Research on car test dummy skin materialRelease time: 2015-08-15 08:49
"Car crash safety performance test" is one of the most popular car test projects. With the rapid growth in the production and sales of passenger cars in China, the safety of automobiles has also received increasing attention from consumers. Car crash test dummy (vehicle safety dummy) is an indispensable basic test equipment for automobile crash safety performance test. The data obtained from the dummy can predict the risk of passenger injury in the actual collision. The more realistic the dummy simulation is, the more accurate the test results will be. Knowing the impact of the vehicle itself, the safety system, and the passengers in a collision, can continuously improve the safety performance of the product. Therefore, to implement China's New Car Safety Evaluation Regulations (C-NCAP), it is necessary to have China's own test dummy for vehicle crash testing [1-2].
The car crash test dummy is a human body model filled with various sensors in a body that realizes the similarity of external shapes, the equivalent of material organization, and the simulation of internal structure. The “skin” of a car crash test dummy is a bionic skin-muscle composite material. As the first line of defense for a car crash test dummy, its mechanical properties such as elasticity, hardness, and rebound properties will directly affect the impact energy of the car crash test. Attenuation, transfer, and deposition. The rebound performance and damage factors of the bionic material will affect the acceleration of the impact response and the time of the impact load, so that the amplitude and phase lag of the signal obtained by the sensor in the dummy will affect the scientificity of the human damage assessment of the car crash test. And accuracy. Due to the particularity of bionic skin materials for car crash test dummy, mechanical parameters such as hardness, strength and elastic modulus of bionic materials are characterized by a single Shore hardness index. The method of testing the mechanical properties of plastic rubber non-metal solid materials is not comprehensive. To evaluate the mechanical properties of the bionic material, the "skin" material of the car crash test dummy is required to be able to resist not only the damage of the impact shock, but also the shock wave information to be embedded in the sensor. Aiming at the particularity of the bionic skin material of the car crash test dummy, the impact test method was used to collect the impact information, and the shock wave spectrum and shock wave impedance analysis were performed, so as to analyze the mechanical characteristics and impact strength of the bionic skin material structure of the car crash test dummy. Comprehensive evaluation of the equivalence has a very important guiding role in providing data analysis and theoretical basis for the design, synthesis, and preparation of bionic skin materials simulated in car crash tests.
1. Establishment of impact model The impact process of a dummy during a car crash test is transient and has a short duration, which is a sudden, violent energy release, energy transfer, and conversion process. Taking the dummy as a test system, the motion generated under the impact is transient, and the motion state is related to the duration of the impact and the natural cycle of the system. From the perspective of theoretical analysis, the shock motion is the response of the system to a transient impulse, step or other transient non-periodic excitation. The system vibration caused by shock response can disappear quickly, but the maximum stress (or displacement) caused by it may damage the system [3-5]. The impact dynamics process is a series of dynamic processes that change with time. A simplified impact model is established as shown in Figure 1: m1 hits m2 at a certain initial speed, and the human skin is simplified into an elastic element k during a car crash test. Assuming that the stiffness coefficient of the elastic material is k and the impact velocity of m1 is v0, the equation of motion can be obtained:
a, x reflects the peak value and pulse width of the positive wave at impact; vp is 1/2 of the maximum speed at impact. When the mass and impact velocity of the impact hammer are constant, the pulse width is related to the stiffness coefficient k of the elastic material. Therefore, by testing the impact waveform, collecting impact information, and analyzing the impact spectrum and impact impedance of the shock wave, the bionic skin material for the car crash test dummy The mechanical properties of the structure and the equivalence of impact strength were comprehensively evaluated.
2 Impact test analysis
2.1 The mechanical properties of the bionic skin material established by the impact test largely determine the advantages and disadvantages of the material in practical application. Due to the difference in the amount of curing agent and filler in the preparation and the post-cure time, it will affect the bionic skin material. Mechanical properties. In order to prepare biomimetic skin with excellent comprehensive performance, and to correctly understand and master the influence of these factors, the test samples were selected from 4 materials with different formulations and preparation times (recorded as test piece 1, test piece 2, test piece 3 and Test piece 4), test with equal volume, the sample diameter of the test piece is 60 mm and the thickness is 15 mm. The principle of the impact test is shown in Figure 2. The vertical impact method is used. The mass of the hammer is 150 g, the height between the working surface of the hammer and the sample is 200 mm, the impact hammer is released, and the impact table (test piece) is hit at a speed of v = 6 m / s. Record shock wave peaks and conducted wave spectra for analysis.
2.2 Analysis of experimental data Figure 3 (a to d) shows the shock wave and conduction wave spectra of the four test pieces. (The upper picture is the shock wave spectrum and the lower picture is the conductive wave spectrum). From the figure, it can be seen that: (a) the test sample The conducted wave of Figure 1 oscillates; (b) the shock wave and conducted wave spectrum of Figure 2 is ideal; (c) the specimen 3 of the conducted wave is a material damage phenomenon; (d) the specimen 4 reflects the impact of the shock wave. The elastic stiffness of the test material is too strong,
The impedance of the conducted wave is large.
Figure 4 shows the stress of the test specimen under impact. Available in the figure
It can be seen that the pulse width and pulse width of the 43 materials of test piece 1, test piece 2 and test piece are 0.5 ms, but the test piece 2 has a larger stress when it is impacted, responds quickly, and has a strong transmitted wave signal. Test pieces 1 and 4 are subject to The stress during shock is basically the same, and the transmitted shock wave signal is weak.
From the analysis of test data, it can be known that the length of the post-cure time has a great impact on the material properties. Too long or too short will not make the material have better elastic properties. The post-cure time of test piece 2 is 5 h. The mechanical properties of the bionic skin material are better; when the amount of filler is 5 parts, the bionic skin material has a very obvious reinforcing effect; test pieces 1 and 4 with the increase of the amount of curing agent, the strength of the material increases, and the transmission wave The impedance also increases, and the impact performance of the bionic skin material decreases. Therefore, the amount of curing agent ethyl silicate has a significant effect on the properties of bionic skin materials.
3 Conclusions The requirement for the bionic skin material of the car crash test dummy is that it can not only resist the damage of the impact impact, but also transmit the shock wave information to the sensor embedded in the test simulation person. The impact test method is used to collect shock wave spectrum and shock wave transmission information. It is feasible to perform shock wave spectrum and shock wave conduction impedance analysis on the car skin test simulation human "skin" material, which can bionic skin material structure of car crash test dummy The mechanical properties and the equivalence of impact strength were comprehensively evaluated. The impact performance analysis data of car crash test dummy bionic skin material provides data analysis and theoretical basis for the design, synthesis and preparation of bionic skin material.
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