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Biomechanical behavior of brain injury caused by sticks using finite element model and Hybrid-III testing
Accepted Manuscript Biomechanical behavior of brain Injury caused by sticks using Finite Element Model and Hybrid-III Testing Kui Li, Jiawen Wang, Shengxiong Liu, Sen Su, Chenjian Feng, Xiaoxiang Fan, Zhiyong Yin PII:
S1008-1275(15)00050-4
DOI:
10.1016/j.cjtee.2015.03.004
Reference:
CJTEE 36
To appear in:
Chinese Journal of Traumatology
Received Date: 3 December 2014 Revised Date:
10 February 2015
Accepted Date: 15 March 2015
Please cite this article as: Li K, Wang J, Liu S, Su S, Feng C, Fan X, Yin Z, Biomechanical behavior of brain Injury caused by sticks using Finite Element Model and Hybrid-III Testing, Chinese Journal of Traumatology (2015), doi: 10.1016/j.cjtee.2015.03.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Original article Biomechanical behavior of brain Injury caused by sticks using Finite Element
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Model and Hybrid-III Testing Kui Lia, Jiawen Wangb, Shengxiong Liuc, Sen Sua, Chenjian Fenga, Xiaoxiang Fanc, Zhiyong Yina,*
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a
Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University,
b
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Chongqing 400042, China
Department of Basic Medical Institute of Pathology, Foshan University, Foshan 528000,
China
School of Pharmacy and Bioengineering, Chongqing University of Technology,
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c
Chongqing 400050, China
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*Corresponding author: Tel: 86-23-68757442, Email: [email protected] Fund: National Natural Science Foundation of China (No. 31200709 and 31170908), and
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Academician Funds (No.cstc2012jjys0004).
Received 03 Dec 2014 Revised 10 Feb 2015
Accepted 15 Mar 2015
Abstract
ACCEPTED MANUSCRIPT Objective: To study the biomechanical mechanism of head injuries beaten with sticks, which is common in the battery or accidental events. Methods: In this study, the Hybrid-III anthropomorphic test device and finite element model (FEM) of the total human model for safety (THUMS) head were used to determine
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the biomechanical response of head while being beaten with different sticks. Total eight Hybrid-III tests and four finite element simulations were conducted. The contact force, resultant acceleration of head center of gravity, intracranial pressure and von Mises stress were calculated to determine the different biomechanical behavior of head with beaten by
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different sticks.
Results: In Hybrid-III tests, the stick in each group demonstrated the similar kinematic
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behavior under the same loading condition. The peak values of the resultant acceleration for thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group were 203.4 g, 221.1 g, 170.5 g and 122.2 g respectively. In finite element simulations, positive intracranial pressure was initially observed in the frontal comparing with negative intracranial pressure in the contra-coup site. Subsequently the intracranial
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pressure in the coup site was decreasing toward negative value while the contra-coup intracranial pressure increasing toward positive values. Conclusions: The results illustrated that the stiffer and larger the stick was, the higher the
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von Mises stress, contact force and intracranial pressure were. We believed that the results in the Hybrid-III tests and THUMS head simulations for brain injury beaten with
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sticks could be reliable and useful for better understanding the injury mechanism. Keywords: biomechanics; head injury; sticks; Hybrid-III; THUMS; FEM
1 Introduction
In forensic practice, head injury is one of the most common injuries in vehicle traffic accident, fall, attack and mishandling,1 which has become a worldwide concerned health issue.2 Head is believed most frequently involving in life-threatening injuries. According to previous studies, traumatic brain injury is the leading cause of death among young people, and some of survivors might also have been paralyzed or permanent disabled.3 In addition, the sticks are usually used as weapons in assaultive cases. Hence, to identification of
ACCEPTED MANUSCRIPT head injury whether it was caused by the stick-battery is an important task of forensic specialists.4 Unfortunately, it is difficult to make a quantitative assessment of the force loaded in head by merely being based on the characteristic injury and the tissue type damaged. As a result, elucidating the biomechanics mechanism of head injury and
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expounding how it produced is essential. In the analysis and simulation of head injuries in forensic practice, blunt injury, following gunshot wound or stabbing wounds, is a very common.5 It is clear that the type of weapon used in assault plays a significant role in the prognosis. 6 The sticks are often used as a weapon in the civilian assault in China or other
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firearm-prohibited countries. While it loads on head, the external mechanical load is transferred into the head and causes the internal biomechanical response, and eventually
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resulted in brain injury.
In recent years, many researchers have studied the biomechanical mechanisms of brain injury in motor vehicle crashes with the dummy test device and the finite element model. On the one hand, the Hybrid III crash dummy is widely used as a standardized impact tests and has been used in automotive or military testing. And some previous studies
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have applied Hybrid III for athletic head injury risk analysis.7,8 Nonetheless, little researches have focused on injury mechanism and simulations in forensic expertise with Hybrid-III On the other hand, the elucidation of the head injury biomechanics could serve
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as a useful tool in forensic practices. A potential approach to predict the internal biomechanical behavior in detail is to apply the finite element analysis, which is widely
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accepted in engineering design and accident investigation.9 Meanwhile, finite element analysis has been used to determine the biomechanical mechanism of bone tissue under different loading scenarios and estimate the level of force used in stabbing incidents in forensic pathology recently. 10,11 In order to clarify the different biomechanical behavior of head injury beaten by sticks with different materials and different sizes, the Total Human Model for Safety (THUMS) human finite element model and Hybird-III device were applied in this study. Thick iron stick, thin iron stick, thick wooden stick and thin wooden stick which represented four different kinds of sticks were used. We hypothesized that such analysis could help forensic pathologists to predict the assaulting tools and the manner of infliction involving the head injury beaten with sticks.
