Nanoindentation applied to the Theories and Experiments for Fatigue of Bulk and Fatigue Fracture Energy of Coating Materials

• Main Authors: Wen-lung Liung, 梁文龍
• Other Authors: Jen-Fin Lin
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/50382681904524282105

碩士 === 國立成功大學 === 機械工程學系碩博士班 === 95 === The aims of this paper are to study fatigue behaviors of bulk and develop a energy method of fatigue fracture for coating materials by using cyclic load of nanoindentation. In the part of fatigue behaviors of bulk, we discuss the Paris Law and fatigue retardation for the specimens 6061 Al and 304 HSS. Paris Law is a theory of fracture mechanics related to fatigue crack propagation which has some different forms related to parameters of stress ratio(R) and stress intensity variance. Based on the mechanism of indentation fatigue, we applie these two parameters to develop a formula for discussing the effects of cyclic load conditions about indentation depth propagation rate(dh/dN), including oscillating mean load(Pm)、oscillating amplitude(Po) and oscillating frequency( f ). The experimental results show that f is the most important factor to dh/dN. And dh/dN of this study is a purely fatigue behavior by avoiding the creep effect of oscillation segment due to max loading-hold(Pmax) setting. In the part of fatigue retardation, the setting of oscillating load is a continuously interrupted oscillation type which oscillating segment is divided to several sub-segments with the oscillating-hold intervals. The side of theroy, dh/dN would decrease as the number of oscillating-hold (i) increasing and the decreasing tendency is a propotional series with a common ration α which is related to oscillating-hold time. Finally, results show the quantity of fatigue retardation is dominated by total oscillating-hold time. The last part of energy method of fatigue fracture for the SiO coating material which substrate is Si. We only consider the plastic energy during the all load-depth of indentation process, using difference between cyclic predicted energy Wi and composite fracture energy Wd to evaluate the fatigue fracture energy of pseudo-film Wf. And Wi is predicted by the depth propagation rate before fatigue fracture (dh/dN)bf during oscillating segment. Experimental results show that the frequency of oscillating load condition is an only effective factor to Wf. Wf would decrease as (dh/dN)bf increasing under relative high oscillating frequency (f >10 Hz), and Wf is asymptotic to a constant having a constant fracture energy limit under relative low oscillating frequency (f≦10 Hz).