THE BIOFIDELITY OF HYBRID III DUMMIES

Transcription

1 THE BIOFIDELITY OF HYBRID III DUMMIES Dimitrios Kallieris, Andreas Rizzetti, Rainer Mattern Institute of Legal Medicine University of Heidelberg ABSTRACT The Hybrid III dummy is the test device used to ascertain compliance with the dynamic crash test requirements of FMVSS 28. lnjury criteria derived from measurements at designated regions of the dummy body must be met and therefore the Hybrid III must display satisfactory biofidelity. In order to investigate biofidelity, crash simulations were performed using human cadavers and Hybrid III dummies. Frontal collisions were simulated at an impact velocity of 5 km/h and a mean car deceleration of between 4 and 6 g. The surrogates were protected with either a 3- point belt or an air bag - knee bolster system. Two belt systems of different stiffnesses were used, i.e 6% and 6% elongation. Assessment of Hybrid III biofidelity was based on the kinematic behaviour and thoracic responses. In the 3-point belt tests, head-neck flexion of the two test subject groups differed in magnitude and phase. Greater flexion was observed with the cadavers compared to the dummy and maximum Hybrid III neck flexion occurr ed earlier. With both 3-point belts, 6% and 6% elongation, the Hybrid III experienced higher acceleration maxima and 3ms values at the sternum (in x- direction) and at Th (resultant). The resultant acceleration at Th 2 was in agreement with the cadaver. X-direction rib accelerations were measured at the medium axillar line of the 8th rib (left and right) in cadavers and 5th rib (left and right) in dummies, and did not show clear differences between the two test subject groups. Thoracic contours and deflections in the horizontal plane were measured with ehest bands. lnter-subject and inter-test variability was observed for thoracic contours and deformations. Chest deflection was generally lower for the dummy than for the cadaver. The results show that in frontal collision simulations the biofidelity of the dummy neck and thorax should be improved to allow for more valid assessment of occupant protection criteria

2 DUMMIES ARE USED as test devices to ascertain compliance with dynamic crash test requirements of FMVSS 28 for frontal impact protection and the FMVSS 24 for side impact protection. In these tests the biofidelity of the prescribed dummies is assumed to be appropriate. At the University of Heidelberg, Institute for Legal Medicine, a large number of human cadaver tests have been performed during the last 2 years. The authors have investigated the biofidelity of side impact dummies (Klaus et al 984 and Kallieris et al 992), and in the 9SOs frontal collision simulations using cadavers and Hybrid II dummies were performed to investigate dummy biofidelity. During frontal collisions at an impact velocity of 5 km/h and a car deceleration of 2 g with belt restrained Hybrid II dummy and cadaver occupants, it was observed that the neck bending angle of the cadaver was clearly greater than the dummy and the maximum angle occurred earlier with the dummy. In the 99s Hybrid III dummies have been tested and used in controlled collisions. The results of padded and rigid Hybrid III dummy and cadaver head impacts at between 2 and 22 km/h were similar to the Hybrid II tests. lt was observed that the maximum cadaver head/neck extension was about 3 % greater than Hybrid III extension. The maximum bending angle occurred earlier with the dummy than the cadaver. The same observations were made for rearend collisions at an impact velocity of 25 km/h. The aim of the paper is to investigate Hybrid III dummy biofidelity, focussing on the.kinematic responses and ehest deflections in identical frontal crash sim ulations. METHODS Test subjects The test subjects were unembalmed human cadavers and Hybrid III dummies. Six cadaver and 5 dummy tests were performed. The most important anthropometric data of the test subjects are shown in table. The cadavers were matched anthropometrically to the Hybrid III dummy. Test Equipment The tests were performed on the University of Heidelberg's deceleration sied. In the tests the front part of the passenger compartment of a mid-sized car was mounted on the sied. Each subject was positioned in the driver's seat and restrained by a 3-point belt. A belt with an elongation of either 6% or 6% was used, furthermore the subject was protected with a driver side air bag-knee

