Influence of forming effects on the axial crush response of hydroformed aluminum alloy tubes

The impact behaviour of tubular hydroformed axial crush tubes is examined. The results of dynamic axial crush tests performed with both non-hydroformed and hydroformed AA5754 aluminum alloy tubes were compared to predictions from finite element models. Explicit dynamic finite element simulations of the hydroforming and crash events were carried out with particular attention to the transfer of forming history from the hydroforming simulations to the crash models. The values of tube thickness, work hardening, and residual stresses at the end of the hydroforming simulations were used as the initial state for the crash models. In general, simulations performed using the von Mises yield criterion with isotropic material behaviour gave reasonable predictions when compared to experimental data. It was found that it was important to account for the forming history of the hydroforming operation in the axial crush models. The results showed that work hardening resulting from hydroforming is beneficial to increasing the energy absorption during crash, whereas thickness reduction decreased the energy absorption. Residual stresses had little effect on the energy absorption characteristics. It was also shown that the energy absorption characteristics of tubes with the same mass could vary greatly by adjusting the geometry of the tube and the amount of work hardening experienced by the tube during hydroforming.     

Methods to mitigate injury to toddlers in near-side impact crashes

This research focuses on the injury potential of children seated in forward-facing child safety seats during side impact crashes in a near-side seated position. Side impact dynamic sled tests were conducted by NHTSA at Transportation Research Center Inc. (TRC) using a Hybrid III 3-year-old child dummy seated in a convertible forward/rearward child safety seat. The seat was equipped with a LATCH and a top tether and the dummy was positioned in forward-facing/near-side configuration. The test was completed using an acceleration pulse with a closing speed of 24.1 km/h, in the presence of a rigid wall and absence of a vehicle body. A fully deformable finite element model of a child restraint seat, for side impact crash investigations, has been developed which has also been previously validated for frontal and far side impacts. A numerical model utilizing a Hybrid III 3-year-old dummy, employing a similar set-up as the experimental sled test was generated and simulated using LS DYNA. The numerical model was validated by comparing the head and the chest accelerations, resultant upper and lower neck forces and moments from the experimental and numerical tests. The simulation results were observed to be in good agreement to the experimental observations. A numerical model of the near-side laboratory tests, utilizing a Q3s child dummy, was also created for parametric studies regarding different ISOFIX configurations. Further, numerical simulations were completed for both the dummy models with rectangular and cross-shaped sections of rigid ISOFIX systems. In addition, studies were conducted to confine lateral movement of the dummy's head by adding energy absorbing foam on the side wings in the vicinity of the contact region of the CRS. It was observed that the use of rigid ISOFIX system reduced the lateral displacement of the CRS and different injury parameters. Addition of energy absorbing foam blocks was effective in further reducing the lateral displacement of the dummy's head. The lateral displacement of the head was reduced by 68 mm by using cross-shaped section ISOFIX with energy absorbing foam near the vicinity of the head of the Hybrid III 3-year-old dummy compared to the flexible LATCH configuration without foam. For the Q3s dummy, the lateral displacement of the head was reduced by 48 mm by utilizing a cross-shaped section rigid ISOFIX system with the addition of energy absorbing foam compared to the flexible LATCH configuration.     

聚氨酯硬泡连续屏障近场隔振效果分析

传统的连续屏障在缓解环境振动方面已取得比较理想的效果,但其整体稳定性差,对低频的隔振效果不佳。基于此背景,提出了锚杆约束的聚氨酯硬泡连续屏障。通过有限元数值分析方法,对聚氨酯硬泡连续屏障和混凝土连续屏障分别在地面简谐激励和桩振源简谐激励作用下的近场隔振性能进行研究。研究表明:地面振源激励下,混凝土连续墙和聚氨酯硬泡连续屏障对中高频振动有较好的隔振效果,混凝土连续墙对低频(10 Hz)振动隔振效果不佳,聚氨酯硬泡连续屏障对5 Hz~10 Hz的低频振动有很好的隔振效果;桩振源激励下,两种屏障的隔振效果比地面振源激励时效果更好,两种屏障对中高频振动及5 Hz~10 Hz的低频振动有较好的隔振效果。     

Injury potential of a three-year-old Hybrid III dummy in forward and rearward facing positions under CMVSS 208 testing conditions

