Explicit Finite Element Analysis Research Articles

Response of reinforced concrete beams to high‐velocity fluid impact. Part II: Numerical modeling and simulation

Fluid impact tests on reinforced concrete beams with rectangular or circular transverse reinforcement were modeled and simulated using explicit finite element analysis software, LS‐DYNA. The mid‐span displacements were measured and compared with the results of simulations. The objective was to test the accuracy and fidelity of the numerical modeling and simulation approach and to confirm that damage caused by fluid impact on the beams can be estimated with a reasonable accuracy over a wide range of impact velocity.

Quantitative Assessments of Mechanical Responses upon Radial Extracorporeal Shock Wave Therapy.

Although radial extracorporeal shock wave therapy (rESWT) has been widely used to treat orthopedic disorders with promising clinical results, rESWT largely relies on clinicians' personal experiences and arbitrary judgments, without knowing relationships between administration doses and effective doses at target sites. In fact, practitioners lack a general and reliable way to assess propagation and distribution of pressure waves inside biological tissues quantitatively. This study develops a methodology to combine experimental measurements and computational simulations to obtain pressure fields from rESWT through calibrating and validating computational models with experimental measurements. Wave pressures at the bottom of a petri dish and inside biological tissues are measured, respectively, by attaching and implanting flexible membrane sensors. Detailed wave dynamics are simulated through explicit finite element analyses. The data decipher that waves from rESWT radiate directionally and can be modeled as acoustic waves generated from a vibrating circular piston. Models are thus established to correlate pressure amplitudes at the bottom of petri dishes and in the axial direction of biological tissues. Additionally, a pilot simulation upon rESWT for human lumbar reveals a detailed and realistic pressure field mapping. This study will open a new avenue of personalized treatment planning and mechanism research for rESWT.

Parallelized implementation of an explicit finite element method in many integrated core (MIC) architecture

Hardware accelerators are becoming increasingly important in boosting high performance computing systems. In this study, we develop a parallel explicit finite element (FE) analysis system based on a many integrated core (MIC) architecture for fast simulation of nonlinear dynamic problems of plate and shell structures. To minimize data transfer between heterogeneous architectures, parallel computation of the all explicit FE calculation is realized by developing a vectorized thread-level parallelism algorithm. The parallelism includes a novel dependency relationship link based method for efficiently solving parallel explicit shell element equations. A heterogeneous model is established to overlap data transfer and offloaded computation, and thus reduce the time required for large intermediate data storage in the actual engineering nonlinear problem simulation. Finally, a high performance nonlinear dynamic simulation system is developed. The simulations of benchmarks and engineering problems show that the parallel computing method proposed in this paper can give full play to the hardware performance of MIC architecture and effectively improve the computation efficiency of an explicit FE solution. For a bus body model containing approximately 3.8 million degrees of freedom, the computational speed is improved 17 times over CPU sequential computation, and the relative speedup grows with the increasing number of threads, the highest relative speedup exceeds 80.

A new damage-mechanics-based model for rolling contact fatigue analysis of cylindrical roller bearing

Abstract The cyclic contact stresses in cylindrical roller bearings are evaluated through the explicit finite element analysis with rolling the roller instead of moving a constant contact pressure in the computational domain. A new damage evolution equation in terms of the amplitude of octahedral shear stress is proposed, which considers the non-proportional variation of stress, and the material parameters in which are easily obtained from torsion fatigue testing data. Numerical simulations of crack initiation, crack propagation, and spalling are performed. The simulation results are consistent with the previous experimental results. Furthermore, the coupling effect between the contact stresses and fatigue damage is investigated, and the effects of contact loading on the fatigue life are studied.

