Corresponding Author:
Dr Yasuhiro Matsui, Japan Automobile Rearch Institute 2530 Karima, Tsukuba, Ibaraki 305-0822, Japan Tel +81-29-856-0885 Fax +81-29-856-1121Email: jp
INTRODUCTION
Pedestrian protection is one of the critical issues for vehicle safety legislation in Europe and Japan. As leg injuries are the most common injuries in nonfatal pedestrian accidents [1], the European Enhanced Vehicle-safety Committee (EEVC)/WG17 [2] propod a test method to evaluate bumper aggressiveness by means of a legform impactor.This test procedure proposal introduces a subsystem test
method in which the legform impactor is propelled into a stationary vehicle. Prently, only the legform impactor with a rigid leg and thigh designed by the Transport Rearch Laboratory (TRL) in 2000 [3] is approved by the EEVC/WG17. The legform impactor consists of an upper leg ction, a lower leg ction, a pair of steel knees covered by foam and a skin as shown in Figure 1. The length of the legform impactor is 926 mm and the mass is 13.4 ± 0.2 kg. The foam ud is 25 mm thick confor foam TM type CF-45, while the skin is made of 6 mm thick neoprene. An uniaxial accelerometer is mounted
欧美健身美女on the non-impacted side of the lower leg ction, 66 mm below the knee joint centre (Figure 1), to measure the lower leg acceleration typically shown in Figure 2. The Factor causing scatter in dynamic certification test results for compliance with EEVC WG17legform impactor standard
Y Matsui a,* and M Takabayashi a
a
Japan Automobile Rearch Institute, 2530 Karima, Tsukuba, Ibaraki 305-0822, Japan
Abstract: A pedestrian legform impactor is a tool for the evaluation of car front bumper aggressiveness when simulating a pedestrian leg hit by a car. The Transport Rearch Laboratory (TRL) developed a legform impactor in compliance with the European Enhanced Vehicle-safety Committee (EEVC)/WG17 specifications. The Commission of the European Communities (EC) propod a dynamic certification test for a legform impactor, however, the test results using the TRL legform impactors manufactured to date have indicated an extremely wide scatter, especially in the maximum lower leg acceleration. Thus, the objectives of the prent rearch are to clarify the factor possibly causing this scatter in the lower leg acceleration of the TRL legform impactor in the tup of the dynamic certification test, and to propo a way to adjust lower leg acceleration so as to comply
with the corridor propod by the EC.
The repeatability and reproducibility of the legform impactor products and different impact points of the ram in the tup for the dynamic certification test were thus investigated. High repeatability and reproducibility of the legform impactor products were obrved. No difference was obrved in the effect of different ram points of impact against a stationary legform impactor on the maximum lower leg acceleration. On the other hand, the lower leg acceleration was found to be greatly affected by humidity in the test apparatus. Therefore, the effect of humidity on the dynamic certification test tup was also investigated. The results indicated that the maximum lower leg acceleration incread drastically with higher humidity. Next, the relation between humidity and acceleration measured by a ram impacting a piece of confor TM foam was investigated using a simplified test rig, since such foam sheathes the metal part of the legform impactor in a dynamic certification test tup. A strong relation between the humidity and acceleration was found. Thus concluded that humidity is a key factor affecting lower leg acceleration, and that adjusting it will be one of the many ways the lower leg acceleration can be made to comply with the propod EC corridor in the dynamic certification test.Key words: EEVC/WG17 Dynamic Certification T est, TRL legform impactor, Lower leg acceleration,Humidity, Scatter, Confor TM Foam
Y Matsui and M Takabayashi
legform impactor is equipped to measure the shear displacement and bending angle between the upper and lower leg at the knee joint level. The lower leg acceleration is ud to evaluate tibia fracture risk, and the shear displacement and bending angle are ud to evaluate cruciate and collateral ligaments injury risks, respectively.The EEVC/WG17 propod injury reference values for tho criteria under the assumption that the impactor respons exactly reprent the human ones. However,Matsui [4] reported that the impact respons of the legform impactor appreciably differ fro
m tho of the human lower extremity . Therefore, in his report [4], cruciate ligament injury risk curves for the legform impactor shearing displacement were found using the injury tolerances of post mortem human subjects (PMHSs) taking into account the difference between the PMHS and the
legform impactor respons. Furthermore, Matsui [5]reported that the collateral ligament injury risk curves and tibia fracture risk curves for the legform impactor were determined bad on the experimental results in which pedestrian lower extremities of car–pedestrian accidents were reconstructed by means of the legform impactor.
