Material Constitutive Behavior Research Articles

Compressive behavior of concrete jacketed in basalt TRM shell: Experiments and predictions

Numerous studies have investigated the behavior of textile reinforced mortar (TRM)-confined concrete, yielding various stress-strain models predominantly derived from fiber-reinforced polymer (FRP)-confined concrete. Yet, these models frequently overlook the intricate constitutive behavior of TRM materials and inadequately capture how TRM delivers its confinement effects. This often leads to inaccurate representation of the true characteristics of the confinement system, particularly the crucial role of mortar. This paper focuses on the impact of variations in textile layers and mortar matrix strength on the stress-strain behavior of basalt TRM (BTRM)-confined concrete, aiming to enhance our understanding of the confinement mechanism. Additionally, the study critically evaluates the key components of an existing analysis-oriented stress-strain model for FRP-confined concrete and introduces a refined version that more precisely depicts the behavior of confined concrete. This refined model integrates an identified confinement mechanism to provide accurate predictions of BTRM-confined concrete behavior. Our results reveal that low-grade mortar significantly decreases the actual confinement stiffness of BTRM jackets, inducing a steeper decline in the stress-strain curve, while high-strength mortar slightly diminishes the hoop rupture strain. To address the challenges of quantifying the complex confinement effect-compounded by the variable stress state and constitutive behavior of TRM-a novel coefficient, termed km, is introduced to gauge the influence of mortar strength on the confinement stiffness within the confining pressure equation. Predictive outcomes, including stress-strain and axial-to-lateral strain curves, show close alignment with experimental data, particularly in the slope at the plateau stage. This research significantly advances the quantitative understanding of TRM confinement effects and proposes the potential for designing more ductile structures using these materials, which could lead to enhanced resilience against seismic events and other structural challenges.

Machine Learning Aided Modeling of Granular Materials: A Review

AbstractArtificial intelligence (AI) has become a buzzy word since Google’s AlphaGo beat a world champion in 2017. In the past five years, machine learning as a subset of the broader category of AI has obtained considerable attention in the research community of granular materials. This work offers a detailed review of the recent advances in machine learning-aided studies of granular materials from the particle-particle interaction at the grain level to the macroscopic simulations of granular flow. This work will start with the application of machine learning in the microscopic particle-particle interaction and associated contact models. Then, different neural networks for learning the constitutive behaviour of granular materials will be reviewed and compared. Finally, the macroscopic simulations of practical engineering or boundary value problems based on the combination of neural networks and numerical methods are discussed. We hope readers will have a clear idea of the development of machine learning-aided modelling of granular materials via this comprehensive review work.

REVIEW: Nonlinear shear rheometry: Brief history, recent progress, and challenges

High-shear rate rotational rheometry provides access to the fast nonlinear dynamics of soft materials and, particularly, their shear stress (exhibiting shear thinning and/or thickening) as well as the first and second normal stress differences, along with their time-dependent behavior. These material functions are valuable for understanding a material's processing performance and constitutive behavior and, hence, for designing new materials with desired rheology. However, their accurate measurement has been one of the most formidable challenges in rheometry. Here, we provide an overview of the different approaches used, along with their merits and drawbacks, while we discuss practical guidelines for the implementation of measurement protocols. We focus on the development and use of cone-partitioned plate fixtures, which have been shown to provide reliable data over a wide range of Weissenberg numbers, when properly used. Furthermore, this review presents selected applications and results from recent developments, identifies operating measurement windows, discusses new capabilities and open problems, and, finally, it provides perspectives for further developments.

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.

