http://www.dynalook.com daily 1 2009-02-12T08:08:41Z http://www.dynalook.com/international-conf-2000/session9-4.pdf Random geometric imperfections are natural in structures. The initial imperfections used to be ignored in structure strength analysis and thus geometric-perfect models were used in most case of numerical simulation. However, collapse of axially compressed square tubes is not such a case. LS-DYNA is used to simulate the effects initial geometrical imperfection has on square tube collapse. This study proves that dynamic progressive buckling of square box columns is sensitive to initial geometrical imperfections. The simulation results show that ideal square tubes tend to buckle in extensional mode, though is not likely to happen in experimental studies. Previous theoretical analysis suggests, that from the view of energy absorption extensional mode is a dynamic procedure of higher energy absorption characteristics than that of each of symmetric and asymmetric mode of square tube in case of high c/h. This phenomenon suggests that extensional mode is an unstable equilibrium that will easily change to another equilibrium – symmetric mode. In a real world, geometrical imperfection renders extensional mode almost unachievable for hollow square tubes. Three kinds of imperfections: deflection of wall, thickness deviation and length of section side unequal were discussed in this paper. The amplitude of imperfection was compared with the geometry tolerance. Numerical simulations are then performed using LS-DYNA. Compared with the experimental datum, deflection of wall is the main reason for the predominance of symmetric mode of axially impacted hollow square tubes. Several characteristic values with regard to the amplitude of wall deflection are discussed in particular. It is found that when the λcr , the initial impact force peak amplitude of deflection is less than a certain critical value value and the critical buckling load are almost the same and unchanged at a determined impact velocity. When deflection exceeds the critical value, buckling take place in elastic area and critical buckling force drops quickly. Energy absorbed before buckling also quickly drops to near zero when deflection is considerably large. No publisher admin 2009-03-26T17:06:19Z File http://www.dynalook.com/international-conf-2000/session9-2.pdf Bird ingestion is a costly and difficult engine test to perform. It is also one of the most challenging and complex analytical investigations in engine design. The capability to model bird ingestion effects is, therefore, critical to the success of any competitive jet engine program. LS-DYNA has been used in the design and analysis of fan blades for bird-strikes. Descriptions of the bird and blade models used in the analyses along with the contact algorithms used to describe their interaction will be presented. In addition, comparisons of analysis and test results from bird-strikes on fan blades will also be presented. No publisher admin 2009-03-26T17:06:16Z File http://www.dynalook.com/international-conf-2000/session9-3.pdf Pressure Sciences Inc. used LS-DYNA to model a propane tank truck colliding with a concrete column. The analysis simulates an accident that occurred in 1994 in White Plains, New York. Correlation between the accident and an LS-DYNA analysis of that crash is described. The ultimate purpose of the analyses is to improve the crashworthiness of propane semi-trailers. To address the stiffening effect of the propane fluid, we correlated several models with drop tests that had been performed on 1/12 scale railroad tank car heads. The heads included unpressurized heads, fluid pressurized heads, and fluid pressurized heads with an air cushion. In order to model the liquid propane, explicit solid elements were used. The material model used for the propane was the elastic material model with the fluid option. The paper describes the procedure used to incorporate the elastic material model with the fluid option. The propane vapor was modeled using explicit solid elements and the null material model with a linear polynomial equation of state. The paper gives the derivation of a simplified version of the linear polynomial equation of state to simulate Boyle’s law. We were able to use LS-DYNA to obtain good correlations with drop tests when we modeled the liquid using the elastic material model with the fluid option and the vapor with a null material with the linear polynomial equation of state. We also obtained reasonable correlations between our LS-DYNA model and the White Plains, NY accident involving a propane tank truck and a concrete column. No publisher admin 2009-03-26T17:06:13Z File http://www.dynalook.com/international-conf-2000/session9-1.pdf Modeling and simulation requirements for uncontained engine debris impact on fuselage skins are described and assessed using the tied-nodes-with-failure (TNWF) approach and the element-erosion (EE) approach for penetration simulation. The TNWF approach is based on coincident nodes generated in selected regions of the target plate that are tied together using a constraint relation and the target plate is modeled with shell elements. The EE approach is based on eliminating or removing of an element once some criterion is reached. No publisher admin 2009-03-26T17:06:11Z File http://www.dynalook.com/international-conf-2000/session2-3.pdf In recent years, CAE (Computer Aided Engineering) has become very popular for effective development of many industrial products. In the development of automobile, CAE has been applied in many fields. About endurance and fatigue analyses of automobile, it is necessary to simulate the force by road input, and accurate tire model is necessary for this. But the construction of tire is very complicated and its model is so complicated that large calculation resource is necessary. Such a simulation is not useful for actual automobile development. Then we tried making simplified tire simulation model that express the tire properties of minimum requirement. After developing tire model, we applied the model to curb striking simulation to confirm the availability of the model. No publisher admin 2009-03-26T17:06:12Z File http://www.dynalook.com/international-conf-2000/session2-2.pdf Finite element side impact dummy models of the USSID and EUROSID are of major interest for industry, as more detailed models are required for better prediction capabilities, but still efficiency has to be maintained to some degree. Both type of models, the so-called FAT- USSID and FAT-EUROSID have been developed by CAD-FEM in cooperation with the German Association for Automotive Research (FAT). The main objective was to achieve highly validated finite element models. During the development process the models are vali- dated at three levels: material, component and assembly and tested finally by sled test appli- cations. Additional input was provided by other type of simulations from the LS-DYNA users within the FAT. This paper summarizes the experience gained during the validation and optimization process which may be used as a guideline for an efficient methodology to generate reliable finite element dummy models. Finally, the good performance of the current USSID and EUROSID models is presented for some selected tests. No publisher admin 2009-03-26T17:06:06Z File http://www.dynalook.com/international-conf-2000/session13-3.pdf Accurate prediction of springback is the precondition of controlling the springback. The precision of springback prediction is affected by many parameters in both forming process and springback process. The 2-D draw bending benchmark of NUMISHEET’93 is used as an example to investigate the influencing of numerical parameters in LS-DYNA and LS-NIKE3D, which includes solution approach, dynamic effect, number of the dies’ corner elements and blank element size on the springback simulation. Comparing the simulation results with experimental results, some basic principles have been given for springback simulation. No publisher admin 2009-03-26T17:03:00Z File http://www.dynalook.com/international-conf-2000/session13-2.pdf Two mesh refinement indicators based on the gradients of effective stresses (GSIG) and effective plastic strains (GEPS), respectively, are proposed for adaptive finite element analysis of the large deformation, quasi-static or dynamic response of shell structures. The mesh refinement indicators are based on equi-distributing the variation of stresses or plastic strains over the elements of the mesh. A program module is developed and implemented in the nonlinear explicit finite element code LS-DYNA. This module provides element-wise refinement evaluations so that selective mesh refinements are carried out in regions of the mesh where the values of local indicators exceed a user-specified tolerance. The FE model of a conventional deep drawing process is used as numerical model, including both material and geometrical nonlinearities, in order to demonstrate the versatility of the two refinement indicators. Four different refinement indicators, based on angle change, thickness change, GSIG and GEPS based are applied in this investigation. To verify the numerical results against experiments, the anisotropic low carbon steel, FEP04, is used as a reference material. The numerical results are compared with experimental results regarding the thickness distribution versus cup height, effective plastic strain in the deformed sheet and punch force. It is shown that the new proposed indicators can identify finite elements, which have high gradients of stresses or strains so that the mesh is refined in the regions undergoing the most severe deformations and the numerical results are improved. No publisher admin 2009-03-26T17:02:58Z File http://www.dynalook.com/international-conf-2000/session13-1.pdf The kernel technology of a computer simulation system and the general procedure of dynamic simulation in sheet metal forming are presented. As an example, processing parameters of the experimental die of a car inner door panel were optimized with eta/DYNAFORM software. The appropriate round corner of punch, BHF and the correct layout of the drawbead were obtained. No publisher admin 2009-03-26T17:00:18Z File http://www.dynalook.com/international-conf-2000/session8-5.pdf A micro-mechanical model is developed for laminated composite materials and implemented in the explicit finite element method. The objective of this study is to get an accurate and simple micro-model, which can be used in the displacement-based nonlinear explicit finite element code DYNA3D. The micro-mechanical model implemented in the explicit finite element code can be used for simulating the behavior of composite structures under various loads such as impact and crash. The stress-strain relation for the