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This paper describes static and fatigue behavior of resistance spot welds with the stack-up of conventional mild and advanced high strength steels, with and without adhesive, based on a set of lap shear and coach peel coupon tests. The coupons were fabricated following specified spot welding and adhesive schedules. The effects of similar and dissimilar steel grade sheet combinations in the joint configuration have been taken into account. Tensile strength of the steels used for the coupons, both as-received and after baked, and cross-section microstructure photographs are included. The spot weld SN relations between this study and the study by Auto/Steel Partnership are compared and discussed.

This paper presents an investigation into the behavior of spot-welded steel connections based on a DOE approach. This work is a part of spot-weld modeling methodology development work being performed at Ford. Control factors such as material, coating, gage size, and noise factors such as loading direction (angle), and speed are considered in this study. Different levels of each variable are included to cover a wide range of practical applications. The test methodology used to generate the responses for the spot-weld coupons have been discussed in a companion paper [1]. From the force-displacement curves obtained from the test, the responses such as peak force, displacement at peak force, and rupture displacement are identified. These responses are then statistically analyzed to identify the relative importance and effect of the design factors. Finally, response surface models are developed to determine responses across different levels of each variable.

In the North American automotive industry, various advanced high strength steels (AHSS) are used to lighten vehicle structures, improve safety performance and fuel economy, and reduce harmful emissions. Relatively thick gages of AHSS are commonly joined to conventional high strength steels and/or mild steels using Gas Metal Arc Welding (GMAW) in the current generation body-in-white structures. Additionally, fatigue failures are most likely to occur at joints subjected to a variety of different loadings. It is therefore critical that automotive engineers need to understand the fatigue characteristics of welded joints. The Sheet Steel Fatigue Committee of the Auto/Steel Partnership (A/S-P) completed a comprehensive fatigue study on GMAW joints of both AHSS and conventional sheet steels including: DP590 GA, SAE 1008, HSLA HR 420, DP 600 HR, Boron, DQSK, TRIP 780 GI, and DP780 GI steels.

To improve the energy absorption capacity of front-end structures during a vehicle crash, a novel 12-sided cross-section was developed and tested. Computer-aided engineering (CAE) studies showed superior axial crash performance of the 12-sided component over more conventional cross-sections. When produced from advanced high strength steels (AHSS), the 12-sided cross-section offers opportunities for significant mass-savings for crash energy absorbing components such as front or rear rails and crush tips. In this study, physical crash tests and CAE modeling were conducted on tapered 12-sided samples fabricated from AHSS. The effects of crash trigger holes, different steel grades and bake hardening on crash behavior were examined. Crash sensitivity was also studied by using two different part fabrication methods and two crash test methods. The 12-sided components showed regular folding mode and excellent energy absorption capacity in axial crash tests.

To evaluate vehicle crash performance in the early design stages, a reliable fracture model is needed in crash simulations to predict material fracture initiation and propagation. In this paper, a generalized incremental stress state dependent damage model (GISSMO) in LS-DYNA® was calibrated and validated for a 780-MPa third generation advanced high strength steels (AHSS), namely 780 XG3TM steel that combines high strength and ductility. The fracture locus of the 780 XG3TM steel was experimentally characterized under various stress states including uniaxial tension, shear, plane strain and equi-biaxial stretch conditions. A process to calibrate the parameters in the GISSMO model was developed and successfully applied to the 780 XG3TM steel using the fracture test data for these stress states.

Finite element models of cast aluminum and stamped steel lower control arms (LCAs) were created to simulate subsystem tests of LCA with bushings and brackets. Several modeling methods were used to simulate the dynamic responses of cast aluminum LCAs, and the advantages and disadvantages of each method are discussed. Factors that are essential for modeling stamped steel components found in previous studies [1, 2] including strain rate, forming, and welding effects are incorporated in the stamped steel LCA models. Difficulties in modeling LCAs subsystem, possible remedies, and further improvements are also discussed in this paper.

Strain rate effects have been identified as one of the most critical factors for the modeling of vehicle components in many previous investigations. The strain rate data available to the authors have been processed to obtain the input decks of a required material law in prior investigations. With the application of strain rate modeling, the strain rate database needs to be expanded. In order to continuously improve the safety CAE quality and efficiency, especially the prediction of a vehicle's pulse in a crash event, the effort has been made to include more strain rate data and extend the material database for safety CAE applications. In this study, strain rate data provided by Ispat Inland Inc. for AISI/DOE Technology Roadmap Program are processed. The material processed in this study include HSS590-CR, 440W-GA, BH300-GI, HSLA350-GI, DP600-HR, TRIP590-EG, TRIP600-CR, TRIP780-CR.

This study is a systematic investigation of the body mounts' dynamic characteristics in component, sub-system and full system levels and its application in the frontal impact analysis of a body-on-frame (BOF) vehicle. Concluded from the component study, the body mount is modeled by non-linear spring with built-in damage and rupture properties. The sub-system study reveals the importance of modeling the interaction between the body mount and its surrounding structure. A general-purpose interaction modeling is developed to provide a realistic CAE simulation of this interaction behavior. The full system is mainly for methodology validation. Four 90-degree frontal and the one IIHS offset frontal crash tests are used to evaluate the performance of the body mount in low and high speeds and its capability of predicting the body mount and the floor pan failures.

The frontal rail is one of the most important components of a vehicle in determining crash performance, especially for a body on frame vehicle. Prior research [1] has shown that the frontal rail absorbs a significant amount of impact energy in a crash condition. In order to optimize crash performance, a component level sensitivity study was conducted to determine the effect different types of triggers would have on the performance of the frontal rail. The objective of this study is to determine the sensitivity of trigger size, trigger shape, and trigger orientation as well as to improve corresponding trigger modeling methodology by comparing crushed components to crushed CAE models. In this sensitivity study, the location of the triggers was held fixed, while the size, shape, and orientation were varied. The metric that will be used to compare the performance of these different trigger shapes is the overall stiffness of the frontal rail.

Edge fracture of advanced high strength steels (AHSS) can occur in both the stamping process and the crash event. Fracture due to poor sheared edge conditions in the stamping process was reduced with a recently developed optimal shearing process for AHSS. Currently, the improvement in the energy absorption due to the improved edge condition during crashes performed under different loading conditions had not been closely verified. The purpose of this study is to design and build a miniature component of AHSS and a three-point bending test for investigating the influence of various conditions of the sheared edge on the energy absorption in crashes. AHSS including DP600, TRIP780, DP980 and DP1180 were selected in the study. A small channel component was developed and fabricated using DP980 to simulate key features of the B-pillar. The exposed non-constrained, as-sheared edge was subject to stretch bending forces in three-dimensional space during the three-point bending test.

Advanced High Strength Steels (AHSS) along with innovative design and manufacturing processes are effective ways to improve crash energy management. Crash trigger hole is another technology which can been used on front rails for controlling crash buckling mode, avoiding crash mode instability and minimizing variations in crash mode due to imperfections in materials, part geometry, manufacturing, and assembly processes etc. In this study, prototyped crash columns with different trigger hole shapes, sizes and locations were physically tested in frontal crash impact tests. A corresponding crash computer simulation model was then created to perform the correlation study. The testing data, such as crash force-displacement curves and dynamic crash modes, were used to verify the FEA crash model and to study the trigger sensitivity and effects on front rail crash performance.

Advanced high strength steels (AHSS) have been extensively used in the automotive industry for vehicle weight reduction. Although AHSS show better parent metal fatigue performance, the influence of material strength on spot weld fatigue is insignificant. To overcome this drawback, structural adhesive can been used along with spot weld to form weld-bond joints. These joints significantly improve spot weld fatigue performance and provide high joint stiffness enabling down-gauge of AHSS structures. However, modeling the adhesive joints using finite element methods is a challenge due to the nonlinear behavior of the material. In this study, the formulation of cohesive element based on the traction-separation constitutive law was applied to predict the initiation and propagation of the failure mode in the adhesively bonded joints for lap shear and coach peel specimens subjected to quasi-static loadings. The predicted load versus displacement relations correlated well with the test results.

Advanced high strength steels (AHSS) offer a good balance of strength, durability, crash energy absorption and formability. Applications of AHSS for lightweight designs of automotive structures are accelerating in recent years to meet the tough new CAFE standard for vehicle fuel economy by 2025. At the same time, the new generation pickup cargo box is to be designed for a dramatic increase in payload. Upgrading the box material from conventional mild steels to AHSS is necessary to meet the conflicting requirements of vehicle light weighting and higher payload. In this paper, typical AHSS grades such as DP590 and DP780 were applied to selected components of the pickup cargo box for weight reduction while meeting the design targets for fatigue, strength and local stiffness.

