SEDL / STP / STP677-EB / STP34931S

An Experimental Study of the Crack Length/Specimen Width (a/W) Ratio Dependence of the Crack Opening Displacement (COD) Test Using Small-Scale Specimens

de Castro, PMST
Research Ph.D. student, teaching fellow, and professor of engineering metallurgy, Cranfield Institute of Technology, Bedford MK43 OAL,

Spurrier, J
Research Ph.D. student, teaching fellow, and professor of engineering metallurgy, Cranfield Institute of Technology, Bedford MK43 OAL,

Hancock, P
Research Ph.D. student, teaching fellow, and professor of engineering metallurgy, Cranfield Institute of Technology, Bedford MK43 OAL,

Pages: 12    Published: Jan 1979

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Abstract

This work deals with the influence of the ratio crack length/specimen width (a/W) on crack opening displacement (COD) tests. A series of tests was performed on a weldable quality structural steel (50D, BS4360), where the ratio a/W was varied from about 0.2 to 0.8, keeping W constant. The influence of temperature was assessed by a series of tests at different temperatures over the range -90°C to room temperature.

It is concluded that critical COD, δ^c, is insensitive to a/W at low temperatures, but becomes dependent on a/W as temperatures approach the transition temperature. This behavior has been quantified and should be borne in mind in situations where the use of specimens with different a/W ratios is required.

The tests were instrumented with a clip gage at the crack mouth and a load point displacement transducer which enabled a relationship between COD and J to be determined.