Explore the vast range of titles available.

Operational asymmetry is a characteristic feature of underground gas storage systems—particularly in salt caverns—where injection phases are typically longer and steadier than withdrawal phases, which are shorter and more abrupt in response to fluctuating energy demand. Although large-scale hydrogen storage in salt caverns remains under development, similar operational patterns are expected once such facilities reach commercial maturity. Understanding how this temporal imbalance influences the mechanical behavior of the cavern is therefore important for assessing long-term performance and supporting the development of robust operational strategies for future hydrogen storage systems. This study introduces a dimensionless parameter, χ , to quantify the temporal asymmetry of cyclic operation. χ accounts not only for the residence times at high and low pressure but also for the different durations required to reach and leave these states. It is defined as the ratio between the effective durations of the high-pressure and low-pressure stages, including both the holding and ramp phases. The numerator represents the total effective time under high-pressure conditions, which includes half of the filling ramp ( 0.5 τ fill ), the full high-pressure holding phase ( τ WGP ), and half of the withdrawal ramp ( 0.5 τ withd ). The denominator represents the complementary effective time under low-pressure conditions, consisting of half of the withdrawal ramp ( 0.5 τ withd ), the full low-pressure holding phase ( τ CGP ), and half of the filling ramp ( 0.5 τ fill ). This formulation expresses the relative exposure of the rock mass to stabilizing (high-stress) versus creep-promoting (low-stress) conditions. A viscoplastic numerical model is developed to reproduce the time-dependent deformation of salt under cyclic pressure loading. Two measurable indicators are analyzed: the vertical displacement at the cavern roof and the volumetric shrinkage associated with viscoplastic mechanical closure. Results show that temporal asymmetry exerts a dominant control on the long-term mechanical response. When χ > 1 —indicating longer effective residence under high pressure—the cavern evolves toward a steady-state equilibrium; when χ < 1 , viscoplastic deformation accelerates, promoting mechanical cavern closure. Comparison with operational data from three underground natural gas storage facilities in the United States is consistent with the χ ranges associated with the stability trends identified numerically. The proposed parameter χ thus provides a physically grounded and practical first-order indicator for interpreting long-term mechanical behavior in future hydrogen storage caverns, within the scope of a viscoplastic mechanical framework that does not explicitly account for damage, fracture, or permeability evolution. Article Highlights Hydrogen production can be used to store the excess from renewable sources. Temporal asymmetry is the key driver of long-term cavern stability. Operational data validate χ as a first-order temporal indicator for future hydrogen storage.

Placed at interfaces, azobenzene-containing materials show extraordinary phenomena when subjected to external light sources. Here we model the surface changes induced by one-dimensional Gaussian light fields in thin azopolymer films. Such fields can be produced in a quickly moving film irradiated with a strongly focused laser beam or illuminating the sample through a cylindrical lens. To explain the appearance of stripe patterns, we first calculate the unbalanced mechanical stresses induced by one-dimensional Gaussian fields in the interior of the film. In accordance with our orientation approach, the light-induced stress originates from the reorientation of azobenzenes that causes orientation of rigid backbone segments along the light polarization. The resulting volume forces have different signs and amplitude for light polarization directed perpendicular and parallel to the moving direction. Accordingly, the grooves are produced by the stretching forces and elongated protrusions by the compressive forces. Implementation into a viscoplastic model in a finite element software predicts a considerably weaker effect for the light polarized along the moving direction, in accordance with the experimental observations. The maximum value in the distribution of light-induced stresses becomes in this case very close to the yield stress which results in smaller surface deformations of the glassy azopolymer.

Purpose This study aims to investigate the compression characteristics of the 3D-printed polylactic acid (PLA) samples at temperatures below the glass transition temperature (Tg) with varying strain rates and develop a thermo-mechanical viscoplastic constitutive model to predict the finite strain compression response using a single set of material parameters. Also, the micro-mechanical damage processes are linked to the global stress–strain response at varied strain rates and temperatures through scanning electron microscopy (SEM). Design/methodology/approach Tg of PLA was determined using a dynamic mechanical analyzer. Compression experiments were conducted at strain rates of 2 × 10–3/s and 2 × 10–2/s at 25°C, 40°C and 50°C. The failure mechanisms were examined using SEM. A finite strain thermo-mechanical viscoplastic constitutive model was developed to analyze the deformations at the considered strain rates and temperatures. Findings Tg of PLA was determined as 55°C. While the yield and post-yield stresses drop with increasing temperature, their trend reverses with an increased strain rate. SEM imaging indicated plasticizing effects at higher temperatures, while filament fragmentation and twisting at higher strain rates were identified as the dominant failure mechanisms. Using a non-linear regression analysis to predict the experimental data, an overall R2 value of 0.98 was achieved between experimental and model prediction, implying the robustness of the model’s calibration. Originality/value In this study, a viscoplastic constitutive model was developed that considers the combined effect of temperature and strain rate for FDM-printed PLA experiencing extensive compression. Using appropriate temperature-dependent modulus and flow rate properties, a single set of model parameters predicted the rise in the gap between yield stress and degree of softening as strain rates and temperatures increased.

