http://www.dynalook.com daily 1 2009-02-12T08:08:41Z http://www.dynalook.com/international-conf-2002/Session_16-4.pdf A response surface optimization algorithm for structural material or parameter identification is evaluated. The algorithm used is the Successive Response Surface Method (SRSM) available in LS-OPT. To illustrate the robustness of SRSM as a material identification tool, two test cases are presented. The first concerns the identification of the power-law material parameters of a simple tensile test specimen. The second test case involves the identification of a model to characterize the brittle damage in a composite laminated structure. It is shown that SRSM is an effective tool for material parameter identification involving strongly nonlinear materials. No publisher admin 2009-03-26T11:26:08Z File http://www.dynalook.com/international-conf-2002/Session_16-2.pdf Recently new materials were introduced to enhance different aspects of automotive safety while minimizing the weight added to the vehicle. Such foams are no longer isotropic but typically show a preferred strong direction due to their manufacturing process. Different stress/ strain curves are obtained from material testing in different directions. A new material model was added to the LS-DYNA code in order to allow a correct numerical simulation of such materials. Ease-of-use was a primary concern in the development of this user-subroutine: we required stress/ strain curves from material testing to be directly usable as input parameters for the numerical model without conversion. The user-subroutine is implemented as MAT_TRANSVERSELY_ANISOTROPIC_CRUSHABLE_FOAM, Mat law 142 in LS-DYNA Version 960-1106. In this paper we summarize the background of the material law and illustrate some applications in the field of interior head-impact. The obvious advantage of incorporating such detail in the simulation lies in the numerical assessment of impacts that are slightly offset with respect to the foam’s primary strength direction. No publisher admin 2009-03-26T11:26:06Z File http://www.dynalook.com/international-conf-2002/Session_16-3.pdf The Continuous Surface Cap Model is a new addition to the LS-DYNA geomaterial modeling library of constitutive models (Material Type 145). This new model should replace the use of the Geological Cap Model (Material Type 25) for most applications. The Continuous Surface Cap Model maintains all the functionality of the Geological Cap Model with the addition of the third stress invariant, strain rate effects, and damage modeling. The Continuous Surface Cap Model has also been reported to be about three times faster than the Geological Cap Model in a large scale application. This article briefly describes some of the model features and illustrates its application. No publisher admin 2009-03-26T11:26:01Z File http://www.dynalook.com/international-conf-2002/Session_16-1.pdf The present study aims at implementation of a strain rate dependent, non-linear, micro- mechanics material model for laminated, unidirectional polymer matrix composites into the explicit finite element code LSDYNA. The objective is to develop an accurate and simple micro- mechanical, rate dependent material model, which is computationally efficient. Within the model a representative volume cell is assumed. The stress-strain relation including rate dependent effects for the micro-model is derived for both shell elements and solid elements. Micro Failure Criterion (MFC) is presented for each material constituent and failure mode. The implemented model can deal with problems such as impact, crashworthiness, and failure analysis under quasi- static loads. The developed material model has a wide range of applications such as jet engine jackets, armor plates, and structural crashworthiness simulation. The deformation response of two representative composite materials with varying fiber orientation is presented using the described technique. The predicted results compare favorably to experimental values. No publisher admin 2009-03-26T11:26:06Z File http://www.dynalook.com/international-conf-2002/Session_3-6.pdf This paper describes a method that can be used to estimate the residual strains from the forming of sheet metal without running forming simulations. For a first-order crash analysis, using estimated residual strains rather than the strains reported from several forming simulations increases the speed of the design process. The method estimates residual forming strains from the part geometry itself and assumes that the part was formed from a planar sheet of metal. The importance of considering the forming history of a part is demonstrated by comparing crash analysis results with and without the consideration of these residual strains. Along with this, physical test results will be compared of a part as formed and an identical part which was heat treated to relieve some of the cold working strains. Once the importance of considering forming history has been established, an alternative method of estimating residual strains will be examined. Crash analysis results using forming simulation residual stresses and strains will be compared to analysis results using estimated strains from the alternative method. Finally the scope of application of this strain estimation method will be discussed. No publisher admin 2009-03-26T11:25:51Z File http://www.dynalook.com/international-conf-2002/Session_3-5.pdf Two barriers are commonly used to evaluate the response of a vehicle in a frontal impact: the rigid barrier and the offset deformable barrier. They produce different deformation patterns, which opens up the possibility that at least one of them does not represent real world crashes. One possible cause of the difference is that an impact into a rigid barrier generates significantly greater stress waves than impacts in the real world resulting in final deformation patterns that are different