Vehicle Stiffness Research Articles

A finite element modelling methodology for the non-linear stiffness evaluation of adhesively bonded single lap-joints: Part 2. Novel shell mesh to minimise analysis time

A new modelling methodology is presented that enables the stiffness of adhesively bonded single lap-joints to be included in the finite element analysis of whole vehicle bodies. This work was driven by the need to significantly reduce computing resources for vehicle analysis. To achieve this goal the adhesive bond line and adherends are modelled by a relatively ‘small’ number of shell elements to replace the usual solid element mesh for a reliable analysis. Previous work in Part 1 has provided the necessary background information to develop and verify the new finite element analysis that reduces the solution runtime by a factor of 1000. Although a joint’s non-linear stiffness is reliably simulated to failure load, it is recognised by the authors that the coarse shell mesh cannot provide accurate peak stresses or peak strains for the successful application of a numerical failure criterion. Given that the new modelling methodology is very quick to apply to existing shell models of vehicle bodies, it is recommended for use by the stress analyst who requires, say at the preliminary design stage, whole vehicle stiffness performance in a significantly reduced timeframe.

Application of the Inverse Substructure Method in the Investigation of Dynamic Characteristics of Product Transport System

Product, packaging and vehicle constitute a complex product transport system in logistics. It is very difficult to obtain accurately the dynamic response of a product transport system under the action of environmental vibration and shock. In this paper, product transport system is treated as a two substructure‐coupled system composed of product system (including critical element) and vehicle connected by packaging and its fixing (location pattern, securing, etc.); the inverse substructure method is applied to the analysis of the dynamic characteristics of the system. For verification of the validity of the inverse substructure method for product transport system, a typical lumped mass model is taken as an example for numerical validation. To check out the accuracy of the method, we completed the experiment, and the predicted substructure‐level frequency response functions are in overall agreement with those measured. The sensitivity of the method to measurement error is also made. To study the influences of the product parameters, packaging and its fixing, we investigated the effects of the coupling stiffness, mass ratio, frequency parameter ratio and damping on the dynamic response of critical element. Reducing the coupling static stiffness of product–vehicle interface can effectively lower the response of critical element, especially when the coupling stiffness is less than the stiffness of product and vehicle. Copyright © 2011 John Wiley & Sons, Ltd.

Interventions to Reduce Risks Associated With Vehicle Incompatibility

Occupants of smaller, lighter passenger cars are more likely to be killed or injured in collisions with larger, heavier sport utility vehicles and light trucks than in collisions with other cars. Interventions are needed to reduce this vehicle "incompatibility" and its consequences. The authors conducted a systematic literature review to identify evaluations of interventions to reduce incompatibility. They reviewed engineering, biomedical, and other technical literature. To be included, a study must have 1) evaluated an intervention to reduce vehicle incompatibility, or its consequences, in a crash; 2) reported new research; and 3) been published in English from 1990 to 2010. Seventeen studies met the inclusion criteria. Interventions were designed to reduce the aggressivity of larger vehicles or improve the crashworthiness of smaller vehicles. Effective interventions included 1) modified bumper heights, 2) improved side strength of smaller vehicles, 3) side-impact air bags, 4) changes to vehicle stiffness, and 5) modifications of other front-end structures. Some of the interventions shown to be effective are now in wide use. However, others have yet to be required by regulators or voluntarily agreed to by manufacturers. If larger, heavier vehicles remain on the nation's roads, countermeasures will be needed to reduce risks for occupants of other vehicles.

Pedestrian head translation, rotation and impact velocity: The influence of vehicle speed, pedestrian speed and pedestrian gait

In road traffic collisions, pedestrian injuries and fatalities account for approximately 11% and 20% of casualties in the USA and the EU, respectively. In many less motorised countries, the majority of victims are pedestrians. The significant influences of vehicle speed, pedestrian speed and pedestrian gait on pedestrian post-impact kinematics have been qualitatively noted in the literature, but there has been no quantitative approach to this problem. In this paper, the MADYMO MultiBody (MB) pedestrian model is used to analyse the influences of vehicle speed, pedestrian speed and pedestrian gait on the transverse translation of the pedestrian's head, head rotation about the vertical head axis and head impact velocity. Transverse translation has implications for injury severity because of variations in local vehicle stiffness. Head rotation is related to pedestrian stance at impact, which is known to affect the kinematics of a collision. Increased head impact velocity results in greater head injury severity. The results show that transverse translation of the head relative to the primary contact location of the pedestrian on the vehicle decreases with increasing vehicle speed and increases linearly with increasing pedestrian speed. Head rotation decreases with increasing vehicle speed and increases linearly with increasing pedestrian speed, but these variations are small. The range of head rotation values decreases with increasing vehicle speed. Head impact velocity increases linearly with vehicle speed and is largely independent of pedestrian speed. Transverse translation, head rotation and head impact velocity all vary cyclically with gait in clearly definable patterns.

