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The understeer of vehicle is desired for the vehicle's handling performance, and the roll rate of rear suspension is one of the key characteristics to achieve the understeer performance. A proper roll rate of the rear suspension is required to assure a certain level of understeer. Generally, in the vehicle dynamic tuning process, several methods are available for improving understeer performance, e.g., changing the hard-points of suspensions, adjusting stiffness of bushings, etc. On the other hand, structure optimization of components can be used in some case to improve the performance. In this paper, the optimization method is applied to the twist beam of rear suspension. The change in local geometry by optimized design leads to appropriate adjustment of the roll rate. Finally the vehicle understeer performance reaches design target.

The design of front rail is very important to vehicle safety performance. The test and CAE analysis are commonly used methods for design on the component level. Based on experience of impact test designed to simulate the performance of rail in vehicle rigid wall frontal impact, an inclined test is designed to simulate the performance of rail in vehicle offset deformable barrier impact. Two LS-DYNA computer simulation models are established including the effects of plastic strain rate, spot-weld failure, and stamping hardening. The deformation and mechanical properties are studied. The simulation results are correlated to the component tests very well in both cases. The usual impact test and inclined impact test for component rail can represent the main features of the rail performances in the vehicle frontal impact and offset impact respectively. Both of the simulation method and the component test method can support the early stage design for vehicle crash safety.

Stiffness is one of the key points for research and development of vehicle body in white (BIW). Fast and effective evaluation of stiffness is very important for reducing the time and cost of research and development. How to realize weight reduction with proper stiffness is also a focus point of automobile design. In general, commercial software is used to optimize the BIW design. But the optimization process is time consuming. Therefore a simple but effective tool for fast evaluation is desired. A method to evaluate stiffness with sensitivity coefficients of sheet metal thickness of body structure is proposed in this paper. The simple mathematical relation of the sensitivity coefficients, the thickness variation of sheet metals, and the stiffness of body structure is established. The stiffness can be evaluated quickly for various combination of sheet metal thickness without running large-scale simulation using commercial software.

The door closing effort is one of the first impressions to customer's mind about the engineering and quality of the vehicle. The door closing force and the minimum door closing speed are two important characteristics for evaluation. But we can obtain these two indices only by experiments and/or subjective assessments. To predict the door closing effort by the simulation method during the design phase, a finite element analysis model is established. The compression load deflection behavior of seals is converted to the parameters of constitutive model of seals by the parameters identification method. Then, the seal resistance force and the minimum door closing speed are calculated. The later correlates very well with the experiment data.

Rubber bushing is an important connection component in vehicle suspensions. It plays an important role in vehicle performance. In the past years, the theories of rubber have been studied, and several forms of the strain energy potential, incompressible or almost incompressible, have been developed. But not all of these models are suitable for all kinds of applications. Therefore, when investigating the rubber bushing, it is necessary to find the effective constitutive equations. Two bushings with different shapes are studied. One is an ax-symmetric uniform bushing. The other one has additional two longitudinal holes. A process of parameter identification is conducted. The axial stiffness and radial stiffness of the bushing are tested and used as objectives. The parameters of constitutive equations are defined as design variables. The nonlinear analysis software ABAQUS and a multi-disciplinary optimization software OPTIMUS are used.

The minimum door closing speed is an important target in vehicle door design. Engineers need a proper method to evaluate the door closing speed during the design phase. Analytical approaches are presented to solve the difficult issues in analyzing the minimum door closing speed. First, the weather strip is simplified into a discrete model with several spring elements. This method does not need to use 3-D contact analysis for the weather strip and can save computing time with acceptable accuracy. Second, the minimum closing speed is solved by using the energy equation which needs one iteration only. The method has high efficiency and can be used to evaluate the door closing speed effectively during the design phase.

Rubber bushing is used in vehicle suspension systems and plays important roles as connection, mounting, or vibration isolation. To study rubber bushings, one method is to acquire parameters of the constitutive models of rubber from tests of material sample, and to obtain stiffness curves by simulation. Generally, the low-cost uni-axial tension or compression test is used for this method. But parameters from these uni-axial tests are not accurate enough and only part of the properties is represented. To get more accurate parameters, other costly tests and special equipments will be needed. Another method is to directly test stiffness of rubber bushing parts in six loading directions. The stiffness can also be approximated by using empirical formulas with dimensions of bushings. This method simplifies the bushing model and is limited. A new approach is proposed in this paper. First, radial and axial stiffness tests of rubber bushing are conducted and stiffness curves are acquired.

To assess the fatigue life of a knuckle more accurately by FEM approach, several types of modeling methodologies, including the component level method, the sub-system level method, and the system level method, used to simulate the knuckle stress/strain distribution are investigated. The simulation results of several load cases by these methods are analyzed. A practical approach for evaluating suspension knuckle at different design phases is proposed, which could be used to guide design and durability evaluation for knuckle.