3 bolster system. Figura illustrates the experimental configuration. Frontal collisions were simulated with an impact velocity of 48 km/h and a trapezoidal deceleration pulse with an average value of between 4 and 7 g. Table : Test - Matrix Run No. II 8 Age [years] Sex Body mass [kg] 75 Body length [cm] C m 34 4 m C2 m 29 C3 f 52 5 m C4 m 3 es m 25 C6 m Instrumentation In each test the subject's thorax was instrumented with a 2-accelerometer array (Robbins et al 976, Eppinger et al 978). The configurations were: Cada ver: Upper/lower sternum: x-direction, 4th rib left/right (medium axillar line): y-direction, 8th rib left/right (medium axillar line): x-direction, Th : 3- axial, Th2: 3-axial. Dummy: Upper/lower sternum: x-direction, 2nd rib left/right (medium axillar line): y-direction; 5th rib left/right (medium axillar line): x-direction, Thorax c.g.: 3-axial, thoracic vertebral column, level 6th rib: 3-axial

4 The 4th and 8th rib of the eadaver eorrespond to the 2nd and 5th rib of the dummy. To measure thoraeie eontours during dynamie loading two ehest bands were used. The first was mounted at the level of the eadaver's 4th rib (dummy 2nd rib) and the seeond at the level of the eadaver's 8th rib (dummy 5th rib} (Eppinger 989). Kinematics Fig. : Test eonfiguration Three high-speed eameras (frame rate frames/s), two on-board and one stationary, were used to doeument the impaet dynamies. Autopsy - lnjury Severity A full autopsy with a detailed investigation of the vertebral eolumn was performed on eaeh eadaver and injuries were eoded aeeording to AIS 99. Data Analysis The data were reeorded in analog format and were digitised at samples per seeond. Eaeh signal was filtered with a ehannel class 8 digital Butterworth Filter. The thoraeie deformation eontours were eomputed using the RBAND-PC Software from NHTSA. A program evaluated the deformation of the front ehest wall in relation to the fixed vertebral eolumn. To evaluate the Viseous Criterion (VC) at the level of the 4th and 8th rib, the deformation veloeity was defined through differentiation of deformation with respeet to time. The deformation veloeity time-histories were by means of spline interpolation. For the evaluation of ehest eompression, the ehest depth was used (instantaneous deformation/ehest depth, Lau and Viano 986)

5 VC(t) = 2ÖD(t) /8 t* D(t) I D where D(t): Deformation of the ehest D: ehest depth measured by the ehest band Biofidelity Biofidelity is a deseription of the extent to whieh passive human-like meehanieal behaviour is simulated in a meehanieal surrogate. Biofidelity ean be assessed through eomparison of the kinematie and meehanieal responses of a meehanieal surrogate to a human volunteer or eadaver. A valid eomparison ean be made when the test speeimens have the same anthropometry and are subjeet to the same impaet eonditions, e.g. impaet direetion, impaet severity, restraint system and belt geometry. Meehanieal responses ean be eompared most effeetively when the same measurement methods are used for eaeh test speeimen. RESULTS A total of frontal eollision tests were undertaken using a 5th. pereentile Hybrid III dummy and six eadavers. The eadavers were matehed anthropometrieally to the Hybrid III dummy. The mean pereentage differenees between the eadavers and dummy for body length and mass were.5% and 4.5% respeetively. Kinematics Head/Neek Flexion Figures 2 and 3 show sequential photographs of a belt restrained eadaver and Hybrid III dummy under the same impaet eonditions, i.e. impaet veloeity of 48 km/h, mean deeeleration of 6 g, and 3-point belt with 6% elongation. The global kinematies of the Hybrid III dummy and eadaver are eomparable, however there are temporal and spaeial differenees in head/neek motion. After a translatory movement of about 4 ms duration post-impaet, a head rotation oeeurs eaused by the restraining effeet of the belt. The magnitude of head/neek flexion is greater with the eadaver and maximum flexion oeeurs later than observed with the Hybrid III dummy. Comparisons between dummy and eadaver head/neek flexion for tests using the two different belts are shown in figure

6 - 4 - <ts c:. cft. <O II c: "- - Q)... > CU C> CU "'C c: <ts..q Q) "'C C> Q) c: c: - -..c <ts..c "- Q) Ci) :::.=: Q)..c. c: <ts (/) -..c: a. <ts CU "-... C> c: +"' "-.....c: C> <O <ts.,... +:i c:..c: "' Q).. :J E c- Q) ""' (f) C\I. O> - LL

7 - - Fig. 3: Sequential photographs of a belted restrained Hybrid III dummy in a 48 km/h, 6 g frontal collision. Seit webbing elongation = 6 /o.

