Explicit Finite Element Analysis Research Articles

Effects of Increasing Mass Scaling in 3D Explicit Finite Element Analysis on the Wire Drawing Process

3D explicit technique based on finite element analysis is usually applied for solving the nonlinear problems in metal forming process such as wire drawing. The mass scaling percentage that related with stable time increment has substantial influence for attaining the optimum simulation results. In this article, the drawing process of A304 stainless wire utilizing analytical and numerical approach without mass scaling was developed to estimate and validate the obtained drawing stresses using different reduction of area. Then, 3D explicit models based on finite element analysis was run using various mass scaling at the low and high reduction of area 12 and 27% for displaying the analysis time, equivalent plastic strain (PEEQ), and drawing stress. The results exposed that the appropriate increase of mass percentage corresponding to the target time increment can be selected for reducing the time of wire drawing analysis to 53 and 50% at reduction of area 12 and 27% respectively. Although the PEEQ and drawing stress had little increase when the mass percentage raises however, it should be taken into consideration through the design of the wire drawing process. Therefore; the mass scaling value must be carefully adopted.

Modeling plastic anisotropy evolution of AISI 304 steel sheets by a polynomial yield function

In this study, a numerical model for the evolution of plastic anisotropy is investigated for the purpose of stamping method design by Finite Element (FE) analysis and proved experimentally via process simulations of a cold-rolled austenitic stainless steel (AISI 304) sheet. The plastic anisotropy of the sheets is described with a fourth-order homogenous polynomial yield function and this modelling approach is enhanced by plastic strain dependent material coefficients. Tensile tests of coupon specimens taken along the different directions from rolling direction, and flow strength and deformation anisotropies are described with the planar variations of yield stress and plastic strain ratio computed at four plastic strain levels (0.002, 0.02, 0.05 and 0.18). A new numerical approach is, then, applied to identify polynomial coefficients ensuring an orthotropic positive-definite, convex yield surface with a well-defined stress gradient at every loading point on plane stress subspace. The developed computational model is implemented into general purpose explicit FE analysis software Ls-Dyna by a user-defined material model subroutine (UMAT) and applied in the stamping simulation of AISI 304 steel rectangular cups for the house-hold applications. The computed thickness distributions and the flange geometries were compared with measurements and it was observed that the best predictions were done with material parameters at %5 plastic strain level.

Experiment and Simulation of Impact Response of Woven CFRP Laminates with Different Stacking Angles

The effects of different laying angles on impact resistance and damage types of woven carbon fibre-reinforced polymer (CFRP) laminates were studied. The drop hammer impact test and simulation analysis of woven CFRP laminates at four different velocities were carried out by means of the combination of experiment and explicit finite element analysis. The effect of impact velocity on damage pattern and fracture of woven CFRP laminates with eight layers and four laying angles (0°, 15°, 30°, and 45°) was studied by drop weight impact test, and the damage area of woven CFRP laminates with different laying angles was measured by ultrasonic nondestructive testing method. A user-defined material model was developed based on LS-DYNA to simulate the impact behavior of woven CFRP laminates. A finite element simulation model was established to effectively predict the complex damage evolution of woven CFRP laminates under low-speed impact loading. Its effectiveness was verified by impact response and damage crack pattern. The energy absorption and impact force of the laminated plate increase gradually from 0° to 45° in the laying angle of woven fabric. With the increase of laying angle from 0° to 45°, the length of fracture crack and the damage area increase. The developed model can accurately predict the impact properties of the composites.

Energy Absorption of Additively Manufactured Porous Metals with Disordered Cells

Lightweight porous metals are focused on as energy absorbing materials for automobiles. Open-cell porous metals were manufactured through additive manufacturing process. Their cell structures were designed based on Voronoi diagrams using a commercial 3D-CAD software. Both ordered and disordered cell structures with the same porosities were successfully designed in this study. Compression tests and explicit finite element analysis revealed heterogeneous deformation behaviors in ordered porous metals. On the other hand, the porous metals with disordered cell structure showed relatively isotropic and uniform deformation, which is suitable as energy absorbing materials. Controlling the disordered cell structure designed by 3D-Voronoi diagram enables to develop the advanced porous metals having various mechanical properties.

