Browsing by Author "Franken, Christian Matthys"

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    Structural fatigue life investigation of a rigidly mounted aluminium fuel tank
    (Stellenbosch : Stellenbosch University, 2012-12) Franken, Christian Matthys; Venter, Gerhard; Terblanche, E.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Structural cracks have formed in the sub-structure of a tank that is rigidly mounted onto a truck chassis. These cracks have all formed at welds joining the various components of the aluminium sub-structure. This thesis proposes a solution methodology to address these failures. The first phase of this methodology (failure investigation) relies heavily on determining the life of the structure with fatigue life calculations. These calculations are done using the stress life method supplemented by the hot spot stress method. Experimental tests were conducted at an operational air force base to compile a composite duty cycle that is representative of the typical operation of the vehicle. This is followed by a finite element analysis which is used to calculate the scaling factor required to determine the hot spot stresses in the structure. These hot spot stresses are determined for three different crack areas and the estimated fatigue life of each of these points are calculated. The estimated fatigue lives are compared to the actual lives that were reported by the maintenance personnel, to determine a correlation factor. The comparison yields a maximum correlation factor of 9.8 and a minimum of 3.9. It is suggested that the minimum correlation factor of 3.9 is used to assess future solutions. It is also suggested to reduce the stresses by at least 37% to achieve the desired service life. Recommendations regarding the design of a repair are given. The methodology presented in this thesis provides the groundwork for a typical solution methodology that can be used at GRW Engineering. Recommendations for improvements to the method and its components are given.