Since it is important to make test tools repeatable in order to achieve uniform standards, the EEVC/WG17propod a dynamic certification test simulating high–speed impact between the legform impactor lower leg and a bumper. In the dynamic certification test tup (Figure 3), the asmbled legform impactor (Figure 1 (3)) is impacted by a linearly guided ram at 7.5 ± 0.1 m/s. The EEVC/WG17 initially propod the mass of the ram to be 16 kg, but this caud excessive crushing of the confor TM
Skin
Upper leg ction
Damper
Pair of steel knees
运动风格Confor™foam
Lower leg
ction
Lower leg ction Figure 1
TRL legform impactor compliance with EEVC/WG17 specifications.
中搜A c c e l e r a t i o n (g )
300
250
200
150
100
50
韩愈师说Legforms
109
876
54
寒假见闻600字3
210
S h e a r (m m )/K n e e a n g l e (°)
Figure 2 Dynamic certification results of the 35 TRL legform impactors produced between September 2000and May 2002, obtained using modified EEVC/WG17 method but with reduced mass of ram (9 kg) [4].
(a) Dimensions
(b) Disasmbled view
(c) Asmbled view
Factor causing scatter in dynamic certification test results for compliance with EEVC WG17 legform impactor standard
foam [6]. Therefore, Lawrence and Hardy went to propo a ram mass of 9 kg [6], that was approved by the Commission of the European Communities (EC) for dynamic certification test [7].
The EC also approved a corridor in terms of maximum lower leg acceleration to be between 120 G and 250 G. In addition, the maximum shear displacement was specified to be between 3.5 mm to 6 mm, while maximum bending angle to be between 6.2° and 8.2° [7]. However, the dynamic certification test results of the 35 TRL legform impactors produced between September 2000 and May 2002 indicated extremely wide scatter, especially in the maximum lower leg acceleration as shown in Figure 2, where the mean and Standard Deviation of the acceleration were 170 G and 41 G, respectively [6]. Some of the legform impactors did not comply with the propod EC corridor. In bumper evaluation testing, a grave problem aro where the u of legform impactors did not compl
y with the specified corridor for dynamic certification.
Thus, the objectives of the prent rearch are to clarify the factor causing the wide scatter in lower leg acceleration of the TRL legform impactor in the dynamic certification test tup, and to propo a way to adjust lower leg acceleration so as to comply with the corridor propod by the EC.
METHOD AND TEST SETUP
Verification of factors affecting lower leg acceleration for dynamic certification test
Factors causing the scatter in lower leg acceleration in a dynamic certification test are considered to be repeatability,reproducibility, and impact position. I n this Section,investigations are carried out in determining the influence of this scatter caud by the above factors in actual dynamic certification tests. In addition the effect of humidity on test measuring equipment was also monitored by keeping
the temperature to 20 ± 1°C, which is within the specified test temperature of 20 ± 2°C.
Repeatability of lower leg acceleration for dynamic certification tests
The asmbled legform impactor, including the foam covering and skin, was suspended horizontally by three wire ropes 2.1 m in length as shown in Figures 3 and 4.The legform impactor was suspended with its longitudinal axis horizontal and perpendicular to the direction of the ram motion. The mass of the ram was 9.0 kg and was made of aluminum. T o propel the ram, a guidance system was utilized to prevent out of plane motions. The ram was propelled horizontally at a velocity of 7.5 ± 0.1 m/s into the stationary legform impactor and was arranged so as to impact a position 50 mm fro
m the knee centre toward the lower leg side (Figure 3 (2)) within a tolerance of 0.5mm. Foam and pairs of steel knees were replaced for each test. Lower leg accelerations were measured and data processing was done using filter class SAE 180. The repeatability investigations of the lower leg acceleration measurements were performed three times per one calendar
month over two different months.
Suspension wires
Figure 3 Test tup for dynamic certification.
吃阿胶糕的禁忌
终极病毒(1) Side view
(2) View from top
Figure 4 Test tup for dynamic certification.
