Present Finite Element Model Research Articles

UNVEILING THE INFLUENCE OF ONE-LEG STANCE AND STANDING UP FROM A CHAIR ON HUMAN HIP JOINT PROSTHESIS USING FINITE ELEMENT CONCEPTS

The hip joint plays an important role in providing stability to the human body. Factors such as aging, wear, and tear, make the hip joint degenerate and, in such cases, the same to be replaced through hip arthroplasty surgeries. The background of this study aims to investigate the contact consequence between the artificial femoral head and the acetabular cup for different bearing couples during one-leg stance and standing up from a chair, utilizing the finite element method. The three-dimensional finite dynamic contact model has been developed with different material combinations. The results obtained by the present finite element model align well with the previously available literature. The parameters investigated include maximum von Mises stress, maximum contact pressure and deformation for different material combinations. The results reveal that the pair i.e., Alumina on Ultra-high molecular weight polyethylene (UHMWPE) exhibits lower contact pressure, von Mises Stress and deformation. Therefore, the material pair i.e., Alumina on UHMWPE can be employed in the Total hip replacement (THR) to mitigate contact consequences under both static and dynamic loading conditions, thereby enhancing the durability of the artificial joints.

Pseudo‐ductility behavior of carbon/glass hybrid composites with unidirectionally arrayed chopped strands: Experimental and numerical research

AbstractAlthough lightweight fiber‐reinforced polymer (FRP) composites are widely used in various engineering fields due to their high specific strength and modulus, the mutual exclusion of strength and toughness is one of the bottlenecks in the field of FRP design because of the inherent brittleness of fiber themselves. In this research, discontinuous fiber structures with vertical and bi‐angled slits are introduced into the thin‐ply carbon fiber prepreg. The fracture energy and delamination degree of the center carbon fiber layer could be controlled by adjusting the structural parameters to design the pseudo‐ductility of carbon/glass (C/G) hybrid laminates and obtain the higher pseudo‐yield stress. The hybrid specimens with 20 mm slits exhibit obvious pseudo‐ductility, and the pseudo‐ductility strain increases as the C/G ratio increases, while the plateau stress decreases. The larger slit distance provides sufficient propagation space for the delamination damage, which dissipates tensile energy and results in a smoother plateau area of the stress–strain curve. The stress–strain curve of the specimen with a smaller slit exhibits a noticeable rapid load decrease caused by the transient propagation of delamination damage. The peak stress of hybrid laminate with bi‐angled slits shows the highest pseudo‐yield stress. The present finite element model successfully analyzed the pseudo‐ductile damage propagation of C/G hybrid laminates with vertical slits, and the results are in good agreement with the experiments.Highlights Revealed the pseudo‐ductility behavior of carbon/glass hybrid composites. The pseudo‐ductility of carbon/glass hybrid composites is controllable. The pseudo‐ductility strain increases with the increase of C/G ratio.

Stiffness Change for Reconfiguration of Inflated Beam Robots.

Abstract Active control of the shape of soft robots is challenging. Despite having an infinite number of passive degrees of freedom (DOFs), soft robots typically only have a few actively controllable DOFs, limited by the number of degrees of actuation (DOAs). The complexity of actuators restricts the number of DOAs that can be incorporated into soft robots. Active shape control is further complicated by the buckling of soft robots under compressive forces; this is particularly challenging for compliant continuum robots due to their long aspect ratios. In this study, we show how variable stiffness enables shape control of soft robots by addressing these challenges. Dynamically changing the stiffness of sections along a compliant continuum robot selectively "activates" discrete joints. By changing which joints are activated, the output of a single actuator can be reconfigured to actively control many different joints, thus decoupling the number of controllable DOFs from the number of DOAs. We demonstrate embedded positive pressure layer jamming as a simple method for stiffness change in inflated beam robots, its compatibility with growing robots, and its use as an "activating" technology. We experimentally characterize the stiffness change in a growing inflated beam robot and present finite element models that serve as guides for robot design and fabrication. We fabricate a multisegment everting inflated beam robot and demonstrate how stiffness change is compatible with growth through tip eversion, enables an increase in workspace, and achieves new actuation patterns not possible without stiffening.

