Head injury prediction capability of the HIC, HIP, SIMon and ULP criteria

The objective of the present study is to synthesize and investigate using the same set of sixty-one real-world accidents the human head injury prediction capability of the head injury criterion (HIC) and the head impact power (HIP) based criterion as well as the injury mechanisms related criteria provided by the simulated injury monitor (SIMon) and the Louis Pasteur University (ULP) finite element head models. Each accident has been classified according to whether neurological injuries, subdural haematoma and skull fractures were reported. Furthermore, the accidents were reconstructed experimentally or numerically in order to provide loading conditions such as acceleration fields of the head or initial head impact conditions. Finally, thanks to this large statistical population of head trauma cases, injury risk curves were computed and the corresponding regression quality estimators permitted to check the correlation of the injury criteria with the injury occurrences. As different kinds of accidents were used, i.e. footballer, motorcyclist and pedestrian cases, the case-independency could also be checked. As a result, FE head modeling provides essential information on the intracranial mechanical behavior and, therefore, better injury criteria can be computed. It is clearly shown that moderate and severe neurological injuries can only be distinguished with a criterion that is computed using intracranial variables and not with the sole global head acceleration.     

Evaluation of head response to ballistic helmet impacts using the finite element method

Injuries to the head caused by ballistic impacts are not well understood. Ballistic helmets provide good protection, but still, injuries to both the skull and brain occur. Today there is a lack of relevant test procedure to evaluate the efficiency of a ballistic helmet. The purpose of this project was (1) to study how different helmet shell stiffness affects the load levels in the human head during an impact, and (2) to study how different impact angles affects the load levels in the human head. A detailed finite element (FE) model of the human head, in combination with an FE model of a ballistic helmet (the US Personal Armour System Ground Troops’ (PASGT) geometry) was used. The head model has previously been validated against several impact tests on cadavers. The helmet model was validated against data from shooting tests. Focus was aimed on getting a realistic response of the coupling between the helmet and the head and not on modeling the helmet in detail. The studied data from the FE simulations were stress in the cranial bone, strain in the brain tissue, pressure in the brain, change in rotational velocity and translational and rotational acceleration. A parametric study was performed to see the influence of a variation in helmet shell stiffness on the outputs from the model. The effect of different impact angles was also studied. Dynamic helmet shell deflections larger than the initial distance between the shell and the skull should be avoided in order to protect the head from the most injurious threat levels. It is more likely that a fracture of the skull bone occurs if the inside of the helmet shell strikes the skull. Oblique ballistic impacts may in some cases cause higher strains in the brain tissue than pure radial ones.     

MRI-based finite element modeling of head trauma: spherically focusing shear waves

A powerful tool for investigating the physical process producing head trauma is finite element (FE) modeling. In this paper, we present a 3D FE model of the human head that accounts for important geometric characteristics of the various components within the human head through an efficient magnetic resonance imaging voxel-based mesh generation method. To validate the FE model, a previous cadaver experiment of frontal impact is simulated, and this is where heretofore unknown wave patterns are discovered. The model is run under either of two extreme assumptions concerning the head-neck junction—free or fixed—and the experimental measurements are well bounded by the computed pressures from the two boundary conditions. In both cases the impact gives rise to not only a fast pressure wave but also a slow and spherically convergent shear stress wave which is potentially more damaging to the brain tissue.     