This research focuses on the injury potential of children in forward and rearward facing child restraint seats in frontal collisions. Vehicle crash tests were completed following the guidelines outlined in the Canadian Motor Vehicle Safety Standard 208 using a Hybrid III three-year-old dummy in a convertible forward/rearward facing child restraint seat. The seat was equipped with a five-point restraining system and the experimental test was completed in the forward facing configuration. A numerical model employing a similar set-up as the experimental crash test was developed and numerically simulated using LS-DYNA. To verify the numerical simulations, the head and chest accelerations as well as neck loads and moments were compared to the experimental findings and it was observed that a reasonable correlation between the experimental and numerical observations existed. Further numerical simulations were completed to investigate the influence of positioning the three-year-old dummy in the rearward configuration on the head and neck injury potential during frontal crash. Through an analysis of injury criteria, using neck loads and head accelerations, it was observed that the rearward facing child dummy sustained significantly lower levels of neck injury criteria while exhibiting similar levels of the head injury criteria as the forward facing child dummy.     

穿越非均匀土体埋地管道地震离心实验研究

穿越非均匀土体经历不同地震作用的埋地管线的变形和残余强度严重影响着管道的安全。该文采用离心振动台分别平行于埋地管道长度方向输入0.6 g和0.3 g峰值地面加速度地震波,研究了埋地管道在一系列地震作用和不均匀土体变形共同作用下的响应,得到了PVC和铝合金两种埋地管道穿越软土/硬土土体的地震响应规律。地震引起不均匀土体的瞬时变形,导致埋地管道最大应变发生在土体分界面和软土中,管道拉伸应变幅值软土要大于硬土,而压缩应变幅值正好相反,硬土中管道拉伸应变幅值小于压缩应变幅值,硬土中管道压缩应变幅值受地震烈度影响比软土大。地震引起的土体永久变形对埋地管道残余变形影响很大,硬土中的管道残余应变为压应变,软土中管道的残余应变为拉压应变交替分布。     

Mixtures of hard and soft grains: micromechanical behavior at large strains

In this paper, several simulations involving the compaction and the shearing of mixtures of hard and soft grains are performed in 2D plane-strain conditions. The multibody meshfree numerical tool developed for this purpose is first presented, and the focus is then put on the influence of the proportions of rigid and deformable grains in the mixture on the mechanical response at large strains. Dedicated postprocessing techniques reveal a wide range of behaviors, both in terms of macroscopic response and in micromechanical phenomena. Broadly speaking, the strength and the dilatancy of the mixture decrease when the proportion of soft grains is increased. There are, however, interesting exceptions to this trend at very high and very low contents of soft grains, which are analyzed in dedicated sections. This preliminary work paves the way to more comprehensive studies of this class of materials, which is still hardly understood but presents some potential in a wide range of applications.     

Crashworthiness of straight section hydroformed aluminium tubes

There exists considerable motivation to reduce vehicle weight through the adoption of lightweight materials, such as aluminium alloys, while maintaining energy absorption and component integrity under crash conditions. The interaction between tube hydroforming and behaviour during crash events was studied using lightweight automotive structural members. Dynamic crush tests were performed on 400 mm length sections of both non-hydroformed and hydroformed EN-AW 5018 aluminium alloy tubes. The force versus crush distance data from 76.2 mm diameter non-hydroformed tubes was compared with results from 76.2 mm square cross-section hydroformed tubes of 2.0 and 3.5 mm initial tube thicknesses. The hydroforming operation was performed using a high-pressure process in which the corner radius of the tube cross-section was varied. Explicit dynamic finite element simulations of the hydroforming and crash events were carried out with particular attention to the transfer of forming history from the hydroforming simulations to the crash models. The values of the tube thickness, work hardening, residual stress, and damage level at the end of the hydroforming simulation were used as the initial state for the crash model. The Gurson–Tvergaard–Needleman constitutive model was used to account for damage based on void nucleation, growth, and coalescence. Numerical predictions of the force versus crush distance response were compared to experimental data. The results have demonstrated that it is important to account for thickness changes and work hardening from previous forming operations, in simulating crash events. The energy absorbing capabilities of the hydroformed aluminium tubes decreased with sharper corner radius due to increased thinning of the material during the hydroforming process. It was found that the simulations slightly over-predicted the mean crush force compared to the experimental data.     

