Pitch "P": is the distance between adjacent thread forms measured parallel to the thread axis. Lead "l": is the distance that the nut moves parallel to the axis of the screw when the nut is given a turn. Note that thread size is specified by giving the pitch p for metric sizes and giving the number of threads per inch "N".
Note that the letter M preceding the diameter is a clue to the metric designation. The ideal bolt length is one where only one or two threads protrude from the nut after you tighten it. The load is achieved by rotating the nut until the bolt is elongated almost to its elastic limit.
If the nut does not loosen, this bolt tension remains equal to the pretension or clamping force. When tightening, the technician should, if possible, hold the bolt head still and turn the nut; this way the bolt shank will not feel the thread friction moment.
Joints Fastener
There are 4 basic types of failure mechanisms for bolted connections under shear
Bolt Shear
A larger diameter bolt
Edge Tear-Out
Bearing Failure
This type of failure occurs when one of the plates is too thin or not strong enough for the loads applied.
Net Section Failure
The distance is specified as not less than 2.5 times the nominal bolt diameter, preferably 3 times the bolt diameter.
The bolted connections can be classified based on geometry and loading conditions into three types
1.Shear connections
2.Tension connections
3.Combined shear and tension connections
Shear Connections
The hip joint tends to bend, so the forces tend to be collinear. The load transfer at the joint will ultimately take place through shear forces in the bolts. In the case of a lap joint or a single cover plate butt joint, there is only one cutting plane and then the bolts are said to be in single shear.
In the case of a double butt joint, there are two shear planes and so the bolts will be in double shear. It should be noted that the butt joint of the single cover type bends so that the center of the cover plate becomes collinear with the forces.
Tension Connection
A through bolt (or simply a bolt) is a cylindrical rod "shank" with a nut thread at one end and a head at the other end. It is passed through drilled holes in the two parts to be fastened together and clamped together when the nut is screwed onto the threaded end. It is screwed into a tapped hole on one of the parts to be fixed without a nut.
One end of the pin is screwed into a tapped hole on the parts to be attached. Bolts are mainly used instead of studs to fasten different kinds of covers (eg engine, pump covers). They can be used instead of a key to prevent relative movement between a hub and a shaft in lightweight power transmission elements.
D : is the diameter of the shaft (in mm) on which the set screw is pressed. The following stresses are induced in a bolt, screw or stud when it is screwed in tight.
Tensile stress due to stretching of bolt (Initial Tightening)
- Combined tension and shear stress
When the joint is not required to be as tight as a fluid tight joint, then the initial stress in a bolt can be reduced to half the above value. If the load tending to separate these parts is neglected, find the stress placed on the bolt by the initial tightening. The following stresses are induced in a bolt when subjected to an external load.
The bolts, studs, and screws usually carry a load in the direction of the bolt axis, creating a tensile stress in the bolt. dc = Root or core diameter of the wire, and. From the standard thread table, the value of the nominal diameter of the bolt corresponding to the value of “dc” or the stress range 𝝅 can now be obtained. Sometimes the bolts are used to prevent the relative movement of two or more parts, such as in flange coupling, where the shear stress is induced in the bolts.
It should be noted that when the bolts are subjected to direct shear loads, they should be positioned so that the shear load is on the body (i.e. shank) of the bolt and not on the threaded portion. In some cases the bolts can be relieved of the shear load by using shear pins. When multiple bolts are used to share the shear load, the finished bolts must be installed in the reamed holes.
The diameter of the bolt shank is obtained from the shear load, and. A diameter slightly larger than that required for shear or tension may be assumed, and stresses due to combined loading should be checked for the following principal stresses. Determine the nominal diameter of the bolt, if the tensile stress should not exceed 100 MPa.
It consists of a circular ring at the head and provided with threads at the lower part to screw into a threaded hole at the top of the machine. From Table (coarse range) the standard core diameter (dc) is 28.706 mm and the corresponding nominal diameter (d) is 33 mm. The flanges of the coupling are fixed with four bolts of the same material at a radius of 30 mm.
Find the size of the bolts if the allowable shear stress for the bolt material is 30 MPa. From the standard bolts table (coarse range), the standard core diameter of the bolt is 3.141 mm and the corresponding size of the bolt is M 4.
