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Simulation of windshield and the influence of A-pillar on vehicle offset crash performance

Abstract: This paper applies the relevant regulations of frontal 40% overlapping deformable barrier collision of C-NCAP to simulate and test a car. Through the comparison and analysis between the simulation model and the test, it is found that the A-pillar has obvious deformation in the test, but this deformation does not occur in the finite element model. Through the analysis of the finite element model, the distortion of the windshield material parameters is the main reason for the undistorted A-pillar of the simulation model. Therefore, the parameters are optimized according to the test results. Based on the optimized finite element model with higher simulation accuracy, the deformation of A-pillar is improved. Through simulation calculation and analysis, it is proved that the problem of A-pillar deformation has been solved, and the safety performance of the whole vehicle has been greatly improved. Then the feasibility of the scheme and the reliability of the simulation model are verified in the experiment

Keywords: windshield, A-pillar, offset collision, finite element analysis, benchmarking, HyperMesh

1 Introduction

with the rapid development of the automotive industry and its demand in China, road traffic accidents are also on the rise year by year. Therefore, the safety performance of vehicles is becoming increasingly important. According to the requirements of frontal 40% overlapping deformable barrier (hereinafter referred to as ODB) collision in the new car star rating procedure (C-NCAP) issued by China, CAE technology will be applied in the vehicle development to simulate the vehicle, so as to reduce the cost and shorten the cycle. CAE technology has gradually replaced some crash tests in vehicle development. However, CAE technology also has its limitations. Especially in the process of vehicle collision, some parts failure problems will bring some difficulties in the simulation, and some failure problems can not be foreseen before the test. Therefore, the comparison between test results and CAE simulation results (hereinafter referred to as benchmarking) is particularly important

through benchmarking analysis, the finite element model can be optimized. The simulation results are closer to the actual situation, and the calculation results have higher accuracy. Based on the benchmarked finite element model, the exposed problems can be improved to solve practical problems more effectively. This paper will elaborate the whole process of how to find problems in simulation and how to apply simulation technology to solve problems. How to improve the safety performance of 40% ODB collision is also discussed

2 collision analysis model

this analysis model uses HyperMesh as the pre-processing software to model the CAD geometric model. The explicit algorithm of radioss is applied to solve the model. Hyperview is used as post-processing software to visualize and analyze the results. The analysis model includes: body in white, closure parts, chassis system, cooling system, powertrain, front 40% overlap deformable barrier, seat, ground and other parts

Figure 1 Schematic diagram of finite element model of whole vehicle and barrier

as shown in Figure 1, it is the finite element model of the whole collision analysis. This model has 1.45 million units and 1.16 million nodes. The average size of the collision sensitive area unit is 3.5mm, the glass area is 15mm, and the other areas are mm. The important parts of the collision are mapped with stamping information. In order to improve the analysis accuracy, the materials of sheet metal parts are the stress-strain curves under multiple strain rates obtained from the material tensile test. The boundary conditions are set in full accordance with the requirements of C-NCAP: the overlap width between the left side of the vehicle and the ODB is 40% of the vehicle width (the vehicle width refers to the widest point on the left and right of the vehicle, excluding the rearview mirror, side marker lamp, tire pressure gauge, side turn signal lamp, clearance lamp, flexible fender, and the deformed part of the side wall where the tire contacts the ground), the lowest point of the deformable barrier is 200mm above the ground, and the collision speed of the whole vehicle is 56 km/h. The barrier is 1000mm long, 540mm wide and 650mm high. It is a standard frontal 40%odb finite element model

3 benchmarking analysis and windshield material parameter optimization

the test and simulation conditions are completely in accordance with the requirements of C-NCAP, and the whole vehicle impacts 40% overlapping deformable barrier at 56 km/h. By observing the test results, it is found that the deformation mode of A-pillar in the test is very different from the CAE results. However, except for the deformation of A-pillar, the deformation mode of other important energy absorbing components such as longitudinal beam is in good agreement with the test. According to the analysis, the reason why the A-pillar cannot be deformed is likely to be the main drawback of these two transmission modes: the former requires regular lubrication because the modeling and testing of components near the A-pillar are different; Or the material is too strong, so that the A-pillar cannot be deformed as the test. According to the analysis idea, check the material parameters of the components near the A-pillar one by one. Finally, it was found that the stiffness of the A-pillar and the side plate of the cowl panel was greatly improved due to the unreasonable setting of the material strength of the windshield, resulting in no deformation of the A-pillar. After readjusting the yield strength of the windshield and adding strain failure, the CAE results are in good agreement with the test

Figure 2 deformation form of A-pillar before and after optimizing glass material parameters

as shown in Figure 2, the left side is the simulation result of glass parameter distortion, and the right side is the policy result after optimizing glass parameters. In the 40%odb collision, the intrusion amount of the cowl panel is one of the important standards to measure the safety performance. After the material parameters of the glass are improved, the A-pillar in the finite element model is deformed, resulting in an increase in the intrusion of the cowl panel. Among them, the upper edge intrusion of the cowl panel increased by 366% (dynamic value), and the dynamic maximum intrusion of the whole cowl panel increased by 26.3%. It can be seen that the distortion of glass parameters masks the truth of excessive intrusion, and also brings hidden dangers to safety. After completing the benchmarking work, based on the optimized model, a series of analysis is carried out for the deformation of A-pillar, and some solutions are put forward. This will be elaborated in the next section

in the process of CAE simulation, the accuracy of material parameters plays a vital role in whether the simulation is true. The deviation of material parameters will cover up some important potential safety hazards in the actual collision. In particular, the material parameters of glass are often ignored. Therefore, benchmarking analysis and model optimization is particularly important

