The effect of a residual stress field on fracture initiation in RPV steel

Abstract

A B S T R A C T Whether flaws in structures containing residual (secondary) stresses will extend under particular operational (primary) loads depends on the extent to which the residual stress field affects: (a) the nature and distribution of initiators; (b) the combined (primary + secondary) stresses and strains experienced by potential initiators. This paper compares fractographic data from specimens loaded by only a primary stress with data from specimens also containing a tensile residual stress field. Three-dimensional elastic-plastic finite element calculations are used to characterize the stress-strain conditions at the initiation sites at the onset of brittle fracture. The introduction of a residual stress changes the dominant stage in fracture nucleation from microcrack extension to particle cracking. This offsets some of the decrease in fracture toughness expected when the residual stress field increases specimen constraint.CT = compact tension specimen E = Young's modulus EDX = energy-dispersive X-ray analysis of composition FE = finite element HT = heat treatment J = contour integral J c = value of J at cleavage K = stress intensity K Jc = stress intensity at specimen failure MVC = ductile microvoid coalescence PCT = pre-loaded compact tension specimen SEM = scanning electron microscope X c = separation of initiation site from pre-crack front (in direction of macroscopic crack growth) Z c = separation from initiation site from mid-line of specimen, in plane normal to loading direction ε 22elastic = elastic portion of ε 22,total ε 22,total = total (elastic+plastic) strain in loading direction, acting on plane normal to loading direction ν = Poisson's σ 22 = principal tensile stress, in loading direction, acting on plane normal to loading direction

Experimental study on mechanical properties and fracture toughness of structural thick plate and its butt weld along thickness and at low temperatures

“…Curve fitting parameters in Eq. (7) by regress of the test data for steel plates and butt weld are also indicated by Fig. 8; the comparison of the results between the base material and the butt weld is made as well.…”

“…23,24 Therefore, in this study, the average d m values obtained by tests were regressed according to Eq. (7) in the form of Boltzmann function, where d 1 , d 2 , T t and T r are curve fitting parameters; T represents the temperature variable; d(T) is the critical value of CTOD at temperature T; d 1 and d 2 are the CTOD critical values of the lower and upper shelf, respectively; T t is the ductile to brittle transition temperature and T r is the temperature range of transition region.…”

The Influence of Selective Laser Melting Process Parameters on the Property of TiAlN/TiN Multilayer Coating on the 316L Steel

“…Thijs et al [6] studied the influence of different scanning speeds with the alternating and the unidirectional scan vector on the microstructure of the Ti-6Al-4V alloy processed by SLM. Ortner et al [7] found that residual stress could improve the fracture toughness of steel. A traditional heat treatment process is also a method of the surface strengthening treatment of SLM specimens.…”

Surface Treatment Effect on Measurement of Welding Residual Stress Using X-Ray Stress Analyzer

“…The effects of WRS would be harmful to safety and intensity of pressure vessel [1][2][3][4]. One of the most important methods to evaluate if the welding structure is safe is calculating stress intensity factor (K) of crack.…”