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Leaf springs must be regarded as safety components of a vehicle which failures can cause severe accidents. They have to fulfill various functions as a spring element and for guiding the axles and are also responsible for driving comfort. Therefore, the durability approval must be carried out under representative service-like loading, which take into account complex leaf deformations in operational usage. In this paper the influencing parameters for the durability approval of leaf spring suspensions are discussed and the test rig and the standardized test program SPRILOS (SPRIng LOad Sequence) for the durability approval are described.

The design of wheel hubs must be based on stresses generated under customer usage through operational loads acting on the wheel. Therefore, the service loading conditions must be taken into account as well as the generated stresses and the hub fatigue properties. In this paper the decisive parameters for design and durability - operational loads, fatigue properties, which depend on material and manufacturing technology, and design - are discussed and the procedure for an optimum light-weight design is treated. Finally, the test procedure for durability approval, the corresponding test facility, the test programs and requirements, and some typical test results are presented.

Air spring systems are increasingly used on suspensions for commercial vehicles. To prove their durability a reliable test procedure is necessary: to be applied already in the development stage to be used to qualify individual air spring manufacturers and to assure manufacturing quality. In this paper the test procedure, the test facility and some test results are presented. In the test facility the air spring is mounted on a fixture and is loaded by a servohydraulic actuator. The mounting of the air spring allows to simulate all operational deformations, being decisive for the durability. Based on the extensive measurements on proving ground and public roads the test program was worked out. The test program includes besides the loading and deformations during driving also kneeling operations as well as high and low temperatures. The accelerated laboratory tests deliver results which correspond to the existing experience at the service usage.

Automotive engineering is continously moving toward the integration of different processes for accelerating vehicle development. Since the products become more and more a system, the methods to assist this transformation process become even more complicated. Experimental proof is an essential measure for reliability, robustness and quality. Since many vehicle components are relevant for operational safety, these parts must not fail causing an accident. This has to be ensured by experimental methods such as rig based durability tests. Hence, service load simulation & evaluation becomes an instrument to actively guide the product development process, rather than to release newly developed parts only. If both, loading as well as assembly interaction are incorporated in a realistic manner, cost and time are saved due to the elimination of specialized on-track measurements. Hence, lab based fatigue evaluation is presented as an integrated part of the overall vehicle development process.

The validation of the wheel/hub assembly has been carried out in the Biaxial Wheel/Hub Test facility since the early ‘1980’s developed at Fraunhofer LBF. This test procedure became a standard at most of the European wheel and truck producers and was also introduced as SAE wheel standard J 2562, issued in 2003. For newly developed Super Single low profile tires 495/45R22.5, which will replace double rear tires on heavy trucks and buses, the corresponding steel and aluminum wheels had to be designed by the suppliers. Because of the lack of information about load data and load programs for testing, extensive research had to be undertaken. The load data had been measured in collaboration with DaimlerChrysler on a M.B. Actros on proving grounds and on the “Black Forest round track” in Germany. Based on the derived data a special “Eurocycle” load program has been developed for accelerated testing of the wheels in the Biaxial Wheel Test Rig.

In this paper the criteria and the requirements for the approval of the service strength and the durability of vital car suspension components are treated. The overview of the main influences on the fatigue life is given and the methodology for the design evaluation and a reliable time and cost saving development, including durability approval, are described. These include: Description of representative, customer related loading Procedure for design evaluation based on customer usage Corresponding test programs for durability approval including the requirements for statistical validation and quality assurance of manufacturing. On two examples - a wheel and a suspension arm - the procedure including individual steps is explained.

Validation of the complex wheel/hub assembly has been carried out in the Biaxial Wheel/Hub Test Facility since the early ‘1980’s, developed at Fraunhofer LBF. This test procedure was applied as standard at most of the European vehicle producers and wheel suppliers and was also introduced as SAE wheel standard J 2562, for wheels of passenger cars, issued in 2003. By extensive test series and investigations a suitable load file has been developed which is able to create fatigue failures and damages on wheel bearings, comparable to real service failures within an acceptable testing time and so far to prove their operational durability. The load program is based on the existing test program for durability approval of wheels and hubs, simulating different driving sections such as straight ahead driving, cornering and, if required, off-road driving and braking operations. The influence of different load programs on the bearing damage is described in this paper.

