Constitutive Model Research Articles

Hot Deformation Behavior of DT4 Pure Iron in the Austenite Single‐Phase Region: Experiment and Finite Element Simulation

The control of grain size and uniformity during the rolling process of DT4 electromagnetic pure iron is critical for its coercive force. Dynamic recrystallization during hot processing is closely related to grain size and uniformity control; therefore, the study of hot deformation and dynamic recrystallization process of DT4 in the γ‐phase region is essential. A 60% hot deformation of DT4 is conducted at temperatures of 950, 1000, and 1050 °C, respectively, with strain rates ranging from 0.01 to 10 s−1. The results indicate that in the γ‐phase region, after hot compression, the grain size and recrystallization fraction of DT4 decrease as the strain rate increases and the temperature decreases. A constitutive model and dynamic recrystallization model for DT4 are established, which can be used to predict the flow stress, recrystallization fraction, grain size, and critical strain of DT4, based on deformation temperature, strain rate, and strain. The dynamic recrystallization model is integrated into the Deform‐3D to simulate the critical strain during the hot deformation process of DT4. According to the correlation coefficient (R) and root mean square error results, the simulated data are consistent with the experimental data.

Robustness Analysis of a Constitutive Model for Cemented Carbide Sintering

Robustness Analysis of a Constitutive Model for Cemented Carbide Sintering

Statistical Damage Constitutive Model for Mudstone Based on Triaxial Compression Tests

For the purpose of precisely depicting the failure and deformation of mudstone at varying burial depths under engineering activities, a statistical meso-damage constitutive model of mudstone was established on the basis of continuum damage mechanics, with the adoption of the compound power function and the Mohr–Coulomb yield criterion. Through triaxial compression tests under diverse confining pressures, the validity of this constitutive model was verified, and the macroscopic effects of mudstone damage evolution induced by internal defects and alterations in meso-structures were analyzed. The results reveal that an increase in confining pressure can remarkably enhance both the peak strength and the residual strength of mudstone. The constitutive model demonstrates relatively high accuracy in predicting the stress–strain responses, as well as the residual strength of mudstone. Moreover, parameter ε0 is capable of reflecting the macroscopic deformation strength of mudstone. Specifically, the larger the value of parameter ε0 is, the greater the peak deviatoric stress of mudstone will be, accompanied by a stronger bearing capacity. Parameter m, on the other hand, governs the brittle-to-ductile transition characteristics under failure. It also demonstrates that the macroscopic brittle failure characteristics of mudstone will become more noticeable as the value of parameter m increases.

Repeated Loading and Damage Progression in Cerebral Arteries.

Repeated Loading and Damage Progression in Cerebral Arteries.

A modified elastoplastic damage structural constitutive model of unsaturated Q3 undisturbed loess

The weakening of loess structure under hydro-mechanical effect is an important reason for collapsible deformation of loess. Therefore, when establishing the constitutive model of unsaturated loess, it is necessary to consider the influence of loess structure to truly reflect the mechanical characteristics. A modified elastoplastic damage structural constitutive model (MEDSCM) is proposed for unsaturated Q3 undisturbed loess based on the modified Barcelona basic model (MBBM), assuming that the yield stress of undisturbed loess is a coupling of remolded loess and structure, and adopting the non-associated flow rule. The structural evolution equations of unsaturated Q3 loess in loading and collapsing are introduced respectively, and obtained the constitutive model of soil skeleton in loading and collapsing. There are a total of 18 parameters for the loading model and 15 parameters for the collapsibility model, which are determined by mechanical tests on unsaturated loess. By comparing the triaxial compression and collapsible test data with the model calculation results, the accuracy of the model is verified, and progress has been made in describing the weak hardening characteristics of unsaturated loess. The research results provide a new attempt for further understanding the mechanical properties of loess.

