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The objective of this study is to reveal the creep-fatigue fracture mechanisms in Aluminum Alloy 2618 (A2618). Load-controlled creep-fatigue tests were performed on A2618 specimens to investigate the influence of the maximum stress holding period on the fatigue life and fracture behavior. The holding periods were selected so that the ratio of creep damage (Dc) to fatigue damage (Df) was set to 1/4, 1, and 4, respectively.
In all conditions, a significant shortening of lifetime was observed due to creep-fatigue interaction, with the most pronounced reduction occurring at a Dc/Df ratio of 1 (see Fig. 1). Under short holding period conditions (Dc/Df = 1/4), typical fatigue…
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The objective of this study is to reveal the creep-fatigue fracture mechanisms in Aluminum Alloy 2618 (A2618). Load-controlled creep-fatigue tests were performed on A2618 specimens to investigate the influence of the maximum stress holding period on the fatigue life and fracture behavior. The holding periods were selected so that the ratio of creep damage (Dc) to fatigue damage (Df) was set to 1/4, 1, and 4, respectively.
In all conditions, a significant shortening of lifetime was observed due to creep-fatigue interaction, with the most pronounced reduction occurring at a Dc/Df ratio of 1 (see Fig. 1). Under short holding period conditions (Dc/Df = 1/4), typical fatigue features were present on the fracture surfaces, such as a crack initiation site and striation patterns. In contrast, under the other conditions, these fatigue-related features were absent, and intergranular fracture surfaces predominated (see Fig. 2). Furthermore, microstructural observations of the cross-sections of specimens subjected to monotonic creep and fatigue tests revealed that grain boundary voids formed exclusively in the creep specimens, while no voids were observed in the fatigue specimens. In the creep-fatigue specimen tested under the long holding period condition (Dc/Df = 4), despite the creep life fraction being approximately 30%, the average and maximum void lengths at positions 10 mm from the fracture surface were comparable to those observed in monotonic creep specimens. These results indicate that the creep-fatigue fracture mechanisms in A2618 alloy can be classified into two types depending on the holding period: a "creep damage-dominated" mode and a "fatigue damage-dominated" mode.