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17 July, 14:28

Chapter 15 - Fasteners: Determine the tensile load capacity of a 5/16 - 18 UNC thread and a 5/16 - 24 UNF thread made of the same material. Which is stronger?

Make the same comparison for M8 x 1.25 and M8 x 1 ISO threads. Hint: see Tables 15-1, 15-2, and 15-3

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  1. 17 July, 17:33
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    The material strength is given as 100,000 PSI

    To find the tensile load capacity of a threaded rod, we multiply the Strength of the material with the Stress area for the bolt.

    A_{t} = 0.7854 (D - / {0.9743}{n}) ^{2}

    Where D is the Basic Major Diameter

    n is the Number of threads per inch

    At is the Tensile strength area of the bolt.

    For 5/16 - 18 UNC thread

    D = 0.3125

    n = 18

    Therefore the tensile load capacity is = 100000 X (0.7854 X (0.3125 - 0.9743 / 18) ^2

    = 5243 lb.

    Similarly for 5/16 - 24 UNF, only the n value changes to 24

    we get the tensile load capacity = 5806.6 lb

    Hence the fine thread bolt is stronger because it has more tensile load capacity.

    For metric Bolts

    We have to consider all values in SI units

    Strength = 689 MPa

    We get for M8 - 1.25

    Tensile load capacity as = 689 X 36.6 = 25223 N = 5670 lb

    For M8 - 1

    Tensile load capacity as = 689 X 39.167 = 26986 N = 6067N

    Strength of 5/16 - 14 Acme thread

    We use the imperial fomula as mentioned above,

    The tensile capacity is 4634 lb.
  2. 17 July, 17:37
    0
    The 5/16 - 24 UNF is stronger because it has more tensile load capacity.

    Tensile load capacity for M8 - 1.25 = 5670 lb

    Tensile load capacity for M8 - 1 = 6067 lb

    Explanation:

    For 5/16 - 18 UNC thread:

    D = 0.3125

    n = 18

    Therefore the tensile load capacity is = 100000 X (0.7854 X (0.3125 - 0.9743 / 18) ^2

    = 5243 lb.

    Similarly for 5/16 - 24 UNF, only the n value changes to 24

    we get the tensile load capacity = 5806.6 lb

    Hence the 5/16 - 24 UNF is stronger because it has more tensile load capacity.

    For metric Bolts:

    We have to consider all values in SI units

    Strength = 689 MPa

    We get for M8 - 1.25:

    Tensile load capacity as = 689 X 36.6 = 25223 N = 5670 lb

    For M8 - 1:

    Tensile load capacity as = 689 X 39.167 = 26986 N = 6067lb
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