Proposed Finite Element Model Research Articles

Plastic Limit Pressure Solutions for Elbows With Slant Through-Wall Cracks

Abstract For leak-before-break (LBB) assessment, an idealized through-wall crack (TWC) is typically postulated to determine the critical crack length of cracked piping. However, such an idealization in terms of crack shape can lead to underestimations of plastic limit pressure. Although many studies have been performed to obtain accurate limit load solutions for cracked straight pipes by considering realistic crack geometries, there is still a lack of information regarding slant TWC at elbow. Therefore, three-dimensional finite element (FE) models of an elbow considering the effects of slant TWC on plastic limit pressure are developed. The proposed FE model and analysis procedure were verified through comparisons to the existing solutions for idealized TWCs in elbow. On this basis, the effect of slant TWC on the plastic limit pressure is analyzed, and a closed-form solution of the plastic limit pressure is proposed, for an elbow containing a longitudinal or a circumferential through-wall crack.

Development and verification of a finite element model for double diaphragm preforming of unidirectional carbon fiber prepreg

A finite element (FE) model for double diaphragm preforming of a unidirectional (UD) carbon fiber prepreg was developed. In the model, a hyperelastic constitutive model considering the effect of temperature was used to describe the nonlinear large deformation behavior of the diaphragm in the preforming process. The prepreg lamina was characterized by a transverse isotropy elastic model. The interfacial behavior between prepreg laminate was characterized by a previously developed analytical three-stage inter-ply slipping model which considers the effects of preforming temperature and pressure. Double diaphragm preforming experiments of the UD carbon fiber prepreg laminates over a C-type mold were implemented and then simulated by using the proposed FE model. Comparisons between experimental results and simulation data verified the numerical model. The proposed FE model provides a numerical tool for processing simulation and optimization for double diaphragm preforming of prepregs.

Nonlinear analysis of ECC-encased CFST columns under axial compression

In order to analyze the mechanical behaviors of engineered cementitious composite (ECC)-encased concrete filled steel tube (CFST) columns under uniaxial compressive loading, a finite element (FE) model was established with the software of ABAQUS/standard solver. The constitutive models for concrete, steel and ECC were discussed and the accuracy of the proposed FE model was verified with the previous experimental results. The failure mechanism of ECC-encased CFST columns under uniaxial compressive loading was investigated with the proposed FE model, it was found that ECC-encased CFST column has better composite effects and compatible deformation behavior between different components. In addition, parameter analysis involving different material strength and sectional dimensions was also conducted. According to the failure mechanism and parameter analysis, a simplified calculating method was proposed and the validity was verified with experimental results.

Seismic Analysis of Steel Cylindrical Liquid Storage Tank Using Coupled Acoustic-Structural Finite Element Method For Fluid-Structure Interaction

A seismic analysis of ground-supported, three-dimensional (3-D) rigid-base steel cylindrical liquid storage tank is investigated, using a coupled acoustic-structural finite element (FE) method for fluid-structure interaction (FSI). In this method, the contained liquid in the tank is modelled using acoustic elements and the cylindrical tank is modelled using shell elements. The impulsive and convective terms are estimated separately by using the appropriate boundary conditions on the free surface of the liquid. The convergence and validation studies of the proposed FE model are conducted by comparing the results reported in the literature. The parametric studies are performed for rigid and flexible tanks for the varying slenderness of the open roof tanks. The sloshing displacement and base shear time history responses are evaluated for the 3-D tanks subjected to harmonic unidirectional ground motions. Further, the results are compared with the commonly used two and three lumped-mass models of the tank. Moreover, the seismic response quantities of the tank subjected simultaneously to the bi-directional horizontal components of earthquake ground motion are also investigated using the 3-D FE model, and the response quantities are compared with the lumped-mass models. The results obtained from the 3-D FE model and lumped-mass model are in close agreement. The average percentage difference in the 3-D FE and lumped-mass models for maximum sloshing displacement prediction is 15 percent to 20 percent and that for the base shear is about 4 to 10 percent, in the case of the uni-directional harmonic ground motions. It is concluded that the sloshing displacement is not affected by the tank flexibility, but the impulsive hydrodynamic pressure and the impulsive component of the base shear increases with the tank flexibility.

