ZHANG YUELIN

To examine the tolerance thresholds of cerebral capillaries and to apply these findings to future head injury standards, we developed a device designed to replicate the pressure fluctuations experienced within the cranium during head trauma. This apparatus features a chamber filled with phosphate buffer solution and sealed at the top with a silicone membrane. An iron ball was released from a predetermined height, penetrating the silicone membrane and exerting compressive pressure on the cells within the chamber. The device can generate compressive pressures ranging from tens of kPa to several hundreds of kPa over durations ranging from several milliseconds to several tens of milliseconds. Additionally, we constructed a finite element model of the device to visualize the pressure distribution within the chamber. Finally, we assessed cell viability under impact loads, demonstrating that cell viability decreased proportionally with the applied pressure.

In baseball, frequent ball head collisions are high-speed collisions with low-mass objects, a characteristic concussion injury situation compared to other sports, suggesting that the mechanism and threshold for concussion onset may be different. In this study, we investigated the mechanical response of the brain during ball impact using finite element analysis. The peak values of all mechanical parameters of the brain increased in dependence on the translational velocity of the ball. As the rotational velocity of the ball was increased, the rotational acceleration and the maximum principal strain increased, but the translational acceleration did not change. The increase in peak values when the translational velocity of the ball was changed was greater than the increase in peak values when the rotational velocity of the ball was changed for all the brain mechanical parameters. This is thought to be due to the increase in impact force, suggesting that translational velocity of the ball has a greater effect on the brain dynamic response than rotational velocity of the ball.

The autopsy is performed when a case is suspected, and the autopsy physician makes an educated guess as to the circumstances of the accident, which is the decisive factor in determining the case. Conversely, in head trauma cases, the injury situation can be inferred by simulation from the mechanical point of view. In this study, we estimated the behavior of the victim by whole-multi-body analysis, calculate the mechanical responses in the brain at the time of collision by head finite element analysis, and compared the calculated results with the location of the victim’s injury to verify the validity of accident reconstruction. In a hit-and-run case, we estimated the violations traffic regulations, the vehicle type, the vehicle speed, and the relative position of the victim and the vehicle. The results demonstrated the possibility of quantitative evaluation by adding mechanical information to the opinion findings of forensic experts.

A method for evaluating the stress triaxiality of thin steel plate is studied. Three-dimensikonal displacements and the surface strains of high strength steel specimen are measured using a stereo image correlation method. The measurement is performed from both sides of the front and back to evaluate not only in-plane strains but also through-thickness strains. From the mesured strains, the principal stresses are calculated based on the total strain theory, and then the stress triaxiality is obtained. Experimental results show that the stress triaxiality history can be obtained by the proposed method.

In this study, the strain evaluation around the fracture area of sheet metal containing U-shaped notch has been conducted by using experiment and numerical calculation. In the experimental approach, DIC method was used for calculating the strain in the specimen. Also, in the numerical simulation, two kinds of FE softwares were used. The variation of stress triaxiality η and the effect of out-of-plane strain on the parameter η were investigated.

第33回宇宙構造・材料シンポジウム（2017年12月8日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)), 相模原市, 神奈川県 33rd Symposium on Aerospace Structure and Materials (December 8, 2017. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 資料番号: SA6000116010 レポート番号: A11

Recent years the number of patients that has articular cartilage disease is increasing. So it needs to make noncontact diagnostic method of articular cartilage for early diagnosis. By making clear mechanical properties of articular cartilage, diagnosing osteoarthritis can be expected before articular cartilage is worn away by rubbing. This paper describes the development of a new method for measuring viscoelastic properties of articular cartilage by acoustic excitation in low frequency range. Low frequency of 1～100Hz load is applied to the articular cartilage when human is walking or running. To evaluate articular cartilage’s mechanical function by using non-contact method is socially demanded for minimally invasive diagnosis. In this study articular cartilage’s complex shear modulus is obtained by measuring phase velocity and damping coefficient of surface wave on articular cartilage that is excited by acoustic vibration. In the acoustic excitation system, the vibration is generated by a wide range speaker and the surface wave displacements in two points are measured by two laser displacement sensors simultaneously. The system is constructed and the measurement experiment of articular cartilage is performed. Frequency of input acoustic vibration is 40~90Hz. The result shows steady-state vibration is excited at surface of articular cartilage. Therefore acoustic excitation is able to produce surface wave at arbitrarily frequency of articular cartilage.