Mechanical Design of Long-Term Body-Adhered Medical Devices to Maximize On-Body Survival

Long-term, body-adhered medical devices rely on an adhesive interface to maintain contact with the patient. The greatest threat to on-body adhesion is mechanical stress imparted on the medical device. Several factors contribute to the ability of the device to withstand such stresses, such as the mechanical design, shape, and size of the device. This analysis investigates the impact that design changes to the device have on the stress and strain experienced by the system when acted on by a stressor. The analysis also identifies the design changes that are most effective at reducing the stress and strain. An explicit dynamic finite element analysis method was used to simulate several design iterations and a regression analysis was performed to quantify the relationship between design and resultant stress and strain. The shape, height, size, and taper of the medical device were modified, and the results indicate that, to reduce stress and strain in the system, the device should resemble a square in shape, be short in height, and small in size with a large taper. The square shape experienced 17.5% less stress compared to the next best performing shape. A 10% reduction in device height resulted in a 21% reduction in stress and 24% reduction in strain. A 20% reduction in device size caused a 7% reduction in stress and 2% reduction in strain. A 20% increase in device taper size led to a negligible reduction in stress and a 6% reduction in strain. The height of the device had the greatest impact on the resultant stress and strain.

Explicit finite element analysis of slope stability by strength reduction

The construction of stable slopes and vertical cuts is an important step in many geotechnical projects. Limit equilibrium methods (LEMs) are well-accepted procedures to compute factors of safety (FoS); however, they fail to provide any information about the distribution of the field variables within the soil mass because they do not include any stress-strain relationship in their formulation. On the other hand, the iterative finite element method (FEM/I) can estimate the field variables, but in the current study, we show that, for steep slopes and vertical cuts, it underestimates the FoS compared to the LEM. To overcome the obstacles that exist in this method, this study proposes a new approach to define the initiation of instability based on an abrupt change in the kinetic energy of the system. We also suggest a procedure to calculate the minimum FoS based on the explicit finite element method (FEM/E). Comparison of the results obtained from the proposed method, LEM, and FEM/I revealed that the FoS computed by the proposed method is in good agreement with the results of the LEM for a wide range of material parameters, geometries and external loading conditions, while no assumption regarding the critical slip surface needs to be made.

Improving failure sub-models in an orthotropic plasticity-based material model

Theoretical details of two failure criteria implemented in an orthotropic plasticity model are presented. Improvements to the well-known Puck Failure criterion and a recently developed Generalized Tabulated Failure criterion are used to illustrate how to link a failure sub-model to existing deformation and damage sub-models in the context of explicit finite element analysis. These models are implemented in LS-DYNA, a commercial transient dynamic finite element code. Two validation tests are used to evaluate the failure sub-model implementation and improvements - a stacked-ply test carried out at room temperature under quasi-static tensile and compressive loadings, and a high-speed, projectile impact test where there is significant damage and material failure of the impacted panel. Results indicate that developed procedures and improvements provide the analyst with a reasonable and systematic approach to building predictive impact simulation models.

Design considerations for joining of tubular members subjected to impact loading

This study explores the effect of impact loading in structural bar and tube welded and threaded joints. Specifically, this work concentrates on stress wave propagation and mechanical impedance to show the effect of geometric parameters on stress distribution and history inside these joined members. In this experimental work, welded and threaded bar-and-tube networks are compared with equivalent length single bars to provide a measure of joint quality. Application to dynamic experimental equipment, known as Hopkinson Bars, is considered herein due to the stringent need for wave uniformity within these systems. Explicit finite element analysis on the experimental setup was performed to provide internal stress history information to provide more insight into the causes of stress risers and spurious load reflections. A key finding in this study shows that joint impact performance reduces when joint size is either too small or too large. This optimized joint size is found to depend on the joint'seffective mechanical impedance. This study serves as a new look at potential joining considerations under impact loading.

