Plastic Stress Research Articles

Modified plastic stress distribution method incorporating size effect for strength prediction of CFST members

Large-size concrete-filled steel tubular (CFST) members are widely applied in long-span and heavily-loaded structures due to increasing engineering demands. However, due to the size effect, applying the existing design methods to large-size CFST members may overestimate the load capacity, leading to unsafe designs. The plastic stress distribution (PSD) method is widely used as the primary method in typical design codes for calculating the strength of CFST members that are not susceptible to local buckling, while the PSD method was mainly used previously to evaluate the strength of CFST members with relatively small size. In this work, the experimental database of short CFST members with compact sections was complied, and the applicability of the PSD method was evaluated. The results showed that the test-to-calculated ratios decreased with increasing size of CFST members, and unsafe designs emerged for large-size CFST members. Based on the observations, the mechanics-based modified plastic stress distribution (MPSD) method was proposed, which not only considered the size effect at the material level similar to the way treated in most of the previous calculation methods, but also incorporated the size effect of the interaction action between the steel tube and concrete at the member level. Finally, the MPSD method was evaluated against the experimental database, and good agreement was achieved. These results provide strong justification for changes to the PSD method in design standards.

Seismic evaluation of steel beam-column connection equipped by circular slit dampers

AbstractThis study evaluates metallic yield dampers, specifically slit steel dampers, for protecting steel beam-to-column connections during seismic events. Finite element model simulations were conducted for the damper and its connection. Analysis of circular parameters, like the radius slot, showed that appropriately sized slit dampers exhibit advantageous seismic behavior. Moment-rotation, hysteresis curves, and plastic stresses comparisons indicate efficient energy absorption. The maximum moment was 25% lower than conventional samples. The slit steel damper model with a ductility factor of 3.5 allows significant plastic deformation before potential failure. Results emphasize the slit damper's potential for optimal performance in steel frames, suggesting its use for efficient energy absorption.

Research on fracture prediction and control of UHSS thin-walled component with complex section in roll forming process

Aiming at the fracture of an ultra-high-strength steel (UHSS) thin-walled component with complex section in the roll forming process, the three-dimensional finite element model was established. It is found that the stress triaxiality and equivalent plastic strain are the main factors affecting the fracture behaviour of the UHSS thin-walled component with complex section, and the influence laws of forming strategies and process parameters on the fracture behaviour were discussed. The results show that the damage value, equivalent plastic strain and stress triaxiality at the fracture position are reduced by increasing the inter-distance and roll diameter, decreasing friction coefficient and forming velocity. The mathematical model of the UDP comprehensive measure with the forming strategies and process parameters was established by the response surface method. The numerical simulation and industrial test verify the effectiveness of the UDP comprehensive measure, which provides a theoretical and practical basis for the fracture prevention control.

Numerical Simulation and Modeling of the Trielectrode-Coupled Corrosion Mechanism at the Laser-Welded Interface of N80 Steel

Laser welding, a prevalent technique in automotive structure manufacturing, can introduce compositional disparities and stresses within the weld zone, exacerbating corrosion complexity at the weld interface. This paper develops a triple galvanic corrosion model for N80 steel welds under stress conditions, leveraging the COMSOL software for simulations. The findings demonstrate that, within the elastic stress range, an elevation in stress intensifies the overall electrode surface potential, ultimately transitioning into plastic stress and fostering a more negative potential. This, in turn, amplifies the cathode-anode potential difference, rendering the material more susceptible to corrosion. The deeper the depression between the weld zone and the heat-affected zone, the higher this potential difference becomes, exacerbating the corrosion risk. Under stress, the corrosion rate markedly surpasses that observed in unstressed conditions. During the 160 day corrosion period, the weld seam and heat affected zone undergo a transition from plastic strain to elastic strain, while the base metal zone experiences both plastic strain and elastic strain simultaneously. This dynamic strain evolution leads to temporal variations in the stress-induced cathode-anode potential differences. In comparison to stress-free corrosion scenarios, the impact of stress on the cathode-anode potential difference initially intensifies, yet this effect tapers off over time.