In this study, to evaluate the strain distribution of the articular cartilage in three-dimension, digital volume correlation method is used. Digital volume correlation program is constructed and used to measure the displacement and strain of the porcine knee joint under compressive load. The deformation of the porcine knee joint is obtained from MR image under non-compressive and compressive load. The result of the analysis of the compression experiment shows that the strains are observed at the compressive area at three-dimensions. It is possible to obtain displacement and strain distribution of the articular cartilage by using MRI.

This paper studies a method for evaluating the stress triaxiality and the fracture strains accurately considering the deformation of thin steel sheets which are used for an automobile body frame. Three-dimensional displacements and surface strains of thin steel sheets are measured using a stereovision. In particular, to measure the deformation of the board thickness of the steel sheets, the measurement is performed from the both sides of the steel sheet. Based on strain incremental theory, the stress triaxiality is evaluated from the measured strains considering the variation of the thickness of the steel sheets. The effectiveness of the proposed procedure is validated by applying it to the evaluation of the stress triaxiality of high strength steel sheets. Results show that the stress triaxiality and the fracture strains can be evaluated by the proposed method.

In this research, a thermal strain on an electronic packaging is measured by digital image correlation with its periodical systematic error elimination method. To evaluate the strain at micro area, a microscopic lens and micro particles for the speckle pattern is used. Prior to the evaluation of the thermal strain on the electronic packaging, the thermal strain of a brazed bi-metal is measured. Results show that the strain distribution not affected with periodical error is evaluated. In addition, the strain distribution affected by mismatch of thermal expansion coefficients is observed around the boundary. However, it seems that some methods such as an introduction of other micro particles for the speckle pattern should be considered to enhance the displacement measurement accuracy.

Typical injury in judo is concussion and acute subdural hematoma by head collision to the judo tatami, but effective guideline for prevention based on biomechanical point of view has not been proposed. In this study some Waza to cause a risk to hit a head on a tatami were performed by judo players and recorded by VICON system. These motions were reconstructed by MADYMO by using VICON data and kinetic data and hit part of a head on the tatami, which were used as input data for a FE human head model, were obtained. The strain and stress of the brain tissue were calculated in detail by the FE human head model and injury risk was predicted.

The collision accident in collegiate football game was simulated based on the game video and the concussive impacts on the head were analyzed. First, the collision motions of players were reproduced based on the video by using MADYMO software, 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 head models as the initial condition, and the brain injury risk was evaluated. In the present study, 2 accident cases concussion suspected were analyzed; The results showed that the all peak values belonged to the dangerous range that may cause concussion and were consistent with the diagnosis of the medical team doctor. It means that the brain injury risk can be estimated by the reconstructed simulation of the game video and finite element 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 finite element analysis by helmeted human head model.

This paper discusses the coefficient of restitution about oblique collision. There are two kinds as a definition of restitution coefficient called as Newton's impact low and Poisson's impact low. The former one is based on the normal velocity change that measured before and after impact. The latter one is based on the impulse change during impact. To observe and compare these coefficients of restitution, use numerical analysis. We formulated the model of rigid body in rigid v-block by using unilateral contact method which contains no approximation but can exactly express a rigid body's transformation on collision. Consider the differences of two kinds of coefficients and find better way of measuring coefficient of restitution.

This paper proposes a health monitoring system for detecting a blockage in a pipe using the acoustic vibration excitation with high power laser. Non-contact acoustic impulse excitation can be applied to acoustic fields by using a shock wave generated by laser-induced breakdown in air. A high-power Nd:YAG pulse laser is used in the present vibration testing system for generating the laser-induced breakdown in acoustic fields. The laser excitation makes a precise measurement of the acoustic resonant frequency in wide frequency range possible with high reproducibility. The acoustic resonant frequency changes by the blockage and its position in the pipe. In this study, the detection of the blockage in the pipe is focused. The acoustic resonant frequencies in the pipe with/without the blockage are measured by a microphone. Then the position of the blockage is identified by evaluating the cross section ratio between the pipe and the blockage analyzed from the measured data.