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2. Materials and methods 2.1 Hybrid-III testing All the tests were conducted in the vehicle/biological crash security laboratory of Third
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Military Medical University in Chongqing, where could provide consistent temperature and humidity. Firstly the Hybrid-III was instrumented with a triaxial linear accelerometer (7264B, ENDEVCO, USA) mounted at the head center of gravity so that the acceleration could be measured. As showed in Fig.1, the beaten device, which has been authorized for
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invention patent in China, was self-developed. Secondly the beaten device was fixed on the barrier vertically, and the Hybrid-III was seated in a chair and secured with tie-down
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straps so that the sticks could beat the midline of the frontal and parietal accurately (Fig.2).
Prior to testing, the left wheel was turned around to make the steel wire rope pulled out and the spring bended simultaneously. The beaten speed was controlled through the spring blending degree during the testing. At last, the switch was triggered so that the
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sticks could beat the Hybrid-III frontal head directly. These tests were divided into four groups: thick iron stick, thin iron stick, thick wooden stick and thin wooden stick (Tab.1). And a total of 8 head beaten tests were conducted, twice trials for each group. The beaten
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parameters were consistent among the four groups. The NA34 data acquisition system (NA34, Messering, Germany) was used and date were collected at a sampling rate of 20
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KHz. The high-speed video camera (Phantom, Vision Research, USA) was placed in the side of Hybrid-III to record the whole beating process. Targets were attached to the sticks to digitize its motion and calculate impact velocity using TEMA motion analysis software package (TEMA, Image Systems AB, Switzerland). A common start trigger was used to trigger the data acquisition system and the high-speed video camera. All the statistical analysis was carried out with SPSS 18.0 (SPSS Inc, Chicago, IL). A value of p < 0.05 was considered statistically significant. 2.2 Finite element simulation In present study, the finite element model of THUMS (version 4.0) with the detailed anatomical information and approximately 2 million elements was widely validated
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ACCEPTED MANUSCRIPT (Fig.3). The THUMS head includes the epidermis, skull, mandible, eyeballs, teeth, meninges, cerebrum, cerebellum, brainstem and CSF. The total mass of THUMS head is 2.92 kg. In addition, the finite element models of sticks were developed based on its real geometry and size, which were consistent with that used in Hybrid-III tests. Meanwhile,
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much emphasis was placed on the mesh quality of the sticks. Then different material and property were assigned to iron sticks and wooden sticks. In order to avoid the improper setup, the mass of sticks were used to compare with the finite element model.
As shown in Fig.4, four virtual experiments with different sticks impacting to THUMS head
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were conducted. The position of THUMS head to be beaten was the midline of the frontal and parietal. In all simulations, the impacting velocity and direction accorded with the
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Hybrid-III tests as well as other loading conditions. The contact characteristic between the THUMS head and sticks were considered. For example, the dynamic and static friction coefficient between THUMS head and stick are 0.3 and 0.3, respectively. The hourglass energy and total energy were applied to assess the accuracy of these simulations in this study. And the head injury beaten with sticks was estimated mainly in
3 Results
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term of the von Mises stress and intracranial pressure.
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3.1 Cerebral kinematic behavior of the sticks In general, the sticks in each group demonstrated the similar kinematic behavior under the
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same loading condition. Initially, the sticks hit the Hybrid-III head in a short time, and then rebounded subsequently. In overall Hybrid-III tests, the loading parameters for each group were consistent. So it is believed that the beating velocity as consistent in the four groups when the effect of sticks mass was negligible under the same boundary condition. As shown in Fig.5, it demonstrated that the beating velocity of sticks in x direction and y direction were 12.994 m/s, -8.2529 m/s respectively. The resultant velocity of the stick was 15.4m/s. And the duration time of contact is 1.5 ms. 3.2 Resultant acceleration and contact force of Hybrid-III head Due to lack of enough testing for each group, the mean value of the resultant acceleration for each group was calculated to analysis the biomechanical response for Hybrid-III head.
ACCEPTED MANUSCRIPT And the resultant acceleration of the four groups was illustrated in Fig.6.The peak value of the resultant acceleration for thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group is 203.4 g, 221.1 g, 170.5 g and 122.2 g respectively. As shown in Fig.6, the head resultant acceleration of gravity center and the time history
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has shown a positive relationship. Hence the regression analysis was performed. The fitting parameters for the four models are summarized in Tab.2. And the fitting models were acceptable according to the value of adjusted R2 and p-value. Then the average contact force of Hybrid-III head suffered from the sticks was calculated based on the
then calculated according to the equation:
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momentum formulation. Because the sticks were static initially, the average force was
F = mv t . And the average acceleration of
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the Hybrid-III head was calculated by integrating the curve a (t ) illustrated in Tab.2. In addition, based on the peak acceleration, the average acceleration and the average contact force , the peak contact force could calculate based on the following equation:
Fmax = F amax
.Thus, the contact force of Hybrid-III head suffered from the sticks was
showed in Tab.3.
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3.3 Biomechanical response of the THUMS head In overall simulations, the hourglass energy, total energy, acceleration of gravity center,
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contact force between sticks and THUMS head, von Mises stress and the intracranial pressure were calculated to estimate biomechanical response of THUMS head. As shown
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in Tab.4, the hourglass energy of each simulation was less than ten percent of the total energy, hence the finite element simulations could be well acceptable. The overall kinematics of THUMS head beaten with sticks depend on the size and material of the sticks. In these simulations in four gourps, the external mechanical load on the head was initially transferred to skull and brain parenchyma in the form of stress wave. However, the distribution of vonMise stress of THUMS brain was significantly different between iron stick group and wooden stick group. As illustrated in Fig.7, the position of stress concentration was in lateral ventricle in iron stick group and in frontal lobe in wooden stick group respectively. Generally, the energy in various parts of the coupling place appeared
ACCEPTED MANUSCRIPT to be attenuated gradually, and finally disappeared. In all simulations, positive intracranial pressure was initially observed in the frontal which was beneath the coup site, comparing with negative intracranial pressure in the contra-coup site (Fig.8). Subsequently the intracranial pressure in the coup site was decreasing toward negative value while the
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contra-coup intracranial pressure increasing toward positive values. However the absolute value of positive intracranial pressure was greater than that of negative intracranial pressure.