8 Fig. 4: Still photographs of the dummy and a cadaver during frontal crash test showing head/ neck flexion under the influence of two different belts (6o/o and 6 /o elongation) dummy ca da ver 6 /o elongation.. N 6 /o elongation dummy cadaver

9 Mechanical Responses Shoulder Belt Force Figure 5 shows shoulder belt force time-histories for one cadaver and two Hybrid III dummy tests. Differences exist between the shape of the time histories for the cadaver and the dummy, however the force duration is comparable between the two subjects. Clear differences exist between the magnitudes of the measured forces. Maximum belt forces of kn were measured in the two identical dummy tests, while the maximum shoulder belt force of 7.3 kn in the cadaver test was about 3% less. The cadaver's body mass and length, 7 kg and 8 cm respectively, were comparable to the Hybrid III anthropometry. Trunk Accelerations Acceleration time-histories from the 2 accelerometer thoracic array were evaluated for each test. Comparisons of signals from identical measuring locations for cadaver and dummy were made and found to be partially in agreement. However, they show clear differences for both subjects in signal magnitude, duration and shape. The best agreement between cadaver and dummy thoracic accelerations was at Th2. At the remaining measurement locations a greater variability was present. Examples of acceleration time-histories for the resultant at the Th and the upper sternum in the X-direction are shown in figures 6 and 7. Clear differences were observed according to duration, shape, and acceleration magnitude for both subjects used. Th acceleration maxima for the dummy were 35% to 4% higher than the cadaver (figure 6). Similar observations were made for the measuring location 'upper sternum'. The dummy maxima were 38% to 4% higher than those of the cadaver (figure 7). Acceleration maxima and 3ms values are presented in table 2. Maxima and 3ms values for dummy and cadaver accelerations show a concurrence within the normal scatter of biodynamic tests, however between the two subjects clear differences exist. Furthermore the acceleration magnitudes depended on the used restraint system. In general: accelerations at Th2 were in agreement for dummy and cadaver; clear differences were found at the 8th left and right ribs for air bag-knee bolster tests; and, differences were observed with sternal accelerations during the tests with 3-point belts of either 6% or 6% elongation (table 2)

10 kn ca da ver ms Fig. 5: Shoulder belt force time-histories for the dummy and a cadaver 6 - g g 47. g dummy r..., I r I I / I / J '-' \.- cadaver "J \ \ \ \J' \ '\ \ " ms Fig. 6: Th. acceleration time-histories for the dummy and a cadaver -44-

11 6 g g dummy, g g ca da ver i!. II '.,,,. i - Fig. 7: Acceleration time-histories measured at the upper sternum for the dummy and a cadaver -45 -

12 Table 2: Thorax acceleration measurements of the dummy and cadaver Impact Dece- up. stern. low. stern. 8. rib right 8. rib left res. TH res. TH2 Run No. velocity leration max. 3 ms max. 3ms max. 3ms max. 3ms max. 3ms max. [km'h] [g] [g] [g] [g] [g] [g] [g] [g] [g] [g] [g] [g] 3ms [g] C 4 C C C4 C C Chest Deformation and Viscous Criterion (VC) Figures 8 and 9 show time-histories for: the evaluated deformation, deformation velocity and VC. For both subjects the presented time-histories were derived from the ehest band positioned at the level of the 4th rib during tests with a 3-point belt of 6% elongation. The duration of the deformation amounted to about 6 ms for both the cadaver and dummy. However, the shape, magnitude and time between impact and deformation maximum were different. A maximum deformation of 6 cm was reached for the cadaver 73 ms post-impact, compared to a maximum deformation of 3.3 cm at 47 ms with the dummy. Maximum deformation velocities were observed in the same time region as the deformation maxima and were of similar magnitudes, 2.4 m/s and 2.32 m/s for the cadaver and dummy respectively. The deformation velocity time-history profile and the time at which the maxima were reached differ. The VC value of the cadaver was more than double that of the dummy

