Formulas to calculate preload and torque of a bolt, tensile stress area of screw thread, length of engagement to prevent stripping and shear area of the internal/external threads.
|
Parameter |
Equation |
|
Preload (Fi) |
$${ F }_{ i }=PPS\cdot { A }_{ t }{ S }_{ p }$$ |
|
Torque (T) |
$$T=K\cdot { F }_{ i }\cdot d$$ |
|
Tensile Stress Area of Screw Thread (At) |
$${ A }_{ t }=0.7854{ (D-\frac { 0.9743 }{ n } ) }^{ 2 }$$ |
|
Length of engagement to prevent stripping (including design
factor) (Le) 1 |
$${ L }_{ e }=\frac { 2\cdot { A }_{ t }{ n }_{ s } }{ 3.1416{ \cdot D }_{ 1max
}\cdot [0.5+0.57735\cdot n\cdot ({ d }_{ 2min }-{ D }_{ 1max })] } $$ |
|
Shear areas of the external threads (As) |
$${ A }_{ s }=3.1416\cdot n\cdot { L }_{ e }\cdot { D }_{ 1max }[\frac { 1 }{ 2n
} +0.57735({ d }_{ 2min }-{ D }_{ 1max })]$$ |
|
Shear areas of the internal threads (An) |
$${ A }_{ n }=3.1416\cdot n\cdot { L }_{ e }\cdot { d }_{ min }[\frac { 1 }{ 2n
} +0.57735({ d }_{ min }-{ D }_{ 2max })]$$ |
|
Relative strength of the external and internal threads (J) 2 |
$$J=\frac { { A }_{ s }\times { S }_{ ut\quad ext } }{ { A }_{ n }\times { S }_{
ut\quad int } } $$ |
|
Required length of engagement to prevent stripping of the internal thread (Q) |
$$Q=J\cdot { L }_{ e }$$ |
Parameters:
PPS:
Percent of Proof Strength,
Sp:Proof Strength, n:
Threads per inch, ns: Design factor against stripping