http://www.dynalook.com daily 1 2009-03-06T17:29:14Z http://www.dynalook.com/international-conf-2006/14MetalForming.pdf LS-971 has several new features to model the hot stamping process. A thick thermal shell formulation allows modeling a temperature gradient through the thickness of the shell. The new keyword, *MAT_ADD_THERMAL_EXPANSION, allows calculating thermal strains for all the mechanical material models. A new feature has been added to thermal contact which turns off thermal boundary conditions when surfaces come in contact. A new thermal one-way contact algorithm has been added which more accurately models heat transfer between a blank and die. New features have been added to thermal-mechanical contact which allows modeling the coefficients of friction as a function of temperature and thermal contact resistance as a function of interface pressure. No publisher admin 2009-03-23T15:13:22Z File http://www.dynalook.com/international-conf-2006/12CrashSafety.pdf The deformable barriers consist mainly of honeycomb blocks with highly anisotropic behaviour. These parts are made from several layers with aluminium foil that is glued and stretched to form the honeycomb structure. Simple compression tests show high stiffness and strength when the cell structure is folded while both stiffness and strength are significantly lower when the deformation mode is mainly bending of the thin foil. Remember that the typical deformation mode involve also transverse displacement of barrier parts, and when the honeycomb structure is folded this may be seen as the interaction between local and global buckling. Therefore, shell elements are used to model the honeycomb structure, and alternative models of the offset and the side impact deformable barriers are made. Note that scaling is used extensively to limit the number of elements and thereby the computational time that is required. These models with about 30 000 shell elements seem able to predict the global response of the deformable barriers, and they may be easily refined to represent more local behaviour as well. No publisher admin 2009-03-23T15:13:18Z File http://www.dynalook.com/international-conf-2006/14ImpactAnalysis.pdf The kinetic feature of weapon fragment is many small masses traveling at extremely high velocities and scattering radially from the explosion center. To simplify the fragment impact analysis, people often convert the fragment momentum into a triangular pressure load with very high magnitude and very short duration, and apply the load directly onto the target. This method may over- or under-predict the impact response due to the complicacy of fragment behaviors such as embedment, perforation and ricochet. It might encounter more difficult situation when involving multi-layer impact and penetration problem. This paper proposes a new method for fragment simulation using the contact technique provided in LS-DYNA. A program was developed which can automatically generate the LS-DYNA keyword input of node, part, initial velocity and contact surface cards for multiple pieces and sets of fragments, based on the given information about mass, location, velocity of each fragment, and other user-defined parameters. This method can be applied not only on multi-piece fragment impact simulation, but also on multi-hit problem in a realistic way. Examples of fragment impact on structure are demonstrated. No publisher admin 2009-03-23T15:13:15Z File http://www.dynalook.com/international-conf-2006/42SimulationTechnology.pdf The user-defined features in LS-DYNA are powerful tools that allow users in academia or industry to verify research results in the context of general and complicated finite element applications. Implementation work concerns only the special field of interest, and there is no need for the comprehensive task of developing and maintaining the complete finite element software. One of the new user-defined features in LS-DYNA v971 is the possibility to define structural solid and shell elements. Up to a total of ten element formulations can be implemented in a single LS-DYNA executable both for explicit and implicit analyses. A high abstraction-level interface is in particular provided for numerically integrated elements, and stabilization schemes can easily be incorporated. There is also the option to implement discrete elements, and property parameters and history variables can be associated with the element. The interface is equipped with additional features that facilitates research on element technology, but also makes it perfectly suited for educational purposes. An overview of the procedure of implementing an element in the new interface as well as invoking it from the keyword input file will be presented. No publisher admin 2009-03-23T15:13:12Z File http://www.dynalook.com/international-conf-2006/12MaterialModeling.pdf Ultra-high molecular weight polyethylene (UHMWPE) is a semi-crystalline polymer with excellent strength, impact resistance, and abrasion resistance. These mechanical properties have led to extensive use of UHMWPE as a bearing material in total joint replacements. In order to accurately capture the experimentally observed response of this important polymer we have developed a new advanced material model—the Hybrid Model (HM). This constitutive model is physically motivated and based on a decomposition of the deformation gradient into elastic and viscoplastic components. The elastic response of the underlying molecular network is captured using the eight- chain hyperelastic model, and the viscoplastic response is represented using energy activated flow driven by the molecular reorganization that occurs during large deformations. The constitutive theory for the HM has been implemented as a user-material model (UMAT) for ls971 and is available for both explicit and implicit simulations. For optimal accuracy and numerical efficiency the UMAT uses a forward Euler integration scheme for explicit simulations, and a higher order backward differentiation formula (BDF) method for implicit simulations. The HM was calibrated to data from uniaxial tension experiments performed at different strain rates and with different loading-unloading segments. For validation, the