Finite Element Analysis Of Creep Damage In Small Punch Test Specimen At Elevated Temperature

Small punch test (SPT) technique has the advantage of 'sampling nondestructively'over the traditional approach, which has been widely adopted to measure creep propertiesof materials such as metals, composites and inorganic material. However, there areseveral weaknesses in currently researching work: Firstly, a lot of qualitative observation(nor quantitative analysis) such as metallurgical analysis, SEM observation, etc havebeen made for small punch creep test (SPCT). Secondly, no relationship between thesmall punch creep test data and traditional unaxial tensile creep test data is available.Thirdly, it is a lack of evaluating creep damage from SPCT data. So, based on the theoryof continuum damage mechanics and finite element analysis, the creep damage in smallpunch specimen at elevated temperature was studied in this dissertation, the main workand conclusions are listed as follow: (1)A set of uniaxial creep tensile test and small punch creep test at elevatedtemperature for SUS 304 stainless steel were carried out, and two kinds of creep damageconstitutive equations were obtained. The comparison of two kinds of constitutiveequations from different test method shows that SPCT has a potential to evaluate thecreep damage. (2)By use of the user subroutine UMAT in the powerful commercial softwareABAQUS, the K-R creep damage constitutive equations have been coupled in creepanalysis of SPCT specimen. The whole process of creep development including thetertiary stage in SPCT specimen was simulated, and the problem that the normal creepnumerical analysis can not obtain the tertiary stage in SPCT specimen was resolved. (3)The creep damage evolution curve from SPCT with three stages is similar tothat of creep strain, being consist of decelerating, constant rate and accelerating stages.The localization of creep damage is very obvious and the failure of specimen occursfirstly on the lower surface that is 0.8mm to the center that agrees well with the neckingplace of the specimen. (4)The creep deformation of small punch specimen is very complicated, which isdifferent from that of unaxial creep tension specimen. The creep strain distribution alongthe radial has very significant scatter, the deformation in the center and that of far from IIIABSTRACTthe center are different in tendency and even reverse. (5)The friction coefficient between the surface of heading and specimen greatlyinfluence the central deflection, creep strain and creep damage of the specimen. Thechoosing zero-friction coefficient results in the most conservative in life prediction. (6)The effects of geometrical factors on small punch creep test were analyzed byfinite element analysis. The results show that the specimen thickness influence therupture time of small punch creep testing very greatly and it is strongly suggested that thespecimen thickness should be in the range of 0.45mm～0.5mm.