Abstract

Experiments were conducted on high purity lead at room temperature using reverse bending and torsion fatigue at low cyclic frequencies (⩽ 1.50 Hz). Metallographie observations after testing show that there is a one-to-one correspondence between the markings from grain boundary migration and the number and pattern of cyclic loading, and this correspondence is maintained up to s>100 cycles. Grain boundary sliding occurs in each cycle in addition to the migration, and this leads to the development of broad triple point folds. If the strain amplitude is maintained constant, it is shown that the average distance migrated in each cycle increases as the imposed frequency is decreased. The distance migrated is often exceptionally large in the first cycle of testing, and there is often a similar large initial displacement if the test is interrupted for periods of time from 1 to 24 h and then continued. For large grain sizes ( ≳ 2000 μm), the migration markings may lead to a zig-zag pattern where the individual segments lie fairly close to 45° to the stress axis. A model is described which accounts for the one-to-one correspondence and which is consistent with a fine structure observed within the migration markings.

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