Probability distribution functions for the ultimate strength of X-joints with collar plates in compressive load at room and fire conditions

In this paper, the results of performing finite element (FE) analysis on 360 tubular X-joints reinforced with collar plates have been used to propose a probability distribution model for ultimate strength at ambient and fire conditions. As far as the authors know, no study has been conducted on the probability distribution of the ultimate strength in X-joints with collar plates. Consequently, according to the reinforced X-joints, a total of ultimate capacity data sets was generated. The FE models were validated and compared with 35 experimental tests and numerical models. Also, in the present FE models, the welds connecting the plates to the chord member were created. Moreover, the contacts between the outer surfaces of the chord member and the inner surfaces of the reinforcing plates were modeled. In addition, nonlinear material and geometry properties were applied. In the following step, twelve theoretical probability density functions (PDFs) were fitted to relative frequency histograms of five databases. The maximum likelihood method was applied to determine the parameters of each distribution. Investigating the goodness-of-fit according to the Kolmogorov-Smirnov, Anderson Darling, and Chi-square tests showed that the Generalized Petro distribution is the best for the ultimate capacity values in collar plate retrofitted X-joints at ambient and different fire conditions. In the following step, six fully defined theoretical PDFs and cumulative distribution functions (CDFs) were established. Also, probability-probability graphs indicated that the proposed theoretical probability distributions are near the given data sets.

A unified buckling formulation for linear and nonlinear analysis of laminated plates using penalty based [formula omitted] FEM-HSDT model

In this paper, the effect of pre-buckling boundary conditions and the type of nonlinearity for stress stiffening used in different linear and nonlinear buckling approaches is studied for laminated composite plates. The study is conducted using a C0 finite element (FE) plate model, employing a unified C1 higher-order shear deformation theory (HSDT). The set of governing equations is derived using the principle of virtual displacement and solved using the tangent-based arc-length method in conjunction with a simple branch switching technique. The performance of the present C0 FE model is assessed through a validation exercise and comparison with results obtained via the use of ANSYS and, for linear analysis, Navier solution, as well as solutions available in the literature. The influence of the different in-plane loads, boundary conditions, side-to-thickness ratio, fiber orientation, types of imperfection and penalty stiffness matrix are also examined. The results show that the same boundary conditions must be utilized in both pre-buckling and linear eigenvalue analyses for accurate and realistic predictions of critical buckling loads, as confirmed from the nonlinear buckling analyses. Furthermore, the critical buckling loads obtained using Green–Lagrange nonlinearity are observed to be more conservative than those obtained using von Kármán nonlinearity. The nonlinear buckling approach is a generalized approach while the nonlinear eigenvalue approach has a limited range of application.

