Explicit Finite Element Analysis Research Articles

Comparative study on deformation and mechanical behavior of corroded pipe: Part I–Numerical simulation and experimental investigation under impact load

Experiments and a numerical simulation were conducted to investigate the deformation and impact behavior of a corroded pipe, as corrosion, fatigue, and collision phenomena frequently occur in subsea pipelines. This study focuses on the deformation of the corrosion region and the variation of the geometry of the pipe under impact loading. The experiments for the impact behavior of the corroded pipe were performed using an impact test apparatus to validate the results of the simulation. In addition, during the simulation, material tests were performed, and the results were applied to the simulation. The ABAQUS explicit finite element analysis program was used to perform numerical simulations for the parametric study, as well as experiment scenarios, to investigate the effects of defects under impact loading. In addition, the modified ASME B31.8 code formula was proposed to define the damage range for the dented pipe.

Investigations of shock-induced deformation and dislocation mechanism by a multiscale discrete dislocation plasticity model

There are many theoretical and computational investigations devoted to the dislocation mechanism based crystal plasticity under static or quasi-static conditions. However, the dislocation behavior, specifically the nucleation and multiplication of dislocations, remains unclear in crystal under shock loading. In this paper, the dislocation mechanism in single crystalline copper under shock loading is investigated through a multiscale numerical model, which couples discrete dislocation dynamics (DDD) with explicit finite element (FE) analyses. Firstly, since the homogeneous nucleation (HN) of dislocations is considered as the dominant dislocation generation mechanism at extremely high strain rates, the typical parameters of HN are obtained by systematic molecular dynamics (MD) simulations, which include critical shear stress, saturation time, stable density, etc. Then, these parameters are implemented into DDD-FE model by a coarse grained method. It can remarkably improve the computational efficiency without loss of typical dislocation characters. The interactions between shock wave and dislocations are studied in detail. Band-like dislocation walls and their shielding effect on other dislocations are observed during the shock wave propagation. The simulation results are in good agreement with experimental observations. It is also found that both fast HN and avalanche-like dislocation multiplication get involved and lead to the softening of shear stress. Finally, by comparing the dynamic behavior under different impact speeds, a threshold speed around 1000m/s for the dislocation dominant mechanism is proposed from the computations in this work. Beyond this speed, the effect of other defects such as stacking fault and twinning would be prominent.

Experimental and numerical investigation of contact laws for the rapid simulation of low-energy impacts on laminated composite plates

A computationally efficient model for the impact simulation of low energy impacts on composite laminated plate structures is developed, which combines a contact law with a new time domain spectral shear plate finite element. Various contact laws are numerically and experimentally investigated based on elastoplastic and fully-plastic indentation theory. The contact laws are correlated with quasi-static indentation test data performed on carbon/epoxy cross-ply laminates and with numerical results of a 3-D finite element analysis (FEA) indentation model with Hill failure criterion. The extracted contact laws are combined with a first-order shear plate time domain spectral finite element with explicit time integration. Obtained impact simulation results are compared with a 3-D continuum explicit FEA model and experimental results. The results demonstrate excellent accuracy of the present method, and drastically improved numerical simulation speed.

Impact or blast induced fire simulation of bi-directional PSC panel considering concrete confinement and spalling effect

In recent years, numerous explosion and collision related tragedies due to military attack, terrorist bombing, and vehicle accident have occurred all over the world. However, researches on Prestressed Concrete (PSC) infrastructures such as Prestressed Concrete Containment Vessels (PCCVs) and LNG storage tanks under extreme loading such as impact, blast, and fire loading scenario are not being studied sufficiently. Especially, researches on possible secondary fire after bomb explosion or accidental collision on concrete structures has not been performed, while most of the past researches related to extreme loadings on structures focused on ideal isolated extreme loading event researches. Therefore, in this study, the PSC panel such as wall of PCCV and LNG storage tank is analytically evaluated under impact-blast-fire combined loading scenarios. For the analytical simulations of impact/blast and fire loaded behavior of the PSC panel, commercial finite element analysis program of LS-DYNA and MIDAS FEA, respectively, were used. Then, a simulation procedure coupling LS-DYNA and MIDAS FEA using element elimination algorithm is proposed to couple explicit and implicit finite element analyses (FEA) to perform structural analysis of impact or blast induced fire loading scenario. Then, the simulation results from the PSC and RC specimens applied with impact induced fire or blast induced fire loadings were compared with those of undamaged PSC and RC specimens. The results showed that PSC panel was more severely damaged from the fire due to the confining effect of prestressing forces. Confining effect increased the thermal conductivity of concrete due to compaction of concrete. Also, the spalling of concrete caused by impact loading followed by fire loading were implemented to the simulation model using the element elimination procedure proposed in the study. The simulation results obtained from the proposed simulation procedure agree well with the impact induced fire test results.

