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This paper discusses an analytical technique for computing the failure rate of steel springs used in automotive part applications. Preliminary computations may be performed and used to predict spring failure rates quickly at a very early stage of a product development cycle and to establish program reliability impact before commitment. The analytical method is essentially a combination of various existing procedures that are logically sequenced to compute a spring probability of failure under various operational conditions. Fatigue life of a mechanical component can be computed from its S-N curve. For steels, the S-N curve can be approximated by formulae which describe the fatigue life as a function of its endurance limit and its alternating stress. Most springs in service are preloaded and the actual stress fluctuates about a mean level. In order to compute an equivalent alternating stress with zero mean, an analytical method based on the Goodman Diagram is used.

The Auto/Steel Partnership established the Light Truck Frame Project Group in 1996 with two objectives: (a) to develop materials, design and fabrication knowledge that would enable the frames on North American OEM (original equipment manufacturer) light trucks to be reduced in weight, and (b) to improve corrosion resistance of frames on these vehicles, thereby allowing a reduction in the thickness of the components and a reduction in frame weight. To address the issues relating to corrosion, a subgroup of the Light Truck Frame Project Group was formed. The group comprised representatives from the North American automotive companies, test laboratories, frame manufacturers, and steel producers. As part of a comprehensive test program, the Corrosion Subgroup has completed tests on frame coatings. Using coated panels of a low carbon hot rolled and pickled steel sheet and two types of accelerated cyclic corrosion tests, seven frame coatings were tested for corrosion performance.

The bulge test in hydroforming is a simple fundamental experiment used to obtain basic knowledge in tube expansion. The results can be used to assist design and manufacturing of hydroformed automotive parts. It also can be used to develop a failure criterion for tubes in hydroforming. For these purposes, a section of a long unsupported tube with fixed ends was simulated numerically to obtain the mechanical states of the tube subjected to internal pressure. Steel and aluminum tubes are used. For the bulge tests, the internal pressure reaches a maximum and then decreases in value without failure while the stress, strain and volume of the tube keep increasing. A failure criterion for the bursting of a tube is proposed based on the stress-strain curve of the material.

In order to engineer Squeak & Rattle (S&R) free vehicles it is essential to develop an objective measurement method to compare and correlate with customer satisfaction and subjective S&R assessments. Three methods for exciting S&Rs -type surfaces. Excitation methods evaluated were road tests over S&R surfaces, road simulators, and direct body excitation (DBE). The principle of DBE involves using electromagnetic shakers to induce controlled, road-measured vibration into the body, bypassing the tire patch and suspension. DBE is a promising technology for making objective measurements because it is extremely quiet (test equipment noise does not mask S&Rs), while meeting other project goals. While DBE is limited in exposing S&Rs caused by body twist and suspension noises, advantages include higher frequency energy owing to electro-dynamic shakers, continuous random excitation, lower capital cost, mobility, and safety.

Fundamental differences exist between sheet metal forming and hydroforming processes. Sheet metal forming is basically a one step metal fabrication process. Almost all plastic deformation of an originally flat blank is introduced when the punch is moved normal to a clamped sheet metal. Hydroforming, however, consists of multiple steps of tube making, pre-bending, crushing, pressurization, etc. Each of the above mentioned steps can introduce permanent plastic deformations. The forming limit diagram obtained for sheet metal forming may or may not be used in hydroforming evaluations. A failure criterion is proposed for predicting bursting failures in tube hydroforming. The tube material's stress-strain curve, obtainable from uniaxial tensile test and subjected to some postulations under large stress/strain states, is used in judging the failure.

A driving simulator development project at the Systems Engineering and Technical Process Center (SE/TP) is exploring the role of driving simulation in the vehicle design process. The simulator provides two vehicle mockup testing arenas that support a wide field of view, computer-generated image of the road scene which dynamically responds to driver commands as a function of programmable vehicle model parameters. Two unique aspects of the simulator are the fast 65 ms response time and low incidence rate of simulator induced syndrome (about 5%). Preliminary model validation results and data comparing driver performance in a vehicle vs. the simulator indicate accurate handling response dynamics within the on-center handling region (<0.3g lateral acceleration). Applications have included supporting the development of new steering system concepts, as well as evaluating the usability of vehicle controls and displays.

