The occupant leaning forward will increase the human injury risk under collision conditions after vehicle braking. In this paper， occupant out of position effect and parameter optimization analysis and research are carried out under the pre-collision braking.The forward displacement interval of the occupant's neck under different braking conditions is obtained through the real vehicle braking test. The MADYMO active human body simulation model is established. The variable analysis method is used to study the characteristics of occupant out of position with different braking waveforms. The orthogonal design method is used to conduct sled impact test to obtain the influence of the occupant dislocation factor on the occupant collision injury. The occupant response surface model is established， using the central composite test design （Central composite design ） method to study the correlation between the active seat belt parameters and the occupant's forward displacement out of position， and the optimal parameter combination is obtained by optimizing the design.
Due to the excellent specific energy absorption characteristics of lattice structure， it has broad application prospect in the passive safety of new energy vehicles. Taking the crash box filled with lattice structure as the research object， the finite element model of the automobile crash boxes with different lattice structure inner cores are established. The crashworthiness performance of different filling crash boxes and traditional crash box under multi-angle oblique collision conditions are comparatively analyzed. The interaction mechanism between the lattice structure and crash box body and the basis of inner core selection are expounded. On this basis， further considering the influence of the body inducement slot on the deformation modes under multiple working conditions， the multi-objective crashworthiness optimization design of the crash box filled with the lattice structure based on the improved body structure is carried out. The results show that the crash box filled with positive Poisson's ratio lantern-like lattice structure has stable and excellent energy absorbing performance. Compared with the original crash box， the mass is reduced by 32.05% using the optimization scheme. On the premise of ensuring that the maximum impact force is less than the threshold， the comprehensive performance indicators are significantly improved.
To solve the problems of low efficiency and difficult convergence of multi-variable nonlinear dynamic structure optimization， this paper proposes a Subdomain Hybrid Cellular Automata for Thickness optimization algorithm （SHCA-T） and multi working condition SHCA-T algorithm to solve the thickness optimization of the body skeleton， so as to realize efficient optimization design of the crashworthiness of the body skeleton under multiple working conditions. The algorithm includes an outer loop and an inner loop： the outer loop is to realize minimization of target mass by conducting crash finite element analysis （FEA）， calculating output responses and updating target mass； the inner loop is to make the current mass of the inner loop to converge to the target mass by adjusting cell thicknesses according to internal energy densities of current cell and neighboring cells and PID control strategy， and finally make the cell internal energy density distribution as close as possible to the step target internal energy density function. In order to validate the accuracy and efficiency， the SHCA-T and multi working condition SHCA-T algorithms are used to solve the thickness optimization problem of body frame under side collision and side column collision. The optimized results obtained from the SHCA-T and multi working condition SHCA-T algorithms are compared with the results from parallel Pseudo expected improvement criterion for parallel EGO algorithm. The results show that the SHCA-T and multi working condition SHCA-T algorithms have higher global search efficiency under the condition of equal convergence accuracy.
In order to understand the application risk of the pedestrian ground collision injury protection method based on braking control under the disturbance of the first time for releasing the braking （t1）， 1 920 simulation tests are designed and conducted by MADYMO based on a virtual simulation system with 3 velocities， 4 pedestrian sizes and 2 pedestrian gaits. After comparison analysis， it is found that the pedestrian-ground collision injury can be effectively reduced without increasing the vehicle induced injury by employing the vehicle braking control method when there is no parameter disturbance. Under the disturbance of the first time for the vehicle to release its braking （t1）， the proportion of cases in which the WIC is reduced， the vehicle related HIC15 is not changed， the ground related HIC15 is reduced and the pedestrian landing posture is not changed is 86.1%、98.61%、90.16% and 90.97% respectively. This means that the vehicle braking control method has a strong anti-disturbance ability. The earlier of t1， the more likely it is to increase the vehicle induced injury； the later of t1， the more likely it is to reduce the protective effect of head ground collision injury. Further analysis shows that main reasons for the increase of the pedestrian-ground collision injury under t1 disturbance are long time no leaving of the pedestrian from the vehicle， the pedestrian falling to the ground from the edge of the vehicle， change of the pedestrian landing posture and already extremely low injury in the complete braking group， etc. Parameters such as bumper length and hood inclination angle significantly affect the anti-disturbance ability of the vehicle braking control method. The smaller the bumper length and the larger the inclination angle of the hood， the stronger the anti-disturbance ability of the method.
