Stresses in Springs Table 1. Correction Factors for Other Materials Compression and Tension Springs Machinery's Handbook, 31st Edition
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Material
Factor
Material
Factor
Multiply the values in the chromium-vanadium curves (Fig. 6) by 0.90 Use the values in the chromium-vanadium curves (Fig. 6) Multiply the values in the corrosion-resisting steel curves (Fig. 5) by 0.95
Silicon-manganese
Multiply the values in the corrosion-resisting steel curves (Fig. 5) by 0.90
Stainless Steel, 316
Valve-spring quality wire Stainless Steel, 304 and 420
Stainless Steel, 431 and 17-7PH
Multiply the values in the music wire curves (Fig. 2) by 0.90
Helical Torsion Springs
Material
Factor a
Material
Factor a
Hard Drawn MB Stainless Steel, 316 Up to 1 ∕ 32 inch diameter
0.70
Stainless Steel, 431 Up to 1 ∕ 32 inch diameter
0.80 0.85 0.95 1.00
0.75 0.70 0.65 0.50 1.00 1.07 1.12 0.70 0.75 0.80 0.90
Over 1 ∕ 32 to 1 ∕ 16 inch Over 1 ∕ 16 to 1 ∕ 8 inch
Over 1 ∕ 32 to 3 ∕ 16 inch Over 3 ∕ 16 to 1 ∕ 4 inch
Over 1 ∕ 8 inch
Chromium-Vanadium Up to 1 ∕ 16 inch diameter
Over 1 ∕ 4 inch
1.05 1.10
Stainless Steel, 17-7 PH Up to 1 ∕ 8 inch diameter
Over 1 ∕ 16 inch
Phosphor Bronze
Over 1 ∕ 8 to 3 ∕ 16 inch
0.45 0.55
Over 3 ∕ 16 inch
Up to 1 ∕ 8 inch diameter
Stainless Steel, 420 Up to 1 ∕ 32 inch diameter
Over 1 ∕ 8 inch
Beryllium Copper b
0.55 0.60 0.70
Over 1 ∕ 32 to 1 ∕ 16 inch Over 1 ∕ 16 to 1 ∕ 8 inch Over 1 ∕ 8 to 3 ∕ 16 inch
Up to 1 ∕ 32 inch diameter
Over 1 ∕ 32 to 1 ∕ 16 inch Over 1 ∕ 16 to 1 ∕ 8 inch
Over 3 ∕ 16 inch 0.80 a Multiply the values in the curves for oil-tempered MB grade ASTM A229 Type 1 steel (Fig. 8) 1.00 Over 1 ∕ 8 inch by these factors to obtain required values. b Hard drawn and heat treated after coiling. For use with design stress curves shown in Fig. 2, Fig. 5, Fig. 6, and Fig. 8. Endurance Limit for Spring Materials.— When a spring is deflected continually it will become “tired” and fail at a stress far below its elastic limit. This type of failure is called fatigue failure and usually occurs without warning. Endurance limit is the highest stress, or range of stress, in pounds per square inch that can be repeated indefinitely without failure of the spring. Usually ten million cycles of deflection is called “infinite life” and is satisfactory for determining this limit. For severely worked springs of long life, such as those used in automobile or aircraft engines and in similar applications, it is best to determine the allowable working stresses by referring to the endurance limit curves seen in Fig. 11. These curves are based princi pally upon the range or difference between the stress caused by the first or initial load and the stress caused by the final load. Experience with springs designed to stresses within the limits of these curves indicates that they should have infinite or unlimited fatigue life. All values include Wahl curvature correction factor. The stress ranges shown may be increased 20 to 30 percent for springs that have been properly heated, pressed to remove set, and then shot peened, provided that the increased values are lower than the torsional elastic limit by at least 10 percent.
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