from those seen in the field. To evaluate this conjecture models of two types of rails each undergoing two different types of impacts, are analyzed using an explicit dynamic finite element code. Results show that the energy perturbation along the rail depends on the barrier type and that the early phase of wave propagation has very little effect on the final deformation pattern. This implies that in the real world conditions, the stress wave propagation along the rail has very little effect on the final deformed shape of the rail. No publisher admin 2009-03-26T11:25:49Z File http://www.dynalook.com/international-conf-2002/Session_3-4.pdf Vehicle manufacturers, in an effort to reduce costs and meet the demand of customers are constantly reducing product development time. At the same time we see more regulations from governments, primarily aimed at vehicle safety. In additions there are variations in global regulations, such as ECE and FMVSS regulations. In order to meet the objective of reducing time and costs, manufacturers are forced to rely more and more on the virtual prototype to avoid the time and cost of constructing and testing prototypes, and to gain the insight necessary to make the current vehicle design better than past products in the area of performance and efficiency. These, in the minds of the engineering community, may be contradicting objectives. We have less time to perform more analyses, and not only that, but more critical analyses which may have more impact on the success of the vehicle when compared to the commercial impact of the analyses performed 5-10 years ago. The automotive industry is legally required to design vehicles to meet the Federal Motor Vehicle Safety Standards (FMVSS) or ECE/EEC Homologation Regulations as well as Corporate/Industry Standards. These standards are ever-increasing due to consumer awareness and the industry focus on vehicle safety, resulting in a conflict – we are increasing the simulation workload, and shrinking the time available to perform the analysis. Therefore, there exists a need to streamline all routine processes, and gain maximum efficiency from the engineer’s limited time. This paper describes the development of a set of tools which enable engineers to automate many routine crash and safety analysis tasks, gaining efficiency, accuracy and productivity. No publisher admin 2009-03-26T11:25:49Z File http://www.dynalook.com/international-conf-2002/Session_3-3.pdf A finite element human model, THUMS (Total HUman Model for Safety), was developed in order to study human body responses to impact loads. This paper briefly describes the structure of the human model, as well as some of the results of the simulations conducted to validate the model. No publisher admin 2009-03-26T11:25:46Z File http://www.dynalook.com/international-conf-2002/Session_3-2.pdf The modular approach developed is a unique methodology for building a full vehicle finite element model which allows the use of a single vehicle model, assembled using component modules, to simulate multiple test configurations. This concept allows multiple users to efficiently contribute to construction of a model that can be used to run any number of test configurations. The benefits of a modular approach to full-vehicle finite element model were demonstrated by the C/K (full size truck) product line. While some configuration must be validated using physical tests, these tests can also be used to correlate a finite element model. Perturbation of the model can then be used to evaluate similar configurations and increase confidence in the design, without requiring additional hardware. This modular process can be implemented on all platforms as well, but with lesser savings for less complex products. No publisher admin 2009-03-26T11:25:41Z File http://www.dynalook.com/international-conf-2002/Session_3-1.pdf This paper describes the multidisciplinary design optimization of a full vehicle to minimize mass while complying with crashworthiness and Noise, Vibration and Harshness (NVH) constraints. A full frontal impact is used for the crashworthiness simulation in the nonlinear dynamics code, LS-DYNA. The NVH constraints are evaluated from an implicit modal analysis of a body-in- white vehicle model using LS-DYNA. Seven design variables describe the structural components of which the thickness can be varied. The crashworthiness constraints relate to crush energy and displacement, while the torsional frequency characteristics are obtained from the modal analysis. The Multidisciplinary Feasible (Fully Integrated) formulation, in which full sharing of the variable sets is employed, is used as the reference case. In an attempt to investigate global optimality, three starting designs are used. Based on a Design of Experiments analysis of variance of the fully-shared variable results for each starting design, discipline-specific variables are selected from the full set using the sensitivity of the disciplinary responses. The optimizer used in all cases is the Successive Response Surface Method as implemented in LS-OPT. It is shown that partial sharing of the variables not only reduces the computational cost in finding an optimum due to fewer, more sensitive variables, but also leads to a better result. The mass of the vehicle is reduced by 4.7% when starting from an existing baseline design, and by 2.5% and 1.1% when starting from a lightest and heaviest starting design respectively. No publisher admin 2009-03-26T11:25:46Z File http://www.dynalook.com/international-conf-2002/Session_15-5.pdf In the United States, in the year 2000, over 100 billion aluminum beverage cans were manufactured. Lightweighting of these aluminum D&I beverage cans has been a continuous process for more than 35 years. Aluminum beverage can "ends" have been made progressively smaller over the years in order to reduce costs. Likewise, cost control efforts have resulted in