How to calculate the torque values for bolts

Bolt is a cylindrical with nut threaded fasteners, mechanical fastening parts, need to cooperate with nut. On the relevant national standards, bolt according to the performance into 3.6, 4.8, 5.6, 5.8, 8.8, 9.8, 10.9, 12.9, eight grades, of which more than 8.8 (8.8) bolt is made of low carbon alloy steel and medium carbon steel and the heat treatment (quenching + tempering), known as high strength bolt, 8.8 the following (not including 8.8) known as ordinary bolts. And, in some mechanical design, bolt as indispensable parts, need to be calculated, detection, and audit. So how to calculate the torque values for bolts, is designing the bolt is a very important subject. By looking for reference books, bolt torque is the unit of N.M, refers to a distance from the center of the bolt of a couple. Destruction of strong torque and torque. Destroy torque than the bolt torque will be destroyed. Strong torque refers to slightly less than or equal to the torque to the bolts completely. Here is through some calculation formula is introduced, to explain to you how to calculate the torque values for bolts. 

   Bolt torque calculation: simplified formula: T = KFd (N.m m), including: (1) K: tightening torque coefficient, according to the state of the surface can be broadly choose a reference value, for general machining surface, if there is a lubrication K can take 0.13 0.15; If there is no lubrication, can take 0.18 ~ 0.21; The range if it is not the general processing surface, then need to speak about specific situation; ; M6 l # Z# @ 9 G) G (2 d: means the thread of the nominal diameter 6 W, d. `, Z9 R; (3) : F is the pre-tightening force, carbon steel bolts take F = (0.6 ~ 0.7) sigma A; Alloy steel bolts take F = (0.5 ~ 0.6) sigma A; The sigma is the bolt material yield point; A = PI / 16 (d2 and d3) 2, d2, hitches for thread d3 = d1 - H / 6; D1 is path, H is thread of the original triangle height; H value according to different thread can be calculated, is about 0.87 times the pitch P. In computing, some data is given, and some data is need you to find some related forms. Finally, substitution formula can calculate the torque value. I think that for any a mechanical worker, how to calculate the torque values for bolts, is one of the most basic computing. ?