Exploring the time-dependent behaviors of the rock mass roof of tunnels in open underground spaces of coal mines through numerical investigation

The stability of rock mass roofs in open underground spaces of coal mines in Iran is a critical concern, as it can have significant implications for mine safety and productivity. The rock mass roofs are prone to degradation and failure due to various factors, including mining-induced stress, water infiltration, and mechanical damage. However, there needs to be more understanding of the time-dependent behaviors of these rock mass roofs. This study aims to investigate the time-dependent behaviors of rock mass roofs in tunnels of open underground spaces of coal mines in Iran using numerical simulations. A 3D numerical model was developed using finite element modeling. The model was validated using field measurements and laboratory tests. The study revealed that the rock mass roof exhibits significant time-dependent behavior in response to mining-induced stress, water infiltration, and mechanical damage. The results show that the rock mass roof deforms significantly over time, increasing the risk of instability and collapse. The study also investigated the influence of bedding planes and roof support on time-dependent behavior, demonstrating the importance of considering these factors in numerical simulations. A novel constitutive model was developed to represent the strain-softening behavior, creep, and relaxation of rocks, as well as strength deterioration with accumulated viscous deformation. The study identified the critical factors contributing to this deformation and instability, including high-stress zones, water infiltration pathways, and mechanical damage. The findings provide valuable insights for developing effective monitoring and mitigation strategies to ensure the safety and productivity of coal mines in Iran.

Dynamic Compressive Damage Constitutive Correction of Concrete Under Freeze-Thaw Cycle

In order to investigate the uniaxial dynamic compression constitutive model for concrete under freeze-thaw conditions, a finite element analysis was employed to model the temperature field of the concrete. The resulting data were subsequently integrated into the thermal stress field as a predefined parameter for a sequentially coupled thermal stress analysis. Following this, a numerical simulation was performed to assess concrete damage progression during a dynamic compression test in a freeze-thaw setting. The constitutive model was developed by adjusting the parameters that govern the development of concrete damage within the uniaxial stress-strain relationship, as specified in the Code for Design of Concrete Structures. The uniaxial compression behavior of concrete subjected to freeze-thaw was simulated utilizing both the modified intrinsic model and the damage plasticity model available in the software while accounting for the effects of the damage factor. The findings indicate that the modified constitutive model aligns closely with the actual experimental results. These research outcomes have potential applications in numerical simulations and various engineering practices related to concrete.

A coupled level set‐arbitrary Lagrangian–Eulerian method applied to numerical simulation of parison pinch‐off in extrusion‐blow molding

AbstractAn outstanding problem in extrusion blow‐molding process of polymers is the precise prediction of the parison shape inside the part along the pinch‐off weld. Such a prediction is highly relevant for producing components with an accurate wall thickness distribution along the parting line as blow‐molded parts often fail at the parison pinch‐off weld of the mold parting line. In this paper, we report on the numerical study of the parison pinch‐off modeling in extrusion‐blow molding using a coupled level set (LS)‐arbitrary Lagrangian–Eulerian (ALE) method. The deformation of the parison‐free surface during the mold closing stage is approximated by means of the level set technique on a deforming mesh domain caused by the simultaneous mold halves displacement. The multi‐mode Phan‐Thien and Tanner (mPTT) constitutive equation is employed to model the parison deformation in the pressure zone, the flash pocket, and along the pinching edge. The developed LS–ALE approach is first validated on a benchmark squeeze flow problem between two parallel coaxial disks for both Newtonian and viscoelastic fluids before the numerical simulation results for the pinch‐off problem are discussed. We report numerical experiments related to the mold closing velocity effects on the parison shape behavior and parison wall thickness distribution along the pinch‐off weld for a high‐density polyethylene (HDPE). For this viscoelastic polymer, the parison exhibits a rounded shape along the pinch‐off weld line inside the part, and this rounding becomes more pronounced as the mold closing velocity increases, in accordance with experimental observations. Whereas, for a Newtonian fluid, the parison displays an angular V‐shape along the pinch‐off weld inside the part and does not depend on the mold closing speed. The parison thickness along the weld line is increased by 126% for the HDPE studied while it only increases by 72% for a Newtonian fluid with the same zero shear‐rate viscosity. The predicted parison wall thickness distribution around the pinching zone represents an important step in optimizing both processing conditions and the mold pinch‐off design.Highlights A coupled LS–ALE method was developed to simulate parison pinch‐off. The method successfully validated on squeeze flow for Oldroyd‐B fluid. Viscoelastic fluids exhibit a rounded shape at pinch‐off weld inside part. Newtonian fluids exhibit a V‐shape along pinch‐off weld inside part. Material rounded shape inside part increases with mold closing speed.