基于三维头部数值模型的颅脑碰撞损伤机理研究

头部碰撞载荷会致使颅脑发生创伤性脑损伤（Traumatic Brain Injury,TBI）。其中,脑组织挫裂伤是最为常见的一种,具有高死亡率与高致残率的特性。该文基于数值模拟方法对其开展相关研究,揭示其损伤机理,对该类损伤的预防救治与相关防护设备的开发都具有重要意义。首先,该文基于颅脑的核磁共振切片建立了人体头部三维数值模型,该模型真实地反映了颅脑的生理特征与细节构造。在该模型中,颅骨采用典型类三明治结构进行表征,其内外层为刚度与密度较大的骨密质,中间层为骨松质。为了真实反映脑组织与颅骨间的相互作用,将脑脊液与蛛网膜小梁简化为均质整体,采用状态方程表征脑脊液的液态特性,并通过较小的剪切模量表征蛛网膜小梁的剪切传递作用。然后,基于死尸前额碰撞实验对三维头部数值模型的有效性进行验证。该头部模型采用三种不同的颈部约束边界条件对前额碰撞实验进行数值模拟,模拟结果表明:自由边界条件下的模拟结果与实验数据吻合良好,验证了该头部碰撞模型的有效性;而在竖向约束边界条件或固定边界条件下颈部的约束过于刚硬,导致撞击处与对撞处的颅内正、负压力交替变换,与实验结果相比出现较大偏差。最后,利用验证的头部碰撞模型对枕部碰撞过程进行数值模拟,并结合前额碰撞的模拟结果,分别从脑组织压力（体积变形）与Mises应力（剪切变形）等方面对颅脑的动态响应规律进行分析;进一步结合医学上颅脑碰撞损伤的统计数据,揭示了脑组织挫裂伤的损伤机理,建立了相应的损伤准则。     

Influence of stiffness and shape of contact surface on skull fractures and biomechanical metrics of the human head of different population underlateral impacts

The objective of this study was to determine the responses of 5th-percentile female, and 50th- and 95th-percentile male human heads during lateral impacts at different velocities and determine the role of the stiffness and shape of the impacting surface on peak forces and derived skull fracture metrics. A state-of-the-art validated finite element (FE) head model was used to study the influence of different population human heads on skull fracture for lateral impacts. The mass of the FE head model was altered to match the adult size dummies. Numerical simulations of lateral head impacts for 45 cases (15 experiments × 3 different population human heads) were performed at velocities ranging from 2.4 to 6.5 m/s and three impacting conditions (flat and cylindrical 90D; and flat 40D padding). The entire force-time signals from simulations were compared with experimental mean and upper/lower corridors at each velocity, stiffness (40 and 90 durometer) and shapes (flat and cylindrical) of the impacting surfaces. Average deviation of peak force from the 50th male to 95th male and 5th female were 6.4% and 10.6% considering impacts on the three impactors. These results indicate hierarchy of variables which can be used in injury mitigation efforts.     

Finite element simulation of the residual stresses in high strength carbon steel butt weld incorporating solid-state phase transformation

This paper presents a sequentially coupled three-dimensional (3-D) thermal, metallurgical and mechanical finite element (FE) model to simulate welding residual stresses in high strength carbon steel butt weld considering solid-state phase transformation effects. The effects of phase transformation during welding on residual stress evolution are modeled by allowing for volumetric changes and the associated changes in yield stress due to austenitic and martensitic transformations. In the FE model, phase transformation plasticity is also taken into account. Moreover, preheat and inter-pass temperature are included in the modeling process. Based on the FE model, the effects of solid-state phase transformation on welding residual stresses are investigated. The results indicate the importance of incorporating solid-state phase transformation in the simulation of welding residual stresses in high strength carbon steel butt weld.     

Nonlinear multibody dynamics and finite element modeling of occupant response: part I—rear vehicle collision

With the rise in vehicle ownership, the need to reduce the risk of injury among vehicle occupants that arises from vehicle collisions is important to occupants, insurers, manufacturers and policy makers alike. The human head and neck are of special interest, due to their vulnerable nature and the severity of potential injury in these collisions. This work is divided into two parts: In Part I, we focus our attention to modeling rear collision that could lead to whiplash. Specifically, two multibody dynamics (MBD) models of the cervical spine of the 50th percentile male are developed using realistic geometries, accelerations and biofidelic variable intervertebral rotational stiffness. Furthermore, nonlinear finite element (FE) simulations of two generic compact sedan vehicles in rear collision scenario were performed. Using the acceleration profiles measured at the driver’s seat of the colliding vehicles, FE simulation of a seated and restrained occupant in rear collision was performed to determine the occupant response. The resultant accelerations, measured at the T1 vertebra of the occupant model, were used as an input to the MBD models to obtain their kinematic response. Validation of the MBD models shows great agreement with experimentally published data. Comparison between the MBD and FE simulations for a 32 km/h vehicle-to-vehicle impact shows similar trends in head trajectory. However, the MBD models reported less peak head displacements compared to the FE model. This is attributed to the failure of the anterior longitudinal ligament at the mid cervical spine leading to increased intervertebral rotation in the FE model.

