General Purpose Finite Element Research Articles

Numerical investigation of steel and composite beam-to-encased composite column connection via a through-plate

A through plate connection consisting of a vertical plate passing through the column is proposed as a moment connection between steel and composite beams to encased columns. A numerical model is developed to simulate the cyclic behavior of the proposed steel beam to the SRC column connection via a through plate using a general-purpose finite element code LS-DYNA. The through plate connection shows a stable hysteresis behavior during the loading process and the plastic hinge forms in the beam away from the column face without a considerable extension in the connection zone. The induced in-plane forces in the through plate are transferred to the column mainly through three load paths: through plate, lateral cover plates and the concrete strut action. Furthermore, the load transfer mechanisms from a steel-concrete composite beam to an SRC column are investigated numerically. The concrete slab adds new mechanisms to the three main load paths of a steel beam to the SRC column. Generally, there are only two mechanisms of load transfer from composite beam to column, including compression on column face and inclined concrete struts formed over the column sides. The finite element analysis demonstrates the two additional paths and the transferred bending moment from beam to column. Accordingly, the two mechanisms cannot transfer the full plastic moment of the composite beam to the column, and thus, a smaller effective width is engaged in load transfer from beam to column.

Design of a non-destructive test for validating models of hydrogen migration

High-strength steels, despite their excellent mechanical properties in normal conditions, can be susceptible to hydrogen embrittlement. Due to the service loads or residual stresses, hydrogen migrates within the component and accumulates in the regions where the highest tensile hydrostatic stress occurs. As a consequence, component brittle failure can occur even if the initial or mean hydrogen concentration is lower than the critical value. The availability of models predicting the hydrogen diffusion within the component is a crucial task for the design. Several diffusive models have been presented in the literature and some general-purpose finite element codes have already implemented some of them. However, the validation of those models is still an open issue due to the difficulty in performing accurate local measurements of the hydrogen concentration. This study deals with the design of a test potentially able to validate hydrogen migration models. In the test, a four-point bending configuration is applied to a properly shaped hourglass specimen, previously charged with hydrogen, extracted from thin high-strength steel sheets. The specimen geometry and the loading configuration were designed to obtain a central region in which the stress and strain field is uniform in plane and exhibits a quasi-uniform gradient in the thickness direction. As a consequence, it is expected a large enough central region of the specimen in which the Hydrogen can migrate only in the thickness direction during the typical duration of the test. The local hydrogen concentration is evaluated by measuring the flux leaving the tensile surface of the specimen by a solid-state hydrogen sensor.

Numerical analysis of strain rate effect on ballistic impact response of multilayer three dimensional angle-interlock woven fabric

This paper investigates the ballistic impact on Kevlar multilayer three-dimensional angle-interlock woven fabric (3DAWF) by proposing the mesoscale geometrical model for the numerical simulation. Multilayer 3DAWF is designed to yarn level configuration by utilizing the membrane elements to reduce computational time and enhance accuracy. The general-purpose finite element code LS-DYNA is employed to predict the ballistic behavior of multilayer 3DAWF under ballistic penetration. The velocity evolution of the projectile, energy absorption mechanism, and failure morphology of multilayer 3DAWF are predicted and validated by the impact test results. It is found that the mesoscale model based on strain rate material models accurately reproduces the ballistic test results. Numerical simulations with strain rate effects in the yarn material properties have a higher precise prediction in the projectile's velocity, energy absorption mechanism, and failure morphology compared with traditional FEA. This study demonstrated the importance of the strain rate effect of material properties in simulating the ballistic impact on the fabric and dramatically improves the ballistic impact simulation's accuracy on fabric.

