Development Of Material Model Research Articles

Temperature- and rate-dependent tensile behaviour of unidirectional carbon/polyamide-6 composite under off-axis loading with oblique tabs

Unidirectional carbon/polyamide-6 (CPA6) is a thermoplastic composite with attractive properties for many industrial applications. However, shortage of experimental data may hinder the development of reliable material models. This paper is the first to provide a complete dataset for the tensile behaviour of unidirectional CPA6, including the longitudinal, transverse, in-plane shear, and off-axis response, at different temperatures and (quasi-static) strain rates. The oblique end tab design, already proven in the literature for off-axis testing of composites at room temperature, was successfully extended to the elevated temperature of 120 °C. The use of cardboard tabs and fast-curing adhesive greatly simplified the tab manufacturing and application for all the combinations of fibre angles, temperatures and strain rates. Digital image correlation (DIC) was performed through the window of the temperature chamber to verify the homogeneous strain field produced by the oblique tabs. The in-plane shear behaviour was extracted from the off-axis tests, allowing to estimate the shear modulus and shear strength. Finally, the robustness of the experimental results generated in this study was demonstrated with well-established analytical models that could excellently predict the elastic modulus, Poisson's ratio, and failure stress at different fibre angles.

Enhanced nonlinear models for critical compressive stress-strain characteristics of rubberized concrete: Comprehensive experimental data and robust evaluation methodology

The integration of rubber aggregate (RA) into concrete presents a pivotal avenue for enhancing the material's sustainability and environmental impact. Despite its potential, a crucial gap persists in the field concerning the development of material models that accurately consider the influence of RA particle size on the stress-strain responses of Rubberized Concrete (RuC). To address this gap, this study explores the effects of incorporating RA into concrete on its ascending compressive stress-strain behavior. In this research, we have compiled a comprehensive database encompassing the compressive stress-strain characteristics of 80 distinct concrete mixes incorporating RA from varied sources, sizes, and attributes. The investigation also evaluated the effectiveness of recent models in predicting key parameters, including modulus of elasticity, peak stress, and strain at peak stress. We proposed more robust models to accurately capture essential features. Notably, the findings suggest that higher RA content leads to dispersed cracks and decreased stiffness, resulting in lower peak stress and strain. Moreover, compressive strength exhibits notable variations with RA content, with significant drops observed across both normal and high-strength concrete mixes. The performance evaluation of existing models underscores the superiority of Li et al.'s model for peak stress prediction and Abbara et al.'s model for elasticity modulus prediction. The proposed simplified nonlinear models in this research offer enhancements over existing ones, promising more accurate predictions. These findings have profound implications for the optimization of rubberized concrete mixes and pave the way for future research directions aimed at further refining predictive models and advancing the application of RA in concrete technology.

Development and Calibration of a Phenomenological Material Model for Steel-Fiber-Reinforced High-Performance Concrete Based on Unit Cell Calculations.

A phenomenological material model has been developed to facilitate the efficient numerical analysis of fiber-reinforced high-performance concrete (HPC). The formulation integrates an elasto-plastic phase-field model for simulating fractures within the HPC matrix, along with a superimposed one-dimensional elasto-plasticity model that represents the behavior of the embedded fibers. The Drucker-Prager plasticity and one-dimensional von-Mises plasticity formulations are incorporated to describe the nonlinear material behavior of both the HPC matrix and the fibers, respectively. Specific steps are undertaken during the development and calibration of the phenomenological material model. In the initial step, an experimental and numerical analysis of the pullout test of steel fibers embedded in an HPC matrix is conducted. This process is used to calibrate the micro-mechanical model based on the elasto-plastic phase-field formulation for fracture. In the subsequent step, virtual experiments based on an ellipsoidal unit cell, also with the resolution of fibers (used as a representative volume element, RVE), are simulated to analyze the impact of fiber-matrix interactions and their physical properties on the effective material behavior of fiber-reinforced HPC. In the final step, macroscopic boundary value problems (BVPs) based on a cuboid are simulated on a single scale using the developed phenomenological material model. The resulting macroscopic stress-strain characteristics obtained from both types of simulations, namely simulations of virtual experiments and macroscopic BVPs, are compared. This comparison is utilized for the calibration of material parameters to obtain a regularized solution and to assess the effectiveness of the presented phenomenological material model.