Numerical Investigation of the Impact of Processing Conditions on Burr Formation in Carbon Fiber-Reinforced Plastic (CFRP) Drilling with Multiscale Modeling

Burrs generated during the drilling of carbon fiber-reinforced plastics (CFRPs) would seriously reduce the service life of the components, potentially leading to assembly errors and part rejection. To solve this issue, this paper proposed a finite element (FE) model with multiscale modeling to investigate the formation and distribution of burrs at various processing conditions. The FE model comprised the microscopic fiber and resin phases to predict the formation process of burrs, while part of the CFRP layers was defined to be macroscopic equivalent homogeneous material (EHM) to improve the computational efficiency. A progressive damage constitutive model was proposed to simulate the different failure modes and damage propagation of fibers. The impact of strain rate on the mechanical properties of the resin and CFRP layers was considered during the formulation of their constitutive models. With this numerical model, the formation process of the burrs and the drilling thrust force were accurately predicted compared to the experimental measurements. Then, the burr distributions were analyzed, and the influences of the drill bit structures and drilling parameters on burrs were assessed. It was concluded that the burrs were easily generated in the zones with 0° to 90° fiber cutting angles at the drilling exit. The sawtooth structure could exert an upward cutting effect on burrs during the downward feed of the tool; thus, it is helpful for the inhibition of burrs. More burrs were produced with higher feed rates and reduced spindle speeds.

New Class of Complex Models of Materials withPiezoelectric Properties with Differential Constitutive Relations of Fractional Order: An Overview

Rheological complex models of various elastoviscous and viscoelastic fractional-type substances with polarized piezoelectric properties are of interest due to the widespread use of viscoelastic–plastic bodies under loading. The word “overview” used in the title means and corresponds to the content of the manuscript and aims to emphasize that it presents an overview of a new class of complex rheological models of the fractional type of ideal elastoviscous, as well as viscoelastic, materials with piezoelectric properties. Two new elementary rheological elements were introduced: a rheological basic Newton’s element of ideal fluid fractional type and a basic Faraday element of ideal elastic material with the property of polarization under mechanical loading and piezoelectric properties. By incorporating these newly introduced rheological elements into classical complex rheological models, a new class of complex rheological models of materials with piezoelectric properties described by differential fractional-order constitutive relations was obtained. A set of seven new complex rheological models of materials are presented with appropriate structural formulas. Differential constitutive relations of the fractional order, which contain differential operators of the fractional order, are composed. The seven new complex models describe the properties of ideal new materials, which can be elastoviscous solids or viscoelastic fluids. The purpose of the work is to make a theoretical contribution by introducing, designing, and presenting a new class of rheological complex models with appropriate differential constitutive relations of the fractional order. These theoretical results can be the basis for further scientific and applied research. It is especially important to point out the possibility that these models containing a Faradаy element can be used to collect electrical energy for various purposes.