Numerical modeling of a ballastless track mockup based on asphalt

A 3D mechanical model of a ballastless asphalt track mockup was developed within the general-purpose finite element software ABAQUS. The mockup (and model) consisted of three wide-base sleepers equipped with a geotextile at the bottom, supported on an asphalt pavement structure encapsulated in a large rigid box. The asphalt layer was modeled as linear viscoelastic; the underlying unbound granular layer was treated as stress-dependent nonlinear-elastic, implemented via a user-defined subroutine. The vast majority of model parameters were calibrated through laboratory element tests, while the remaining parameter values were based on technical literature or material specifications; only very few were calibrated using experimental data from the mockup itself. Implicit dynamic analysis was carried out under a loading history that simulated a train passage by sequentially exciting the three sleepers with a time delay. Vertical stresses at the bottom of the unbound granular layer, horizontal strains at the bottom of the asphalt layer, vertical accelerations at the track surface, and relative displacements at different locations were numerically evaluated. Subsequently, model predictions were validated by comparison against corresponding response-traces measured in the mockup. Overall, the predicted responses were in very good agreement with the experimental measurements. The peak vertical stresses below the unbound granular layer were moderately overestimated, while the peak horizontal asphalt strains were underestimated. In particular, the characteristic shape-features recorded by the stress and strain sensors at multiple locations in the mockup could be replicated. Pearson's correlation coefficients between measured and calculated response histories for stresses and strains were higher than 0.96. Predicted and measured vertical accelerations were of the same order of magnitude, and their corresponding frequency spectra exhibited a correlation value greater than 0.97. The validated model has verified that during a simulated train passage, the substructure of a ballastless track mockup experiences low-magnitude vertical deformations, 77% of which develop in the rail pad, 15% in the geotextile, and 6% within the unbound granular layer. Moreover, the peak vertical stress in the unbound granular layer (33 kPa) and the peak horizontal tensile strain in the asphalt layer (18με) are lower than limiting design values.

Local and global tensile deformation behavior of AA7075 sheet material at 673oK and different strain rates

The constitutive behavior of AA7075 aluminum sheet like other metallic sheet materials is highly temperature and strain rate dependent at elevated temperatures. The uniaxial tensile test is commonly employed to characterize the temperature and strain rate dependent deformation behavior. However, the traditional uniaxial tensile testing and data analysis procedure treats the gauge length of sample as a uniformly-deforming (or homogeneous) region. This may not be accurate due to early localized deformation that is initiated in the gauge region at elevated temperatures. Treating the post-necking hardening behavior of uniaxial tensile samples has been an important task to expand the effective range of true stress-true strain curves at elevated temperatures for metal and alloys. To explore this issue, uniaxial tensile tests on AA7075-F sheets (with as-fabricated temper) were conducted at 673o K and four different test speeds. The test procedure also utilized an on-line 2-D digital image correlation (DIC) system method to obtain full-field strain map from the deforming gauge region of the test specimen. Local stress-strain curves at different points along the gauge length were then calculated based on the recorded local in-plane principal stress and strain values from macroscopic force data and current cross-section of the specimen at the chosen points. In this manner, the DIC strain analysis not only enabled the determination of stress-strain response but also the determination of strain rates at specific chosen points along the gauge length. The local stress-strain curves revealed significant deviation at an earlier stage of deformation from the global (or macroscopic) stress-strain response based on the entire gauge region. To estimate the constitutive behavior at different strain rates, a correction method to traditional stress-strain curves was applied to obtain a family of stress-strain curves at different constant strain rates based on the local stress-strain curves. Additionally, the material deformation response in the stress, strain and strain rate space in the 3D Cartesian coordinate system was also constructed for tests conducted at different stretching speeds. Further, a verification test was conducted to see if the above methodology could provide an accurate estimation of local deformation behavior of AA7075 sheet. Furthermore, the above experimental method was also coupled with the Gurson-Tvergarrd-Needleman (GTN) ductile void damage model and incorporated into ABAQUS-Explicit general purpose finite element (FE) analysis code via a VUMAT material subroutine. Good agreement was obtained for both the local and global stress-strain curves between the FE test simulation and experimental stress-strain results. The proposed experimental methodology and the resulting stress-strain-strain rate behavior is believed to be applicable in describing the strain rate-dependent constitutive behavior of AA7075-F sheet metals at 673o K.

Development of welding simulation technology using general-purpose finite element analysis code

Welding simulation using an instantaneous heat source was performed using ANSYS, which is a general-purpose finite element analysis code, and deformation and residual stress of various test pieces were evaluated. As a result, the effects of the heating region, heating time during welding, number of element divisions in the thickness direction, number of time divisions, etc. on the calculation accuracy were clarified, and the optimum analysis conditions were obtained.