In order to study the permanent deformations of bituminous mixtures, a temperature-controlled triaxial test has been set up. By means of triaxial creep tests at imposed stress, the influence of different parameters on the behaviour of bituminous materials (confining pressure, deviatoric stress and temperature) has been investigated. A viscoelastic-viscoplastic model has been developed to simulate the creep tests and has shown good ability for simulating the test results.

A solution to improve the formability of aluminum alloy sheets can consist in investigating warm forming processes. The optimization of forming process parameters needs a precise evaluation of material properties and sheet metal formability for actual operating environment. Based on the analytical M-K theory, a finite element (FE) M-K model was proposed to predict forming limit curves (FLCs) at different temperatures and strain rates. The influences of initial imperfection value (f0) and material thermos-viscoplastic model on the FLCs are discussed in this work. The flow stresses of AA5086 were characterized by uniaxial tensile tests at different temperatures (20, 150, and 200 °C) and equivalent strain rates (0.0125, 0.125, and 1.25 s−1). Three types of hardening models (power law model, saturation model, and mixed model) were proposed and adapted to correlate the experimental flow stresses. The three hardening models were implemented into the FE M-K model in order to predict FLCs for different forming conditions. The predicted limit strains are very sensitive to the thermo-viscoplastic modeling of AA5086 and to the calibration of the initial geometrical imperfection which controls the onset of necking.

Using high‐resolution surface imaging and a split‐cylinder technique, we mapped the strain heterogeneity in Carrara marble samples deformed to bulk strains <25%, under conventional triaxial loading, at 400–700°C, 300 MPa confining pressure, and strain rates of 10−4 to 10−5 s−1. To map strain, we deposited grid markers on the polished surface of a half cylinder, performed mechanical tests on composites of two half cylinders, compared the positions of each marker in undeformed and deformed samples, and computed the spatial distribution of strain. Strains over the scale of a few microns varied by as much as 300%. Localized deformation occurred along twins and grain boundaries but was also present as patches in intragranular regions. The heterogeneity is more pronounced at scales smaller than grains, but the strain averaged over individual grains also varied by 50%. After deformation, the crystallographic orientation of individual grains relative to the compression direction was measured by electron backscattered diffraction. Inverse pole figures of the aggregate lattice‐preferred orientation (LPO) have a maximum near e(018) and are consistent with previous studies. The observed LPO is qualitatively consistent with that produced by simulations using a simple viscoplastic self‐consistent (VPSC) code that did not include mechanisms other than slip or twinning. The qualitative comparison of observed and simulated LPO was not sensitive to the model for the crystallographic resolved shear stresses for slip. However, the VPSC simulation was ineffective in predicting individual grain rotations.

Due to the rapid cooling and directional heat flow inherent in metal-based additive manufacturing, Ti-6Al-4V results in epitaxial grain growth and a fiber texture of the prior β phase. While Ti-6Al-4V produced via powder bed, electron beam melted processing can exhibit a range of strength characteristics, recent studies have shown superior strength properties, compared to similar orientations, of conventional plate material (AMS 4911) across a range of elevated temperatures (204 to 371 °C). To investigate this phenomenon, a series of crystal plasticity models was developed for the representative grain structures of Ti-6Al-4V to rationalize if the columnar, fiber texture produced by additive manufacturing (AM) was sufficient to explain the observed strength attributes. As a first step towards understanding this behavior, the grain structure was characterized via electron backscattering diffraction for AM material taken from four specimens (with different build directions), as well as material taken from baseline plate material (along and transverse to the rolling direction), and the resulting microstructures were modeled via a crystal plasticity framework. As expected, the results showed the AM material accounting for only the α grain structure was stronger in the vertical builds and weaker in the horizontal builds compared to the conventional plate counterparts. This suggested that grain morphology and α grain orientation alone provided some information about the relative strengths, but did not explain the overall trends observed from the experiments. To account for the role of texture, the characterized α phase was converted, via variant selection, to its prior β phase for use in the simulations. The results showed that each simulation of the AM prior β phase exhibited a higher strength compared to the baseline plate material, except for one specimen (horizontally built), which had large colonies of soft microtextured regions for the prior β structure. This suggests that some variability was experienced (as anticipated), but the texture (especially of the prior β macrozones) was a key contributor for the unusually high strength observed of the AM Ti-6Al-4V material.