Development of a Point Pyroshock Source Simulator

We developed a point pyroshock source simulator (PPSS) for the study on the source isolation approach (SIA) in this study. In spite of the potentiality of the SIA for avionics protection against pyroshock, it has rarely been investigated due to lack of pyroshock source simulators. To overcome such a situation, we proposed the PPSS using a mechanically excited tuned resonator simulating a release device itself. The PPSS was designed using explicit finite element analysis and Seigel’s gas gun model. To verify the proposed PPSS, the prototype was fabricated and tested. From the results, we have shown that the prototype of the PPSS simulates a near-field pyroshock and is able to evaluate the SIA.

SPH High Velocity Impact Analysis-Influence of Bird Shape on Rigid Flat Plate

Bird impact usually occurs during taking off or landing of flights. The aircraft structures should absorb impact energy generated due to ingested birds, ice balls or hail stone and hard body objects. etc. This paper deals with a sensitivity study of hydrodynamic bird models which is performed by numerical simulation. The analysis is carried out by using an explicit Finite Element Analysis (FEA) code AUTODYNE for impact of substitute birds on square plate of rigid Aluminum. The bird body is modeled as a porous water-air material in the shape of a Cylindrical, Cylindrical with Hemispherical ends, Ellipsoidal and Spherical. The finite element bird modeling was carried out by the use of Smooth Particle Hydrodynamics (SPH) method for materials of 10% porosity. The Stagnation and Hugoniot Pressures with time were achieved from four bird models are presented and theoretical results were compared with simulation results.

Temperature study in Turning Inconel-718: 3D Simulation and Experimentation

In cutting, nearly all of energy dissipated in plastic deformation is converted into heat that in turn raises the temperature in the cutting zone. Cutting temperature, a) affects the wear of the cutting tool; b) can induce thermal damage to the machined surface and c) causes dimensional errors in the machined surface. This paper presents a simulation model for the estimation of temperature developed in machining process. The FEM software used for this study is ABAQUS. A practical explicit 3D finite element analysis model is developed and implemented to analyze turning Inconel 718 using TiAlN coated carbide inserts. The finite element analysis incorporated the thermo-elastic-plastic properties of the work material in machining. The results from simulation model are compared with experimental data. A Taguchi’s L9 orthogonal array is used for the experimental runs. It is found that simulation results were in good agreement with experimental results. It has been observed that cutting temperature increases with the increase in cutting speed. A valid simulation models helps the tool engineers to gather relevant process related information without resorting to costly and time consuming experimentation.

An optimized neck-spinning method for improving the inner surface quality of titanium domes

Abstract Welded titanium-based cylinders are widely used as high pressure gas containers. However, the welding joints reduce their fatigue life and airtightness. As a result of it, seamless cylindrical vessels are needed to solve this problem, but the conventional neck-spinning process for manufacturing seamless vessels is challenging due to the formation of winkles and cracks on their inner surfaces of its spun parts. In this study, an optimized neck-spinning technique is proposed by reversing the materials’ flowing direction with respect to the feeding direction of the spinning roller. A significant improvement in inner-surface finishing has been achieved. Explicit 3D finite element analysis was conducted to simulate such a forming process. The inner-surface strain distribution and development were analyzed, which provided insights into its underlying defect formation mechanisms.