Direct measurement of shot velocity and numerical analysis of residual stress from pneumatic shot peening

Shot peening is widely used in several fields to improve the fatigue strength of manufactured parts via the introduction of compressive residual stresses. The shot velocity is significant physical factor; however, it is difficult to measure this velocity directly in pneumatic shot peening. In this study, an experiment was performed to record shot movement with a high-speed camera. Particle image velocimetry (PIV) was used to measure the shot velocity distribution: the shot accelerated after being projected from the nozzle and reached a steady shot velocity at approximately 80 mm from the nozzle. The steady shot velocity was proportional to approximately the 0.51st power of the air pressure: 30 m/s at 0.14 MPa and 49 m/s at 0.35 MPa for steel shot ASR170. For an A7075 aluminum alloy, the depth of the compressive residual stress increased with the shot velocity and was greater than 0.5 mm at 0.35 MPa air pressure. Finite element analysis (FEA) was performed on the residual stress distribution with the shot velocity measured by PIV as the input value. Peening with multiple shots was evaluated through dynamic explicit FEA. The residual stress distribution after shot peening was obtained through subsequent static implicit FEA. The analytical results for the residual stress distribution complied with the experimental results. Thus, the shot velocity measurement technology and the FEA model that were used to calculate the residual stress from shot peening were both validated.

Dynamic finite element simulation of wheel–rail contact response for the straight track case

The dynamic effects, mainly including the inertia effect and strain-rate effect, on the dynamic wheel–rail contact behavior become more and more serious as the train speed increases. The inertia effect can be automatically taken into account in explicit finite element analysis codes, while the strain-rate effect needs to be considered via inputting the related material parameters. In the present paper, the influence of strain rate on the dynamic wheel–rail contact response for the straight track case was explored, based on a 3D wheel–rail rolling contact finite element model, via LS-DYNA/explicit algorithm. Effects of the axle load and train speed on typical dynamic wheel–rail responses were discussed, and the results indicate that the coupled train speed with strain rate has a non-negligible influence on dynamic contact responses. The strain rate hardening effect increases the maximum contact pressure and stress, and inhibits the plastic deformation of the wheel–rail system. A rate-sensitive factor (RSF) was then introduced to describe the strain rate hardening effect, confirming that the rail is more sensitive to strain rate compared to the wheel. Finally, an error analysis of the wheel–rail Hertz contact theory was conducted, which further verify the differences between elastic and elastic-plastic contact solutions.

CRASHWORTHINESS OPTIMIZATION OF MULTI-CELL TRIANGULAR TUBES

This paper aims to design the multi-cell cross-sectional thin-walled columns with two crashworthiness criteria. An explicit finite element analysis (FEA) is used to derive higher-order response surfaces for these two objectives. In the process of multiobjective crashworthiness optimization, Deb and Gupta method was utilized to find out the knee points from the Pareto solutions space. The efficiency of the crashworthiness optimization design method based on surrogate models is identified.

Effect of the Reinforced Concrete Slab on the Blast Shock Wave Properties

Based on advanced numerical simulation technologies, such as the birth and death of element technique, large displacement technique, and fluid-solid coupling mechanism, and combined with the strain rate effect of concrete and steel materials, a complicated finite element model of a TNT–air–slab system is set up using the nonlinear explicit dynamic finite element analysis software LS-DYNA. A series of numerical simulation analyses is conducted on the reinforced concrete slab to evaluate the properties of the blast shock wave at the back of the slab. First, the typical characteristics of the blast shock waves at the front and back of the slab are described concisely. Then, the relation between the incident wave and the reflected wave is built by further studying the influence of the slab on the properties of the reflected wave at the front of the slab. And then, the relation between the reflected wave and the reformed wave is established by analyzing the effect of the slab on the change law of the reformed wave at the back of the slab. Finally, the basic steps for predicting the properties of the reformed wave are given considering the effect of the reinforced concrete slab on it. In addition, the case study demonstrates that the predicted results are true and reliable, and it indicates that the proposed method can accurately and effectively predict the properties of the reformed wave at the back of the reinforced concrete slab.

Stress Transfer Mechanism of Flange in Split Hopkinson Tension Bar

To reveal the stress transfer mechanism of the flange in a split Hopkinson tension bar, explicit finite element analyses of the impact of the hollow striker on the flange were performed across a range of flange lengths. The tensile stress profiles monitored at the strain gauge position of the incident bar are interpreted on a qualitative basis using three types of stress waves: bar (B) waves, flange (F) waves, and a series of reverberation (Rn) waves. When the flange length (Lf) is long (i.e., Lf > Ls, where Ls is the striker length), the B wave and first reverberation wave (R1) are fully separated in the time axis. When the flange length is intermediate (~Db < Lf < Ls, where Db is the bar diameter), the B and F waves are partially superposed; the F wave is delayed, then followed by a series of Rn waves after the superposition period. When the flange length is short (Lf < ~Db), the B and F waves are practically fully superposed and form a pseudo-one-step pulse, indicating the necessity of a short flange length to achieve a neat tensile pulse. The magnitudes and periods of the monitored pulses are consistent with the analysis results using the one-dimensional impact theory, including a recently formulated equation for impact-induced stress when the areas of the striker and bar are different, equations for the reflection/transmission ratios of a stress wave, and an equation for pulse duration time. This observation verifies the flange length-dependent stress transfer mechanism on a quantitative basis.

