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Elongation Chart for Common Bolting Materials

Bolt & Screw Torque Charts and Equations

Typical Elongation Chart for Common Bolting Materials

The amount of bolt stretch you want in your end ite design will, of course, be determined by the amount of preload you want in the fastener. You won’t be able to answer the question until after you have considered working loads on the bolt, and failure modes. stretch you might see in various bolts, per inch grip length, if they were loaded to 50% of their yield strength. It would be advisable for you to calculate the expected stretch in your application or, better still, by determining the preload–stretch relationship experimentally, especially if your bolt has a grip-to-diameter ratio below 4:1.

Bolting Material
20% of
Yield
40% of
Yield
60% of
Yield
80% of
Yield
100% of
Yield
Monel 40 K psi y.s.
0.3
0.5
0.8
1.1
1.3
SAE GR 2 55 K psi y.s.
0.4
0.7
1.1
1.5
1.8
SAE Grade 3; B7 and B16 over 4 in.
diameter 80 K psi y.s.
0.5
1.1
1.6
2.1
2.7
SAE Grade 5; A325; B7 and B16 up
to 4 in. diameter 96 K psi y.s.
0.6
1.3
1.9
2.6
3.2
SAE Grade 8; A490 120 K psi y.s.
0.8
1.6
2.4
3.2
4.0
Inconel 718 180 K psi y.s.
1.2
2.4
3.6
4.9
6.1
4340 steel, RC47 200 K psi y.s.
1.3
2.7
4.0
5.3
6.6
Best available high-bolt material
240 K psi y.s.
1.6
3.2
4.8
6.4
8.0
Titanium (6A14V) 134 K psi y.s.
E = 17 x 106
1.6
3.2
4.8
6.4
8.0

Note: Indicated elongation figures (in thousandths of an inch) are for various percentages of yield strengths (y.s.) of different bolts with a 1 in. grip length. (Modulus of elasticity assumed to be 30 x 106 unless otherwise noted.) To obtain desired elongation for a particular metal, read the elongation figure under the appropriate percentage of yield and multiply by the grip length in inches. For example, to obtain the expected elongation for an SAE Grade 5 bolt stretched to 80% of yield, with a 5 in. grip length, select the appropriate figure, which in this case is 2.6, and multiply by 5. The answer is 0.013 in. Note and warning: Many factors determine the "correct" stretch for a given fastener and application. Use this table with caution.

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Reference:

  • Source: Courtesy of Raymond Engineering Inc., Middletown, CT.

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