     

Finite-element simulation of firearm injury to the human cranium

An advanced physics-based simulation of firearms injury to the human cranium is presented, modeling by finite elements the collision of a firearm projectile into a human parietal bone. The space-discretized equations of motion are explicitly integrated in time with Newmark's time-stepping algorithm. The impact of the projectile on the skull, as well as the collisions between flying fragments, are controlled through a nonsmooth contact algorithm. Cohesive theories of fracture, in conjunction with adaptive remeshing, control the nucleation and the propagation of fractures. The progressive opening of fracture surfaces is governed by a thermodynamically irreversible cohesive law embedded into cohesive-interface elements. Numerical results compare well with forensic data of actual firearm wounds to human crania.     

Effects of PVA sponge containing chitooligosaccharide in the early stage of wound healing

Poly(vinyl alcohol) (PVA) sponges with different chitooligosaccharide (COS) content were prepared for wound-dressing application. The morphological structure of PVA sponges was observed by scanning electron microscopy. As the concentration of COS-loaded PVA sponge increased, the average pore size of sponge decreased and the release rate of COS from the sponge also slightly decreased. The accelerating effect of the COS-loaded PVA sponges on open wound healing in rats was investigated by macroscopic examination and measurement of wound area. The COS-loaded sponges were found to be very effective as a wound-healing accelerator in the early stage of wound healing. The wound treated with the COS-loaded PVA sponge was almost reepithelialized, granulation tissues in the wound were considerably replaced by fibrosis at 8 days after initial wounding. The COS-loaded PVA sponge was considered to be a suitable wound-healing formulation due to its easy preparation and high effectiveness.     

超高强钢制电池包底部球击试验与仿真方法研究

目的 研究超高强钢电池包底部球击工况的仿真分析方法,通过实物试验验证仿真分析方法的准确性。方法 通过建立电池包底部球击的仿真模型,对底部球击工况进行数值模拟,分析球击过程中应力–应变分布和底板承受变形的能量情况。开展底部球击实物试验,并与模拟结果进行对比分析。结果 在球击过程中,随着球击头撞击底板位移的增大,挤压力逐渐增加,底板变形能量也逐渐增加;当挤压力达到10 k N时,仿真位移为19.127 mm,试验结果位移为20 mm。当位移达到20 mm时,仿真底板变形能量为73.716 J,试验结果为70.581J,仿真与试验结果较为一致。结论 超高强钢电池包在底部球击试验中未发生开裂,满足标准要求,数值模拟方法可以为电池包底部球击工况提供指导。     

Optimization of the Chin Bar of a Composite-Shell Helmet to Mitigate the Upper Neck Force

The chin bar of motorcycle full-face helmets is the most likely region of the helmet to sustain impacts during accidents, with a large percentage of these impacts leading to basilar skull fracture. Currently, helmet chin bars are designed to mitigate the peak acceleration at the centre of gravity of isolated headforms, as required by standards, but they are not designed to mitigate the neck force, which is probably the cause of basilar skull fracture, a type of head injury that can lead to fatalities. Here we test whether it is possible to increase the protection of helmet chin bars while meeting standard requirements. Fibre-reinforced composite shells are commonly used in helmets due to their lightweight and energy absorption characteristics. We optimize the ply orientation of a chin bar made of fibre-reinforced composite layers for reduction of the neck force in a dummy model using a computational approach. We use the finite element model of a human head/neck surrogate and measure the neck axial force, which has been shown to be correlated with the risk of basilar skull fracture. The results show that by varying the orientation of the chin bar plies, thus keeping the helmet mass constant, the neck axial force can be reduced by approximately 30% while ensuring that the helmet complies with the impact attenuation requirements prescribed in helmet standards.     

On the mechanism of collective action of a flux of solid particles upon an obstacle

The results of two-and three-dimensional numerical calculations are presented for a steel ball penetrating (i) into a continuous aluminum plate and (ii) into a plate with a longitudinal channel modeling the state of a material resulting from interference of the unloading waves. The data confirm efficiency of the interference mechanism of the action of a flux of solid particles upon an obstacle.     