continuous reduction of the net metal requirements for the can body. To reduce the weight and cost of the "bodies", cans with thinner sidewalls, reduced neck diameters and smaller base diameters have been developed. The reduction in cost has been achieved while maintaining functionality, structural performance, and formability of the can. Today, the gauge of can body stock is as low as 0.0098 inches. With small base diameter cans and a sheet thickness that continues to decrease, the likelihood of profile wrinkling during can forming increases, particularly in the redraw process. Redraw wrinkling is influenced by many factors such as mechanical properties of the aluminum sheet, tooling geometry, contact conditions including the effects of lubrication, and process boundary conditions. These factors are readily handled using the finite element method. A numerical technique for calculating the severity of the redraw wrinkling or wrinkle factor from an LSDYNA finite element analysis is employed. Using this wrinkle factor, and a fully parametric input generator, improvements to the beverage can redraw process are developed. No publisher admin 2009-03-26T11:25:38Z File http://www.dynalook.com/international-conf-2002/Session_15-4.pdf Finite element analysis (FEA) has proven to be a useful tool for stamping process analyses. FEA has also been used increasingly for hydroforming analysis in the industry. In this paper, some examples for various hydroforming process simulations using LS-DYNA are presented. The effects of material characteristics and process parameters on tubular hydroforming are discussed. A sensitivity study has been conducted on a simple geometry. Three steel grades: DS, HSLA and DP, and process parameters such as internal pressure, end feeding and lubricant are included in this study. Simulation results are also compared with experimental data. It is demonstrated that computer simulation can be used as an aid for optimal selection of those parameters to reduce time and cost in tool tryout. In addition, some of the simulation limitations are discussed in this paper. No publisher admin 2009-03-26T11:27:58Z File http://www.dynalook.com/international-conf-2002/Session_15-3.pdf Sheet forming simulations have been shown to have a profound impact on the tool and die industry, but accurate solutions for large panels often require large amounts of CPU time. The development of MPP-DYNA has allowed a large number of CPUs to be applied to a single problem thus reducing total elapsed time. This paper discusses the use of MPP-DYNA for obtaining accurate solutions in small amounts of elapsed time using inexpensive PC-based clusters of computers No publisher admin 2009-03-26T11:33:06Z File http://www.dynalook.com/international-conf-2002/Session_15-2.pdf In sheet-metal-forming the forming limit curve (FLC) is used for ductile sheets to predict fracture in deep drawing. However the use of the FLC is limited to linear strain paths. The initial FLC cannot be used in a complex nonlinear strain history of a deep drawing process or a successive stamp and crash process including a significant change in strain rate. The CRACH software has been developed to predict the forming limit of sheets for nonlinear strain paths [1]. It has been validated to predict instability for bilinear strain paths with static loading in the first path and dynamic loading in the second path for mild steels [2]. As the postprocessing of strain paths from single finite elements in CRACH is not economic for industrial applications MATFEM initiated a project to couple CRACH directly with FEM-Code LS-DYNA using a user- defined material model. This allows a prediction of possible failure during the simulation for all elements with respect to their complete strain history. A special strategy has been developed to include CRACH without extensive increase in total CPU time. The developed interface to LS-DYNA allows also the implementation of other failure criteria demanding the history of deformation like for example a tensorial fracture criterion. In order to test the reliability of the calculated safety factor experimental tests for bilinear strain paths have been simulated [2]. In this case the experimental and numerical investigations have been made on two-stage forming processes (static in the 1st stage and both static/dynamic in the 2nd stage) . The static-static case should simulate a stamping process with bilinear strain path. The static-dynamic case should simulate a successive stamp and crash process. The simulation of a complex deep drawing problem including areas with significantly nonlinear strain paths has been simulated with LS-DYNA/CRACH-coupling. It can be shown that the prediction of CRACH can differ significantely from a “standard” prediction based on the initial FLC. The coupling of LS-DYNA and CRACH showed the potential to predict possible fracture in deep drawing and crash loading at an early design stage and allowed to optimise geometry and material quality to significantly reduce later problems in real components. No publisher admin 2009-03-26T11:33:05Z File http://www.dynalook.com/international-conf-2002/Session_15-1.pdf The purpose of this study is to develop a methodology for springback compensation in sheet metal stamping operations. An optimization method is employed to minimize the difference between the simulation results and the intended design. This procedure results in an optimized die shape. LS-DYNA, LS-OPT and TrueGrid are used to input original tool geometry, material, and process parameters, identify design variables, perform springback simulations, and output optimized tool geometry. It is found that springback trends are consistent with changes in the die shape, which provides an effective strategy for springback compensation. The standard NUMISHEET’96 S-Rail is used as a benchmark example in this study. No publisher admin 2009-03-26T11:33:02Z File