Development Of Material Model Research Articles

Numerical modelling of stainless steel preloaded bolted connections

AbstractThe use of stainless steel in construction has become more popular in recent years. It is used for a wide range of structural applications in aggressive environments where reliable performance over long periods with little maintenance is required. Although structural design standards are available for stainless steel, currently there are no rules covering the design of preloaded slip‐resistant bolted connections because of the lack of knowledge about their long‐term viscoplastic behaviour. Viscoplastic creep and stress relaxation in the preloaded bolt assemblies will lead to a certain loss of clamping force and may cause the failure of the connection if not accounted for. This paper presents the development of material models and finite element models for bolt assemblies based on an extensive experimental study of creep, relaxation and tension effects on austenitic, ferritic, duplex and lean duplex steel plates and bars for different loading rates. These models were verified against slip tests with stainless steel bolt assemblies according to EN 1090‐2 and then used in a parametric study to extend the scope of the connections investigated. Both experimental programmes were carried out in the European RFCS research project SIROCO (Execution and reliability of slip‐resistant connections for steel structures using Carbon Steel and Stainless Steel) as well as finite element calculations.

Load Testing of GFRP Composite U-Shape Footbridge

The paper presents the scope of load tests carried out on an innovative shell composite footbridge. The tested footbridge was manufactured in one production cycle and has no components made from materials other than GFRP laminates and PET foam. The load tests, performed on a 14-m long structure, were the final stage of a research program in the Fobridge project carried out in cooperation with: Gdańsk University of Technology (leader), Military University of Technology in Warsaw, and ROMA Co. Ltd.; and co-financed by NCBR. The aim of the tests was to confirm whether the complex U-shape sandwich structure behaves correctly. The design and technological processes involved in constructing this innovative footbridge required the solving of many problems: absence of standards for design of composite footbridges, lack of standardized material data, lack of guidelines for calculation and evaluation of material strength, and no guidelines for infusion of large, thick sandwich elements. Obtaining answers during the design process demanded extensive experimental tests, development of material models, validation of models, updating parameters and extensive numerical parametric studies. The technological aspects of infusion were tested in numerous trials involving the selection of material parameters and control of the infusion parameters. All scientific validation tests were successfully completed and market assessment showed that the proposed product has potential applications; it can be used for overcoming obstacles in rural areas and cities, as well as in regions affected by natural disasters. Load testing included static and dynamic tests. During the former, the span was examined at 117 independent measurement points. The footbridge was loaded with concrete slabs in different configurations. Their total weight ranged from 140 kN up to 202 kN. The applied load at the most heavily loaded structural points caused an effect from 89% to 120%, compared to the load specified by standards (5 kN/m2). Dynamic tests included standard actions (walking, running, synchronous jumps) as well as aggressive tests, all designed to confirm the usability of the footbridge. The performed trials allowed the identification of the modal and damping parameters of the structure. The designated first natural frequency with a value of 7.8 Hz confirmed the correctness of the U-shape cross-section design due to its significant structural rigidity.

Long‐ and short‐term serviceability behavior of reinforced concrete beams: Mechanics models for deflections and crack widths

Analysis and design of reinforced concrete (RC) flexural members at the serviceability limit state is complicated by the localized bond slip or partial interaction (PI) between tensile reinforcement and the surrounding concrete. Localized slip is responsible for crack formation, crack widening, and tension stiffening and is further complicated by the time‐dependent nature of concrete, which results in reduced tension stiffening and widening of cracks. Analysis techniques commonly applied in design are typically formulated on the assumption of full interaction between the reinforcement and the surrounding concrete. Hence, they do not simulate the behaviors observed in practice, but rather they correlate analytical predictions with experimental observations through the use of empiricisms, such as effective flexural rigidities and statistically derived expressions for crack widths. In this paper, it is shown how PI theory can be directly incorporated into elastic analysis procedures to develop simple expressions for flexural rigidities and crack widths under both instantaneous and sustained loading. The proposed approach should simplify not only the design process but also the development of design guidelines and material models, as it provides a simple rational method for investigating the time‐dependent flexural behavior of RC members.