DEVELOPMENT OF AN OPEN-SOURCE FINITE ELEMENT ANKLE MODEL FOR IN-SILICO INVESTIGATION OF THE ANKLE JOINT

AbstractObjectivesThis abstract provides an update on the Open Ankle Models being developed at the University of Bath. The goal of this project is to create three fully open-source finite element (FE) ankle models, including bones, ligaments, and cartilages, appropriate musculoskeletal loading and boundary conditions, and heterogeneous material property distribution for a standardised representation of ankle biomechanics and pre-clinical ankle joint analysis.MethodsA computed tomography (CT) scan data (pixel size of 0.815 mm, and slice thickness of 1 mm) was used to develop the 3D geometry of the bones (tibia, talus, calcaneus, fibula, and navicular). Each bone was given the properties of a heterogeneous elastic material based on the CT greyscale. The density values for each bone element were calculated using a linear empirical relation, ρ= 0.0405 + (0.000918) HU and then power law equations were utilised to get the Young's Modulus value for each bone element [1]. At the bone junction, a thickness of cartilage ranging from 0.5–1 mm, and was modelled as a linear material (E=10 MPa, ν=0.4 [2]). All ligament insertions and positions were represented by four parallel spring elements, and the ligament stiffness and material attributes were applied in accordance with the published literature [2]. The ankle model was subjected to static loading (balance standing position). Four noded tetrahedral elements were used for the discretization of bones and cartilages. All degrees of freedom were restricted at the proximal ends of the tibia and fibula. The ground reaction forces were applied at the underneath of the calcaneus bone. The interaction between the cartilages and bones was modelled using an augmented contact algorithm with a sliding elastic contact between each cartilage. A tied elastic contact was used between the cartilages and the bone. FEbio 2.1.0 (University of Utah, USA) was used to construct the open-source ankle model.ResultsWhen the double-legged stance phase loading condition was taken into consideration, stress at the antero-medial tibial wall (ranged from 1 to 7 MPa) was found to be similar to the prior work [2], indicating bulk of the load transfer was through this region. The maximum principal strain was predicted at the different regions on bones around the ankle joint. The proximal surface of the talus, and tibial distal surface were shown to have the highest maximum principal strains followed by antero-medial walls of the tibia bone, at the proximal location.ConclusionsThe present open 3D FE model of the ankle will assist researchers in better understanding ankle biomechanics, precisely predicting load transfer, and examining the ankle to address unmet clinical needs for this joint. The results of the current investigation are realistic in terms of load transfer and stress-strain distribution across the ankle joint and well comparable to those reported in the literature [2]. However, sensitivity and ankle instability simulations will be performed in future work to investigate the model's reliability and robustness.Declaration of Interest(b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Thermo-electro-elastic coupled modeling and simulation of functionally graded piezoelectric structures

Compared with the composite materials, the functionally graded materials can not only provide better specific stiffness but also reduce the risk of layered damage. Therefore, the graded distribution forms have become the development trend of advanced structures. An efficient finite element (FE) modeling method and numerical simulation of plate and shell with nonlinear temperature gradient coupling are developed based on the FOSD hypothesis for thermo-electro-elastic coupled functionally graded piezoelectric material (FGPM) integrated with smart structures in this paper. The constitutive model for thermo-electro-elastic coupled FGPM is derived. Assuming that the temperature gradient distribution changes secondarily through the thickness, two nonlinear physical models for temperature change are constructed. Based on the FOSD hypothesis, the multi-field coupled FE equation of plate and shell is derived. The accuracy of the present FE model is verified by the commercial calculation structures. The parametric simulation of FGPM shells is carried out based on the FE model.

Verification of Composite Beam Theory with Finite Element Model for Pretensioned Concrete Members with Prestressing FRP Tendons.

Composite beam theory was previously developed to establish an analytical solution for determining the transfer length of prestressed fiber-reinforced polymers (FRP) tendons in pretensioned concrete members. In the present study, a novel finite element (FE) modeling approach is proposed to provide further verification of the developed analytical method. The present FE model takes into account the friction coefficients obtained from pull-out tests on the FRP tendons and prestressed concrete members. Convergence analysis of two numerical simulations with different mesh densities is carried out as well. The results demonstrated that the transfer length predicted by the fine FE model with a friction coefficient of α = 0.3 for high pretension is in good agreement with the measured values and the analytical solutions. The consistency between the analytical solution and FE simulation not only further proves the reliability of composite beam theory but also demonstrates the importance of the bond-slip relationship in predicting the transfer length of pretensioned concrete members prestressed with FRP tendons.

The effect of interphase and agglomeration on the mechanical properties of aluminum matrix nanocomposites reinforced with carbon nanotubes

The interphase phenomena are a critical problem for estimating the mechanical behavior of carbon nanotube-reinforced aluminum composites. In this research, the Aluminum-carbide (Al4C3) interphase and carbon nanotubes (CNTs) agglomeration effects on the mechanical properties of Aluminum /Carbon nanotubes composites are investigated using a numerical micromechanical model. Moreover, the impacts of the CNTs fraction, agglomeration, Al4C3 interphase, and their diameter on the elastic modulus of Aluminum (Al) composites are explored. The results demonstrated the effect of CNTs agglomeration and Al4C3 interphase on Young’s modulus of Al composites significantly when the CNT fraction increases; In addition, it observed that with increasing interphase thickness, Young’s modulus of Al composites increases and is changed with variation of agglomeration shape. The Literature’s experimental results validated the applicability of the present finite element (FE) model. The results of this study are hard evidence for CNT/ Aluminum composites creating potential applications in industry, especially for automobile and aircraft fields.