For the failure of the cab of a heavy truck during the fatigue test on the bench， a bi-directional evolutionary structural optimization method （FA-BESO） aiming at maximizing the fatigue life is proposed in this paper. Firstly， the bench test of the cab is carried out to find the weak position of the cab fatigue. Furthermore， the sensitivity of the element low-cycle fatigue analysis is deduced， and this value is utilized as the basis for element deletion. The FA-BESO of the continuum structure is realized through the secondary development of the finite element software. Then， the effectiveness of FA-BESO is verified by a standard example. Finally， in order to improve the optimization efficiency， a simplified model of the beam frame for the cab is established， and it is verified that the simplified model has good predictability for the fatigue failure position. The FA-BESO is applied to the topology optimization of the A-pillar reinforcement plate considering fatigue performance， and the result shows that the fatigue life of the cab can be increased to 2 times compared with that before optimization， which verifies the feasibility of the FA-BESO to improve the fatigue life of the cab.
The axle housing of heavy-duty truck has large dimension， and high load-carrying capacity， and the stress on the axle housing cover part is complex. There is cracking phenomenon in the process of development test and engineering application. The design method of heavy-duty truck axle housing by seamless steel pipe bulging forming is proposed in this paper， and the process flow of bulging forming is given. The axle-housing sample of 1：1 axle load with load of 11.5 tons is designed and trial-produced. Through the finite element simulation of the bulging forming process， the changes of the wall thickness of the axle housing， as well as the stress distribution law of the transition arc surface of the rear cover are revealed， which shows that the deformation strengthening coefficient of the bridge package reaches 1.37~1.61. Through the static strength simulation and test under the torsion condition with a 65 kN longitudinal force applied on the upper thrust rod support of the sample， it is revealed that the maximum tangential strain and normal strain of the axle housing are 317με， with the maximum longitudinal deformation per meter of wheelbase less than 0.91mm. Moreover， the design basis for the front plane width of the bridge package higher than both sides and the wall thickness of the seamless steel pipe is given. Based on the load spectrum collected from the real vehicle， the fatigue test under the torsional condition is carried out and the axle housing sample remains intact after five stages of 1.419 million cycles in total. The research results show that the axle housing of heavy-duty truck by seamless steel pipe bulging forming has light weigh， high strength and stiffness， which provides an important reference for solving thoroughly the failure of axle housing.
The transverse trigger fixation width of the autonomous emergency breaking （AEB） system is one of the important factors for collision avoidance failure in the collision accident between automobiles and electric two-wheeled vehicles. In order to improve the collision avoidance reliability of the AEB system， this paper establishes an AEB longitudinal and transverse trigger TTC difference model based on the analysis of the longitudinal and transverse TTC （Time to collision） difference range of the critical conditions of the collision between an automobile and an electric two-wheeled vehicle. Based on PreScan， Matlab/Simulink and CarSim simulation platforms， two typical collision accident scenarios between cars and electric two-wheelers are established and compared with the AEB strategies with fixed transverse trigger widths of 1.75 and 3.75 m. The results show that the proposed AEB longitudinal and transverse triggering TTC difference model performs better in collision avoidance rate and can achieve collision avoidance at vehicle speeds below 54 km/h. In typical scenario 1， the crash avoidance rate is 88.9% （45 cases）， and the average crash speed of unavoidable crashes decreases from 70.6 to 29.7 km/h. In typical scenario 2， the crash avoidance rate is 80% （30 cases）， and the average crash speed of unavoidable crashes decreases from 66 to 18.2 km/h. The AEB longitudinal-triggering TTC differential model has good reliability and robustness， improves road safety of cars and electric two-wheelers， and provides an important theoretical reference for the development of automotive active safety systems.
The dynamic whiplash test of the second row seats in CNCAP is the first whiplash test item proposed in the international NCAP evaluation system， which leads to the lack of awareness of the OEMs and high attention. In order to deeply understand the second row seat whiplash test， 226 groups of sample data are collected in this paper. Through classification and summary， the dispersion laws of the static measurement parameters of whiplash， such as the head back clearance， the headrest height， the seat torso angle and the dynamic score of the second row seats whiplash are obtained， and the correlation between the static parameters and the dynamic score of whiplash is established. The results show that the scoring rate of the second row seat whiplash is low and the dispersion is high， with a poor performance in protection the human neck in the rear end collision accident as a whole. Optimizing the static parameters of seats can improve the whiplash injury index to some extent and the dynamic whiplash score of the second row seats. This study provides data support for OEMs to master the current situation of the second row seat whiplash， and has guiding significance for optimizing the second row seat whiplash protection performance.
