Nonlinear Explicit Finite Element Code Research Articles

Numerical simulation of continuous damage and fracture in metal-forming processes with 2D mesh adaptive methodology

An h-adaptive remeshing scheme dedicated to the simulation of macroscopic ductile cracks initiation and propagation during metal forming processes, is proposed. Cracks are represented using a procedure based on fully damaged elements deletion. Element size inside the domain and along the crack path, located inside highly localized zones, is driven by error indicators based on geometrical considerations and the derivatives of physical quantities calculated by diffuse approximation. Saw tooth effects along the crack are smoothed with the use of Bezier curves in order to reduce computational inaccuracy. The mesh can be refined and an important issue of this work is mesh coarsening in order to ensure a reasonable computational cost. Multiple domains can be handled. The procedure can be easily integrated in any standard nonlinear explicit finite element code. Specific fields transfer procedures and an automatic adaptation of the time loading sequences are also presented. The efficiency and robustness of the proposed strategy are validated through some examples which show a good agreement with experimentally observed ductile crack paths under large inelastic strains.

Research on three-dimensional surface parts in multi-gripper flexible stretch forming

Multi-gripper flexible stretch forming (MGFSF) is a novel flexible forming process of sheet metal based on the multi-point forming principle. The straight jaws in traditional transverse stretch forming (TSF) are replaced by several discrete clamping mechanisms on both sides. To help understand the forming characters of MGFSF, spherical and concave–convex parts were selected as the research objects and finite element analyses on TSF and MGFSF were implemented using an explicit nonlinear finite element code. The influence of the transition length on the forming results in MGFSF was also taken into account in the present work. The simulation results reveal that a shorter transition length in MGFSF would result in an easier conformability of the sheet metal to the desired shape as well as a smaller strain variation in the forming zone. It is also found that, compared to TSF, the sheet metal can be formed without transition zone by utilizing MGFSF, which could significantly improve the material utilization and save the manufacturing costs. Finally, experimental validations were conducted on the self-developed MGFSF apparatus and the experimental results show a good agreement with the numerical results.

Finite element simulation of barge impact into a rigid wall

The forces and locations of inland barge impacts currently control the design specifications for lock walls. This has resulted in a significant increase in the final construction costs of these walls. Thus, the loads from barge impacts on lock approach walls become an important evaluation and/or design factor when working toward reducing construction costs.Many approaches have been developed in order to obtain these impact loads. In general, collision mechanics for floating units is classified into, external mechanics and internal mechanics. In external mechanics, analytical approaches are used to determine the absorbed energy acting on the vessel from the collision, while in internal mechanics analytical approaches are used to determine the ability of the ship’s structure to withstand the absorbed energy. Due to the difficulty and the highly expected cost to perform model testing and impact data for validation, finite element simulation provides an alternative tool for physical validation. In this study, a simulation of barge impact to a rigid wall is presented using the explicit nonlinear finite element code LS-DYNA3D. A conventional fine mesh finite element barge model is created. Impact results are obtained at two different speeds in order to show the consequence of barge and wall damage.

Dynamics Simulation of Sounding Rocket Water Landing Recovery with Fluid-Structure Interaction Method

This paper presents the water landing dynamics simulation of a sounding rocket, obtaining dynamics characteristics of the interaction between the rocket payload module, the floatation airbag and the water. Using an explicit nonlinear dynamic finite element code, the model contains Lagrangian shell elements for rocket payload, membrane elements for the airbag and Eulerian elements for the water. The Fluid-Structure Interaction (FSI) technology is employed in the computation by transferring forces on nodes of coupling surfaces. In the paper, two landing attitudes are analyzed and compared. After analyzing dynamic response of airbag under different operating conditions, the minimum size is concluded. This dynamics simulation builds the foundation for the Engineering Model of the recovery system.

Rollover crashworthiness analysis of a railroad passenger car

Rollover of railroad passenger cars is one of the most serious accidents having high rates of injuries and fatalities. Therefore, the railroad passenger car structures should satisfy the rollover crashworthiness requirements in order to protect the occupants. In this paper, rollover crashworthiness of a railroad passenger car called ‘N13-type’ used by Turkish State Railways is investigated. To assess the rollover crashworthiness, rollover simulations of the full scale and detailed passenger car models onto a rigid ground are completed by using a non-linear explicit finite element code, Abaqus. The numerical model is validated with static and modal experimental measurements before running rollover analyses of the railroad passenger car. Good agreement is observed between tests and finite element results, which indicate that the numerical model accurately represents the real structure. Simulations are performed in accordance with the regulation of ECE R66. Based on this standard, two different rollover scenarios are considered. In the first scenario, lateral rollover simulation is performed at the standard angular velocity due to ECE R66 regulation. The second scenario is performed at the double of this angular velocity to investigate the crashworthiness behaviour under exaggerated conditions. As a result of the analyses, it is observed that the residual space remains undamaged during and after the rollover, and passenger car is able to pass the required regulations.