Axial behavior of reinforced concrete column with ultra-high performance concrete stay-in-place formwork

This paper presents the experimental and numerical study on the axial compressive behavior of a novel composite column that consists of a prefabricated grid-reinforced ultra-high performance concrete (UHPC) stay-in-place (SIP) formwork and post-cast concrete. Eight specimens, including six composite columns and two reinforced concrete columns were tested. The test variables included the type and number of grid layers as well as the thickness of UHPC formwork. According to the test results, the composite columns showed both higher axial load carrying capacity and elastic modulus, whereas the brittle nature of UHPC caused a decrease in ductility and toughness. The use of carbon fiber reinforced polymer (CFRP) grid could provide a more sufficient lateral confinement than stainless steel (SS) grid to achieve a strain hardening behavior and thus increased the ductility and toughness of the specimens. The use of more layers of SS grids could also have a positive effects on brittleness reduction. Furthermore, an analytical model was developed using a finite element (FE) program to simulate axial compressive response of the column. The whole failure process of the composite column and almost all the key characteristics of the load-strain curves were reasonably captured, and a good agreement was found between the calculated and measured load-strain curves, indicating the capability of the proposed FE model to predict the axial compressive behavior of the composite columns.

Thermo-mechanical analysis of train wheel-rail contact using a novel finite-element model

PurposeThe purpose of this paper is to develop a novel method for analyzing wheel-rail (W-R) contact using thermo-mechanical measurements and study the effects of heating on the characteristics of W-R contact under different creepages.Design/methodology/approachThis study developed an implicit-explicit finite element (FE) model which could solve both partial slip and full sliding problems by setting different angular velocities on the wheels. Based on the model, four material types under six different creepages were simulated.FindingsThe results showed that frictional heating significantly affected the residual stress distribution under large creepage conditions. As creepage increased, the temperature of the wheel tread and rail head rose and the peak value was located at the trailing edge of the contact patch.Originality/valueThe proposed FE model could reduce computational time and thus cost to about one-third of the amount commonly found in previous literature. Compared to other studies, these results are in good agreement and offer a reasonable alternative method for analyzing W-R contact under various conditions.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0298

Experimental study on precast concrete sandwich panel with cross-shaped GFRP connectors

Precast concrete sandwich panels (PCSPs) have been extensively used as a facade wall in buildings to improve thermal efficiency. The connectors that link the two concrete wythes are mainly used for in-plane shear transfer. In this study, two cross-shaped glass-fibre-reinforced polymer connectors with different section areas are proposed, with the aim of achieving optimal performance and easy construction in PCSPs. First, the pull-out and shear capacities of the connectors were evaluated. Then four PCSPs and two reinforced concrete solid panel counterparts were fabricated and tested under out-of-plane static loads in order to evaluate their flexural behaviour. The parameters investigated included the connector section area and spacing. Moreover, two-dimensional finite-element (FE) analysis was conducted to reproduce the test. The results indicate that: (a) the proposed connectors can provide considerable performance in terms of anchorage and shear capacity; (b) the failure mode of the PCSP specimens was governed by connector failure; (c) the degree of composite action in terms of ultimate strength can be obviously enhanced by increasing the connector section area and/or reducing its spacing; and (d) based on a comparison with the test results, the proposed FE model can predict the flexural behaviour of the tested PCSPs.