A General Purpose Formulation for Nonsmooth Dynamics With Finite Rotations: Application to the Woodpecker Toy

Abstract The aim of this work is to extend the finite element multibody dynamics approach to problems involving frictional contacts and impacts. The nonsmooth generalized-α (NSGA) scheme is adopted, which imposes bilateral and unilateral constraints both at position and velocity levels avoiding drift phenomena. This scheme can be implemented in a general purpose simulation code with limited modifications of pre-existing elements. The study of the woodpecker toy dynamics sets up a good example to show the capabilities of the NSGA scheme within the context of a general finite element framework. This example has already been studied by many authors who generally adopted a model with a minimal set of coordinates and small rotations. It is shown that good results are obtained using a general purpose finite element code for multibody dynamics, in which the equations of motion are assembled automatically and large rotations are easily taken into account. In addition, comparing results between different models of the woodpecker toy, the importance of modeling large rotations and the horizontal displacement of the woodpecker's sleeve is emphasized.

Structural and Thermal Analysis of Brake Drum

The brake drum is a specialized brake that uses the concept of friction to decelerate or to stop the vehicle. The deceleration is achieved by the assistance of the friction generated by a set of brake shoes or pads. During the brake operation heat is ejected out this causes damage to the brake. Disc (Rotor) brakes are exposed to large thermal stresses during routine braking and extraordinary thermal stresses during hard braking. To satisfy this condition the drum material should possess a high thermal conductivity, thermal capacity and high strength .The common material used for construction of brake drum is cast iron. The aim of the project is to design, model a disc. Modeling is done using catia. Structural and Thermal analysis is to be done on the drum brakes using four materials Stainless Steel, gray Cast iron, carbon carbon composite & aluminum metal matrix. The shoes of this kind of brake are contained within the drum and expand outwards when the brake is applied. Such kind of brakes is used in medium heavy-duty vehicles. Structural analysis is done on the drum brake to validate the strength of the drum brake and thermal analysis is done to analyze the thermal properties. Comparison can be done for deformation; stresses, temperature etc. form the three materials to check which material is best. Catia is a 3d modeling software widely used in the design process. ANSYS is general-purpose finite element analysis (FEA) software package. Finite Element Analysis is a numerical method of deconstructing a complex system into very small pieces (of user-designated size) called elements.

Postbuckling resistance of high strength steel welded I-section beams based on interactive slenderness

The steel, whose nominal yielding strength fy is greater than or equal to 460 MPa, is generally referred to as high strength steel (HSS). Through the comparison with conventional strength steel (CSS) members, HSS members are more vulnerable to local buckling since the component plates are usually designed to be more slender in order to exploit higher material strength. The different mechanical properties between HSS and CSS, including yielding strength, ductility and so on, may lead to different local buckling behavior of steel members. However, little guidance is applicable in existing standards for the stability design of HSS members. In this paper, elaborate finite element (FE) models of HSS welded I-section beams under the loading conditions of uniform moment (four-point loading) and moment gradient (three-point loading) were developed by means of the general-purpose FE software package and validated against the available test results. Continuous lateral supports were ideally applied to restrict the occurrence of coupling with overall lateral‐torsional buckling. Comprehensive parametric analyses on key parameters containing the plate width-to-thickness ratio and the steel material properties were further conducted, reflecting the influence of these parameters on the mechanical performance of local stability. Through this work, the variation rules on rotation capacity and postbuckling resistance of HSS welded I-section beams with plate width-to-thickness ratio and steel nominal yielding strength were clarified. Taking into account the interaction of local buckling modes between flanges and webs, new cross-section classification of HSS welded I-section beams was proposed based on the FE analysis results. After the introduction of the concept of interactive local slenderness, the design methods of postbuckling ultimate moment resistance for HSS welded I-section beams subjected to uniform moment and moment gradient were also proposed, which were assessed by comparing the design results with the ones obtained from the corresponding design approaches in Eurocode 3, ANSI/AISC 360–16 and GB 50017–2017. And the reliability of the new proposals was also confirmed by further statistical analysis.

