Dynamic Explicit FEM Research Articles

Impact analysis on an integrated carbon composite wing spar of fixed wing aircraft

The paper deals with the impact analysis on an integrated wing spar. The focus of this study is to analyze the structural integrity, energy conservation and the deformation that took place in an integrated wing spar, where the wing spar and the leading edge of the wing is made into a single part. With 3D printing technology, it can be made into a single component. Integrated wing spar is used instead of conventional spar as it eliminates the need of riveting the spar and the airfoil. The cost of production is less and the omission of fasteners and overlapping joints in the airframe make it advantageous with its ease in construction along with reduced structural weight. The integrated wing spar model as well as conventional wing spar model are designed using Catia software and the structural analyses are performed using LS-Dyna software. An explicit dynamic FEM analysis is carried so that the short loading response of structure can be simulated using Lagrangian formulation. The bird model (2 kg bird) is assigned to impact the wing structure at different velocities ranging from 100 m/s to 300 m/s for the integrated wing spar and conventional wing spar at different velocities. The numerical results revealed that the integral design promises to have a significantly longer fatigue life, energies conserved and with less deformation than the conventional design. There is 14.76% improvement in the energy absorption rate and 37% reduction in energy gain rate by integrated spar with comparison to conventional spar. Thus, the integrated wing spar is found to be suitable alternate to conventional wing spar design.

Seismic Behavior of Qinghai-Tibetan Railway Embankment in Permafrost Regions: A Case Study

The temperature is a critical factor that determines the unfrozen water content and ice content in the frozen soil. In view of mechanical properties of the frozen soil depend on the volume of components of the four-phase systems, thus the temperature has a significant impact on the mechanical behaviors and deformation properties. The thermal state of the embankment in permafrost regions has a significant seasonal difference, then the seismic performance of the embankment alters with the season. In addition, the seismic performance is highly influenced by the properties of the earthquake motion, especially the seismic intensity. Combining these factors, a numerical simulation was conducted in this study. In this study, taking a typical section of Qinghai-Tibet Railway as an example, a numerical case study on the seismic behavior of embankment was carried out using the dynamic explicit FEM code ABAQUS/Explicit. The El Centro excitation with different intensities was performed in numerical analysis and two distinct thermal states of the embankment in extreme cold and warm days were considered as well. The seismic behaviors of the embankment, including the acceleration responses, the strain response, and the displacement response, were studied effectively. This paper proposes approaches and methods to study the seismic failure mechanism of the infrastructures, and the results can serve as a scientific basis for resisting earthquakes and preventing disasters in cold regions.

Experimental-numerical study of wrinkling in rotary-draw bending of Tight Fit Pipes

The paper focuses on tight fit pipe (TFP) wrinkling in rotary-draw bending (RDB), where TFP is a double-walled pipe. To this end, a corrosion-resistant alloy liner is fitted inside an outer carbon steel pipe through a thermal-hydraulic manufacturing process. A 3D elastic–plastic finite element (FE) model (the dynamic explicit FEM code ABAQUS/Explicit) is developed in this study. This model simulates the manufacturing process in the first step of the analysis and proceeds in the rotary-draw bending analysis of the lined pipe. Then, in the third step, the springback of the two-layer pipe is analyzed. This integrated three-stage process considers geometric nonlinearities, geometric and thickness imperfections, inelastic material behavior, and contact between the two pipes. Contact pressure during the process in the presence of various imperfections is monitored by the histogram to predict wrinkling. Furthermore, the best bending angle, with minimum possibility of wrinkling in the inner pipe, is obtained by these histograms. ABAQUS scripting via the Python programming language is used to study the effect of various imperfections on RDB. Numerical results on imperfection sensitivity demonstrate the significant influence of imperfections’ amplitude on liner wrinkling. The ovality and thinning of the lined pipe via bending angle were investigated. By comparing the experimental results with those of the simulation, an appropriate agreement is observed.