A design procedure is developed to simulate the durability behavior of an electric wiper linkage mechanism subjected to operation cycles. The first stage determines the stress and strain levels that the linkage components are subjected to during the operation cycles. This requires the reaction loads at the joints of the wiper linkage. It is achieved by performing the mechanism dynamic analysis using multi-body dynamics software (MSC.ADMAS) together with a three dimensional transient finite element analysis (MSC.NASTRAN). Once the stress and strain of the wiper linkages are obtained during the operation cycle, the low cycle fatigue analysis is applied in the time domain. This analysis is based on strain-life curve, the Palmgreen-Miner’s rule, to compute the cumulative damage, the rain flow method for cycles counting, and the mean stress effect. Using the methodology presented in this paper, good correlation with laboratory test can be achieved.

Ten sets of mesh parameters are considered in building the model for aerodynamic numerical simulation of a CHERY sedan. It is found that, in comparison with the wind tunnel test data, the error in drag coefficient computed by using these meshes is less than 4%. Especially, in one case, the error is found within 1%. The CAE method discussed in this paper can be used to assist the design of vehicle aerodynamics.

The Cowper-Symonds constitutive equation is used for simulation of vehicle crash. The effects of strain rate sensitivity to the behavior of vehicle structure in material modeling in the frontal impact are investigated. As an illustrative example, a series of impact analyses of the front rail of a vehicle are carried out. The results show that the energy absorption and the loading capacity of the structure are significantly influenced by strain rate. The effects of strain rate to a full vehicle frontal crash analysis are then investigated. Two analyses are performed with the same FE model. One considers strain rate effect and another without strain rate effect. The results from this study indicate that when incorporating strain rate in the frontal crash analysis, computed crush displacement, velocity, and the deceleration of vehicle are closer to test results than those without strain rate effect.

To have better confidence on CAE prediction of crashworthiness analysis, the process of verification and validation for the explicit finite element method is essential. Selected examples are presented to study the convergence behavior and the quality of the explicit finite element method for transient dynamics. For the axial vibration of a rod, the computed displacement and velocity, and the frequencies calculated by using Fast Fourier Transform achieve the optimal convergence rates when mesh is refined. For a clamped rectangular plate subjected to lateral load, the elastic deflection and rotation calculated by using Reissner-Mindlin plate element, achieve the optimal convergence rates within a range of thickness. For the motion excited by initial velocity, when the thickness is reduced however, the deterioration in convergence of velocity related terms is observed.

In the past twenty years, the explicit finite element method has been successfully employed for crash simulation. At present, crashworthiness analysis is still basically a calibration based engineering practice, but not a fully predictive process. The increasing expectations and requirements on CAE are even more challenging. To develop a predictive and reliable CAE tool, it is important to investigate the root causes that affect the numerical accuracy and the availability of the analytical method. Some of the challenging issues are discussed here from both theoretical and engineering aspects, such as convergence of explicit finite element method, locking-free shell element, analysis of material rupture, and modeling of spot weld.

Crashworthiness analysis involves highly nonlinear transient dynamic problems with large deformation of thin shell structures, elastic-plasticity, surface contact, etc. Accuracy, robustness and efficiency are always the fundamental requirements for engineering applications. Adaptive methods of finite element analysis are considered powerful tools for many engineering applications, to obtain good accuracy efficiently. This paper is to report a preliminary study on the application of h-adaptivity to crashworthiness analysis using LS-DYNA. The performance of the component axial crash simulation using adaptive method is presented with comparisons to uniform refinement. The roles and effects of the control parameters of the software are discussed. It is found that the error indicator based on shell element normal rotation is effective for the solutions of bending dominated crashworthiness applications.

Failure behavior of spot welds is investigated under impact loading conditions. Three different impact speeds were selected to test both HSLA steel and mild steel specimens under combined opening and shear loading conditions. A test fixture was designed and used to obtain the failure loads of spot weld specimens of different thicknesses under a range of combined opening and shear loads with different impact speeds. Accelerometers were installed on the fixtures and the specimens for investigation of the inertia effects. Optical micrographs of the cross sections of failed spot welds were obtained to understand the failure processes in both HSLA steel and mild steel specimens under different combined impact loads. The experimental results indicate that the failure mechanisms of spot welds are very similar for both HSLA steel and mild steel specimens with the same sheet thickness. These micrographs show that the sheet thickness can affect the failure mechanisms.

Failure loads of spot welds are investigated under static and impact loading conditions. A test fixture was designed and used to obtain maximum loads of spot welds under a range of combined opening and shear loads with different loading rates. Optical micrographs of the cross sections of spot welds before and after failure were obtained to understand the failure processes under various loading rates and different combinations of loads. The experimental results indicate that under nearly pure opening loads, the failure occurs along the nugget circumferential boundary. Under combined opening and shear loading conditions, the failure starts from the tensile side of the base metal near the nugget in a necking/shear failure mode. The effects of sheet thickness and combined load on the load carrying behavior of spot welds are investigated under static and impact loading conditions based on the experimental results.

The paper presents a method of analysis based on the theory of damage mechanics to quantify the degree of damage in an engineering structure under load. The method is incorporated into a Ford in-house finite element program called FCRASH that is applied to analyze the cumulative damage in a bumper under multiple low speed impacts. The numerical results calculated at the peak value of the contact force are compared with the test results. The FEA results are used to identify the locations of the hotspot in the bumper system and the predicted location where a potential crack would initiate. The microscopic observations showed damage in the area predicted with the finite element program after the specified number of impacts.