calibrated HM was then used to simulate a small punch test. A direct comparison between the experimental data and model predictions of the calibration and validation data demonstrate that the HM accurately captures the non-linear response of UHMWPE. The ability to simulate large-scale contact problems was examined by simulating the deformation behavior of a total knee replacement component and the CharitéTM artificial discs. No publisher admin 2009-03-23T15:13:09Z File http://www.dynalook.com/international-conf-2006/21SimulationTechnology.pdf A numerical investigation of the vibration behavior and the sound of a specific bell is performed and validated by experimental modal analysis. In the numerical simulations a number of modifications of the geometry mimicking or- naments and reliefs is investigated as such ornaments have lead to mistunes in a very popular case in Germany. It is also shown, how the influence of ornaments on the modification of eigenfrequencies can be reduced. The numerical results obtained by eigenvalue analyses as well as transient analyses with LS-DYNA compare very well with the experimental results. It is shown that LS-DYNA- Finite Element analysis can be well used for bell de- sign [14]. No publisher admin 2009-03-23T15:13:06Z File http://www.dynalook.com/international-conf-2006/14MaterialModeling.pdf Predictive techniques for the analysis and design of metallic or composite components and structures subject to severe loading can lead to significant mesh sensitivity if cracking or tearing or penetration occurs. This is especially important for composite materials in which the material has an elastic brittle response with little or no plastic behaviour, in which energy could be dissipated. Hence, the full potential use of composite in the design of advanced composites and structures has not yet been exploited fully. This work constitutes an effort directed towards the development of an objectivity algorithm for strain softening material models based on the ‘smeared cracking formulation’. The algorithm has been implemented into LS-DYNA for hexahedron solid elements and correctly accounts for crack directionality effects. Thus enabling the control of energy dissipation associated with each failure mode regardless of mesh refinement and element topology. The advantage of the present technique is that mesh size sensitivity on failure is removed leading to results, which converge to a unique solution, as the mesh is refined. If such a scheme were not introduced results could change significantly from mesh to mesh leading to an incorrect structural response. The proposed algorithm has been validated by a series of benchmark tests using different degrees of mesh refinement and element topologies. No publisher admin 2009-03-23T15:13:04Z File http://www.dynalook.com/international-conf-2006/2Optimization.pdf An overview of LS-OPT features is given with special emphasis on new features available in LS-OPT Version 3.1. The main features added to Version 3 include discrete optimization, 3-D metamodel plotting, additional statistics features, and a simplification of parameter identification. LS-OPT is now available for MS Windows®. No publisher admin 2009-03-23T15:13:02Z File http://www.dynalook.com/international-conf-2006/42CrashSafety.pdf Automobile durability and fatigue life prediction depend on road load generation approaches including proving ground testing, laboratory measurement and CAE simulations. Traditionally, the road load simulations are done with ADAMS using rigid body and modal flexible body approaches. With the newly available MD Nastran SOL700 capability, a new approach of using FEA-based flexible body modeling for suspension systems will be an attractive supplemental solution. MD Nastran SOL700 is an LS-DYNA based explicit solution which is capable to correctly simulate FEA flexible body structure, motions, and kinematics while accurately accounting for the material and geometric non-linearity of a suspension system. This paper will focus on the methodology development to enable efficient conversion from an ADAMS model in XML format into MD Nastran SOL700 or LS-DYNA format in ETA’s VPG environment. In the VPG environment, a rigid body suspension model can be easily changed to FEA based flexible body model for either MD Nastran SOL700 or LS-DYNA solution. A demonstration case will also be provided to illustrate the process and approach. No publisher admin 2009-03-23T15:12:43Z File http://www.dynalook.com/international-conf-2006/14SimulationTechnology.pdf In this paper the dynamic pulse buckling of laminated composite beams was analyzed using LS-DYNA and another widely used commercial FE code, namely NISA (Ver.12), developed by EMRC (Engineering Mechanics Research Corp). Two types of impact loadings that could induce dynamic pulse buckling of composite beams were analyzed. The first one was a force applied to the structure in a very short duration (i.e., an impulse load). The other one was the impact of a moving mass having a certain initial velocity. This problem brings considerable challenges if one is to simulate the phenomenon accurately. The main objective of this technical exercise was to investigate the influence of certain numerical parameters on the integrity of the out coming results. The objective was also to assess the performance of a “conventional, general purpose” type FEM program versus LS-DYNA, which is considered as a leading FEM code for the analysis of highly nonlinear phenomena. This was an interesting exercise in demonstrating why one should use codes like LS-DYNA, as oppose the general purpose FEA codes when considering such highly non-linear phenomena. Both abovementioned loading types were considered in this study. In the analysis using LS-DYNA, the force function was introduced by applying an impulse force at one end of the FRP beam. The moving object was also modeled in LS-DYNA by means of a rigid wall having a mass and an initial velocity. The impact by moving object could not be accommodated by NISA, so only the pseudo-impulse type loading could be considered in NISA. Parametric studies were also conducted to investigate the effect of the slenderness ratio, the curvature and the