micro-model is derived for shell element. Micro Failure Criterion (MFC) is presented for each material constituent and failure mode. The implemented model is validated through several test examples. As a demonstration case of the stability of the developed micro-model a finite element model of Graphite/Epoxy tube structure is developed and simulated under axial crash. No publisher admin 2009-03-26T17:00:21Z File http://www.dynalook.com/international-conf-2000/session8-4.pdf In order to obtain the desired coupling between deformation modes that can occur in composite material plates having unbalanced and/or unsymmetric lamination schemes, the appropriate shell element formulation must be selected from the available formulations in LS- DYNA. An investigative study was conducted to determine which of the shell element formulations in LS-DYNA 950 can be used for modeling such plates prior to performing in- depth studies on the behavior of more complex composite material structures. Unbalanced/symmetric and balanced/unsymmetric lamination schemes were studied for single-element and four-element “patch” tests. The elastic response of these models to in- plane tensile loads and out-of-plane bending loading was investigated. The shell elements were used with material model 54 (MAT_ENHANCED_COMPOSITE_DAMAGE). The study focused on determining which of the shell element formulations would produce the expected coupling between deformation modes. The Belytschko-Leviathan shell formulation was found to be the best choice for coupled elastic response. Progressive failures of laminates under in-plane tensile and compressive loads were also investigated using this element formulation. No publisher admin 2009-03-26T17:00:25Z File http://www.dynalook.com/international-conf-2000/session8-3.pdf An eight-node hexahedral solid element is incorporated into LS-DYNA to simulate thick shell structure. The element formulations are derived in a corotational coordinate system and the strain operator is calculated with a Taylor series expansion about the center of the element. Special treatments are made on the dilatational strain component and shear strain components to eliminate the volumetric and shear locking. The use of consistent tangential stiffness and geometric stiffness greatly improves the convergence rate in implicit analysis. No publisher admin 2009-03-26T17:00:28Z File http://www.dynalook.com/international-conf-2000/session8-2.pdf A new homogenization procedure for Finite Element (FE) analysis of sandwich shells was recently developed and presented by the authors. To the authors’ knowledge all present FE approaches to sandwich structures are incorporated into the FE formulation on the element formulation level. Unlike other formulations the present approach works on the constitutive level. A homogenization of the sandwich shell is performed at each call of the corresponding constitutive subroutine. Thus the sandwich nature of the problem is hidden from the main FE program. As a consequence there is no need to develop a new shell element formulation, but instead all available homogeneous shell elements in the utilized FE code can be used for the analysis of sandwich shells. This would provide versatility of the FE analysis and potentials to trade off between the level of accuracy and computational efficiency by using more accurate or simpler shell elements. Furthermore, the sandwich homogenization procedure (SHOP) can be easily coupled with a composite homogenization model to enable analysis of sandwich shells with composite faces. To validate the present approach and check its accuracy, efficiency and overall performance it is implemented in a finite element package and combined with existing first order shear deformable shell elements for homogeneous materials. Results are obtained and herein presented for problems previously investigated experimentally and by different theoretical and numerical techniques. The presented results show good agreement with published results from far more complicated and computationally intensive analyses, which builds confidence in the approach and motives its future elaboration and development. No publisher admin 2009-03-26T17:00:30Z File http://www.dynalook.com/international-conf-2000/session8-1.pdf The present work concentrates on the development of correct representation of the transverse shear strains and stresses in Mindlin type displacement based shell finite elements. The formulation utilizes the robust standard first order shear deformation shell finite element for implementation of the proposed representation of the transverse shear stresses and strains. In this manner the need for the shear correction factor is eliminated. In addition, modification to any existing shell finite element for the correct representation of transverse shear quantities is minimal. Some modifications to correct Mindlin type elements are presented in the literature. These modifications correct the distribution of the transverse shear stresses only and use the constant transverse shear strains through the thickness. As compared to the above, the present formulation uses the correct distribution and is consistent for both transverse shear stresses as well as transverse shear strains. No publisher admin 2009-03-26T17:00:33Z File http://www.dynalook.com/international-conf-2000/session1-1.pdf No publisher admin 2009-03-26T17:00:35Z File