A simplified calculation model for the sliding contact boundaries in a hydrostatic piston mechanism

The objective of this study was to discuss simplified calculation models for the piston/cylinder sliding mechanism in which boundary contact partly occurs invariably. An efficient prediction of the boundary leakage and friction is often needed, such as in a swash-plate axial piston machine whose lubrication test is hard to perform due to the mechanism complexity. In order to model this physically uncertain lubrication regime, two calculation models were compared to compute the lubrication behaviors: “rigid boundary model”, whose theoretical concept was previously reported in the literature, and “elastic boundary model”, newly proposed in this study. Developed numerical algorithms commonly facilitated the simultaneous calculation of body motion and fluid film pressure to observe piston motion, reaction forces, and power loss. The results showed that simulations using the elastic boundary model should be more helpful for the prediction in the earlier development stage than the previous model since the methodology provides much less simulation time than full-order calculation, higher accuracy than the rigid model, and useful engineering parameters such as surface stress. The proposed calculation model can be extended to various asymmetrically loaded reciprocating piston mechanisms for efficiently predicting the lubrication behavior.     

Rigid body water impact-experimental tests and numerical simulations using the SPH method

Statistics show that water impact of an aircraft in emergency is likely to have tragic consequences and therefore new researches on this topic are recommendable. In 2005, the GARTEUR AG15 was established to improve the SPH method for application to helicopter ditching. As a contribution, water impact drop tests using rigid bodies were performed at the Politecnico di Milano LAST Crash Lab to collect data and validate the numerical models. During the tests, impact decelerations were measured and suitably pressure transducers were developed to measure the impact pressures. Numerical simulations were carried out by adopting the SPH method to model the fluid region. A close experimental-numerical correlation was obtained. Findings are reported and guidelines for further investigations are proposed.     

Excluded Volumes of Anisotropic Convex Particles in Heterogeneous Media: Theoretical and Numerical Studies

Understanding the excluded volume of anisotropic particle is of great importance in the evaluation of continuum percolation and random packing behaviors of soft/hard particle systems in heterogeneous disordered media. In this work, we obtain the excluded volumes of several anisotropic convex particles including prolate spheroids, oblate spheroids, spherocylinders, and Platonic particles, using theoretical and numerical approaches. According to the second virial coefficient, we first present a theoretical scheme for determining the excluded volumes of anisotropic particles. Also, the mean tangent diameters of anisotropic convex particles are formulated by the quantitative stereology. Subsequently, Monte Carlo simulations are demonstrated to numerically evaluate the excluded volumes. The theoretical results of the dimensionless excluded volume are thereafter compared with that of the numerical results to verify the validity of the theoretical scheme. We further investigate the dependence of the dimensionless excluded volume on the geometric characteristics of anisotropic particles based on the proposed theoretical and numerical schemes. Results show that the dimensionless excluded volume mainly relies on the shape and surface information of anisotropic particles. The developed theoretical and numerical schemes can provide theoretical insights into the percolation threshold and packing density of soft/hard anisotropic particle systems in heterogeneous materials, physics, and chemistry fields.     

大型商用飞机撞击核电站屏蔽厂房荷载研究

采用有限元方法建立飞机与核电站屏蔽厂房非线性模型,利用发动机以不同速度撞击钢筋混凝土板试验验证撞击分析中飞机与核电站屏蔽厂房有限元模型非线性材料本构及参数,并分析飞机网格尺寸效应。对大型商用飞机以200m/s速度撞击核电站屏蔽厂房非线性撞击过程模拟计算及假设核电站分别为线弹性、刚性本构模型撞击过程计算。获得大型商用飞机撞击核电站屏蔽厂房的荷载时程曲线,分析飞机撞击力及核电站屏蔽厂房结构变形特点及核电站结构刚度对撞击力影响规律,并讨论在核电站初步设计中常用飞机撞击力计算方法-Riera方法的适用性。     

Development of crash-severity-index models for the measurement of work zone risk levels

