Developed Material Model Research Articles

Contribution of geometrical infill pattern on mechanical behaviour of 3D manufactured polylactic acid specimen: Experimental and numerical analysis

Additive manufacturing is regarded as a very efficient fabrication technique since it permits the manufacturing of any three-dimensional product. The present work determines the effect of various infill pattern on the mechanical properties in term of tensile strength, yield strength and hardness of poly-lactic acid (PLA) samples fabricated by fused deposition modeling method. The mechanical behaviour of the 3D-printed PLAs investigated using dog-bone specimens with six distinct infill patterns: line, triangle, tri-hexagon, cubic, octet, and gyroid. The mechanical characteristics were evaluated using the uniaxial tensile test and shore D type hardness tester. The strain and deformation criteria were employed to substantiate the ductile and brittle characteristics. The fractural surface morphology analyzed using the field emission scanning electron microscope. Nonlinear Finite Element Analysis (FEA) was employed to simulate the uniaxial tensile test and establish a Yeoh third order hyperelastic material model for the predictions of the stress-strain response. This model is chosen for its precise ability to predict the nonlinear stress-strain responses for significant deformation and is crucial in applications that involve high degrees of flexibility and elasticity, such as in tire modeling, polymer and elastomer analysis, sports equipment designing, 3D printed components etc. Results revealed that the cubic infill had a maximum tensile strength 32.648 ± 1.42 MPa and octet infill had a minimum tensile strength 22.373 ± 0.79 MPa. The majority of experimental data indicated a brittle behaviour for line-infilled, but triangular, trihexagonal, cubic, octet, and gyroid infill patterns demonstrated ductile behaviour. In comparison to other geometrical infills, cubic shown relatively superior mechanical responses. Consequently, the geometrical infill effect plays a significant role in finding the appropriate mechanical property for industrial applications. The developed material model possesses potential utility in non-linear FEA investigations pertaining to 3D printed PLA objects that are predicted to sustain tensile strength.

Multi-parameter viscoelastic material model for denture adhesives based on time-temperature superposition and multiple linear regression analysis

BackgroundRestorative solutions designed for edentulous patients such as dentures and their accompanying denture adhesives operate in the complex and dynamic environment represented by human oral physiology. Developing material models accounting for the viscoelastic behavior of denture adhesives can facilitate their further optimization within that unique physiological environment. This study aims to statistically quantify the degree of significance of three physiological variables - namely: temperature, adhesive swelling, and pH - on denture adhesive mechanical behavior. Further, based on these statistical significance estimations, a previously-developed viscoelastic material modelling approach for such denture adhesives is further expanded and developed to capture these variables’ effects on mechanical behavior.MethodsIn this study a comparable version of Denture adhesive Corega Comfort was analysed rheologically using the steady state frequency sweep tests. The experimentally derived rheological storage and loss modulus values for the selected physiological variables were statistically analyzed using multi parameter linear regression analysis and the Pearson’s coefficient technique to understand the significance of each individual parameter on the relaxation spectrum of the denture adhesive. Subsequently, the parameters are incorporated into a viscoelastic material model based on Prony series discretization and time-temperature superposition, and the mathematical relationship for the loss modulus is deduced.ResultsThe results of this study clearly indicated that the variation in both the storage and loss modulus values can be accurately predicted using the oral cavity physiological parameters of temperature, swelling ratio, and pH with an adjusted R2 value of 0.85. The R2 value from the multi-parameter regression analysis indicated that the predictor variables can estimate the loss and storage modulus with a reasonable accuracy for at least 85% of the rheologically determined continuous relaxation spectrum with a confidence level of 98%. The Pearson’s coefficient for the independent variables indicated that temperature and swelling have a strong influence on the loss modulus, whereas pH had a weak influence. Based on statistical analysis, these mathematical relationships were further developed in this study.ConclusionsThis multi-parameter viscoelastic material model is intended to facilitate future detailed numerical investigations performed with implementation of denture adhesives using the finite element method.