Fiber Metal Laminate （FML） is a new type of lightweight hybrid material， which is gradually used in the field of transportation equipment such as automobiles. However， its forming process is affected by various parameters， and the distribution law of stress and strain in the forming process is still unclear. In this paper， T300 carbon fiber aluminum alloy composite laminate is selected as the research object. Its stamping forming process is simulated by ABAQUS finite element software， and the accuracy is verified. The stress distribution and wall thickness change law of FML under the influence of factors such as the type of prepreg， the thickness of the laminate and the number of laminates are studied. The results show that the calculation of the established FML stamping model is accurate. The type of prepreg mainly affects the stress distribution and wall thickness change of the fiber layer. The thickness of the laminate and the number of laminate have impact on the wall thickness change of each layer. By reducing the thickness of the laminate or increasing the number of layers can alleviate the problem of excessive thinning. The thickness and number of layers also affect the stress distribution of the aluminum alloy layer. With the increase of the thickness and number of layers， the stress distribution of the aluminum alloy layer tends to be uniform.
In a collision accident， violent yaw and lateral motion often occur at the same time after the side impact of a vehicle. It is difficult for ordinary drivers to correctly deal with such emergency situation， obviously the vehicle may lose stability， or even cause more serious accidents. In order to reduce the secondary collision caused by vehicle instability and the misoperation of the driver， this paper proposes a two-stage auxiliary driving control strategy that takes over the vehicle driving authority after the collision. In the first stage， the cost function is designed by integrating the two indicators of vehicle stability and lateral displacement. Through hierarchical control， the vehicle can quickly return to stability after collision and reduce the lateral displacement to reduce the risk of secondary collision. After that， according to the stability region divided by the phase plane method， a switching criterion for the control system is formulated. After judging that the vehicle state is stable， the control system switches to the path tracking control in the second stage. The model predictive path tracking controller will drive the vehicle back to the original lane to reduce the impact on the adjacent lane. Finally， the effectiveness of the control strategy proposed in this paper is verified through simulation experiments in different strength side impact.
In this paper， roll stamping technology is introduced into the design and manufacture of trailer chassis. Through continuous molding of high strength materials， an integrated chassis rail is constructed， and the corresponding structural improvement is made for a typical trailer chassis. The stress conditions of the two chassis under full load bending and full load braking conditions are compared and analyzed. The results show that because the roller punching process can realize the processing of ultra-long parts with variable section and one punch， the material improvement， structural improvement and the reduction of the number of main components brought by this advantage make the processing of chassis rail significantly improved in terms of production efficiency and assembly efficiency while realizing the lightweight. In addition， the variable section longitudinal beam based on the high strength sheet greatly improves the designability of the structure， which in turn makes it possible to significantly improve the bearing performance. Compared with the base plate with a fixed load mass of 1.4 t， the optimized chassis can bear the load of 2.4 t， and the deformation of the two is similar.
In order to enhance the accuracy of frame fatigue life calculation and accurately predict the frame life in the design stage, it is necessary to consider the influence and coupling effect of the dynamic load on the fatigue of the frame at the outer connection point of the main structure. In this paper, a research method of frame fatigue based on complex boundary is proposed. The whole vehicle load spectrum is collected in the test field to obtain the whole cycle damage value. Based on the damage equivalent principle, the damage value of various surface road combinations is obtained, which is equivalent to the target value of the full cycle, with an accuracy of 99.5%. A finite element frame model with outer points of the main structure is constructed and the unit stress field of the complex boundary is output. The high-precision vehicle dynamics model with saddle and trailer system is established based on the test field load spectrum and the bench test data, to obtain the dynamic load of the outer connection point. The fatigue of the frame is calculated by the fatigue damage theory, with the fatigue analysis results verified by field tests. The results show that the frame model with the complex boundary has high simulation accuracy. Through local optimization and model reconstruction, the frame life can meet the requirements.