Dynamic Response of Railway Track Resting on Variable Foundation Using Finite Element Method

At high train speed, differential settlement of railway track arises due to the variation in stiffness and yield characteristics of foundation along its length. In the present study, the effect of nonhomogeneous elastic foundation on dynamic response of railway track due to a moving load is studied. The railway track is modeled as an infinitely long beam on nonhomogeneous elastic foundation subjected to a moving load. The foundation stiffness is varying harmonically, about a mean value, along the length of beam. The dynamic response is obtained using a finite element (FE) approach. Adequacy of the proposed FE model is ascertained by comparing the FE results with the results available in the literature. The comprehensive new results are obtained to quantify the effect of amplitude (e) and wavelength (λ) of harmonic foundation on the dynamic response of beam. The peak displacement of beam increases with e, λ and velocity. It is further shown that for harmonically varying foundation, higher-order harmonics are significantly present in the response making it irregular. Also, the critical velocity (Vcr) is considerably affected by e and λ. The variation of peak displacement with velocity is found to be irregular and instead of a distinct peak at Vcr, a plateau is obtained, implying that for a range of velocities peak displacement is quite high. This is also demonstrated through modal mass contribution by a large number of modes. The FE model used in this study can be naturally extended to predict the differential track settlement by including yielding characteristics of foundation.

Linear Finite Element Modeling of Joined Structures With Riveted Connections

Abstract Riveted connections are widely used to join basic components, such as beams and panels, for engineering structures. However, accurately modeling joined structures with riveted connections can be a challenging task. In this work, an accurate linear finite element (FE) modeling method is proposed for joined structures with riveted connections to estimate modal parameters in a predictive manner. The proposed FE modeling method consists of two steps. The first step is to develop nonlinear FE models that simulate riveting processes of solid rivets. The second step is to develop a linear FE model of a joined structure with the riveted connections simulated in the first step. The riveted connections are modeled using solid cylinders with dimensions and material properties obtained from the nonlinear FE models in the first step. An experimental investigation was conducted to study accuracy of the proposed linear FE modeling method. A joined structure with six riveted connections was prepared and tested. A linearity investigation was conducted to validate that the test structure could be considered to be linear. A linear FE model of the test structure was constructed using the proposed method. Natural frequencies and corresponding mode shapes of the test structure were measured and compared with those from the linear FE model. The maximum difference of the natural frequencies was 1.63% for the first 23 out-of-plane elastic modes, and modal assurance criterion values for the corresponding mode shapes were all over 95%, which indicates high accuracy of the proposed linear FE modeling method.

Behavior of ECC-encased CFST columns under eccentric loading

In this paper, the eccentric load behavior of engineered cementitious composite (ECC)-encased concrete filled steel tube (CFST) is analyzed based on ABAQUS/standard solver. A finite element (FE) model was established with consideration of different constitutive models, and the accuracy of proposed FE model was verified with experimental results. Failure mechanisms of ECC-encased CFST columns under eccentric loading were investigated; it was found that the eccentricity ratio has a great influence on the failure processes of the composite column, also the confinement effect decreased as eccentricity ratio increased. Based on the proposed FE model, parameter analysis was conducted to investigate the influences of different material strength and sectional dimensions. Based on stress analysis from the proposed FE model, a theoretical model for predicting sectional capacity of ECC-encased CFST columns has also been proposed and verified.

Experimental and Finite Element Analysis of Force and Temperature in Ultrasonic Vibration Assisted Bone Cutting.

Bone cutting is an essential procedure of orthopedic surgery, while irreversible bone damage would be inevitably caused using the conventional cutting (CC) method. In this study, an ultrasonic vibration-assisted cutting (UVAC) method was applied in bone cutting to investigate the cutting performance, considering the cutting force and temperature rise, in comparison with CC. In addition, a finite element (FE) model was developed to investigate the cutting mechanism and the influence of a wide range of processing parameters on the performance of cutting bone. The results indicate that the proposed FE model shows good correlation with the experimental results for both cutting force and temperature. UVAC can significantly reduce the cutting force and increase the temperature in comparison with CC from the experimental and predicted results. The cutting force tends to decrease with the increasing vibrational parameters and decreasing cutting speed, while the temperature increases. The verified FE bone cutting model provides an efficient way to assist the optimization of the processing conditions in bone cutting operations.

