Structural fatigue life investigation of a rigidly mounted aluminium fuel tank

[摘要] ENGLISH ABSTRACT: Structural cracks have formed in the sub-structure of a tank that is rigidlymounted onto a truck chassis. These cracks have all formed at welds joiningthe various components of the aluminium sub-structure. This thesis proposesa solution methodology to address these failures. The first phase of thismethodology (failure investigation) relies heavily on determining the life of thestructure with fatigue life calculations. These calculations are done using thestress life method supplemented by the hot spot stress method.Experimental tests were conducted at an operational air force base to compilea composite duty cycle that is representative of the typical operation of thevehicle. This is followed by a finite element analysis which is used to calculatethe scaling factor required to determine the hot spot stresses in the structure.These hot spot stresses are determined for three different crack areas and theestimated fatigue life of each of these points are calculated.The estimated fatigue lives are compared to the actual lives that werereported by the maintenance personnel, to determine a correlation factor. Thecomparison 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 assessfuture solutions. It is also suggested to reduce the stresses by at least 37% toachieve the desired service life. Recommendations regarding the design of arepair are given.The methodology presented in this thesis provides the groundwork for atypical solution methodology that can be used at GRW Engineering. Recommendationsfor improvements to the method and its components are given.

[发布机构] Stellenbosch University