On stability and reflection‐transmission analysis of the bipenalty method in contact‐impact problems: A one‐dimensional, homogeneous case study

SummaryThe stability and reflection‐transmission properties of the bipenalty method are studied in application to explicit finite element analysis of one‐dimensional contact‐impact problems. It is known that the standard penalty method, where an additional stiffness term corresponding to contact boundary conditions is applied, attacks the stability limit of finite element model. Generally, the critical time step size rapidly decreases with increasing penalty stiffness. Recent comprehensive studies have shown that the so‐called bipenalty technique, using mass penalty together with standard stiffness penalty, preserves the critical time step size associated to contact‐free bodies. In this paper, the influence of the penalty ratio (ratio of stiffness and mass penalty parameters) on stability and reflection‐transmission properties in one‐dimensional contact‐impact problems using the same material and mesh size for both domains is studied. The paper closes with numerical examples, which demonstrate the stability and reflection‐transmission behavior of the bipenalty method in one‐dimensional contact‐impact and wave propagation problems of homogeneous materials.

A finite element study on the mechanical response of the head-neck interface of hip implants under realistic forces and moments of daily activities: Part 1, level walking.

This paper investigates the mechanical response of a modular head-neck interface of hip joint implants under realistic loads of level walking. The realistic loads of the walking activity consist of three dimensional gait forces and the associated frictional moments. These forces and moments were extracted for a 32mm metal-on-metal bearing couple. A previously reported geometry of a modular CoCr/CoCr head-neck interface with a proximal contact was used for this investigation. An explicit finite element analysis was performed to investigate the interface mechanical responses. To study the level of contribution and also the effect of superposition of the load components, three different scenarios of loading were studied: gait forces only, frictional moments only, and combined gait forces and frictional moments. Stress field, micro-motions, shear stresses and fretting work at the contacting nodes of the interface were analysed. Gait forces only were found to significantly influence the mechanical environment of the head-neck interface by temporarily extending the contacting area (8.43% of initially non-contacting surface nodes temporarily came into contact), and therefore changing the stress field and resultant micro-motions during the gait cycle. The frictional moments only did not cause considerable changes in the mechanical response of the interface (only 0.27% of the non-contacting surface nodes temporarily came into contact). However, when superposed with the gait forces, the mechanical response of the interface, particularly micro-motions and fretting work, changed compared to the forces only case. The normal contact stresses and micro-motions obtained from this realistic load-controlled study were typically in the range of 0-275MPa and 0-38µm, respectively. These ranges were found comparable to previous experimental displacement-controlled pin/cylinder-on-disk fretting corrosion studies.

Topology Synthesis and Optimal Design of an Adaptive Compliant Gripper to Maximize Output Displacement

This paper presents the optimal design process of an innovative adaptive compliant gripper (ACG) for fast handling of objects with size and shape variations. An efficient soft-add topology optimization algorithm is developed to synthesize the optimal topology of the ACG. Unlike traditional hard-kill and soft-kill methods, the elements are equivalent to be numerically added into the analysis domain through the proposed soft-add scheme. A size optimization method incorporating Augmented Lagrange Multiplier (ALM) method, Simplex method, and nonlinear finite element analysis with the objective to maximize geometric advantage (which is defined as the ratio of output displacement to input displacement) of the analyzed compliant mechanism is carried out to optimize the design. The dynamic performance and contact behavior of the ACG is analyzed by using explicit dynamic finite element analysis. Three designs are prototyped using silicon rubber material. Experimental tests are performed, and the results agree well with the simulation models. The outcomes of this study provide numerical methods for design and analysis of compliant mechanisms with better computational efficiency, as well as to develop an innovative adaptive compliant gripper for fast grasping of unknown objects.

Simulation Research on Micro Contact Based on Force in Silicon Wafer Rotation Grinding

Silicon wafer rotation grinding with cup type diamond wheel is a typical ultra precision grinding process. In this paper, a simulation model based on force for micro contact between wheel micro unit and silicon wafer is established from the stable ductile grinding process. Micro contact process in grinding is simulated using the nonlinear explicit finite element analysis software LS-DYNA. The stress-strain results on silicon wafer and wheel micro unit are analyzed by finite element method. The results show that the critical displacement and load corresponding elastic to plastic - plastic to brittle exist on silicon wafer. In silicon plastic zone tangential sliding can produce plastic groove and uplift. Wear of wheel micro unit can be based on the simulation data to judge. The research provides support for wafer grinding and wheel wear mechanism.