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4 Discussion
In forensic practice, the head injuries beaten with sticks may result in permanent disability
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even more fatal prognosis because the brain is one of the most vital organs for humans. In addition, head is easy to be targeted by sticks. Although a lot of works have been done to clarify the physiological and pathological response to the external load on head, it remains a great challenge for quantifying the loading force exerted as well as identifying injury tools. In order to address this problem, it is necessary to elucidate the biomechanical
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mechanism of head injury beaten with sticks. With the development of the anthropomorphic test device and computer simulation technology, the application of Hybrid-III dummy coupling with finite element analysis has become an important approach
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for biomechanical mechanism research on the head injury in forensic pathology. It is very useful to quantify the external loading force exerted based upon the head injury severity. The Hybrid-III dummy is a standardized impact testing, which has widely been used in
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automotive and military testing.8 However, the Hybrid-III is mainly developed to measure the mechanics parameters, from which the human biomechanical response for the vehicle design could be assessed. Finite element analysis could be potentially helpful in the understanding of the injury mechanism of head injury beaten with sticks in forensic practice. Furthermore, THUMS head is a useful tool to clarify the internal stress-strain response for forensic pathologist, such as the distribution and transformation of stress. Fridenbery13 has firstly applied the finite element analysis in the medical domain in 1969, which has provided a new method for human biomechanics research. Then Hardy14 and Nickell15 made the first attempt towards finite element modeling of the human head.
ACCEPTED MANUSCRIPT The severity of damage in head injury beaten with sticks mainly depends on how much energy absorbs. And the brain injury is significantly influenced by intensity and time duration of the external mechanical loading force. In this study, the blunt beaten device developed by the Third Military Medical University was applied to beat the Hybrid-III head
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so as to simulate the head injury beaten with stick in forensic pathology practice. THUMS simulations for head injury beaten with stick were conducted under the same boundary condition, such as the impact velocity and direction. According to previous studies, HIC , 16-18
HIP, 19 GAMBIT, 20 CSDM,21,22,SFC,23 contact force, von Mises stress and intracranial
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pressure could be used to assess the biomechanical response of head injury. Although HIC is the first extensive quantification of head tolerance to impact,24-26 it is improper to be
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applied in this study due to its limitation of translational acceleration. Hence, contact force, SFC and resultant acceleration of head center of gravity were applied to assess the kinematic behavior in the Hybrid-III tests. And acceleration of center of gravity, contact force, von Mises stress and intracranial pressure were applied to predict the response in finite element simulations.
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Yavuz et al27 suggested that the occurrence, degree of deformation and extent of fracture is related to the striking power, area of strike and physical properties of the skull at the point of impact. Skull fracture could be easily found in the blunt brain injury, and many experiments had been performed to explore the skull tolerance.28,29 Hodgson and
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Thomas30 drew a conclusion that the tolerance of frontal skull was 3.6-9.0KN. While other studies on the postmortem human subject tests found that the force about 8300N could be
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able to result in frontal skull fracture.31 In the present study, the maximum contact force of thick iron stick, thin iron stick, thick wooden stick and thin wooden stick in Hybrid-III tests were 9142.6N, 5464.1N, 3491.1N and 1487.6N respectively, and that were 9257.1N, 8021.1N, 4122.4N and 1846.2N in THUMS head simulations. In addition, the frontal skull fracture might occur in iron stick group but not in wooden stick group. The maximum contact force in Hybrid-III tests in each group was almost consistent with the THUMS head simulations except for thin iron stick group. The possible explanation might rely on the different duration time in Hybrid-III tests and THUMS head simulations. The SFC was a probability-based index for predicting skull fracture in frontal collision, according to its
ACCEPTED MANUSCRIPT calculation formula, the finding could be draw that it was equal to the average resultant acceleration of gravity. Hence the SFC in thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group was 105 g, 75.2 g, 120.4 g and 46.0 g respectively. However, the SFC in this study was less than 165 g which represented fifty
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percent probability of skull fracture. In all finite element simulations, the von Mises stress of frontal skull in thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group were 207.1 MPa, 236 MPa, 58.8 MPa and 6 MPa respectively. The skull fracture would most likely occur in iron stick group according to the yield stress
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of 90 MPa for cortical bone reported in Willinger R’s research.32However, the failure level of von Mises stress of skull bone is not clear yet. And a study demonstrated that the failure
relatively close to our results.