Post-fire structural material behaviour of high- and ultra-high-strength steels – Experimental study and aids for assessment for further use and potential reuse after fires

A thorough understanding and realistic modelling of the essential post-fire material behaviour is crucial for a safe assessment of the residual structural performance of steel components and the reliable further usage of steel structures after fires. This paper presents a comprehensive experimental study of the constitutive material behaviour after heating-cooling cycles of two quenched and tempered high-strength steels (S690QL, S960QL) as well as two thermomechanically rolled steels (S960M, S1100M). The results are compared to both the behaviour of grade S355J2+N mild steels and a comprehensive database of existing post-fire tests. Except for high- and ultra-high-strength steels, which are exposed to very high temperatures above the A1-phase-transformation-temperature during fires, the assumption of reversibility of the mechanical properties for structural designs of steel structures has been confirmed. At high and very high steel temperatures, the microstructure changes and the strength properties after fire are significantly lower than those of virgin high-strength steel specimens. The study thus provides the basis for reliable structural designs and future normative guidance of the post-fire structural steel designs.

Constitutive behavior of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy

The constitutive behavior of engineering materials can predict the change of flow stress with processing parameters, which is of great significance for the selection of processing parameters. In the present work, the constitutive behavior of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy was investigated by using thixotropic compression tests performed at semi-solid temperatures ranging from 500 °C–530 °C with strain rates ranging from 0.01 s−1–1 s−1, and the microstructure evolution was observed. The results indicate that the thixotropic compression deformation process of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy can be divided into three stages: the flow stress increasing stage, the flow stress decreasing stage and the steady-state flowing stage. The peak stress of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy increases with the increase of strain rate. With the increase of deformation temperature, the peak stress decreases obviously. A reasonable constitutive model of the peak stress of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy as a function of strain rate, deformation and liquid fraction was obtained. The average relative error between the calculated and experimental values is 6.35%.

Tensile Tests for Material Characterisation of High- and Ultra-High-Strength Steels S690QL and S960QL under Natural Fire Conditions

The mechanical material behavior of mild steels is reversible in the cooling phase of natural fires, which is proven by experimental evidence. For the material behavior of high-strength steels during cooling, no results are yet available. The paper provides the first comprehensive test program on the constitutive material behavior of high-strength steels S690QL and S960QL as well as mild steel S355 J2 + N in the case of natural fires. It is elaborated that the mechanical material behavior of high-strength steels in the cooling phase differs from the behavior in the heating phase and is not reversible due to phase changes of the microstructure. A constitutive material model for structural fire design purposes is developed on the basis of experimental data and the soundness and reliability of the model are proven by a statistical study that systematically evaluates the deviation of the model prediction from the test data.

Multiphysics-Lattice Discrete Particle Model: possible strategies for upscaling

The optimization of civil infrastructure maintenance and management is a challenging task, littered of open issues requiring the synergic development of effective structural health monitoring systems and reliable models to be addressed. Relevant to concrete structures, models cannot disregard the multi-physics nature of the problem: moisture and heat transport phenomena in uncracked and cracked conditions, the ingress of aggressive agents, and the ensuing chemical reactions - that the latter may trigger - heavily affect the mechanical performance. Most of the mentioned processes happen at a scale typically smaller than the structural one. Then, it is also necessary to perform multiscale analysis, capable of adapting structural models to the insights resulting from lower scale analyses. In the last decade, Multiphysics-Lattice Discrete Particle Model (M-LDPM) has been successfully adopted to model a wide range of phenomena in civil engineering involving concrete structural members: ageing, environment-induced degradation, shrinkage, creep, and usage of advanced construction materials. Furthermore, the discrete nature of the model has shown the capability of predicting the cracking patterns accurately. However, such a comprehensive and accurate model simulates the material at the mesoscale, and the path towards the exploitation of the insights resulting from lower-scale modelling at the structural level is paved of computational and theoretical burdens. In this work, a review of the state-of-the-art concepts that allow upscaling M-LDPM is presented. The aim is to explore alternatives for the formulation of computationally efficient macroscale models that leverage on both the predictive quality of M-LDPM in capturing and predicting the material constitutive behaviour, and the computational affordability that features the classical Finite Element Method for the structural analysis of complex systems.