Modelling of residually stressed, extended and inflated cylinders with application to aneurysms

The paper presents the localized bifurcation abnormal enlargement associated with certain human diseases such as abdominal aortic aneurysms (AAA), among others. The constitutive framework herewith proposed is constructed relying on the modelling of non-linear elastic materials under the action of residual stresses. The suitable incorporation on the mechanical response of residual stresses in the analysis is regarded important for the formation of aneurysms in soft tissues. From a mechanical perspective, the onset of aneurysms formation can be interpreted through bifurcation conditions, whose localization is relatively sensitive to different material and geometrical parameters as it is shown here. In order to reduce the risk and interpret aneurysm formation, we perform a thorough sensitivity analysis of the effect of design parameters such as tube diameter, length, thickness and strength of the residual stress field on bifurcation of a tube under inflation and extesion. A consistent residually stressed material model is formulated in terms of invariants for a general elastic strain-energy function. The dependence of applied pressure, axial stretch and different geometrical and constitutive parameters on bulging and bending bifurcation is illustrated. The numerical procedure to analyse the bifurcation of the finite deformation boundary-value problem at hand is developed based on the modified Riks method. The proposed formulation is implemented in the general-purpose finite element code ABAQUS using user-defined material subroutines.For a given material model, bulging bifurcation is expected for sufficiently large values of the axial stretch while the onset of bifurcation is found to be the bending mode for small values of the axial stretch. This transition zone from bending bifurcation to bulging bifurcation is analyzed for the different parameters considered.

Development of Sheet Metal Forming Analysis Incorporating Phase-transformation Model for Hot Stamping

To predict the spring back after hot stamping of sheet metals, a user material routine incorporated with phase transformation effects has been developed and implemented in general-purpose commercial finite element software. The mechanical response of the metallographic structure incorporates variation of transformation plastic strain and transformation volume expansion. Additionally, the thermal response incorporates the dependencies of thermal properties and latent heat of phase transformation. The start timing of diffusive transformation was determined using Scheil’s law, and the Kolmogorov–Johnson–Mehl–Avrami equation was adopted for the progression of diffusive transformation. The Koistinen and Marburger equation was used for the progression of martensite transformation. Using the developed model, we considered the effects of phase transformation on shape fixability. We conducted experiments that focused on measuring the shape fixability of U-bend hot formed parts. In this study, we show that the spring back of the U-bend parts increases under conditions in which phase transformation occurs before formation has been completed. Furthermore, the spring back could accurately predict by using the developed model.

Effect of Slenderness Ratio on Fatigue Life of CFRP Strengthened Steel I-Beam

Carbon fiber reinforced polymers (CFRP) to repair and strengthen the steel I-beam has been increasingly used since last decade. CFRP composites bonded to steel members offer many advantages over steel plate bonding including excellent corrosion resistance, high stiffness and high strength to weight ratios etc. This study numerically investigates the fatigue performance of CFRP strengthened steel I-beam. One non-strengthened control beam and several strengthened beams using steel plates and CFRP strips were investigated primarily. The effect of slenderness ratios of web on fatigue behavior of CFRP strengthened steel I-beam is investigated. The beams were simulated in full three-dimension and fatigue life was investigated by using general-purpose finite element program, ANSYS. Simply supported beam subjected to two loads on compression flange is analyzed to show the effect of CFRP and slenderness ratios on fatigue behavior of steel I beam. The results show, that the life cycle of a CFRP strengthened beam before failure is higher than that of bare beam. It is also observed that beams with higher slenderness ratios (fixed thickness of the web) give better fatigue performance.

Analysis and Research on the Temperature and Thermal Change of NC Machine Tool Electric Spindle Based on ANSYS Software

With the improvement of CNC technology, CNC machine tools are gradually moving towards high speed, high precision and multi-function. Due to the comprehensive effect of internal and external heat sources, the thermal deformation of the motorized spindle has become the main factor affecting the machining accuracy of the machine tool in high-speed machining. ANSYS software is a large-scale general-purpose finite element analysis software integrating structure, fluid, electric field, magnetic field, and sound field analysis. It can interface with most CAD software, realize data sharing and exchange, and can effectively analyze the temperature and thermal changes of CNC machine tools. Therefore, this paper analyses the thermal deformation mechanism of the spindle of CNC machine tools in computer software, to provide the basis for reducing the thermal deformation of the motorized spindle of CNC machine tools in the future.

