The resulting preload changes on the bolt and joint are. The equations are developed to allow for the calculation of an upper torque specification limit that will result in a desired maximum equivalent stress in the bolt shank due to the tension and shear combined stresses. Many of the common tightening methods achieve the preload force by applying a torque to the nut or to the bolt head. Bolt pretension varies because of a spread in friction values and precision of tightening method. Square and Acme Threads ... Best way to measure bolt preload is by relating measured bolt
•The diameter of this unthreaded rod is the average of the pitch diameter and the minor diameter of the threaded rod.

Fatigue life of a bolt is determined by the magnitudes of mean and alternating stress imposed on the bolt by external cyclic loads.

It is problematic to consume 50 to 60 percent of a very narrow bolt preload safety margin with preload … When tightening a fastener with a torque wrench, which is one of the easiest and most common methods, the fastener is considered to be properly tightened once the specified torque is achieved. calculations. Installed Bolt PreLoad Equations: F = cA t S p. Where: F = Preload Tension Force A t = Tensile Shear Area of Bolt S p = Proof Load of Bolt (or some percentage less than 100% of yield load of bolt, typically 85 % of yield S y) c = 0.75 For connections requiring reuse c = 0.89 For permanent connections .

For a steel bolt clamping Aluminium plates this value is typically 0.41 4) TIGHTENING FACTOR - The tightening factor is the ratio of the minimum preload to maximum preload when a batch of bolts are tested. [5]A rough estimate of the required Bolts in tension should exert as much force on the joint as it and the joint members will stand[4].

Torque to Obtain Preload. bolt preload or torque applied to secure the component be properly determined. Open --> Bolt Preload Tension Force Calculator the fasteners, the bolt shank and threaded section are stressed in tension and additionally in shear due to the applied torque.
Bolt-load-sharing ratio is an important parameter because it can be used to more-accurately calculate bolt stresses than using the sum of preload and external load. such as: thermal cycling, vibration, cyclic fatigue, flange thickness, flange rotation, bolt stress relaxation, additional bolt preload, externally applied loads, etc.

While tension and high clamping force are critical for joints, applied forces (often cyclic) can significantly reduce preload. 4.3 Installation of High-Strength Bolts, 52 4.4 Relaxation, 61 4.5 Reuse of High-Strength Bolts, 62 4.6 Galvanized Bolts and Nuts, 63 4.7 Use of Washers, 65 4.8 Corrosion and Embrittlement, 66 4.9 Effect of Nut Strength, 69 4.10 Basis for Design Recommendations, 70 4.10.1 Bolts Subjected to Tension, 70 4.10.2 Bolts Subjected to Shear, 71 Relationship between bolt fatigue life and bolt preload. The customer is responsible for the flange design and for ensuring that the flanges, bolts and bolt loads are sufficient for the application. Shigley’s Mechanical Engineering Design.

A bolt goes in to a state of tension when torque is applied on the joint some of the factors that affect the bolt tension with the amount of torque applied are nominal bolt diameter, friction coefficient and bolt strength. Some typical values are: If there is no bolt preload in loaded bolt joint, the bolt … The limiting bearing load is the same as that of equation (72) except the bearing area is replaced by the effective projected area over which the load acts.

The bolt preload assumptions include a specified preload torque T and a nut factor k.5 The preload torque is related to the preload axial force F by [5]: T =kFdbolt (1) A nominal preload torque of 400 ft-lb and a nut factor of 0.15 result in a bolt preload axial force of 36,500 lb. The ±25 to 30 percent accuracy range of using torque to preload bolts and nuts should be considered when determining the suitability of 20.5 to 50 percent (preload and operating) safety margins. Bearing under the head of the bolt (or nut) may need to be examined in situations of high preload, large external loads, or soft abutment materials. A rule of thumb is to load the bolt to 60% of the material’s yield strength[5].