Comparative Study on Reliability and Advanced Numerical Analysis of BGA Subjected to Product-Level Drop Impact Test for Portable Electronics

In this paper, drop reliability of various PBA (printed board assembly) mounting structures is investigated and compared. Then, we built SAC305 (Sn3.0Ag0.5Cu) interconnects for BGA (ball grid array) package failure model to evaluate the drop impact reliability of handheld devices. In order to simulate actual behavior of the solder joint under the drop impact load of handheld devices, we perform explicit full FEA (finite element analysis) modeling. However, this takes a lot of computing time because of the large aspect ratio of element size between solder joints and other structures such as PCB (printed circuit board) and electronic packages. Therefore, an effective way to represent solder interconnects for FEA is needed which would be relatively simpler yet detailed. Comparable board-level drop tests are conducted after equipping test vehicles with various fixtures considering PBA mounting structures, which make it possible to apply different loading conditions to BGA packages. The results show different drop impact life for solder interconnects depending on the mounting design of the PBA. Particularly, the solder interconnect of the component located at the middle of the PCB exhibits the shortest impact life where the highest tensile stress occurs. Also, the mounting design restraining PBA deflections shows better reliability under the drop impact loading. Sequentially, simulating with a PBA composed of the BGA package and the PCB is considered to assess the feasibility of the solder ball failure modeling when the drop impact load is applied. Especially, for the modeling of the solder balls, detailed solid model and simple beam model are compared regarding computational efficiency and numerical accuracy. We found that the simple beam model significantly shortens computational time from 110 h to less than an hour. Accordingly, the feasibility of the beam model for the solder balls is shown by correlating the stress level and the drop impact life obtained from the experiments.

The Application of CEL Technique to Simulate the Behavior of an Underwater Explosion Bubble in the Vicinity of a Rigid Wall

The dynamic process of an underwater explosion (UNDEX) is a complex phenomenon that involves several facets. After detonation, the shockwave radially propagates at a high speed and strikes nearby structures. Subsequently, bubble oscillation may substantially damage the structures because of the whipping effect, water jet impact, and bubble pulse. This paper presents an application of explicit finite element analyses to simulate the process of an UNDEX bubble in the vicinity of rigid wall, in which the coupled Eulerian-Lagrangian (CEL) approach was developed to overcome the difficulties regarding the classical finite element method (FEM), large deformations, and flow simulation of fluid and gas. The results demonstrate that the method is well suited to manage the UNDEX bubble problem and can be used to model the major features of the bubble dynamics. Furthermore, the behavior of an UNDEX bubble near a rigid wall was also examined in the present study, which showed that the migration of the bubble and the development of the water jet are influenced strongly by the standoff distance between the initial bubble position and the wall. This method can be used in future studies to examine UNDEX bubbles in the vicinity of deformable and complex structures.

An adaptive shell element for explicit dynamic analysis of failure in laminated composites Part 1: Adaptive kinematics and numerical implementation

To introduce more fibre-reinforced polymers in cars, the automotive industry is strongly dependent on efficient modelling tools to predict the correct energy absorption in crash simulations. In this context, an adaptive modelling technique shows great potential. However, as the critical energy absorption in a crash occurs over a very short period of time, and since the deformation behaviour is very complex, car crash simulations are usually performed using explicit dynamic finite element solvers. Therefore, any practical adaptive technique must be adapted to an explicit setting in a software available to the automotive companies. In this paper, we propose an adaptive method for explicit finite element analysis and describe its implementation in the commercial finite element solver LS-DYNA. The method allows for both so-called weak discontinuities (discontinuities in strain), which are crucial for accurate stress and intralaminar damage predictions, and strong discontinuities (discontinuities in displacements), needed for a proper representation of growing delamination cracks. In particular, we detail the implementation of the proposed method into LS-DYNA and also how we propose to remedy the non-physical oscillations arising from the implementation of the adaptive scheme in a explicit dynamic setting. The paper is concluded with numerical examples where we demonstrate the potential for the adaptive approach and also perform a detailed study on its accuracy and stability.

