Finite Element Analysis Procedure Research Articles

Topology Optimization of Periodic Structures With Substructuring

Topology optimization of macroperiodic structures is traditionally realized by imposing periodic constraints on the global structure, which needs to solve a fully linear system. Therefore, it usually requires a huge computational cost and massive storage requirements with the mesh refinement. This paper presents an efficient topology optimization method for periodic structures with substructuring such that a condensed linear system is to be solved. The macrostructure is identically partitioned into a number of scale-related substructures represented by the zero contour of a level set function (LSF). Only a representative substructure is optimized for the global periodic structures. To accelerate the finite element analysis (FEA) procedure of the periodic structures, static condensation is adopted for repeated common substructures. The macrostructure with reduced number of degree of freedoms (DOFs) is obtained by assembling all the condensed substructures together. Solving a fully linear system is divided into solving a condensed linear system and parallel recovery of substructural displacement fields. The design efficiency is therefore significantly improved. With this proposed method, people can design scale-related periodic structures with a sufficiently large number of unit cells. The structural performance at a specified scale can also be calculated without any approximations. What’s more, perfect connectivity between different optimized unit cells is guaranteed. Topology optimization of periodic, layerwise periodic, and graded layerwise periodic structures are investigated to verify the efficiency and effectiveness of the presented method.

Proposal of residual stress mitigation in nuclear safety-related austenitic stainless steel TP304 pipe bended by local induction heating process via elastic-plastic finite element analysis

Abstract This paper proposes a residual stress mitigation of a nuclear safety-related austenitic stainless steel TP304 pipe bended by local induction heating process via performing elastic-plastic finite element analysis. Residual stress distributions of the pipe bend were calculated by performing finite element analysis. Validity of the finite element analysis procedure was verified via comparing with temperature histories measured by using thermocouples, ultrasonic thickness measurement results, and residual stress measurement results by a hole-drilling method. Parametric finite element stress analysis was performed to investigate effects of the process and geometric shape variables on the residual stresses on inner surfaces of the pipe by applying the verified procedure. As a result of the parametric analysis, it was found that it is difficult to considerably reduce the inner surface residual stresses by changing the existing process and geometric shape variables. So, in order to mitigate the residual stresses, effect of an additional process such as cooling after the bending on the residual stresses was investigated. Finally, it was identified that the additional heating after the bending can significantly reduce the residual stresses while other variables have insignificant effect.

Deflection of Composite Cantilever Beams with a Constant I-Cross Section

Laminated composite beams are widely used as structural components in aerospace and wind energy industries. For airplane wings and wind turbine blades, the beams, commonly called spars, provide principal stiffness against bending deformation of the structures. The present work is focused on composite cantilever beams with a constant I-cross section. A unidirectional (UD) Glass/Epoxy lamina was chosen for composite material. The overall dimension of the beam is 50 × 55.2 × 2,500 mm. Various stacking sequences were assigned to the flanges and the web of the beam. A uniform distributed load was applied to the upper flange. The deflection results from First-Order Shear Deformation Theory (FSDT) and Finite Element Analysis (FEA) are in good agreement. The effective longitudinal modulus (Ex) of the flanges has strong influence on the bending stiffness and the beam deflection. Understanding important roles of materials and beam construction can help improving the design of I-beams. The validated FEA procedure can be extended to the analysis of realistic spars, which is based on an I-cross section plus curve, taper, and twist along the length.

Stress Analysis and Performance Evaluation of Flange Spool Subjected to Pressure

In the present scenario, the prevention of failure of a component is having a vital role in piping industry. Failure of a single component can cease the entire functionality of the system. So the prevention of failure is significant to satisfy the customer needs not only aesthetic but also functionality, reliability and utility of the system. With the advancement of new technologies, finding out the failures and giving a pertinent solution is possible. Value engineered component is an added advantage to the industry in all aspects. A flange spool is a basic type of dismantling joint that connect long pipes with flanges at the ends so that they can be bolted to another pipe with matching flange. The flange joint involves interaction between bolts, flange and gasket and it is the most essential part of Pressure vessel, Condenser, Heat exchanger and Storage tank. This flange joint aims at preventing fluid leakage and maintaining the structural integrity of the joint. The objective of this paper is to design and analyze a flange spool which is used to carry and transport processed fluid and gas. This work deals with the replacement of molybdenum steel material flange spool with a silicon-manganese flange spool. The modeling was done using CATIA software as per API standards. The flange spool is modeled and simulated using ANSYS 15 Software. The design optimization also showed significant potential improvement in the performance of flange spool. In the present work finite element analysis procedure is used in ANSYS simulation to predict the levels of stress and deformation of flange spool under subjected loads.