Highway work zones interrupt regular traffic flows and create safety problems. Improving safety without sacrificing the main function of highways is a challenging task that traffic engineers and researchers have to confront. In this study, the concept of using crash severity index (CSI) for work zone safety evaluation was proposed and a set of CSI models were developed through the modeling of work zone crash severity outcomes. A CSI is a numerical value between zero and one that is estimated from given work zone variables. It is interpreted as the likelihood of having fatality/fatalities when a severe crash occurs in a given work zone. The CSI models were developed using a three-step approach. First, a wide range of crash variables were examined in a comprehensive manner and the significant risk factors that had impact on crash severity were selected. Second, the CSI models were developed using logistic regression technique by incorporating the selected risk factors. Finally, the developed models were validated using the recent crash data and their ability in assessing work zone risk levels were analyzed. Results of this study showed that CSI models can provide straightforward measurements of work zone risk levels.     

Modelling of thermal response of oil-heated tools due to different flow rates for the manufacture of composite structures

Aimed at optimising the heat-transfer process during the cure of resin, a series of numerical simulations on thermal responses of an oil-heated tool for the manufacture of composite structures were performed and results of the study were discussed by authors [Compos. Struct. 47 (1999) 491]. There it was found that the temperature response and distribution of the tool was highly dependent on the oil flow rate. Hence, control of thermal response of an oil-heated tool might be achieved by controlling the flow rate of the oil. To verify the numerical simulations, an oil-heating test rig was built at the Department of Mechanical Engineering, Monash University, Australia, and a series of experimental investigations using different flow rates of the thermal oil of BP product – Transcal-N – were conducted. The results of the experimental study presented in this report were found to be in a very good agreement with the results of corresponding numerical simulations. Based on these findings, analytical and empirical models were developed to describe the heat-transfer process using oil-heated tools, including the time period of the transient heat transfer and the maximum temperature of the tools. The results predicted by the alternative models agreed well with those from the experimental and numerical investigations.     

Modelling of safety glass for crash simulation

In this paper, we present a numerical technique to simulate the crash behaviour of laminated safety glass via finite elements. As the main aspect of this work, we consider two coincided elements: a shell element for glass and a membrane element for the hyperelastic PVB-interlayer. We give an overview of hyperelastic models, which are used in crash simulations and investigate the material laws by Blatz–Ko, Mooney–Rivlin and Ogden. The obtained stress–strain curves are fitted by experimental results of the interlayer. For a comparison, we use an one-material-model with piecewise linear plasticity and a laminated glass model assigning material properties to the integration points. As practical applications, we simulate an impact of a sphere into a glass plate and investigate the behaviour of a windscreen during a roof crash.     

SRP 加固预制节段拼装桥墩在车辆撞击下的动态响应

为了减轻车辆对预制节段拼装桥墩的撞击作用,采用高强钢丝织物复合材料（Steel Reinforced Polymer,SRP）加固预制节段拼装桥墩并进行数值模拟与分析。使用 LS?DYNA 建立预制节段拼装桥墩受冲击的数值模型,并与已有实验数据对比,验证了该数值模拟方法的准确性。在相同车辆撞击条件下,对比分析了 RC 墩与 SRP 加固墩撞击力时程曲线、侧向位移和墩身损坏情况。以 SRP 加固位置、SRP 包裹层数和初始预应力水平为变量,研究其对车辆?桥墩接触面撞击力和桥墩变形的影响规律。研究结果表明：采用 SRP 对预制节段拼装桥墩进行合理加固,可以有效减小接触面撞击力、墩身位移和桥墩损伤;在桥墩底部及接缝处采用 SRP 加固对墩身具有更好的保护作用;SRP 包裹层数由 1 层增加到 3 层可以更好地限制墩身位移变形。     

Impact on planar kinematic chain of rigid bodies: Application to movements of anthropomorphic dummy in a crash

Numerical simulation of crash phenomena in rigid multi-body approach brings up problems when the various bodies constituting the mechanical system come into contact. The planar modeling of contact requires bodies' geometry to be taken into account. The method used permits the simultaneous management of constraints due to their contact and to kinematic joints, by introduction of holonomic constraints. We validate this method on Biomechanical applications. The results arising from a numerical model, and from a sled test, where we recreated the dummy seating conditions, are compared.     

