ZHANG YUELIN

American football is a sport that requires high safety precaution for players because it entails very fast and powerful movements. The players’ helmets are one of the most important means of ensuring their safety, and so the mechanical design of these helmets is extremely difficult for the manufacturer. Therefore, in this report, the mechanical behavior of the pad material is measured experimentally and then it is formulated by theoretical simulation for design of the helmet numerically. Then, an analysis of the collision problem of the helmet is carried out using the characteristics of the pad material obtained in these mechanical tests. Numerical analyses are carried out by changing the material characteristics and movement of physical model while keeping the structure of the helmet and head constant. LS-Dyna is used in the numerical simulation because of its availability in crash analysis. In the analysis results, it was first confirmed that the optimum characteristics of the pad material can be defined by the mechanics of plateau stress. With these results, the concept of a usage limit due to deterioration of the pad material is discussed in addition to the suggestion of helmet specifications according to the physique and exercise capacity of the football players.

The strain distribution of the facial skin surface at the local area near eyes at the instant of blinking are measured for evaluating the effect of cosmetics products. The motion of the skin at the local area as well as the whole face is observed using multiple digital high-speed cameras. Images of the typical blink motion are extracted from the mass of the local images by evaluating the blink motion in the whole face images. Two-dimensional digital image correlation is used for measuring strain. Irregularities and textures of the skin near the eyes are utilized as random patterns in digital image correlation. The strain distribution and its variation with time under various condition of skin such as bare skin, skin care, and foundation are obtained. The effect of cosmetic product on the skin behavior is elucidated by performing the series of the measurement for several subjects.

Many patients are unable to recover completely their social function follow­ing head trauma caused by traffic accidents. Prediction on occur­rence of higher brain dys­function is important for those who will be able to return home after head trauma. In this study we tried to reproduce injury condition in cases with traumatic higher brain dysfunction caused by traffic accidents and discussed the relationship between the mecha­nical impact to brain and higher brain dysfunction. We reproduced 6 cases using combination of multi­body analysis and finite element (FE) head modeling. As a result, the strain on the frontal lobe caused by an injury condition was suggested to contribute to the onset of attention disturbance during the chronic phase of treatment. This method has the possibility to predict the onset and severity of traumatic higher brain dys­function.

Following head trauma caused by traffic accidents, many patients are unable to completely recover their social functions due to higher brain dysfunction although they are able to return home. To predict the onset and severity of post-traumatic higher brain dysfunction, the visualization of responsible injury is considered urgent. In this study, we focused on five patients with higher brain dysfunction following head trauma caused by traffic accidents to establish a method for quantitatively evaluating higher brain dysfunction. The injury conditions were reproduced on the basis of multibody dynamic and collision analyses using finite element (FE) modeling of the human head to determine mechanical responses inside the cranium of these patients. The strain on the frontal lobe generated by an injury condition was suggested to contribute to the onset of attention disturbance during the chronic phase of medical treatment. Reproduction analysis of the injury conditions using FE modeling of the head could predict the onset and severity of traumatic higher brain dysfunction.

Severe head injuries can occur in cyclists involved in traffic accidents. In Japan, head injuries accounted for 62% of cyclist fatalities in 2015 (ITARDA, 2016). The purpose of this study is to estimate head injuries for cyclists and quantify the effectiveness of a bicycle helmet by performing finite element (FE) simulations of head impacts against roads. Impacts with and without a helmet over a range of relative head velocities and head impact angles were simulated. A number of possible head injuries were assessed skull fracture by skull strain, traumatic intracerebral hematoma (ICH) by brain pressure, brain contusion by brain negative-pressure and von Mises stress, and moderate and severe diffuse axonal injuries (DAIs) by von Mises stress. Results showed that without a helmet, the peak values of all metrics exceeded the 50% probability point for head injury in all impacts. The 50% probability points of moderate and severe DAIs were exceeded under impacts of 8.22 m/s at 26.5 degrees and 10.33 m/s at 15.0 degrees for moderate DAI, and 10.33 m/s at 15.0 degrees for severe DAI, without a helmet. All the peak values were reduced when a bicycle helmet was worn, and the largest reduction was found in the skull strain. These results predict that the risks of head injuries due to road impacts may be considerably decreased by helmet use.