AA5754 aluminium alloy springback reduction by post forming electro plastic effect (PFEPE)

Post Forming Electro Plastic Effect (PFEPE) has been proposed as a promising technology for mitigating forming forces and addressing springback challenges in the metal forming industry. However, several research gaps remain unaddressed for the industrialization of this technology. Firstly, there is a lack of experimental validation regarding the impact of stress reduction on springback. Secondly, the potential effect of the skin-effect on the current metrics of stress reduction needs to be evaluated. Additionally, a post-forming electrically assisted elastoplastic material model is necessary for further technology development in stamping processes. This study tackles these challenges by utilizing AA5754H22 as a reference material and integrating a comprehensive experimental campaign with finite element numerical models and empirical material model developments. Our findings confirm that PFEPE facilitates a significant reduction in springback, achieving approximately a 100% reduction. Although the skin-effect introduces non-uniform current flux density distribution, its impact at the macroscopic level is negligible for the studied thin samples. While the numerical results of springback fails to accurately replicate experimental results, the developed material model aligns well with experimental trends.

Developing linear-elastic material models for pressure measurement films in steel-steel and wheel-rail contact

Abstract The contact between two steel components can be identified by using multiple methods, for example, by experiment using pressure measurement films or by computational simulations with finite element analysis (FEA). For FEA material models of all components are required. When the experimental setup of an implemented pressure measurement film is reproduced simulatively, material models for the films are also necessary. Here, we developed linear-elastic material models for pressure measurement films which allow to simulate steel-film-steel contact situations. The material models were developed for Hertzian contact situations and afterward validated for the non-Hertzian wheel-rail contact. It was possible to develop material models for two different pressure measurement film types. In the case of a third film type, the developed model could not be validated successfully.

Comparative Study on Different CNN Architectures Developed on Microstructural Classification in Al-Si Alloys

Recent advances in artificial intelligence have opened up new avenues for microstructure characterization, notably in metallic materials. Physical and mechanical properties generally depend on the microstructure of the metallic material. On the other hand, microstructural characterization takes time and calls for specific techniques that don’t always lead to conclusive results quickly. To address this issue, this research focuses on the application of artificial intelligence approaches to microstructural categorization. We demonstrate the advantages of the AI approach using an example of Al-Si alloy, a material that is widely employed in a variety of industries. To specify a suitable convolutional neural network (CNN) approach for the microstructural classification of the Al-Si alloy, CNN models were trained and compared using DenseNet201, Inception v3, InceptionResNetV2, ResNet152V2, VGG16, and Xception architectures. Resulting from the comparison, it was determined that the developed supervised transfer learning model can execute the microstructural classification of Al-Si alloy microstructural images. This paper is an attempt to advance methods of microstructure recognition/classification/characterization by using Deep Learning approaches. The significance of the established model is demonstrated and its accordance with the literature data. Also, necessity is shown of developing material models and optimization through systematic microstructural investigation, production conditions, and material attributes.

A 3D viscoelastic–viscoplastic behavior of carbon nanotube‐reinforced polymers: Constitutive model and experimental characterization

AbstractDue to the widespread use of carbon nanotube (CNT)‐reinforced polymers in various industries, investigating the dynamic mechanical response of these materials under impact loading is of significant importance. A three‐dimensional viscoelastic (VE)–viscoplastic (VP) constitutive model for CNT/epoxy nanocomposites is developed. A proper rheological model is established using the generalized Maxwell model to represent the VE behavior and propose an exponential function to express the elasto‐VP response. Employing an empirical logarithmic relationship to estimate material properties at different strain rates, the VP behavior is modeled based on the overstress concept. The 3D numerical discretization of the proposed rate‐dependent material model is also carried out to develop a user‐defined material model (UMAT) for the commercial finite element (FE) software of Abaqus. The performed FE simulations based on the proposed rate‐dependent constitutive material can properly capture stress relaxation and hysteresis behaviors of the nanocomposites. Comparing the estimated tensile and shear stress–strain curves through developed material models with experimental measurements, an excellent agreement is observed.Highlights Tensile/shear properties of CNT/epoxy are measured at three strain rates. An empirical constitutive model is proposed for any arbitrary strain rates Viscoplastic behavior is captured based on over‐stress concept A 3D incremental form of a viscoelastic–viscoplastic material model is developed.