刚性地面对爆炸冲击波传播规律的影响

为研究刚性地面对爆炸冲击波传播特性的影响,采用ANSYS/LS-DYNA对TNT炸药在刚性地面工况下起爆后的整个过程进行了数值分析,得到了刚性地面工况下爆炸冲击波的传播规律以及特征参数,并将其与自由空气工况下爆炸冲击波的传播规律以及特征参数进行了对比分析。建立了TNT炸药在刚性地面工况下起爆后,比例距离在0.5 m/kg^1/3≤Z≤3 m/kg^1/3之间时的冲击波超压峰值简便计算公式,分析了起爆高度对刚性地面附近冲击波的影响规律,并得到了刚性地面反射增强效应作用范围的判别公式。数值分析所得结果可为结构或构件在刚性地面上发生爆炸时荷载的初步确定提供一定的参考。     

Design of an aluminium-based vehicle platform for front impact safety

The current paper examines the design of an aluminium-intensive small car platform for desirable front impact safety performance. A space frame-type architecture comprised of extruded aluminium members with welded joints is considered for inherent structural rigidity, and low investment in terms of tooling. A finite element model of the vehicle is employed for crash analysis using the explicit code LS-DYNA. Confidence in analysis is established at the component level by benchmarking finite element models of welded joints against experimental data, and axial crushing of aluminium tubes against published numerical results and theoretical prediction. A numerical design of experiments is conducted for arriving at a front-end design that will yield desirable safety performance during impact against a rigid barrier at 30 mph (FMVSS 208 condition). For comparable new car assessment program performance at a higher speed of 35 mph, a lumped parameter idealization is used to identify the principal design changes that may be necessary. The current approach of component level testing combined with finite element and lumped parameter-based simulations can be regarded as an effective and time-saving procedure in the crash safety design of new vehicles.     

灭火飞机投放试验地面附着密度测量方法研究

基于水体投放的扩散特性和工程试验的要求,设计了一种灭火飞机量化落水地面附着特性的测量方法。该方法主要包含地面数据采集的试验设备、矩阵布局和精度评估3个方面,考虑到工程试验费用的有限性,根据飞机投水的计算流体力学仿真计算结果,采用纸杯地面布阵的方法进行落水质量采集,综合数值模拟和线性插值等数学方法,给出了适用于大型水陆两栖飞机投水任务系统性能评估的试验矩阵方案和投水精度评估的具体方式,并通过与国外特定型号的投放试验数据绘图结果的比对,验证了测量方法的有效性。     

A numerical investigation into the effect of CRS misuse on the injury potential of children in frontal and side impact crashes

This research focuses on an investigation into the head and neck injuries sustained by toddlers due to CRS misuse under frontal and side impact crashes. A fully deformable FE model incorporating a Hybrid III 3-year-old dummy was developed which has been previously validated for frontal impacts under CMVSS 208 and FMVSS 213 testing conditions. Furthermore, this model has also been validated under near-side impact conditions in accordance to crash tests carried out by NHTSA. In addition, numerical models incorporating a Q3/Q3s prototype child crash test dummies were developed. The objective of this research was to study the effect of seatbelt slack and the absence of the top tether strap on the head and neck injuries sustained by toddlers in a vehicle crash. Numerical simulations were conducted under full frontal and near side impact crash testing conditions in accordance with FMVSS 213 for the Hybrid III 3-year-old dummy and Q3/Q3s dummies in the absence and presence of slack in the seatbelt webbing, and in the absence and presence of the top tether strap. In addition, the effect of using a cross-shaped rigid ISOFIX system was also investigated. An analysis of the head and chest accelerations, neck loads and moments was completed to investigate the potential of injury due to CRS misuse. An increase in HIC₁₅ by approximately 30–40% for the frontal impact and 10–20% for the near-side impact respectively was observed for the Q3 child dummy due to both forms of CRS misuse. In the absence of the top tether strap the forward head excursions were observed to be increased by approximately 70% for the Hybrid III 3-year-old dummy and 40% for the Q3 dummy, respectively. Use of the cross-shaped rigid ISOFIX system illustrated a reduction in head and neck injury parameters, for both frontal and side impact conditions, in the absence and presence of CRS misuse. CRS misuse results in a significant increase in injury parameters and potential for contact related head injuries. Use of a rigid ISOFIX system to restrain a CRS provides better CRS and dummy confinement and reduced injury potential than a flexible ISOFIX system.