Flexural performance of composite walls under out-of-plane loads

This paper presents a new structural system to use as retaining walls. In civil works, there is a general trend to use traditional reinforced concrete (RC) retaining walls to resist soil pressure. Despite their good resistance, RC retaining walls have some disadvantages such as need for huge temporary formworks, high dense reinforcing, low construction speed, etc. In the present work, a composite wall with only one steel plate (steel–concrete) is proposed to address the disadvantages of the RC walls. In the proposed system, steel plate is utilized not only as tensile reinforcement but also as a permanent formwork for the concrete. In order to evaluate the efficiency of the proposed SC composite system, an experimental program that includes nine SC composite wall specimens is developed. In this experimental study, the effects of different parameters such as distance between shear connectors, length of shear connectors, concrete ultimate strength, use of compressive steel plate and compressive steel reinforcement are investigated. In addition, a 3D finite element (FE) model for SC composite walls is proposed using the finite element program ABAQUS and load-displacement curves from FE analyses were compared against results obtained from physical testing. In all cases, the proposed FE model is reasonably accurate to predict the behavior of SC composite walls under out-of-plane loads. Results from experimental work and numerical study show that the SC composite wall system has high strength and ductile behavior under flexural loads. Furthermore, the design equations based on ACI code for calculating out-of-plate flexural and shear strength of SC composite walls are presented and compared to experimental database.

Quantifying Fire Insulation Effects on the Fire Response of Hybrid-Fiber Reinforced Reactive Powder Concrete Beams

The fire performance of reinforced reactive powder concrete (RPC) beams has raised much concern due to the sensitivity of these beams to high temperature and relatively lower fire resistance. To achieve the fire-resistance ratings as specified in building design codes, a fire insulation layer is often required. However, very limited research has been conducted on the effect of fire insulation on the fire resistance of reinforced RPC beams. Hence, using the commercial software ABAQUS, a three-dimensional sequentially coupled thermal-stress finite element (FE) model was developed to simulate the response of insulated reinforced RPC beams to fire. Comparisons between the FE predictions and the existing fire test results are presented to demonstrate the accuracy of the proposed FE model. In addition, the validated FE model was used to study the effect of fire insulation parameters, including the thermal properties, thickness, height, setting mode, and local fire insulation damage, on the fire response of reinforced RPC beams. The results showed that the failure of reinforced RPC beams with partial loss of fire insulation occurred at the area of missing fire protection. Additionally, the effect of the following important parameters on the fire resistance of insulated reinforced RPC beams was investigated: compressive strength of RPC, reinforcement ratio, load ratio, thickness of RPC cover, beam width, and span-depth ratio.

Research on machining compacted graphite iron under oil-on-water cooling and lubrication conditions based on modified material model

Oil-on-water (OoW) techniques, including external OoW sprayed to both the rake face and flank face (EOoWrf), as well as cryogenic air mixed with OoW (CAOoW), improve the machinability of compacted graphite iron (CGI). This paper proposes a modified material model for RuT400 CGI cutting, based on flow softening and weak thermal softening effect, as observed during split-Hopkinson pressure bar tests. Employing a modified material model and Cock-Latham damage model, a thermo-mechanical coupled finite element (FE) model, for RuT400 cutting, is presented. The simulations, considering dry cutting, EOoWrf, and CAOoW, are conducted for the purpose of revealing the causes for the RuT400 difficult-to-cut property and for establishing how the mechanism of OoW can improve cutting performance. The results show that the effective stress, required to form chip segments in RuT400 machining, is much lower than in hardened steel, so RuT400 is more likely to form a serrated chip. In dry cutting, the chip bottom surface is subject to high strain and temperature, leading to the work-material phase transformation, followed by aggravating adhesive and abrasive wears. Although EOoWrf has little influence on chip morphology and effective stress, it reduces the temperature and strain on chip bottom surface by reducing friction, thus suppressing the occurrence of phase transformation. Due to low friction and high heat exchange, CAOoW produces the lowest tool-chip interface temperature and minimal adhesive wear. For high-speed cutting of RuT400, compared to dry cutting, EOoWrf and CAOoW can effectively reduce cutting forces and maintain the tool temperature in a lower range, where low friction on tool-chip interface plays a key role. The proposed FE model can be used in the future to improve CGI’s machinability, by changing cooling parameters, tool geometry/material, and other machining variables.