<p> The aim of this study is to visualize Judo accident using the reconstruction analysis for the medical field, and propose an injury risk assessment system based on detailed statistical analysis of the past cases for calling medical field's attention. In the assessment system, the mechanical input caused by the accident is obtained from replication of the motion called as Waza in Judo based on game video by using whole body numerical simulation, then the obtained acceleration response of the head was input to a human head finite element model to evaluate the injury risk by using the calculated mechanical parameter inside the skull. In this study, the replicated motion based on the video was verified by comparing the movement loci of the player's head analyzed by a three-dimensional motion analysis system experimentally. In this paper, two concussion suspected accident cases were analyzed by using the purposed evaluation system, and the concussion was evaluated by seven mechanical parameters generated inside the skull caused by the collision. The injury risk evaluated by the parameters belonged to the dangerous range that may cause concussion. The brain injury risk can be successfully estimated by the reconstructed simulation of the game video and FE analysis.</p>

In order to predict how much the human ligamentum flavum (LF) will be deformed during insertion of an epidural needle, the elastic modulus of a porcine LF was determined with a tensile test. LF specimens collected from porcine spines in a slaughterhouse were prepared into a rectangular shape with connecting vertebral bones. Preconditioning was repeated 20 times up to 0.1 MPa before the porcine LF specimens were tested. Strain rate was set at 0.03 and 0.5 s^-1, in reference to previous studies. To calculate strain, we divided elongation length, measured with a laser distance sensor, by the initial length of each specimen. The stress-strain diagram exhibited a linear relation up to 30% strain. When tensile test stopped at 30% strain, force maintained a constant value without stress relaxation, which meant the specimen was exhibiting an elastic property only. Average Young's modulus was 0.13 ± 0.054 MPa (mean ± SD) for 0.03 s^-1, and 0.14 ± 0.055 MPa (mean ± SD) for 0.5 s^-1. Effect of strain rate was not statistically significant. Elastica-von-Gison stained image of the specimens revealed that they consisted of the LF and adipose, and that the average thickness of the porcine LF was thinner than that of specimens. Young's modulus of the porcine LF was estimated as 0.21 MPa in the thoracic and 0.19 MPa in the lumbar.

The collision accident in collegiate football game was simulated based on the game video and the concussive impact on the head was analyzed. First, the collision motion of players was reproduced based on the video by using motion analysis, and the translational and rotational velocities, relative position and contact location of the struck and the striking players' heads just before the collision were calculated. Then the data obtained were input to two helmeted finite element (FE) human head models as the initial condition, and the brain injury risk was evaluated by using the impact analysis. The FE helmet model was validated by a drop test of the helmet in which the head impactor was embedded. In the present study, two concussion suspected accident cases were analyzed then the concussion was evaluated by ten mechanical parameters generated inside the skull caused by the collision. The injury risk evaluated by multi parameters belonged to the dangerous range that may cause concussion and was consistent with the diagnosis of the medical team doctor. The brain injury risk can be successfully estimated by the reconstructed simulation of the game video and FE analysis. To our knowledge, this study is the first attempt in Japan to estimate the brain injury risk systematically by a combination of game video analysis which is originally introduced for the players' health care and FE analysis by helmeted human head model. In the future, brain injury risk caused by an accident can be evaluated with higher accuracy by analyzing more accident cases.

This study proposes a tuning method of model-based controller with adaptive parameters in the controller, that is effective to maintain the control performance and stability for characteristic variation of the structures. The main idea of this tuning method is tuning the poles of the controller that have great effect on the control performance and stability. Simultaneous perturbation stochastic approximation (SPSA) is used as tuning algorithm. The vibration control simulation by using the proposed tuning method is carried out. The perturbations are given to the model of the controlled object to change its physical characteristics, and the controller is tuned for adapting to these changes. This study shows the effectiveness of the proposed tuning method by conducting the simulations.

Diffuse axonal injury (DAI), a major component of traumatic brain injury, has been suggested to result from inertial forces applied on the head. DAI is a manifestation of microstructural cellular trauma and is accompanied by distinct morphological changes. Focal axonal swellings are the morphological hallmarks of DAI pathology and lead to the disconnection of neurons from target tissues resulting in neuronal death. Our goal is the understanding of the quantitative relation between strain acting on the axons and generation of axonal swellings. In present study, we developed an in vitro two dimensional stretch device that reproduced axonal swellings of in vivo DAI, and verified the input-output relation of the device. Then using this device, we exposed PC12 cells, which extend structurally axon-like cylindrical protrusions in culture, to 10% or 20% strains and measured the length of neurites and number of swellings in PC12 cells until 48 hours after the exposure to stretch by microscope observation. As a result, the length of neurites transiently shortened at 5 minutes and 1 hour after exposure to strain compared to those before exposure to strain. On the other hand, swellings were generated at 5minutes after exposure to strain and were the most in number at 1 hour after exposure to strain compared to swellings in normal neurites. Moreover, the number of swellings in neurites exposed to 20% strain was significantly larger than that exposed to 10% strain at 5 minutes after exposure to strain. These results suggest that production of axonal swellings correlate with strain magnitude acting on the axons.

In this study, the mechanism of cerebral contusion was investigated using finite element analysis. A finite element human head model was constructed and used to simulate of 9 real-world fatal cerebral contusion accident cases. In these simulations, the impact velocities of the impact objects were estimated on the basis of the available information such as the regions of skull fracture and cerebral contusion. The pressure fluctuations inside the skull and the input force durations in each case were obtained using these simulations. These results show that in case of coup contusion, a negative pressure occurs on the impact side and is directly correlated with short force durations. In contrast, in case of contrecoup contusion, negative pressure occurs on the opposite side of impact and is directly correlated with long force durations. As the result, coup contusions are caused when the input force durations are short, contrecoup contusions are caused when the input force durations are long. © 2011 by JSME.