33
which were
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level of von Mises stress of long bone was approximately 125M Pa,
In this study, Hybrid-III tests and THUMS head simulations were combined to explore the injury mechanism of head injury beaten with stick. And the estimation of contact force and resultant acceleration between Hybrid-III tests and THUMS head simulations seemed to
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be consistent under the same loading condition. Due to lack of internal response in Hybrid-III test, finite element model was helpful to observe the internal response for head injury beaten with stick. The von Mises stress and intracranial pressure were used to
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estimate the head injury risk. Initially, the brain von Mises stress of thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group were 2.4 KPa, 2.7 KPa, 0.4 KPa and 0.2 KPa respectively. These values were less than 14.8KPa, which
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was the toleration for AIS3+ brain injuries in previous studies. 32, 34 And the intracranial pressure of thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group was 421.1 KPa, 308.6 KPa, 106.4 KPa and 47 KPa at the coup comparing with -93 KPa, -77.6 KPa, -25.7 KPa and -18 KPa at the contra-coup. According to Ward’s study, 35 the values of intracranial pressure of iron stick groups in our study would result in severe brain injury comparing with slight brain injury in wooden stick groups. In addition, the intracranial pressure was positive on the beaten side and negative on the contra-coup side, which was consistent with the results of Ruan’s Wang’s
37
36
study and
reports. Hence, this finding could preliminarily be concluded that the stiffer and
ACCEPTED MANUSCRIPT larger the stick was, the higher the von Mises stress and intracranial pressure were. Besides, in our study, the site of stress concentration in brain was the lateral ventricle in iron stick groups and the frontal lobe in wooden stick groups. The bio-fidelity of Hybrid-III dummy and THUMS head finite element model have great
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influence on the experimental results. Due to good validation, we believe that the results of the Hybrid-III tests and THUMS head simulations of head injury beaten by stick are reliable and useful. In addition, modern imaging techniques have become a minimalinvasive tool for inertial injury assessment. 38 Hence, in the further researches, we
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incline to combine the imaging techniques with THUMS human finite element model and Hybrid-III to determine the correlative relationship between beaten force with different
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kinds of sticks and head injury severity in forensic practice. Then we could better understand the injury mechanism and benefit for the identification of injury tools in forensic practice. In conclusion, Hybrid-III and THUMS head model are useful tools to study the head injury beaten with sticks. Under the same loading conditions, the biomechanical response in four different groups was with good consistence. In addition, the head
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stress-strain response could be observed in THUMS head simulations. In addition, the conclusion could be that the intensity and size of stick could induce the higher the von Mises stress, contact force and intracranial pressure. The site of stress concentration in
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groups.
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brain was the lateral ventricle in iron stick groups and the frontal lobe in wooden stick
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ACCEPTED MANUSCRIPT 28. Allsop DL, Perl DR, Warner CY. Force/deflection and fracture characteristics of the tomporo-parietal region of the human head. In: Proceedings of the 35th Stapp Car Crash Conference. San Diego: Society of Automotive Engineers. 1991:269-278. 29. Yang JK. Review of injury biomechanics in car-pedestrian collisions. Int J Veh
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ACCEPTED MANUSCRIPT Figure legends Fig.1. The structure of the blunt impact device Fig.2. The relative position between head and tube (A: thick iron stick group; B: thin iron stick group; C: thick wooden stick group; D: thin wooden stick group)
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Fig.3. THUMS academic version 4.0 model (AM50th) and head FE model Fig.4. The setup of the simulations of the clubs and THUMS head collisions
Fig.5. The velocity of sticks while contacting the Hybrid-III head (A: in the x direction; B: in the y direction)
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Fig.6. Resultant linear cg acceleration of Hybrid-III head (A: thick stick bar; B: thin iron stick; C: thick wooden stick; D: thin wooden stick)
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Fig.7. The von Mises of THUMS brain (A: thick iron stick; B: thin iron stick; C: thick wooden stick; D: thin wooden stick)
Fig.8. Intracranial pressure of THUMS brain (A: thick iron stick; B: thin iron stick; C: thick wooden stick; D: thin wooden stick)
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Tab.1 Dimensions of four sticks and consistent impact parameter Types of stick
Mass (kg)
Length (cm)
0.46
30
Thin iron stick
0.29
30
Thick wooden stick
0.15
30
Thin wooden stick
0.09
30
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Thick iron stick
Groups
Thick iron
R
Adjusted
Square
R Square
0.971
0.968
F
289.537*
0.583
0.549
16.801*
25 25 25 25
Regression equation a(t)=-5.302 × 1011t3+1.615 × 109t2-1316269.7t+327.035 a(t)=1.449 × 1010t3-1.797 × 108t2+328589.06t-62.649 t=[0.00025,0.00175]
0.964
0.958
185.047*
stick Thin wooden
(cm)
t=[0.0005,0.00195]
stick Thin iron
inside diameter: 2.7 outside diameter: 3.2 insided iameter: 1.5 outside diameter: 2.0 outside diameter: 3.2 outside diameter: 2.0
Impact parameter
Tab.2 Model summary and regression equation
stick Thick wooden
Diameter (cm)
a(t)=-7.034 × 1011t3+1.761 × 109t2-1075257.366t+182.647 t=[0.0005,0.00195]
0.934
0.926
122.177*
a(t)=-3.459 × 109t3-1638983t2+195943.210t-105.464
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t=[0.0005,0.00195]
*p<0.001
Tab.3 The acceleration and contact force of Hybrid-III head Peak
Peak
Peak contact
Peak contact
acceleration
acceleration
force (N)
force (N)
(g)
(g)
203.4
105.0
4720.6
Thick wooden stick
170.5
75.2
1539.3
Thin iron stick
221.1
120.4
2976.0
74.0
46.0
923.6
Thin wooden stick
9142.6
3491.1
5464.1
1487.6
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Thick iron stick
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Groups
Tab.4 Simulation results of the four groups Hourglass
Total
Acceleration
energy
energy
of gravity
(J)
(J)
(g)
Von Mises (MPa)
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Group
cranium
brain
Contact force
Intracranial pressure (KPa) coup
contre-coup
(N)
4312.6
54517.5
216.1
207.1
2.4E-3
9257.1
421.1
-93.0
Thick Wooden stick
757.3
17413.1
142.3
58.8
0.4E-3
4122.4
106.4
-25.7
Thin iron stick
1200.1
33153.3
244.5
236.0
2.7E-3
8021.1
308.6
-77.6
Thin wooden stick
885.0
10713.7
72.5
6.042
0.2E-3
1846.2
47.0
-18.0
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Thick Iron stick
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S1008-1275(15)00050-4
DOI:
10.1016/j.cjtee.2015.03.004
Reference:
CJTEE 36
To appear in:
Chinese Journal of Traumatology
Received Date: 3 December 2014 Revised Date:
10 February 2015
Accepted Date: 15 March 2015
Please cite this article as: Li K, Wang J, Liu S, Su S, Feng C, Fan X, Yin Z, Biomechanical behavior of brain Injury caused by sticks using Finite Element Model and Hybrid-III Testing, Chinese Journal of Traumatology (2015), doi: 10.1016/j.cjtee.2015.03.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Original article Biomechanical behavior of brain Injury caused by sticks using Finite Element
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Model and Hybrid-III Testing Kui Lia, Jiawen Wangb, Shengxiong Liuc, Sen Sua, Chenjian Fenga, Xiaoxiang Fanc, Zhiyong Yina,*
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a
Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University,
b
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Chongqing 400042, China
Department of Basic Medical Institute of Pathology, Foshan University, Foshan 528000,
China
School of Pharmacy and Bioengineering, Chongqing University of Technology,
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c
Chongqing 400050, China
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*Corresponding author: Tel: 86-23-68757442, Email: [email protected] Fund: National Natural Science Foundation of China (No. 31200709 and 31170908), and
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Academician Funds (No.cstc2012jjys0004).