13 DU [CM) _-;,;:.;--:::..::: i cm i i! - 8 L ,...,...i!,...,r-r--T...,."'"T"""r..,...,.."T""T"",-r"-r-T"".,...,-r-r-i"""T!-.--r"""T""T(""T,...,...,..,.-r-r-"r"T"""T"' VDEF T [MS] [M/S ] -----, m/s EO 8 2 vc [M/S]. 6 T [ MS l m/s r [MS] 2 Fig. 8: Chest deformation, deformation velocity and VC time-histories measured from a belt restrained (6 /o) Hybrid III dummy at the level of the 2nd. rib

14 OEF (CM) 2! , cm T (MS] VDEF (M/S ) l m/s vc (M/S ) m/s T (MS) l L,--r---r-r--r-r--r-r...,..., i--r--r-T"".,...,...,.-, r-i...,-,r-T""""-r-T-r-r-r-r...,...,...-r-r"T""T"-i--r--i--r-T-r' T [MS) Fig. 9: Chest deformation, deformation velocity and VC time-histories measured from a belt restrained (6o/o) cadaver at the level of the 4th. rib

15 Figures and show the same time-histories as figures 8 and 9, but at the level of the 8th rib. The deformation durations for both subjects were shorter and the deformation time-histories had different profiles. The cadaver shows higher deformation velocity values and much higher VC values, 2.2m/s and.3 m/s respectively, in comparison to.44 m/s and.2 m/s respectively for the dummy. Thoracic deformation velocities and VC are presented in table 3. According to the restraint system used, deformations between 2 cm and 7 cm for the cadaver were observed via the ehest band method. The dummy usually showed smaller deformation and VC values than the cadaver, while the deformation velocity values are comparable. With air bag tests some cadaver values were higher than in belt restraint tests. Table 3: Chest deformation values - VC values for dummy and cadaver Run deformation [cm] defo. velocity VC [m/s] defo [m/s] standard No. upper lower upper lower upper lower [cm] C C C C4 2. 3, es C

16 DEF [CM) i r I,..,.. : """'= --:-::': --==-::': pm i T [MS] VDEF (M/S ) 3 2 o -:i m/s -3 '-T-r-.-r--r-r--.-.-,...-,-,...-, ,..-,.-..-r-ir-r-r--r-i--r-r...-r-r-r-i--r-,...-,--r-r-r-r-r-r-ir-r-ir-r-r--r-i--r-r-r-r T (MS) vc (M/S], m/s ===----==== T (MS] Fig. O: Chest deformation, deformation velocity and VC time-histories measured from a belt restrained (6 /o) Hybrid III dummy at the level of the 5th. rib

17 OEF (CM) l i j -4.8 cm! _ -8 '-T r-"T"""T""""T"'""r"'""T"'""r"'"...,-...,-r-r-ir--r-t-r-r-,-,-..,..."T"""T"""...-r-.,-.,-.,-.,-...,-r-r-i,-...,,...,-,.-,-,.-r-T T [MS] VOEF [M/S) m/s vc [M/S] m/s T [MS] T [MS ) Fig. : Chest deformation, deformation velocity and VC time-histories measured from a belt restrained (6 /o ) cadaver at the level of the 8th. rib

18 Medical findings No rib fractures were found when the driver air bag - knee bolster restraint system was used (subjects' age 25 to 38 years). In tests with the 3-point belt restraint (6% elongation) sternum and rib fractures (AIS 2) were observed in two cadavers (age: 29 and 52 years). In one case (age: 34 years) no rib fractures were found when a 3-point belt with 6 % elongation was used. Except for one laceration of the ligamentur.n flavum at Th!Th2 (C3, AIS 2), no vertebral column injuries were observed in the investigated cadavers. DISCUSSION Frontal collisions with restrained Hybrid III dummy and cadavers under identical crash conditions and restraint systems were performed. The kinematic behaviour of both test subjects compare well globally, however cadaver head-neck flexion is greater. A possible reason for the greater neck flexibility observed in cadavers is that the upper thoracic vertebral column is included in the bending process. This may also account for injuries observed at the transition zone between the thoracic and cervical spines. The authors observed previously that the Hybrid III dummy neck stiffness was greater in comparison to a cadaver's during rigid and padded frontal head impacts at an impact speed of 2 and 22 km/h. This was also observed in 25 km/h rear-end collisions. Measured thoracic accelerations demonstrated a similar behaviour. While the acceleration magnitudes and profiles over time at the measuring location Th 2 were in agreement between the two subjects, greater differences were found for accelerations measured at the level of Th and sternum. In these cases accelerations of the dummy's thorax were higher than those of the cadaver, which suggests that the Hybrid III trunk and trunk articulations may be stiffer than the cadaver. Shoulder belt forces depend upon the body mass and tissue deformability in frontal collisions. Clear differences between the dummy and cadavers were observed even for anthropometrically matched pairs. Higher belt forces were observed for the dummy, as body masses were similar this also indicates that the dummy thorax is stiffer than in a cadaver. Finally, thoracic deformations were measured using ehest bands. They were greater with the cadaver's thorax, and in anthropometrically matched pairs twice that of Hybrid III deformation. This observation was also made by Cesari et al. ( 99, 994) and Backaitis et al. ( 986) who used cadavers and -52 -