Effect of increase in weight and stiffness of vehicles on the safety of rear seat occupants

In this study, full-scale finite element (FE) simulations have been performed to identify factors affecting the protection of rear seat occupants. An FE model based on the 2001 Ford Taurus was used and coupled with a Hybrid III 5th percentile female dummy model in the rear seat of the vehicle. The dummy model was restrained using a three-point belt system. The effects of changes in the vehicle design, including changes in vehicle weight and stiffness, on injury readings of the rear seat dummy, including head injury criterion (HIC), chest acceleration and Nij, were evaluated. The simulation results were first validated against available test data for a Ford Taurus vehicle and later used for the analysis. The analysis showed that an increase in the stiffness of the vehicle can significantly increase rear seat dummy injury measures. It was shown, for example, that the HIC15 of a rear seat dummy can increase from 478 to 755 between two vehicles with an increase in stiffness from 1000 to 1557 N/mm.

车载光学平台双层隔振系统设计与试验研究

The paper analyzes the damages of shock and vibration to precise mobile vehicle-mounted optical systems during transportation process and working condition, points out that structural deformation and vibration are the main factors influencing optical system stability and vehicle installation implementation, and notes that it is the key technique to achieve the optical system stability by improving the overall vehicle stiffness, stability and vibration isolation performance of the mobile vehicle-mounted optical platform. The structure and composition of the vehicle-mounted optical platform as well as high stiffness and double-layer isolation design solutions are discussed. The modal analysis of the designed double-layer optical platform isolation system is carried out with ANSYS finite elem

Methodology for the selection of weapons mounted on light terrain wheeled vehicles

Nowadays, a number of light terrain wheeled vehicles are used for various purposes. Their basic performances are related to achieving high average speed off roads and to overcoming various obstacles. This type of vehicles is mainly used for commercial purposes. Models of these vehicles have been modernized and upgraded during the time but their basic purpose remains the same. However, nowadays there is a need to use these vehicles for other purposes. This is carried out through the process of conversion. The conversion means that a vehicle changes its purpose by the application of various technical solutions. One of conversions is related to the application of weapons on the vehicle chassis. The weapon mounting is connected with various problems such as vehicle stiffness, weapon precision, presence of various oscillations, overall vehicle layout and crew deployment. In order to mount weapons efficiently, the methodology of its selection is proposed. It consists of several phases and the most important of them are the following ones: the consideration of performances of modern light terrain wheeled vehicles, analysis of weapons convenient for application, creation of the vehicle-platform-weapon system mathematical model, analysis of the dynamic characteristics of the created model and the selection of the best solution, experimental research and analysis of theoretical and experimental results. The realization of the proposed methodology will considerably improve the quality of the design of vehicle- platform-weapon systems.

Experimental evaluation of underride analysis techniques and empirical validation of a new analytical technique

Accident reconstructionists are often faced with damage patterns and locations on vehicles that are not well defined by available barrier impact data. One such example is a frontal underride collision. Underride impacts occur when there is a height mismatch between the primary structural components of the impacting vehicles, and the vehicle with the lower height is forced beneath the structure of the other vehicle. The lack of structural engagement typically allows for significantly different damage patterns due to the inherently lower stiffness of the underriding vehicle's contacting surfaces coupled with complex interactions between varying surfaces. In this study, a series of two-vehicle impact tests between a small pickup (bullet vehicle) and a large dump truck (target vehicle) were performed and studied. These tests involved a severe underride configuration in which the dump truck bed's vertical alignment was above the base of the windshield of the pickup. Coupled with these impacting surfaces was a single vertical support, a remnant of a commonly referred to ICC (Interstate Commerce Commission) bumper, which caused a narrow object-type impact, but did not extend down to the pickup's bumper. Multiple prior authors’ analytical and empirical relationships to predict impact speed based on crush damage were evaluated using the results of these tests as well as other published underride tests. No single model was sufficient at predicting the mixed mode of impact present in these impact scenarios. However, a system of equations was developed to predict the impact parameters utilizing a combination of previously reported methods and a new empirical relationship presented in this study. This new method shows high correlation and supports the authors’ hypothesis that separate crush models can be applied to multiple discrete areas of a vehicle and then combined to form a more complete predictive systematic model.