Experimental and numerical study on crashworthiness of cold-formed dimpled steel columns

The UltraSTEEL® forming process forms plain steel sheets into dimpled steel sheets and this process increases the sheet material's strengths by generating plastic deformation on the material during the process. This paper presented experimental testing and developed a finite element (FE) model to predict the energy absorption characteristics of dimpled thin-walled structures under axial impact loads, and compared the energy absorption efficiencies (specific energy absorption) of plain and dimpled columns. Dynamic experimental tests were conducted using the drop tower at two different impact velocities. Explicit FE analysis were then carried out to simulate the experiments. The FE method was validated by comparing the numerical and experimental failure modes, crushing force response and specific energy absorptions. The validated FE method was then applied in an optimization study on the parameter of forming depth. The effects of forming depth on both geometry and material properties have been taken into account in the optimization study. It has been found that the specific energy absorption of dimpled columns is up to 16.3% higher than the comparable plain columns.

Low-speed bending impact behavior of adhesively bonded single-lap joints

This study addresses the low-speed impact behavior of adhesively bonded single-lap joints. An explicit dynamic finite element analysis was conducted in order to determine the damage initiation and propagation in the adhesive layers of adhesive single-lap joints under a bending impact load. A cohesive zone model was implemented to predict probable failure initiation and propagation along adhesive–adherend interfaces whereas an elasto-plastic material model was used for the adhesive zone between upper and lower adhesive interfaces as well as the adherends. The effect of the plastic deformation ability of adherend material on the damage mechanism of the adhesive layer was also studied for two aluminum materials Al 2024-T3 and Al 5754-0 having different strength and plastic deformation ability. The effects of impact energy (3 and 11 J) and the overlap length (25 and 40 mm) were also investigated. The predicted contact force-time, contact force-central displacement variations, the damage initiation and propagation mechanism were verified with experimental ones. The SEM and macroscope photographs of the adhesive fracture surfaces were similar to those of the explicit dynamic finite element analysis.

Three-Dimensional Dynamic Explicit Finite Element Analysis of Charpy Impact Test

Dynamic explicit finite element (FE) analysis of the Charpy impact test was conducted in this study to investigate the inertial effect on the stress field ahead of the V-notch in a Charpy specimen. The deformation behavior of the Charpy specimen and the constraint effect on the stress field in the plastic zone near the V-notch were numerically simulated using three-dimensional FE analysis, while considering the contact of the specimen with the striker and anvil. The effect of the strain rate on the flow stress and the increase in temperature during impact loading were included in the dynamic analysis. This analysis shows that the impact load exhibits oscillation and the contact stiffness between the specimen and the striker affects the oscillation of the impact load. The analysis was validated by comparison with experimental results obtained using an instrumented Charpy impact testing machine, which measured the impact load and the load point displacement. The oscillation of the load–time curve was recorded. The magnitude and period of the peak inertia load obtained by the FE analysis were almost consistent with the experimental results. The contact stiffness between the specimen and the striker affected the stress field near the V-notch in the specimen. This indicates that the stress field in the Charpy specimen should be analyzed by the dynamic analysis procedure considering the contact stiffness based on the Hertzian contact theory.

Prediction of plastic deformation under contact condition by quasi-static and dynamic simulations using explicit finite element analysis

We compared the quasi-static and dynamic simulation responses on elastic-plastic deformation of advanced alloys using Finite element (FE) method with an explicit numerical algorithm. A geometrical model consisting of a cylinder-on-flat surface contact under a normal load and sliding motion was examined. Two aeroengine materials, Ti-6Al-4V and Super CMV (Cr-Mo-V) alloy, were employed in the FE analysis. The FE model was validated by comparative magnitudes of the FE-predicted maximum contact pressure variation along the contact half-width length with the theoretical Hertzian contact solution. Results show that the (compressive) displacement of the initial contact surface steadily increases for the quasi-static load case, but accumulates at an increasing rate to the maximum level for the dynamic loading. However, the relatively higher stiffness and yield strength of the Super CMV alloy resulted in limited deformation and low plastic strain when compared to the Ti-6Al-4V alloy. The accumulated equivalent plastic strain of the material point at the initial contact position was nearly a thousand times higher for the dynamic load case (for example, 6.592 for Ti-6Al-4V, 1.0 kN) when compared to the quasi-static loading (only 0.0072). During the loading step, the von Mises stress increased with a decreasing and increasing rate for the quasi-static and dynamic load case, respectively. A sudden increase in the stress magnitude to the respective peak value was registered due to the additional constraint to overcome the static friction of the mating surfaces during the sliding step.