Prediction of rolling resistance and wheel force for a passenger car tire: A comparative study on the use of different material models and numerical approaches

In this research, the characteristics of tire-road interaction of a 185/65R14 88H passenger car tire are investigated using the Finite Element Method in Abaqus commercial software. Moreover, the effect of various material models on tire performance is studied by implementing Visco-Hyperelastic, Parallel Rheological Framework, and Mullins effect. The novelty of this research is devoted to the development of the complex material models particularly considering the Mullins effect of the rubber compounds in the tire structure for the load-displacement criteria. For this purpose, a tire finite element model was generated using Abaqus/Standard command line in two different methods including an Arbitrary Lagrangian-Eulerian formulation for steady state rolling and implementing a pure Lagrangian approach for the transient dynamic analysis carried out implicit and explicit process respectively. Rolling resistance force was computed according to ISO 28580 with 210 kPa inflation pressure and 4155 N vertical load. The footprint test results were extracted in both static and transient dynamic analyses. Additionally, the wheel reaction force was predicted using an indirect method by extracting the tire-terrain contact patch reaction force in Abaqus/Explicit to observe the effect of the material convection along with stress softening phenomena of the rubber compounds of tire structure. In the post-processing analysis, the wheel reaction was filtered by implementing SAE60 filter to reduce the numerical noise in the final response.

Analysis of dynamic recrystallization through austenite grain reconstruction of additively manufactured martensitic M789 steel

This work examines the hot compression behavior of additively manufactured M789 steel via laser powder bed fusion (LPBF) at temperatures ranging from 850 °C to 1050 °C and strain rates between 0.01 s-1 and 1 s-1. Combined corrections for friction and deformation heating were applied to the flow curves to acquire accurate stress-strain data, followed by phenomenological and physical-based constitutive modelling. In particular, the application of Sellars and Tegart hyperbolic sine model, the Kocks-Mecking model and the Johnson-Mehl-Avrami-Kolmogorov equation facilitated the development of physical material models that accurately depict the behavior of LPBF-fabricated M789 steel, highlighting the inadequacy of traditional models, such as the modified Johnson-Cook model, in capturing the complexities and metallurgical phenomena associated with high-temperature deformation. The activation energy for deformation of M789 steel was determined to be lower than that of conventional M250 steel, indicating an accelerated recrystallization process at elevated temperatures. The study also introduces a novel quantitative analysis of dynamically recrystallized grains via combined austenite parent grain reconstruction (based on the Kurdjumov-Sachs orientation relationship combined with the Markov clustering technique) and shape factor measurements, confirming the occurrence of dynamic recrystallization (DRX). The findings suggest that DRX more readily occurs at higher strain rates and higher deformation temperatures, whereas at lower temperatures, a lower strain rate is preferred to generate a higher fraction of DRX grains along with finer grains. Additionally, the work indicates that specific variants from the Kurdjumov-Sachs orientation relationship are favored during the solidification process in LPBF, which seem to disappear when the alloy is subjected to its austenitization temperature.

CEFR-based Model of Indonesian Grammar Teaching Materials for Foreign Students

Law No. 24/2009 mandates the internationalization of the Indonesian language that is in line with the increase in the learning of the Indonesian language for foreign speakers. The number and location of Indonesian speakers are increasing and expanding in various parts of the world. However, the existing teaching materials are not optimal in supporting BIPA teaching, especially in the aspect of grammar—the most difficult language component for foreign students to learn. Thus, it is imperative to develop a model of Indonesian grammar teaching materials based on the current curriculum that refers to CEFR. This research focuses on the development of an Indonesian grammar teaching material model for A1-level BIPA students. The development design employed is an adaptation of the R&D design by Borg and Gall, which consists of several phases, such as (1) model development, (2) model evaluation, and (3) production and dissemination. This initial research constitutes a model development phase that includes (a) needs analysis, (b) needs identification based on the existing Indonesian grammar teaching materials and studies on the document of CEFR-based BIPA Graduate Competence Standard, and (c) compiling Indonesian grammar teaching materials. This preliminary research results in the mapping and drafting the initial product of the model of Indonesian grammar teaching materials for students at the A1 level.
 Keywords: teaching material model, Indonesian grammar, BIPA (Indonesian Language for Foreign Speakers), CEFR

