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**Published:** Jan 1984

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**Source: **STP833-EB

*J-R* curves and *δ-R* curves were measured on 5-mm-thick compact, three-point bend, and center cracked tension specimens with different widths and different precrack lengths. The crack tip opening displacement (*δ*) was measured at the fatigue crack tip. The materials tested were an age-hardened aluminum alloy; the same alloy in a furnace cooled, very soft condition; and an alloy steel. It was found that the *J*-integral correlates three to five times as much crack growth in the tension specimens as in the compact and bend specimens, or, in other words, a valid *R*-curve detemined on a center cracked tension specimen covers at least three times more crack growth than a valid *R*-curve determined on a compact or bend specimen of the same width and crack length. Furthermore, *δ* correlates even more crack growth: a valid *δ-R* curve determined on a compact or bend specimen covers about five times more crack growth than a valid *J-R* curve. For center cracked tension specimens the amount of crack growth measured was not sufficient to establish limits for a valid *δ-R* curve; however, at least 60% of the original ligament width can be expended by crack growth for a valid *δ-R* curve.

It is worth noting that no geometry effect on the *J-R* curve and *δ-R* curve was found as long as the *R*-curve data could be considered “valid.”

**Keywords:**

nonlinear fracture mechanics, geometry effect, size effect, J-R, curve, δ-R, curve, crack tip opening displacement, plane stress

**Author Information:**

Hellmann, D *Research Engineer and Head of Materials Technology Department, GKSS-Research Center Geesthacht, Geesthacht,*

Schwalbe, K-H *Research Engineer and Head of Materials Technology Department, GKSS-Research Center Geesthacht, Geesthacht,*

**Committee/Subcommittee:** E08.06

**DOI:** 10.1520/STP32575S