Human umbilical veinendothelial cells (HUVECs) were exposed to an impact pressure of -100 kPa and changes in morphology of HUVECs and expression of vascular entodhelial (VE)-cadherin were examined in order to investigate effect of exposure to impact pressure on endothelial permeability. In the results, HUVECs exposed to impact pressure were absent locally. VE-cadherin in control were continuously expressed along peripheral region of cells. However, VE-cadherin in HUVECs exposed to impact pressure were sparsely expressed along peripheral region of cells and partly distributed in cells. These findings suggest that the exposure to impact pressure may change the expression and the distribution of VE-cadherin, influencing endothelial permeability.

When the human head is loaded by the rotational impact, a diffuse axonal injury (DAI) is caused in human brain. DAI is caused by the shear strain and shear strain rate that arises at the brain stem when the head does the rotation movement by the angular acceleration. However, the influences on the shear strain and shear strain rate by the change in parameters of the angular acceleration were not described. In this study, various accelerations that differs parameters were given to a human head finite element model, the influence on the shear strain and shear strain rate caused on the brain stem was considered. In this report, rise time of angular acceleration was focused on. As the result, the change in rise time did not influence the shear strain so much. But the change in the rise time greatly influenced the shear strain rate.

In this study, the effects of a dynamic strain in the cytotoxicity and mortality of the PC12 cell line were evaluated by using impact experiment with huge acceleration. In order to consider the influence of axonal damage on nerve cells, 2 types of nerve cells were used for the impact experiments, i.e. with and without axons. The cytotoxicity and mortality of cells were evaluated by the input acceleration, strain and strain rate and the strain rate seemed to be the most appropriate to evaluate the cytotoxicity and mortality of cells. Cells with axons showed higher cytotoxicity and mortality than cells without axons, when the strain rate was larger than 13.11 (1/s). Damage to axons was confirmed by terminal swellings and beadings of the axons. These data indicated that the presence of axons increased the cytotoxicity and mortality of cells. Copyright © 2010 by JSME.

When a human receives a heavy impact on the head, a focal brain injury and/or a diffuse axonal injury (DAI) are caused. The focal brain injury is caused by partial strain of a brain and/or rapid pressure fluctuation inside the skull. DAI is widespread damage to the white matter of the brain and caused by the shear stress. A focal brain injury is usually associated with brain tissue damage visible to the naked eye. However, the pathological basis of DAI can be observed only under the limited condition, and the bases are very difficult to be found in morbid anatomy. DAI may be unnoticed when focal brain injury concurs. In this study, various impacts were given to a finite element human head model, the condition of causing the focal brain injury and DAI was evaluated using average acceleration and the duration of the head which obtained from the computer simulations, and the possibility of concurrence of both damages was verified. As a result of computer simulation which is based on judicial autopsy report, it was shown the possibility of concurrence of DAI and focal brain injury was high, even though the cause of death was judged as focal brain injury.

The mechanism of coup contusion and contrecoup contusion was studied by impact experiment and finite element analysis. The finite element analysis of the cerebral contusion was carried out by taking skull fracture into consideration to show the relationship of the force duration, pressure fluctuation inside the human head model and the coup contusion, contrecoup contusion. The threshold of the skull fracture was evaluated by using Japan Head Tolerance Curve as -10MPa. The result showed coup contusion would occur when impacted by light weight impactor with high velocity which yields short force duration, and contrecoup contusion would occur when impacted by heavy weight impactor with low velocity which yields long force duration. The result showed on 5 second or less of the force duration, coup contusion occurs dominantly, and contrecoup contusion occurs dominantly over 5 second.

The mechanism of cerebral contusion was studied by using finite element analysis. Prior to numerical analysis of a finite element human head model, experimental study of an impact loading for a water-filled acrylic cylindrical container was carried out. The frequency of fluctuation of internal pressure was close to the natural frequency of the acrylic container. The human head model was analyzed by finite element analysis and the numerical result was compared with the result of the experimental study reported by Nahum and good agreement was obtained. In impact analysis, mass and velocity of the impactor were changed so as to keep the energy constant and intracranial pressure fluctuations of the impact side and the opposite side were obtained. When the input force duration was short, the thumping pressure fluctuation between the positive and negative pressure with higher frequencies were observed both at the impact side and the opposite side. As the input force duration became longer, the pressure fluctuation was suppressed and the positive pressure became dominant at the impact side and the negative pressure became dominant at the opposite side, and lower frequencies became dominant. © 2008, The Japan Society of Mechanical Engineers. All rights reserved.