Development of a high temperature material model for grade s275jr steel

The paper presents test results for the mechanical and creep properties of the European steel grade S275JR at high temperatures. The objective of the research was to obtain a reliable estimate of creep strain development in the temperature range 400–600°C, and to identify the critical thermo-mechanical parameters which activate the creep mechanism. Tests of mechanical properties at temperature levels up to 600°C have shown good agreement with the reduction factors for yield strength and modulus of elasticity given in Eurocode 3 and other comparable studies. A critical temperature for creep development of approximately 400°C was identified in the tests. The creep tests conducted have also shown that the creep strain rate starts to develop significantly at temperatures around 500°C when coupons are exposed to a mid-range stress level equal to 60% of the stress at 0.2% strain. The temperature level of 600°C is identified as the upper-bound temperature for creep development, since creep develops very rapidly, even at very low stress levels. Finally, the paper presents an analytical creep model suitable for implementation in Finite Element-based numerical models.

Verification and adaptation of plasticity models under complex variable loading with intermediate complete and partial unloadings

The experimental studies of elasto-plastic deformation of tubular steel samples under proportional and non-proportional (monotonic and cyclic) loadings, including partial and intermediate loadings, have been conducted with the aim of improving the accuracy of the description of the complex passive loading processes. The plastic strain accumulation was observed in the course of tests carried out under passive loading. However, this effect turned out not to be described by the plastic flow theory. This result required the development of an alternative material model. The comparisons of experimental results with the predictions of the structural (rheological) elasto-plastic model and the multisurface theory of plasticity with one active surface were made. Modifications of the constitutive equations were proposed in order to improve the accuracy of the material response prediction.

Eurocode conforming design of BRBF – Part II: Design procedure evaluation

Buckling Restrained Braces (BRB) are innovative displacement dependent devices having balanced hysteretic behavior. Frames equipped with such devices are known as Buckling Restrained Braced Frames (BRBF). Application of BRB elements in Europe is seriously limited by the lack of a standardized European design procedure for BRBF.In the first part of this paper the authors propose a Eurocode conforming design procedure for BRBF and provide the seismic design parameters and capacity design rules by enhancing Eurocode 8 specifications on steel Concentrically Braced Frames. This second part introduces 24 BRBF archetypes designed with the proposed procedure. Their performance under seismic excitation is investigated by nonlinear dynamic analysis in an environment developed by the authors through improvement of the methodology in FEMA P-695. Feasibility of the proposed design procedure is evaluated as a function of conditional failure probability of the archetype buildings.The presented assessment required detailed experimental studies on BRB behavior and development of a novel material model that can simulate complex nonlinear hardening under irregular cyclic loading. The material model is implemented in the OpenSees finite element code. A software environment was developed for automatic evaluation of braced frames using OpenSees.The sufficiently low collapse probability of BRBF archetypes confirms the applicability of the proposed design procedure in Europe.

Seismic Assessment of Reinforced Concrete Bridge Under Chloride-Induced Corrosion

Chloride-induced corrosion continues to the main cause of deterioration of concrete structures in the marine areas. To introduce the high rate of corrosion in Persian Gulf area, the axial load-carrying capacity of reinforced concrete columns, which have been exposed to the real corrosive condition of this area about 1.5 years, is measured. Then, a new framework for long-term seismic evaluation of existing corroded reinforced concrete bridge in this area is proposed. Calculation of corrosion initiation time, development of material model considering effects of corrosion, moment–curvature analysis of bridge columns, determination of plastic hinge characteristics, and pushover analysis in longitudinal and transverse directions of the bridge are the main steps of proposed framework. Effects of corrosion include the degradation of cover and core concrete, steel bar, and bonding between concrete and steel bar. By comparing the obtained seismic capacity of bridge at specific time points in bridge service life, effect of corrosion on the long-term seismic performance of bridge is determined. On the basis of analysis results, due to ensuring the long-term seismic performance of seismically designed reinforced concrete bridge in the marine area after 90 years of service, it is suggested in this paper that the design base shear should be increased by 12.5%.