纵肋与横隔板交叉构造细节穿透型疲劳裂纹扩展特性及其加固方法研究

纵肋与横隔板交叉构造细节是正交异性钢桥面板最易发生疲劳开裂的构造细节,通过建立有限元数值模型,采用断裂力学方法,研究栓接角钢加固方式对该处疲劳易损细节穿透型裂纹的加固效果。基于疲劳试验足尺节段模型相对应有限元模型,建立了纵肋与横隔板焊接处穿透型疲劳裂纹模型,针对栓接角钢和纵肋外侧栓接钢板两种加固技术的加固效果进行评估。研究结果表明:钢桥面板纵肋与横隔板交叉构造细节的疲劳裂纹扩展至一定长度后将发展成穿透型裂纹,裂纹面受力复杂,纵肋腹板内外侧疲劳裂纹扩展特性表现的不一样,但是随着裂纹扩展的逐步进行,裂纹尖端的开裂模式均以复合型开裂为主;栓接角钢加固方式主要抑制纵肋与横隔板交叉构造细节易损部位疲劳裂纹的I型开裂,因此能很好地抑制短裂纹的扩展,但对于该细节处以复合形式扩展的穿透型疲劳裂纹的加固效果并不显著;在纵肋外侧栓接半U形钢板的加固方法能有效改善穿透型疲劳裂纹的等效应力强度因子,并且加固之后均保持在裂纹扩展阈值以下,表明该加固方式对穿透型疲劳裂纹有良好加固效果。     

不同测试方法对射孔弹穿孔性能的评价

采用地面模拟装枪穿钢靶试验、整枪穿环形混凝土靶试验和地面模拟装枪穿砂岩靶试验3种不同的测试方法评价一种114型射孔弹穿孔性能。结果表明:在射孔弹方案研制阶段,选择地面模拟装枪穿钢靶试验,试验成本较低,对优化穿深性能有指导意义;地面模拟装枪穿砂岩靶试验作为射孔弹研制后期的评价方法,贴合射孔弹对地层的射孔效能,对油气增产和射孔弹应用更具指导意义。     

In vivo time-resolved reflectance spectroscopy of the human forehead

We present an in vivo broadband spectroscopic characterization of the human forehead. Absorption and scattering properties are measured on five healthy volunteers at five different interfiber distances, using time-resolved diffuse spectroscopy and interpreting data with a model of the diffusion equation for a homogeneous semi-infinite medium. A wavelength-tunable mode-locked laser and time-correlated single-photon counting detection are employed, enabling fully spectroscopic measurements in the range of 700-1000 nm. The results show a large variation in the absorption and scattering properties of the head depending on the subject, whereas intrasubject variations, assessed at different interfiber distances, appear less relevant, particularly for what concerns the absorption coefficient. The high intersubject variability observed indicates that a unique set of optical properties for modeling the human head cannot be used correctly. To better interpret the results of the analysis of in vivo measurements, we performed a set of four-layer model Monte Carlo simulations based on different data sets for the optical properties of the human head, partially derived from the literature. The analysis indicated that, when simulated time-resolved curves are fitted with a homogeneous model for the photon migration, the retrieved absorption and reduced scattering coefficients are much closer to superficial layer values (i.e., scalp and skull) than to deeper layer ones (white and gray matter). In particular, for the shorter interfiber distances, the recovered values can be assumed as a good estimate of the optical properties of the first layer.     

聚乙烯醇水凝胶/不锈钢摩擦性能研究

利用球-盘摩擦试验机研究润滑状态、载荷、滑动速度和不锈钢球直径对PVA水凝胶/不锈钢球摩擦副摩擦系数的影响.研究结果表明PVA凝胶内的自由水对摩擦副起着良好的润滑作用.在摩擦的起始阶段,干摩擦和润滑剂润滑状态下的摩擦系数相差甚微,随摩擦时间的延长,干摩擦状态下的摩擦系数在短时间内急剧上升,而润滑剂润滑状态下的摩擦系数基本保持不变;摩擦副的摩擦系数随滑动速度和不锈钢球直径的增加而下降,当滑动速度从45r/min升至225r/min时,摩擦副的摩擦系数下降54.24%;摩擦系数随载荷的增加而上升,但在低载荷区,摩擦副的摩擦系数的上升速率明显大于其在高载荷区的上升速率.随着载荷的增加,凝胶中自由水对摩擦副的润滑作用逐渐增强.     