Circular steel tube-confined ultra-high performance concrete beam-column: Database, modeling, and design

The fiber beam element (FBE) model is widely used to simulate and predict the nonlinear behavior of structures owing to its simplicity and high computational efficiency. The accuracy of the FBE simulation of ultra-high-performance concrete (UHPC) filled steel tubular (UHPCFST) members is mainly dependent on the input materials and interactions between the steel tubes and concrete, such as second-order effect, yielding of steel tubes and passive confinement effect to the UHPC. This work proposes uniaxial effective stress-strain models of UHPC confined by circular steel tubes based on existing experimental data that are integrated into the FBE model to predict the nonlinear behavior of UHPCFST members. The robustness and reliability of the proposed material models are comprehensively verified against a database encompassing a wide range of materials and geometric parameters under different loading conditions (monotonic and cyclic loading). Furthermore, the application of existing design codes for computing ultimate bending strengths is assessed using an established experimental database. Finally, the ultimate bending strengths of circular UHPCFSTs are calculated using a novel and simplified N–M interaction equation. It is demonstrated that the developed material models could predict the nonlinear behaviors of circular UHPCFST members with good satisfaction, and that current design codes, to some extent, underestimate the ultimate bending strengths of circular UHPCFST columns, the proposed practical method in this study is highly accurate, with a mean value of 1.00.

Thermal-structural analysis for reusable thrust chamber using temperature-dependent CuZr alloy model adapted to cryogenic to elevated temperature

The inner liners of reusable regeneratively-cooled thrust chambers endure significant thermal and mechanical loads, resulting in doghouse deformation and even cracks during cyclic operations. To correctly reveal the failure mechanism of the thrust chamber inner liner, this study investigates the material properties for CuZr alloy and develops a temperature-dependent material model spanning from cryogenic to elevated temperatures. Firstly, we experimentally obtain the thermal and mechanical properties of the material in the temperature range from 77 K to 900 K. The experimental data reveal that the material properties vary considerably with temperature. Then, to precisely characterize the mechanical behavior of CuZr alloy under cyclic loading across a wide temperature range, a material model that combines Voce nonlinear isotropic hardening model with Chaboche nonlinear kinematic hardening model is proposed, and temperature-dependent parameters of this model are calibrated and verified. Finally, the developed material model is applied to perform the thermal-structural analysis on a reusable thrust chamber, with the aim of investigating its failure mechanism. The results demonstrate the capability of the developed model to accurately replicate the doghouse deformation of the inner liner and quantitatively capture the ratcheting effect.

Mechanical modeling of the maturation process for tissue-engineered implants: Application to biohybrid heart valves

The development of tissue-engineered cardiovascular implants can improve the lives of large segments of our society who suffer from cardiovascular diseases. Regenerative tissues are fabricated using a process called tissue maturation. Furthermore, it is highly challenging to produce cardiovascular regenerative implants with sufficient mechanical strength to withstand the loading conditions within the human body. Therefore, biohybrid implants for which the regenerative tissue is reinforced by standard reinforcement material (e.g. textile or 3d printed scaffold) can be an interesting solution. In silico models can significantly contribute to characterizing, designing, and optimizing biohybrid implants. The first step towards this goal is to develop a computational model for the maturation process of tissue-engineered implants. This paper focuses on the mechanical modeling of textile-reinforced tissue-engineered cardiovascular implants. First, an energy-based approach is proposed to compute the collagen evolution during the maturation process. Then, the concept of structural tensors is applied to model the anisotropic behavior of the extracellular matrix and the textile scaffold. Next, the newly developed material model is embedded into a special solid-shell finite element formulation with reduced integration. Finally, our framework is used to compute two structural problems: a pressurized shell construct and a tubular-shaped heart valve. The results show the ability of the model to predict collagen growth in response to the boundary conditions applied during the maturation process. Consequently, the model can predict the implant’s mechanical response, such as the deformation and stresses of the implant.

