Comprehensive study of ductile damage behavior and formability in hole expansion process

GSK3β functions as a mechanosensitive regulator that links flow stress to Shh signaling.

For cold-drawn carbon steels, the regularities governing the influence of alternating deformation and temperature on the development of dynamic strain aging (DSA) processes have been established. It was found that a change in the deformation sign (compression-tension) leads to a shift in the onset of the first flow stress serrations toward higher strain levels. Based on the analysis of a stress unrevised motion of dislocation and coefficient of strain hardening, it is shown that the suppression of DSA during reverse loading is caused by a disruption in the kinetic relationship between the dislocation waiting time (for interaction with solute atoms) and the duration of their free motion. It has been established that applying alternating bending within the temperature range of 250—275 °C achieves a plasticization effect in high-carbon wire without compromising its strength properties. The results are explained by dislocation recombination processes and changes in the conditions of their pinning by impurity atom atmospheres. The necessity of forced cooling of the metal after deformation is justified to prevent the development of static strain aging (SSA) in coils, thereby preserving the positive effect of increased ductility.

Machine Learning-Based Model for Predicting Flow Stresses in High-Temperature Deformation of Titanium Alloys

Condition-driven mechanism transitions: Superplastic deformation and microstructural response of Inconel 718

Abstract The dispersal of meltwater discharged from the Laurentian Channel (LC) is investigated from numerical experiments with an eddy-resolving model representing the western North Atlantic during the last ice age. Meltwater dispersal is simulated over a full summer, when glacial ablation rates were presumably the highest. In our experiments, meltwater forms a buoyant plume, which flows to the southwest along the continental slope owing to the Coriolis force. Four mechanisms of offshore export are identified. 1) Meltwater is carried seaward by Ekman currents driven by upwelling-favorable winds along the slope. 2) Part of it is entrained away from the slope by meander crests and warm-core rings of the Gulf Stream (GS) between the LC and Cape Hatteras. 3) The other part is generally diverted offshore by the GS near Cape Hatteras, where the GS leaves the slope. 4) Meltwater can be trapped in a GS meander trough that pinches off and produces a cold-core ring, leading to its penetration into the subtropical gyre. In turn, the buoyant plume has relatively small but noticeable effects on the GS. In the western, weakly meandering segment of the GS, the vertical shear in horizontal velocity is generally reduced due to the presence of melt (light) water along the inshore flank of the GS. Our results are discussed in light of (i) a two-layer theory of a surface density front subjected to background flow and wind stress and (ii) sediment records from the Laurentian Fan and the Sargasso Sea.

Integrating DEM and flow stress factors to identify sedimentation-transportation zone in the eastern Himalayan foothill region.

Synergistic enhancement of cryogenic tensile properties and toughness in HSLA steel through intercritical heat treatment

A grain size dependent constitutive model of hot deformation Nd-Fe-B permanent magnetic material

The Zircaloy-4 alloy is a key structural material for nuclear reactor cores. However, its behavior under warm deformation conditions and during phase transformations requires in-depth investigation to improve technologies for producing ultrafine-grained (UFG) structures using severe plastic deformation methods. This work presents a comprehensive study of the rheological properties, phase stability, and microstructural evolution of the alloy in the temperature range from 20 to 950 °C at strain rates of 0.5 and 15 s−1. The experimental part included plastometric testing, dilatometric analysis, and microstructural characterization. It was established that the optimal window for plastic deformation corresponds to warm deformation at 650 °C. Dilatometric analysis confirmed that heating to 650 °C ensures the preservation of a stable initial α-phase structure, since the formation of secondary phases and the α→β transformation are initiated at higher temperatures, namely 694 °C (onset) and 847 °C (completion). At 650 °C, the deformation resistance decreases by approximately 70% compared to cold processing, while the strain-rate sensitivity of the flow stress is minimized. EBSD analysis showed that deformation under these conditions leads to intensive grain fragmentation via mechanisms of dynamic recovery and the initial stages of continuous dynamic recrystallization. The decisive role of the kinetic factor was demonstrated: reducing the strain rate to 0.5 s−1 promotes the formation of a finer and more homogeneous grain structure. In contrast, high strain-rate deformation (15 s−1) results in coarser grains and increased non-relaxed intragranular residual stresses. The obtained results provide a physical basis for optimizing thermomechanical processing regimes and can be used to produce UFG structures in zirconium alloys without the risk of phase degradation.