Y Matsui and M Takabayashi
Reproducibility of lower leg acceleration for dynamic certification tests
During the period between September 2000 and 2002,
TRL sold approximately 35 legform impactors. Four of
the were ud in the reproducibility investigations. Each
legform impactor was impacted three times using the same
tup mentioned in Section 1.1, and lower leg acceleration
was measured.
Effect of different impact points in vertical direction on lower leg acceleration
In the dynamic certification test procedure propod by
the EC, the propelling direction of the ram was arranged
814海战
so that the centre of the ram would align with a position
50 mm from the knee centre-line, that has a tolerance of ±3 mm laterally and ±3 mm vertically. Since the shape of the ram contact area is elliptical as shown in Figure 5,
when the ram centre impact position is not in line with
the cross ction of the legform impactor direction, the
direction of the force exerted by the ram on the legform
impactor will not be uni-directionally applied in the
horizontal plane. Therefore, the impactor position was
arranged so as to impact the legform impactor at zero, 3
mm and 10 mm (Figure 6). To check repeatability, the
tests were carried out three times in all the three cas
and acceleration data recorded for analysis.
Effect of relative humidity on lower leg acceleration in dynamic certification test
Bad on the results obtained through preliminary investigations in Section 1.1, the maximum lower l
eg acceleration varied with the time of the month in which the test was conducted. In Japan, the relative humidity varies widely throughout the year. Therefore, the prent investigators focud on a further possibility that the relative humidity could affect the results of maximum lower leg acceleration in the dynamic certification test. I n this Section, the dynamic certification tests were conducted under 4 different relative humidity conditions; 18%, 31%, 46% and 63%. The temperature was controlled at 20 ±1°C. I n a given relative humidity condition, dynamic certification tests were performed three times, and the lower leg acceleration was then measured.
Effect of relative humidity on ram acceleration in impact against confor TM foam
Bad on the results obtained through preliminary investigations in Section 2, the lower leg acceleration was strongly affected by humidity. Since confor TM foam was utilized to sheathe the metal part of the legform impactor, in this Section investigations are carried out in determining the relationship of relative humidity and acceleration measured by a ram impacting a piece of foam using a simplified test rig (hereafter referred to as the drop test tup). To perform the test, it is necessary to pre–soak a specimen of confor TM foam to a given relative humidity.The volume of water in the test foam depends on the soak time. T o investigate a suitable soak time for the test foam using a drop test tup, first, the relation of the mass of the test piece and soak time was deter
mined at a given relative humidity (RH).
Relation of mass of confor TM foam specimen and soak time The relation of the mass of the foam specimen and soak time at a given relative humidity (RH) was investigated using the tup shown in Figure 7. A piece of the confor TM foam specimen measured 300 × 300 × 25 mm using a digital scale with an accuracy of 0.01 g. The specimen mass was 212.55 g in the initial condition at RH35.7%. The foam specimen soaked at RH35.7% was placed within the enclod micro-climate chamber, in which the humidity was kept at the following three virtually uniform levels: RH42%, RH60% and RH87%. The mass of the specimen and the RH were measured every minute for 50 minutes in the tup. The temperature was also controlled at 20 ± 1°C.
Relation of relative humidity and maximum ram acceleration in impact against confor TM foam specimen soaked at different humidity
The drop test was performed within the enclod micro-climate chamber, in which the humidity can be controlled at stable temperatures (Figure 8). The spherical core part of the JAMA-JARI child headform impactor [8] was utilized as a ram (hereafter referred to as the ram) in the
drop test tup. Near the geometric centre of this sphere Figure 5 View of ram from front.
Factor causing scatter in dynamic certification test results for compliance with EEVC WG17 legform impactor standard
Center of
legform
impactor
3 mm or 10 mm.
Figure 6 Test tup of dynamic certification to investigate effect of impact
location on lower leg acceleration (side view).
ram, three accelerometers were installed to measure acceleration in the respective direction of the ram’s three cartesian axes [8]. The mass of the ram was 2.724 kg and was dropped from a height of 1150 mm in such a way as to ensure instant relea onto the confor TM foam specimen placed on the rigid supporting flat horizontal steel plate (50 mm thick and 600 mm × 600 mm square), Figure 9. The impact location of the centre of the ram was arranged
