| Fatigue life of material can be enhanced by applying various techniques. This dissertation aims to provide a novel design and technique to enhance the fatigue life and blunt the fatigue crack growth of stainless steel304. The research proposes that fatigue crack can be arrested by the application of carbon nano-tubes. To accomplish this technique a novel conceptual design of the fatigue crack arresting device has been proposed.The main innovation in this work is the application of the carbon nano-tube to arrest the fatigue crack through laser. The MWCNTs was applied at the crack tip with CO2laser. The main idea of this technique is to hinder the grain boundary slip-on with nano filler (MWCNTs). Pre-cracked compact tension (CT) specimens were used for the fatigue test; crack growth length (a) and number of cycles (N) was measured to generate the (a-N) curve. The fracture surfaces of the treated and untreated304SS were examined by using SEM, EDX, XRD and EPMA. It was found that the incorporation of a small amount of MWCNTs increased the fatigue life and slowed down the rate of the fatigue crack of the304SS.The laser power800W,700W,550W, and450W for10and5-seconds exposure effect on fatigue crack growth behavior of the stainless steel were investigated. It was found that laser power is inversely proportional to the fatigue life. Laser beam exposure duration also makes a significant change in fatigue crack growth. The maximum fatigue crack growth suppressed was found at550W with10-seconds exposure.The new conceptual design of the fatigue crack arrest device provides the user with flexible operating. The proposed device design consists of a handle, body, closed-circuit television (CCTV) assembly, nozzle, material flow nozzle, material tanks and piston assembly. The component can be repaired by laser; the laser flows to the nozzle central aperture. The nano-material channel outlets are around the nozzle aperture, nano-material aligned at working focal point follow the laser beam. Presence and detection of a flaw by proximity sensor enable the repairing process. The temperature sensor enables the material flow once achieved the required set temperature. Piston assembly may follow the material flow process. These all processes are accomplished by a compact design. This novel conceptual design provides high degree of freedom to arrest the fatigue crack with simple mechanism.It demonstrates that the proposed technique alters the fatigue crack behavior of the stainless steel304with application of a small amount of the multi-walled carbon nano-tubes (MWCNTs). |
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