Crosspave: a multi-layer elastic analysis programme considering stress-dependent and cross-anisotropic behaviour of unbound aggregate pavement layers

ABSTRACT This manuscript describes the development of a new pavement analysis programme called CrossPave based on the Multi-Layered Elastic Theory (MLET) framework, but capable of accommodating stress-dependent and cross-anisotropic behaviour of unbound pavement layers. Generally, Finite Element (FE) based programmes such as ILLI-PAVE, MICH-PAVE, SENOL, GT-PAVE etc. or general-purpose FE programs with special user-defined material sub-routines have been used to model the stress-dependent nature of unbound materials. However, these FE programme are time consuming and need certain expertise, making them unfavourable for implementation into practice. Few MLET-based programmes such as KENLAYER and Everstress are capable of considering the stress-dependent nature of unbound materials, but fail to accommodate some of the recently developed material models. The newly developed pavement analysis programme, CrossPave, addresses these issues, and incorporates five different non-linear stress-dependent resilient modulus models for unbound materials. Details of the developmental effort are presented in this manuscript, along with results from validation efforts highlighting close agreement between KENLAYER, ILLI-PAVE and GT-PAVE. Critical pavement response parameters for two full-scale pavement sections were calculated using CrossPave, and have been compared against field-measured values. The CrossPave programme has been presented as an enhanced, ready-to-implement programme compared to other MLET-based alternatives.

Tensile behavior of the connection between nut-free high-strength bolt and endplate

Nut-free high-strength bolt permits easy installation and has been widely used in the connection between the column and the corner fitting in assembled-type light steel modular house. 33 specimens were tested under static tension to study the tensile behavior of the connection between the nut-free high-strength bolt and the endplate. The pivotal parameters considered in this experiment include the diameter of the high-strength bolt, the material property of the high-strength bolt, the length of the high-strength bolt, the material property of the endplate, and the thickness of the endplate. The tensile behavior and failure mode of the connection were evaluated and discussed based on the test results. A three-dimensional nonlinear finite element model (FEM) was established by the general-purpose finite element software ABAQUS and validated against the test results. The tensile capacity and failure mode are in good agreement with the test results and the FEM can be adopted for the analysis of the tensile behavior of the connection. The key parameters that influence the tensile capacity of the connection were the diameter, material property and length of the bolt. Whereas, the thickness and material property of the endplate have less influence. Furthermore, the simplified computation formulas were derived and a theoretical design model was established. The design model was verified by comparing the theoretical results with the test ones. It indicates that the design model can well predict the tensile behavior of the connection, which will provide useful references for the design of the connection.

Prediction of Damage Level of Slab-Column Joints under Blast Load

The behavior of a slab-column joint subjected to blast loads was studied by numerical analysis using a general-purpose finite element analysis program, LS-DYNA. Under the explosive load, the joint region known as the stress disturbed zone was defined as a region with a scaled distance of 0.1 m/kg1/3 or less through comparison with ConWep’s empirical formula. Displacement and support rotation according to Trinitrotoluene (TNT) weight and scaled distance were investigated by dividing in and out of the joint region. In addition, fracture volume was newly proposed as an evaluation factor for blast-resistant performance, and it was confirmed that the degree of damage to a member due to blast loads was well represented by the fracture volume. Finally, a prediction equation for the blast-resistant performance of the slab-column joint was proposed, and the reliability and accuracy of the equation were verified through additional numerical analysis.