Finite Element Analysis of Laminated Composite Shells with Piezoelectric Elements

The concept of incorporating some degree of smartness or intelligence in a system is gaining wide acceptance for utilisation in a variety of practical applications from aircraft to medical diagnostics because of the capability of smart materials to execute specific functions intelligently in response to changes in environmental stimuli. In this paper, the effectiveness of a simple finite element model in ANSYS is established for analyzing laminated composite shells with piezoelectric elements under static and dynamic loading. The substrate in smart shell is discretised using SOLSH190 element and the piezoelectric layer is discretised using coupledfield element, SOLID5. The basic behaviour of a smart composite shell depends on the behaviour of substrate with the response reduced/controlled by the properties of smart materials used, which is predicted effectively by the present finite element model.

Thermal–Structural Linear Static Analysis of Functionally Graded Beams Using Reddy Beam Theory

In this work, a finite element model to perform the thermal–structural analysis of beams made of functionally graded material (FGM) is presented. The formulation is based on the third-order shear deformation theory. The constituents of the FGM are considered to vary only in the thickness direction, and the effective material properties are evaluated by means of the rule of mixtures. The volume distribution of the top constituent is modeled using the power law form. A comparison of the present finite element model with the numerical results available in the literature reveals that they are in good agreement. In addition, a routine to study functionally graded plane models in a commercial finite element code is used to verify the performance of the proposed model. In the present work, displacements for different values of the power law exponent and surface temperatures are presented. Furthermore, the normal stress variation along the thickness is shown for several power law exponents of functionally graded beams subjected to thermal and mechanical loads.

Lateral torsional buckling analysis of corrugated steel web girders using homogenization approach

Corrugated web beams have become popular in recent years due to their high strength-to-weight ratio, ductility and high shear resistance without stiffeners. The developments in the automated production of corrugated steel plates have further amplified their use as structural elements in bridges and buildings. In this paper, we develop a strain energy-based homogenization scheme to convert corrugated sections into equivalent flat sheets with modified elastic properties. The thin-walled theory is implemented in a one-dimensional (1D) finite element (FE) framework along with a modified analytical expression to study the lateral torsional buckling of corrugated web girders. The homogenization-based FE modelling reduces the computational requirement of finer mesh sizes on the corrugation profile. The present thin-walled FE model is implemented to different corrugation profiles and lengths, and their responses are compared with methodologies available in the literature. The effects of the geometrical parameters and loading on the lateral torsional buckling behaviour are investigated and important observations are made for structural designs.

End diaphragm and interior cross frame modeling in steel tub girder superstructures

Composite steel tub girders are proven to be an economical choice for long span bridges. However, detailed analysis of such superstructures requires extensive Finite Element (FE) modeling that includes many internal and external diaphragms. This paper is an attempt to study diaphragms and interior cross frames in tub girders and present simplified FE modeling details for the tub girder superstructures under gravity and seismic loadings incorporating accurate end diaphragm and interior cross frame stiffness equations. The simplified model is applicable to design of new tub girder bridges as well as load rating, health monitoring and retrofitting of existing bridges which require more sophisticated models. To this end, first a parametric study using 18 different FE models was carried out to better understand the behavior of tub girder superstructure and its components such as end diaphragms, the composite concrete deck and interior cross frames. Second, the stiffness equations for the end diaphragms and interior cross frames were derived analytically. These were associated with equivalent beam elements, which were used in combination with girder/deck elements to arrive at the simplified model. The resultant FE modeling was validated against detailed 3D FE models under gravity and seismic loads as well as the fundamental modes of vibration. Results indicated that the modeling approach is able to efficiently simulate different component behaviors and estimate the static and dynamic demands on the girders with remarkable accuracy.