Wrinkling Defect in Sheet Metal Process using Finite Element Analysis

Abstract: Deep drawing is popular sheet metal forming process. Deep drawing process is the most common metal forming process frequently used in automobile industry, the packaging industry and the house hold appliances industry to manufacture products with more complicated shapes and curvatures. Any metal that can be processed into sheet form by a rolling process should be sufficiently ductile to be capable of deep drawing. Both hot and cold rolled sheet products are used in deep drawing processes. The basic theories governing the deep drawing are based on application of theory of plasticity to the deep drawing process. It is very difficult to apply these theories and arrive at a general solution which can handle any arbitrary geometry. The idea of finite element analysis is to find the solution of complicated problem in relatively easy way. The finite element analysis has been a powerful tool for the numerical solution of a wide range of engineering problem. There are some possible failures likely occur during the process, like wrinkling, necking, scratching and surface defects. As thinner materials tend to be used in automotive industry, wrinkling has become the most important problem among the other defects. The study also aims to investigate wrinkling and its prevention. For this purpose, the commercial finite element analysis code Explicit Dynamic FEM model will be used

Combined numerical and experimental studies on the dynamic and quasi-static failure modes of brittle rock

Loading rate affects not only the mechanical properties of rock but also the cracking behaviour or the failure mode. Firstly, experimental studies on the mechanical properties and the related cracking behaviour are studied based on the Carrara marble specimens containing a preexisting flaw under different loading rates. The result shows that both the compressive and tensile strengths are rate-dependent but with different sensitivities to strain rate. Meanwhile, the cracking processes of the single-flawed specimens are also found to be rate-dependent with the aid of an ultra-high-speed video system. Secondly, to investigate the mechanism behind the experimental phenomena, a material model based on the experimental strength data is proposed and applied to the numerical model. The influence of the rate-dependent strength on the cracking behaviour is studied comprehensively by using the 2D and 3D explicit dynamic FEM code. The numerical results reveal how the rate-dependent strength affect fracturing behaviour, as well as the failure stress of the single-flawed specimen. The plastic zones do not equal the damaged zone or the cracks. The dynamic loadings lead to the “X” shaped failure mode of the single-flawed specimen regardless of the flaw inclination angle. In contrast, the quasi-static loadings lead to the diagonal failure mode. It indicates that shear displacement dominates the whole cracking process under dynamic loadings, while it only dominates the failure period under quasi-static loadings.

Numerical Analysis of the Impact Fracture of Metallic Glass Based on Free Volume Model

The yield behavior of amorphous metals including the metallic glass shows intrinsic dependence on the hydrostatic stress, so that yield criterion models such as Mohr-Coulomb and Drucker-Prager are often used. Both the models can explain the asymmetry in the yield stress under uniaxial compression and tension conditions, while the asymmetry in the angle of fracture surface is not able to be determined based on any of those models. The free volume model is able to provide that foundation. Shibutani et al. proposed a new constitutive model for amorphous metals that was derived from some free volume models and the flow rule using the Drucker-Prager yield function as a plastic potential, and investigated the yield behavior and the formation of localized shear band under some temperature conditions using the implicit static FEM code. The formation of shear bands is an unstable phenomenon that is greatly affected by the initial imperfection. In this model, on the other hand, the temperature or the strain rate also affects the yield behavior considerably. In this study, the impact fracture of metallic glass was investigated by implementing the constitutive model proposed by Shibutani et al. into the explicit dynamic FEM code DYNA3D, with laying emphasis on reproducing asymmetry in the angle of fracture surface and the examination of effects of strain rate and temperature change.