基于ABAQUS二次开发的球形破片侵彻UHMWPE软质防弹衣数值模拟

为准确模拟破片侵彻防弹衣的过程,揭示破片与软质防弹衣相互作用机制,本文基于ABAQUS用户子程序VUMAT编写了适用于模拟软质防弹衣材料力学性能的本构模型,建立了球形破片侵彻软质防弹衣的有限元模型,数值模拟结果与实验吻合较好。本构模型中材料失效模式数据表明,无纬布主要发生纤维拉伸、基体拉伸和压缩失效;在钢球侵彻防弹衣的初期,无纬布上的应力云图一般呈现较规则的圆形或椭圆形,然后再慢慢向四周扩散;钢球侵彻软质防弹衣的过程中伴随有较明显的纤维层间分层失效,未穿透的纤维层中也出现了分层的现象,分层面积从迎弹面到背弹面先减小后增大再减小。      

Nonlinear Dynamic Behavior of Granular Materials in Base Excited Silos

Nonlinear behavior of granular materials stored in steel silos subjected to dynamic base excitation due to earthquake is presented in the current article. Three-dimensional finite element (FE) modeling of the granular material silo is carried out under three-directional earthquake ground acceleration time histories. Granular material is modeled by adopting a continuum approach. The nonlinearity of the granular materials is represented by a hypoplastic material law in the FE approximation. The interface between the granular material and the silo wall is modeled by using surface-to-surface based contact formulation. The horizontal and vertical displacements of the granular material under earthquake ground acceleration at various depths of the silo are studied. Moreover, the stresses induced in the steel silo are also investigated. The static FE simulation and the analytical solution obtained by using Janssen's theory are observed to be in close agreement. Also, the dynamic FE simulations compare with the calculated results using Eurocode 8 part 4 with reasonable accuracy. The stresses in the steel silo wall are higher for loose packing of the granular material as compared to that for the dense packing.     

A study of local deformation and damage of dual phase steel

Deformation and fracture behavior of Dual Phase (DP) high strength steel were investigated by means of a microstructure based Finite Element (FE) modeling. Representative Volume Elements (RVEs) were applied to consider effects of various microstructure constituents and characteristics. Individual stress–strain curves were provided for ferrite, martensite as well as transformation induced Geometrically Necessary Dislocations (GNDs) taking into account in the RVEs. Principally, the GNDs occurred around phase boundaries during quenching process due to the austenite–martensite transformation. Flow behaviors of individual phases were defined on the basis of dislocation theory and partitioning of local chemical composition. Then, flow curves of the examined DP steel were predicted. Furthermore, the Gurson–Tvergaard–Needleman (GTN) model was used to represent ductile damage evolution in the microstructure. Occurrences of void initiation were characterized and damage parameters for RVE simulations were hence identified. Finally, influences of the GNDs, local stress and strain distributions and interactions between phases on predicted crack initiation in the DP microstructure were discussed and correlated with experimental results.     

Three-dimensional finite element analysis of threaded fastener loosening due to dynamic shear load

The two most widespread causes of failure of threaded fasteners subjected to dynamic loads are fatigue and vibration induced loosening. This paper presents results of a study on failure of threaded fasteners by vibration induced loosening caused due to dynamic shear loads. Previous experimental work has revealed that fastener loosening occurs as a result of complete or localized slip at the thread and head contact surfaces. A three-dimensional finite element (FE) model is used to study details of four different loosening processes that are characterized by either complete or localized slip at the head and thread contacts. The FE model is found to be capable of adequately modeling factors that influence slip and predicting the different loosening processes. Primary factors that influence slip at fastener contacts are discussed. The results show that loosening can occur at relatively low shear loads due to the process of localized slip.