A design of experiments is used to study the effect of laser weld parameters on formability of welded blanks for two different material combinations of cold rolled (bare) steel to cold rolled steel and cold rolled steel to hot dipped galvanized steel. Critical weld parameters influencing the formability of welded blanks are identified and the optimum weld set-up condition is obtained based on formability performance and consistency of formability for laser welded blanks. The results are applied to an automotive body side frame. The robustness of welded blank production is also assessed and the final welded set-up condition for the body side frame is obtained based on both the formability of welded blanks and the robustness of welded blank production. The body side frame is successfully made from the welded blanks with this final weld set-up condition.

A rear full overlap car-to-car high speed impact simulation using the DYNA3D Finite Element Software was performed to examine the crush mode for rear structure of a vehicle and to observe the effect of rear bumper system in order to maintain the fuel system integrity. The study was conducted first for two different bumper system configurations, namely: (1) validating the model for struck vehicle with steel rear bumper system, (2) simulating rear end collision with composite rear bumper system attached to the rear rails of struck vehicle. Later a third simulation of the model was conducted with a viable design modification to the composite bumper system for improved crashworthiness. It was identified that a more comprehensive FEA model of the bullet car including front end structure, powertrain components, cooling system and other components which constitute the load paths should be incorporated in the analysis to obtain more meaningful correlation and crashworthiness prediction.

This paper describes a numerical simulation technique applicable to the FMVSS 214 side impact test through the use of the finite element method (FEM) technology. The paper outlines the development of the side impact dummy (SID), moving deformable barrier (MDB) and the test vehicle FEM models, as well as the development of new advanced constitutive models of materials and algorithms in LS-DYNA3D which are related to the topic. Presented in the paper are some initial simulation problems which were encountered and solved, as well as the correlation of the simulation data to the physical test.

Casting technology developmentshave led to a manufacturing process that allows the casting of thin wall (2-3mm) heat resistant ferritic stainless steel exhaust manifolds which can replace stamped and tubular weldments as well as iron castings where temperature requirements are increased. This casting process combines the thin wall and clean metal benefits of the counter gravity, vacuum-assist casting process using thin, light-weight bonded sand molds supported by vacuum-ridgidized sand. This combination is called the LSVAC (Loose Sand Vacuum Assisted Casting) process, a patented process. This process will significantly contribute to the growth of near-net shape steellstainless steel castings for automotive and allied industries. For exhaust manifolds, a modified grade of ferritic stainless steel with good oxidation resistance to 950°C in high dew point synthetic exhaust gas atmospheres was developed.

This paper describes some methods for greatly reducing or possibly eliminating subjective tuning of suspension parts for ride and handling. Laptop computers can now be used in the vehicle to guide the tuning process. The same tools can be used to select solutions that reduce sensitivity to production and environmental variations. OBJECTIVE Reduce or eliminate time required for tuning of suspension parts for ride characteristics. Improve the robustness of ride performance relative to variations in ambient temperature and production tolerances. PROBLEM REQUIRING SOLUTION AND METHOD OF APPROACH Traditional development programs for new vehicles include time-consuming subjective ride evaluations. One example is shock absorber tuning. Even if sophisticated models define force-velocity curves, numerous hardware iterations are needed to find valvings that will reproduce the curves. Many evaluation rides are needed to modify the valvings to meet performance targets.

From November 1970 through August 1971 an extensive program of static and dynamic air cushion inflation tests utilizing human volunteers was conducted at Holloman Air Force Base, New Mexico, sponsored by the Department of Transportation. Forty-one full cushion deployment static firings were made, with air cushion hardware and seating buck environment designed by General Motors. The static series was followed by 35 dynamic sled firings of human volunteers, beginning at 8.6 g (15.1 mph) and culminating at 21.7 g (31.5 mph). A major objective of both the static and dynamic test series was to identify changes in air-cushion design found necessary to improve its protective capability for human beings. Because of the severity of cushion deployment, one modification was made following the initial static tests: The orifice diameter size of the bag inlet was reduced from 1.0 to 0.6 in to diminish the rapidity of bag inflation. This modification proved effective in the dynamic series.