On lateral compression of circular aluminum, CFRP and GFRP tubes

Thin-walled structures made of lightweight materials, e.g. aluminum, fiber reinforced composites, have been increasingly used as energy absorption structures in vehicles. This work aimed to characterize the lateral crushing behaviors of circular aluminum, glass fiber reinforced plastics (GFRP) and carbon fiber reinforced plastics (CFRP) tubes with different geometric configuration such as diameter-to-thickness (D/T) ratio or thickness. In the experimental investigation, four different D/T ratios varied from 10.78 to 48.02 were considered here for the aluminum, GFRP and CFRP tubes. Crushing behaviors such as force-displacement curves, deformation histories, and crushing force were quantified. The experimental results revealed that the load carrying capacities, energy absorption (EA) and specific energy absorption (SEA) of the circular tubes decline with increasing D/T ratio. It was found that better crashworthy characteristics of thicker composites, with a smaller D/T ratio, were due to the more favorable failure modes occurring throughout lateral compression. The lateral crashworthy performance of the GFRP tubes was marginally better than that of the CFRP counterparts. Due to ductile behavior of aluminum tubes and brittle behavior of composites, aluminum tubes showed much better lateral crashworthiness than that of the composite counterparts. Moreover, with the increase in the D/T ratio, aluminum tubes exhibited greater advantage on crashworthiness than the composite tubes. On the basis of the experimental data, explicit finite element analysis was further carried out for modeling the lateral crushing behavior of aluminum, GFRP and CFRP tubes. The numerical results were in good agreement with the experimental data, demonstrating the validity of these finite element (FE) models in predicting lateral crushing responses of aluminum, GFRP and CFRP tubes. The proposed FE models can be exploited to further study similar thin-walled metal and composite structures for design optimization.

Micromechanical modeling of the machining behavior of natural fiber-reinforced polymer composites

This paper aims to develop a 2D finite element (FE) model at microscale for numerical simulation of the machining behavior of natural fiber-reinforced polymer (NFRP) composites. The main objective of this study is to reproduce the experimentally observed specific cutting behavior of natural fibers within the composite material. Flax fiber-reinforced polypropylene (PP) composites are modeled separately using an elasto-plastic behavior with a ductile damage criterion for flax fibers and PP matrix, while the microscopic interfaces are represented using the cohesive zone modeling (CZM). Numerical outputs are compared with experimental results for the FE model validation. Results show that the proposed FE model can reproduce the cutting force with a good precision for a large cutting speed range (12–80 m/min). The FE model shows also an efficiency and accuracy in predicting the cutting behavior of flax fibers by reproducing the fiber deformation, the fibers torn-off, and the fracture of the interfaces during machining. Moreover, the FE model can be an effective tool for analyzing the quality of the microscopic interfaces in the NFRP composites after machining.

Parameter optimisation of a 2D finite element model to investigate the microstructural fracture behaviour of asphalt mixtures

To mitigate the risk of asphalt degradation of pavement surfaces and to increase the durability, there is a need to investigate the fracture behaviour of asphalt mixtures at low and intermediate temperatures. The indirect tensile test (IDT) is widely used to characterise the fracture resistance in terms of tensile strengths of the asphalt mixtures. This paper presents an optimised method for two-dimensional (2D) finite element (FE) modelling of the IDT to simulate crack initiation and propagation within the asphalt mixtures on the microscale. X-ray computed tomography (X-ray CT) scanning and digital image processing (DIP) techniques were applied to detect and reconstruct the microstructure of asphalt specimens. Cohesive zone modeling (CZM) techniques were applied in the FE simulations to represent the fracture behaviour. The procedure of the FE modelling and parameter optimisation are described comprehensively. Four important parameters governing the numerical solutions during the simulation process were optimised based on counts of accuracy as well as computational efficiency. The optimised models were also validated based on experimental results. As a case study, the influence of the loading orientation on the fracture behaviour of asphalt mixtures was investigated. The validation and case study prove the reliability and applicability of the proposed FE modelling algorithm; further improvements will be carried out to facilitate the development of the pavement design process.

