This study applies a non-local integral Gurson-Tvergaard-Needleman model, incorporating two characteristic material length scales as regularization parameters, linked to shear deformation and hydrostatic tension, to simulate fracture in low alloy A533B. The model accounts for void growth, nucleation, and coalescence, including a shear-enhanced mechanism. Experiments under various stress triaxialities were used to assess model performance, including: uniaxial tensile test, fracture test, and simple shear test. The aim is to predict both global load-deformation responses and fracture modes using a single, physically motivated parameter set. While some parameters are well-established in the literature and linked to micro-structural observations and micromechanical analysis, others are less studied and require calibration against experiments. The calibration process is challenging due to nonlinear parameter interactions causing complex dependencies. A trade-off between competing effects was frequently observed. To address this, three parameter sets were investigated. Set 1 used physically motivated values and successfully reproduced the cup-cone fracture in round smooth bar, but underestimated the strains to failure for round smooth bar and modified Iosipescu specimens. Set 2 employed phenomenological values to closely match all the global load-deformation responses, but failed to replicate the experimentally observed fracture mode. Set 3 slightly adjusted parameters in Set 1, achieving improved failure strain predictions and a more accurate cup-cone pattern.

Fatigue properties of low-alloy steels, LAS, are well defined in air and at the beginning of life. However, the potential influence from thermal ageing under conditions relevant for the nuclear industry is uncertain. In this study, the fatigue properties of LAS base and weld metals, aged at 345 °C for 215,000 h, are compared to as-delivered archive reference materials. In the weld material, ageing appears as an increase in yield and ultimate tensile strength. Ageing also manifests as an inclined strain–cycle (ε-N) fatigue curve, where fatigue life decreases in the low-cycle fatigue region and conversely increases in the high-cycle fatigue region. The results further show that both as-delivered and aged weld metals exhibit a significantly shorter fatigue life in the low-cycle fatigue region and a longer fatigue life in the high-cycle fatigue region when compared to the ASME Code best-fit curve.

Fracture toughness testing was conducted on 81 SE(B)-specimens extracted from the weld metal of an aged pressurizer weld, of which 42 were deep-cracked and 39 shallow-cracked specimens. The crack tips were positioned in distinct zones in the weld metal, which was achieved by polishing and etching the material to reveal prior-austenite grain boundaries prior to specimen manufacturing. Deep-cracked specimens with crack tips located in the as-welded zone and where dendrites exhibit a low inclination to the pre-crack plane, frequently showed pop-in events during testing. The length of these pop-ins correlated directly with the length of the weld zone in front of the crack tip. Toughness was evaluated both at the pop-in and at final failure, and values were assigned to the corresponding weld zones. The ductile-to-brittle transition temperature was determined separately for each zone, confirming that the as-welded zone with low dendrite inclination is the most critical in the aged weld.

This paper presents an elastoplastic framework for mechanical-electrochemical damage in metals for simulating corrosion fatigue. The proposed numerical approach combines classical rate-independent isotropic von Mises elastoplasticity with an electrochemical kinetics model to simulate anodic dissolution-driven corrosion. The model's capabilities are demonstrated through benchmark tests and experiments. A hollow specimen was tested in a water environment, incorporating a membrane electrode for corrosion potential measurement and potential drop for crack initiation detection. The formulation accurately reproduces key features of corrosion fatigue, including diverse pit morphologies, time-dependent corrosion kinetics and the formation of multiple crack initiation sites, consistent with experiments.

The fracture surfaces of 49 SE(B) toughness tests performed on five different geometries, were carefully investigated by SEM imaging and cross-section analysis. The specimens were extracted from a large multi-pass weld in T-S orientation. The failure characteristics were associated with three distinctly different zones of the weld. Transgranular fracture occurred primarily in the reheated zone and in the as-welded zone with a dendritic microstructure inclined relative to the crack plane. With a dendritic microstructure aligned with the crack plane intergranular fracture occurred. The toughness of the as-welded zone with a low inclination angle, was significantly lower than that obtained in the other two weld zones. Due to the relatively large size of the zones compared to the fracture process zones of the tests, it is appropriate to characterize the failure behavior as large-scale heterogeneity. Weakest-link modeling may be applied locally in each weld zone, giving rise to three different sets of model parameters. A new calibration technique is introduced and used to fit a local weakest-link model to the toughness distribution curves of the individual zones.