Crashing Behaviour Analysis of TWB Tubular Structures with Different Cross-Sections

The present paper investigates the crashing behavior and energy absorption characteristics of thin-walled (tubular) structures with different cross-sections made from tailor welded blanks (TWB) which were subject of axial quasistatic loadings. Resulted data were obtained by using explicit nonlinear finite element code LS_Dyna V971. Implementing the TWB into the auto industry was an efficient method to decrease the general weight of different structures. By far, these kind of bimetallic structures are largely utilized in auto and naval industries because it led to important decrease of scarp quantities and general manufacturing costs, improved material use and probably the most important, great fuel efficiency. After reviewing the literature it was concluded that proper combination between mechanical characteristics of sheet metals, different thicknesses and cross-section shapes into the same thin-walled structure is far too little researched and understood. The aims of this study are better understandings of the crashing behavior regarding thin-walled structure with various cross-sections made from TWB blanks subject to quasistatic loadings. The non-linear finite element platform LS_Dyna V971 was used for the numerical analysis of the crushing behavior regarding the thin-walled structures. Having two materials constituting the thin-walled structures, the crashing behavior changed during the quasistatic loading. Thus, the crashing inertia of the structure is somehow limited and controlled. It is noted that material ratio should not be randomly chosen due to the unexpected crashing mode which could aggravate the prediction and control of the crashing behavior of the thin-walled structure.

Mechanical behaviour of dual-phase high-strength steel under high strain rate tensile loading

The effects of strain rate on the tensile properties of two commercial steels (DP700 and DP500) were investigated. Quasi-static tests (0.001s−1) were performed using an electromechanical universal testing machine, whereas a split Hopkinson tensile bar apparatus was used for testing at high strain rates (~1100s−1, ~1800s−1, and ~3200s−1). The two high-strength steels show significant strain rate sensitivity. The material parameters of the existing Johnson–Cook model were determined from experimental results. This model fits the experimental data well in the plastic zone. Digital image correlation was used together with high-speed photography to study the strain localisation in the tensile specimens at high strain rates. By using digital image correlation, the in-plane strain field and local fracture strain of the specimen were obtained. The contours of the strain field indicate an early localisation even before the peak load is attained. Numerical simulations of the dynamic tensile tests were performed using the non-linear explicit finite element code LS-DYNA with the Johnson–Cook model. Good correlation between the experiments and numerical predictions is achieved, in terms of the strain gauge signals, deformed geometry, and strain field.

비선형 수치해석을 통한 단자유도 얕은기초 구조물의 지진 응답특성 검증

Seismic response of single degree of freedom system supported by shallow foundation was analyzed by using nonlinear explicit finite difference element code. Numerical analysis results were verified with dynamic centrifuge test results of the same soil profile and structural dimensions with the numerical analysis model at a centrifugal acceleration of 20 g. Differences between the analysis and the test results induced by the boundary conditions of control points can be reduced by adding additional local damping to the natural born cyclic hysteretic damping of the soil strata. The analysis results show good agreement with the test results in terms of both time histories and response spectra. Thus, it can be concluded that the nonlinear explicit finite difference element code will be a useful technique for estimating seismic residual displacement, earthpressure etc. which are difficult to measure during laboratory tests and real earthquake.

Delamination of impacted composite structures by cohesive zone interface elements and tiebreak contact

Abstract Maximising impact protection of fibre reinforced plastic (FRP) laminated composite structures and predicting and preventing the negative effects of impact on these structures are paramount design criteria for ground and space vehicles. In this paper the low velocity impact response of these structures will be investigated. The current work is based on the application of explicit finite element software for modelling the behaviour of laminated composite plates under low velocity impact loading and it explores the impact, post impact and failure of these structures. Three models, namely thick shell elements with cohesive interface, solid elements with cohesive interface, and thin shell elements with tiebreak contact, were all developed in the explicit nonlinear finite element code LS-DYNA. The FEA results in terms of force and energy are validated with experimental studies in the literature. The numerical results are utilized in providing guidelines for modelling and impact simulation of FRP laminated composites, and recommendations are provided in terms of modelling and simulation parameters such as element size, number of shell sub-laminates, and contact stiffness scale factors.