Received 03 Dec 2014 Revised 10 Feb 2015
Accepted 15 Mar 2015
Abstract
ACCEPTED MANUSCRIPT Objective: To study the biomechanical mechanism of head injuries beaten with sticks, which is common in the battery or accidental events. Methods: In this study, the Hybrid-III anthropomorphic test device and finite element model (FEM) of the total human model for safety (THUMS) head were used to determine
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the biomechanical response of head while being beaten with different sticks. Total eight Hybrid-III tests and four finite element simulations were conducted. The contact force, resultant acceleration of head center of gravity, intracranial pressure and von Mises stress were calculated to determine the different biomechanical behavior of head with beaten by
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different sticks.
Results: In Hybrid-III tests, the stick in each group demonstrated the similar kinematic
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behavior under the same loading condition. The peak values of the resultant acceleration for thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group were 203.4 g, 221.1 g, 170.5 g and 122.2 g respectively. In finite element simulations, positive intracranial pressure was initially observed in the frontal comparing with negative intracranial pressure in the contra-coup site. Subsequently the intracranial
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pressure in the coup site was decreasing toward negative value while the contra-coup intracranial pressure increasing toward positive values. Conclusions: The results illustrated that the stiffer and larger the stick was, the higher the
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von Mises stress, contact force and intracranial pressure were. We believed that the results in the Hybrid-III tests and THUMS head simulations for brain injury beaten with
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sticks could be reliable and useful for better understanding the injury mechanism. Keywords: biomechanics; head injury; sticks; Hybrid-III; THUMS; FEM
1 Introduction
In forensic practice, head injury is one of the most common injuries in vehicle traffic accident, fall, attack and mishandling,1 which has become a worldwide concerned health issue.2 Head is believed most frequently involving in life-threatening injuries. According to previous studies, traumatic brain injury is the leading cause of death among young people, and some of survivors might also have been paralyzed or permanent disabled.3 In addition, the sticks are usually used as weapons in assaultive cases. Hence, to identification of
ACCEPTED MANUSCRIPT head injury whether it was caused by the stick-battery is an important task of forensic specialists.4 Unfortunately, it is difficult to make a quantitative assessment of the force loaded in head by merely being based on the characteristic injury and the tissue type damaged. As a result, elucidating the biomechanics mechanism of head injury and
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expounding how it produced is essential. In the analysis and simulation of head injuries in forensic practice, blunt injury, following gunshot wound or stabbing wounds, is a very common.5 It is clear that the type of weapon used in assault plays a significant role in the prognosis. 6 The sticks are often used as a weapon in the civilian assault in China or other
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firearm-prohibited countries. While it loads on head, the external mechanical load is transferred into the head and causes the internal biomechanical response, and eventually
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resulted in brain injury.
In recent years, many researchers have studied the biomechanical mechanisms of brain injury in motor vehicle crashes with the dummy test device and the finite element model. On the one hand, the Hybrid III crash dummy is widely used as a standardized impact tests and has been used in automotive or military testing. And some previous studies
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have applied Hybrid III for athletic head injury risk analysis.7,8 Nonetheless, little researches have focused on injury mechanism and simulations in forensic expertise with Hybrid-III On the other hand, the elucidation of the head injury biomechanics could serve
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as a useful tool in forensic practices. A potential approach to predict the internal biomechanical behavior in detail is to apply the finite element analysis, which is widely
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accepted in engineering design and accident investigation.9 Meanwhile, finite element analysis has been used to determine the biomechanical mechanism of bone tissue under different loading scenarios and estimate the level of force used in stabbing incidents in forensic pathology recently. 10,11 In order to clarify the different biomechanical behavior of head injury beaten by sticks with different materials and different sizes, the Total Human Model for Safety (THUMS) human finite element model and Hybird-III device were applied in this study. Thick iron stick, thin iron stick, thick wooden stick and thin wooden stick which represented four different kinds of sticks were used. We hypothesized that such analysis could help forensic pathologists to predict the assaulting tools and the manner of infliction involving the head injury beaten with sticks.