The effect of tooling design and properties of materials on fracture and deformation through equal channel angular pressing technique

The submicrometer range of grain sizes was reached for AA5083 by using equal channel angular pressing at room temperature. While the submicrometer grains of AA5083 were stable up to annealing temperatures of 300 °C, the stability of these grains was only moderately maintained up to annealing temperatures of about 200 °C. Tensile tests conducted after one pass of equal channel angular pressing—that is, strain introduction of roughly one—showed a significant increase in the 0.2% proof stress and ultimate tensile stress values for each alloy. Concurrent with this improvement, the elongations to failure decreased. The analysis shows that the square root of the magnesium content in each alloy corresponds with the magnitudes of these stresses. In samples that were cold rolled, comparable values of proof stresses and ultimate tensile stress were obtained at equivalent strains. However, because of the induction of a very small grain size, elongations to failure were higher after applying equal channel angular pressing to similar strains greater than one. The effects of material constitutive behaviour, tool design, and friction conditions on metal flow, stress fields, and the tendency for tensile fracture during the equal channel angular pressing process were studied using a finite element modelling technique. A degree of non-uniform flow was noted that extended past the head and tail of the extrusion when materials were subjected to equal channel angular pressing with varying constitutive behaviours or when utilising tooling with a radiused front leg. It is anticipated that tool design and material qualities will have a considerable effect on tensile stresses and, in turn, the development of tensile damage during equal channel angular pressing.

Microstructure evolution accounting for crystal plasticity in the context of the multiphase-field method

The role of grain boundaries (GBs) and especially the migration of GBs is of utmost importance in regard of the overall mechanical behavior of polycrystals. By implementing a crystal plasticity (CP) theory in a multiphase-field method, where GBs are considered as diffuse interfaces of finite thickness, numerically costly tracking of migrating GBs, present during phase transformation processes, can be avoided. In this work, the implementation of the constitutive material behavior within the diffuse interface region, considers phase-specific plastic fields and the jump condition approach accounting for CP. Moreover, a coupling is considered in which the phase-field evolution and the balance of linear momentum are solved in each time step. The application of the model is extended to evolving phases and moving interfaces and approaches to strain inheritance are proposed. The impact of driving forces on the phase-field evolution arising from plastic deformation is discussed. To this end, the shape evolution of an inclusion is investigated. The resulting equilibrium shapes depend on the anisotropic plastic deformation and are illustrated and examined. Subsequently, evolving phases are studied in the context of static recrystallization (SRX). The GB migration involved in the growth of nuclei, which are placed in a previously deformed grain structure, is investigated. For this purpose, three approaches to strain inheritance are compared and, subsequently, different grain structures and distributions of nuclei are considered. It is shown, how the revisited method contributes to a simulation of SRX.

Viscoelastic constitutive artificial neural networks (vCANNs) – A framework for data-driven anisotropic nonlinear finite viscoelasticity

The constitutive behavior of polymeric materials is often modeled by finite linear viscoelastic (FLV) or quasi-linear viscoelastic (QLV) models. These popular models are simplifications that typically cannot accurately capture the nonlinear viscoelastic behavior of materials. For example, the success of attempts to capture strain (rate)-dependent behavior has been limited so far. To overcome this problem, we introduce viscoelastic Constitutive Artificial Neural Networks (vCANNs), a novel physics-informed machine learning framework for anisotropic nonlinear viscoelasticity at finite strains. vCANNs rely on the concept of generalized Maxwell models enhanced with nonlinear strain (rate)-dependent properties represented by neural networks. The flexibility of vCANNs enables them to automatically identify accurate and sparse constitutive models of a broad range of materials. To test vCANNs, we trained them on stress-strain data from Polyvinyl Butyral, the electro-active polymers VHB 4910 and 4905, and a biological tissue, the rectus abdominis muscle. Different loading conditions were considered, including relaxation tests, cyclic tension-compression tests, and blast loads. We demonstrate that vCANNs can learn to capture the behavior of all these materials accurately and computationally efficiently without human guidance. Our source code is available at https://github.com/ConstitutiveANN/vCANN.