Gradient-extended damage modelling for polymeric materials at finite strains: Rate-dependent damage evolution combined with viscoelasticity

While the strong rate-dependent effects of polymeric materials in the elastic regime are well studied, the time-dependent effects that arise in the inelastic damage regime are still difficult to model and are therefore the subject of investigation. In this work, we propose a simple but flexible formulation for the description of rate-dependent damage combined with viscoelasticity at finite strains. This model is based on a finite viscoelastic material formulation combined with a Perzyna-type approach to describe the damage evolution equation. With this formulation we are able to describe both damage due to creep and relaxation of the polymer matrix in both a qualitative and quantitative manner. Besides the main aspects of thermodynamic consistency, we describe the numerical implementation into finite elements and present numerical examples to demonstrate the capabilities of the proposed model. At last, we compare the model with experimental data and show the good predictive capabilities of this newly developed material model.

A micro‐CT investigation of densification in pressboard due to compression

AbstractAs a non‐destructive inspection method, micro‐computed tomography has been employed for determining local properties of a cellulose‐based product, specifically pressboard. Furthermore, by utilizing the determined properties in a detailed numerical model, by means of a finite element analysis, we demonstrate a continuum anisotropic viscoelastic‐viscoplastic model. Through such a combination of non‐invasive experiments with accurate computations in mechanics, we attain a better understanding of materials and its structural integrity at a pre‐production stage increasing the success of the first prototype. In detail, this combination of micro‐computed tomography and finite element analysis improves accuracy in predicting materials response by taking into account the local material variations. Specifically, we have performed indentation tests and scanned the internal structure of the specimen for analysing the densification patterns within the material. Subsequently, we have used a developed material model for predicting the response of material to indentation. We have computed the indentation test itself by simulating the mechanical response of high‐density cellulose‐based materials. In the end, we have observed that pressboard, having initially a heterogeneous density distribution through the thickness, shows a shift in the densification to the more porous part after indentation. The densification maps of the simulated results are presented by comparing with the experimental results. A reasonable agreement is observed between the experimental and the simulated densifications patterns, which suggests that the proposed methodology can be used to predict densification also for other fibre‐based materials during manufacturing or in service loading.

A physically based elasto-viscoplastic constitutive model for modeling the hot deformation and microstructure evolution of a near α Ti alloy

In this work, a general elasto-viscoplastic constitutive model incorporating a finite strain viscoplastic flow law, the Kocks-Mecking dislocation density evolution, work hardening, stress softening due to dynamic recovery and dynamic recrystallization (DRX), and the Johnson-Mehl-Avarmi-Kolmogorov (JMAK) DRX kinetics was established for modeling the deformation and microstructure evolution of a near-α Ti alloy. A full-implicit stress integration scheme was proposed to implement the constitutive model into the commercial FEM solver ABAQUS/Standard. Isothermal hot compression experiments under various deformation conditions and detailed microstructure characterizations were conducted to study the deformation and DRX behaviors of the alloy, as well as to validate the developed material model. The alloy exhibits a typical discontinuous DRX behavior, macroscopically sensitive to various deformation conditions and microscopically strongly affected by the orientation of prior grains. The simulation results regarding the macroscopic flow stress curves and the local volume fractions of DRX in various regions in the specimen agree well with the experimental results. The proposed material model and the robust numerical implemental scheme can be extended to consider more physical deformation mechanisms and microstructure evolution of advanced structural metals and alloys.