ABSTRACT In the classic strain-rate equation for thermally activated dislocation intersection, the applied shear stress, τ, was introduced into the probability of thermal activation in response to the imposed shear strain rate, γ ˙ . The chemical model assumed that the pre-exponential term was comprised of the total number of activation sites times the frequency of attempts. The formulation did not explicitly address the experimental insensitivity of flow stress, σ, to strain-rate magnitude, ε ˙ . Devolution of the pre-exponential term indicates that the change in magnitude response is in the frequency term. The +rate of doing work, τ γ ˙ and in turn γ ˙ must arise from the operative velocity of dislocation segments. The modified strain-rate relation becomes γ ˙ = B 0 ( τ m ∗ + 2 ) γ 0 e − ( Δ G o − τν kT ) , analogous to Orowan, wherein B0 converts dislocation velocity to stress, γ0 is the number of sites times incremental strain areasΔν , G0 is free energy change due to dislocation intersection, ν, is activation volume, and kT is thermal energy. Constant strain rate is maintained by the decrease of m*, and the integral strain rate sensitivity, minteg, slope of log(σ-σ0) versus log( ε ˙ )|T, where σ0 is a yield stress, may increase with strain whereas the differential one, mdif = ∂ln(σ-σ0)/∂ln( ε ˙ )|T, remains constant, because change in τν is equally offset by change in ΔG0. The correlation of m* to mdif shows that the experimentally determined activation volume is twice the theoretical one, meaning the pre-exponential term is proportional to the strain rate. Moreover, the derivation of m* as a function of τ predicts a linear relation of log(υ) to log(τ) as validated by experiment.

Aluminum 7000 series alloys are widely used for aerospace and transportation applications due to their high strength-to-weight ratio. This research investigates the impact of zinc (Zn) and magnesium (Mg) content on the hot extrudability and tribological behavior. Elemental quantities straight away impact flow stress, determining the manufacturing parameters, whereas galling and adhesion frequently degrade tool life. This work illustrates that by assessing essential ram speeds and temperature limits, adjusting Zn and Mg concentrations considerably improves the extrudability limit. A decreasing flow stress during deformation reduces micro-cracking tendency and improves surface quality. The findings provide critical compositional guidelines for high-strength aluminum alloys, effectively balancing processing efficiency with improved surface quality and reduced element adhesion behavior, ensuring better industrial outcomes for advanced structural components.

To overcome the low strength of conventional polytetrafluoroethylene/aluminum (PTFE/Al) reactive materials and the insufficient reaction efficiency of aluminum, this study introduces highly reactive aluminum-cerium alloys (Al-Ce-1#, -2#, and -3#, with Ce contents of 30, 50, and 70%, respectively; the primary phase in Al-Ce-3# is Al2Ce) with a multiscale structural design (comprising both micron-sized and nano-sized particles) into an ammonium perchlorate (AP) matrix. Al/AP reactive materials and Al-Ce/AP reactive materials with varying Ce contents were prepared. The thermal decomposition characteristics, dynamic mechanical properties, and impact ignition behavior were systematically investigated using differential scanning calorimetry (DSC) and split Hopkinson pressure bar (SHPB) experiments. The results demonstrate that the addition of Al2Ce significantly alters the thermal decomposition process of AP, substantially lowering its decomposition temperature (by approximately 69 °C) and promoting concentrated exothermic decomposition. SHPB tests reveal that Al2Ce/AP composites exhibit higher dynamic yield strength and flow stress than the Al/AP, accumulating faster strain energy density under impact loading, which indicates a more violent fragmentation failure mode. This enhanced mechanical failure behavior, which provides highly reactive interfaces and promotes hotspot formation, synergizes with the catalytic effect of Al2Ce on AP decomposition. Together, these mechanisms jointly improve the impact ignition sensitivity of the material, significantly lowering its ignition threshold and shortening its combustion duration. This study confirms that Al2Ce/AP is a novel reactive material combining excellent dynamic mechanical properties with outstanding impact reactivity, providing theoretical and technical support for the application of highly reactive rare-earth aluminum alloys in aluminum-based reactive materials.