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2. Materials and methods 2.1 Hybrid-III testing All the tests were conducted in the vehicle/biological crash security laboratory of Third
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Military Medical University in Chongqing, where could provide consistent temperature and humidity. Firstly the Hybrid-III was instrumented with a triaxial linear accelerometer (7264B, ENDEVCO, USA) mounted at the head center of gravity so that the acceleration could be measured. As showed in Fig.1, the beaten device, which has been authorized for
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invention patent in China, was self-developed. Secondly the beaten device was fixed on the barrier vertically, and the Hybrid-III was seated in a chair and secured with tie-down
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straps so that the sticks could beat the midline of the frontal and parietal accurately (Fig.2).
Prior to testing, the left wheel was turned around to make the steel wire rope pulled out and the spring bended simultaneously. The beaten speed was controlled through the spring blending degree during the testing. At last, the switch was triggered so that the
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sticks could beat the Hybrid-III frontal head directly. These tests were divided into four groups: thick iron stick, thin iron stick, thick wooden stick and thin wooden stick (Tab.1). And a total of 8 head beaten tests were conducted, twice trials for each group. The beaten
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parameters were consistent among the four groups. The NA34 data acquisition system (NA34, Messering, Germany) was used and date were collected at a sampling rate of 20
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KHz. The high-speed video camera (Phantom, Vision Research, USA) was placed in the side of Hybrid-III to record the whole beating process. Targets were attached to the sticks to digitize its motion and calculate impact velocity using TEMA motion analysis software package (TEMA, Image Systems AB, Switzerland). A common start trigger was used to trigger the data acquisition system and the high-speed video camera. All the statistical analysis was carried out with SPSS 18.0 (SPSS Inc, Chicago, IL). A value of p < 0.05 was considered statistically significant. 2.2 Finite element simulation In present study, the finite element model of THUMS (version 4.0) with the detailed anatomical information and approximately 2 million elements was widely validated
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ACCEPTED MANUSCRIPT (Fig.3). The THUMS head includes the epidermis, skull, mandible, eyeballs, teeth, meninges, cerebrum, cerebellum, brainstem and CSF. The total mass of THUMS head is 2.92 kg. In addition, the finite element models of sticks were developed based on its real geometry and size, which were consistent with that used in Hybrid-III tests. Meanwhile,
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much emphasis was placed on the mesh quality of the sticks. Then different material and property were assigned to iron sticks and wooden sticks. In order to avoid the improper setup, the mass of sticks were used to compare with the finite element model.
As shown in Fig.4, four virtual experiments with different sticks impacting to THUMS head
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were conducted. The position of THUMS head to be beaten was the midline of the frontal and parietal. In all simulations, the impacting velocity and direction accorded with the
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Hybrid-III tests as well as other loading conditions. The contact characteristic between the THUMS head and sticks were considered. For example, the dynamic and static friction coefficient between THUMS head and stick are 0.3 and 0.3, respectively. The hourglass energy and total energy were applied to assess the accuracy of these simulations in this study. And the head injury beaten with sticks was estimated mainly in
3 Results
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term of the von Mises stress and intracranial pressure.
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3.1 Cerebral kinematic behavior of the sticks In general, the sticks in each group demonstrated the similar kinematic behavior under the
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same loading condition. Initially, the sticks hit the Hybrid-III head in a short time, and then rebounded subsequently. In overall Hybrid-III tests, the loading parameters for each group were consistent. So it is believed that the beating velocity as consistent in the four groups when the effect of sticks mass was negligible under the same boundary condition. As shown in Fig.5, it demonstrated that the beating velocity of sticks in x direction and y direction were 12.994 m/s, -8.2529 m/s respectively. The resultant velocity of the stick was 15.4m/s. And the duration time of contact is 1.5 ms. 3.2 Resultant acceleration and contact force of Hybrid-III head Due to lack of enough testing for each group, the mean value of the resultant acceleration for each group was calculated to analysis the biomechanical response for Hybrid-III head.
ACCEPTED MANUSCRIPT And the resultant acceleration of the four groups was illustrated in Fig.6.The peak value of the resultant acceleration for thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group is 203.4 g, 221.1 g, 170.5 g and 122.2 g respectively. As shown in Fig.6, the head resultant acceleration of gravity center and the time history
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has shown a positive relationship. Hence the regression analysis was performed. The fitting parameters for the four models are summarized in Tab.2. And the fitting models were acceptable according to the value of adjusted R2 and p-value. Then the average contact force of Hybrid-III head suffered from the sticks was calculated based on the
then calculated according to the equation:
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momentum formulation. Because the sticks were static initially, the average force was
F = mv t . And the average acceleration of
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the Hybrid-III head was calculated by integrating the curve a (t ) illustrated in Tab.2. In addition, based on the peak acceleration, the average acceleration and the average contact force , the peak contact force could calculate based on the following equation:
Fmax = F amax
.Thus, the contact force of Hybrid-III head suffered from the sticks was
showed in Tab.3.
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3.3 Biomechanical response of the THUMS head In overall simulations, the hourglass energy, total energy, acceleration of gravity center,
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contact force between sticks and THUMS head, von Mises stress and the intracranial pressure were calculated to estimate biomechanical response of THUMS head. As shown
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in Tab.4, the hourglass energy of each simulation was less than ten percent of the total energy, hence the finite element simulations could be well acceptable. The overall kinematics of THUMS head beaten with sticks depend on the size and material of the sticks. In these simulations in four gourps, the external mechanical load on the head was initially transferred to skull and brain parenchyma in the form of stress wave. However, the distribution of vonMise stress of THUMS brain was significantly different between iron stick group and wooden stick group. As illustrated in Fig.7, the position of stress concentration was in lateral ventricle in iron stick group and in frontal lobe in wooden stick group respectively. Generally, the energy in various parts of the coupling place appeared
ACCEPTED MANUSCRIPT to be attenuated gradually, and finally disappeared. In all simulations, positive intracranial pressure was initially observed in the frontal which was beneath the coup site, comparing with negative intracranial pressure in the contra-coup site (Fig.8). Subsequently the intracranial pressure in the coup site was decreasing toward negative value while the
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contra-coup intracranial pressure increasing toward positive values. However the absolute value of positive intracranial pressure was greater than that of negative intracranial pressure.