A hybrid first/third-order plate theory for finite element analysis of sandwich plates with a transversely compressible core

Sandwich structures with thick soft cores subjected to transverse loads are usually resulting in deformations with various modes, including bending, twisting and compressing. In addition, the compression of the core results in a significant influence of the structural response. All classical plate theories are inadequate in predicting the behavior sandwich structures with thick soft core due to the assumption of no thickness change during deformation. To overcome this issue, a hybrid first/third-order shear deformation hypothesis with consideration of compressive effect is proposed for sandwich structures with thick soft cores. The first-order shear deformation theory is applied to both the top and bottom layers, while a refined third-order shear deformation theory that releases the assumption of no thickness change is developed for the thick soft cores. An eight-node quadrilateral plate element with twelve degrees of freedom including compressible displacements is created for finite element modeling. Based on the proposed refined hybrid first/third-order theory, a finite element model is developed using the Hamilton’s principle. The numerical model is first validated by the computational results of sandwich structures using commercial software. Then, the influences of various parameters on static displacements, vibrations and compressive deformations are systematically investigated, including e.g. boundary conditions, thickness of the core and face layers, elastic modulus of the core layer and the plate size. The present finite element modeling approach provides a powerful tool to accurately investigate the mechanical response of sandwich structures.

A new higher-order mixed four-node quadrilateral finite element for static bending analysis of functionally graded plates

In this paper, a new C0 four-node quadrilateral plate element (MiQ4) is proposed for the static bending analysis of functionally graded (FG) plates based on a C0 higher-order shear deformation theory. By introducing a quadratic shape function for higher-order terms and a constant shear result, which is eliminated at the element level, the transverse shear stresses are free on two surfaces of the plates. The present finite element model has high accurateness and a fast rate of convergence, especially for both thin and very thin plates. In addition, the proposed element is insensitive to distorted mesh, hence, it is compatible with the investigation of complex geometrical plates. Although the proposed element does not need any shear correction coefficients and selected or reduced integrations, the shear-locking phenomenon does not appear even for very thin plates. Therefore, the computation cost and time are reduced and the spurious deformation or hourglass modes are avoided. A large number of examples have been exhibited that help to validate the convergence rate, correctness, and reliability of the proposed element. Then the present element is applied for analysis of FG structures to demonstrate the potential applications of the present plate element. Significantly, the paper provides a good element that can be used in many areas of engineering for the design, testing, analysis, and optimization of complex structures to reduce the computation cost and time as well as increase the reliability of the numerical results.

Shear behaviour of RC deep beams retrofitted with externally bonded GFRP fabrics: Experimental and numerical study

The structural behaviour of reinforced concrete (RC) deep beams strengthened in shear by externally bonded (EB) glass fibre reinforced polymer (GFRP) fabrics are investigated employing both experiment and finite element (FE) analysis using commercial software. Four RC deep beams of 1000 mm length, 120 mm width and 420 mm depth are prepared. One un-retrofitted and other three beams retrofitted with U-wrapping of GFRP fabrics along the shear spans are tested under two-point loading to obtain the various structural responses. Thereafter, the FE model is validated by comparing its structural responses with those of the experiment. From both investigations, it is found that there is a significant enhancement in structural responses, such as load-carrying capacity, deflection, shear capacity, stiffness and energy absorption capacity due to the retrofitting of beams. Then, a comparison of the shear strengths of the experiment, FE model and existing design models is made to check the efficiency of the present FE model. Finally, a numerical study is conducted to examine the influence of various wrapping patterns of GFRP fabrics on the structural performance of the retrofitted beams. From this study, it is found that the wrapping pattern influences the structural performance of the beam remarkably.

