A method for reconstruction of residual stress fields from measurements made in an incompatible region

AbstractA method is introduced by which the complete state of residual stress in an elastic body may be inferred from a limited set of experimental measurements. Two techniques for carrying out this reconstruction using finite element analysis are compared and it is shown that for exact reconstruction of the stress field via this method, the stress field must be measured over all eigenstrain-containing regions of the object. The effects of error and incompleteness in the measured part of the stress field on the subsequent analysis are investigated in a series of numerical experiments using synthetic measurement data based on the NeT TG1 round-robin weld specimen. It is hence shown that accurate residual stress field reconstruction is possible using measurement data of a quality achievable using current experimental techniques

Applying electron backscattering diffraction to macroscopic residual stress characterisation in a dissimilar weld

AbstractDissimilar metal welds are complicated in nature because of the complex microstructure characteristics in the weld fusion zone. It is often necessary to know the phase distribution in a dissimilar metal weld especially at the interface such as fusion zone and heat affected zone to be able to predict the behaviour of the joint and its fitness for service. In this paper, a dissimilar metal weld made between ferritic/martensitic modified 9Cr-1Mo steel (P91) and austenitic AISI 316LN stainless steel using autogenous electron beam (EB) welding was analysed. The weld fusion zone has a local segregation of bcc and fcc phases. The EBSD technique was applied to determine the volume fractions of each of these phases in the weld fusion zone. This information was incorporated into the analysis of neutron diffraction data from the weld zone, and the macro-scale residual stresses were calculated from phase-specific stresses arising from the welding process. The results indicate that the overall macroscopic residual stress distribution in the weld centre is predominantly compressive in nature driven by the solid-state phase transformation of the weld pool during rapid cooling, with tensile peaks pushed adjacent to the heat affected zone (HAZ)/Parent boundaries on both sides of the fusion zone

Study on the Effect of Post Weld Heat Treatment Parameters on the Relaxation of Welding Residual Stresses in Electron Beam Welded P91 Steel Plates

AbstractResidual stresses are created by localised heating effects that occur during the welding process. Post weld heat treatment (PWHT) is the most convenient method for stress relief of welds. But PWHT cannot completely eliminate the residual stresses. So, it is essential to determine the influence of PWHT parameters like holding temperature and time on the stress relaxation for optimising the process. The selected material is modified 9Cr-1Mo (Grade 91) steel in the form of plates welded together using a high intensity electron beam. To facilitate the study, a numerical thermo-elastic-plastic model has been developed to simulate the welding of the plates. As P91 steels undergo phase transformations, the corresponding volumetric change and transformation plasticity are taken into consideration during the analysis and welding residual stresses are predicted. PWHT is implemented using Norton creep law and the residual stresses after relaxation are determined. The developed model and the predictions are validated using neutron diffraction measurements on as welded and post weld heat treated plates. A good agreement has been achieved between the measurements and predictions. The validated model has been used to study the effect of variation of heat treatment parameters like holding temperature and time on the relaxation of welding stresses

Genome-Wide Divergence and Linkage Disequilibrium Analyses for Capsicum baccatum Revealed by Genome-Anchored Single Nucleotide Polymorphisms

Principal component analysis (PCA) with 36,621 polymorphic genome-anchored single nucleotide polymorphisms (SNPs) identified collectively for Capsicum annuum and Capsicum baccatum was used to show the distribution of these 2 important incompatible cultivated pepper species. Estimated mean nucleotide diversity (π) and Tajima’s D across various chromosomes revealed biased distribution toward negative values on all chromosomes (except for chromosome 4) in cultivated C. baccatum, indicating a population bottleneck during domestication of C. baccatum. In contrast, C. annuum chromosomes showed positive π and Tajima’s D on all chromosomes except chromosome 8, which may be because of domestication at multiple sites contributing to wider genetic diversity. For C. baccatum, 13,129 SNPs were available, with minor allele frequency (MAF) ≥0.05; PCA of the SNPs revealed 283 C. baccatum accessions grouped into 3 distinct clusters, for strong population structure. The fixation index (FST) between domesticated C. annuum and C. baccatum was 0.78, which indicates genome-wide divergence. We conducted extensive linkage disequilibrium (LD) analysis of C. baccatum var. pendulum cultivars on all adjacent SNP pairs within a chromosome to identify regions of high and low LD interspersed with a genome-wide average LD block size of 99.1 kb. We characterized 1742 haplotypes containing 4420 SNPs (range 9–2 SNPs per haplotype). Genome-wide association study of peduncle length, a trait that differentiates wild and domesticated C. baccatum types, revealed 36 genome-wide SNPs significantly associated. Population structure, identity by state (IBS) and LD patterns across the genome will be of potential use for future genome-wide association study of economically important traits in C. baccatum peppers

Residual stress measurement round robin on an electron beam welded joint between austenitic stainless steel 316L(N) and ferritic steel P91

This paper is a research output of DMW-Creep project which is part of a national UK programme through the RCUK Energy programme and India's Department of Atomic Energy. The research is focussed on understanding the characteristics of welded joints between austenitic stainless steel and ferritic steel that are widely used in many nuclear power generating plants and petrochemical industries as well as conventional coal and gas-fired power systems. The members of the DMW-Creep project have under- taken parallel round robin activities measuring the residual stresses generated by a dissimilar metal weld (DMW) between AISI 316L(N) austenitic stainless steel and P91 ferritic-martensitic steel. Electron beam (EB) welding was employed to produce a single bead weld on a plate specimen and an additional smoothing pass (known cosmetic pass) was then introduced using a defocused beam. The welding re- sidual stresses have been measured by five experimental methods including (I) neutron diffraction (ND), (II) X-Ray diffraction (XRD), (III) contour method (CM), (IV) incremental deep hole drilling (iDHD) and (V) incremental centre hole drilling (iCHD). The round robin measurements of weld residual stresses are compared in order to characterise surface and sub-surface residual stresses comprehensively