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4 Discussion
In forensic practice, the head injuries beaten with sticks may result in permanent disability
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even more fatal prognosis because the brain is one of the most vital organs for humans. In addition, head is easy to be targeted by sticks. Although a lot of works have been done to clarify the physiological and pathological response to the external load on head, it remains a great challenge for quantifying the loading force exerted as well as identifying injury tools. In order to address this problem, it is necessary to elucidate the biomechanical
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mechanism of head injury beaten with sticks. With the development of the anthropomorphic test device and computer simulation technology, the application of Hybrid-III dummy coupling with finite element analysis has become an important approach
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for biomechanical mechanism research on the head injury in forensic pathology. It is very useful to quantify the external loading force exerted based upon the head injury severity. The Hybrid-III dummy is a standardized impact testing, which has widely been used in
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automotive and military testing.8 However, the Hybrid-III is mainly developed to measure the mechanics parameters, from which the human biomechanical response for the vehicle design could be assessed. Finite element analysis could be potentially helpful in the understanding of the injury mechanism of head injury beaten with sticks in forensic practice. Furthermore, THUMS head is a useful tool to clarify the internal stress-strain response for forensic pathologist, such as the distribution and transformation of stress. Fridenbery13 has firstly applied the finite element analysis in the medical domain in 1969, which has provided a new method for human biomechanics research. Then Hardy14 and Nickell15 made the first attempt towards finite element modeling of the human head.
ACCEPTED MANUSCRIPT The severity of damage in head injury beaten with sticks mainly depends on how much energy absorbs. And the brain injury is significantly influenced by intensity and time duration of the external mechanical loading force. In this study, the blunt beaten device developed by the Third Military Medical University was applied to beat the Hybrid-III head
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so as to simulate the head injury beaten with stick in forensic pathology practice. THUMS simulations for head injury beaten with stick were conducted under the same boundary condition, such as the impact velocity and direction. According to previous studies, HIC , 16-18
HIP, 19 GAMBIT, 20 CSDM,21,22,SFC,23 contact force, von Mises stress and intracranial
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pressure could be used to assess the biomechanical response of head injury. Although HIC is the first extensive quantification of head tolerance to impact,24-26 it is improper to be
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applied in this study due to its limitation of translational acceleration. Hence, contact force, SFC and resultant acceleration of head center of gravity were applied to assess the kinematic behavior in the Hybrid-III tests. And acceleration of center of gravity, contact force, von Mises stress and intracranial pressure were applied to predict the response in finite element simulations.
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Yavuz et al27 suggested that the occurrence, degree of deformation and extent of fracture is related to the striking power, area of strike and physical properties of the skull at the point of impact. Skull fracture could be easily found in the blunt brain injury, and many experiments had been performed to explore the skull tolerance.28,29 Hodgson and
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Thomas30 drew a conclusion that the tolerance of frontal skull was 3.6-9.0KN. While other studies on the postmortem human subject tests found that the force about 8300N could be
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able to result in frontal skull fracture.31 In the present study, the maximum contact force of thick iron stick, thin iron stick, thick wooden stick and thin wooden stick in Hybrid-III tests were 9142.6N, 5464.1N, 3491.1N and 1487.6N respectively, and that were 9257.1N, 8021.1N, 4122.4N and 1846.2N in THUMS head simulations. In addition, the frontal skull fracture might occur in iron stick group but not in wooden stick group. The maximum contact force in Hybrid-III tests in each group was almost consistent with the THUMS head simulations except for thin iron stick group. The possible explanation might rely on the different duration time in Hybrid-III tests and THUMS head simulations. The SFC was a probability-based index for predicting skull fracture in frontal collision, according to its
ACCEPTED MANUSCRIPT calculation formula, the finding could be draw that it was equal to the average resultant acceleration of gravity. Hence the SFC in thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group was 105 g, 75.2 g, 120.4 g and 46.0 g respectively. However, the SFC in this study was less than 165 g which represented fifty
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percent probability of skull fracture. In all finite element simulations, the von Mises stress of frontal skull in thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group were 207.1 MPa, 236 MPa, 58.8 MPa and 6 MPa respectively. The skull fracture would most likely occur in iron stick group according to the yield stress
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of 90 MPa for cortical bone reported in Willinger R’s research.32However, the failure level of von Mises stress of skull bone is not clear yet. And a study demonstrated that the failure
relatively close to our results.
