Peening Test Strips Holder and Gage

SAE standard J442 describes the test strips, strip holder, and gage used in measuring shot peening intensity.

If a thin flat piece of steel is clamped to a solid block and exposed to a blast of shot, it will be curved after removal from the block. The curvature is convex on the peened side. The extent of this curvature on a standard sample serves as a means of measurement of the intensity of the peening.

Standard test strips of three thicknesses used are shown in Fig. 14. Made of 1070 cold-rolled spring steel, these strips have a specified hardness of 44 to 50 HRC. Strip A is recommended for testing intensities that produce curvatures having arc heights ranging from 0.15 to 0.60 mm (0.006 to 0.024 in.). For lesser intensities, the N strip is recommended. For greater intensities, the C strip is used. The relationship between strips A, C, and N is shown in Fig. 15. The data represent readings for conditions of identical blast and exposure.

Fig. 14 Designations and dimensions of standard Almen test strips used in measuring shot peening intensity test srpjJJ N 0.031 1 0 001 in A 0 051 ■ 0001 HI CO 094 ' 0 001 in

Fig. 14 Designations and dimensions of standard Almen test strips used in measuring shot peening intensity

0-75

0-75

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0.05 0.10 0.1 s O.ÏO 0,25 Almen intensify, mm o o o

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0.30

0.20

0.10

0.10

1-

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0 10 0.20 0.3a 0.40 0.50 Almen jntenjjty, mm

0.60

0.70

0 10 0.20 0.3a 0.40 0.50 Almen jntenjjty, mm

0.60

0.70

Fig. 15 Correlation of intensities as indicated by arc heights of A, C, and N strips peened under identical blast and exposure conditions. (a) C strip. (b) N strip (SAE J442)

During peening, the test strip is mounted on a holder as shown in Fig. 16. After being peened, the strip is removed and placed in an Almen gage (Fig. 17), located so that the dial indicator stem bears against the unpeened surface. The curvature of the strip is determined by a measurement of the height of the combined longitudinal and transverse arcs across standard chords. This arc height is obtained by measuring the displacement of a central point on the unpeened surface from the plane of four balls forming the corners of a rectangle. Almen gages are available with either analog or digital readout. In digital units, accuracy can be posted to four decimal places.

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Test slnp

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Test slnp

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0,940. , 1. 0.945 1 2 '

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■ 3 in. -— -

23 33m

0.192 0.194

Folk No. 10-3? or No, I0 i4 raond-headed sCftwi wlh fiux nutl

Fig. 16 Assembled Almen test strip and holder

Fig. 16 Assembled Almen test strip and holder

Fig. 17 Almen gage for measuring arc height for test strip

The standard designation of intensity includes the gage reading or arc height and the test strip used. For example, 0.013 A signifies that the arc height of the peened test strip is 0.33 mm (0.013 in.) and that the test strip used was of the A thickness. Uniform procedures for using the standard test strips described in the above digest of SAE J442 are provided in SAE Recommended Practice J443.

Topography of Surfaces

R.K. Morton, Rank Taylor Hobson Inc.

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