Evaluation Study on Iterative Inverse Modeling Procedure for Determining Post-Necking Hardening Behavior of Sheet Metal at Elevated Temperature

The identification of the post-necking strain hardening behavior of metal sheet is important for finite element analysis procedures of sheet metal forming process. The inverse modeling method is a practical way to determine the hardening curve to large strains. This study is thus focused on the evaluation of the inverse modeling method using a novel material performance test. In this article, hot uniaxial tensile test of a commercially pure titanium sheet with rectangular section was first conducted. Utilizing the raw data from the tensile test, the post-necking hardening behavior of the material is determined by a FE-based inverse modeling procedure. Then the inverse method is compared with some classical hardening models. In order to further evaluate the applicability of the inverse method, biaxial tensile test at elevated temperatures was performed using a special designed cruciform specimen. The cruciform specimen could guarantee that the maximum equi-biaxial deformation occurs in the center section. By using the inverse modeling procedure, the hardening curves under biaxial stress state are able to be extracted. Finally the stress-strain curves obtained from the two experiments are compared and analysis studies are provided.

An Investigation on Ultimate Strength of High Strength Aluminum Alloys Four-Bolted Connections with Out-of-plane Deformation

An experimental study for the structural behaviors of high strength aluminum alloys (7075-T6) single shear bolted connections with three types of bolt arrays has been carried out by authors. Out-of-plane deformation in the direction of plate thickness (hereafter, curling) occurred in some specimens with long end distances parallel to the direction of applied force. It is known that the curling reduced ultimate strength for curled specimens and it contributed to deciding the ultimate state of 7075-T6 bolted connections. In this paper, finite element analysis model has been developed based on the previous experimental results of 7075-T6 four-bolted connections and previous finite element analysis procedures related to singe shear bolted connections. The validation of finite element analysis method for predicting the ultimate behaviors of 7075-T6 bolted connections was verified through the comparison of test results and analysis results. Additional analyses with extended parameters of end and edge distances were conducted. As a result, strength reduction ratio (up to maximum 19%) by curling was investigated quantitatively and the curling occurrence conditions for end distance and edge distance were presented. In addition, analysis strengths were compared with design strengths by AAA (American Aluminum Association), AISI (American Iron Steel Institute) design specifications and proposed equation for 6061-T6 aluminum alloys four-bolted connections. Lastly, revised strength equation was suggested considering the actual fracture mechanism at ultimate state and curling influence (strength drop) by bolt bearing action.

Finite Element Analysis of an Aluminum Alloy Using Progressive Failure Algorithm

This study aims to develop a reliable finite element analysis procedure to model the complete fracture of ductile specimens using the progressive degradation of the material stiffness algorithm under tensile load. The ductile specimen in this study is an aluminum alloy. The progressive failure algorithm used here is based on the assumption that the material behaves like a stable progressively fracturing solid. The stiffness reduction is carried out at the reduced integration gauss points of the finite element mesh depending on the mode of failure. A number of material properties are necessary for such simulation to carry out and experimentation of the metal are needed to evaluate these properties. The actual tensile tests data are applied to the finite element simulation. The verified simulation method has a great importance in practical design of structures and metals. A renowned finite element analysis software ABAQUS is used in this study.

Uniaxial Tensile Simulation of 3D Orthogonal Woven Fabric

Mesoscale modelling approach has shown close simulation approximations of woven fabric tensile performance. The main purpose of the work is to develop understanding of geometrical model development, finite element analysis procedure and to compare the differences of 2D and 3D woven fabric uniaxial tensile stress-strain. 3D woven fabric structures selected for the work is three-layer orthogonal woven fabrics. The woven structure will have 2 through-thickness warps, 4 non-crimps warp and 6 wefts. Through-thickness warp yarn will apply plain 1/1 weave structure for stitching all weft layers and non-crimps weft yarn together. Woven geometric models were developed with pre-processor program at detail yarn configurations. Simulation results showed that 3D orthogonal woven fabric had a better tensile response than its 2D woven fabric structures.