Coupled effect of microstructure heterogeneity and hydrogen on local embrittlement of CGHAZ and IC-CGHAZ in X65 pipeline steel

The local embrittlement of the coarse-grained heat-affected zone (CGHAZ) and intercritically reheated CGHAZ (IC-CGHAZ) in X65 pipeline steel was investigated using an in situ crack-tip opening displacement test in air and H2S, combined with microstructure-based simulation. The IC-CGHAZ exhibited significantly lower cracking resistance, with the fracture toughness reduced by 50% compared to CGHAZ in both environments (0.160 mm in air and 0.017 mm in H₂S for IC-CGHAZ, compared to 0.307 mm in air and 0.034 mm in H₂S for CGHAZ). The martensite/austenite (M/A) constituents showed exceptionally higher intrinsic hardness than the ferrite matrix. The continuous distribution of M/As along the prior austenite grain boundaries resulted in local hardening and the formation of heterogeneous hard zones in IC-CGHAZ. Such microstructure heterogeneity resulted in the unique partitioning of plastic strain localization and stress triaxiality that promotes premature fracture, particularly with the coupled effect of hydrogen. This study provides a novel perspective on the fracture mechanisms and the typical fracture morphology of IC-CGHAZs in pipeline steel under the coupled effect of microstructure heterogeneity and hydrogen.

Inertia effect of deformation in amorphous solids: A dynamic mesoscale model

Shear transformation (ST), as the fundamental event of plastic deformation of amorphous solids, is commonly considered as transient in time and thus assumed to be an equilibrium process without inertia. Such an approximation however poses a major challenge when the deformation becomes non-equilibrium, e.g., under the dynamic and even shock loadings. To overcome the challenge, this paper proposes a dynamic mesoscale model for amorphous solids that connects microscopically inertial STs with macroscopically elastoplastic deformation. By defining two dimensionless parameters: strain increment and intrinsic Deborah number, the model predicts a phase diagram for describing the inertia effect on deformation of amorphous solids. It is found that with increasing strain rate or decreasing ST activation time, the significant inertia effect facilitates the activation and interaction of STs, resulting in the earlier yield of plasticity and lower steady-state flow stress. We also observe that the externally-applied shock wave can directly drive the activation of STs far below the global yield and then propagation along the wave-front. These behaviors are very different from shear banding in the quasi-static treatment without considering the inertia effect of STs. The present study highlights the non-equilibrium nature of plastic events, and increases the understanding of dynamic or shock deformation of amorphous solids at mesoscale.

INTERLAYER EFFECT ON DEFORMATION AND FRACTURE OF DENDRITIC STRUCTURE FORMED DURING WIRE-FEED ELECTRON-BEAM ADDITIVE MANUFACTURING OF AL-SI ALLOY

Interfaces and surfaces play an important role in tribology, mechanics and materials science, causing plastic strain localization and stress concentration of different spatial scales. The interfacial inhomogeneity is highly pronounced in 3D printed materials due to thermo-cycling and layer-by-layer building. In this paper, the inlayer and interlayer structure of a eutectic Al-Si alloy fabricated by wire-feed electron-beam additive manufacturing is investigated by optical and electron microscopy. Model structures inheriting the experimental morphology are created, and their deformation and fracture are simulated using ABACUS/Explicit, with the user-defined subroutines being developed to describe the constitutive behavior of aluminum dendrite, silicon and eutectic materials. A two-scale computational approach is implemented to study the influence of the interlayer formed in the heat-affected zone on the dendritic structure strength.

Mechanical properties and JC constitutive modification of tungsten alloys under high strain rates and high/low temperatures

The original Johnson-Cook model's poor prediction of W90 alloy stress at high strain rate and high and low temperatures restricts research and utilization of this alloy. This study used a Split Hopkinson Pressure Bar (SHPB) device to conduct dynamic compression tests on W90 alloy over a temperature range of [-90℃,700℃] and analyze its mechanical behavior. We examined the material's different plastic phase characteristics at high and low temperatures and conducted microstructure research on impact test specimens. Then, we analyzed the stress-strain data from SHPB experiments and quasi-static compression tests on the classical Johnson-Cook model. The original Johnson-Cook model was calibrated using the stress-strain data from SHPB and quasi-static compression tests, and the modified Johnson-Cook model was established and verified. The results show that: low temperature significantly strengthens the material's stress, while increasing temperature thermal softening reduces stress; increasing strain rate increases the strain generated by the workpiece, causing faster strain hardening and thermal softening effects, resulting in higher and more stable stress; low temperature makes thicker grain boundaries, increasing plastic stress, and increasing strain rate also increases plastic stress, as well as making the material's grain boundaries thicker. The increase of strain rate makes the grain more dense, which will also show up in the increase of stress on the macroscopic level; the modified Johnson-Cook model in this paper has high agreement with experimental data, with a mean value of MAPE of only 1.85 %,which is 90.20 % lower than the traditional model, and the average value of the RMSE is 85.56 % lower than the traditional model. The modified model significantly outperforms the traditional model in predicting stress and better describes stress changes in W90 at different temperatures.