On the Material Constitutive Behavior of the Aortic Root in Patients with Transcatheter Aortic Valve Implantation

BackgroundTranscatheter aortic valve implantation (TAVI) is a minimally invasive procedure used to treat patients with severe aortic valve stenosis. However, there is limited knowledge on the material properties of the aortic root in TAVI patients, and this can impact the credibility of computer simulations. This study aimed to develop a non-invasive inverse approach for estimating reliable material constituents for the aortic root and calcified valve leaflets in patients undergoing TAVI. MethodsThe identification of material parameters is based on the simultaneous minimization of two cost functions, which define the difference between model predictions and cardiac-gated CT measurements of the aortic wall and valve orifice area. Validation of the inverse analysis output was performed comparing the numerical predictions with actual CT shapes and post-TAVI measures of implanted device diameter.ResultsA good agreement of the peak systolic shape of the aortic wall was found between simulations and imaging, with similarity index in the range in the range of 83.7% to 91.5% for n.20 patients. Not any statistical difference was observed between predictions and CT measures of orifice area for the stenotic aortic valve. After TAVI simulations, the measurements of SAPIEN 3 Ultra (S3) device diameter were in agreement with those from post-TAVI angio-CT imaging. A sensitivity analysis demonstrated a modest impact on the S3 diameters when altering the elastic material property of the aortic wall in the range of inverse analysis solution.ConclusionsOverall, this study demonstrates the feasibility and potential benefits of using non-invasive imaging techniques and computational modeling to estimate material properties in patients undergoing TAVI.

Leadfree SnAgCu Solder Materials Characterization at High Strain Rates at Low Test Temperatures and Drop and Shock Simulation Using Input-G Method

Abstract Electronics will experience high and low working temperatures during operations, handling, and storage in severe environments applications such as download drilling, aircraft, and transportation. Temperatures in the vehicle underhood applications can range from −65 °C to +200 °C. Lead-free solder materials continue to evolve under varying thermal workloads. Material characteristics may deteriorate if operating conditions are harsh or heavy. Nonetheless, lead-free solders are susceptible to high strains, which can lead to electronic device failure. A better understanding of solder alloys is needed to ensure reliable operation in harsh environments. New doped solder alloys have recently been created by adding Ni, Co, Au, P, Ga, Cu, and Sb to SnAgCu (SAC) solder alloys to improve mechanical, thermal, and other qualities. SAC-Q has recently been made using Sn–Ag–Cu and the addition of Bi (SAC+Bi). It was discovered that adding dopants to SAC alloys may enhance mechanical characteristics and reduce aging damage. There is no published data on SAC solder alloys after prolonged storage at high strain rates and low functioning temperatures. The materials characterization of SAC (SAC105 and SAC-Q) solder after extended storage at low working temperatures (−65 °C–0 °C) and high strain rates (10–75 per sec) is investigated in this article. To characterize the material constitutive behavior, the Anand viscoplastic model was utilized to derive nine Anand parameters from recorded Tensile data. The generated nine Anand parameters were used to validate the Anand model's reliability. A strong correlation was established between experimental data and Anand's predicted data. The Anand parameters were used in a finite element framework to simulate drop events for a ball-grid array package on printed circuit board assembly to calculate hysteresis loop and plastic work density. The plastic work per shock event measures the damage progression of the solder interconnects. Thermal aging effects have been studied in terms of the hysteresis loop and the evolution of PWD.

Investigation of microstructure evolution accounting for crystal plasticity in the multiphase‐field method

AbstractRegarding microstructured materials, a quantitative prediction of phase transformation processes is highly desirable for a wide range of applications. With respect to polycrstalline materials, the plastic material behavior is commonly investigated using a crystal plasticity (CP) theory, since it accounts for the underlying microstructure, that is, slip systems of the crystal lattice. In classical continuum mechanics, grain boundaries (GBs) are commonly modeled as material singular surfaces. However, the tracking of moving GBs, present during phase transformation processes, is numerically challenging and costly. This can be circumvented by the use of a multiphase‐field method (MPFM), which provides a numerically highly efficient method for the treatment of moving interfaces, considered as diffuse interfaces of finite thickness. In this work, the microstructural evolution is investigated within the MPFM accounting for CP. The implementation of the constitutive material behavior within the diffuse interface region accounts for phase‐specific plastic fields and the jump condition approach. To improve the understanding of the impact of plastic deformation on the phase evolution, a single inclusion problem is analyzed. Within a plastically deformed matrix, the shape evolution of a purely elastic inclusion with a different Young's modulus, referred to as inhomogeneity, is investigated. It is shown, how the anisotropic plastic behavior affects the phase evolution. The resulting equilibrium shapes are illustrated and examined.