Developing Elastic–Plastic Material Models for Pressure Measurement Films in a Steel–Steel Contact for Smooth and Rough Surfaces

AbstractThe contact zone between two steel components can be identified by utilizing a pressure measurement film in the contact between them. To reduce the number of necessary experiments, it is possible to simulate the contact situation using “finite element analysis.” This analysis requires material models for the contact partners and for the pressure measurement films. It is known that the pressure measurement film deforms not only elastically but also plastically. Taking this plastic deformation into account requires an appropriate material model such as the Drucker–Prager model. Based on published data of experiments with pressure measurement films that had been inserted between smooth and rough Hertzian bodies, we developed material models for three pressure measurement films. The roughness of a Hertzian body was studied by determining multiple pressure–clearance curves for three different surface roughnesses and for three different pressure measurement films. These curves were developed with micromodels, which represented a small section of the rough contact surface. An average curve for each material was then implemented in the macromodel for each roughness representing the contact situation. Subsequently, the resulting contact areas were compared with the published experimental data. This comparison showed that the material model for the smooth contact was able to emulate the experimentally determined contact areas. Including the pressure–clearance curves in the material model allowed the simulation of the rough contact situation. However, the deviation between the simulated and the experimental data was slightly larger for the rough surface than for the smooth surface.

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.

Temperature-dependent model for ferroelectrics embedded into two-dimensional polygonal finite element framework

A two-dimensional constitutive model, which is based on micromechanical rotation of domains, is presented in this work to demonstrate the non-linear behavior of ferroelectric materials under different loading conditions. A temperature-dependent combined material model that incorporates both phases i.e., tetragonal and rhombohedral phases is embedded into two-dimensional polygonal finite element framework. The developed material model which has easily overcome shortcomings related to tetragonal model and rhombohedral model alone. This model is developed on the morphotropic phase boundary which has produced desired behavior based on macroscopic material parameters. Temperature effects on behavior of combined material model are obtained in the work. Furthermore, polarization rotation test and temperature effects on polarization rotation are also studied in present work. There are numerous studies conducted on ferroelectric materials. All of them incorporate behavior of ferroelectric material confined to specific conditions. Either tetragonal model or rhombohedral model has been used extensively to get the desired behavior based on macroscopic material parameters. This model has some limitations in either satisfying one or another condition related to experiments conducted to study the behavior of ferroelectric materials. The tetragonal material model is capable of producing results with microscopic material properties but in case of macroscopic material parameters the tetragonal model is insufficient to produce the desired behavior for PZT ceramics. The rhombohedral material model is sufficient to produce results based on macroscopic material parameters. Therefore, model is extended by rhombohedral phase, allowing a mixture of both phases with varying quantities inside the grain. Though, rhombohedral model is also not used to that extent. We have developed material model that gives desired behavior and overcomes the hurdles in the existing model.

Characterization and modeling of damage behavior of a casting aluminum wheel considering inhomogeneity of microstructure and microdefects

For a meaningful description of casting processes on component behavior, the inhomogeneities of the microstructure, microdefects, and mechanical properties including damage behavior in a casting aluminum wheel were experimentally characterized. Both effects of microstructure/microdefects and stress state on damage behavior were determined by performing smooth and notched tensile tests and torsion tests on specimens extracted from different positions. The distribution of microstructure and microdefects in the cast wheel and the corresponding effects on damage development were analyzed using metallography, 3D X-ray CT, and SEM. Casting simulations were performed to determine distributions of local parameters like solidification time, secondary dendrite arm spacing (SDAS), and porosity. It is clear that the ultimate strength and elongation decrease with increasing porosity and SDAS. A material model describing the influence of porosity on flow stress and a damage model describing the relationships of fracture strain with porosity and triaxiality were developed based on the experimental and numerical results. The correlations of yield stress and elongation with porosity were applied to calibrate the models. Additionally, the influence of stress triaxiality on fracture strain was determined using torsion and notched tensile tests for selected porosities and the corresponding inverse simulations. Simulations of the different specimen tests with the developed material model and damage model could satisfactorily describe the experimental results. This method builds a good basis for coupling between casting simulation and structural simulation to optimize manufacturing processes and develop lightweight products. Improving the precision of microdefect calculation in casting simulations and applying of a stochastic model in structural simulations are important future works.