Plastic Limit Pressure and Stress Intensity Factor for Cracked Elbow Containing Axial Semi-Elliptical Part-Through Crack

The aim of this study is to provide a solution for the plastic limit pressure and stress intensity factor of the elbows containing a part-through axial semi-elliptical crack by considering various crack sizes. The supporting system and loading conditions of the pipeline are described. The critical part of the observed pipeline was isolated for analysis and subjected to various sizes of semi-elliptical cracks. By performing numerical analysis, results were obtained for crack dimension ratios of c/a, and depth/thickness ratios of a/t. The obtained results include plastic limit pressure and stress intensity factor. The results were analyzed with a symbolic regression algorithm, and closed-form solutions for the limit pressure and stress intensity factor were proposed. To validate pipeline integrity, the Structural Integrity Assessment Procedure (SINTAP) was applied, and the FAD (Failure Assessment Diagram) was generated for cracks below the FAD function. The failure pressure was calculated by determining the points where the loading paths intersect the FAD function.

A phase‐field framework for stress corrosion cracking prediction in elastoplastic metallic materials

AbstractTo capture the stress corrosion cracking (SCC) in metallic materials, a phase‐field framework considering localized plastic deformation and stress states is established. A new function of critical energy release rate is proposed to describe the degradation of cracking resistance of materials in the SCC process. This proposed framework can reproduce SCC results consistent with experimental observations in C‐ring steel SCC tests, especially capturing the directionally characteristic of the cracks. Furthermore, the influences of localized plastic deformation and stress states on the SCC process are studied. This novel phase‐field framework can capture (1) the influences of coupled electricity, mechanics to the SCC mechanisms; (2) the contribution of plastic strain energy as the driving force for the phase‐field; (3) the potential and preferential crack initiation and propagation morphology within the complex stress and strain domain; and (4) the dependence of SCC rate and propagation direction on stress state and localized plastic deformation.

Numerical model for penetration process of a deformable projectile into ductile metallic target plate considering the interaction of projectile and target

The interaction of projectile and target in a penetration process is key for precise prediction and safety design. However, this interaction is instantaneous and varying with complex physical phenomena, that induces a challenge of panoramically illustrating the penetration process. This work develops a new numerical model that can capture the penetration process of a deformable projectile impacting ductile target plate and meanwhile the interaction of projectile and target is considered. Here, physical mechanisms are explored and accordingly mathematical derivations for theoretical analysis are carried out. The issues of plastic stress wave, contact stress, shear perforation and energy dissipation are involved. Both the deformation of projectile and failure of target plate are addressed which include the upsetting deformation of projectile, pit-opening performance of target plate and perforation of target plate. This model presents the history of the deformation of projectile and target, velocity evolution, penetration resistance and shear perforation with timing. The modelling results show a high-precision prediction by comparing with experimental data of a flat-ended projectile penetrating Weldox 460E steel target plate [54] and other developed models of plugging failure model [13] and plastic wave model [48] for both cases of 16mm- and 20 mm-thickness target plates. This work offers the comprehensive calculation and analysis of penetration process and reveals the insights of the transient phenomena for impact engineering.

Constitutive and impact response of AA7475-T7351 under different projectile shapes and velocities: An experimental and numerical investigation

Through experimental and numerical investigation, this article investigates the constitutive and impact response of the 1.6 mm thick AA7474-T7351 plate under the impact of blunt and hemispherical-nosed projectiles at different velocities. The Johnson-Cook plasticity and failure model parameters were calibrated for the target material using experimental data from the tensile experiments, which took into consideration the effects of plastic strain, strain rate, temperature and stress triaxiality. Further, JC plasticity model parameters were also optimised using a parametric optimisation process. The flow stress of AA7475-T7351 shows positive and negative sensitivity toward loading rate and temperature. It is observed that the ductility of AA7475-T7351 decreases with increases in stress triaxiality, whereas the flow stress increases. Perforation experiments on 1.6 mm thick circular AA7475-T7351 plates were carried out using a single-stage gas gun along with the high-speed Digital Image Correlation (3D-DIC) technique. The blunt nose projectile causes shear failure, whereas hemispherical nose projectile causes combined tension-shear failure; a microscopic study is performed to confirm this phenomenon. Experimental results obtained from DIC were validated using the numerical analysis in the Abaqus/Explicit platform in terms of transient out-of-plane deformation of the target plate. The quantitative error between experimental and numerical analysis was evaluated using the Russell error technique. Numerical analysis revealed that constitutive relations could predict the physical fracture mechanisms during perforation qualitatively as well as quantitatively.