Development of a multilayer fetal membrane material model calibrated using bulge inflation mechanical tests

The fetal membranes are an essential mechanical structure for pregnancy, protecting the developing fetus in an amniotic fluid environment and rupturing before birth. In cooperation with the cervix and the uterus, the fetal membranes support the mechanical loads of pregnancy. Structurally, the fetal membranes comprise two main layers: the amnion and the chorion. The mechanical characterization of each layer is crucial to understanding how each layer contributes to the structural performance of the whole membrane. The in-vivo mechanical loading of the fetal membranes and the amount of tissue stress generated in each layer throughout gestation remains poorly understood, as it is difficult to perform direct measurements on pregnant patients. Finite element analysis of pregnancy offers a computational method to explore how anatomical and tissue remodeling factors influence the load-sharing of the uterus, cervix, and fetal membranes. To aid in the formulation of such computational models of pregnancy, this work develops a fiber-based multilayer fetal membrane model that captures its response to previously published bulge inflation loading data. First, material models for the amnion, chorion, and maternal decidua are formulated, informed, and validated by published data. Then, the behavior of the fetal membrane as a layered structure was analyzed, focusing on the respective stress distribution and thickness variation in each layer. The layered computational model captures the overall behavior of the fetal membranes, with the amnion being the mechanically dominant layer. The inclusion of fibers in the amnion material model is an important factor in obtaining reliable fetal membrane behavior according to the experimental dataset. These results highlight the potential of this layered model to be integrated into larger biomechanical models of the gravid uterus and cervix to study the mechanical mechanisms of preterm birth.

Composite Medical Tabletops Made of CFRP with Different Cross-Sections: Numerical Analysis and Laboratory Testing.

This paper presents the results of laboratory tests of CFRP (carbon fiber-reinforced polymer) laminates, which allowed the development of numerical material models. The obtained data were used in a further stage to perform numerical simulations of four variants of medical tabletops, differing, among other features, in the shape of the cross-section. Maximum deflections and effort in the composite material were analyzed. The final step was to perform a laboratory test for one of the tabletop versions, the results of which confirmed the correctness of the numerical calculations. This work is aimed at both researchers and designers involved in the practical application of fiber-reinforced polymer matrix composites.

Gleeble Simulation of HAZ in S690QL Steel: Microstructural and Mechanical Properties

When investigating the heterogeneous properties of welded joints, mechanical testing of certain Heat Affected Zone (HAZ) regions, using standard approach test specimens, is very difficult or sometimes even impossible. Inability to precisely position and extract mechanical test specimens, even ones of the subsize dimensions, from the narrow HAZ regions is a limiting factor in the mechanical testing implementation. Detailed investigation of the HAZ is made possible by the use of thermo-mechanical simulations on the Gleeble welding simulator. In scope of this paper several characteristic HAZ microstructures of S690QL grade High Strength Steel (HSS) are being simulated. Multi-pass welding simulations are done on special 10x10 mm square section bar specimens in order to reproduce thermal gradients and characteristic microstructures at any location in a weld. Such simulated HAZ microstructures are of a sufficiently large volume, with homogeneous and repeatable properties, that standard specimen methods for mechanical testing can be readily implemented. Metallographic optical examinations, as well as hardness measurements were done initially. Mechanical properties are focused on determining stress-strain curves for each characteristic weld region. The paper investigates whether the mechanical properties of Gleeble simulated hard-soft combined HAZ regions are better in comparison to exclusively hard or soft HAZ regions. The obtained results can subsequently be used for the material model development.

Quantifying the microstructural and biomechanical changes in the porcine ventricles during growth and remodelling.