Data driven modeling of plastic deformation

In this paper the application of machine learning techniques for the development of constitutive material models is being investigated. A flow stress model, for strain rates ranging from 10−4 to 1012 (quasi-static to highly dynamic), and temperatures ranging from room temperature to over 1000 K, is obtained by beginning directly with experimental stress–strain data for Copper. An incrementally objective and fully implicit time integration scheme is employed to integrate the hypo-elastic constitutive model, which is then implemented into a finite element code for evaluation. Accuracy and performance of the flow stress models derived from symbolic regression are assessed by comparison to Taylor anvil impact data. The results obtained with the free-form constitutive material model are compared to well-established strength models such as the Preston–Tonks–Wallace (PTW) model and the Mechanical Threshold Stress (MTS) model. Preliminary results show candidate free-form models comparing well with data in regions of stress–strain space with sufficient experimental data, pointing to a potential means for both rapid prototyping in future model development, as well as the use of machine learning in capturing more data as a guide for more advanced model development.

Automated methods for the quantification of 3D woven architectures

Serial sectioning was used to characterize the three-dimensional (3D) architecture of metallic textiles, a new class of periodic cellular materials for structural applications. Reconstructing the serial sectioned data required the development of an adaptive stitching algorithm to montage individual tiles from each section due to the sparse nature of this periodic structure where a predefined stitching pathway does not perform well. This dataset was used to develop computational tools to automate the quantification of the bonding efficiency and weave geometry to inform the weave processing as well as incorporate these parameters in the development of material models for more accurate performance prediction. An inverse correlation was present between the wire spacing and the bonding efficiency of wire joints where bonding efficiency increased with a decrease in wire spacing. These tools could have broader applications analyzing other periodic cellular materials, containing similar sized struts, utilizing different materials or processing routes.

Life cycle analysis of HDPE Pipe Manufacturing – A Case Study from an Indian Industry

The growth in thermoplastic market is increasing rapidly as a replacement of cement, wooden, and metal products. The growth in plastic production has been around 9% since 1950s. 80% of the consumed plastic is thermoplastic. HDPE pipes are commonly used thermoplastic for the municipal pipelines, industrial pipeline, mining, cable duct, etc. as HDPE costs less and require fewer repairs. The plastic at end of life has nearly zero biodegradability, consumes natural resources (i.e. fossil fuel) and requires large area for landfills. This study assesses the environmental impact of the HDPE pipe by means of life cycle assessment methodology. The inventory analysis was carried out at the production site of a company. The Umberto NXT Universal software has been used to visualize the material and energy flow modeling and to conduct the impact assessment. The well-known eco-invent dataset is utilized for development of material and energy flow model. Impact assessment has been carried out by using ReCiPe method. Both mid-point and end-point impact assessments have been carried out to visualize the environmental impacts in details. It is found in the study that the raw material phase of the HDPE pipe production has highest environmental impact, followed by end-of-life and manufacturing phases.

Finite element modeling of a novel cutting deformation mode of AA6061-T6 tubes employing higher order Lagrangian element formulations

A finite element model of axial cutting of an aluminum extruded tube was developed with the IMPETUS Afea solver®. Uniaxial tensile tests and VDA 238 plate bending tests were completed to identify material model parameters including the necessary data for a Cockcroft-Latham damage model. Inverse material model development was completed with a custom interface between LS-OPT and IMPETUS. The Cockcroft-Latham parameter was noted to be approximately 100% larger when identified from inverse material modeling with respect to analytical calculations from uniaxial tensile tests. The model is capable of accurately capturing the force versus deflection response with Oberkampf–Trucano validation metrics exceeding 0.9 demonstrating greater accuracy than previous modeling efforts with an alternative commercial solver. Additionally, the IMPETUS model captures deformation mechanisms critical to the development of an analytical model with less than 20% error enhancing confidence in both approaches.

Development of a non-orthogonal macroscale material model for advanced woven fabrics based on mesoscale structure

Abstract A macroscale non-orthogonal constitutive material model for woven fabrics based on a mesoscale unit cell is developed and implemented in an explicit finite element code. The model utilizes two important deformation mechanisms involved in woven fabrics: (1) Yarn elongation, and (2) Relative yarn rotation due to shear loads. The yarns' uniaxial tensile response is modeled using nonlinear springs within the unit cell formulation while a nonlinear rotational spring is used to define the fabric's shear stiffness. Continuum mechanics are employed to keep track of the yarn orientations at a given unit cell configuration. Material properties/parameters of the model can be easily determined from standard experimental tests. The material model is validated using uniaxial tensile, bias extension, 30° off axis tension and indentation tests for two different plain weave Kevlar fabrics. The results show that the developed model is capable of the mechanical response of the woven fabrics under various loading conditions.