Acoustic Wave Propagation in Air-Filled Pipes Using Finite Element Analysis

The major objective of this work is to develop an efficient Finite Element Analysis (FEA) procedure to simulate wave propagation in air-filled pipes accurately. The development of such a simulation technique is essential in the study of wave propagation in pipe networks such as oil and gas pipelines and urban water distribution networks. While numerical analysis using FEA seems superficially straight forward, this paper demonstrates that the element type and refinement used for acoustic FEA have a significant effect on the accuracy of the result achieved and the efficiency of the computation. In particular, it is shown that the well-known, better overall performance achieved with 3D solid hexahedral elements in comparison with 2D-type elements in most stress and thermal applications does not occur with acoustic analysis. In this paper, FEA models were developed taking into account the influence of element type and sizes using 2D-like and 3D element formulations, as well as linear and quadratic nodal interpolations. Different mesh sizes, ranging from large to very small acoustic wavelengths, were considered. The simulation scheme was verified using the Time of Flight approach to derive the predicted acoustic wave velocity which was compared with the true acoustic wave velocity, based on the input bulk modulus and density of air. For finite element sizes of the same order as acoustic wavelengths which correspond to acoustic frequencies between 1 kHz and 1 MHz, the errors associated with the predictions based on the 3D solid hexahedral acoustic elements were mostly greater than 15%. However, for the same element sizes, the errors associated with the predictions based on the 2D-like axisymmetric solid acoustic elements were mostly less than 2%. This indicates that the 2D-like axisymmetric solid acoustic elements are much more efficient than the 3D hexahedral acoustic elements in predicting acoustic wave propagation in air-filled pipes, as they give higher accuracies and are less computationally intensive. In most stress and thermal FEA, the 3D solid hexahedral elements are much more efficient than 2D-type elements. However, for acoustic FEA, the results show that 2D-like axisymmetric elements are much more efficient than 3D solid hexahedral elements.

Vulnerability analysis of tunnel linings under blast loading

In the present study, a comparative assessment on the performance of conventional and advanced tunnel lining materials subjected to blast loading is done using a three-dimensional non-linear finite element analysis procedure. The conventional tunnel lining materials analyzed herein are plain concrete, steel, reinforced cement concrete, and steel fiber–reinforced concrete. The advanced tunnel lining materials analyzed herein are dytherm, polyurethane, and aluminum syntactic foam sandwich panels with steel–foam–steel composites. The pressure generated by 10 kg Trinitrotoluene (TNT) is applied to each element on the inner wall of the tunnel which has an effect equal to the scaled distance Z = 1.16 m/kg1/3. Analyses are conducted by varying the thickness of lining materials for a tunnel built in rock domain. The response of the tunnel lining materials, for example, deformation, stresses, and strains generated at different interfaces, is compared with each other to assess the best suitable material for the present blast scenario discussed herein. It is observed from the simulations that the reinforced cement concrete and steel–aluminum syntactic foam (90 µm)–steel are found to be the suitable tunnel lining materials for the present blasting scenario described herein. Moreover, a set of probabilistic analysis is also performed for the suitable tunnel lining materials decided through deterministic analyses using Monte Carlo simulations. The results obtained are normal random distribution curves depicting the extent of deformation in lining materials. A probability failure curve is also proposed for the suitable lining materials.

Extended finite element procedures for analysis of bolt crossing multiple intersecting rock joints

An enriched finite element procedure is proposed for formulating interaction of rock bolts with multiple intersecting/ non-intersecting joints in a rock mass. The numerical method involves analysis of reinforced rock mass having arbitrary joint dip angle, bolt angle and joint-bolt-grout properties in extended finite element (XFEM) platform. Shifted Heaviside and junction enrichment is incorporated for the intersecting jointed element. The paper presents procedures and formulation of stiffness matrices of a bolt crossing multiple joints (BCMJ) which may or may not intersect each other. Hence an element may contain two intersecting joints and a bolt. In that case for a 2D element, each node is enhanced to eleven degrees of freedom, 2 for rock displacements, 2 each for displacements of rock joints, 2 for displacements of the junction of joint intersection and 3 for displacements and rotation of bolt. The procedure also allows traction to be applied to a side of an enhanced element and to be transformed as nodal forces at enhanced degrees of freedom. The paper considers elastoplastic behaviour of joint surface and bolt-grout interface using Mohr-Coulomb criterion. For yielding of bolt rod unified tensile and bending criterion is adopted. The proposed method is implemented using 3-noded triangular elements and can be upgraded for higher order elements. The efficacy of the proposed procedure is evaluated by analyzing behaviour of a bolt reinforced jointed sample under direct shear test. The method is also applied to analyze displacements and stresses around a circular tunnel made in rock mass having multiple intersecting joints at different orientations, reinforced by bolts along the periphery of the tunnel. The results in terms of displacements and stresses are compared with those of unbolted rock mass model. The proposed method shows that effect of an individual joint, bolt and their interaction can be analyzed to understand the stability of excavation under given loading conditions and can be applied in wide variety of applications.

