Fatigue cracking at girth welds threatens offshore-pipeline integrity and requires uncertainty in flaw size, crack-growth behaviour, loading and weld geometry to be considered. A probabilistic fatigue-reliability framework is developed for a semi-elliptical surface crack in an API 5L X65 pipeline under cyclic global bending. Geometry-consistent stress-intensity-factor histories from a three-dimensional finite-element model provide 60 training and six case-wise held-out simulations. The Paris-law and loading distributions are identified as DNV code-calibrated benchmark inputs, not site-specific X65 measurements. For the fixed Paris exponent, normalisation by CeffΔσeq3 reduces the primary surrogate to a one-dimensional Gaussian process in initial crack depth. The model achieves R2 = 0.997 and MAPE = 4.04% on the test cases, and R2 = 0.996 with MAPE = 3.70% in leave-one-out validation. Using conditionally truncated inputs, the posterior-mean life distribution has a median of 6.84 × 108 cycles and a 95%-reliability design life of 2.12 × 108 cycles. Correlated latent-GP posterior-function propagation gives Pf = 4.147% at Nd = 2 × 108 cycles, with a 95% GP-posterior interval of 3.858–4.444%. Sensitivity analysis identifies the stress-range scale as dominant, showing that site-specific loading characterisation is essential for field application.
Closed wheel-tread cracks can remain compression-dominated during rolling contact while sustaining substantial in-plane and out-of-plane shear. A sequential ABAQUS–FRANC3D–Python framework resolves this response over ten crack-geometry updates. A closure-aware nominal driving force combines event-paired differences in the mode-II and mode-III stress-intensity factors. Four arc-length descriptors summarise its front distribution: mean, peak, peak coordinate and coefficient of variation. Controlled comparisons evaluate initial crack size and orientation, axle load, speed and wheel–rail friction. Thirty Latin-hypercube finite-element conditions provide 4,272 front points for condition-grouped machine-learning validation. ExtraTrees achieves a case-macro cross-validation RMSE of 16.9587 MPa·mm1/2. Four held-out numerical conditions, comprising 579 front points, give a pointwise RMSE of 8.5794 MPa·mm1/2. Front coordinate and initial orientation have the largest mean absolute SHAP contributions. The predicted terminal profiles quantify differences in driving-force magnitude and localisation across conditions within the sampled domain.
This study is dedicated to the investigation of the influence of the pre-impact loading on the residual properties of composite sandwich panels. The methodology was proposed for pre-impact testing followed by quasi-static and cyclic tension of structurally representative composite specimens and structural elements. The material was additively manufactured sandwich panels consisted of honeycomb core made of acrylonitrile butadiene styrene (ABS) thermoplastic and two load-bearing face sheets made of ABS reinforced with 15% carbon fibers. Novel experimental data was obtained on the residual load-bearing capacity and fatigue life after pre-impact loading at various impact energy. Several phenomenological models were used to approximate obtained data on impact sensitivity, that demonstrated high descriptive ability.
Friction Stir Welding (FSW) is widely validated as a solid-state joining process that has gained significant attention for the welding of aluminum alloys in aerospace and automotive applications. In this study, the effect of Tool Pin Profiles (TPP)—Taper Threaded (TTPP), Square (SPP), and Cylindrical Threaded (CTPP)—on the flow of material, mechanical properties, corrosion properties and microstructure of dissimilar aluminum alloys AA6061-T6 and AA2024-T3 was investigated. A Taguchi L9 orthogonal array (OA) was employed for the optimization of process parameters, which included Tool Pin Profile (TPP), Tool Rotational Speed (TRS) of 600, 700, and 800 rpm and Welding Speed (WS) of 25, 30, and 35 mm/min. Mechanical properties were evaluated in terms of Ultimate Tensile Strength (UTS), Stir Zone (SZ) microhardness, and Percentage elongation. Microstructural characterization was conducted using optical microscopy and Scanning Electron Microscopy (SEM). Post‑weld performance was evaluated using potentiodynamic polarization and immersion corrosion tests. The TTPP condition yielded the highest measured UTS (210 MPa), SZ microhardness (162 HV), and elongation (8.89%) within the tested parameter range. This performance is attributed to improved material mixing, refined grain structure, and a favourable thermal cycle during processing. Through Taguchi optimization analysis, it was confirmed that the most favorable conditions for joining AA6061-T6 and AA2024-T3 alloys are provided by the TTPP.
Stress corrosion cracking (SCC) in structural components often involves the simultaneous development of multiple cracks; however, the mechanism by which a dominant crack emerges under sustained loading remains insufficiently resolved. This exploratory study investigates competitive multi-crack SCC behavior in AISI 316L stainless steel under sustained tensile loading in flowing 1 M HCl. Five naturally nucleated surface cracks formed around a central hole were monitored using repeated in situ optical imaging. Interval-based crack growth rates (Δa/Δt) were calculated from five discrete inspection times. Post-test fracture paths were analyzed, supported by SEM fractography and SEM–EDS to assess localized degradation. Fracture-path analysis showed that Cracks 3 and 4 controlled the final trajectory. Interval-based descriptors identified Crack 4 as kinetically dominant within the tested specimen, exhibiting the highest mean and maximum growth rates and the largest cumulative extension. SEM–EDS revealed localized degradation, secondary branching, higher oxygen content, and a detectable chlorine signal in the Crack 4 region. Within the tested multi-crack configuration, dominant-crack behavior could be distinguished using interval-based growth descriptors from discrete observations. The findings are consistent with a combined influence of stress redistribution and localized corrosion-assisted degradation and provide a proof-of-concept basis for comparing crack-growth persistence from discrete observations.