Influence of X-Ray beam exposure on the development of gas bubbles during triaxial testing of sand using 3D synchrotron micro-computed tomography

The constitutive behavior of granular materials is highly influenced by the degree of saturation and whether a saturated or unsaturated framework is adopted to model the behavior of granular materials. Conventional axisymmetric triaxial compression (CTC) testing of saturated specimens tends to assume that the specimen remains saturated during shearing. X-ray computed tomography (CT) has allowed for 3D in-situ measurements beyond the global scale to investigate microscale and localized events such as fabric evolution. The literature reported several CT-coupled geotechnical experiments of saturated specimens; however, no study examined how X-ray exposure might affect the specimen, specifically the radiolysis of pore water. In this study, we present the synchrotron micro-computed tomography (SMT) results of experiments performed on sand specimens without shearing (acrylic tubes) and with shearing (CTC experiments) to assess the influence of X-ray exposure on the development of the gas phase of saturated sand. The observed phase changes were dependent on the initial pore water pressure and duration of exposure to the X-ray; the behavior of individual gas bubbles was dependent on the bubble’s surrounding sand grains and pore throat sizes leading to changes in the degree of saturation.

Material characterisation tests of ultra‐high‐strength steels S960QL and S1100M under natural fire conditions

AbstractFire hazards represent one of the most important threats to the built environment with serious economic consequences for society and most dangerous threats to life. Fire engineering is the key discipline to improve fire safety in the building environment in a cost‐effective manner. Comprehensive knowledge of the material behavior is the basis for a thorough understanding and a realistic modeling of the structural fire behavior of steel structures. For state‐of‐the‐art buildings with increasing requirements, the utilization of high‐strength steels is favorable, as they can contribute to resource and energy efficiency due to their good strength‐to‐weight ratio. Modern production processes enable the production of structural steels with very high nominal yield strengths. For those ultra‐high‐strength steels there are currently no experimental results available regarding the material behavior in case of fire and the post fire residual strengths. The paper provides experimental data of the first test program regarding the constitutive material behavior of ultra‐high‐strength steels of grades S960QL and S1100M in the case of fire, taking into account the entire fire progress including the heating and cooling phases and the post fire range.

Numerical analysis of the impact behaviour of a composite eco-structure

An explicit numerical model is developed for the impact behaviour of a new composite eco-structure made of a plywood core and flax/epoxy composite skin. A constitutive orthotropic material behaviour is imposed to model the elastic response of plies of plywood core and flax skin. A stress-based modified Hashin-3D damage model with four independent failure criteria in tensile and compressive mode is incorporated for predicting the damage initiation. A strain threshold based exponential method is adopted to predict the damage scaling and its evolution. The above proposed model is implemented through user material subroutine (VUMAT) in ABAQUS Explicit. The developed model is validated with experimental low-velocity impact test results and can accurately predict the stiffness degradation, plateau, and post-peak softening of wooden plies. A good agreement with the better accuracy is achieved between the predictions and the test results.

Mechanical Characterization of MWCNT-Reinforced Cement Paste: Experimental and Multiscale Computational Investigation.