Linear woodcutting of European beech: experiments and computations

Hardwood species are becoming increasingly important with the growing need for a diversity of forests that have recently been facing global temperature changes or conifer pests. This further leads to the growth of its potential as a building material that may originate from sustainable production. As hardwoods need to be properly processed, the article deals with the disintegration of European beech. The influence of wood grain direction, uncut chip thickness and cutting speed on the cutting force magnitudes was experimentally investigated using the device with a rotating arm of approximately 4 m in diameter. Then, the disintegration process was modelled using the finite element method in Abaqus/Explicit. The developed material model consisting of orthotropic elasticity and plasticity with rate-independent and rate-dependent tensile–compressive failure asymmetry was implemented through the user subroutine, while the crack initiation and propagation were realized using the element deletion technique. The computationally predicted average values of cutting forces and chip shapes were, except for a few tests, in good agreement with the experiments. It means that the model may be used for further investigation, such as the influence of tool wear.

An innovative constitutive material model for predicting high temperature flow behaviour of inconel 625 alloy

Inconel 625 nickel alloy with its attractive high-temperature strength, excellent corrosion and oxidation resistance is mainly used for critical applications in demanding environments, in both as-cast and wrought conditions. Hot processing of this alloy is crucial for achieving its tailored mechanical properties due to the significant variation in microstructural changes with varying process parameters like temperature, strain, and strain rate. In this study, isothermal hot compression tests were carried out at temperatures ranging from 900 to 1100 °C, and under strain rates ranging from 0.01 to 1 s−1. The flow curves revealed three stages of deformation, including a substantial work-hardening stage followed by dynamic recovery and flow softening. Microstructural observations showed the occurrence of discontinuous dynamic recrystallisation (DDRX) as the dominant recrystallisation mechanism during the flow softening. Microstructural analysis suggested that the DRX was more sensitive to the test temperature as compared to the strain rate. An innovative material's constitutive model was developed, by combining Johnson–Cook (JC) and Avrami approaches, to predict work-hardening, dynamic recovery, and flow softening stages of deformation. The predicted flow behavior was in a good agreement with the experimentally measured data. The developed material model was integrated into DEFORM® 3D finite element (FE) simulation software as a user subroutine for the prediction of deformation behaviour in a double truncated cone (DTC) sample. Comparison between the experimentally measured data and the results of FE simulation on the DTC sample showed a very good convergence, indicating the suitability of the proposed material’s constitutive model for large scale simulations.Graphical

Crush simulations of composite energy absorbing structural systems

A recently developed material model for orthotropic composites is demonstrated by modeling an energy absorbing crush event used in the development of automotive components. The material model (MAT213) provides a wide variety of capabilities such as tension/compression asymmetric behavior, visco-elastic/plastic behavior, damage modeling, rate and temperature effects with the ability to support these features in shell and solid finite elements. Data from limited laboratory testing of composite coupons is used to construct the material model input. Data from laboratory conducted crush testing is used to validate the material model. The predictions from the explicit finite element (FE) simulations are compared against the laboratory data as well as a popular constitutive model used in the automotive industry (MAT058). Results show that even with incomplete material data to build the constitutive model, MAT213 yields superior results that match experimental validation data reasonably well.

An experimental investigation on tensile behaviour of corroded ultra-high-performance concrete

When UHPFRC is exposed to a corrosive environment, steel fibres may undergo corrosion which may affect the interfacial bond and therefore the overall tensile behaviour of UHPFRC. Previous studies have predominately investigated the influence of fibre corrosion on the tensile behaviour of UHPFRC using the flexural test method. In this approach, the significant variation in crack width may lead to variation in the level of corrosion, making it more difficult to develop material models. In this study, the influence of corrosion on the tensile resistance of UHPFRC has been studied using direct tensile test of thirty-nine grooved prisms with a range of different pre-cracking conditions and corrosion levels. The results show that even when crack widths are large, fibre corrosion has a relatively minor impact on the tensile performance of UHPFRC, and the expected level of deterioration is reduced due to self-healing of cracks and continued hydration of the cement when immersed in the chloride solution. When uncracked specimens are subjected to corrosive environments it was shown that the tensile strength was significantly increased due to enhanced hydration of the binder and associated pozzolanic reaction with silica fume. Despite the degree of experimental scatter and the competing mechanisms of corrosion and self-healing, the residual response of the corroded specimens has been found similar to that of the control specimens.