Validation of a numerical method for predicting shear deformation of reinforced concrete beams

The objective of this paper is to validate a 2D nonlinear finite element (FE) model for estimating the post-cracking shear deformation of reinforced concrete (RC) beams. The proposed FE model treated the cracked concrete as an orthotropic material in the framework of the fixed-crack approach. The experimental data for both the overall response (including the total and shear-induced deflection) and the detailed response (including the mean shear strain, mean vertical strain and principal compressive strain angle) of five I-section RC beams, monitored by the main authors of this paper with the Digital Image Correlation technique, were used to verify the proposed model. In addition, 27 further test beams evaluated in independent research programs were collected to assemble a database. The proposed FE model was further verified against the database. Two additional FE models (the rotating-crack model developed in this work and Response-2000 developed by Bentz (2000)) were also evaluated by simulating the detailed responses of the beams in the database. The results obtained validate the proposed FE model for predicting the post-cracking shear deformation of RC beams and indicate that the proposed FE model is more suitable for simulating the shear behaviour of RC beams than the rotating-crack model or Response-2000.

Simulations and Experiments of EMFY-1 Electromagnetic Launcher

ASELSAN Inc. has been conducting experimental research on electromagnetic launch technologies since 2014. The first prototype, EMFY-1, has 25 $\text {mm} \times 25$ mm square bore and 3-m-length rails. In addition, two capacitor-based pulsed-power supplies (PPSs) with 1- and 4-MJ stored energy are built to supply launcher. During the design process of EMFY-1, a 3-D finite element (FE) model has been developed to simulate the electromagnetic and mechanical aspects of the railgun. This paper presents the simulation and experimental results of EMFY-1 with C-type aluminum armature. FE model, developed using COMSOL Multiphysics, includes both launcher and the PPS system. In addition to the velocity and position of the armature with respect to time, it is possible to observe the magnetic field, current density distributions and breech voltage using the FE model. In the experiments, pulse currents of the PPS modules, breech, and muzzle voltages are measured. The velocity of the projectile is measured using the B-dot probes. In this paper, two experiments of EMFY-1 will be presented. In the first experiment, the launch package with 42-g total mass is accelerated to 2778 m/s, and in the second experiment, the launch package with 130-g total mass is accelerated to 1560 m/s. The simulation results of the proposed FE model are compared with the experiments. It is observed that there is a good agreement between experimental and simulation results.

Buckling behaviors and ultimate strengths of 6082-T6 aluminum alloy columns under eccentric compression – Part I: Experiments and finite element modeling

Aluminum alloys, which function as load-bearing components or decorative materials, have been commonly applied to architectural structures. In this study, a combination of experiments and finite element analyses was conducted to investigate the stability behaviors and ultimate strengths of the 6082-T6 aluminum alloy columns subjected to eccentric compression. Prior to the loading tests, tensile coupon tests and measurement of the initial geometric imperfections for the columns were performed. The buckling behaviors of 30 pin-ended specimens, including 11 extruded square hollow section (SHS) columns and 19 extruded circular hollow section (CHS) columns, were investigated and the observed failure modes of the tested columns included overall buckling, local buckling and the coupling modes. Meanwhile, the ultimate strengths, deflections and surface strains in whole process under eccentric compression were recorded. The finite element (FE) models of the tested columns were developed using the non-linear finite element analysis (FEA) software ABAQUS, and the geometric and material nonlinearities were considered in the FE models. The validation of the FE models was performed against the test results; it was observed that the proposed FE models are sufficiently accurate to predict the ultimate strengths and buckling behaviors of the tested columns.