Large deformation of an arc-Miura structure under quasi-static load

Miura-Ori based foldcores have been regarded asa potential substitute for conventional honeycomb cores due to many advantages, such as open structure and continuous manufacturing process. Arc-Miura foldcore is one of the Miura-derivative cores which does not have curvature limitations. In this research, the arc-Miura specimens were successfully manufactured using a stamping process and tested under a quasi-static out-of-plane compressive load. An explicit finite element analysis (FEA) of arc-Miura models was developed and validated with the experimental results. Furthermore, a parametric study of arc-Miura models subjected to quasi-static out-of-plane compression was performed, through which the relationships between the mechanical properties and the geometric parameters were established. Finally, the mechanical properties of arc-Miura models and corresponding monolithic arches were compared. It was shown that arc-Miura patterns perform better than the corresponding monolithic arches in terms of force and energy absorption.

Experimental Study on the Deformation and Failure of the Bellows Structure Beyond the Designed Internal Pressure

Bellows structure is used to absorb the thermal expansion maintaining the boundary of the inside to outside, and it is applied to constitute the containment vessel (CV) boundary of the nuclear power plant. In this study, in order to develop the evaluation method of the ultimate strength of the bellows structure subject to internal pressure beyond the specified limit, the failure test and finite element analysis (FEA) of the bellows structure were performed. Several types of the bellows structure made of SUS304 were tested using pressurized water. The failure modes were demonstrated through the test of five and six specimens with six and five convolutions, respectively. Water leakage was caused by contact of the expanded convolution and the neighbor structure in the specimens with the shipping rod mounts. On the other hand, local failure as leakage in the deformation concentrated location and ductile failure as burst in the expanded convolution were observed in the specimen without shipping rod mounts. The maximum pressures in the test observed local and ductile failure were over ten times larger than the estimated values of the limited design pressure for in-plane instability by the EJMA standard. To simulate the buckling and deformation behavior during the test, the implicit and explicit FEA were performed. Because the inversion of the convolution accompanied by convolution contact observed in the test was too difficult a problem for implicit analysis, the maximum pressures in the step of solution converged were compared to the maximum pressures in the tests. On the other hand, explicit analysis enabled to simulate the complex deformation during the test, and the results were evaluated considering ductile failure to compare the test results.

Agricultural aircraft wing slat tolerance for bird strike

PurposeThe aim of this study is to assess and describe possible consequences of a bird strike on a Polish-designed PZL-106 Kruk agricultural aircraft. Due to its susceptibility to such events, a wing slat has been chosen for analysis.Design/methodology/approachSmooth particle hydrodynamics (SPH) formulation has been used for generation of the bird finite element model. The simulations were performed by the LS-Dyna explicit finite element analysis software. Several test cases have been analysed with differing parameters such as impact velocity, initial velocity vector direction, place of impact and bird mass.FindingsResults of this study reveal that the structure remains safe after an impact at the velocity of 25 m/s. The influence of bird mass on slat damage is clearly observable when the impact velocity rises to 60 m/s. Another important finding was that in each case where the part did not withstand the applied load, it was the lug where first failure occurred. Some of the analysed cases indicated the possibility a consequent wing box damage.Practical implicationsThis finding provides the manufacturer an important insight into the behaviour of the slat and suggests that more detailed analysis of the current lug design might improve the safety of the structure.Originality/valueEven though similar analyses have been performed, they tended to focus on large transport aircraft components. This investigation will enhance our understanding of structural response of small, low-speed aircraft to a bird impact, which is a realistic scenario for the chosen case of an agricultural plane.

Combined necking & fracture model to predict ductile failure with shell finite elements

The implementation of recent progress on stress state dependent ductile fracture models is inhibited by the break-down of shell element solutions whenever through-thickness necking occurs. The concept of the Domain of Shell-to-Solid Equivalence (DSSE) is therefore introduced to capture the onset of localized necking with shell element meshes. As long as the elasto-plastic loading paths lie inside the DSSE, ductile fracture may be predicted with shell elements using exactly the same models as for solid elements. A simple criterion describing the boundary of the DSSE is proposed based on the results from Marciniak-Kuczynski type of localization analysis. It is combined with the stress triaxiality and Lode angle dependent Hosford-Coulomb (HC) fracture initiation model and implemented as a user material subroutine for explicit finite element analysis. The combined DSSE-HC model is validated for a DP780 steel for notched tension, hemispherical punch loading, stretch bending, and V-bending of strips.