Numerical 3D modeling of the effects of strain rate and confining pressure on the compressive behavior of Kuru granite

This paper deals with numerical modeling of the compressive behavior of granite rock under high strain rate dynamic loading and wide range of confining pressure. For this end, a constitutive model based on damage mechanics and viscoplasticity for rock is formulated and implemented in explicit dynamics FEM. The viscoplastic part is based on a simple power law type yield criterion that incorporates the rate-dependency with a linear viscosity term. Moreover, a Rankine type of tensile cut-off is employed. The damage part of the model is formulated with separate scalar damage variables in tension and compression. The model is calibrated for Kuru granite and validated with the experimental data from dynamic compression tests at the strain rate of 600 1/s up to 225MPa of confining pressure. The numerical simulations demonstrate that, despite the underlying continuum modeling approach, the model captures the correct experimental failure modes, including the transition from single-to-multiple fragmentation, as well as the dynamic compressive strengths at different confining pressures.

A new bi-tubular conical–circular structure for improving crushing behavior under axial and oblique impacts

In this study single and double wall structures for crashworthiness are investigated to introduce a novel system with better energy absorption and crushing characteristics under both axial and oblique loading. The new developed double wall structure is constructed from inner conical and outer circular tubes, incorporated with and without foam filler. Foam filled bi-tubular structure subject to direct axial and oblique impact loadings are simulated using nonlinear finite element analysis software package LS-DYNA. Numerical simulations obtained via non-linear explicit dynamic FEM are firstly validated using theoretical and experimental solutions. Next, effectiveness of the new developed bi-tubular structure has been shown by comparing with similar common thin-walled structures. Different types of structures namely bi-tubular empty and foam filled new design, empty and filled frusta as well as empty and foam filled circular tubes were considered in order to make a more insightful of capabilities of the proposed structure. A parametric study including the effect of geometrical and material properties of the structure on the crashworthiness has been carried out. Results show the possibility of amending the peak crushing load along with keeping other energy absorption characteristics unchanged or even improved. Also an improvement in absorbed energy under oblique loading by using the new developed structure is observed.

Study on the Flange Spread of H-Beam

According to the production data of a rolling H-beam factory, the FE model of hot continuous rolling process of H-beam is built. The rolling process of H-beams is simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece is analyzed. The simulation results show that the flange width, elongation ratio between flange and web and flange thickness are the major influencing factors on the spread of rolling piece.

FEM Research on the Residual Stress of Corrugated Waist Rail in Hot Rolling

The rolling process of corrugated waist rail is simulated by explicit dynamic FEM module ANSYS/LS-DYNA. The distribution of residual stress of the rolled piece after rolling is analyzed, The influence of rolling velocity, the reduction ratio, and rolling temperature on the residual stress are analyzed. According to the result of simulation, it is helpful to the actual production.

ビル用マルチエアコン室外機の準静的変形解析への動的陽解法の適用

Generally speaking, it is difficult to obtain simulation results for a nonlinear quasi-static problem of a large-scale structure using the static implicit FEM. This is because not only the calculation cost such as necessary memory consumption becomes enormous but also iterative calculation does not often converge for a large-scale analysis model in consideration of the contact between the parts and material nonlinearity of the structure. Therefore, in this paper, we tried to perform a torsion deformation analysis of a multi-split type air-conditioning outdoor unit using the dynamic explicit FEM with the system damping method and mass scaling method. The torsion displacement based on the dynamic explicit method shows good agreement with the test result. It is found that the dynamic explicit method has an advantage in large-scale model analysis.

Thermo-Mechanical Coupled Analysis of Heavy Shell Ring Hot Rolling Mill with Two Drive Rolls

The heavy shell ring rolling mill which produces the large shell ring used in nuclear power, large-scale hydrogenation reactor and coal liquefaction reactor was taken as subject investigated. Because the size of shell ring is very large and the material of shell ring is special, the double drive rolls was taken in the shell ring rolling mill. Based on the elastic-plastic FEM and MARC software platform, the three dimensional thermal-mechanical coupled model of shell ring rolling process was built in this paper. First, the heat simulation text of the shell ring material has been carried out on the Gleeble-3500 thermal simulation test machine and the material properties were obtained. Then, considering the characteristics of heavy shell ring hot rolling mill with two drive rolls, the key problems such as geometry, material and thermo-boundary conditions were solved, the thermo-mechanical coupled finite element model of heavy shell ring hot rolling has been establised. At last, based on explicit dynamic FEM, the thermo-mechanical simulation of heavy shell ring rolling process was made. The stress field, strain field and temperature field were studied, the metal plastic deformation and its influence factors were investigated. The conclusions are agreement with the real rolling process. The conclusions are significant for designing equipments of shell ring rolling mill and developing new rolling schedule.