Spot welding is the primary joining method used for the construction of the automotive body structure made of steel. A major challenge in the crash simulation today is the lack of a simple yet reliable modeling approach to characterize spot weld separation. In this paper, an attempt has been made to develop a spot weld modeling methodology to characterize spot weld separation in crash simulation. A generalized two-node spring element with 6 DOF at each node is used to characterize the spot weld nugget. To represent the connection of the nugget with the surrounding plates, tied contacts are defined between the spring element nodes and the shell elements of the plate. Three general separation criteria are proposed for the spot weld that include the effects of speed and coupled loading conditions. The separation criteria are implemented into a commercially available explicit finite element code.

This study focuses on the modeling of a frame in a body-on-frame (BOF) vehicle to improve the prediction of vehicle response in crashes. The study is divided into three phases - component (frame material modeling), subsystem (frame sled test) and full system (full vehicle test). In the component level, we investigate the available strain rate data, the performance of various material models in crash codes and the effect of the strain rate in crash simulation. In the subsystem phase, we incorporate the strain rate modeling and expand the scope to include both the forming and the welding effects in the subsystem CAE model to improve the correlation between CAE and test. Finally the improved frame modeling methodology with strain rate, forming and welding effects is adopted in full vehicle model. It is found that the proposed frame modeling methodology is crucial to improve the pulse prediction of a full vehicle in crashes.

Statistic shows the majority of real world frontal collisions involve only partial overlap of the vehicle front end. Thus the European Experimental Vehicle Committee (EEVC) has established a safety standard and test procedure utilizing a deformable barrier for offset impacts. The offset deformable barrier (ODB) is designed to represent the characteristics of a vehicle front end. Therefore, it can replace a target vehicle and the offset test can be conducted economically. Many component, sub-assembly and full vehicle system tests have been conducted in Ford using the EEVC ODB. Based on the various tests, the barrier responds differently depending on the front end design and the size of an impacting vehicle. Sometimes the front end of a test vehicle punches through the barrier. Also rupture of aluminum sheets and tearing of honeycomb materials are often observed in post-test barriers.

Advanced High Strength Steels (AHSS) have been implemented in the automotive industry to balance the requirements for vehicle crash safety, emissions, and fuel economy. With lower ductility compared to conventional steels, the fracture behavior of AHSS components has to be considered in vehicle crash simulations to achieve a reliable crashworthiness prediction. Without considering the fracture behavior, component fracture cannot be predicted and subsequently the crash energy absorbed by the fractured component can be over-estimated. In full vehicle simulations, failure to predict component fracture sometimes leads to less predicted intrusion. In this paper, the feasibility of using computer simulations in predicting fracture during crash deformation is studied.

The purpose of this paper is to show that certain steel skid plates can achieve up to a 50% weight reduction, with little or no increase in cost, by simply changing the shape and utilizing high strength steel. There are many factors that can influence the skid plate shape, including rail width, ground clearance, attachment points, drive shaft location, and the general shape of the object for which it is the skid plate's sole purpose to protect (fuel tank, transfer case, etc.). A skid plate is usually considered last from a design standpoint so that its design is dependent upon the environment which it is set in. For this reason, skid plates are generally heavy and flat to meet ground clearance requirements and have ribs inserted to increase stiffness. Sometimes design parameters require a skid plate to be heavy and flat. But more often, a stiffer lightweight design can be obtained.

The dynamic response of a front lower control arm (LCA) is very important in crash safety. In the event of a crash, the deformation of the LCA affects the frame rail's ability to crush and absorb energy on impact. Therefore, the deformation and rupture of the LCA during a crash may indirectly influence the deceleration pulse which is needed for safety sensor calibration of airbag deployment [1]. Depending on compliance, bushings have a significant effect on the deformation and rupture of the LCA. During a high speed impact test, the bushings allow the LCA to rotate at the joints or points where the LCA connects to the frame. The development of new LCA and bushing designs, constructed of different materials and geometries, require a standard test to measure their performance. The overall goal of this study was to develop a standardized procedure to test the stiffness, deformation, and strength of LCA bushings.

The conversion between cast aluminum lower control arms (LCAs) and stamped steel LCAs has prompted the need for new LCA designs to achieve parallel levels of performance. Component tests procedures and CAE modeling methodologies need to be utilized to assess future LCA designs across a variety of vehicle lines to meet or exceed performance criteria. Therefore the overall goal of this study was to develop a standardized test procedure to test the stiffness, deformation and strength of LCAs. In addition, CAE modeling methodologies to better model LCAs will be developed. The test procedures and CAE modeling methodologies would then be used to set performance targets for future LCA designs. To standardize the LCA test procedure, component test fixtures were developed in this work. The objective of the fixtures is to test LCAs with similar boundary conditions they would experience in vehicle crash. Three different test modes are examined in this project.