Vehicle Body Structure Research Articles

Friction Characteristics of Low and High Strength Steels with Galvanized and Galvannealed Zinc Coatings

As vehicle body structures become stronger and part designs more complex for lightweight, controlling frictional properties in automotive press forming has gained critical importance. Friction, a key factor in formability, is influenced by variables such as contact pressure, sliding velocity, sheet strength, and coatings. This study investigates the friction characteristics of steels with tensile strengths of 340 MPa and 980 MPa, under galvanized (GI) and galvannealed (GA) zinc coatings. Experimental results reveal that asperity flattening, a significant factor in determining friction, increases with contact pressure normalized by tensile strength, particularly for GI-coated steels. However, the relationship between friction and surface flattening deviates from conventional expectations, with the friction coefficient initially rising with increased flattening area up to ~20% before decreasing as flattening progresses. These findings suggest that traditional empirical formulas may not fully capture friction behavior under specific conditions. By understanding this inflection point, where friction reduces under high contact pressure, the study provides valuable insights for optimizing formability and improving sheet metal forming processes, especially in scenarios where precise friction control is critical for producing high-quality automotive parts.

A machine learning-based crashworthiness optimization for a novel pine cone-inspired multi-cell tubes under bending

Bionic tubes are of interest in vehicle engineering due to their superior crashworthiness potential. This study proposes a crashworthiness response investigation and machine learning-based multi-objective optimization of pine cone-inspired muti-celled tubes (PCMTs). The base computer PCMT model was correlated using existing experiments, followed by a dynamic response evaluation of different PCMT geometrical and thickness configurations to assess their structural performance. Surrogate models of these PCMTs were then constructed using machine learning algorithms, and their main and interaction effects were analyzed. A non-dominated sorting genetic algorithm II (NSGA-II) approach was employed to perform a multi-objective optimization. The results demonstrate that thickness change had more effect on the initial peak force (IPF) and the mean crushing force (MCF) than the specific energy absorption (SEA). Besides, due to the coupling effect, IPF, MCF and SEA of the optimal design solution of the PCMTs could reach a 36.82 %, 61.66 % and 72.95 % increase than the sum case, suggesting that embedding inner tubes could significantly increase energy absorption with a relative minor IPF increase. Moreover, the MCF and SEA of optimal design gave an average difference of 18.01 % and 5.91 % from the original tubes. PCMTs, therefore, could be used as an ideal energy absorption structure in the vehicle body structures.

Research on Lightweight Rail Vehicle Body Based on Sensitivity Analysis

In view of the development trend of rail vehicles towards higher operating speed and low power consumption, a scheme for a lightweight rail vehicle body is proposed, based on sensitivity analysis. Using topology optimization of the vehicle body section structure, finite element models of the vehicle body section structure under single working conditions and multiple working conditions were established, respectively, and the force transmission path of the vehicle body structure under different working conditions was obtained under different working conditions. The topology of the cross-sectional structure of the vehicle body was optimized by the compromise planning method with weights. Then, a reconstruction and performance analysis of the car body section was carried out based on the optimization results and finally the finite difference method was used to analyze the sensitivity of the vehicle body structure and the vehicle body size was optimized based on the sensitivity analysis results. The results showed that the weight reduction rate of the railway vehicle body section stiffened plate was 4.47% compared to the optimization period and the modal performance analysis results of the optimized structure met the requirements. The weight reduction ratio of the optimized body structure was 21.6%

Efficient performance analysis and rapid evaluation for spot-welded stainless steel vehicles

Abstract The structural performance analysis and solder joint strength evaluation of spot-welded stainless-steel vehicles are associated with many working conditions, significant data, and repeated work. This will help researchers evaluate and improve calculation efficiency quickly. Taking the body structure of a spot-welded stainless-steel vehicle as the research object, this study conducted a finite element simulation analysis of its stiffness, static strength, mode, fatigue strength, and solder joint strength by the EN12663 standard. A rapid evaluation system for the solder joint strength was developed. The results showed that the performance of the vehicle body under various working conditions can meet the design requirements, and the evaluation results of the solder joint strength confirm the practicability and rapidity of the system, which can provide technical support for the subsequent improvement and optimization of vehicle body structures.