19 volunteers, but loaded the subject's thorax in a different configuration than the authors. With regards to ehest biofidelity, Horsch et al. (99) observed that Hybrid III it was satisfactory in compression during blunt sternal impacts, but 'stiff' during belt loading. lndeed Hybrid III ehest calibration is performed via a blunt frontal impact. The biofidelity of the Hybrid III for blunt sternal impacts was not confirmed in the presented driver air bag tests. In agreement with Cesari et al. (99), it was observed that the VC values of the cadaver were twice as high as those calculated from the dummy's responses. CONCLUSIONS ) The global kinematic behaviour of the Hybrid III dummy in frontal collisions restrained with a 3-point belt is comparable with those of the cadaver. However, the magnitude of cadaver head-neck frontal flexion is clearly greater. 2) By observing the acceleration and deformation measurements it appears that the dummy's thorax is stiffer than the cadaver. REFERENCES Backaitis S, St-Laurent A (986), 'Chest Deflection Characteristics of Volunteers and Hybrid III Dummies', SAE Paper No , Proceedings of the 3th. Stapp Gar Crash Conference, p Cesari D, Bouquet R (99), 'Behaviour of Human Surrogates Thorax under Seit Loading', SAE Paper No. 923, Proceedings of the 34th. Stapp Gar Crash Conference, p Cesari D, Bouquet R (994), 'Comparison of Hybrid III and Human Cadaver Thorax Deformations Loaded by a Thoracic Seit', SAE Paper No , Proceedings of the 38th. Stapp Gar Crash Conference, p Eppinger RH, Augustyn K, Robbins DH (978), 'Development of a Promising Universal Thoracic Trauma Prediction Methodology', SAE Paper No. 7889, Proceedings of the 22th. Stapp Gar Crash Conference, p Eppinger RH, (989), 'On the Development of a Deformation Measurement System and lts Application Toward Developing Mechanically Based lnjury Indices', SAE Paper No , Proceedings of the 33th. Stapp Gar Crash Conference, p

20 Harsch JD, Melvin JW, Viano DC, Mertz HJ (99 ), 'Thoracic lnjury Assessment of Belt Restraint Systems Based on Hybrid III Chest Compression', SAE Paper No , Proceedings of the 35th. Stapp Gar Crash Conference, p Kallieris D, Mattem R, Mclntosh A, Boggasch F, (992), 'The Biofidelity of Eurosid and Biosid', SAE Paper No , Proceedings of the 36th. Stapp Gar Crash Conference, p. 3-7 Klaus G, Sinnhuber R, Hoffmann G, Kallieris D, Mattem R, (984), 'Side Impact- A Comparison Between Dummies and Cadavers. Correlations Between Cadaver Loads and lnjury Severity', SAE Paper No.84655, Proceedings of the 28th. Stapp Gar Crash Conference, p Lau, Viano D,(986), 'The Viscous Criterion-Bases and Application of an lnjury Severity Index for Soft Tissue', SAE Paper No , Proceedings of the 3th. Stapp Gar Crash Conference, p Robbins OH, Melvin JW, Stalnaker AL, (976), 'The Prediction of Thoracic Impact lnjuries', SAE Paper No , Proceedings of the 2th. Stapp Gar Crash Conference, p