Thermo-Mechanical Coupled Analysis of Heavy Shell Ring Hot Rolling Mill with Two Drive Rolls

The heavy shell ring rolling mill which produces the large shell ring used in nuclear power, large-scale hydrogenation reactor and coal liquefaction reactor was taken as subject investigated. Because the size of shell ring is very large and the material of shell ring is special, the double drive rolls was taken in the shell ring rolling mill. Based on the elastic-plastic FEM and MARC software platform, the three dimensional thermal-mechanical coupled model of shell ring rolling process was built in this paper. First, the heat simulation text of the shell ring material has been carried out on the Gleeble-3500 thermal simulation test machine and the material properties were obtained. Then, considering the characteristics of heavy shell ring hot rolling mill with two drive rolls, the key problems such as geometry, material and thermo-boundary conditions were solved, the thermo-mechanical coupled finite element model of heavy shell ring hot rolling has been establised. At last, based on explicit dynamic FEM, the thermo-mechanical simulation of heavy shell ring rolling process was made. The stress field, strain field and temperature field were studied, the metal plastic deformation and its influence factors were investigated. The conclusions are agreement with the real rolling process. The conclusions are significant for designing equipments of shell ring rolling mill and developing new rolling schedule.

Analysis of Dynamic Displacement Response of Bridge with Impact of Standard Energy

Conventional method is getting static displacement calculated by dynamic displacement and impact coefficient aim at making the detection of the bridge faster and more precise. But in fact, it is too difficult to ensure the dynamic displacement under the influence of roughness of the bridge deck. For the reasons given above, this paper simulates the bumping testing on the cross section of midspan by explicit dynamic FEM. A vehicle passes through the cross tie which is higher than the highest unevenness, and then gives an impact load to the cross section of the midspan for getting the maximum dynamic displacement of the cross section. This method can eliminate the influence of roughness of the bridge deck and it is a new pathway of bridge dynamic testing.

Multiscale modelling of the induced plastic anisotropy in bcc metals

This paper presents a new framework to predict the qualitative and quantitative variation in local plastic anisotropy due to crystallographic texture in body-centered cubic polycrystals. A multiscale model was developed to examine the contribution of mesoscopic and local microscopic behaviour to the macroscopic constitutive response of bcc metals during deformation. The model integrated a dislocation-based hardening scheme and a Taylor-based crystal plasticity formulation into the subroutine of an explicit dynamic FEM code (LS-DYNA). Numerical analyses using this model were able to predict not only correct grain rotation during deformation, but variations in plastic anisotropy due to initial crystallographic orientation. Optimal results were obtained when {1 1 0}〈1 1 1〉, {1 1 2}〈1 1 1〉, and {1 2 3}〈1 1 1〉 slip systems were considered to be potentially active. The predicted material heterogeneity can be utilised for research involving any texture-dependent work hardening behaviour, such as surface roughening.

動的陽解法FEMを基にした大規模構造のための溶接過渡変形・応力解析手法の提案

In the analysis of welding mechanics, it is difficult to analyze large-scale structures because of welding-specific moving local nonlinearity. In this research, the authors proposed a new numerical method for welding mechanics based on the Dynamic Explicit FEM. In the proposed method, the temperature step is divided into hundreds of time steps as implicit FEM and the displacements are computed for each time step based on dynamic explicit FEM until the whole system reaches the static equilibrium state. And, to achieve the static equilibrium state faster, modified mass and damping matrix are introduced. The modified mass and damping matrix are based on the Courant condition and the vibration theory, respectively. The proposed method and static implicit FEM are compared at the final path of multilayer welding of thick bead-on-plate to verify validity and accuracy. The transient and residual deformation and stress distribution of the proposed method show good agreement with those of static implicit FEM. In addition, the computing time and memory consumption of the proposed method are 1/12 and 1/40 times shorter than those of static implicit FEM, respectively, in 243,243 degree of freedom model. It is found that the proposed method has an advantage in large-scale analysis whose nodal points are more than tens of thousands.

