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Developing lightweight, stiff and crash-resistant vehicle body structures requires a balance between part geometry and material properties. High strength materials suitable for crash resistance impose geometry limitations on depth of draw, radii and wall angles that reduce geometric efficiency. The introduction of 3rd generation Advanced High Strength Steels (AHSS) can potentially change the relationship between strength and geometry and enable simultaneous improvements in both. This paper will demonstrate applicability of 3rd generation AHSS with higher strength and ductility to replace the 780 MPa Dual Phase steel in a sill reinforcement on the current Jeep Cherokee. The focus will be on formability, beginning with virtual simulation and continuing through a demonstration run on the current production stamping tools and press.

Experimental procedures and results of a benchmark test for springback are reported and a complete suite of obtained data is provided for the validation of forming and springback simulation software. The test is usually referred as the Slit-Ring test where a cylindrical cup is first formed by deep drawing and then a ring is cut from the mid-section of the cup. The opening of the ring upon slitting releases the residual stresses in the formed cup and provides a valuable set of easy-to-measure, easy-to-characterize springback data. The test represents a realistic deep draw stamping operation with stretching and bending deformation, and is highly repeatable in a laboratory environment. In this study, six different automotive materials are evaluated.

Advanced high-strength steels (AHSS) are a class of steels that have a minimum tensile strength of 500 MPa. The advantages of AHSS include superior formability and better crash energy absorption compared with conventional low-strength steels having a minimum tensile strength of 270 MPa. Several steels with a minimum tensile strength of 590 MPa have already found use in current vehicles, and others with minimum tensile strength up to 980 MPa have been qualified for use in future vehicle models. Two 780 MPa steels of interest are 780 DP (Dual Phase) and 780 TRIP (TRansformation Induced Plasticity). In this study, an examination was undertaken to compare the resistance spot-welding behavior of commercially produced 1.6 mm-thick, hot-dipped galvannealed, 780 MPa DP and TRIP steel sheet. Included in the study were evaluations of the weld lobes, weld microhardness, and the shear- and cross-tension strengths of resistance spot welds for the two steels.

Once the design of a door sheetmetal and accessories is confirmed, the acoustics of the door system depends on the sound package assembly. This essentially consists of a watershield which acts as a barrier and a porous material which acts as an absorber. The acoustical performance of the watershield and the reverberant sound build-up in the door cavity control the performance. This paper discusses the findings of a design study that was developed based on design of experiments (DOE) concepts to determine which parameters of the door sound package assembly are important to the door acoustics. The study was based on conducting a minimum number of tests on a five factor - two level design that covered over 16 different design configurations. In addition, other measurements were made that aided in developing a SEA model which is also compared with the findings of the results of the design study.

Studies in an Angular Stretch Bend Test (ASBT) have demonstrated that the failure location moves from the side wall to punch nose area. This occurs as the R/T ratio decreases below a certain limit and applies to most low carbon steels with the exception of Dual Phase (DP) steels. Such behavior in DP steels indicates that bending effects have a severe impact on the formability of DP materials. Therefore, the traditional criterion using the forming limit curve (FLC) is not suitable to assess the formability at punch radius areas for DP steels due in part to its uniqueness of unconventional microstructures. In this paper, a new failure criterion, ‘Bending-modified’ FLC (BFLC), is proposed by extending the traditional FLC using the “Stretch Bendability Index” (SBI) concept for the stretch bendability assessment.

Laser lap welding quality is a non-linear response based on a host of categorical and numeric material and process variables. This paper describes a Grammatical Evolution approach to the structure identification of the laser lap welding process and compares its performance with linear regression and a neuro-fuzzy inference system.