stacking sequences of the FRP beams, as well as the examination of the influence of the initial imperfection used to promote structural instability. No publisher admin 2009-03-23T15:12:39Z File http://www.dynalook.com/international-conf-2006/2PenetrationExplosive.pdf This paper introduces the very first step on the development of a guided ammunition system. It presents high level physics based simulations of a guided 60-mm projectile system, which intention is to enable the sub-projectile to hit and kill an incoming hostile missile at an extended range within a very limited time frame. The projectile requires a very high muzzle exit velocity in order to carry out the mission. Due to high inertia loads derived from immense breech pressure, understanding the survivability of the projectile system during launch becomes very important. The structural system of interest includes sub-projectile body, sabot, penetrator and electronics. This study focuses on overall projectile system configuration design and addresses the concern of structural integrity among components due to propellant pressure forces. LS-DYNA, a popular transient dynamics finite element program, will be adopted to perform in-bore dynamic analysis. The topology of the projectile was initiated based on gun barrel specifications and certain aerodynamics characteristics. Preliminary structural design of sabot and sub-projectile was then performed with pseudo-static analysis. Subsequently, a 3-D finite element model was created and validated by LS-DYNA explicit dynamic analysis. A characteristic centerline variation of a gun barrel was also taken into account in the study. From simulation results, the muzzle velocity reached only 85% of target value due to 25% overweight of the launch package. However, the projectile system shall survive according to effective stress responses. No material failure is anticipated through in-bore travel. It should be noted that the structural configuration is not optimal as far as the launch package mass is concerned. In the next development phase, rigorous optimization efforts will be made on the projectile system, particularly sabot component. No publisher admin 2009-03-23T15:12:35Z File http://www.dynalook.com/international-conf-2006/35CrashSafety.pdf In this paper bending resistance of thin-walled channel beam is applied to create simplified model for truck chassis. In the simplified model, beam and nonlinear spring elements are used to model the side-rails, and equivalent beams are applied to represent the cross members. Both detailed and simplified models are used for crashworthiness analyses, and the results are recorded and compared. Relatively good agreement is achieved between these analyses, while the computing time is significantly reduced for the presented modeling method. No publisher admin 2009-03-23T15:12:40Z File http://www.dynalook.com/international-conf-2006/5Optimization.pdf In the mobile electronic appliances market, the feature of products is getting smaller, thinner and more multi- functional. Therefore, mobile products are easily damaged from drop/impact and thermal cycling load. To make them more reliable under these conditions, the junction area between chips and PCB should be designed to bear up under drop/impact. And the heat caused by main chip (Memory & DMB channel chip) should be dissipated as quickly as possible. From the viewpoint of CAE simulation, although those two problems (drop & heat) should be considered simultaneously, they should not. Because the outline of PCB mainly depends on the location of main chip, positioning the main chip is one of the most important steps in the initial design stage. And the dynamic stress from free drop and heat caused by main chip are the one of the most critical factors to position the main chip. This paper presents the design process for positioning the main chip on PCB of PMP using MDO method. That is, the trade-off design variables between drop and thermal loading analysis were identified and system level optimization is performed in parallel. The main theme of this paper is to provide a way to get MDO solution of the PMP model in the early design stage. No publisher admin 2009-03-23T15:12:28Z File http://www.dynalook.com/international-conf-2006/21MaterialModeling.pdf An approach for modeling sandwich structures with a Nomex® honeycomb core and phenolic composite faces in the commercial finite element code LS-DYNA with solid elements for the core and shell elements for the thin faces is presented, which accounts for the major sandwich failure modes. Extensive material testing was conducted to determine the parameters for the composite face material model and for the orthotropic honeycomb material model. Strain rate dependency of the material parameters as well as face-to-core debonding phenomena were also investigated and included in the model. In order to design aircraft interior components for dynamic loads, finite element models of lateral and center bins of a widebody aircraft cabin were created and simulations of different load cases were performed. A good correlation to experimental dynamic test results could be achieved. No publisher admin 2009-03-23T15:12:27Z File http://www.dynalook.com/international-conf-2006/31ImpactAnalysis.pdf Consumer products are many times used under extreme use conditions which have the potential to damage a device in a manner such that the internal components become damaged, and non-functioning. Designing engineers must consider these shock, impact and vibration conditions when designing products, as well as the shipping containers or packaging of the product for transport to the end user. In addition, there are many different variations of the impact condition, including height, and angle of impact. Drop Tests are performed to test physical prototypes for such inputs. LS-DYNA analyses can be used to simulate these tests, thereby reducing the number of tests and improving the product design prior to prototype construction. A case study of how process automation within eta/VPG has enabled engineers to consider many different drop test simulation scenarios in an efficient manner will be presented. No publisher admin 2009-03-23T15:12:21Z File