Crashworthy response of fibre metal laminate top hat structures

The axial crushing response of fibre metal laminates (FML), in particular GLARE top-hat structures, has been investigated using experimental and numerical techniques, which are reported in this paper. Crushing performance (crush force, energy absorption) was evaluated for formed GLARE top-hat structures as an analogue for an energy absorbing aircraft sub-floor structure. A numerical simulation methodology was established which could accurately predict the crushing performance of GLARE top hat structures using commercial explicit finite element (FE) analysis tool LS-DYNA. Material characterisation at coupon level was conducted to measure the appropriate material properties required for the model to achieve good predictability. The successful demonstration of GLARE energy absorbing structures widens options to enhance crashworthiness; numerous applications of such GLARE structures could be envisaged, including reinforcement of aircraft sub-floors.The crushing modes of GLARE top-hat structures were found to be complex, exhibiting mixed-mode failure which was a combination of the individual constituent failure modes. The metallic layers plastically deformed by folding and tearing while the composite layer failed with a wide range of failure patterns i.e. splaying, delamination and cracking. The top hat structures, most importantly, crushed in a stable progressive manner making them suitable for energy absorbing (EA) applications. The GLARE top hat structure’s crushing response is superior to its bare metal equivalent.Given the complexity of the FML crushing process, there is tremendous scope for optimisation of the laminate parameters to maximise energy absorption. The good agreement obtained between the numerical and experimental results highlights the benefits of using simulation to predict the overall crashworthiness of FMLs.

Polypropylene fiber reinforced concrete plates under fluid impact. Part II: modeling and simulation

Fluid impact tests on plates containing mesh reinforcement and polypropylene fibers were modeled and simulated using explicit finite element analysis software, LS-DYNA. The scabbing dimensions obtained by the experiments and the simulations were compared and crack formations were matched. The objective was to test the accuracy and fidelity of the model and to confirm that damage caused by fluid impact on the plates can be estimated with a reasonable accuracy over a wide range of impact velocity.

Experimental and Numerical Investigation of Impact Characteristics of the E-Glass/Toughened Vinylester Composite Car Hood Panels

This study involves experimental and numerical investigation on the impact response of a section of typical car hood having reinforcement in its inner layer containing a common X-shaped hat section. The hood specimens were developed by utilizing E-glass/Vinylester prepreg. The effect of stiffening the inner layer’s reinforcement region by placing a balsawood layer in the X-shaped hat section was also studied. Impact test was performed by driving the impacting pendulum by using the pneumatic device at a velocity of 4.1 m/s to evaluate the impact response of the composite hood panels having balsawood layer and of those without it. Impact test results; load-time, displacement–time, load–deflection history from experimental is presented at 200 kJ impact energy. Explicit finite element analysis was performed by utilizing commercially available LS-Dyna code. The computational model was developed to predict the response of both types of composite car hood panels under dynamic loading. A comparison of the experimental results i.e., deflection-time, load-time histories and kinetic energy with FEA results for both types of composite car hood panels was made. Results correlate well and form the basis for analyzing and designing such new lightweight material systems for automotive applications.

Preliminary and time-efficient vulnerability assessment of structural columns subjected to blast loading

The determination of the nonlinear response of structural members subjected to a close-in explosive threat is challenging. There are various ways to quantify the blast resistance and mode of failure of a structural member, e.g. experimental testing which is expensive and time-consuming, or high-fidelity finite element analysis which is also time-consuming. The familiar analytical approach using an equivalent single-degree-of-freedom (SDOF) system is much less costly, however, as will be shown in this paper, may lack accuracy. Based on an extensive study of the nonlinear response of a ground-floor column of a high-rise building subjected to close-in explosive threat, using nonlinear explicit finite element analysis as well as analytical single-degree-of-freedom (SDOF) system approach, the source of inaccuracy of the analytical approach is identified, and an empirical approach using Multivariable Polynomial Regression (MPR) is established. The paper presents a head-to-head comparison of the results produced by finite element analysis, the SDOF system analysis, the empirical approach, and experimental test data to emphasize the accuracy and time-efficiency of the proposed approach. The approach has the potential to establish itself as a time-efficient preliminary vulnerability assessment methodology of structural members subjected to close-in blast loading.