33
which were
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level of von Mises stress of long bone was approximately 125M Pa,
In this study, Hybrid-III tests and THUMS head simulations were combined to explore the injury mechanism of head injury beaten with stick. And the estimation of contact force and resultant acceleration between Hybrid-III tests and THUMS head simulations seemed to
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be consistent under the same loading condition. Due to lack of internal response in Hybrid-III test, finite element model was helpful to observe the internal response for head injury beaten with stick. The von Mises stress and intracranial pressure were used to
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estimate the head injury risk. Initially, the brain von Mises stress of thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group were 2.4 KPa, 2.7 KPa, 0.4 KPa and 0.2 KPa respectively. These values were less than 14.8KPa, which
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was the toleration for AIS3+ brain injuries in previous studies. 32, 34 And the intracranial pressure of thick iron stick group, thin iron stick group, thick wooden stick group and thin wooden stick group was 421.1 KPa, 308.6 KPa, 106.4 KPa and 47 KPa at the coup comparing with -93 KPa, -77.6 KPa, -25.7 KPa and -18 KPa at the contra-coup. According to Ward’s study, 35 the values of intracranial pressure of iron stick groups in our study would result in severe brain injury comparing with slight brain injury in wooden stick groups. In addition, the intracranial pressure was positive on the beaten side and negative on the contra-coup side, which was consistent with the results of Ruan’s Wang’s
37
36
study and
reports. Hence, this finding could preliminarily be concluded that the stiffer and
ACCEPTED MANUSCRIPT larger the stick was, the higher the von Mises stress and intracranial pressure were. Besides, in our study, the site of stress concentration in brain was the lateral ventricle in iron stick groups and the frontal lobe in wooden stick groups. The bio-fidelity of Hybrid-III dummy and THUMS head finite element model have great
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influence on the experimental results. Due to good validation, we believe that the results of the Hybrid-III tests and THUMS head simulations of head injury beaten by stick are reliable and useful. In addition, modern imaging techniques have become a minimalinvasive tool for inertial injury assessment. 38 Hence, in the further researches, we
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incline to combine the imaging techniques with THUMS human finite element model and Hybrid-III to determine the correlative relationship between beaten force with different
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kinds of sticks and head injury severity in forensic practice. Then we could better understand the injury mechanism and benefit for the identification of injury tools in forensic practice. In conclusion, Hybrid-III and THUMS head model are useful tools to study the head injury beaten with sticks. Under the same loading conditions, the biomechanical response in four different groups was with good consistence. In addition, the head
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stress-strain response could be observed in THUMS head simulations. In addition, the conclusion could be that the intensity and size of stick could induce the higher the von Mises stress, contact force and intracranial pressure. The site of stress concentration in
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groups.
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brain was the lateral ventricle in iron stick groups and the frontal lobe in wooden stick
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ACCEPTED MANUSCRIPT Figure legends Fig.1. The structure of the blunt impact device Fig.2. The relative position between head and tube (A: thick iron stick group; B: thin iron stick group; C: thick wooden stick group; D: thin wooden stick group)
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Fig.3. THUMS academic version 4.0 model (AM50th) and head FE model Fig.4. The setup of the simulations of the clubs and THUMS head collisions
Fig.5. The velocity of sticks while contacting the Hybrid-III head (A: in the x direction; B: in the y direction)
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Fig.6. Resultant linear cg acceleration of Hybrid-III head (A: thick stick bar; B: thin iron stick; C: thick wooden stick; D: thin wooden stick)
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Fig.7. The von Mises of THUMS brain (A: thick iron stick; B: thin iron stick; C: thick wooden stick; D: thin wooden stick)
Fig.8. Intracranial pressure of THUMS brain (A: thick iron stick; B: thin iron stick; C: thick wooden stick; D: thin wooden stick)
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Tab.1 Dimensions of four sticks and consistent impact parameter Types of stick
Mass (kg)
Length (cm)
0.46
30
Thin iron stick
0.29
30
Thick wooden stick
0.15
30
Thin wooden stick
0.09
30
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Thick iron stick
Groups
Thick iron
R
Adjusted
Square
R Square
0.971
0.968
F
289.537*
0.583
0.549
16.801*
25 25 25 25
Regression equation a(t)=-5.302 × 1011t3+1.615 × 109t2-1316269.7t+327.035 a(t)=1.449 × 1010t3-1.797 × 108t2+328589.06t-62.649 t=[0.00025,0.00175]
0.964
0.958
185.047*
stick Thin wooden
(cm)
t=[0.0005,0.00195]
stick Thin iron
inside diameter: 2.7 outside diameter: 3.2 insided iameter: 1.5 outside diameter: 2.0 outside diameter: 3.2 outside diameter: 2.0
Impact parameter
Tab.2 Model summary and regression equation
stick Thick wooden
Diameter (cm)
a(t)=-7.034 × 1011t3+1.761 × 109t2-1075257.366t+182.647 t=[0.0005,0.00195]
0.934
0.926
122.177*
a(t)=-3.459 × 109t3-1638983t2+195943.210t-105.464
ACCEPTED MANUSCRIPT stick
t=[0.0005,0.00195]
*p<0.001
Tab.3 The acceleration and contact force of Hybrid-III head Peak
Peak
Peak contact
Peak contact
acceleration
acceleration
force (N)
force (N)
(g)
(g)
203.4
105.0
4720.6
Thick wooden stick
170.5
75.2
1539.3
Thin iron stick
221.1
120.4
2976.0
74.0
46.0
923.6
Thin wooden stick
9142.6
3491.1
5464.1
1487.6
SC
Thick iron stick
RI PT
Groups
Tab.4 Simulation results of the four groups Hourglass
Total
Acceleration
energy
energy
of gravity
(J)
(J)
(g)
Von Mises (MPa)
M AN U
Group
cranium
brain
Contact force
Intracranial pressure (KPa) coup
contre-coup
(N)
4312.6
54517.5
216.1
207.1
2.4E-3
9257.1
421.1
-93.0
Thick Wooden stick
757.3
17413.1
142.3
58.8
0.4E-3
4122.4
106.4
-25.7
Thin iron stick
1200.1
33153.3
244.5
236.0
2.7E-3
8021.1
308.6
-77.6
Thin wooden stick
885.0
10713.7
72.5
6.042
0.2E-3
1846.2
47.0
-18.0
AC C
EP
TE D
Thick Iron stick
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT