Mechanisms influencing the plane-strain fracture toughness behavior of commercial aluminum-lithium alloys at cryogenic temperatures are investigated as a function of microstructure and plate orientation. It is confirmed that certain alloys show a markedincrease in tensile ductility and toughness withdecrease in temperature, although such behavior is not found in the short-transverse orientations, or for all alloys and aging conditions. Specifically at lower temperatures, the majority of Al-Li alloys, namely 2090-T8E41, 8091-T8X, 8090-T8X, and 2091-T351, show a significantincrease in fracture toughness in the in-plane orientations (L-T, T-L), without any apparent change in fracture mode. Such behavior is attributed primarily to loss of through-thickness constraint resulting from enhanced short-transverse delamination (termed crack-divider delamination toughening), consistent with observed reductions in plane-strain ductility and short-transverse (S-L, S-T) toughness. Conversely, in underaged microstructures of 8091, 8090, and peak-aged 2091, a decrease in toughness with decreasing temperature is found for both L-T and S-L orientations, behavior, which is associated conversely with a fracture-mode change from ductile void coalescence to brittle transgranular shear and integranular delamination at lower temperatures.

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Cryogenic toughness of commercial aluminum-lithium alloys: Role of delamination toughening

A method of fabricating 18% Ni maraging steel laminates of varying alloy compositions by roll bonding. Laminates composed of a plurality of different grades of Cobalt-containing or Cobalt-free maraging steels are disclosed.

Fabrication of 18% Ni maraging steel laminates by roll bonding

Comparison of Fracture and Fatigue Properties of Clad 7075-T6 Aluminum in Monolithic and Laminated Forms

In this experimental study, fracture toughness of heat-treated metal matrix composite was investigated. The gray cast iron was reinforced with steel wire of volume fraction of Vr = 0.05 and three-point bend specimens were manufactured to determine fracture toughness. Heat treatment was applied to the specimens at the normalization temperatures of 850°C and then cooled in three distinct environments (water, air, and furnace). Fracture toughness of the metal matrix composite was calculated by unloading compliance method. The study shows that the fracture toughness of the steel-wire-reinforced gray cast iron increases with the increase in cooling rate. Scanning electron microcopy (SEM) analyses were used to examine the microstructure and fracture surface. It is observed that the carbon diffuses from the gray cast iron to the steel wire and transition region having partially dissolved graphite was observed due to carbon diffusion, and it plays an important role in the fracture toughness depending on the cooling media.

Effect of heat treatment on fracture behavior of steel-wire-reinforced gray cast iron

Laminates containing 25 percent of tough (unaged) maraging steel plates and 75 percent of brittle (aged) maraging steel plates were prepared by a special diffusion bonding and heat treating technqiues so that the thickness of the tough constituent was either 0.02, 0.04, 0.06, or 0.08 in. Compact tension fracture toughness specimens were machined so that the laminates were parallel to the sides of the specimens. They were then fractured according to the recommendations of the ASTM and the following three indices of toughness were measured: (1) the plane-strain fracture toughness according to the ASTM recommendations; (2) the fracture toughness based on the maximum load and the initial crack length; and (3) the fracture toughness based on the maximum load and the instantaneous crack length. Four tests were performed at each thickness of the tough constituent; two each at crack lengths of approximately 0.30 and 0.55 in. The plane-strain fracture toughness of the laminates was slightly higher than the plane-strain fracture toughness of the monolithic brittle constituent and was independent of either crack length or the dimensions of the tough constituent. Regardless of the thicknesses of the tough phase the composite toughness was highest for specimens containing cracks 0.30 in. long when the toughness was measured in terms of the other two indicates of fracture toughness. The toughness as a function of thickness exhibited a relative maximum when the tough phase was 0.04 in. thick and a relative minimum when the tough phase was 0.06 in. thick for both the 0.30 and 0.55-in. crack lengths. The experimental results are in broad agreement was a proposed model for crack extension in the divider orientation. /Author/

Karthiga Kasi

Papers

Fracture Toughness of Duplex Structures: Part II — Laminates in the Divider Orientation