Fatigue of metal matrix composites

Abstract

One unidirectional and two laminated 6061-0 A~e-B composite plates were tested under various cyclic loading conditions. Three types of material response to cyclic loading were identified; No evidence of damage at relatively low cyclic loads, damage accumulation caused primarily by growth of long matrix cracks parallel to the fibers in off-axis layers at higher loads, and sudden localized failure of the fibers. Quantitative analysis of the results shows that the extent of internal damage, demonstrated by a reduction in axial elastic modulus, depends on the applied stress range and is independent of mean stress. The stress range at which damage first starts to appear coincides with the shakedown range of the laminate.

Fatigue Damage and Shakedown in Metal Matrix Composite Laminates

“…i -1 --The Hi is the stress distribution factor in (2), and L, M are the overall in-plane stiffness and compliance of the laminated plate; all are (3 X 3) matrices.…”

Analytical and Experimental Characterization of Damage Processes in Composite Laminates

“…Figure 1 shows various examples of these cracks in a (0/90/±45) laminate, which were constructed S from observations of actual crack systems described in [1,[3][4][5]. The right part of this figure, section A-A', shows an in-plane view of a crack in the 900 ply.…”

Fatigue Testing and Damage Development in Continuous Fiber Reinforced Metal Matrix Composites

“…Even so, local plastic straining can be permitted in the composite during the first few load cycles, provided that the composite "shakes downtt during these few cycles. The shakedown stress is reached if the matrix cyclically hardens to a yield stress, Y, such that, subsequently, only elastic deformation occurs under load cycles [2]. Previous tests have shown that the matrix fatigue limit coincides with the stable cyclic yield stress for annealed aluminum [11,12] and steels 1121.…”

“…Dvorak and Tarn suggested that the shakedown stress was related to laminate S-N type fatigue failure. Since 1979 Dvorak and Johnson [2,3,10], have examined theoretically and experimentally both unidirectional and laminated 6061-0 B/A1 composites. They found that the shakedown stress was related to the onset of fatigue damage in the composite's matrix material but not necessarily to laminate failure.…”

“…28, we now know the modulus for each of the two linear segments, as well as the strain ranges. Therefore, the overall laminate stress range A S can be calculated as follows Equation (4) is rewritten using Eq (2).…”