| Corrosion mechanics is an emerging discipline related to electrochemistry,metal physics and metallurgy. Continuous eforts have been made in this feld.However, scientists fail to extract reliable experiment data due to the difcultiesin determining corrosion fatigue test with proper environmental and loading con-ditions. The dilemma also lies in precisely predicting initiation or propagationof fatigue crack under corrosion environment since widely accepted mechanicalcriteria are still absent. Specifcally, corrosion of aluminum alloy has drawn theattention of aeronautics and automobile communities for decades. The factorsof fatigue, such as load condition and corrosion efects, are taken into accountseparately in traditional studies. Such a methodology results in signifcant er-ror regarding load and corrosion not coupled with material properties as long asfailure is normally resulted from the combined efects of load condition and cor-rosion environment. Hence, further detailed study and comprehensive analysisare necessary in this feld.The main focuses of this study are aiming at corrosion mechanics of alu-minum alloys, for example, initiation of stress fatigue crack under tension-compressionload, and characteristics of curve of corrosion fatigue life/propagation of corro-sion fatigue crack under uni-axial tension-compression load. Then an applicablefailure criterion is proposed to predict fatigue life of aluminum alloys under com-plex corrosion condition coupled with load. Highlights of this study are listed asfollows.First, a new method is employed to measure corrosion rate through currentintensity, which is gauged by a new established model. Experiments are con-ducted to study characteristics of aluminum alloy, for examples, corrosion rateafected by artifcial corrosion solution ratio, resistance to impact of pre-corroded sample, corrosion mode on cross-section and attenuation law of energy absorptionunder diferent corrosion time or corrosion rate.Secondly, this study uncovers the stress corrosion cracking（SCC） behav-ior under tension-compression load and that stress corrosion may occur undercompression for aluminum alloy. With controllable corrosion rate, variationof strain near crack front in stress corrosion fatigue test is obtained throughmeasuring strain with thin WOL samples. The result is verifed by numeri-cal simulation. The efects of initial stress to stress corrosion are also studied.The KISCCand the relationship of initial stress to time of initiation of crackingare yielded from the former step. Thirdly, the research introduces a corrosionrate/time/frequency assumption, based on which an estimation law of life on cor-rosion fatigue Ni=f(icor)n（△σ）m is proposed with corrosion rate and frequencyof load as parameters. During this step, smooth aluminum alloy specimens,subjected to corrosion and cyclic tension, are tested to extract S-N curves inconsideration of corrosion environment and cyclic tension at the same time. Inaddition, the frequency efect is studied. Discussions are present to uncover theapplicable conditions for high-frequency equipment in terms of studying corrosionfatigue. Attempts are also made to study how to get efective contact betweencorrosion solution and specimens.Finally, an innovative application of recording equipment, not build for cor-rosion tests, is adopted to record fatigue crack propagation. A modifed Paris-with interaction factor α, deviation factor βand corrosion rate, is proposed to analyze practicality and feasibility of the fa-tigue model. During the experiment, three diferent frequencies, three temper-ature levels and solutions with three diferent ratios are successfully applied tofatigue cracking. Then the trend of fatigue-crack-propagation is obtained throughcomparing our experiment result to the propagation rate at room temperature.The dominant factors on fatigue-crack-propagation rate are analyzed to uncovertheir variation range and efects. |
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