Load data representing severe customer usage is required during the chassis development process. One area of current research is the use of road profiles for predicting chassis loads. The most direct method of predicting these loads is to run dynamic simulations of the vehicle using numerous road profiles as the excitation. This onerous task may be avoided, and a greatly reduced number of simulations would be required, if roads having similar characteristics can be grouped. Currently, road profiles are characterized by their spectral content. It has been noted by several researches, however, that road profiles are generally nonstationary signals that contain significant transient events and are not well described in the spectral domain. The objective of this work, then, is to develop a method by which the characteristics of the road can be captured by describing these constitutive transient events.

A simple strategy for building lightweight automobile body-in-whites (BIWs) is developed and discussed herein. Because cost is a critical factor, expensive advanced materials, such as carbon fiber composites and magnesium, must only be used where they will be most effective. Constitutive laws for mass savings under various loading conditions indicate that these materials afford greater opportunity for mass saving when used in bending, buckling or torsion than in tensile, shear or compression. Consequently, it is recommended that these advanced materials be used in BIW components subject to bending and torsion such as rails, sills, “A-B-C” pillars, etc. Furthermore, BIW components primarily subject to tension, compression, or shear, such as floor pans, roofs, shock towers, etc., should be made from lower cost steel. Recommendations for future research that are consistent with this strategy are included.

Low carbon steels are being replaced by advanced high strength steels (AHSS) due to high demand of the future lighter weight vehicle, while still maintaining good or even better crash performance. However, sidewall curl and springback (section opening) have been found to increase as the strength of the sheet metal increases. Experiments have been conducted on the bending under tension (BUT) test to seek an effective control methodology regarding the applications of the advanced high strength steels (AHSS) in this study. Steels that were studied included a low carbon steel (DQSK), two dual phase steels (DP) and a transformation induced plasticity (TRIP) steel. Two different gauges of each AHSS were also included for a gauge sensitivity study. Different processing variables (four different diameter pins combining with five different back tension forces) were applied to the tests, and the springback angle and sidewall curl were measured for bend and bend-unbend areas of the specimen.

A novel performance classification system has been developed for advanced high-strength steel (AHSS). This system considers intrinsic global and local formability parameters derived from standard uniaxial tension tests and is applicable to all current and future AHSS materials. The overall AHSS performance index (P.I.) is defined herein as the product of the ultimate tensile strength (UTS) and the formability index (F.I.), where F.I. is an intermediate strain value between the true uniform strain and the true fracture strain (TFS). Target P.I. values are defined for First Generation AHSS (GEN1), Improved First Generation AHSS (GEN1+), Third Generation AHSS (GEN3), and AHSS Future. Performance is further distinguished by local, balanced, and global formability characteristics and by relative yield strength (yield-to-tensile ratio). Additionally, the influence of tension test specimen geometry and fracture area measurement method on the TFS value was explored.

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 deals with the multi-parameter and boundary mannequin techniques in creating human models in automotive applications. The concepts and applications of single-parameter, multiple parameter and boundary mannequin method are discussed respectively to clarify certain confusion. Emphasis is put on how to create boundary mannequins for a specific application, which may have been puzzling many engineers in practical applications. The authors would like to share their experience in using the digital human modeling software and make discussions on some common issues. A number of case studies from typical automotive manufacturing assembly operations are also presented to demonstrate the usage of the multi-parameter and boundary mannequin techniques.

A typical forming operation of chassis components (control arms, cross members, etc.) often involves edge stretching and/or hole expansion. As a result, the edge split is a common forming failure mode. To overcome this problem, Japanese and European automakers use stretch flange high strength (SFHS) steel due to its high strength and excellent edge stretch capability. Recently, SFHS steel has gained greater attention in North America and is currently being used for upper and lower control arm applications. This paper includes a discussion on general edge stretch issues in forming operations, including material data that demonstrate the higher stretch limit of SFHS steel as compared to other high strength steels. In a case study, SFHS steel is applied to a control arm and finite element analysis (FEA) is conducted to evaluate forming and structural performance.