Accidents of head injury have been increasing since judo became a required class in junior high school at April 2012 in Japan. Although typical injury in judo is concussion and acute subdural hematoma by head collision to the judo tatami, effective guideline for prevention based on biomechanical point of view has not been proposed. In this study some Waza to cause a risk to hit a head on a tatami were performed by judo players and recorded by VICON system. These motions were reconstructed by MADYMO by using VICON data and kinetic data and hit part of a head on the tatami, which were used as input data for a FE human head model, were obtained. The strain and stress of the brain tissue were calculated in detail by the FE human head model and injury risk was predicted.

In this study, Judo and American Football (AF) are spotlighted as typical physical contact sports that concussion or subdural hematoma could happen during a play. In Judo, "waza" to cause a risk to hit a head on a tatami were performed by Judo players and recorded by VICON system and the motions were reconstructed by MADYMO by using VICON data and kinetic data and hit part were generated. In Americal football, the moment of concussion was reconstructed by MADYMO by observing the accident data in real play recorded on a video and kinetic data and hit pat were generated. In both cases the strain and stress of the brain tissue were calculated in detail by the FE human head model and injury risk was predicted, respectively.

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.

In this study, in order to measure the softness of cultured tissue, ball indentation tests were performed. As first step, the principle of ball indentation test was applied to the thin silicone rubber sheet (t=0.1mm), which achieved results confirm the validation of the measurement result. Next step, Young's modulus of monolayer cultured nerve cell (PCI2) was measured, and the validation of the measured results was confirmed by comparing with previous studies. The Young's modulus of the cell body is 36.5kPa, and distal, middle and proximal of neuritis are 50.2kPa, 21.8kPa and 51.5kPa, respectively. In addition, Young's modulus of three-dimensional gel-culture system consisting of primary human gingival fibroblasts (GF) and gingival epithelial (GE) cells in collagen gels were measured. The Young's modulus of whole gel and gingival epithelial cells are 3.46kPa and 81.9kPa, respectively. The results were shown the possibility of measuring the Young's modulus of each layer of cultured tissue in the case of laminate structure.

Degradation of extra-cellular matrices is an integral pathophysiological part in periodontitis. Previously, we have isolated "aggressive fibroblasts" derived from severe periodontitis regions from human patients and established an in vitro periodontitis model using a three dimensional (3D) culture system. We have been screened candidate drugs for periodontitis by evaluating inhibition of collagen degradation employing this model. Although several drugs effectively inhibited collagen gel degradation, some of them have resulted fragile collagen gel. Therefore, we tried to evaluate collagen gel "softness" using ball indentation tests together with residual amount of collagen. Evaluation of candidate drugs by the Young's modulus of in vitro periodontitis model was useful, and one of the drugs (herbal medicines) successfully improved "softness" of the gel. These results suggested that the measurement of the Young's modulus of in vitro periodontitis model may be a useful tool for screening of candidate drugs for periodontitis.

In studying considered two different boundary conditions for human head impact response by using a finite element analysis(FEM). In tied condition all nodes are connected tightly and in slide condition relative displacement between two contact-faces are allowed in the direction of contact face. The three-dimensional finite element human head model constructed hexahedron solid elements based on MRI data to explain the mechanism of closed head impact injury. This investigation was to examine the boundary conditions of human head organization with validity of modeling. By this report, a procedure of constructing the model only with MRI data is reported and the results of both boundary conditions were compared with the impact experiment by acrylic cylindrical container and Nahum's cadaver experiment.

In this study, the resistance of PC 12 cells against strain is investigated by the impact test. The resistance of cell body is evaluated by the cell mortality and the citotoxicity. The axonal injury is evaluated by the morphological observation. The cell mortality and the citotoxicity increase according to the increase of strain rate. PC 12 cells with axons show larger cell mortality and citotoxicity than without axons, and the axons of injured/dead cells show the morphological features of axonal injury. This result shows the difference between the impact resistance of neuronal cells with axons and without axons quantitatively.

The finite element analyses of the cerebral contusion based on judicial autopsy reports were performed in order to show the relationship between the input force duration and occurrence of the coup contusion, contrecoup contusion. In finite element analysis the skull fracture was taken into consideration. The result showed that coup contusion would occur when impacted by light weight impactor with high velocity which yielded short force duration, and contrecoup contusion would occur when impacted by heavy weight impactor with low velocity which yielded long force duration. When force duration was less than 5ms, coup contusion tended to occur, and contrecoup contusion tended to occur when force duration was more than 5ms.