This study investigates an adaptive die concept for cold extrusion that actively modulates radial preload during the main forming and ejection phases. A Gaussian process regression (GPR) surrogate, trained on fewer than 400 finite-element simulations, provides a highly data-efficient model capable of accurately predicting geometric tolerances, residual stresses, and process forces. Experimental spot measurements validate the physical trends captured by the surrogate, demonstrating reliable reproduction of the underlying mechanical interactions. The results show that increased preload during forming enables micrometer-level calibration of final diameters, while higher preload during ejection promotes beneficial compressive residual stresses at the cost of elevated ejector forces. A part-to-part control strategy effectively improves accuracy by independently steering two target properties through separate preload adjustments. Furthermore, a reinforcement learning-based controller, enhanced by flow stress estimates derived from hardness measurements, reduces variance and compensates for stochastic fluctuations in material and friction conditions. Overall, the adaptive die system, combined with surrogate-and RL-based control provides a robust foundation for achieving high dimensional precision and stable product properties under future variability scenarios, such as green steel and sustainable lubrication systems.

Abstract. Tubes with non-uniform thickness are needed to even out wall thickness in draw bending and provide higher stiffness in specific directions in some applications. Tailored local heating of the tubes in tube sinking operations should reduce the local flow stresses and facilitate differential deformation along the circumference of tubes to form tubes with uneven wall thicknesses. Local heating of tubes prior to entry into the die in tube sinking is implemented in this research to form tubes with higher thickness in desired directions. Initial experiments are conducted using plasma heating by tungsten inert gas (TIG) welding equipment on EN AW 6060 AlMgSi0.5 aluminum tubes. The process window is described by varying the process temperature (weld current between 50 A and 80 A) while altering the degree of deformation, the tube diameter, and tube thickness. Tubes with no defects were formed at 50 A. Increasing the weld current led to a higher wall thickness (up to 25% thickness increase), however, high weld currents also favored the formation of surface defects, wrinkle formation, or burn-through holes depending on the process setup. The process window was larger for tubes with higher wall thickness.

In the transition to a circular economy in the automotive sector, it is essential to integrate recycled (or secondary) aluminum alloys into extrusion processes, while ensuring that their performance is as close as possible to that of primary alloys. Within the Horizon Europe ZEvRA project, this study aims to analyze and investigate the hot deformation behavior of four aluminum alloys, two primary alloys (AA6082 Primary and AA7108) and two recycled alloys (AA6082 Recycled and AA6061), in order to demonstrate their potential suitability for automotive applications. Hot torsion tests were conducted under temperature and strain rate conditions representative of industrial extrusion processes. Four different temperatures (400, 450, 500, and 550 °C) and four different strain rates (0.01, 0.1, 1, and 10 s⁻¹) were investigated, allowing the achievement of significantly higher strain levels compared to conventional standard tensile and compression tests. Subsequently, the flow stress curves obtained from the torsion tests were analyzed to evaluate the influence of temperature and strain rate on the plastic deformation behavior of the material and on the associated dynamic softening mechanisms. The results demonstrate a comparable deformation behavior between primary and secondary alloys, confirming the feasibility and full compatibility of recycled alloys for high-performance industrial extrusion applications. Furthermore, the experimental results provide a solid basis for the development of robust constitutive models to support FEM simulations aimed at optimizing metal forming pocesses within a circular manufacturing framework.

BackgroundSigmoid sinus wall dehiscence (SSWD) is the most common etiology of venous pulsatile tinnitus (PT). However, the exact blood flow mechanisms of SSWD-PT remain unclear, and intracranial pressure is closely associated with its development. This study aimed to assess the hemodynamic characteristics of the sigmoid sinus in SSWD-PT patients with normal intracranial pressure using four-dimensional (4D)-flow magnetic resonance imaging (MRI) and explore potential noninvasive markers for identifying SSWD as the true etiology of PT.MethodsThis is a case-control study. We enrolled 23 SSWD-PT patients with normal intracranial pressure and 35 age-, sex-matched healthy controls. Hemodynamics of the sigmoid sinus were evaluated by 4D-flow MRI, including average velocity (Vavg), maximum velocity (Vmax), average and maximum through-plane velocity (Vtp_avg, Vtp_max), forward and backward flow volumes (FFV, BFV), average blood flow (Flowavg), regurgitant fraction (RF), and average wall shear stress (WSSavg). Blood flow patterns were visually evaluated for vortex or turbulence. Interobserver agreement was assessed using interclass correlation coefficient (ICC). Hemodynamic parameters in the bilateral sigmoid sinuses of controls were compared using paired samples t-test or Wilcoxon signed-rank test. Group differences between SSWD-PT patients and controls were assessed using independent samples t-tests or Mann-Whitney U tests for continuous variables and Chi-squared tests for categorical variables. Logistic regression analysis was performed to identify independent predictors and build a diagnostic model. Receiver operating characteristic (ROC) curves were used to assess the diagnostic efficacy of the hemodynamic parameters. Internal validation of the model was conducted using bootstrapping with 1,000 iterations to assess model stability and robustness. The P<0.05 was considered statistically significant.ResultsCompared with the corresponding side in controls, the symptomatic side of PT patients presented significantly higher Vavg (P<0.001), Vmax (P<0.001), BFV (P<0.001), RF (P<0.001), and WSSavg (P=0.002), and significantly lower Vtp_avg (P<0.001), FFV (P=0.006), and Flowavg (P<0.001). Vortex or turbulence were observed in 78.3% of symptomatic sigmoid sinuses (P<0.001). Interobserver agreement was excellent for all hemodynamic parameters (ICC =0.88–0.94). Logistic regression identified Vavg and WSSavg as independent predictors (both P<0.001). ROC analysis showed predictive value for Vavg [area under the curve (AUC) =0.880] and WSSavg (AUC =0.740), with the combination achieving superior performance (AUC =0.934; sensitivity 82.6%, specificity 94.3%, accuracy 87.9%, P<0.001). Bootstrapping validation confirmed the combined model’s stability (AUC =0.932, sensitivity 85.2%, specificity 89.8%, accuracy 88.0%).ConclusionsSSWD-PT patients with normal intracranial pressure demonstrated increased blood flow complexity and hemodynamic changes in the symptomatic sigmoid sinus. The combination of Vavg and WSSavg may serve as a noninvasive marker to identify SSWD as the true etiology of PT.

In cold bulk metal forming, coatings based on zinc phosphate are commonly used for lubrication. This has a negative impact on the environment, negatively affects human health, and requires significant pre-and post-surface treatments. Powder metallurgical (PM) components are a promising alternative to zinc phosphate coatings due to the process related porosity of the workpiece which acts as lubricant reservoir. During the forming process, the lubricant stored in the pores is released and lubricates the tool and workpiece surfaces. For an efficient process design of such components, finite element method (FEM) is an effective tool to analyse forming and friction behaviour. To this end, a realistic material model is essential for accurate simulation results. Hence, in this work, the flow behaviour of PM semi-finished products is characterised by means of compression and tensile tests. The results indicate that the material exhibits different behaviour under compression and tension. In compression, the material demonstrates higher yield strength and flow stresses compared to tension. Additionally, inhomogeneity of the material distribution can be observed, characterised by a denser core and more porous outer regions. The porous outer regions make it suitable for storing lubricant for application in forming processes.

Machine learning-assisted modelling of hot deformation behaviour in Inconel 718 alloy

ABSTRACT As-quenched lath martensitic steels exhibit a low elastic limit followed by high-strain-hardening without reasonable dislocation multiplication. The role of numerous dislocations in the unique stress–strain behaviour is unclear. Here, we investigated the obstacles to dislocation motion and evolution of dislocation properties (density, fraction of screw dislocations, and distribution parameter) using 0.1 mass%C steel with and without ausforming. X-ray line profile analysis revealed that these dislocation properties were barely changed after tensile tests. Stress relaxation tests indicated that the internal stress, arising from long-range obstacles such as dislocation tangles, constantly accounts for more than 90% of the applied stress. The effective stress, arising from short-range obstacles, was negligibly small at the elastic limit and increased proportionally with the internal stress. This trend implies that the short-range obstacles are dependent on dislocation density, such as dislocation intersections. These findings support two key conclusions: (1) At the elastic limit, dislocations are sufficiently mobile that the distance a dislocation moves is too short to cause dislocation intersections and (2) the strain hardening results from the sequential yielding of soft (low) to hard (high dislocation density) regions. Thus, the elevated flow stress observed in ausformed specimens is attributed to a higher initial screw dislocation density, which intensifies both internal and effective stresses.