The paper explains the most important criteria for the design of cast aluminum wheels on examples of recently developed European wheels. The basic differences in material behavior between steel and aluminum, such as fatigue strength, cyclic stress-strain properties and crack behavior are treated. The optimization of the wheel design is based on the fatigue strength of individual wheel sections which is determined through special test fixtures. The final proofout test for adequate fatigue life of the total wheel is established through a programmed test carried out in a new biaxial wheel test machine whereby the load program for testing European wheels represents European service conditions.

The keen competition in the automobile industry has in many cases necessitated the adoption of new manufacturing techniques for vehicle components. Forgings especially are being replaced today by castings and fabricated components. The authors show on the example of a forged front wheel hub how weight savings of up to 30% may be achieved on a standard hub forging. The weight savings are achieved through a design methodology called “Service Strength Analysis,” whereby both structural analysis and testing are done under simulated service loadings. The wheel hub is a highly stressed safety component on which the function of other components such as axles, wheels and brakes depend. Service Strength Analysis allows lightweight design to be carried out without sacrifices of reliability; it also allows an effective evaluation of the influence of new low cost manufacturing techniques on the service strength of parts.

The paper describes a method for optimal wheel design and shows a systematic procedure for determining acting and allowable stresses in the wheel. The traditional wheel fatigue test procedures are criticized because no definite relationship to customer service exists in most cases. The basic design concept, that dimensions should be based on service stresses and allowable stresses is strictly adhered to in the approach and is accomplished by providing a method for simulating service loads in the laboratory and by determining allowable stresses by fatigue testing of representative wheel areas. The operational wheel loads as well as frequency distribution of service stresses are discussed. A Flat Base Wheel Roll Test Facility for determining wheel stresses is presented. Also described is a new Biaxial Wheel Durability Test Machine which provides improved simulation of wheel loading conditions and makes it possible to test the total wheel in a single procedure.

The method of fatigue life evaluation and validation testing under operational conditions is a prerequisite to achieve optimal designs with respect to weight and long-term durability of the structure considered. Criteria like driving behavior and braking performance, influenced by global stiffness as well as fatigue life evaluation were taken into account when optimizing a forged 6.5 front axle beam of a heavy truck. The procedure for weight optimization includes the following steps: Stress analysis e.g. using strain gage techniques and/or Finite Element Method, Road load data acquisition and derivation of design spectrum describing customer usage, Fatigue testing under constant amplitude and/or variable amplitude loading to establish component related SN-curves and/or fatigue life curves, Fatigue life evaluation using damage accumulation hypothesis (Miner's Rule), Optimization and weight reduction (in this case 14% weight savings were achieved) based on fatigue life evaluation.

The complex design and loading conditions of the wheel-hub assembly and decisive safety demands make it necessary to proof the wheel fasteners under reliable, service-like testing conditions. In this paper main parameters, the function and fatigue life of wheel fasteners and consequences for testing are described and discussed. The test procedure is based on the Biaxial Wheel Test Method, whereby the existing load program »Eurocycle« was extended by additional braking and torsional force sequences. The test requirement and some typical test results are presented.

For the design of suspension components the behavior under extreme, special events, loading as well as the durability under operational usage are decisive. While the behavior under extreme loading depends on the component stiffness, which is mainly influenced by the design and the material mechanical properties, durability is influenced by the fatigue properties under operational loading. For this purpose the fatigue properties on aluminum alloys 5083 and 6009 using different types of stresses (tension, shear, torsion, bending), loading-time histories (constant and variable amplitude loading) and welding technology were investigated and will be presented in this paper.