OS0402 理想化陽解法を用いた多層溶接時における残留応力解析(OS4-1 シミュレーション技術,OS-4 溶接変形・残留応力の計測技術,シミュレーション技術)

In this research, the authors proposed a new numerical method for welding mechanics based on the dynamic explicit FEM, named Idealized Explicit FEM. The proposed method and static implicit FEM are compared at the final path of multilayer welding of thick bead-on-plat. It is verified that the transient and residual deformation and stress distribution of the proposed method show good agreement with those of static implicit FEM. In addition, the computing time and memory consumption of the proposed method are 1/12 and 1/40 times shorter than those of static implicit FEM, respectively, in 243,243 degree of freedom model. In addition, parallelization using Graphic Processing Unit (GPU) are applied to idealized explicit FEM to achieve faster computation. The developed method is applied to large scale welding problem that has more than 1 million degree of freedom. As a result, it is found that the developed method is very useful to analyze the large scale welding mechanics problem that has almost the same simulation scale as the practical structures.

Straightening Regulation Optimization on the Residual Stress Induced by the Compound Roll Straightening in the Heavy Rail

Residual stress is very important to the straightened quality of rail, this paper adopts explicit dynamics FEM to study on residual stress. We established compound roller model and calculated the residual value of heavy rail through 9 roller horizontal straightening and 8 roller vertical straightening. The reductions of straightening rollers are taken as the main effective factor to the residual stress in the straightening process. We adopt orthogonal calculation method to obtain the main effective factor to residual stress. On the base of assurance of the straightness, we obtained the optimal regulation in which the residual stress is the smallest, so the paper makes the important theoretical and actual sense to formulate the rational straightening regulation and improve the straightening quality of rail.

Straightening Regulation Optimization on the Residual Stress Induced by the Compound Roll Straightening in the Heavy Rail

Residual stress is very important to the straightened quality of rail, this paper adopts explicit dynamics FEM to study on residual stress. We established compound roller model and calculated the residual value of heavy rail through 9 roller horizontal straightening and 8 roller vertical straightening. The reductions of straightening rollers are taken as the main effective factor to the residual stress in the straightening process. We adopt orthogonal calculation method to obtain the main effective factor to residual stress. On the base of assurance of the straightness, we obtained the optimal regulation in which the residual stress is the smallest, so the paper makes the important theoretical and actual sense to formulate the rational straightening regulation and improve the straightening quality of rail.

Numerical modelling of bit–rock fracture mechanisms in percussive drilling with a continuum approach

SUMMARYThis paper presents a numerical method for continuum modelling of the dynamic bit–rock interaction process in percussive drilling. The method includes a constitutive model based on a combination of the recent viscoplastic consistency model, the isotropic damage concept and a parabolic compression cap. The interaction between the drill bit and rock is modelled using contact mechanics by treating the bit as a rigid body. As the bit–rock interaction in percussive drilling is a transient event, the method is implemented in explicit dynamics FEM. The rock strength heterogeneity is characterized at the mesoscopic level statistically using the Weibull distribution. The bit–rock interaction is simulated under axisymmetric conditions using cylindrical and hemispherical buttons. The choice of the quite complex constitutive model accounting, e.g. for plastic compaction, viscoplastic shear and tensile failure along with induced damage and rate dependency is justified by numerical simulations. Moreover, the quasi‐static and dynamic cases are compared in plane strain simulations. Finally, some results clarifying the discrepancy of opinions found in the literature concerning the side (lateral) crack formation are obtained. Copyright © 2010 John Wiley & Sons, Ltd.