Pressings shape evaluation by modern contactless methods

As part of the Industry 4.0 concept, companies are adopting new processes that utilize contactless methods to assess the shapes of pressings. Evaluating the pressings is essential due to the springback phenomena that occur after plastic deformation, which is more pronounced when high-strength steels are used in car bodies. Although photogrammetric methods based on 2D images have been used in the industry for over a decade, 3D optical scanning methods are preferred because they offer increased precision. This article evaluated cylindrical pressings made of dual-phase steel DP800 with a thickness of 1.6 mm—specifically flat-bottomed and hemispherical-bottomed cups. The shape of the pressings was determined using optical scanning with the GOM Scan 1 device alongside a photogrammetric system called ARGUS. The surfaces obtained from both methods were then compared to assess the accuracy of the scanned surface against the real surface acquired through photogrammetry. The scanned surfaces of the pressings were also used to compare the results of numerical simulations conducted in PamStamp software. In these simulations, the material was modelled using two sets of constitutive laws: the Hill48 yield law combined with the Hollomon hardening law as the first set and the Vegter Lite yield law combined with the Krupkowski hardening law as the second set. Real cups with a diameter of 50 mm were created using a deep-drawing process on the Erichsen 145-60 testing machine, starting with a blank diameter of 90 mm and lubricated with plastic foil to preserve the electrochemically etched grid. A comparison between the scanned surfaces and the real surfaces obtained through photogrammetry showed a strong correlation, validating 3D scanning as an effective method for evaluating pressing shapes. Furthermore, comparing the scanned surfaces with the results of the numerical simulations demonstrated similar findings for both sets of constitutive laws used to model the dual-phase steel in the experiments.

Understanding entangled human-technology-world relations: use of intelligent voice assistants by older adults

Introduction. Emerging technologies like intelligent voice assistants or social robots can shape human relations with the world. To illustrate how an emerging technology mediates relations and shapes social practices in the context of aging, we present findings on use of voice assistants by older adults. Method. We analysed interviews with 24 older adults by adopting a post-phenomenological perspective to examine how an emerging technology actively mediates relations between older individuals and their larger social world. Results. Our findings surface the different types of relations that voice assistants mediate between older adults and their larger social world, unpacking how these relations shape social practices around what it means to give company to pets, to live alone, or to give and receive care. Discussion. We discuss implications for understanding the mutually constitutive relations between older adults and the emerging technologies they use and opportunities in designing to support neglected relations, and accounting for nonhuman actors in technology and aging research. Conclusion. We provide a preliminary understanding on how an emerging technology shapes social practices in later life. This understanding is crucial for aging and technology research, as several emerging technologies (e.g., social robots) target older adults, yet little is known about the relationships and discursive practices that shape their use.

Ambivalence and Agonism of Public Participation in Contemporary Societies

In this editorial we introduce the thematic issue “Public Participation Amidst Hostility: When the Uninvited Shape Matters of Collective Concern.” The aim of this issue is twofold. First, it takes stock of various ways in which public participation can be hindered, directly and indirectly. Second, it investigates different kinds of participatory practices that emerge in situations of hostility towards public participation. Given that participation in such situations often involves working around formal procedures and public spaces and depends on remaining hidden, particular attention is paid to de‐publicised participatory practices. Overall, the articles in this thematic issue show how hostilities co‐develop with specific participatory practices that, in turn, attune to, navigate, and resist the particular (hostile) circumstances in which they arise. The articles draw attention to the ambivalence and, in some cases, agonistic quality of participatory processes in contemporary societies, where mutually constitutive relations between participation and hostilities towards it shape matters of collective concern, political agendas, and possible futures.

Prediction of Residual Stresses During the Hot Forging Process of Spherical Shells Based on Microstructural Evolution

A unified viscoplastic constitutive model based on internal physical variables was proposed to predict the viscoplastic mechanical behavior and microstructure evolution of metals during hot forging. Based on the phase transformation theory of materials under the effect of temperature, the evolution mechanism of residual stress during the cooling process after hot forging and stamping was explored. The determined unified viscoplastic constitutive equation was written in the VUMAT subroutine and employed for the explicit FE analysis of the hot forging and stamping process of thin-walled spherical shells. In the data transfer process, the stress field, temperature field, and deformation characteristics calculated during the high-temperature transient of the hot forging and stamping process were inherited. Meanwhile, the thermoplastic constitutive equation considering the influence of phase transformation was written in the UMAT subroutine and utilized for the implicit FE analysis of the cooling process of thin-walled spherical shells. Through comparison with the measured stress results of the spherical shells after actual forging, it was shown that the proposed constitutive model can effectively predict the microstructural evolution and the final residual stress distribution pattern of medium-carbon steel during the hot forging process.