Correlating Micromorphology and Nanomorphology to High Strain Rate Performance of Nanoparticle Reinforced Polymeric Materials

AbstractThis paper focuses on correlating micromorphology and nanomorphology to the performance of nano-enhanced polymers subjected to blast loading, studying the behavior of these materials at high strain rates, and evaluating the effect of voids’ size and amount on the strain rate sensitivity of nanomaterials. Three polyurea-based elastomeric materials are investigated in this study: unreinforced polyurea, exfoliated graphene nanoparticle (xGnP)–reinforced polyurea, and polyhedral oligomeric silsesquioxane (POSS)–reinforced polyurea. Three-dimensional computed tomography scan images show large amounts of randomly distributed voids in the materials. The study found that POSS-reinforced polyurea has the largest number but the smallest void size among the three tested materials. Computational parametric evaluation is conducted to investigate the effect of such defects on the behavior of these materials. Dynamic nonlinear explicit finite-element code AUTODYN is used to perform three-dimensional analyses for...

Elastomeric Polymers for Retrofitting of Reinforced Concrete Structures against the Explosive Effects of Blast

The main distinction of blast load from other types of dynamic loadings is its impulsive nature, where the loads usually act for a very short duration but transmit very high impulsive pressures. This paper presents an overview of the present retrofitting techniques in use to enhance the capacity of structural elements to withstand the effects of blast loads, and introduces an alternative retrofitting approach by utilizing polymer coatings. The authors have demonstrated the positive effects of this approach by conducting a numerical investigation on the behavior of an unretrofitted reinforced concrete panel subjected to the blast load from a 2 kg charge at 1.6 m stand-off distance, and subsequently comparing its performance with several polymer coated panels. The analysis was performed by using an explicit nonlinear finite element (FE) code. The results demonstrate the contributions of this technique in terms of panel displacement control and energy dissipation. Considering that the polymer coating can also act as a protective layer in improving the durability of structural materials, this technique can also be optimized favorably to enhance the overall sustainability of structures.

Energy Absorption of an Re-Entrant Honeycombs with Negative Poisson’s Ratio

In the present paper, we have investigated a negative Poisson’s ratio structure with regular re-entrant cell shape to study its structural response under crush by rigid wall. Firstly, we created the geometry of cellular material in HYPERMESH. The developed geometrical model is imported into LS-DYNA. Then we use commercially available nonlinear explicit finite element code LS-DYNA to simulate the NPR material under uniformly distributed load. The deformation modes and energy absorption characteristics of NPR material were analyzed. Numerical results indicate that this NPR material have good ability of energy absorption.

Simulating blast effects on steel beam-column members: Applications

Validation and application examples are presented for a beam-column element that uses bounding surface plasticity models to characterize the effects of blast-induced damage in structures with steel wide-flange members. Element formulation and implementation within the nonlinear explicit dynamic finite element code CU-BAMM appears in the companion paper [1]. The current paper details the creation of a library of bounding surfaces for various wide-flange members and explosive scenarios, and library integration with the code. A validation example shows favorable agreement between CU-BAMM simulation results and results obtained from a high-resolution model for prediction of the post-blast collapse load for an A-frame system.

Simulating blast effects on steel beam-column members: Methods

A beam-column element is formulated and implemented within a nonlinear explicit dynamic finite element code for simulating explosive effects in steel skeletal structures composed of wide-flange members. Blast damage is encapsulated by a bounding surface plasticity model in stress-resultant space. Bounding surfaces are formed by fitting numerical failure data to a basis of real-valued spherical harmonics: the data are obtained through numerical experiments in which a shell element-based model of a member is exposed to a blast and then statically loaded to failure for various combinations of proportional moment-thrust loading. Code validation and examples are presented in a companion paper [1].

Blank Optimization in Elliptical-Shape Sheet Metal Forming Using Response Surface Model Coupled with Reduced Basis Technique and Finite Element Analysis

The present study aims to determine the optimum blank shape design for the deep drawing of Elliptical-shape cups with a uniform trimming allowance at the flange i.e. cups without ears. This earing defect is caused by planar anisotropy in the sheet and the friction between the blank and punch/die. In this research, a new method for optimum blank shape design using finite element analysis has been proposed. Present study describes the approach of applying Response Surface Methodology (RSM) with Reduced Basis Technique (RBT) to assist engineers in the blank optimization in sheet metal forming. The primary objective of the method is to reduce the enormous number of design variables required to define the blank shape. RBT is a weighted combination of several basis shapes. The aim of the method is to find the best combination using the weights for each blank shape as the design variables. A multi-level design process is developed to find suitable basis shapes or trial shapes at each level that can be used in the reduced basis technique. Each level is treated as a separated optimization problem until the required objective – minimum earing function – is achieved. The experimental design of RSM method is used to build the approximation model and to perform optimization. MATLAB software has been used for building RSM model. Explicit non-linear finite element (FE) Code Abaqus/CAE is used to simulate the deep drawing process. FE models are constructed incorporating the exact physical conditions of the process such as tooling design like die profile radius, punch corner radius, etc., material used, coefficient of friction, punch speed and blank holder force. The material used for the analysis is Stainless steel St12. A quantitative earing function is defined to measure the amount of earing and to compare the deformed shape and target shape set for each stage of the analysis. The cycle is repeated until the converged results are achieved. This iterative design process leads to optimal blank shape. So through the investigation the proposed method of optimal blank design is found to be very effective in the deep drawing process and can be further applied to other stamping applications.

