Formula for Calculating Tensile Stress?

About stress in bolts that joint 2 plates?

• machine design:if bolt joints 2 plates,and 2 equal forces but in oppiste direction are appled on the plate,,,so why we calculater tensile stress on the bolt and not shear stress.???this question is reagarding the case that there is 1 mm gap beatwean the diameter of the bolt and the diamters on the plates(the holes\\bores on the plater)...and why if there was no gap beetwean the diameter of the bolt and the holes(bores)on the plates for the same case with the forces above we r calculating shear force and not tensile force??in both case the forces r (geometry) perpendicular to the axis of the bolt so why in first case we calculate tensile and on the second case its shear,,,,though that the formula looks the same...its force /area??

• Answer:

  In general there are 3 methods of bolting, snug tight and fully tensioned and fully tensioned - friction grip. If snug tight and fully tensioned, the plates that have the shear force will slip slightly and the holes in the plate will come into contact with the bolts causing the bolts to take the force out in shear. If you are designing a friction grip joint (especially usefull in vibrating machinery) the plates surfaces have a roughned finish and when the bolts are tightened, they must be tensioned to such a level that the shear force in the plates are resisted in friction by the faying surfaces. The bolts must be tensioned to the required level to ensure that the faying surfaces can resist the shear force. The bolts are generally tightened to just above the elastic limit with the tension in the bolts estimated by a torque wrench or load indicating washers, or by ultrasonics measuring the elongation of the bolts. I hope this helps.