COMPARISON OF GAUSSIAN HEAT FLOW OF FSW RELYING ON VON MISES CRITERION AND CONSTITUTIVE MODELS OF YIELD STRENGTH

In the Friction Stir Welding (FSW) operation, the role of thermal applied load modeling is no secret to simulate the heat distribution produced from this process. Unfortunately, this modeling implemented in transient mode did not present an accurate model for the moving heat source resulting from FSW operation. The main reason for this issue is attributed to the confidence and deviation ratios, especially with the Gaussian Distribution (GD). Besides, the models adopted in this modeling did not utilize the constitutive models of yield strength for comparison. Accordingly, the current study aims to use GD with 99.75% and 0.25% ratios for confidence and deviation, respectively, in this thermal load. It also employed the Von Mises criterion with Voce, Hollomon, and Swift for this comparison as constitutive models. Accordingly, the hybrid models of the thermal load of FSW represented by Von Mises-Voce, Von Mises-Hollomon, and Von Mises-Swift have been adopted in the present study. These hybrid models were used with finite element simulation to validate the experimental thermal history of FSW for Al 6061-T6 under 800 rpm, 10 mm/min, and 15 kN for rotational speed, linear velocity, and applied force sequentially. Finally, this validation has proved the dominance of the Von Mises-Voce model for thermal history compared to other hybrid models. Moreover, this dominant model has also investigated the peak temperature with a 2.54% error ratio over the other hybrid models of thermal applied load in FSW.

Probing mechanical attributes and microstructural ties in modified concrete blended with recycled rubber and straw powder

In order to investigate the interaction of rubber particles and straw powder coupling on concrete mechanics, the rubber particle mixing, straw powder mixing, and silane coupling agent KH570 modification as the three main factors were compared through a compressive strength test. Results show that when rubber particles were added with 10%, 20%, and 30% volume fractions, the compressive strength of rubber concrete was 42.45 MPa, 36.82 MPa, and 30.25 MPa, respectively, which decreased by 15.4%, 26.6%, and 39.7% compared with ordinary concrete, respectively. And the addition of straw powder also has adverse effects on the compressive strength of concrete. The uniaxial compressive damage constitutive model was proposed for modified recycled rubber-straw powder concrete based on the analysis of the entire compressive stress-strain curve, which fits well with the experimental test data. Furthermore, the numerical simulation of the proposed model is conducted using the FEA software ABAQUS, predicting properties such as compressive strength for modified recycled rubber-straw powder concrete with other admixtures.

Study on the bonding behavior of concrete-filled aluminum alloy tube

Aluminum alloy has been widely used in modern engineering structures due to its good corrosion resistance, light-weight, convenient processing, and recyclability. To study the bonding behavior of concrete-filled aluminum alloy tubes (CFAT) columns and obtain the bond strength formula and bond-slip constitutive model of CFAT, the push-out tests of three circular and three square CFAT specimens were conducted. The failure patterns, load-slip/strain curves and the stress distribution of the stubs were investigated. The results show that the longitudinal strain of both square and circular CFAT specimens increased from the loading end towards the free end. Based on the elastic assumption, the interfacial bond stress of CFAT was calculated. The ultimate bond strength for the circular specimens ranged from 0.77 to 1.77 MPa, whilst the square ones ranged from 0.22 to 0.51 MPa. As the section size increased, the bond strength of CFAT gradually decreased. When the diameter-to-thickness ratio or the width-to-thickness ratio increased from 48.0 to 80.0, the ultimate bond strength of the square and circular specimens decreased by 67.2% and 67.5%, respectively. Additionally, a calculation formula for the ultimate bond strength of CFAT is proposed. Based on the proposed formula for characteristic points, a bond-slip constitutive model for CFAT columns is proposed and validated. Finally, based on the verified bond-slip constitutive model of CFAT, the finite element (FE) models of spring element and cohesive model are established, respectively. The modeling result of the spring element is more accurate and the calculation efficiency is higher. However, the modeling process is complex.