Performance evaluation of steel and composite bridge safety barriers by vehicle crash simulation

The performance of full-scale steel and composite bridge safety barriers under vehicle crash is evaluated by using the nonlinear explicit finite element code LS-DYNA. Two types of vehicles used in this study are passenger car and truck, and the performance criteria considered include structural strength and deformation, occupant protection, and post-crash vehicle behavior. It can be concluded that the composite safety barrier satisfies all performance criteria of vehicle crash. Although the steel safety barrier satisfies the performance criteria of occupant protection and post-crash vehicle behavior, it fails to satisfy the performance criterion of deformation. In all performance evaluations, the composite safety barrier exhibits a superior performance in comparing with the steel safety barrier.

A Numerical Study of the High-Velocity Impact Response of a Composite Laminate Using LS-DYNA

The failure of a Kevlar29/Phenolic composite plate under high-velocity impact from an fragment simulation projectile was investigated using the nonlinear explicit finite element code, LS-DYNA. The composite laminate and the impactor were idealized by solid elements, and the interface between the laminas was modeled as a tiebreak type in LS-DYNA. The interaction between the impactor and laminate was simulated using a surface-to-surface eroding contact algorithm. When the stress level meets the given failure criteria, the layer in the element is eroded. Numerical results were verified through existing test results and showed good agreement.

Energy absorption of longitudinally grooved square tubes under axial compression

This paper investigates the energy absorption characteristics of longitudinally grooved square tubes under axial compression by using explicit nonlinear finite element code LS-DYNA. The grooves are fabricated by stamping and the distributions of the effective plastic strain and the thickness variation from the stamping process are considered in the following crash analyses. From the simulation results, we find that when grooves are introduced on the sidewalls, the specific energy absorption of conventional tubes can be increased by up to 82.7% and the peak force can be reduced by up to 22.3%. The influences of several parameters, including the width of the tube, the length of the groove and the number of the grooves, are analyzed and the features of the deformation modes of grooved tubes are described. The introduction of groove is found to be an effective way to improve the crashworthiness of thin-walled structures.

Crushing analysis of polygonal columns and angle elements

Abstract Energy absorption characteristics of regular polygonal columns and angle elements under dynamic axial compression are investigated by using non-linear explicit finite element code LS-DYNA. The influence of central angle on deformation mode and mean crushing force of angle elements is studied. Based on two types of deformation mechanisms known by experiments, two types of initial indentation triggers are introduced. By assuming appropriate boundary condition on the edges, a simplified finite element model is adopted in the analysis of angle elements and validated by comparing with full polygonal column model. Numerical investigations are also carried out to study the influence of angle on angle elements with three and four panels by using the simplified model. Several useful conclusions are drawn about the axial crushing of polygonal columns and angle elements and can be used to guide the design of crashworthiness structures. In addition, a comparison is conducted between the numerical results and theoretical predictions of the mean forces of some special angle elements. Good agreement is obtained.

Crash response of advanced high-strength steel tubes: Experiment and model

The performance of non-hydroformed and hydroformed structural steel tubes in component-level crash testing was investigated using both experimental and analytical techniques. In particular, the focus was on high-strength steels that may have potential to enhance crashworthiness of automobiles. Monolithic tubes made from multiple materials and wall thicknesses were considered in this study. The following materials were used: conventional drawing quality (DDQ) steels; high-strength low alloy (HSLA-350) steels; and advanced high-strength steel (AHSS) materials comprising the dual phase alloys DP600 and DP780. The goal of this research was to study the interaction between the forming and crash response of these materials in order to evaluate their potential for use in vehicle design for crashworthiness. The tubes were hydroformed using two methods known as low- and high-pressure processes. Material characterization of all materials was carried out through quasi-static and high strain rate tensile tests in the range of 0.00333–1500 s −1, and rate sensitive constitutive models for all materials were developed. The nonlinear explicit dynamic finite element code LS-DYNA, in conjunction with the validated constitutive models, was used to simulate both the hydroforming processes and the crash tests performed on the tubes. The energy absorption characteristics of the different tubes were calculated and the results from the numerical analyses were compared against the experimental data. This comparison was performed in order to determine whether the interactions between forming and crush could be adequately predicted using finite element analysis. The effects of thickness changes, work hardening, and component geometry, which resulted from hydroforming, on the crash response were also investigated. A study of the significance of strain rate and the importance of performing detailed material characterization on the accuracy of the numerical analysis was performed. Also, a parametric study on the effect of transferring forming history data between simulations on the accuracy of the numerical analysis was performed, and the importance of carrying forward the histories between multiple forming simulations was demonstrated.