Cardiac tissue growth and remodelling (G & R) occur in response to the changing physiological demands of the heart after birth. The early shift to pulmonary circulation produces an immediate increase in ventricular workload, causing microstructural and biomechanical changes that serve to maintain overall physiological homoeostasis. Such cardiac G & R continues throughout life. Quantifying the tissue's mechanical and microstructural changes because of G & R is of increasing interest, dovetailing with the emerging fields of personalised and precision solutions. This study aimed to determine equibiaxial, and non-equibiaxial extension, stress-relaxation, and the underlying microstructure of the passive porcine ventricles tissue at four time points spanning from neonatal to adulthood. The three-dimensional microstructure was investigated via two-photon excited fluorescence and second-harmonic generation microscopy on optically cleared tissues, describing the 3D orientation, rotation and dispersion of the cardiomyocytes and collagen fibrils. The results revealed that during biomechanical testing, myocardial ventricular tissue possessed non-linear, anisotropic, and viscoelastic behaviour. An increase in stiffness and viscoelasticity was noted for the left and right ventricular free walls from neonatal to adulthood. Microstructural analyses revealed concomitant increases in cardiomyocyte rotation and dispersion. This study provides baseline data, describing the biomechanical and microstructural changes in the left and right ventricular myocardial tissue during G & R, which should prove valuable to researchers in developing age-specific, constitutive models for more accurate computational simulations. STATEMENT OF SIGNIFICANCE: There is a dearth of experimental data describing the growth and remodelling of left and right ventricular tissue. The published literature is fragmented, with data reported via different experimental techniques using tissues harvested from a variety of animals, with different gender and ages. This prevents developing a continuum of data spanning birth to death, so limiting the potential that can be leveraged to aid computational modelling and simulations. In this study, equibiaxial, non-equibiaxial, and stress-relaxation data are presented, describing directional-dependent material responses. The biomechanical data is consolidated with equivalent microstructural data, an important element for the development of future material models. Combined, these data describe microstructural and biomechanical changes in the ventricles, spanning G &R from neonatal to adulthood.

Smoothed Particle Hydrodynamics to Model Spinal Canal Occlusion of a Finite Element Functional Spinal Unit Model under Compression

<div>Compressive impacts on the cervical spine can result in bony fractures. Bone fragments displaced into the spinal canal produce spinal canal occlusion, increasing the potential for spinal cord injury (SCI). Human body models (HBMs) provide an opportunity to investigate SCI but currently need to be improved in their ability to model compression fractures and the resulting material flow. Previous work to improve fracture prediction included the development of an anisotropic material model for the bone (hard tissues) of the vertebrae assessed in a functional spinal unit (FSU) model. In the FSU model, bony failure was modeled with strain-based element erosion, with a limitation that material that could occlude the spinal canal during compression was removed when an element was eroded. The objective of this study was to implement a multi-physics modeling approach, using smoothed particle hydrodynamics (SPH) with element erosion, to simulate the movement of fractured material during central compression of a C5-C6-C7 cervical spine segment and assess spinal canal occlusion. The calculated maximum occlusion in the original model was 11.1%. In contrast, the enhanced model with SPH had a maximum occlusion of 79.0%, in good agreement with the average experimental maximum occlusion of 69.0% for age-matched specimens. The SPH implementation to preserve fractured material volume enabled the assessment of spinal canal occlusion.</div>

Morpho-mechanical mapping of human dura mater microstructure

The human dura mater is known to impact vastly traumatic brain injury mechanopathology. In spite of this involvement, dura mater is typically neglected in computational and physical human head models. The lack of location-dependent microstructural and related mechanical data of dura mater may be considered a rationale behind this simplification. The anisotropic nature of dura mater under various loading conditions so far remains unelucidated. Furthermore, principal collagen fiber orientation is yet to be quantified for a morpho-mechanically-informed material model on the dura mater. This study aims to assess how location-dependent mechanical anisotropy is linked to principal collagen fiber orientation. Uniaxial extension tests were performed in a heated tissue bath for 60 samples from six individuals and correlated to the three-dimensional collagen structure in four individuals using second-harmonic generation (SHG) imaging. Failure stress and stretch at failure, elastic modulus, and a microstructurally motivated material model were integrated to examine local differences in dura mater morpho-mechanics. The quantitative observation of collagen fiber orientation and dispersion confirmed that collagen is highly aligned in the human dura mater and that both fiber orientation and dispersion differ depending on the location investigated. This observation provides a possible explanation for the previously observed isotropic mechanical behavior, as the main collagen fiber direction is not oriented along the anterior-posterior or medial-lateral direction at most of the mapped locations. Additionally, these site-dependent structural properties have implications for the mechanical load response and therefore potentially for the regional functions dura mater has to fulfill. The here chosen non-symmetrical fiber dispersion material model fits the data well and provides a comprehensive parameter base for further studies and future finite element models. Statement of significanceThe human dura mater greatly affects traumatic brain injury mechanisms, but it is often ignored in computational and physical head models. This is because there is a lack of detailed microstructural and mechanical data specific to the dura mater. Its anisotropic nature and collagen fiber orientation have not been fully understood, hindering the development of an accurate material model. Hence, this study combines morphological data on collagen fiber orientation and dispersion at multiple locations of human cranial dura mater, and links microstructure to location-specific load-displacement behavior. It provides microstructurally informed mechanical information towards realistic head models for predicting location-dependent tissue behavior and failure for assessing brain injury and graft material development.