A Novel Model for Optimizing Roundabout Merging Decisions Based on Markov Decision Process and Force-Based Reward Function

Autonomous vehicles (AVs) are increasingly operating in complex traffic environments where safe and efficient decision-making is crucial. Merging into roundabouts is a key interaction scenario. This paper introduces a decision-making approach for roundabout merging that combines human driving behavior with advanced reinforcement learning (RL) techniques to enhance both safety and efficiency. The proposed framework models the decision-making process of AVs at roundabouts as a Markov decision process (MDP), optimizing the state, action, and reward spaces to more accurately reflect real-world driving behaviors. It simplifies the state space using relative distance and speed and defines three action profiles based on real traffic data to replicate human-like driving behavior. A force-based reward function, derived from constitutive relations, simulates vehicle-roundabout interactions, offering detailed, physically consistent feedback that enhances learning results. The results showed that this method effectively replicates human-like driving decisions, supporting the integration of AVs into dynamic traffic environments. Future research should address the challenges related to partial observability and further refine the state, action, and reward spaces. This research lays the groundwork for adaptive and interpretable decision-making frameworks for AVs, contributing to safer and more efficient traffic dynamics at roundabouts.

Numerical study on cutting mechanism of TBM cutter in sandy pebble stratum considering the influence of calcareous cement layer

The calcareous consolidated sand pebble stratum has a great influence on shield tunnelling due to its strong random distribution of pebbles, large particle size difference and obvious cementation. Based on the characteristics of the sand-pebble stratum in Lanzhou metro, a two-dimensional finite element model of the sand-pebble stratum and cutter was established with the cohesive constitutive model. The cutting mechanism and characteristics of cutting tools in calcareous cemented sand pebble formation were analysed from the aspects of the dynamic cutting process, cutting force, crack development, and evolution. The results indicated that, firstly, the sand pebble within the cutting depth was stripped off as a whole through the crack extension to the free surface, secondly, compression shear failure was caused by direct contact between the cutter and the pebble, thirdly, the crack penetrated along the pebble surface and caused the pebble to peel off as a whole under the action of tool disturbance. The influence of pebble content on cutting force was great under different cutting depths, and the number of cracks and cutting force increased with the increase of cutting speed. Meanwhile, when the cutter front angle exceeded a certain value, the stress mode of the cutter would change from horizontal stress to vertical stress.

Research on the Long-Term Mechanical Behavior and Constitutive Model of Cemented Tailings Backfill Under Dynamic Triaxial Loading

Cemented tailings backfill (CTB) plays an important role in mine filling operations. In order to study the long-term stability of CTB under the dynamic disturbance of deep wells, ultrafine cemented tailings backfill was taken as the research object, and the true triaxial hydraulic fracturing antireflection-wetting dynamic experimental system of coal and rock was used to carry out a static true triaxial compression test, a true triaxial compression test under unidirectional disturbance, and a true triaxial compression test under bidirectional disturbance. At the same time, the acoustic emission monitoring and positioning tests of the CTB were carried out during the compression test. The evolution law of the mechanical parameters and deformation and failure characteristics of CTB under different confining pressures is analyzed, and the damage constitutive model of the filling body is established using stochastic statistical theory. The results show that the compressive strength of CTB increases with an increase in intermediate principal stress. According to the change process of the acoustic emission ringing count over time, the triaxial compression test can be divided into four stages: the initial active stage, initial calm stage, pre-peak active stage, and post-peak calm stage. When the intermediate principal stress is small, the specimen is dominated by shear failure. With an increase in the intermediate principal stress, the specimen changes from brittle failure to plastic failure. The deformation and failure strength of CTB are closely related to its loading and unloading methods. Under a certain stress intensity, compared with unidirectional unloading, bidirectional unloading produces a greater deformation of the rock mass, and the failure strength of the rock mass is higher. This study only considers the confining pressure within the compressive limit of the specimen. Future research can be directed at a wider range of stresses to improve the applicability and reliability of the research results.