Fretting fatigue of 42CrMo4+QT steel: Experimental and numerical assessment

This paper focuses on an experimental and numerical assessment of fretting fatigue in cyclically loaded specimens from 42CrMo4+QT steel in contact with bridge pads of the same material. Four different pad configurations were employed, varying the radii of the pad legs, to achieve various stress gradient conditions in the fatigue process zone. A qualitative change in terms of the number of contact initiation locations observed in relation to fatigue life served as one of the aspects of the evaluation of a set of 11 fatigue prediction methods. It was observed that elastic–plastic stress analysis is crucial for capturing this phenomenon. Among the tested methods, Papuga’s quadratic parameter criterion (QCP) performs best in terms of risk assessment of crack initiation and prediction of its location.

Effect of wet grinding carbonation of sintering red mud on the performance of carbon sequestered mortar

The use of alkaline solid waste to CO2 capture is a potential way to upgrade the recycling of solid waste and reduce CO2 emission. In previous work, we proposed a novel wet grinding carbonation technique to achieve rapid carbonation of sintering red mud (SRM). Herein, the effect of wet grinding carbonation of SRM (WGCS) replacement rate (0 %, 5 %, 10 %, 15 %, 20 % and 25 %) on the hydration and hardening of Portland cement was further explored, such as rheology, compressive strength, hydration products and water transfer properties. The plastic viscosity and yield stress of carbon sequestered paste rose together with the WGCS replacement rate, which was due to the decreased D50 of SRM after wet grinding carbonation. When the WGCS replacement rate was 15 %, the 56 d compressive strength of carbon sequestered mortar was increased by 14.1 %. The microscopic characterization showed that the nucleation of calcite crystals and the pozzolanic reaction of silica-rich gels clearly improved the microstructure compactness. The electric flux and porosity of cement mortar was decreased by 25.7 % and 11.4 %, respectively. In terms of environmental and economic benefits, the CO2 sequestration of carbon sequestered mortar reached as high as 24.7 kg/m3 and the CO2 emission was reduced by 30.9 %.

Blast resistance of 3D-printed Bouligand concrete panels reinforced with steel fibers: Numerical investigations

3D-printed concrete structures inspired by Bouligand architecture with helically twisted sequences exhibit excellent mechanical performance owing to its aligned fiber orientation. In this study, 3D-printed concrete panels with different numbers of layers (five, ten, and 15 layers) and spiral angles (0°, 15°, 30°, and 45°) are designed for numerical investigations of their blast-resistant capacity. A multi-scale model is developed to capture the isotropic and anisotropic properties of the fiber-concrete composite. The adequacy and accuracy of the model are evaluated and validated by experimental data in the literature. Blast resistance of different types of panels in terms of time histories of central-point deflection, contact explosion-induced plastic dissipation energy, stress propagation, and principal stress distribution is examined. It is found that extrusion-based concrete panels with aligned fiber orientation substantially enhance the blast resistance compared to traditional cast concrete panels with random fiber orientation. Furthermore, more layers of printed concrete panels prove to be more efficient in filtering blast waves. In particular, shifting a pitch angle of 30° after printing each layer plays an important role in reducing the maximum deflection. Meanwhile, 3D-printed concrete panels with a pitch angle of 0° can better mitigate blast-induced damage. Through parametric studies, the intrinsic mechanism of steel fibers aligned in 3D-printed panels is numerically analyzed to support the conclusions.

Study on unified strength theory and elastic–plastic stress update algorithm

The unified strength theory with the two-piecewise linear equations is more convenient and concise to calculate the strength of materials. It can fully explore the potential in the strength of materials and improve the economic benefits of engineering design. This study combines the semi-implicit return mapping algorithm and the Aitken accelerated iteration scheme and develops a plastic constitutive algorithm for isotropic softening materials based on the unified strength theory. The combining method can simplify the stress update and make the calculation of consistent tangent modulus easier. Furthermore, it can avoid solving the partial derivatives of the plastic flow rule and overcome the stress-deviating problem. The self-developed constitutive algorithm is used to simulate the elastic–plastic excavation process of a deep-lying circular tunnel. The numerical simulation results match well with the theoretical solution, verifying the correctness of the self-developed constitutive algorithm. Based on the self-developed constitutive algorithm, the stability of an underground mining stope is comprehensively analyzed, and its structural parameters are optimized. The research reveals the mechanism of stope instability, provides a reliable scientific basis for the mining design and decision-making, ensures the safe and efficient production of the stope, and achieves the expected goal.