Investigations on the Johnson-Cook Constitutive and Damage-Fracture Model Parameters of a Q345C Steel

Due to the rapid development of high-speed trains, the service safety of vehicle body materials and structures has become a focal point in transport and impact engineering. Numerical simulations on the collision resistance of vehicle materials and structures are crucial for the safety assessment and optimal structural design of high-speed trains but have not been fully investigated due to the lack of damage model parameters. This study focuses on the Johnson-Cook (J-C) constitutive and damage-fracture models of a typical vehicle material, Q345C steel. A series of mechanical tests are conducted on the Q345C steel, including the quasi-static and dynamic compression/tension tests, quasi-static tension tests at different temperatures, and fracture tests along different stress paths, using the material test system and the split Hopkinson pressure/tension bar. Then, the parameters of the Johnson-Cook constitutive and damage-fracture models are calibrated based on the experimental results. In terms of the damage parameters related to stress paths, a new method of combining experiments and simulations is proposed to obtain the real, local fracture strains of the Q345C steel samples. This method allows the measurements of equivalent plastic strain and stress triaxiality histories under nonlinear stress paths, which are hardly accessible from individual experiments, and facilitates the accurate calibration of stress-path-related damage parameters. In addition, a high-speed plate penetration test is used to validate the J-C parameters, which can be directly implemented in the commercial finite element software Abaqus. The projectile trajectories from the simulation and experiment agree well with each other, demonstrating the reliability of the model parameters for impact scenarios and the efficiency of the experimental procedures utilized for calibration.

An intelligent body frame structure modeling and optimization system based on conceptual design

The conceptual design stage is an indispensable and important stage in the development of the modern body. However, due to the lack of sufficient body structure parameter support, the design defects generated at this time are difficult to make up for in the subsequent design stage. Therefore, it is of great significance to develop a conceptual design software for body structure that integrates design, analysis, and optimization. This paper proposes an intelligent body frame structure modeling and optimization system based on conceptual design, S-iVCD (Intelligent System for Conceptual Design of Vehicle Body Structure). Based on deep learning methods and body design sketches, a conceptual model of body structure is quickly established. Based on the data parameters stored in the Excel table, the system is seamlessly connected to the domestic independent finite element software SIPESC to calculate the simulated working conditions. The body structure optimization module is driven by the MMA (method of moving asymptotes), and takes the body structure performance and total mass as the optimization goals or constraints of the mathematical model to achieve body structure performance improvement and lightweight design.

A new resistance insert spot welding method for injection-molded FRP–steel component

For weight reduction, multi-material designs comprising metal and fiber-reinforced plastic (FRP) components in vehicle body structures have been increasingly used. However, the commonly used resistance spot welding (RSW) technology for car body assembly cannot be employed to join sheet metal and FRPs, limiting the use of FRPs. To solve this problem, a novel resistance insert spot welding (RISW) technique was developed in this work for RSW of steel parts and FRP structure parts made by injection molding. Small inserts were developed by using finite element method and experiments that may be welded to different micro-alloyed and dual-phase sheet steels using the projection welding method. The usual flange width of original equipment manufacturers could be kept unchanged. Using the developed insert and welding parameters, the maximum temperature in the FRPs surrounding the inserts was limited to 255 °C, minimizing the damage to polyamide 6 (PA6) material (with 40 wt% glass fiber). A weldability range between 2.5 and 7 kA could be achieved. The joining strength of RISW between a micro-alloyed HC340 steel in 0.75 mm and 1.5 mm thickness and a 2.5 mm/3.0 mm PA6-GF40 material is 20 to 80% higher than self-piercing riveting (SPR). For high-speed loading, RISW strength increases by 39 to 56% further. Finally, RISW was successfully applied to an FRP–steel roof-frame sub-assembly that consists of 19 simultaneously integrated inserts, achieving 10% weight reduction.