Development of material model for assessment of brittle cracking behavior of plexiglas

The objective of this study is to investigate the brittle cracking behavior of Plexiglas material when subjected to indentation loading. Indentation tests were conducted on Modified Vickers testing machine to acquire the experimental data in the form of load-displacement curve. Several mechanical properties such as hardness, yielding stress and fracture toughness have been ascertained from the analysis of the experimental data. The experimental data then used to create a mathematical model of Plexiglas for its brittle cracking behavior with indentation loading. Furthermore, a numerical simulation based study was carried out to simulate the brittle cracking in Plexiglas plate when subjected to indentation loading. The simulations were performed in the FE solver Abaqus. The brittle cracking model in Abaqus/Explicit is used which determines the required force and displacement to produce crack in Plexiglas. Finally a comparison of simulation results was made to the experimental data to validate the FEA procedures and accuracy of predictions. The numerical predictions of load-displacement curve found remarkably consistent with experimental results.

Micromechanical Characteristics of Hardly Deformable Mg Alloys

Mechanical characterization of individual microstructural phases of hardly deformable magnesium alloys is of crucial importance for the development of multi-scale material models. The magnesium alloys are used for preparation of fine tubes with diameter of a few millimeters and tens of millimeters wall thickness. It is hard to control an ordinary drawing process for the preparation of such tubes. However, the tubes can be prepared with a laser dieless drawing process that is, in contrary to conventional drawing, able to draw low formability materials and it is able to produce variable cross-sections of the tube or a wire with high precision. The magnesium alloy tubes are used in various fields as micro-electro-mechanical systems, medicine, electrical, biological and chemical fields. In this paper, preliminary microstructural studies and local mechanical characterization of pure Mg, MgCa0.8 and AZ31 magnesium alloys used for tube extrusion, is provided. The material microstructure is studied by means of scanning electron, atomic force microscopes and nanoindentation. Elastic properties and volume fractions of mechanically distinct phases that are not accessible by standard testing methods are provided in the paper.

Consumption and diffusion of oxygen during the thermoxidative ageing process of elastomers

Thermoxidative ageing of elastomers is investigated by having a closer look on the consumption and diffusion of oxygen during the exposure to elevated temperatures. After the introduction of some basic theory an experimental set‐up is described, which enables the measurement of the oxygen amount being absorbed during weathering. Hence the oxygen consumption of natural rubber was detected at elevated temperatures and for varying exposure times. The correlation of changes in the mechanical properties and the oxygen consumption is analysed in order to get new awareness of oxidation affecting the mechanical behaviour. Influences of diffusion effects on the degradation are investigated by the use of micro X‐ray tomography, which detects minor changes in density generated by oxidation. Density profiles over the cross‐section of the samples are created, which illustrate the appearance of diffusion‐limiting oxidation. The results offer a closer look at the thermoxidative ageing of natural rubber and should help to get a better understanding of the degradation during ageing. Finally the findings may improve the life‐time prediction of elastomeric components by providing the basis for the development of advanced material models.

Interaction of run-in edge dislocations with twist grain boundaries in Al-a molecular dynamics study

Grain boundaries play an important role in outlining the mechanical properties of crystalline materials. They act as sites for absorption/nucleation of dislocations, which are the main carriers of plastic deformation. In view of this, the interactions between edge dislocations and twist grain boundaries-dislocation pileup, dislocation absorption and dislocation emission were explored by performing molecular dynamics simulations in face-centered cubic Al using embedded atom method. The 1 1 0 twist grain boundaries with various misorientation angles were selected for this purpose. It was found that the misorientation angle of boundary and stress anomalies arising from repeated dislocation absorption at the grain boundaries are the important parameters in determining the ability of the boundary to emit dislocations. Complex network of dislocations results in later stages of deformation, which may have a significant effect on the mechanical properties of the material. The peculiarities of dislocation nucleation, their emission from twist grain boundaries and the ramifications of this study towards development of higher length scale material models are discussed.

