“We used the DIAdem for measurement, evaluation, and automation tasks, and we completed the study efficiently. The program is easy to use, and dialog-based operations can prevent many errors, which saves a lot of time.â€
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challenge:
In the course of pedestrian impact, compared to the safety level of the hoods of aluminum and steel, the two hoods are made according to the special structural requirements related to the deformation characteristics of the head when the pedestrian collides with the vehicle.
solution:
Create an analysis program in NI DIAdem using the integrated scripting language Visual Basic to evaluate head impact effects.
Our research aims to compare the safety of steel and aluminum hoods to pedestrians. The test vehicle's hood does not meet pedestrian safety requirements, which means that the results of comparing steel and aluminum products can be used to evaluate which is more suitable for protecting pedestrian hood materials.
We used a test device for pedestrian head impact protection and created an evaluation program in DIAdem to perform the head impact test. This program processes the acceleration and photosensor signals, calculates the damage according to the standard, and automatically generates the chart. The analysis of head impact is the focus of this test. In this case, the functions of determining the impact velocity, head injury criterion (HIC), and maximum/average acceleration are applied. Test results can be provided in a variety of formats, such as charts and PDFs or files compatible with Microsoft Excel.
In order to develop a front that meets pedestrian safety requirements, we must test a range of accident types and impact locations. Since the test of the whole body dummy requires a lot of time and expense, we have developed a test procedure that conforms to European standards based on the development site, such as the head, pelvis or leg of a pedestrian. We can clearly define test conditions (such as speed and impact angle), so it is easy to run test procedures and analyze test results.
We analyzed the potential relationship between car hood materials and pedestrian protection. The models used were replaced by hood materials in 2002, replacing the original steel with aluminum, while the other designs were unchanged. .
Vehicles produced between 1999 and 2001 have the same engine power and component construction as those produced in 2002 and later, so that the material effects can be compared separately.
We use DIAdem as the measurement and evaluation software and automate the testing tasks using the integrated scripting language Visual Basic.
Structural test of the car hood
Before conducting the pedestrian test, we compared the structural properties of the aluminum and steel hoods. We used the alternate hood for structural testing and still used them in subsequent pedestrian safety tests. We used DIAdem to evaluate the results and then compare them with the results of the original hood that passed the hood benchmark. These test results show the difference between the aluminum and steel hoods and the difference in structural stiffness between the original and the spare parts (bake hardening treatment). The results of the lateral stiffness and torsional stiffness of the mass produced steel and aluminum hoods and associated spare parts are shown in Figures 1 and 2.
A comparison of the hood materials shows that the steel hood is stiffer than aluminum. The following ratios represent the performance of the steel hood over the aluminum hood under test load:
• Lateral stiffness +46%
• Vertical stiffness +53%
• Torsional stiffness +42%
We must also consider that the aluminum hood is 47% lighter than steel. The comparison between the original parts and the spare parts indicates that there is no significant difference in structural stiffness. Although the elastic deformation test does not provide any accurate information about the hardening effect in dynamic tests with high plastic deformation (such as head impact), we can perform pedestrian impact tests on the alternate hood and fender.
Head impact test
The test setup is shown in Figure 3. We use servo hydraulic test equipment for testing. During the test, the pedestrian protection test equipment was positioned at the point of impact at the required angle and the impactor was mounted at the end of the piston. The piston accelerates the head to the desired speed of 40 km/h and then releases the head so that it moves freely against the hood.
For both hood types, we performed 9 trials using an adult head impactor and 9 trials using a child head impactor for a total of 36 tests. The test results we recorded included HIC values, time intervals for calculating HIC values ​​(a3ms, amax), high-speed recordings, and digital photos of hood deformation. We used video sequences for detailed analysis to analyze the maximum hood deformation behavior of 3ms and the main (head-to-hood) and secondary (hood-to-underground) impacts.
We place a three-dimensional accelerometer in the center of each impactor. Figure 4 shows an example where we use DIAdem for automated test evaluation.
DIAdem can evaluate a single or a series of test values. Figure 5 shows an example of how the user enters the measurement file to be evaluated and the variables that need to be calculated in the user dialog. We use the script definition dialog created in DIAdem.
We also use DIAdem to verify the specified impact speed. The photosensor records the acceleration of the impactor on the piston. The reflective film mounted on the piston reflects the laser light. This reflective film has a specified light-dark transition grid. Use another Visual Basic displacement-time curve calculation script to analyze the recorded rectangular signal. The above calculation determines the time interval between the peak of the rectangular signal and two consecutive equal values. We can use the distance specified between the light and dark transitions to determine the speed.
The user enters the shaded grid and other variables in the user dialog at the beginning of the program. This provides the flexibility needed to use different test types, but essentially the same calculation method is always performed. This saves time and guarantees a high degree of consistency because the user does not need to adjust the variables within the script.
Evaluation of 36 tests performed on the hood of the car showed that in 13 of the 18 cases, the steel hood had a lower impact on the head. When analyzing the results, it must be taken into account that most of the results of the materials of the two hoods greatly exceed the biomechanical safety limit (HIC1000).
The secondary collision of the underlying vehicle structure causes the HIC value to greatly exceed the safety limit. The deformation displacement (5 to 20 mm) between the metal and the underlying structure inside the hood, especially the displacement around the spring-loaded strut and the hood hinge is particularly short. The high stiffness of the components affected by this creates huge acceleration peaks and HIC values.
The effects of the secondary collision were analyzed by the acceleration curve and HIC in Fig. 6, and the two points were selected as an example of the comparison between steel and aluminum. During the impact of the Ch-M-2 point, no significant impact occurred on the underlying structure. The resulting acceleration curve leads to the following results:
• Aluminum version of HIC calculation requires a larger window
• Steel plate acceleration produces greater peaks
• Aluminum version produces 15% to 20% deformation displacement
• Steel plate produces higher HIC values
During the impact of the Ch-M-3 point, the underlying structure produced a strong secondary collision, resulting in the following results:
• The calculated window of HIC is almost equal because the acceleration curve is essentially affected by the impact of the underlying structure.
• The first acceleration peak of the steel plate is slightly higher
• Aluminum plate has a higher secondary acceleration peak
• Aluminum version has a higher HIC value
to sum up
This result refutes the widely accepted view that aluminum hoods generally provide better protection for pedestrians. The results of the head impact test showed that in 13 of the 18 cases, the steel hood had a lower impact on the head.
By using DIAdem for measurement tasks, assessment tasks, and automated tasks, we completed the study efficiently and effectively. User-friendly dialogs prevent errors and allow you to choose to analyze the results of all test series, which further saves time. The evaluation data can be displayed in charts, PDF format, or in Excel format, which will help with the follow-up work.
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