Analysis of procedures for assessing the technical condition of passenger car bodies after post-accident repairs

The rapid development of the automotive industry is associated with a large number of motor vehicles on public roads. As the number of active road users increases, the probability of a road accident increases. As a result of a collision, cars have minor or major damage, often related to damage to the vehicle's body structure. The paper discusses issues related to the assessment of the quality of post-accident repairs and their impact on the technical condition of the post-accident vehicle in further operation.

Numerical modeling of liquid metal embrittlement initiation during resistance spot welding of third generation advanced high strength steel – Effect of welding schedule and electrode alignment

Third generation (GEN3) advanced high-strength steels are increasingly used to reduce vehicle body structure weight for improved fuel economy. Zinc-induced liquid metal embrittlement (LME) has become a prevalent challenge when these steels are welded by resistance spot welding (RSW). In the literature, various numerical models have been developed to study LME during RSW of GEN3 steels. Those models tend to have a limited utility in predicting how various factors such as RSW parameters affect LME cracking. In this study, a novel LME calculation method has been developed by integrating an electro-thermo-mechanical finite element model of RSW process with an LME ratio for crack initiation established from hot tensile testing data. The onset of different types of LME cracking is tracked throughout the weld region over the entire course of RSW including the final cooling stage after electrode retraction. The model is validated using an existing set of literature data that involves different welding schedules, electrode geometries and electrode misalignments. The local temperature and stress conditions during RSW are calculated and used to understand how different welding parameters affect the severity of LME cracking. It is found that electrode misalignment exacerbates crack initiation on outer surfaces of the spot weld due to the tensile stress arisen from the off-centered squeeze force as well as the reduced surface cooling to electrodes. Initiation of cracks between the steel sheets, taking place mainly after electrode retraction, is not significantly affected by the welding schedule and the electrode tip diameter.

Modeling of multi-material beams in analytical SEA

This study presents a method for predicting vibrations in multi-material, multi-layer beams using Analytical Statistical Energy Analysis (ASEA) by considering them as homogeneous beams with equivalent bending characteristics. This approach enables the simultaneous achievement of weight reduction and noise and vibration performance, which is essential in the current trend of using lightweight materials such as high strength steel, aluminum, and fiber-reinforced plastics in vehicle body structures. The proposed method is validated through Finite Element Method (FEM) calculation and the vibration energy transfer characteristics of multi-layer beams are examined. Additionally, an example of replacing a steel single-unit beam with a multi-layer beam is presented to demonstrate the potential of the proposed method in achieving lightweight and low vibration.

Topography optimization in vibration acoustic radiation of vehicle body structure

Topography optimization in vibration acoustic radiation of vehicle body structure

Structural design of solar car body based on solid mechanics analysis of solar panel surface

With the increasingly serious problem of global warming and the growing scarcity of energy represented by oil, automobile development has reached a historical tipping point. Nowadays, the most popular solution is to use other clean and sustainable energy to replace current oil and natural gas, thereby addressing both environmental and energy shortage issues. Solar energy, as a "inexhaustible" source of energy, has made significant technological advances over the course of human history. There is, however, a gap in the application of solar energy technology in automotive technology. This paper uses COMSOL software to model the most commonly used solar panels and simulates and studies the streamline distribution, velocity distribution, pressure distribution, and stress distribution of the solar surface under high-speed movement of 90km/h. SoildWorks simulation is used to design a vehicle body structure for future solar cars based on these data. FLUENT software is used to simulate and study the streamline distribution and pressure distribution of the car body at a high speed of 90km/h. Finally, the design's logic and feasibility are validated. The fluids on the surface of a single solar panel and a vehicle body are simulated in this paper. Testing the pressure distribution and stress and strain tests can reveal the rationality and feasibility of the structural design.

Billion-design-variable-scale topology optimization of vehicle frame structure in multiple-load case

In topology optimization, sufficient resolution and a constraint volume of less than 1% are required to obtain a practical vehicle body structure without solid circular-section frames. To meet the requirement for sufficient resolution, the authors are developing voxel topology optimization software, including a finite element solver that utilizes the building cube method framework available in massively parallel environments. The authors have performed a topology optimization of billions of elements intended for a vehicle frame using 35,000–66,000 processors and measured its parallel performance. In addition, four different methods to treat multiple-load cases required for vehicle performance into single objective functions are examined. As a result, normalizing compliance with the appropriate target energy obtained by the original body-in-white frame balances the optimization performance across cases. In the single-load case, thick solid beams are generated through optimization. In contrast, such solid frames are suppressed in multiple-load cases, resulting in a structure similar to a practical body-in-white frame.