Insights into the structural design strategies of multi-spot ultrasonic welded joints in thermoplastic composites: A finite element analysis

Ultrasonic welding is a typical spot-welding technique for thermoplastic composites (TPCs) with high weld strength and short welding time. Therefore, the most straightforward way to apply ultrasonic welding to large-scale TPC structures is adopting multi-spot welded configurations fabricated by a sequential welded method. In order to gain an insight into the structural design optimization strategies of multi-spot welded joints, a finite element (FE) model was proposed in this paper to analyse the mechanical behaviour of a single-lap TPC joints assembled by ultrasonic spot welding. The welded areas were simulated by using cohesive zone elements. The presented FE model was firstly validated by a comparative study between the numerical results and the experimental data. On the basis of that, a comprehensive study was conducted on the effects of typical geometrical parameters, i.e. spot diameters and spot spacing, on the overall mechanical behaviour of the multi-spot welded TPC joints. The numerical results provide a potential guidance for the structural design of ultrasonic welded TPC joints in aircraft structures.

An Efficient Approach into Finite Element Method for Lateral Buckling Analysis of Fiber-Metal Laminates Tapered I-Beams

In this paper, lateral stability analysis of fiber-metal laminated (FML) doubly-symmetric tapered I-beams with symmetrical lay-up for all section walls is perused by presenting a new finite element solution. Vlasov’s thin-walled beam theory is utilized to consider the bending–twisting coupling effect. Based on the classical lamination theory as well as the energy method, the total potential energy is derived for the flexural displacements and the twist angle. Using an auxiliary function, the variational formulation is then constructed only in terms of the twist angle. To precisely determine 4*4 elastic and buckling stiffness matrices, Hermitian cubic polynomial is applied as the shape functions into the resulting variational statement. The most beneficial feature of the present finite element model is to provide a two-node laminated I-beam element with a low number of degrees of freedom. Lateral buckling strength of thin-walled FML profile having varying I-section has been calculated for E-glass/epoxy as composite and aluminum as metal. The obtained results are compared with finite element solutions using ANSYS software and showed excellent agreement with them. Also, the effects of different consequential parameters such as fiber orientation, lay-up sequence, metal volume fraction, web tapering ratio, and transverse load height position on lateral stability resistance of fixed-free FML tapered I-beams subjected to uniformly distributed load are comprehensively investigated.

Adaptive finite element simulation and experimental verification for fretting wear of PVDF piezoelectric thin films

An adaptive finite element method linked with user-defined subroutine UMESHMOTION is developed for simulating the tangential fretting wear of PVDF piezoelectric thin films. The three-dimensional (3D) sphere-on-flat contact model is established for the fretting wear simulation by using commercial software ABAQUS, where the Si3N4 ceramic ball is used as the punch in contact with PVDF piezoelectric thin films. The variable friction coefficient obtained from experiments is taking into consideration. The calculation of wear is based on the Archard's wear model. The tangential fretting motion with different loads and variable friction coefficients are applied in the finite element simulation. The fretting wear test are carried out to verify the numerical results under the same conditions. The results indicate that the present adaptive finite element model has a certain accuracy comparable to the experiment results for the fretting wear of PVDF piezoelectric thin films.

Axial compressive strength of preloaded CHS stubs strengthened by CFRP

Failure process of circular hollow section (CHS) stubs strengthened by carbon fiber reinforced polymers (CFRP) at both unloading and preloading conditions was experimentally investigated. A total of 11 CHS stub specimens were tested under axial compressive loads. The specimens are divided into three categories: un-strengthened CHS stubs, CFRP-strengthened CHS stubs at no preloading condition, and CFRP-strengthened CHS stubs at preloading condition. The compressive strengths of the specimens were investigated by considering the effects of several parameters including preloading percentage, the number of CFRP laminates, the tube thickness and the configuration of CFRP laminate. For the preloaded CHS stubs, their yield strengths after CFRP strengthening reduce slightly with an increase of the preloading. However, the ultimate strengths of the CFRP-strengthened CHS stubs at different preloading percentages are almost same, i.e., the CFRP strengthening efficiency is not influenced by the preloading conditions. Finite element (FE) model was also established, and the accuracy of the FE model is verified through comparing the FE simulations with the experimental results. Using the presented FE model, parametric study is carried out to study the efficiency of CFRP strengthening technique to improve the ultimate strength of CHS stubs at preloading condition. The effects of wall thickness and diameter-to-thickness ratio of the steel tube and the CFRP wrapping method on the strengthening efficiency of CFRP to CHS stubs are also investigated.