4 structural optimization scheme and simulation verification analysis

according to the simulation results after benchmarking, there are two main deformations. First, it is the upper part of the A-pillar, close to the top cover; The second is the lower part of the A-pillar and the side plate of the cowl panel. Therefore, for these two deformations, further analysis is carried out. By analyzing the transmission path of force, and considering the cost and operability, two sets of optimization schemes are proposed

a. add stiffeners at the connection between the A-pillar inner plate and the top cover longitudinal beam to solve the deformation problem of the upper part of the A-pillar. At the same time, add reinforcement at the side plate of the cowl panel

b. extend the inner plate of the A-pillar to solve the deformation problem of the upper part of the A-pillar. At the same time, add reinforcement at the side plate of the cowl panel

Figure 3. The deformation form of A-pillar in schemes a and B

after simulation calculation, as shown in Figure 3, scheme a strengthens the A-pillar more effectively than scheme B. By comparing the change angle of column a, it can be seen that scheme a is also better than scheme B. From the perspective of the opening of the front door, scheme a is also significantly better than scheme B. That is to add stiffeners at two places with serious deformation, which more effectively solves the problem of A-pillar deformation. In addition, the intrusion of the cowl panel and the acceleration of the lower part of the left B-pillar have also been significantly improved. As shown in Figure 4, the maximum value of dynamic intrusion of baseline (initial model) appears in the upper left corner. Due to the excessive deformation of the lower part of the A-pillar, the trend of increasing intrusion is not well prevented, which is also called impact toughness test. It can be seen from the distribution area of intrusion volume in the figure that scheme a and scheme B are better than baseline. This conclusion can also be drawn from the deformation. According to the comparison of the dynamic value of intrusion, it is found that the model with stiffeners is 28% better than the previous one, that is, the intrusion is reduced by 28%. In terms of scheme a and scheme B, the intrusion volume of scheme a is 7% less than that of scheme B

Figure 4 initial model (baseline), scheme a and scheme B cowl panel intrusion and deformation

Figure 5 shows the deceleration curve of the lower end of the left B-pillar in baseline, scheme a and scheme B. It can be seen from the figure that the three curves are almost the same in the previous period, which indicates that the collision deformation of the front of the car body and the barrier is basically the same. The main changes of the curve occur in the middle period of time. Schemes a and B are slightly different from baseline in phase, and the peak and trough appear later than baseline. It can be seen that the A-pillar reinforcement plays a certain role. It can be seen from the maximum deceleration that scheme a is significantly better than scheme B and baseline, and the deceleration is reduced by 5%. The A-pillar in scheme B and baseline finally has different degrees of deformation. Because scheme a is not only better than scheme B in terms of intrusion volume, but also less than scheme B in terms of peak deceleration. Therefore, scheme a is finally selected for implementation

Figure 5. The deceleration waveforms of the initial model (baseline), scheme a and scheme B

5 try to verify the feasibility of the scheme and the reliability of the model

after simulation analysis, scheme a is determined to be the final scheme. According to this scheme, the CAD data of the sample vehicle is determined. Considering other problems such as technology, the specific design of reinforcement and hole digging is carried out without changing the general shape. The finite element model is used to verify that the modification will not affect the deformation and safety performance of the A-pillar. Then, in the 40% offset crash test of the sample vehicle, the deformation of the A-pillar was satisfactorily solved. The reliability of the finite element simulation model is verified. The simulation analysis not only solves the practical problems, but also completely predicts the test results. The deceleration waveform at the lower left of the B-pillar is in good agreement with the test. The intrusion amount of the cowl panel is also quite close to the test. The error of most measuring points (including important areas) is within 5mm, and the error of a few points is within mm

6 conclusion

according to the regulation of frontal 40% overlap deformable barrier collision at 56 km/h, this paper simulates and analyzes the safety performance of vehicle collision by using CAE simulation technology. In the process of benchmarking, the distortion of glass data in the previous finite element model was found through the analysis and research of the deformation causes of A-pillar. In the finite element model of vehicle collision, the simulation of glass materials is often ignored. However, whether the glass simulation is true or not sometimes directly affects the collision performance of the finite element model, especially in the offset collision, which also makes the sample slip significantly in the process of the experiment. This also shows the importance of benchmarking. To push CAE technology to a higher level, we must closely and reasonably combine this technology with experiments. After benchmarking and optimization, the finite element model will have higher reliability. At the same time, it also laid a solid and reliable foundation for CAE simulation technology to guide designers to design

based on the more reliable finite element model after benchmarking, the deformation of A-pillar is improved. Through simulation analysis and verification, the scheme of adding stiffeners to the A-pillar is adopted, which we are optimistic about the development prospect of Xinjiang Zhonghe. This scheme not only improves the deformation of A-pillar, but also greatly improves the safety performance of the whole vehicle. The test results proved the reliability and predictability of the finite element model. This paper proves once again the importance of CAE Technology in product development

7 references

[1] C-NCAP (China new car evaluation procedure) management regulations (2009 Edition) (end)