Computational approaches could provide a viable and cost-effective alternative to expensive experiments for accurately evaluating the nonlinear constitutive behavior of cementitious nanocomposite materials. In the present study, the mechanical properties of cement paste reinforced with multi-wall carbon nanotubes (MWCNTs) are examined experimentally and numerically. A multiscale computational approach is adopted in order to verify the experimental results. For this scope, a random sequential adsorption algorithm was developed to generate non-overlapping matrix-inclusion three-dimensional (3D) representative volume elements (RVEs), considering the inclusions as straight elements. Nonlinear finite element analyses (FEA) were performed, and the homogenized elastic and inelastic mechanical properties were computed. The use of a multiscale computational approach to accurately evaluate the nonlinear constitutive behavior of cementitious materials has rarely been explored before. For this purpose, the RVEs were analyzed both in pure tension and compression. Young's modulus as well compressive and tensile strength results were compared and eventually matched the experimental values. Moreover, the effect of MWCNTs on the nonlinear stress-strain behavior of reinforced cement paste was noted. Subsequently, three-point bending tests were conducted, and the stress-strain behavior was verified with FEA in the macro scale. The numerical modeling reveals a positive correlation between the concentration of MWCNTs and improved mechanical properties, assuming ideal dispersion. However, it also highlights the impact of practical limitations, such as imperfect dispersion and potential defects, which can deteriorate the mechanical properties that are observed in the experimental results. Among the different cases studied, that with a 0.1 wt% MWCNTs/CP composite demonstrated the closest agreement between the numerical model and the experimental measurements. The numerical model achieved the best accuracy in estimating the Young's modulus (underestimation of 13%), compressive strength (overestimation of 1%), and tensile strength (underestimation of 6%) compared to other cases. Overall, these numerical findings contribute significantly to understanding the mechanical behavior of the nanocomposite material and offer valuable guidance for optimizing cement-based composites for engineering applications.

Durability and Performance Analysis of Polymer Electrolyte Membranes for Hydrogen Fuel Cells by a Coupled Chemo-mechanical Constitutive Model and Experimental Validation.

In this paper, a chemo-mechanically coupled behavior of Nafion 212 is investigated through predictive multiphysics modeling and experimental validation. Fuel cell performance and durability are critically determined by the mechanical and chemical degradation of a perfluorosulfonic acid (PFSA) membrane. However, how the degree of chemical decomposition affects the material constitutive behavior has not been clearly defined. To estimate the degradation level quantitatively, fluoride release is measured. The PFSA membrane in tensile testing shows nonlinear behavior, which is modeled by J2 plasticity-based material modeling. The material parameters, which contain hardening parameters and Young's modulus, are characterized in terms of fluoride release levels by inverse analysis. In the sequel, membrane modeling is performed to investigate the life prediction due to humidity cycling. A continuum-based pinhole growth model is adopted in response to mechanical stress. As a result, validation is conducted in comparison with the accelerated stress test (AST) by correlating the size of the pinhole with the gas crossover generated in the membrane. This work provides a dataset of degraded membranes for performance and suggests the quantitative understanding and prediction of fuel cell durability with computational simulation.

Strain rate effect and dynamic constitutive model of 7A04-T6 high-strength aluminium alloy

In recent decades, various aluminium alloys have been developed and employed in construction engineering. They are light, corrosion-resisting and recyclable, making them attractive to engineers and researchers. Among these aluminium alloys, 7A04 high-strength aluminium alloy, which is an Al-Zn-Mg-Cu alloy, has now gained focus for its excellent strength-to-weight ratio, hardness, formability, etc. To date, the investigations into its dynamic mechanical properties are still limited. In this context, the mechanical behaviour of 7A04-T6 aluminium alloy at high strain rates was studied in this work. A split Hopkinson pressure bar test system was employed to conduct the dynamic experiments. 6061-T6 aluminium alloy was also included in the tests for reference. Then, comparisons were made between the tested 7A04-T6 and 6061-T6 aluminium alloys and among the studied 7A04-T6 aluminium alloy and steels with approximate yield strengths (Q420 and Q550 structural steels) and similar strength-density ratios (4340 M and Aermet 100 steels), to assess the strain rate sensitivity of 7A04-T6 aluminium alloy. Based on the Johnson-Cook model and the Cowper-Symonds model, which are widely used models that describe the dynamic constitutive behaviour of metallic materials, a modified dynamic constitutive model was developed for 7A04-T6 aluminium alloy, in which the influence of deformation-induced temperature rise on the dynamic mechanical properties is well considered.