This work investigates the interaction between two competing mechanisms on the fatigue life of 304L stainless steel, martensitic transformation and viscoplastic relaxation, as well as the potential fatigue life enhancement of a single hold time applied prior to cyclic loading. At 300 °C, a tensile load hold time of 15 h applied prior to alternating cyclic loading resulted in an increase in mean fatigue life, exceeding 20 % in the studied low cycle fatigue regime. The observed enhancement is primarily attributed to viscoplastic effects during the hold time, which reduces the maximum stress and fatigue crack growth rate in cyclic loading. At room temperature, the opposite effect was observed. A strain-induced martensitic transformation resulted in a secondary cyclic hardening and a brittle final softening phase. The transformation was enhanced by the hold time, which led to increased brittleness and therefore reduced fatigue life. However, viscoplastic relaxation attenuated the detrimental effect of martensite, as was observed by a 15 % decrease in maximum stress. This study not only demonstrates the positive impact of an extended hold time at elevated temperature on the low cycle fatigue behavior but also analyzes underlying competing mechanisms at room temperature through an in-depth experimental investigation.

High-Ni, high-Mn welds are the life-time determining components in reactor pressure vessels (RPVs) of Nordic reactors at desired operating times of pressurized water reactors (PWR) of 60 or even 80 years due to embrittlement that is caused by pronounced clustering of Ni, Mn and Si. To understand early stages of clustering we performed atom probe tomography (APT) measurements on an axial weld of the boiling water RPV from Barsebäck Unit 2 decommissioned after 28 years of operation. Contrary to our previous work on the same weldment, here we report observation of clustering. The cluster number densities vary significantly between individual APT measurements, which we attribute to variations in local Ni and Mn concentrations, a trend even seen within single grains. Based on comparison with high fluence samples containing more and larger clusters we propose that NiMnSi cluster formation and growth is an irradiation-induced continuous process without a relevant threshold dose.

Microstructure has a significant effect on material's integrity and in a heterogeneous weld microstructure the discontinuities affect the brittle fracture initiation and propagation and determine the fracture toughness. The knowledge of brittle fracture initiation mechanisms in high-Mn/high-Ni welds is limited. The brittle fracture initiation behaviour of the decommissioned Barsebäck Unit 2 reactor pressure vessel (RPV) welds of high-Mn/high-Ni weld metal from three different locations, the RPV head and the beltline regions, were investigated and compared with specimens from the surveillance program with high fluence. Systematic fractography has been performed on impact and fracture toughness specimens and the main features of the brittle fracture initiation in the component weld are presented and discussed. Two main types of initiators are identified as the weakest links to initiate the cleavage fracture and the initiation mechanism is found independent from the operation condition. The high-fluence surveillance specimens have a larger amount of intergranular cracking. The cleavage fracture initiation appears to be independent of the operation conditions but dependent on the welding process and metallurgical features. The findings aid in the development of improved material-property correlations which will result in better computational tools for predicting aging of welds based on microstructure.

This study addresses the critical need for a constitutive model to analyze the cyclic plasticity of additively manufactured 316L stainless steel. The anisotropic behavior at both room temperature and 300 °C is investigated experimentally based on cyclic hysteresis loops performed in different orientations with respect to the build direction. A comprehensive constitutive model is proposed, that integrates the Armstrong-Frederick nonlinear kinematic hardening, Voce nonlinear isotropic hardening and Hill's anisotropic yield criterion within a 3D return mapping algorithm. The model was calibrated to specimens in the 0° and 90° orientations and validated with specimens in the 45° orientation. A single set of hardening parameters successfully represented the elastoplastic response for all orientations at room temperature. The algorithm effectively captured the full cyclic hysteresis loops, including historical effects observed in experimental tests. A consistent trend of reduced hardening was observed at elevated temperature, while the 45° specimen orientation consistently exhibited the highest degree of strain hardening. The applicability of the model was demonstrated by computing energy dissipation for stabilized hysteresis loops, which was combined with fatigue tests to propose an energy-based fatigue life prediction model.

This work presents a systematic investigation of the combined effect of hydrogen embrittlement and loss of constraint. The fracture mechanics experiments are performed on an advanced martensitic high strength steel using a single-edge-notch bend specimen, with different crack over height ratio, subjected to electrochemical in-situ hydrogen charging at various loading rates. It is found that the environmentally driven ductile-to-brittle transition region in fracture toughness is obtained for both the high and low constraint specimen configurations. This region is characterized by a change from transgranular dimple rupture to an intergranular mode of fracture. The transition region for the low constraint specimen is shifted towards longer hydrogen exposure times, which is an effect of the reduced hydrostatic stress ahead of the crack front compared to the high constraint specimen. The low constraint specimen exhibits significant plastic straining, which is reflected in a significant decrease in the fracture toughness due to hydrogen assisted transgranular dimple rupture.