Flexural analysis of laminated solid wood beams with different shear connections

The paper discusses the mechanical response of laminated solid wood beams with different shear connections. Experimental, analytical (gamma method) and numerical (finite element analysis) procedures were performed to estimate the effect of shear connections on the stiffness and the failure capacity of laminated solid wood beams. The 4-point bending tests were carried out on the simply supported laminated wood beams with rigid adhesive bonding, on laminated wood beams with elastomeric adhesive bonding, on screw-laminated beams (with vertical and inclined screws) and laminated beams without bonding. The results obtained from the experimental tests, and the analytical and the numerical test calculations were analysed and compared. These results show that the flexural stiffnesses of inclined screw-laminated wood beams and of laminated beams with elastomeric adhesive bonding are similar. Both stiffnesses are up to twice the amount of that of vertical screw-laminated wood beams. However, the stiffness of the laminated beams with rigid adhesive is even fifty per cent higher than that of the previously mentioned two similar stiffnesses.

A Mathematical Model Development for the Lateral Collapse of Octagonal Tubes

Many researches has been done on the lateral collapse of tube. However, the previous researches only focus on cylindrical and square tubes. Then a research has been done discovering the collapse behaviour of hexagonal tube and the mathematic model of the deformation behaviour had been developed [8]. The purpose of this research is to study the lateral collapse behaviour of symmetric octagonal tubes and hence to develop a mathematical model of the collapse behaviour of these tubes. For that, a predictive mathematical model was developed and a finite element analysis procedure was conducted for the lateral collapse behaviour of symmetric octagonal tubes. Lastly, the mathematical model was verified by using the finite element analysis simulation results. It was discovered that these tubes performed different deformation behaviour than the cylindrical tube. Symmetric octagonal tubes perform 2 phases of elastic - plastic deformation behaviour patterns. The mathematical model had managed to show the fundamental of the deformation behaviour of octagonal tubes. However, further studies need to be conducted in order to further improve on the proposed mathematical model.

Direct displacement-based seismic assessment of concrete frames

Five previously-tested reinforced concrete frames were modelled using a nonlinear finite element analysis procedure to demonstrate the accurate response simulations for seismically-deficient frames through pushover analyses. The load capacities, story drifts, and failure modes were simulated. This procedure accounts for the effects of shear failures and the shearaxial force interaction, and thus is suitable for modeling seismically-deficient frames. It is demonstrated that a comprehensive analysis method with a capability of simulating material constitutive response and significant second-order mechanisms is essential in achieving a satisfactory response simulation. It is further shown that such analysis methods are invaluable in determining the expected seismic response, safety, and failure mode of the frame structures for a performance-based seismic evaluation. In addition, a new computer program was developed to aid researchers and engineers in the direct displacementbased seismic design process by assessing whether a frame structure meets the code-based performance requirements by analyzing the analysis results. As such, the proposed procedure facilitates the performance-based design of new buildings as well as the numerical assessment and retrofit design of existing buildings. A sample frame analysis was presented to demonstrate the application and verification of the approach.

Functional morphology in the pages of the AJPA

Functional morphology in the pages of the <i>AJPA</i>

Re-design of a uniplanar, monolateral external fixator.

This work deals with the structural analysis of screw clamps for external fixator devices. Screw clamps are widely used in external fixators as a means to connect the half-pins to the fixator body. The analysis is carried out by both numerical and experimental techniques, based on the case study of a clamp produced by Citieffe (Bologna, Italy). As a preliminary activity, the tribological parameters involved in the screw-clamp interaction have been characterized by means of a mixed finite element analysis and experimental procedure. Then, an assessment of the current design of the clamp has been carried out. A re-design has been proposed, which, based on some targeted geometrical modifications, allows achieving higher strength requirements with the same overall dimensions and type of materials. A higher load-bearing capability for a given size may allow the fixator to be used on a broader population. Finally, a list of good practices for the design of this kind of clamps has been proposed.

