Effect of Biodiesel Fuel on a Fatigue Crack Growth Behavior of Al Cast Alloy

概要

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In order to investigate the effect of biodiesel fuel on a fatigue crack growth behavior of a squeeze cast Al alloy, AC4CH-T6, rotating bending fatigue tests were carried out using plain specimens in biodiesel fuel based rapeseed oil. The results were compared with those in mineral oils of light oil and turbine oil and in ambient air. Fatigue life was longer in turbine oil and shorter in biodiesel fuel than in air. Fatigue life in each environment tested was mainly occupied by the growth life of a crack smaller than 1mm, meaning that the difference in fatigue strength affected by environment was mainly yielded in the growth process of a small crack. The crack growth rates were suppressed in turbine oil and accelerated in biodiesel fuel in comparison with those in air. Biodiesel fuel contained much water dissolved from air in the early stage of fatigue process. In biodiesel fuel, there are both effects of the suppression of crack growth due to wedging effect of oil and the acceleration due to corrosion causing by dissolved water, and the former effect was larger than the latter one causing the decrease in fatigue life.