In order to investigate in depth the injury mechanisms and the different causes affected by the front-end and the speed on lower extremity injuries of child pedestrian in the car-pedestrian collision， thirty-two car-pedestrian collision simulations are set up using the injury bionic model of six-year-old pedestrian （TUST IBMs 6YO-P） with detailed anatomical structures and four types of common passenger cars given eight crash speeds. The kinematic and biomechanical responses of lower extremity are analyzed. The nonlinear regression prediction models are developed to assess the injuries of lower extremity. The results indicate that the severity of pediatric lower extremity long bone fractures and knee injuries are directly influenced by the collision speed. The height of the bumper affects the femur injury and knee bending angle， and the height of the spoiler from the ground affects the severity of tibia and fibular injury. By analyzing the data about the knee bending angle and ligament fracture， it is concluded that the medial collateral ligament （MCL）， anterior cruciate ligament （ACL） and posterior cruciate ligament （PCL） are fractured with the knee bending angle exceeding 25.9±0.9°， 38.6±0.7° and 43.2±0.2°， respectively. Furthermore， the injury prediction model of knee bending angle based on the collision velocity and front bumper height is validated to be effective in predicting the knee joint injury. Combining the evaluation parameters of long bone fracture and predicting model of the bending moment of six-year-old child pedestrian lower extremity， it is concluded that the critical velocity for lower extremity long bone fractures of child pedestrian is 17.94 km/h. These results will provide a scientific reference for the formulation of pedestrian safety regulation， the development of pedestrian protection devices， the design of AEB system and digital evaluation.
In order to understand the typical pedestrian vehicle collision scenarios and accident characteristics after the vehicle is equipped with the automatic emergency braking system （AEB）， 187 accidents are reproduced and the parameters before the collision are collected. Then the effect of the traditional AEB system is evaluated using the combined simulation technology. After 73 accidents （39%） that are not avoided are analyzed with statistical methods， 6 typical types of pedestrian vehicle collision scenarios that are not avoided are obtained. The study shows that the accidents that are not avoided mainly occurr at non-intersections with good lighting conditions and dry road， and the collision speed is lower than 40 km/h in 95.88% cases. The pedestrian vehicle collision injury is significantly reduced， with different reduction magnitude in different scenarios. Uncertainty exists in the reduction of pedestrian ground collision injury， and 61.9% of the cases in typical scenarios have an increased risk of pedestrian ground collision injury， with the proportion of injury increase varying with the change of collision scenarios. Further analysis shows that the main reasons for the increase of pedestrian ground collision injuries are the change of pedestrian landing sequence after AEB reduces the speed， the re-contact of pedestrian lower limbs with the front end of the vehicle， and the change of pedestrian vehicle collision position. The research results can not only provide boundary conditions for the experimental design of intelligent vehicle owners and passive safety research， but also provide support for the design of safer AEB systems.
The directional importance sampling method is a structural reliability simulation method， which is suitable for evaluating nonlinear， multi-dimensional complex structural reliability problems. However， for multidimensional problems， it is relatively inefficient and poorly executable to obtain significant vector samples using the accept/reject method. Therefore， it is necessary to improve or reconstruct distribution functions that are easy to sample. By summarizing the existing distribution functions， the distribution function based on vector-angle geometric mapping is approximated by interpolation methods， and the important angles are sampled uniformly using the one-dimensional Latin hypercube method and then mapped to the important vector samples. The obtained vector samples have stratified uniformity， avoiding aggregation phenomena while covering the entire sample space. The method is effectively used in the analysis of reliability problems of multiple design points and multiple failure modes， and sample allocation scheme is further developed. The applicability and accuracy of the proposed method are verified by nonlinear numerical examples and body structure engineering.
Accurate estimation of tire-road friction is a prerequisite for vehicle active safety control. Firstly， a single-wheel dynamics model is established， and precise estimation of the longitudinal tire force is realized using the Kalman filter. Then a particle filter （PF）-based tire-road friction estimator is developed based on the Magic Formula tire model. Secondly， a forward road adhesion coefficient prediction method based on image recognition is proposed. The DeeplabV3+， semantic segmentation network and the MobilNetV2 lightweight convolutional neural network are used for road segmentation and classification， based on which the tire-road friction is obtained through table look-up. Finally， the spatiotemporal synchronization method and fusion mechanism of dynamics and image recognition are established to realize effective correlation and reliable fusion of the two estimation methods. The Carsim-Simulink co-simulation shows that the proposed estimation method based on image recognition and dynamics fusion can efficiently improve the tire-road friction estimation accuracy.