Capturing fracture initiation and crack propagation of car windshields

To facilitate the development of accurate material models for glass, there is a need for reliable experimental procedures that capture the stochastic nature of the material. The experimental setup must be easy to model numerically and output relevant data for validation of important material characteristics. We conducted an experimental study on three types of windshields exposed to quasi-static loading. A robust and repeatable testing procedure was designed with the aim of revealing the stochastic behavior of windshields. 3D-Digital Image Correlation (3D-DIC) was used to monitor the windshield displacement field and we were able to capture fracture initiation locations and crack propagation data by using high-speed cameras combined with a pose estimation-based post-processing tool implemented in Python. We performed finite element (FE) simulations in LS-DYNA to estimate major principal stress values at first fracture. The results from the experimental study provided new insight and valuable data for the development of numerical models of the problem at hand.

Development of New Material Models for Thermal Behavior of Cold-Formed G-450 and G-550 Steels in OpenSees Software

In this study, new steel material classes were added to the OpenSees 3.0.0 library to model their behavior within cold-formed profiles under high temperatures. The new material classes that were added are capable of modeling G-450 and G-550 grade galvanized steels under mechanical and thermal loads. Gypsum panel, a nonstructural material within walls, significantly contributed to the lateral resistance of cold-formed structures. For the first time, the relevant material class was added to OpenSees. First, heat transfer analysis was performed to determine the temperature distribution within different parts of the frame structure. Second, the structure was analyzed under gravity loads, followed by thermal loads. Results from the first step were applied to the structure, and a transient thermomechanical analysis was performed. The output of this analysis included the deformation and force of the members of the structure. The behavior of each new material class was compared with the experimental results to determine the accuracy of the developed OpenSees scripts. Moreover, the results related to modeling with this material class were compared with those of the material classes available in OpenSees. The results exhibited high accuracy with the new material class, and the difference in the results obtained with the current material classes in OpenSees was significant.

An Entropy Dynamics Approach for Deriving and Applying Fractal and Fractional Order Viscoelasticity to Elastomers

Abstract Entropy dynamics is a Bayesian inference methodology that can be used to quantify time-dependent posterior probability densities that guide the development of complex material models using information theory. Here, we expand its application to non-Gaussian processes to evaluate how fractal structure can influence fractional hyperelasticity and viscoelasticity in elastomers. We investigate how kinematic constraints on fractal polymer network deformation influences the form of hyperelastic constitutive behavior and viscoelasticity in soft materials such as dielectric elastomers, which have applications in the development of adaptive structures. The modeling framework is validated on two dielectric elastomers, VHB 4910 and 4949, over a broad range of stretch rates. It is shown that local fractal time derivatives are equally effective at predicting viscoelasticity in these materials in comparison to nonlocal fractional time derivatives under constant stretch rates. We describe the origin of this accuracy that has implications for simulating large-scale problems such as finite element analysis given the differences in computational efficiency of nonlocal fractional derivatives versus local fractal derivatives.

Characterization of the compaction and frictional behaviors of the green anode paste at various temperatures

The aim of this work was to investigate the effect of the green anode paste temperature on its compaction behavior and on its frictional behavior with a steel mold during the anode forming process. An experimental campaign composed of monotonic compaction tests and friction tests was carried out at temperatures ranging from 130 °C to 170 °C. The compaction tests were performed with an instrumented thin-walled mold to characterize the axial and radial behaviors of the anode paste. The results highlight that the nonlinear behavior of the anode paste is significantly affected by temperature. Friction tests were performed under various normal loads to evaluate the static and kinetic friction coefficients of the paste/steel at different interface temperatures. The results bring a new insight into the behavior of the anode paste and pave the way for the development of a temperature-dependent material model of the anode paste compaction process.