Experimental data reduction for hyperelasticity

WYPiWYG hyperelasticity is a data-driven, model-free computational procedure for finite element analysis of soft materials. The procedure does not assume the shape of the stored energy function and does not employ material parameters, predicting accurately any smooth prescribed behavior from a complete set of experimental tests. However, fuzzy experimental data may yield useless highly oscillatory, unstable stored energy functions, and classical curvature smoothing gives frequently unsatisfactory results. Aside, the possibility of having experimental data from different specimens for the same test was not considered in previous procedures. In this work we present a novel technique based on spline regression and smoothing penalization using stability conditions. In general, this procedure reduces noisy experimental data or data from multiple specimens for ulterior determination of the stored energy. The procedure only needs the solution of a linear system of equations. Instead of classical curvature-based smoothing, we employ a novel stability-based smoothing, determining for each branch of the uniaxial stress-strain curve the most restrictive stability condition during uniaxial and equibiaxial tests. The resulting stored energy functions are smooth and stable. The procedure has little sensitivity to the number of spline segments or to the choice of the penalization parameter, which are computed automatically.

Developing Topology Optimization with Additive Manufacturing Constraints in ANSYS®

Topology Optimization is an effective technique to optimize structural design and to minimize waste. Additive manufacturing (AM) is potentially a great approach to fabricate the complex organic geometric features of these optimized designs. However, topology optimization without considering manufacturing constrains may result in topologies that are expensive and difficult to manufacture. In order to satisfy the constraints imposed by AM processes, this paper proposes a topology optimization methodology using the compliance minimization approach with a constraint on overhanging surfaces. Compliance of a body is approximated through a finite element analysis procedure. To constrain the gradient and converge towards a structure without overhang surfaces, a function has been developed to estimate the overhang sensitivities. The gradient of the compliance with respect to densities are penalized using the determined overhang sensitivities. To introduce a reliable platform for research, as well as solving the resulting constrained topology optimization problems, a topology optimizer has been developed in ANSYS® using ANSYS Parametric Design Language (APDL). Using a conventional topology optimization method, the results of two different case studies solved by the developed APDL program are shown. Finally, an implementation of the proposed topology optimization methodology with AM constraints is used to solve a problem. The result is a structure that does not need support material to be manufactured.

SOIL-STRUCTURE INTERACTION ANALYSES OF PILE SUPPORTED BUILDING FRAME

The effect of the soil-structure interaction on the simple single storeyed and two bayed space frame resting on pile group of two piles with flexible cap is examined in this paper by resorting to more rational approach and realistic assumptions. Initially, 3-D FEA is carried out independently for the frame on the premised of fixed column bases. Later, pile foundation is worked out separately. The stiffness so obtained for foundation is used in the interactive analysis of frame to quantify the effect of soil- structure interaction on the response of the superstructure. For modeling the foundation system two approaches of finite element analysis are used. In the first approach complete three dimensional finite element analysis is resorted to wherein pile, pile cap along with the soil are discretized into 20 noded isoparametric continnum elements and interface between pile and soil is idealized as 6 noded isoparametric interface elements. In the second approach simplified finite element analysis procedure is used wherein beam element, plate element and spring elements are used to model pile, pile cap and soil respectively. The salient feature of the investigation is that the interaction between pile cap and soil underlying it is considered. In the parametric study presented here, effect of pile spacing and pile configuration is evaluated on the response of superstructure in the form top displacement in frame and bending moment at top as well as bottom of the superstructure columns. Results obtained by either analysis are compared.

Implementation of a finite element analysis procedure for structural analysis of shape memory behaviour of fibre reinforced shape memory polymer composites

Shape memory polymers (SMPs) offer a unique ability to undergo a substantial shape deformation and subsequently recover the original shape when exposed to a particular external stimulus. Comparatively low mechanical properties being the major drawback for extended use of SMPs in engineering applications. However the inclusion of reinforcing fibres in to SMPs improves mechanical properties significantly while retaining intrinsic shape memory effects. The implementation of shape memory polymer composites (SMPCs) in any engineering application is a unique task which requires profound materials and design optimization. However currently available analytical tools have critical limitations to undertake accurate analysis/simulations of SMPC structures and slower derestrict transformation of breakthrough research outcomes to real-life applications. Many finite element (FE) models have been presented. But majority of them require a complicated user-subroutines to integrate with standard FE software packages. Furthermore, those subroutines are problem specific and difficult to use for a wider range of SMPC materials and related structures. This paper presents a FE simulation technique to model the thermomechanical behaviour of the SMPCs using commercial FE software ABAQUS. Proposed technique incorporates material time-dependent viscoelastic behaviour. The ability of the proposed technique to predict the shape fixity and shape recovery was evaluated by experimental data acquired by a bending of a SMPC cantilever beam. The excellent correlation between the experimental and FE simulation results has confirmed the robustness of the proposed technique.