http://www.dynalook.com daily 1 2012-03-08T14:07:29Z http://www.dynalook.com/european-conf-2003/computational-micro-mechanical-model-of-composite.pdf No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/improved-plasticity-and-failure-models-for.pdf The Crash Simulation of Magnesium Structures with Finite Element Methods demands the use of suitable material and failure models. An associated plasticity model describing the complex asymmetric yield behaviour in tension and compression of Mg extrusions has been developed during the InMaK-project (Innovative Magnesium Compound Structures for Automobile Frames) supported by the German Federal Ministry for Education and Research (BMBF). Differences to the material model 124 in LS-DYNA are exposed. In order to describe the failure behaviour of Mg extrusions under multiaxial loading in FEM crash simulation this constitutive model has been combined with a fracture model for ductile and shear fracture. The fracture model has been added to the user defined constitutive magnesium model in LS-DYNA. The experimental investigations carried out on model components are compared with numerical derived results. Experimental methods for fracture parameter evaluation are shown and general aspects of metal failure due to fracture as well as different modelling techniques are discussed. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/a-new-constitutive-model-for-nitrogen-austenitic.pdf Quasi-static, quasi-dynamic and dynamic compression tests have been performed on a nitrogen alloyed austenitic stainless steel. This alloy achieves a high hardening modulus and a good ductility at all strain rates. In addition, this steel is very sensitive to strain rate. The temperature sensitivity has been determined for temperatures varying between 20°C and 400°C. Microstructural analysis has been performed on samples subjected to different loads in order to relate the microstructure to the material behaviour. Johnson-Cook and Zerilli-Armstrong models have been selected to fit the experimental data into constitutive equations. These models are unable to reproduce the behaviour of this type of steel over the complete range of tests. A new constitutive model that better fits all the experimental data at different strain, strain rate and temperature has been determined. This empirical model supposes that the influence of the main parameters is independent. Single Taylor impact tests have been realized to validate the models. Live observations of the specimen during impact have been achieved using a special CCD camera set-up. The overall profiles at different times were compared to numerical predictions performed with LS-DYNA. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/a-simplified-approach-to-the-simulation-of-rubber.pdf The simulation of rubber materials is becoming increasingly important in automotive crashworthiness simulations. Although highly sophisticated material laws are available in LS-DYNA to model rubber parts, the determination of material properties can be non-trivial and time consuming. In many applications, the rubber component is mainly loaded uniaxially at rather high strain rates. In this paper a simplified material model for rubber is presented allowing for a fast generation of input data based on uniaxial static and dynamic test data. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/implementation-and-validation-of-the-johnson.pdf Ceramic materials are commonly used in protective armour applications and may be subject to high-energy ballistic impacts in these situations. Under simple loading conditions, ceramics may be regarded as elastic-brittle materials. However, when considering ballistic impacts, the post-yield response of the ceramic becomes significant. One of the most widely used constitutive models for simulating the postyield response of ceramic materials is the JH-2 ceramic model. This constitutive equation was developed by Johnson and Holmquist and incorporates the effect of damage on residual material strength and the resulting bulking during the compressive failure of a ceramic material. The relevant equations describing the response of the material are described. In particular, the model parameters currently available for common ballistic ceramic materials are presented. The JH-2 constitutive model has been implemented in LS-Dyna as material 110 (*MAT_JOHNSON_HOLMQUIST_CERAMICS). Validation against the available test cases in the literature is discussed, and a sample calculation of a sphere impacting a ceramic material is presented. The JH-2 model in LS-Dyna has also been used by Kaufman et al. to successfully simulate the ballistic impact of 12.7 mm armourpiercing projectiles on supported alumina tiles. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/the-application-of-the-damage-fracture-material.pdf In an evaluation of crashworthiness for the cars that are made of aluminum alloys, the evaluations that consider a fracture phenomenon come to be needed because conventional aluminum alloys have low fracture strain (10 - 20%). Since an original damage & fracture material model of LS-DYNA, namely MAT_PLASTICITY_WITH _DAMAGE: MAT81 has a damage & fracture characteristic in case of compressive strain state, real collision phenomena can not be simulated in some cases. Therefore, we reviewed the damage & fracture criterion of this material model. We newly introduced some sort of a damage & fracture criterion into the MAT81 of LS-DYNA V960 in later revision and performed crashworthiness evaluations for an aluminum car using this improved damage & fracture model. This criterion has nondamage & non-fracture characteristic in compressive strain state and it is known as "Orthogonal an-isotropic (Orthotropic) damage & fracture model". No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/implementation-of-a-material-model-for-trip-steels.pdf This paper describes the implementation of a new material model into LS-DYNA version 960, LSTC (1-4), a material model capable of predicting the TRIP-effect of HyTensX for different forming operations in different temperature scenarios. The implementation is verified by comparing measurements from three tension tests with simulations of the tension tests. The comparison shows good to excellent agreement, which is a strong indication that the implementation is correct and that the material model can be used to predict the hardening behavior of the material with good accuracy. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/modelling-of-foams-using-mat83-2013-preparation.pdf Foam materials are widely used in automotive industry such as energy absorbers and comfort enhancers. Because of high energy absorbing capability of foams, they became very important in vehicle crashworthiness. So in this manner, FE modelling of foam materials also becomes important. Although foam materials are very promising materials, not that much study has been done about foams comparing to other commonly used materials like steel, etc. Some different approaches are available to define the behaviour of foam materials. One micro-structural approach to define the mechanical behaviour of foam materials, considers the foam material as a cubic model and uses the standard beam theories with solid-fluid interaction to describe the in- and out-flow of fluid inside the foam material (see Gibson and Ashby [1]). There are also macro-structural approaches those consider the foam material as a continuum with solid-fluid interaction in order to describe the in- and out-flow of the pore-fluid in the foam material (e.g. Ehlers [2]). In contrast to such quite sophisticated models, in LS-DYNA for practical engineering purposes the foam model *MAT_FU_CHANG_FOAM (MAT83) is available. The main assumption of MAT83 is, that Poisson’s ratio is equal to zero for foams and therefore no coupling between the material axes is present. This leads to a one-dimensional material law, where experimental curves of uni-axial test can be used directly. The aim of this work is to provide a method and to develop a computer program in order to generate reliable input data for the simulation of EPP foam with MAT83 in LS-DYNA. Experimental raw data have to be prepared and extended respectively. In addition, suitable density laws have to be developed in order to provide LS-DYNA input data for intermediate densities, where no experimental data are available. To verify the reliability of the results, simulations with the generated curves are compared to an independent experimental database and to some real experimental applications. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/on-constitutive-equations-for-elastomers-and.pdf The Hill-Ogden elastic constitutive equation for incompressible and compressible rubber-like materials is presented. The derivation and computer programs to determine the material constants for these equations from uniaxial and biaxial tests are included. These constitutive equations and the computer programs for determining the material constants have been implemented into LS-DYNA. A few examples are shown. Some special cases are given to demonstrate the versatility of these constitutive equations. The Mooney-Rivlin constitutive equation is a special case. The Feng-Christensen viscoelastic foam model in one-dimensional compression, developed in 1986, can be written in a mathematical form and implemented in finite element codes. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/modelling-of-foams-using-mat83-preparation-and.pdf Foam materials are widely used in automotive industry such as energy absorbers and comfort enhancers. Because of high energy absorbing capability of foams, they became very important in vehicle crashworthiness. So in this manner, FE modelling of foam materials also becomes important. Although foam materials are very promising materials, not that much study has been done about foams comparing to other commonly used materials like steel, etc. Some different approaches are available to define the behaviour of foam materials. One micro-structural approach to define the mechanical behviour of foam materials, considers the foam material as a cubic model and uses the standard beam theories with solid-fluid interaction to describe the in- and out-flow of fluid inside the foam material(see Gibson and Ashby [1]). There are also macro-structural approaches those consider the foam material as a continuum with solid-fluid interaction in order to describe the in- and out-flow and pore-fluid in the foam material (e.g. Ehlers [2]). In contrast to such quite sophisticated models, in LS-DYNA for practical engineering pruposes the foam model *MAT_FU_CHANG_FOAM (MAT83) is available. The main assumption of MAT83 is, that Poisson's ratio is equal to zero for foams and therefore no coupling between the material axes is present. This leads to a one-dimensional material law, where experimental curves of uni-axial test can be used directly. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/fat-side-impact-dummy-modles-remarks-on-usage-and.pdf Detailed finite element side impact dummy models of the USSID, EUROSID, and ES-2 have been developed in cooperation with the German Association for Automotive Research (FAT) during the last 5 years. All models are validated using tests at material and component levels as well as fully assembled models. The models are used by nearly all car manufacturers worldwide who use LS-DYNA for occupant safety simulations. The paper describes modeling aspects of the dummies and gives an overview of their performance in sled tests. Furthermore emphasis is put on difficulties and potential pitfalls that might arise during the everyday work with the models in predicting occupant injury risks. In addition to the knowledge gained during the development process, experiences from the support for and the consulting with the FAT dummy models are presented. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/simulation-of-proposed-fmvss-202-using-ls-dyna.pdf Federal Motor Vehicle Safety Standard 202 applies to automotive seat head restraints, and their attachment assemblies. The regulation is aimed at reducing the frequency and severity of neck injuries due to huge forces resulting from vehicle crashes. The main objective of this paper is to discuss the LS-DYNA IMPLICIT code vis-à-vis the simulation of the proposed FMVSS 202 regulation. The proposed changes to the FMVSS 202 standard incorporates a permanent set requirement for the head restraints. Since a quasi-static FE simulation cannot do permanent set calculations, LS-DYNA IMPLICIT code was used for this purpose. The paper explains in detail about the setting up of a seat model for the test, the various modeling techniques used and the correlation of results for the seat model. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/on-airbag-simulation-in-ls-2013dyna-with-the-use.pdf In the present paper a basic finite element model of an ALE thorax side airbag with a simplified gas generator will be considered. In particular, it will be discussed how to define boundary conditions and properties of the inflating gas. A possible general approach to ALE airbag validation to fit results of a standard body block test will be described. Finally numerical results for a push-away test for an ALE and corresponding CV airbag will be compared. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/biomechanical-analysis-of-whiplash-injuries-women.pdf Whiplash is the most common soft tissue injury sustained in car accidents. The term is commonly associated with hyperextension of the neck as the head rotates backwards in rear end collisions but the exact injury mechanism is not fully understood because the neck is an anatomically and mechanically complex structure. Experimental studies of the mechanism of injury are limited by several ethical and practical factors, so biomechanical computational simulation, based upon experimental research and mathematical modelling, appears to be the most appropriate method of investigation. During the last decade, significant progress has been made in improving car occupant safety through the use of safety devices, such as airbags and advanced seat belts, as well as the construction of the car body itself. Much still needs to be done, especially for female occupants, because statistically they incur twice the risk of whiplash injury as male car occupants. No simple explanation has so far been found for this difference. It is thought that the anatomic dissimilarity of the sexes is the principal reason, but there are undoubtedly a number of secondary, sociological reasons: women tend to drive smaller cars than men and are more likely to be passengers. The lack of a full explanation arises from the fact that, although there have been several FE-models of the male cervical spine reported, female models are rarely documented. This paper addresses the problem by developing a biomechanical FEM model of the 50th and the 5th percentile female cervical spines, based on the earlier published male model created at the Nottingham Trent University, which relies on grafting a detailed biomechanical model of the neck and head onto a standard HYBRID III dummy model. All numerical analyses have been undertaken using LS-DYNA. Special attention was paid to the behaviour of the scaled down male model in comparison with the model, which included female characteristic features. FEM models of males and females in a representative seat were therefore subjected to 9.5 km/h rear-end simulated collisions and were compared against reported experimental tests. The detailed behaviour varied significantly with gender. The female models revealed greater and earlier peak horizontal acceleration of the head and smaller peak relative extension than the male models. It was concluded that the presented FE models were reasonably in accordance with available crash data on instrumented volunteers in terms of head motion. No publisher admin 2009-03-06T19:00:00Z File http://www.dynalook.com/european-conf-2003/more-realistic-virtual-prototypes-by-means-of.pdf This paper is concerned with closing a gap in the process chain of metal forming. Tools for simulating the metal forming process like LS-DYNA® produce output geometries and stress information which cannot be easily re-imported in CADSystems or structure analysis programs for further processing. A concept has been developed and implemented with a corresponding program which allows the re-importation of parts with certain topologies (tube, plane) from LSDYNA® into any STEP-conformant CAD program. This method is mainly based on using the interconnection information which is contained in the LS-DYNA® output file. This information allows the construction of interpolating cubic B-Spline surfaces which can be represented in the STEP standard format. Thus, it is not necessary to reinvent general purpose surface reconstruction programs but rather to harvest the additional information available in the given situation. Furthermore, a method to make the strength hardening information available in structure analysis is represented. This hardening results from the forming process and should be considered to obtain a more realistic virtual prototype and is of assistance to save weight and material costs. Introduction The forming simulation by means of finite element analysis (FEA) is becoming more and more important in the field of process quality assurance and process design of mechanical and fluid media formed components. Using the finite element simulation in the development process of hydroforming components from the first draft through to the serial production of a component provides an enormous saving of development time and costs. However, due to the constantly increasing competition in terms of costs, development time and quality, a further reduction of processing time and costs is necessary. Moreover, there is the demand for even more exact predictions and results in the area of the virtual component, in order to reduce the weight and to ensure that the component produced will have enough stability and low material costs. Due to this demand the integration of the forming simulation into the process chain must be improved. In order to point out the optimisation potential, the sequence of the processes from the design phase to the finished component is represented in Figure 1. No publisher admin 2009-03-06T19:00:00Z File