DEVELOPMENT AND TESTING OF A CORROSION FATIGUE TESTING RIG FOR METALS

ABSTRACT

The purpose of undertaking this project was to design and fabricate a simple and cost effective corrosion fatigue testing machine. Numerous industries in Kenya and around the world face the economic and safety burdens of equipment that underperforms or fails through the process of corrosion fatigue. These critical industries range from power generation, trade, manufacturing and the transport industry. The development of a testing rig that can simulate fatigue in a corrosive environment would provide insight to the factors influencing this failure, leading to a better material selection and design process.

The high cost of purchasing fatigue machines or hiring testing services is a challenge to the testing of corrosion fatigue and modifications on existing machines to include the simulation of a corrosive environment is complex and dependent on the type of machine used. Combining the factors above with the vast impact of corrosion fatigue in industry formed the necessity of developing an economic way of testing corrosion fatigue at the University of Nairobi.

A brief review was carried out on the fundamental concepts of corrosion fatigue. Common types of fatigue testing machines were studied and the advantages and disadvantages of each explored. A review of existing corrosion fatigue rig set-ups was carried out in order to aid our design decisions. A plane bending type, displacement controlled testing rig was chosen as it has a low capital input, easy modification to incorporate a corrosive environment, a simple mechanism to generate large forces on a specimen and the ability to test several specimens simultaneously.

Our design and fabrication led to the development of a testing rig which included a loading mechanism that was displacement controlled, a rigid and robust frame that housed all components, a system of load transmitting members which loaded four specimens simultaneously and the provision of a corrosion chamber that housed the four specimens. All this was achieved with a total budget of 33,700/=. The machine was tested with a primary mode of testing, in which connecting elements and alignment were checked and recomendations given. Furthermore, helpful information on the geothermal industry regarding corrosion fatigue failure was obtained for future research to be carried out with use of the testing rig. With these factors considered, our objectives were achieved.