For the durability development problem of an vehicle with super-size integral die casing aluminum alloy rear end body， the E-N data of the cast aluminum alloy for the die casting body is tested and the key parameters of die-casting alloy E-N curve are obtained by fitting the experimental measured data of fatigue samples. Finite element model of Trim body is built and the dynamic stress response of the die casting body is calculated based on the modal transient method. Rain flow statistics is carried out to the stress time history response signal. Combined with the measured material E-N curve and Miner’s damage accumulation principle.， the body fatigue damage of initial design and optimized design are analyzed and compared. Finally， the optimized integral die casting part is loaded into the vehicle for the four-column strengthening durability test. The investigation results show that the E-N relation curve of die casting aluminum alloy can be described by Manson-Coffin-Basquin equation. Compared with the original design， the maximum damage of the improved integrated die casting aluminum alloy body is reduced from 2.67 to 0.32， and the risk of fatigue cracking is eliminated. No cracks are found in the body after the reinforced four-column endurance experiment verification. The research results can provide a reference for the development of integral die-cast aluminum alloy body to achieve the goal of vehicle durability properties.
In order to study the type of neck sports injury of the passenger in the front passenger seat of a vehicle during the rollover process， LS-Dyna software is used to simulate the slope rollover， platform vehicle rollover and spiral rollover process， analyze the neck force and moment response of the passenger during the rollover process， and judge the neck injury state of the passenger. Based on the neck force and moment， a hypothesis is established to judge the neck posture of the occupant at a certain moment， which can reproduce the motion posture of the dummy without recording the dummy’s motion in the test. The slope rollover test of a vehicle is carried out to verify the accuracy of the slope rollover simulation results. The analysis results show that the neck movement state of the passenger in the process of rollover can be accurately judged by combining the response of neck force and neck moment， and it is concluded that the contact collision between the head of the passenger and the vehicle body has an important impact on the neck injury of the passenger in the process of rollover.
Oblique impact is common in vehicle accidents， and a reasonable inductive structure of energy absorbing components is crucial for comprehensive crashworthiness. In this paper， the design method of inductive structure based on aluminum/CFRP hybrid tube is studied. Firstly， a high-precision finite element model of aluminum/CFRP hybrid tube is established， which is verified by experiments. Then， based on the multi-angle compression conditions， the effect of the location parameter， number parameter， shape parameter and size parameter of the induction groove on the crashworthiness of aluminum/CFRP hybrid tube is studied respectively. The results show that the location parameter has the greatest influence on the comprehensive crashworthiness. Setting a rectangular induction groove in the upper part of the hybrid tube can largely reduce the peak force and enhance the energy absorption stability. Finally， based on the NSGA-II algorithm， the multi-objective optimization design of the induction groove is carried out. The optimization results show that the peak force of the hybrid tude is reduced by 35.5% on the premise of ensuring the comprehensive energy absorption under different weight schemes， effectively solving the problem of balancing high energy absorption and low peak crushing force. The research results provide important guidance in the design and application of energy absorbing components.
For the research on intelligent vehicle safety and digital assessment technology in the future， in order to effectively predict and evaluate the kinematic responses， biomechanical responses and injury mechanisms of the small size female in traffic accidents， an injury biomimetic model of the 5th percentile Chinese female physiological characteristics is developed with independent intellectual property based on CT images of a volunteer， named TUST IBMs F05-O. Five groups blunt impact cadaver tests on the thorax and abdomen of small-sized female are reconstructed using four regional loading methods and the validity of the model is evaluated by the force-deflection curve and the biomechanical response data. At the same time， the simulation results from the whole-body model is compared with the results from the thoracic-abdominal partial model under the same loading conditions to analyze the influence of limbs on the stiffness responses of the chest and abdomen. The results show that for the five groups of cadaver tests with different impact velocity and mass， the predicted results by the model are consistent with the cadaver test data， proving the high bio-fidelity of the model. Therefore， it can be applied to the simulation calculation of the occupant protection test of automotive safety assessments in order to reduce the development cost. The thoracoabdominal stiffness of the whole-body model is slightly larger than that of the thoracic-abdominal partial model because of the influence of limbs kinematic responses， which proves that the whole-body model is more accurate to simulate and evaluate the injury than the partial model. The TUST IBMs F05-O can predict and assess quantitatively the injury of human tissues and organs to study the injury mechanisms of small size female occupants with Chinese physical characteristics， which can provide basic data and technical support for vehicle digital assessment technology， vehicle active and passive safety integration research and the development of the intelligent vehicle cockpit safety protection devices.