In industrial applications, rolling is commonly performed with lubrication to prevent undesirable modification of the sheet. Although it is well established that lubrication influences the microstructure and texture of deformed sheets through its effect on shear deformation, the underlying mechanisms remain insufficiently understood. In this study, we investigated how lubrication affects slip system activity during asymmetrical rolling, using viscoplastic modeling of BCC ferritic steel. Two conditions—lubricated and non-lubricated samples—were examined under asymmetrical rolling. Slip system activity was inferred from the rotation axes between pairs of orientations separated by low-angle grain boundaries, based on the assumption that such boundaries represent the simplest form of orientation change. A Viscoplastic Self-Consistent (VPSC) model employing an affine linearization scheme was used. This proved sufficient for evaluating slip system activity in BCC polycrystalline metals undergoing early-stage plastic deformation involving either plane strain or combined plane strain and shear. The results demonstrated that lubrication had a limiting effect by reducing the penetration of shear deformation through the thickness of the sample. Understanding this effect could enable the optimization of lubrication strategies—not only to minimize defects such as bending, but also to achieve microstructural characteristics favorable for industrial applications.

Nonlinear finite element (FE) analysis of reinforced concrete (RC) structures is characterized by numerous modeling options and input parameters. To accurately model the nonlinear RC behavior involving concrete cracking in tension and crushing in compression, practitioners make different choices regarding the critical modeling issues, e.g., defining the concrete constitutive relations, assigning the bond between the concrete and the steel reinforcement, and solving problems related to convergence difficulties and mesh sensitivities. Thus, it is imperative to review the common modeling choices critically and develop a robust modeling strategy with consistency, reliability, and comparability. This paper proposes a modeling strategy and practical recommendations for the nonlinear FE analysis of RC structures based on parametric studies of critical modeling choices. The proposed modeling strategy aims at providing reliable predictions of flexural responses of RC members with a focus on concrete cracking behavior and crushing failure, which serve as the foundation for more complex modeling cases, e.g., RC beams bonded with fiber reinforced polymer (FRP) laminates. Additionally, herein, the implementation procedure for the proposed modeling strategy is comprehensively described with a focus on the critical modeling issues for RC structures. The proposed strategy is demonstrated through FE analyses of RC beams tested in four-point bending—one RC beam as reference and one beam externally bonded with a carbon-FRP (CFRP) laminate in its soffit. The simulated results agree well with experimental measurements regarding load-deformation relationship, cracking, flexural failure due to concrete crushing, and CFRP debonding initiated by intermediate cracks. The modeling strategy and recommendations presented herein are applicable to the nonlinear FE analysis of RC structures in general.

PurposeFused Filament Fabrication (FFF) is an extrusion-based manufacturing process using fused thermoplastics. Despite its low cost, the FFF is not extensively used in high-value industrial sectors mainly due to parts' anisotropy (related to the deposition strategy) and residual stresses (caused by successive heating cycles). Thus, this study aims to investigate the process improvement and the optimization of the printed parts.Design/methodology/approachIn this work, a meshless technique – the Radial Point Interpolation Method (RPIM) – is used to numerically simulate the viscoplastic extrusion process – the initial phase of the FFF. Unlike the FEM, in meshless methods, there is no pre-established relationship between the nodes so the nodal mesh will not face mesh distortions and the discretization can easily be modified by adding or removing nodes from the initial nodal mesh. The accuracy of the obtained results highlights the importance of using meshless techniques in this field.FindingsMeshless methods show particular relevance in this topic since the nodes can be distributed to match the layer-by-layer growing condition of the printing process.Originality/valueUsing the flow formulation combined with the heat transfer formulation presented here for the first time within an in-house RPIM code, an algorithm is proposed, implemented and validated for benchmark examples.