Physical and Numerical Simulation of Cold Rolling and Heating during Continuous Annealing of DP Steel Strips

Development of fast and efficient finite element model for rolling industrial grades of two DP steels was the subject of the present paper. Basis of the finite element framework, as well as material model development stages, are presented first. Model validation with experimental measurements is shown next. Finally, selected examples of multi scale modelling including microstructure level are presented to complement presented investigation and show possibilities of future developments.

In-air and pressurized water reactor environment fatigue experiments of 316 stainless steel to study the effect of environment on cyclic hardening

Argonne National Laboratory (ANL), under the sponsorship of Department of Energy's Light Water Reactor Sustainability (LWRS) program, is trying to develop a mechanistic approach for more accurate life estimation of LWR components. In this context, ANL has conducted many fatigue experiments under different test and environment conditions on type 316 stainless steel (316 SS) material which is widely used in the US reactors. Contrary to the conventional S ∼ N curve based empirical fatigue life estimation approach, the aim of the present DOE sponsored work is to develop an understanding of the material ageing issues more mechanistically (e.g. time dependent hardening and softening) under different test and environmental conditions. Better mechanistic understanding will help develop computer-based advanced modeling tools to better extrapolate stress-strain evolution of reactor components under multi-axial stress states and hence help predict their fatigue life more accurately. Mechanics-based modeling of fatigue such as by using finite element (FE) tools requires the time/cycle dependent material hardening properties. Presently such time-dependent material hardening properties are hardly available in fatigue modeling literature even under in-air conditions. Getting those material properties under PWR environment, are even harder. Through this work we made preliminary attempt to generate time/cycle dependent stress-strain data both under in-air and PWR water conditions for further study such as for possible development of material models and constitutive relations for FE model implementation. Although, there are open-ended possibility to further improve the discussed test methods and related material estimation techniques we anticipate that the data presented in this paper will help the metal fatigue research community particularly, the researchers who are dealing with mechanistic modeling of metal fatigue such as using FE tools. In this paper the fatigue experiments under different test and environment conditions and related stress-strain results for 316 SS are discussed.

Development of a hyperelastic material model of subsynovial connective tissue using finite element modeling

Carpal tunnel syndrome (CTS) is one of the most common disorders of the hand. Assessment of carpal tunnel tissue mechanical behavior, especially that of the subsynovial connective tissue (SSCT), is important to better understand the mechanisms of CTS. The aim of this study was to develop a hyperelastic material model of human SSCT using mechanical test data and finite element modeling (FEM). Experimental shear test data of SSCT from 7 normal subjects and 7 CTS patients collected in a prior study was used to define material response. Hyperelastic coefficients (μ and α) from the first-order Ogden material property definition were iteratively solved using specimen-specific FEM models simulating the mechanical test conditions. A typical Ogden hyperelastic response for the normal and CTS SSCT was characterized by doing the same with data from all samples averaged together. The mean Ogden coefficients (μ/α) for the normal cadaver and CTS patient SSCT were 1.25×10−5MPa/4.51 and 1.99×10−6MPa/10.6, respectively when evaluating coefficients for individual specimens. The Ogden coefficients for the typical (averaged data) model for normal cadaver and CTS patient SSCT were 1.63×10−5MPa/3.93 and 5.00×10−7MPa/9.55, respectively. Assessment of SSCT mechanical response with a hyperelastic material model demonstrated significant differences between patient and normal cadaver. The refined assessment of these differences with this model may be important for future model development and in understanding clinical presentation of CTS.

Numerical Modeling of Functional Fatigue in NiTi Wires

AbstractMotivated by the high potential of shape memory alloys (SMA) in several industrial applications, we investigate the material response under cyclic loading. In particular, the focus is set on the modelling of functional fatigue, which results in the deterioration of the specific features of SMA. In fact, functional fatigue restricts SMA in terms of its applicability for real structures and workpieces. This necessitates the development of material models which take this phenomenon into account. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)