Organic mechanochromic luminescence‐based visualization of fatigue damage and life prediction of aluminum to steel resistance spot welds

AbstractDissimilar material joined structures are increasingly used in the automotive industry to reduce weight in the vehicle body structure for better fuel economy. Therefore, it is necessary to reveal the fatigue damage and develop the fatigue life prediction method of dissimilar material joined structures. Unlike conventional detection methods, mechanoresponsive luminogen‐based method can directly visualize stress distribution and fatigue crack growth. An organic mechanochromic luminescence material (TPE‐4N) is therefore used to detect the fatigue damage of coach peel Al‐steel resistance spot welds. The fatigue crack initiation and propagation are detected as visible green fluorescence under ultraviolet excitation. The results show that the fluorescence intensity increases linearly in the early stage of fatigue cycles while grows much faster in the specimen with lower fatigue life. A new fatigue life prediction method has been developed based on the response of fluorescence intensity.

Resistance insert spot welding: a new joining method for thermoplastic FRP–steel component

Recently, multi-material designs consisting of metal and FRP components are being increasingly used in vehicle body structures to reduce weight and thus energy consumption and emission. Because the most commonly used resistance spot welding (RSW) technology for body assembly cannot be applied to join sheet metals and FRPs, the usage of FRPs is strongly limited. Therefore, a new resistance insert spot welding (RISW) method was developed. During the manufacturing process of FRPs, here compression molding of PA6 GF40 materials, specially designed steel inserts are directly integrated into the FRP part. Later, via the steel inserts, the FRP part can be spot welded to other steel parts in the structure. In this work, the design and development process of RISW is presented. Starting with the design concept of inserts, welding tests were conducted, and the parameters for the welding simulation were calibrated. After that, the detailed insert design was performed using welding simulation and tests with several restrictions, such as insert dimensions, the temperature in FRPs, the weldability range, and joining strength. In the end, an appropriate insert geometry was found, which met all requirements. The mechanical properties of RISW joining are better than or equal to those of SPRs. The new RISW technology was also demonstrated on a real vehicle component. A seat cross member was designed using FRP with 42% weight reduction and produced by compression molding with 30 simultaneously integrated inserts. The cross member was finally successfully welded to a steel closing plate using RISW.

Analytical Approach for Vehicle Body Structures Behaviour Under Crash at Aspects of Overloading and Crumple Zone Length

Abstract Road safety problem is still topical, especially since the number of vehicles and the volume of traffic are increasing. It is possible to increase the safety of road users through systemic changes in many areas related to transport. The deformation of the vehicle body during an accident has an impact on the loads acting on the passengers. Vehicle body deformation depends on complex parameters, and knowledge of these parameters is essential for designing crumple zones and the accident reconstruction process. Knowledge of the mechanical parameters of the vehicle structure during deformation is also a reference to passenger injury indicators assessment. This paper reports results from the analytical approach for determining the protection level of personal vehicles. The proposed conception is based on the results from the static stiffness characteristic of the Ford Taurus, which gives the possibility of phenomenological and simple body crumple analytical description at a speed equal to 10 km/h, 40 km/h, 56 km/h and 60 km/h, which is an original part of the work. The approach enables us to describe the vehicle crash by focusing on variations of deformation in time, stiffness, vehicle collision time (duration), deceleration and dynamic crash force. Basing on the body stiffness data of the personal vehicle, the length of the deformation zone in the front of the car and the maximum values of force at the crash for a speed of 60 km/h are presented. Results obtained by the authors show that is possible to estimate the overloading level during the crash time of a vehicle based on the stiffness characteristic of the car body. The proposed methodology can be developed and the advantage of the presented procedure is an uncomplicated useful tool for solving complex problems of a vehicle crash.