Large‐scale elasto‐plastic topology optimization

AbstractThis work presents large‐scale elasto‐plastic topology optimization for design of structures with maximized energy absorption and tailored mechanical response. The implementation uses parallel computations to address multi million element three‐dimensional problems. Design updates are generated using the gradient‐based method of moving asymptotes and the material is modeled using small strain, nonlinear isotropic hardening wherein the coaxiality between the plastic strain rate and stress is exploited. This formulation renders an efficient state solve and we demonstrate that the adjoint sensitivity scheme resembles that of the state update. Furthermore, the KKT condition is enforced directly into the path dependent adjoint sensitivity analysis which eliminates the need of monitoring the elasto‐plastic switches when calculating the gradients and provides a straight forward framework for elasto‐plastic topology optimization. Numerical examples show that structures discretized using several millions degrees of freedom and loaded in multiple load steps can be designed within a reasonable time frame.

Creation of a nickel composite using surface structuring of the reinforcing phase with titanium carbide nanostructures to improve strength properties

Abstract The development of metal matrix composite (MMC) materials is one of the demanded areas of research in materials science. In line with this trend, there is an increasing interest in nickel-based MMC materials, which have already become classic in science and technology. This is due to the high demand for Ni-based materials with high strength characteristics, high hardness, and increased heat resistance. In this research, we proposed an approach to obtain a MMC material using the surface structuring process, ALD (Atomic Layer Deposition) and powder metallurgy method. The developed approach provides a composite with TiC nanostructures (1-5 nm) uniformly distributed throughout the Ni matrix. The absence of interphase boundaries between the Ni matrix particles and carbide nanostructures made it possible to minimize the internal porosity of the sample. This is due to the strength of the interphase boundaries between the matrix and the reinforcing phase in the composite and to the solidity of the structure. As a result, the created material effectively resists plastic deformation and stress. This allows not only to enhance the strength properties of the composite, but also to maintain the MMC plasticity, which increases its processing ability.

DSM design of cold-formed steel fixed-ended lipped channel columns undergoing distortional-global interaction

This work reports a numerical investigation dealing with the post-buckling behaviour, strength, and Direct Strength Method (DSM) design of cold-formed steel fixed-ended lipped channel columns experiencing coupling between distortional and global (flexural-torsional) buckling − distortional-global (D–G) interaction. Various cross-section dimensions and lengths are considered, to ensure that the columns selected undergo different levels and types (“true”, “secondary-bifurcation distortional” or “secondary-bifurcation global”) of D–G interaction. The results presented and discussed, determined by means of Abaqus shell finite element geometrically and materially non-linear analyses, consist of elastic and elastic-plastic post-buckling equilibrium paths, failure loads and collapse modes. The steel material behaviour is deemed elastic-perfectly plastic and several yield stresses are considered, thus making it possible to cover a wide column D–G slenderness range. Particular attention is devoted to identifying the most detrimental initial geometrical imperfection shapes, in the sense that they lead to the lowest column failure loads. The numerical failure load data gathered are subsequently used to assess the merits of the available DSM-based design approaches developed to handle cold-formed steel columns undergoing D–G interaction. Since these design approaches are shown to be either inefficient and/or improvable, the above failure load data are also used to propose modifications/improvements aimed at achieving an efficient failure load prediction in the specific context of fixed-ended lipped channel columns. The success of this endeavour provides encouragement to the authors in their search for a safe, accurate and reliable DSM-based design approach capable of handling cold-formed steel columns with arbitrary cross-section shapes and/or end support conditions that fail in D–G interactive modes.

Research on Stability of Mining Roadway of "Three Soft" Coal Seam based on FLAC3D

In order to reduce the serious roadway deformation during mining, the support scheme is optimized. Based on the actual geological data of mining roadway 11070, the plastic zone morphology, stress field and displacement distribution of roadway under different support schemes are analyzed by numerical simulation. The results show that scheme 1 has better supporting effect and higher roadway stability, which provides a reference for the same type of roadway support.