Accident reconstruction methods

While reconstructing a car accident, there are several questions that must be answered, such as the movement of all the vehicles involved or of other people involved, or of objects from the point of first visual contact to their rest positions. Time history of velocities, positions as well as crash-related data such as velocity changes, deformation energies, or passenger loads must also be analysed. Methods to aid in accident reconstruction combine the simulation of pre-collision, collision, and post-collision dynamics for multiple vehicles. This paper presents trajectory and collision models used for accident reconstruction as well as useful optimisation strategies. The model for predicting the 3D kinematics of a vehicle's pre- and post-impact trajectory, which is based on a discrete kinetic time forward simulation of vehicle dynamics, has been described. The tyre model, steer angle, wheel braking, weight shift, and suspension effects have been introduced and a method of handling pre-impact yaw, braking, acceleration, and pre-impact steering have been outlined. The momentum-based collision model, which relies on restitution rather than vehicle crush or stiffness coefficients, has been defined and a method for dealing with secondary impacts, inter-vehicle friction, and impulse vectors with a vertical component have been explained. The second part of the paper deals with various collision models used to simulate the motion of the vehicles during the collision. Within the last part of the paper, various optimisation methods have been introduced which are used to generate the simulation results partially automated.

Simplified modelling of joints and beam-like structures for BIW optimization in a concept phase of the vehicle design process

The paper proposes an engineering approach for the replacement of beam-like structures and joints in a vehicle model. The final goal is to provide the designer with an effective methodology for creating a concept model of such automotive components, so that an NVH optimization of the body in white (BIW) can be performed at the earliest phases of the vehicle design process. The proposed replacement methodology is based on the reduced beam and joint modelling approach, which involves a geometric analysis of beam-member cross-sections and a static analysis of joints. The first analysis aims at identifying the beam center nodes and computing the equivalent beam properties. The second analysis produces a simplified model of a joint that connects three or more beam-members through a static reduction of the detailed joint FE model. In order to validate the proposed approach, an industrial case-study is presented, where beams and joints of the upper region of a vehicle's BIW are replaced by simplified models. Two static load-cases are defined to compare the original and the simplified model by evaluating the stiffness of the full vehicle under torsion and bending in accordance with the standards used by automotive original equipment manufacturer (OEM) companies. A dynamic comparison between the two models, based on global frequencies and modal shapes of the full vehicle, is presented as well.

General Torsional Stiffness Matching of Off-road Vehicle

Increasing frame torsional stiffness of off-road vehicle will lead to the decrease of body torsional deformation, but the increase of torsional loads of frame and suspension system and the decrease of wheel adhesive weight. In severe case, a certain wheel will be out of contact with road surface. Appropriate matching of body, frame and suspension torsional stiffnesses is a difficult problem for off-road vehicle design. In this paper, these theoretically analytic models of the entire vehicle, body, frame and suspension torsional stiffness are constructed based on the geometry and mechanism of a light off-road vehicle's body, frame and suspension. The body and frame torsional stiffnesses can be calculated by applying body CAE method, meanwhile the suspension's rolling angle stiffness can be obtained by the bench test of the suspension's elastic elements. Through fixing the entire vehicle, using sole timber to raise wheels to simulate the road impact on a certain wheel, the entire vehicle torsional stiffness can be calculated on the geometric relation and loads of testing. Finally some appropriate matching principles of the body, frame and suspension torsional stiffness are summarized according to the test and analysis results. The conclusion can reveal the significance of the suspension torsional stiffness on off-road vehicle's torsion-absorbing capability. The results could serve as a reference for the design of other off-road vehicles.

Fatigue analysis for a multi-lap spot welded joint of high strength steel using quasi static tensile-shear test

The welding quality of spot weldment is an important factor that significantly affects the strength, stiffness, safety, and other performance characteristics of vehicles. Therefore, quality control and fatigue life evaluation of spot weldment are necessary processes. This paper presents a method for determining the fatigue life of multi-lap spot weldment of a high strength steel sheet. In this method, the fatigue life is estimated using the lethargy coefficient, which is the total defect coefficient according to rupture stress and time obtained by the quasi static tensile-shear test. The DC potential drop method was used to check initiation and propagation of cracks in addition to the test. Also, in this study, we modified the lethargy coefficient by using the welding current. Furthermore, we define a specific lapping constant, which is a characteristic constant of 2 or 3 lap weldments. The fatigue life obtained by the fatigue estimate equation, which contains a specific lapping constant was compared and verified with an experimental value. Finally we analyzed the relation of lap number, welding current and fatigue life. This method can save processing time and cost for predicting the life cycle of a structure.

강성 배분비를 고려한 고강성화 경량화 차체 설계

Lightweight body due to the decrease of panel thickness and reinforcing member might cause low stiffness. On the other hand, high stiffness body requires an increase of mass. Front pillar section area has been decreased for increasing the driver's visual field. Global vehicle stiffness is affected by stiffness distribution ratio between upper part and lower part at a side body structure. This paper describes a process used to evaluate the stiffness distribution ratio based on strain energy. In addition, optimum design schemes are presented for high stiffness and lightweight body structure considering the investigated stiffness distribution ratio.

Fatigue Analysis of Multi-Lap Spot Welding of High Strength Steel by Quasi Static Tensile- Shear Test

The welding quality of spot weldment is an important factor that significantly affects the strength, stiffness, safety, and other performance characteristics of vehicles. Therefore, quality control and fatigue life evaluation of spot weldment are necessary processes. This paper presents a method for determining the fatigue life of multi-lap spot weldment of a high strength steel sheet. In this method, the fatigue life is estimated by using the lethargy coefficient, which is the total defect coefficient according to rupture stress and time obtained by the quasi static tensile-shear test. Also, in this study, we modified the lethargy coefficient by using the welding current. And, we define a specific lapping constant, which is a characteristic constant of 2 or 3 lap weldments. The fatigue life obtained by the fatigue estimate equation, which contains a specific lapping constant was compared and verified with an experimental value. And we analyzed the relation of lap number, welding current and fatigue life. This method can save processing time and cost for predicting the life cycle of a structure.

Determination of the Crush Stiffness Coefficients of a Typical Aftermarket Frontal Protective Guard Used in Light Trucks and Vans with Comparisons between Guard Stiffness and Frontal Vehicle Crush Coefficients

Crush stiffness coefficients were determined for a typical I-beam constructed frontal grill guard used in the aftermarket on vehicles classified as light trucks or vans. These crush coefficients were determined by virtual impacts of a typical guard construction into a rigid barrier using finite element analysis (FEA) methods and collision stiffness computations. It was found that the addition of a frontal protection guard is capable of significantly changing the frontal stiffness of the vehicle to which it is attached. The federal motor vehicle safety standards (FMVSSs) require vehicles to give a certain crash response in order to protect occupants. Engineers have designed features such as frontal and rear crash zones to dissipate crash energies to meet the FMVSS requirements. Changing the stiffness of the vehicle by the addition of a frontal guard may alter the crash response and airbag deployment of the vehicle to which it is attached, along with the crash response of the guard-struck vehicle. The determination of the crush stiffness coefficients for a frontal guard will allow a comparison with the engineered frontal stiffness of vehicles in order to start the examination of the effect of frontal guard stiffness on crashworthiness of the collision partners. In addition, the determination of these coefficients will allow accident reconstructionists to assess the change in velocity of vehicles involved in collisions with frontal guards from guard crush damage.

Parametric Analysis of Vehicle Design Influence on the Four Phases of Whiplash Motion

Objective. The objective is to establish a basis for motor vehicle test requirements that measure component contributions to Whiplash Associated Disorders (WAD). Methods. Selected vehicle design features are evaluated with regard to their relative contributions to WAD measures. The motion of the occupant cervical spine associated with WAD is divided into four phases: retraction, extension, rebound, and protraction. Injury measures from the literature (NIC, extension moment, N km , and flexion moment) represent the injury potential during each of these phases. Four vehicle design factors that affect WAD motion (vehicle stiffness, seat stiffness, head restraint height and head restraint backset) were evaluated for their contributions to the injury measures. A detailed 50th percentile male model with a biofidelic neck was used in a 100-run Monte Carlo analysis of a rear impact, varying the design factors across the values documented in the literature. Total energy was held constant and Delta V was 10 kph. Results. Vehicle stiffness has a strong influence on the retraction (70%), rebound (43%), and protraction (47%) phases. Headrest backset demonstrates a strong influence on the extension (49%) and rebound (39%) phases. Conclusions. For WAD protection rating, the vehicle should be viewed as a system whereby the complex interactions among the vehicle, seat, and occupant characteristics all contribute to the WAD potential.