Interior Head Impact Analysis of Automotive Instrument Panel for Unrestrained Front Seat Passengers

This study presents the numerical and experimental interior head impact analysis of automotive instrument panel according to the United Nations Economic Commission for Europe Regulation 21 (ECE R21). To minimize the possible injury risk for unrestrained front seat passengers due to the interior head impact with the instrument panel, the panel design needs to meet the ECE R21 standard which defines a pendulum-type head form as the impactor. The measured acceleration response of the head form should not exceed 80g continuously for more than 3ms. Motivated by the need to develop a simulation-based technique to evaluate the design of the instrument panel, a numerical model based on the explicit dynamic finite element analysis (FEA) by using the commercial FEA solver, LS-DYNA, is developed. To minimize the experimental cost, a gravity-based impactor with a smaller impact speed is develop as the test apparatus for verification purpose. The simulated results agree well with the experimental data; the average accuracy for the maximum value of impact acceleration at the head form is 95.4%. After the verification, the standard test conditions (with higher impact speed) are performed to evaluate the design. The outcome of this study can provide an efficient and cost-effective method to predict and improve the design of the instrument panel for interior head impact protection.

Design and Analysis of Automotive Bumper Covers in Transient Loading Conditions

This paper presents the analysis methods for design of automotive bumper covers. The bumper covers are plastic structures attached to the front and rear ends of an automobile and are expected to absorb energy in a minor collision. One requirement in design of the bumper covers is to minimize the bumper deflection within a limited range under specific loadings at specific locations based on the design guideline. To investigate the stiffness performance under various loading conditions, a numerical model based on the explicit dynamic finite element analysis (FEA) using the commercial FEA solver, LS-DYNA, is developed to analyze the design. The experimental tests are also carried out to verify the numerical model. The thickness of the bumper cover is a design variable which usually varies from 3 to 4 mm depending on locations. To improve the stiffness of the bumper, an optimal design for the bumper under a pre-defined loading condition is identified by using the topology optimization approach, which is an optimal design method to obtain the optimal layout of an initial design domain under specific boundary conditions. The outcome of this study provides an efficient and cost-effective method to predict and improve the design of automotive bumper covers.

Reliability-based design optimization of composite stiffened panels in post-buckling regime

This paper focuses on Deterministic and Reliability Based Design Optimization (DO and RBDO) of composite stiffened panels considering post-buckling regime and progressive failure analysis. The ultimate load that a post-buckled panel can hold is to be maximised by changing the stacking sequence of both skin and stringers composite layups. The RBDO problem looks for a design that collapses beyond the shortening of failure obtained in the DO phase with a target reliability while considering uncertainty in the elastic properties of the composite material. The RBDO algorithm proposed is decoupled and hence separates the Reliability Analysis (RA) from the deterministic optimization. The main code to drive both the DO and RBDO approaches is written in MATLAB and employs Genetic Algorithms (GA) to solve the DO loops because discrete design variables and highly nonlinear response functions are expected. The code is linked with Abaqus to perform parallel explicit nonlinear finite element analyses in order to obtain the structural responses at each generation. The RA is solved through an inverse Most Probable failure Point (MPP) search algorithm that benefits from a Polynomial Chaos Expansion with Latin Hypercube Sampling (PCE-LHS) metamodel when the structural responses are required. The results led to small reductions in the maximum load that the panels can bear but otherwise assure that they will collapse beyond the shortening of failure imposed with a high reliability.

Blast response of composite pipeline structure using finite element techniques

This paper investigates the blast response of a glass fiber reinforced polymer pipeline using explicit finite element analysis. In this study, a fluid-structure interaction methodology was employed to obtain the deformation and damage of pipeline under explosive impact using LS-DYNA. The purpose of this research is to evaluate the influence of the stand-off distance, the tube diameter, the internal pressure of tube and the explosive quantity on dynamic response of composite pipe. Simulations were carried out not only in the case of empty pipe but also in the case of water-filled pipe with different internal pressures. The analysis was performed in two phases; initialization phase, where the pressurization and gravity loads are applied on the pipeline, and the blast phase. Comparing the analysis results, it was proved that the internal pressure influences significantly the deformation of the tube. The results of the present study can serve as a reference guide for the prediction of pipe response under blast loading, since no guidelines exist in pipeline standards for design under blast loading conditions.