Safety Assessment of Liquid Launch Vehicle Structures Based on Interpretable Belief Rule Base

A liquid launch vehicle is an important carrier in aviation, and its regular operation is essential to maintain space security. In the safety assessment of fluid launch vehicle body structure, it is necessary to ensure that the assessment model can learn self-response rules from various uncertain data and not differently to provide a traceable and interpretable assessment process. Therefore, a belief rule base with interpretability (BRB-i) assessment method of liquid launch vehicle structure safety status combines data and knowledge. Moreover, an innovative whale optimization algorithm with interpretable constraints is proposed. The experiments are carried out based on the liquid launch vehicle safety experiment platform, and the information on the safety status of the liquid launch vehicle is obtained by monitoring the detection indicators under the simulation platform. The MSEs of the proposed model are 3.8000e-03, 1.3000e-03, 2.1000e-03, and 1.8936e-04 for 25%, 45%, 65%, and 84% of the training samples, respectively. It can be seen that the proposed model also shows a better ability to handle small sample data. Meanwhile, the belief distribution of the BRB-i model output has a high fitting trend with the belief distribution of the expert knowledge settings, which indicates the interpretability of the BRB-i model. Experimental results show that, compared with other methods, the BRB-i model guarantees the model’s interpretability and the high precision of experimental results.

Dynamic crush response of compression molded planar isotropic carbon fiber reinforced composites

AbstractVehicle mass reduction can be achieved through the utilization of carbon fiber reinforced composites within the vehicle body structure. In this study, planar isotropic compression molded carbon fiber reinforced composites are studied for their potential utilization as automotive primary energy absorbing structures. The energy absorption behavior of a discontinuous randomly oriented 2‐D planar isotropic carbon fiber reinforced nylon 6 thermoplastic composite and a continuous 2 × 2 twill quasi‐isotropic carbon fiber reinforced epoxy thermoset composite are studied by dynamic flat plaque crush testing. Post‐mortem failure modes of both materials are related back to their load‐displacement and energy‐displacement curves under different test conditions. It is shown that crush fixture support length dictates the failure mode and specific energy absorption (SEA) of all fiber reinforced composites tested. In addition, elevated temperature testing of the nylon 6 carbon fiber reinforced composites reduces the SEA in all test configurations. Finally, an automotive carbon fiber composite front end energy absorbing structure is considered as the replacement over a legacy metallic energy absorbing structure. Mass reduction benefits beyond the improved SEA of the composite as compared to the metallic structure it replaces are discussed by considering the increased crush length efficiency of the composite structure which can reduce the vehicle front end length, and therefore the mass of the vehicle. These results are expected to direct the future development of fiber reinforced composites structures in energy absorbing automotive structures.

Fracture Strain of Al-Si-Coated Press-Hardened Steels under Plane-Strain Bending.

Press-hardened steel (PHS) is widely applied to fabricate vehicle body structures for attaining mass reduction and fuel economy without sacrificing occupant safety. The VDA bendability test is often used to characterize the fracture resistance of PHS under plane-strain bending conditions. As lightweighting continues to be a design imperative in the automotive industry, it is desirable to develop and adopt more press-hardened components with higher fracture resistance. In this work, four Al–Si-coated 22MnB5 steels with various initial thicknesses and coating weights were studied. A newly developed methodology was used to calculate the fracture limit strain under plane-strain bending. The results indicate that although the four investigated 22MnB5 steels exhibit similar tensile properties under uniaxial tension, their bending performance per the VDA 238-100 standard differs significantly. The PHS with a low coating weight possesses a higher bending angle and, hence, a larger fracture limit strain. Meanwhile, the peak bending force can be 10% higher than the PHS with a standard coating weight at the same sheet thickness. Therefore, it is expected that PHS with higher fracture strain will have the potential for lightweighting due to its enhanced resistance to fracture and higher energy absorption capability.

Feasibility of Approximate Model Optimization for Lightweight Design of Vehicle Body Structure Based on Sequential Quadratic Programming Algorithm

Feasibility of Approximate Model Optimization for Lightweight Design of Vehicle Body Structure Based on Sequential Quadratic Programming Algorithm