Axial drop tower crash tests were carried out on a variety of 70-mm outer-diameter continuous-welded cylindrical steel tubes with several thicknesses (t). Ultimate tensile strength (UTS) ranged from less than 300 MPa for a fully stabilized steel to greater than 800 MPa for the advanced high strength steels (AHSS). In the tests, a 520-kg weight is dropped from a height of 3.3 meters to achieve impact velocities of 6.1 to 6.7 m/s (14 to 15 mph). Load and acceleration data are recorded as a function of time as the tube is crushed axially. The results show that, for a given impact condition, the peak and average crush loads of a steel tube is directly proportional to UTS × t2, while axial crush distance is inversely proportional to UTS × t2. As such, crash deformation can be reduced by substituting higher strength steels of the same thickness, or existing crash deformation can be maintained and weight reduction achieved by substituting higher strength steels with reduced thickness.

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.

One of the major NVH concerns for automobile manufacturers is the response of a vehicle to the impact of the tire as it encounters a road discontinuity or bump. This paper describes methods for analyzing the impact response of a vehicle to such events. The test vehicle is driven on a dynamometer, on which a bump simulating cleat is mounted. The time histories of the cleat impact response of the vehicle can be classified as a transient and a repeated signal, which should be processed in a special way. This paper describes the related signal processing issues, which include converting the time data into a continous spectrum, determination of the correct scaling factor for the analyzed spectrum, and smoothing out harmonics and fluctuations in the signal. This procedure yields a smooth frequency spectrum with a correctly scaled amplitude, in which the frequency contents can be easily identified.

This paper contains a review of methods for deriving risk curves from biomechanical data obtained from impact experiments on human surrogates. It covers many of the problems and pitfalls of obtaining realistic human risk curves from impact experiments. The strength and weakness of both parametric and non-parametric methods are evaluated. The limitations of standard analysis of censored impact test data are presented. Methods are given for determining risk curves from both doubly censored data and data obtained from impacts to body regions in which there are more than one mechanism of injury. A detailed set of examples is presented in which different experimental data are analyzed using the Consistent Threshold method and the logistic approach. Finally risk curves for published data are presented for the femur, head, thorax, and neck.

Computer applications have been widely used to assist product design. The successes and sophistication of computer aided engineering (CAE) techniques are respectfully recognized in this field. CAE applications in the manufacturing area however are still developing, although the manufacturing community is increasingly starting to pay attentions to computer simulations in its daily workings. This paper will briefly introduce some of these applications and promote awareness of computer simulations in manufacturing area. It contains four main sections: finite element analysis (FEA) in machining fixture design, FEA applications in component assembly, machining process simulations and machining vibrations in the milling operation. Each section comes with a practical case study, potential benefits are identified and conclusions are presented by using an integrated design and analysis approach.

Advanced high strength steels (AHSS), such as dual phase (DP) and transformation induced plasticity (TRIP) steels, have been increasingly used in automotive industry. One of the major advantages of AHSS is the excellent crash energy absorption capability. In this study, crash performances were evaluated for four AHSS including DP980, DP780, TRIP780 (780T), and TRIP590 (590T). Axial crush and bending crush tests were performed to evaluate the material crush performance. High strain rate tension test results for those materials were also presented. FEA analyses with parameter sensitivity studies were conducted including strain rate sensitivity effect, part geometry effects, welding models and forming effects. Good correlations between simulation and experimental data were achieved.

Fracture strain data provide essential information for material selection and serve as an important failure criterion in computer simulations of crash events. Traditionally, the fracture strain was measured by evaluating the thinning at fracture using tools such as a microscope or a point micrometer. In the recent decades, digital image correlation (DIC) has evolved as an advanced optical technique to record full-field strain history of materials during deformation. Using this technique, a complete set of the fracture strains (including major, minor, and thickness strains) can be approximated for the material. However, results directly obtained from the DIC can be dependent on the experiment setup and evaluation parameters, which potentially introduce errors to the reported values.