Research on Response Characteristics of Hydraulic Gate Subjected to Non-contact Underwater Explosion Load

In this paper, the response characteristics of deep-hole planar steel gates under the separate induction of bubble pulsating load are studied. Through the large-scale finite element simulation software ABAQUS, using the explicit dynamic finite element analysis method, the contact surface of the gate and the water is taken into account by the fluid-solid coupling algorithm. When the water level is constant, the gate is subjected to explosion and the impact of the generated bubble impact on the gate structure and its anti-explosion ability are analyzed. The equivalent stress, displacement, and equivalent plastic strain of the gate under six different cases were simulated. Then, the effect of bubble pulsating load on the stress characteristics of the gate and the anti-explosion ability of the gate were summarized.

An effective finite element modeling approach for prediction of the behaviour of a jute fibre-reinforced composite tube under axial impact

The focus of the work reported here is on the prediction of the behaviour of a hollow cylindrical jute– polyester composite tube under axial impact using the explicit finite element analysis code, LS-DYNA. An efficient finite element modelling approach using a single shell element through the thickness of a thin-walled structural part has been chosen. Effective orthotropic material properties of a laminate which can be determined through standard ASTM tests have been used as input data for a popular constitutive model titled ‘Enhanced Composite Damage’ with the option of specifying either the Chang–Chang criteria or the Tsai–Wu criterion for failure. A unique feature of the current approach is to verify the modeling procedure initially for coupon-level tensile, compressive and flexural tests through a numerical design of experiments involving a set of physically meaningful fibre and matrix failure strain parameters, and then extend the same toward successfully predicting the mechanical behaviour of a jute composite tube subject to axial drop-weight impact. Theoretical predictions of peak responses for flexural and tube impact tests are also presented.

Numerical study of top-and seat-angle with double web-angle connection with high-strength steel

Past experimental research on top-and seat-angle with double web-angle connection (TSACW) was limited by the rate and magnitude of actuator displacement and hence results did not give information on failure mode and ultimate capacities of connection. Furthermore, extensive literature review on TSACW revealed the need for developing an accurate finite element approach to represent the characteristics of the moment-rotation behavior. Therefore, this study examined the influence of connection parameters on flexural resistance, stiffness, rotation, ductility and failure modes obtained for such joints. Explicit Finite element (FE) analyses of connection models were carried out by using ABAQUS/CAE to explore the effect of material properties of bolts and angles on moment-rotation (M-ϕ) characteristics of TSACW under monotonic loading. Applicability of six currently available M-ϕ functions was assessed by comparing them with those obtained from FE analyses. In most cases, the ultimate flexural resistance of TSACW was increased whilst its rotational capacity was decreased with the use of A572 or A514 angles with less pronounced effect on the initial stiffness. The connection failure was controlled via large deformations achieved by the top angle. Among the six selected M-ϕ functions, Richard-Abbott model was found suitable for fitting the normalized moment-rotation curves for TSACW joints.

Determination of the Impact Damage Threshold Point of Composite Material Using Fuzzy-Base Taguchi Method

In this study, the impact damage threshold point of the composite material was determined using the optimum design parameters obtained from Fuzzy Based Taguchi Method (FBTM). It is known that both Taguchi and Fuzzy methods provide optimization of design parameters yet, in Taguchi method, optimization of design parameters is not sufficient in order to solve multi response optimization problem. Therefore, Fuzzy Logic system was combined with the Taguchi system for working out the multi response optimization problem. In this study, the low velocity impact damage analyses were implemented in a LS-DYNA 3D explicit finite element program. ASTM D7136/D7136M standard was considered during the low velocity impact analyses. In explicit finite element analyses, contact algorithms were executed to observe better damage zone shapes. Furthermore, the control parameters (termination and computation time step) were tuned to provide perfect correlation with the force-energy-time histories. Eventually, it was seen that Fuzzy Based Taguchi Method (FBTM) is much more capable of optimizing the design parameters that predict the impact damage threshold point of the composite material.