Simulation of Cyclic Loading on Pipe Elbows Using Advanced Plane-Stress Elastoplasticity Models1

Abstract This work investigates the response of industrial steel pipe elbows subjected to severe cyclic loading (e.g., seismic or shutdown/startup conditions), associated with the development of significant inelastic strain amplitudes of alternate sign, which may lead to low-cycle fatigue. To model this response, three cyclic-plasticity hardening models are employed for the numerical analysis of large-scale experiments on elbows reported elsewhere. The constitutive relations of the material model follow the context of von Mises cyclic elasto-plasticity, and the hardening models are implemented in a user subroutine, developed by the authors, which employs a robust numerical integration scheme, and is inserted in a general-purpose finite element software. The three hardening models are evaluated in terms of their ability to predict the strain range at critical locations, and in particular, strain accumulation over the load cycles, a phenomenon called “ratcheting.” The overall good comparison between numerical and experimental results demonstrates that the proposed numerical methodology can be used for simulating accurately the mechanical response of pipe elbows under severe inelastic repeated loading. Finally, this paper highlights some limitations of conventional hardening rules in simulating multi-axial material ratcheting.

Delamination Propagation Study on Aircraft Composite Rib Subjected to Fatigue Loading

A computational fatigue study of the propagation of delamination in a composite wing rib has been conducted. A typical Boeing 747 rib having a circular hole with a semi-elliptical delamination was taken as the rib of interest; gust loads experienced during the cruise phase of flight were identified as the source of fatigue. A square section surrounding the circular hole comprising of laminated carbon–epoxy prepreg was isolated from the rib for computational analysis. The lack of analytical solutions for such a problem encouraged the use of the general-purpose finite element software ABAQUS. The delamination mechanism was simulated using the energy-based virtual crack closure technique in tandem with the Paris–Erdogan equation. The delamination propagation with respect to aircraft flight hours was obtained for the aircraft rib, with Mode III tearing dominating the delamination process. A parametric analysis was further conducted for various ply orientations where delamination modes were compared via a frame-based analysis. Significant differences in delamination propagation were observed, and better performing orientations for the given conditions were identified.

A novel floor-isolated re-centering system for prefabricated modular mass timber construction – Concept development and preliminary evaluation

Prefabricated modular mass timber (MT) construction provides a resource-efficient, consistent-quality, and eco-friendly solution for the building industry. Connections that facilitate the assembly of prefabricated modules to form the final structure usually do not possess the characteristics needed for performance of these systems in high seismic zones. In this study, a novel seismic force resisting system called FIRMOCS that incorporates floor-isolation and re-centering techniques, is proposed for the prefabricated modular MT construction. Finite element models of the Floor Isolated Re-entering Modular Construction System (FIRMOCS) and of regular modular construction Seismic Force Resisting Systems (SFRS) were developed in ABAQUS, a general-purpose finite element program. The seismic performance of the regular prefabricated modular MT SFRS and that of FIRMOC systems was evaluated using nonlinear dynamic time-history analysis along the principles of the National Building Code of Canada. The preliminary results showed that FIRMOC Systems significantly reduced the seismic demand on the prefabricated modular MT construction, thus leading to improved seismic response. Using the proposed novel SFRS, an efficient and resilient prefabricated modular MT construction solutions can be achieved in high seismic zones.

Effect of position of hexagonal opening in concrete encasedsteel castellated beams under flexural loading

Castellated beams fabricated from standard I-sections are being used for several structural applications such as commercial and industrial buildings, multistory buildings, warehouses and portal frames in view of numerous advantages. The advantages include enhanced moment of inertia, stiffness, flexural resistance, reduction in weight of structure, by passing the used plate girders, the passage of service through the web openings etc. In the present study, experimental and numerical investigations were carried out on concrete encased steel castellated beams with hexagonal openings under flexural loading. Various positions of openings such as along the neutral axis, above the neutral axis and below the neutral axis were considered for the study. From the experimental findings, it has been observed that the load-carrying capacity of the castellated beam with web opening above neutral axis is found to be higher compared to other configurations. Nonlinear finite element analysis was performed by using general purpose finite element software ABAQUS considering the material nonlinearities. Concrete damage plasticity model was employed to model the nonlinearity of concrete and elasto-plastic model for steel. It has been observed that FE model could able to capture the behaviour of concrete encased steel castellated beams and the predicted values are in good agreement with the corresponding experimental values.