been analysed according to the Garofalo's equation.The transient depletion rate is presented,and its relationship with the steady-state displacement rate is a power law,approximately inversely proportional to the time of creep and fracture time.The master curve is established and the method for predicting creep curves under different loading conditions is presented.(3)Based on the bending constitutive model of TPBSF,the effect of the specimen size on the creep property evaluation of TPBSF is investigated by using finite element method.The result shows that when the ratio of width to thickness of the cross section is in the range of 0.5-2.0,the error between the creep steady displacement rate and the theoretical value is small.When the transition angle of fixed end is in the range of 15-45°,the specimen can not only describe the mechanical response of clamped beam more accurately,but also can significantly reduce the effects of fixed end chamfering on creep.It is concluded that the best two kinds of specimens are the ratio of width to thickness is 2:1,the transition angle of fixed end is 300°and the ratio of width to thickness is 1:1,the transition angle of fixed end is 45°.