Revision and development of material models of ultra-high performance concrete containing coarse aggregate and applications in structural-level flexural response predictions

Ultra-high performance concrete recently has attained immense attention in the construction industry for its superior mechanical characteristics. Nevertheless, its application remains restricted by its high cost. Reintroducing coarse aggregate (CA) to the constituents of UHPC mixtures is a solution promoted by many researchers for addressing the high production cost and insufficient shrinkage performance. Although adding CA to UHPC does not significantly subvert its high performance, it alters its microstructure and adjusts its characteristics. Accordingly, developing new material and structural models is imperative. This paper establishes compressive and tensile material models accounting for the effect of CA, and then employs the developed material models in structural-level analytical and numerical models for predicting the flexural responses of CA-UHPC slabs. The experimental parameters used in the material models are obtained from a collection of a wide range of experimental data available in the literature. The proposed models account for the size effect by scaling the tensile strain values of CA-UHPC in accordance with the member size. The proposed models are validated against previous test data, which confirm the capability of the developed models in capturing the response of CA-UHPC on a material level and a structural level.

Behaviour and material properties of versaloc semi-interlocking mortarless masonry

Masonry construction is popular around the world, but the use of mortared masonry presents numerous challenges. In recent decades, masonry construction systems incorporating interlocking masonry units have been proposed to eliminate mortar. The interlocking between masonry units can be achieved using specially shaped units. This paper presents a comprehensive experimental study to determine the behaviour as well as basic material properties of one such semi-interlocking mortarless masonry. The experiments included testings of ungrouted masonry units, prisms, and wallets. In addition, masonry prisms and wallets with grouted cores were also investigated to study the effect of grouting. A detailed description of the construction procedure is explained. The failure mechanisms, maximum strengths, force–displacement relationships, and modulus of elasticity of the samples are obtained and contrasted with the relevant results from the literature. Finally, recommendations are made that may assist material model development required for micro- and macro-modelling of mortarless masonry. The new information generated in this research will enable better understanding of the behaviour and properties of semi-interlocking mortarless masonry and will be useful for validating numerical models in future research.

Uncertainty Quantification of Material Properties in Ballistic Impact of Magnesium Alloys.

The design and development of cutting-edge light materials for extreme conditions including high-speed impact remains a continuing and significant challenge in spite of steady advances. Magnesium (Mg) and its alloys have gained much attention, due to their high strength-to-weight ratio and potential of further improvements in material properties such as strength and ductility. In this paper, a recently developed computational framework is adopted to quantify the effects of material uncertainties on the ballistic performance of Mg alloys. The framework is able to determine the largest deviation in the performance measure resulting from a finite variation in the corresponding material properties. It can also provide rigorous upper bounds on the probability of failure using known information about uncertainties and the system, and then conservative safety design and certification can be achieved. This work specifically focuses on AZ31B Mg alloys, and it is assumed that the material is well-characterized by the Johnson–Cook constitutive and failure models, but the model parameters are uncertain. The ordering of uncertainty contributions for model parameters and the corresponding behavior regimes where those parameters play a crucial role are determined. Finally, it is shown that how this ordering provides insight on the improvement of ballistic performance and the development of new material models for Mg alloys.

Material model development and fire resistance research on CLT wall-floor angle bracket connections in OpenSees

When analyzing the fire resistance of cross-laminated timber (CLT) joints, traditional finite element (FE) analysis software encounters problems such as long computing times and low calculation efficiency. This situation is more common when performing multi-physics coupling analysis. OpenSees is open-source software that has high computational efficiency and the advantage that it can be developed by users. It is widely used in analyses of the effects of fire on steel and concrete structures, but it contains no analogous material model for timber connections. To make full use of the calculation efficiency of OpenSees, this study adds a spring element constitutive model that enables the simulation of CLT wall-floor angle bracket connections during and after a fire, and the calculation of CLT node thermo-mechanical coupling. The proposed model numerically simulates and analyzes the fire resistance of CLT wall-floor angle bracket connections, the effects of different load ratios (5–80%) and of two different length self-tapping screws (60 and 80 mm), and different tree species. This provides a source for designers when using open-source software to analyze the fire resistance of CLT joints.