Improved axle detection for bridge weigh-in-motion systems using fiber optic sensors

Bridge weigh-in-motion (B-WIM) systems provide a non-destructive means of gathering traffic loading information by using an existing bridge as a weighing scale to determine the weights of vehicles passing over. In this research critical locations for sensors for the next-generation B-WIM were determined from a full 3D explicit finite element analysis (FEA) model. Although fiber optic sensors (FOS) have become increasingly popular in SHM systems there are currently no commercially available fiber optic WIM systems available. The FEA in this research facilitated the development of the first ever full fiber optic B-WIM and its potential has been demonstrated with the site installation of this system. The system combined nothing-on-the-road axle detection and alternative methods of measuring strain at the supports. The system was installed on a 20-m span beam and slab RC bridge in Northern Ireland and the results presented in this paper confirm the suitability of FOS in providing the clear defined peaks required for accurate axle detection in B-WIM.

The generation of the forming path with the springback compensation in the CNC incremental forming

Aiming at the problem of the springback in the CNC incremental forming, a method for predicting the springback and generating the compensated forming trajectory was proposed based on the explicit and implicit finite element analysis. First, the middle surface of the simulated sheet metal part was reconstructed after the springback simulation with the coordinates of all nodes obtained from the numerical simulations, and the reconstructed middle surface was compared with the middle surface of the theory model to calculate the normal deviation values. Second, the theory model was offset with the unequal distances of the deviation values to generate the compensated facet and the forming path. Once more, the finite element analysis was done until the compensatory effect met the required precision. Meanwhile, aiming at the roughness of the compensated facet caused by the multi-compensation process, the smoothing method was given to guarantee the smooth of the forming path. According to the predicted result of the numerical simulations, three times compensation meets the required precision and the normal deviation value is decreased from 0.696 mm to 0.194 mm. The forming experiments indicate that the springback of the target part in Z direction is decreased from 1.107 mm to 0.427 mm. Therefore, the predicting and compensating method of the springback proposed in the paper is available, which can improve the forming precision of the sheet metal part.

Research on centrifugal compressor disk containment of auxiliary power unit

To investigate the centrifugal compressor disk containment of auxiliary power unit (APU) in gas turbine, research on specific compressor is conducted in combination of simulations and tests. Nonlinear explicit finite element analysis of tri-hub fragments impacting containment assembly is carried out using LS-DYNA. Impacting characteristics in each period are discussed. Strength of the outer cover, the back shroud and the connecting bolts between them is further studied through simulation. The results show that the fragments interact with the outer cover and the back shroud both in rotating plane and axial direction. The internal energy is mostly composed of the strain energy of the impeller. Insufficient strength of each component leads to an uncontained result. Potential failure modes are discussed. Verification tests on high-speed spin tester revealing both contained and uncontained cases have been conducted and showed that the outer cover, the back shroud and the connecting bolts between them all play a significant role to containment. Adequate strength of these components is essential. Otherwise the outer cover will detach away and the back shroud will be damaged.

Explicit finite element analysis and experimental verification of a sliding lead rubber bearing

Based on the explicit finite element (FE) software ANSYS/LS-DYNA, the FE model for a sliding lead rubber bearing (SLRB) is developed. The design parameters of the laminated steel, including thickness, density, and Young’s modulus, are modified to greatly enlarge the time step size of the model. Three types of contact relations in ANSYS/LS-DYNA are employed to analyze all the contact relations existing in the bearing. Then numerical simulations of the compression tests and a series of correlation tests on compression-shear properties for the bearing are conducted, and the numerical results are further verified by experimental and theoretical ones. Results show that the developed FE model is capable of reproducing the vertical stiffness and the particular hysteresis behavior of the bearing. The shear stresses of the intermediate rubber layer obtained from the numerical simulation agree well with the theoretical results. Moreover, it is observed from the numerical simulation that the lead cylinder undergoes plastic deformation even if no additional lateral load is applied, and an extremely large plastic deformation when a shear displacement of 115 mm is applied. Furthermore, compared with the implicit analysis, the computational cost of the explicit analysis is much more acceptable. Therefore, it can be concluded that the proposed modeling method for the SLRB is accurate and practical.