A search for methods of switching a proposed three beam headlight system led to the evaluation of 41 possible schemes. Human factors criteria reduced the original 41 to three systems which were tested in a laboratory with a broad range of subjects. Recordings of practice trials, learning trials, and the responses to visual cues projected on a screen were analyzed. The same test procedure was also used to compare three alternative ways of switching conventional two beam headlight systems. Summary data is presented for the six systems tested grouped by test subject age, sex, and driving experience. The most pronounced difference observed was in the subjective preference rating among two beam switching systems. All systems tested resulted in remarkably few learning and practice trials. Small differences were recorded among systems in operational response time.

Mechanical properties and welding characteristics of a commercial, dual-phase, low-carbon, cold-rolled steel are described. The new steel, HI-FORM 80d, exhibits a total elongation of about 24% as produced and develops a yield strength of about 625 MPa (91 ksi) in a formed and paint-baked part. Property uniformity is excellent and the weldability essentially equivalent to an AISI 1006 steel. In addition, the aging response of HI-FORM 80d is such that yield strengths near 550 MPa (80 ksi) can be achieved with strains of less than 2% and lower paint-bake temperatures than are currently in use.

CHEVROLET has made its new air-suspension system easily interchangeable in production line assembly with standard full-coil suspension by adopting a 4-link-type rear suspension with short and long arms. A feature of the system is the mounting of the leveling valves within the air-spring assemblies. These valves correct riding height continually at a moderate rate, regardless of whether the springs are leveling or operating in ride motion. The system provides constant frequency ride—ride comfort remains the same whether the car is occupied by the driver alone or is fully loaded.

THIS paper describes the springs, control system, and ride of the air suspension system on the 1958 Buick. The system is a semiclosed one, providing a variable-rate suspension, automatic leveling and trim control, and manual lift. The latter feature is a knob below the instrument panel which can be operated when necessary to cope with unusual clearance conditions. The car remains at the same height with loads of up to five passengers and 500 lb in the trunk. The authors describe the road-holding ability of a car with this suspension system as excellent.

As component and systems sophistication in both cars and trucks increase, improved diagnostic capabilities are required to assure proper and expedient serviceability. Replacement of electrical modules, starter motors, carburetors, fuel injectors and even whole engines or transmissions is encouraged by high labor costs and continued vehicle mobility mandates. The remanufacturing business has grown and components previously discarded now provide valuable core elements to feed the industry. To achieve efficient utilization of capital, equipment and labor, remanufacturers must estimate when this supply of core elements will be available and plan their production schedules accordingly. In order to properly service private individuals and commercial fleets, minimize vehicle downtime and reduce life cycle costs, adaptation of available analytical tools must be made.

THE PURPOSE of this experiment was to determine the role of residual stresses in fatigue strength independent of other factors usually involved when residual stresses are introduced. It consisted of an investigation of the influence of residual stresses introduced by shotpeening on the fatigue strength of steel (Rockwell C hardness 48) in unidirectional bending. Residual stresses were varied by peening under various conditions of applied strain. This process introduced substantially the same amount and kind of surface cold working with residual stresses varying over a wide range of values. It was found that shotpeening of steel of this hardness is beneficial primarily because of the nature of the macro-residual-stresses introduced by the process. There is no gain attributable to “strain-hardening” for this material. An effort was made to explain the results on the basis of three failure criteria: distortion energy, maximum shear stress, and maximum stress.*

The performance and production requirements for future passenger vehicles has increased the efforts to replace metal body panels with plastic materials. This has been accomplished, to a large extent on some production vehicles that have been introduced recently. Unfortunately, these plastic body applications have necessitated special off-line handling or low temperature paint processing. However, the advantages of RIM nylon, offer the potential for uniquely new plastic body designs, that can be processed through existing assembly plants, much like the steel panels they are intended to replace. The intent of this paper is to discuss the rationale for future plastic body panel material selection and related nylon RIM development efforts.

The potential of bake hardenable steel as a substitute for SAE 1008 steel to reduce gage and improve dent resistance is investigated in this report. Outer body panels in particular are susceptible to palm printing and other forms of denting. Conventional SAE 1008 steel and a developmental continuous annealed bake hardenable steel from Inland Steel Company are compared for dent performance properties. Bake hardenable (BH) steel is a medium strength (200-350 MPa) steel that receives an increase in yield strength during the heating of the paint bake cycle. An increase in yield strength would result in an increase in dent resistance. The increase in dent resistance is more quantitatively evaluated by comparing the BH steel with the current production material (SAE 1008) of a rear compartment lid outer.