Analysis of complete contact problems, with particular reference to gas turbine engines

• Main Author: Balasubramanian, Arun Prasath
• Format: Dissertation
• Language: English
• Published: University of Oxford 2017

Frictional contacts are often found in different engineering assemblies (for e.g., dovetail/fir-tree contact) and are frequently subjected to constant centrifugal loads, vibration and other forms of cyclic loads and cause a damage phenomenon called fretting fatigue. Fretting occurs mainly due to the oscillatory micro-slip between contacting interfaces and accelerates the nucleation and early propagation of cracks, and thereby causes a significant reduction in the fatigue life of the engineering components. Therefore the aim of this thesis is to study elaborately the behaviour of complete contacts, especially the interfacial conditions, in the long run to minimize the occurrence of fretting damage. An asymptotic solution has been formulated for a particular case of complete contact, where the edge of contact is located near to an adjacent wall of material and separated by a finite clearance. Semi-infinite crack, wedge and trench asymptotes were used to investigate the behaviour of the edge of contact, when the side clearance is negligible, infinite and finite respectively. The interfacial requirements, namely the edge closure criteria and minimum coefficient of friction needed for adhered conditions, are established for various internal edge angles. The second part of my thesis concerns the study of wedging behaviour in complete contacts found in blade root assemblies. A contact is considered to be wedged when the friction present at the interface is enough to retain the deformed configuration in the absence of external load. However wedging occurs for the specific case where the coefficient of friction exceeds a particular value. A condition for the occurrence of wedging was derived in terms of the internal dovetail angle. Finite element simulations of the dovetail assembly have been carried out and the results are compared with the analytical calculations. Attention has also been focussed on the numerical aspects of the work, where a finite element code exploiting the static reduction method was implemented for Rolls-Royce proprietary software SC03, to solve quasi-static frictional elastic contact problems. At present level of implementation, the procedure is intended to work for two dimensional, frictional contact problems where the contact interface is located approximately along a straight line.