블로우 모터 케이스 이음부 기계적 결합 강도 예측에 관한 연구

In order to reduce the weight of the blow motor case and to maintain the strength of the motor joint, the mechanical joining strength is to be predicted. The true stress - true strain curves for finite element analysis were obtained through tensile tests of HGI and DP 780 steel. The mechanical joining strength was predicted through an explicit finite element analysis and the accuracy of the predicted results was verified by actual sample test. The regression equation for predicting the mechanical joining strength to the thickness of the DP 780 steel was derived. The minimum thickness of DP 780(1.2mm), which is equivalent to the joining strength of HGI(2.6mm), was derived from the equation.

Using Virtual Tests to Complete the Description of a Three-Dimensional Orthotropic Material

AbstractGeneralized constitutive models, which can be used in explicit finite-element analysis, are being developed to accurately model composite systems under impact conditions. These models requi...

Mechanical Stability of the Taper Connection of Large Metal Femoral Heads With Adapter Sleeves in Total Hip Arthroplasty Analyzed Using Explicit Finite Element Simulations

BackgroundLarge diameter heads (LDHs) of metal-on-metal bearings in total hip arthroplasty provide increased range of motion and reduced dislocation rates. However, major concerns grew over high wear rates from the modular connection between femoral stem and head, especially in combination with adapter sleeves. MethodsA computational study on the taper connection stability of LDH (50 mm) with adapter sleeves of different lengths (S, M, L, and XL) compared with a standard femoral head (32 mm) without adapter sleeves was conducted using explicit finite element analyses. Four different impact configurations were considered resulting from varied mallet mass (0.5 vs 1.0 kg) and velocity (1.0 vs 2.0 m/s). The taper stability was evaluated by determination of the pull-off forces and micromotions due to simulated joint loads during walking (2 kN and 7.9 Nm, respectively). Moreover, the deformations of the adapter sleeves and the contact area in the taper connections were evaluated. ResultsAlthough the pull-off forces of the LDH with different-sized adapter sleeves were comparable, contact area decreased and adapter sleeve deformations increased (up to 283%) with an increasing adapter sleeve length. Moreover, the micromotions of LDH with adapter sleeves were up to 7-times higher, as compared with the standard femoral head without an adapter sleeve. ConclusionThe present numerical study confirms that the assembly technique of LDH with adapter sleeves reveals increased micromotions compared with standard femoral head sizes. We could demonstrate that deviations of the stem trunnion geometry and improper surgical instructions led to worse mechanical stability of the taper connection.

Evaluation of Foot Protection Effectiveness Against AP Mine Blasts: Effect of Deflector Geometry

Abstract In this study, the effectiveness of blast deflectors used in protective footwear against antipersonnel (AP) mines was investigated. The tip angle of a V-shaped deflector and the overall shape (symmetrical, unsymmetrical) were chosen as the design parameters to be examined, whereas parameters such as deflector material and wall thickness were kept constant. Both explicit dynamic finite element analysis (LS-Dyna) and blast tests were performed to evaluate the effectiveness of these design parameters. The analysis results were also verified with the blast tests. A visual (qualitative) comparison between the analysis results and the blast tests showed a good agreement on the final deformed geometry of the deflector, which suggested that the simulation was able to capture the energy absorption mechanism of the deflector. The analysis results showed that the peak force transmitted to the leg decreased tremendously with the addition of blast deflectors. When compared to the case with no deflectors, an unsymmetrical and symmetrical deflector reduced the peak force by a factor of 24 and 36, respectively.