ASTM E740 | Structural Components | Residual Strength
ASTM E740 describes the determination of residual strength of surface-crack tension (SCT) specimen having a semi-elliptical or circular-segment fatigue crack in one surface. The test is performed under continuously increasing force and excludes cyclic and sustained loadings.
Residual strength is the maximum value of the nominal stress, neglecting the area of the crack, that a cracked specimen is capable of sustaining. The residual strength of an SCT specimen is a function of the crack depth and length and the specimen thickness as well as other characteristics of the material.
Before conducting ASTM E740, it is important to read the entire specification in the relevant ASTM publication.
ASTM E740 | Structural Components | Residual Strength
- Prepare the SCT samples as described in the standard. Measure and record the specimen thickness at the point midway between each crack tip and the nearest specimen edge. Measure the specimen width at the crack plane.
- Place the specimen in the tensile grips. For wider specimens, the pin-and-clevis arrangement can be used. Attach the displacement gauge to the crack opening of the specimen, if crack mouth opening displacement (CMOD) is measured.
- Apply the load at a loading rate such that the rate of increase of nominal stress is less than 100,000psi (690 MPa) per minute.
- Continue the test until the specimen can sustain no further increase in an applied force. Record the maximum force.
- Measure the crack depth and the crack length after fracture. Record load vs CMOD.
Calculations:
- Residual Strength
- Yield Strength (determined in accordance with Test Method E8)
- Maximum stress intensity factor during fatigue precracking, KIc
ASTM E740 | Structural Components | Residual Strength
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