RELIABILITY ANALYSIS OF STIFFNESS DEGRADATION IN AUTOMOTIVE SPOT-WELDED JOINTS

This paper develops a reliability-based methodology for the evaluation of stiffness degradation of spot-welded joints under high mileage. A global-local finite element analysis is used, with the loads on the detailed three-dimensional joint model coming from finite element analysis of the entire car model with proving ground loads. Probabilistic fatigue crack propagation analysis is developed for multi-axial variable amplitude loading history on the joint. Multiple spot welds contribute to the stiffness of the joint. Hence the problem is addressed through system reliability techniques. The effect of spot-weld separation on joint stiffness, and on global vehicle stiffness, is incorporated. This results in the computation of the statistics of vehicle stiffness degradation with mileage.

Application of a model of collision between cars to the analysis of compatibility and its sensitivity to the variation of certain design parameters

Frontal collisions between vehicles are one of the most severe accidents that usually occur in our roads, and the incompatibility between masses, stiffness and geometries of vehicles has a great influence in the consequences of the collision. It is necessary to go forward in the reduction of the aggressiveness of vehicles to each other without reducing self-protection. In order to research about compatibility, simplified mathematical models of collision will be very useful. In this paper, the development is described of a frontal collision model especially conceived to reproduce the factors that may influence the compatibility. The model was adjusted to represent the behaviour of several vehicle types representative of the car-park, and was validated through real accidents data and vehicle-to-vehicle crash tests. Finally, the usefulness of the model for compatibility study is shown by an application example, an analysis of the sensitivity to the variation of certain design parameters.

IDENTIFICATION OF SYSTEM PHYSICAL PARAMETERS FOR VEHICLE SYSTEMS WITH NONLINEAR COMPONENTS

SUMMARY In this paper a time-domain direct identification method is presented for the identification of vehicle system mass, damping and stiffness matrices, as well as for parameters of nonlinear components which are “linear-in-the-parameters”. The method is based on least-square type of error costs which are constructed from system dynamic equations. The estimated system parameters are then tuned to minimize each of these cost functions. The parameters are directly identified from the deduced algorithm without iteration. To demonstrate the proposed identification procedure, the method is applied to a four degree-of-freedom vehicle; different nonlinear suspension components, such as cubic springs, nonlinear hydraulic and frictional dampers and their combinations are considered. It can be seen that by using the proposed method, all the unknown system parameters are identified with sufficient accuracy, low memory and computation time.

Modeling of occupant-roof interaction in an automobile rollover

An automobile can be conceived as a structure that houses living occupants within. During a crash environment interactions exist between the occupant and the vehicle interior. Deformations of the root of the vehicle play an important part in the mechanics of rollover accidents. An understanding of the interaction between the roof deformations and occupant kinematics leads to a better structural design of the vehicle and hence, an improved occupant protection against trauma. In this study, a multi-degree-of-freedom system lumped parameter model simulated a rollover accident during the initial phase wherein the airborne automobile is contacting the ground surface with a certain initial drop velocity. The vehicle is simulated by a mass-spring system, the mass representing the vehicle weight, the spring simulating the superstructure crushability characteristics of the roof and the pillars. The occupant torso, head and neck are simulated by a combination of mass and 2 springs. The effect of occupant restraint and the compressibility of the seat is incorporated by suitable tensile and compressive stiffnesses for the corresponding springs. The resulting coupled differential equation of motion can be solved numerically with suitable end conditions. The occupant survival space, defined as the net available clearance between the head of the occupant and the bottom of the vehicle roof interior, an important parameter that influences the forces in the occupant, is also included in the analysis. Parametric studies were conducted to study the effect of geometric and material variables on the forces imparted to the occupant. A direct relation was found to exist between the forces in the occupant and initial roll velocity. A reduction in the occupant force occurred due to an increase in the superstructure rigidity, increased survival space and decreased compressibility of the seat. These parameters had, on the contrary, only marginal effects on the vehicle dynamic forces. Decrease in vehicle mass resulted in a decrease of the forces both on the occupant and the vehicle. In addition, the restraining force on the occupant was small up until the time it comes in contact with the superstructure. This time it was found to be insensitive to changes in the structural stiffness of the vehicle. Lower vehicle stiffness delayed the time at which the peak force in the vehicle and occupant occurred. Whilst a detailed non-linear analysis is recommended to completely describe the mechanics of rollover, this simple linear multi-degree-of-freedom lumped parameter technique provides an insight into the modeling of the occupant-vehicle interaction.