The solution to bolting problems!

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Bolt/nut loosening issues

A key advantage of threaded fasteners over the majority of other joining methods is that they can be dis-assembled and re-used. Unintentionally self-loosening has been a problem since the start of the industrial revolution and for the last 150 years inventors have been devising ways in which it can be prevented. The program will assist in preventing self-loosening by providing information to allow the joint to be engineered such that the causes of self-loosening will not arise.

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Bolt overload issues

The majority of bolts are tightened and hence are preloaded. This preloading tends to reduce the loading acting on the bolt but does not eliminate it. When external loads are applied to the joint, the bolt will sustain a proportion of that load. If the load is sufficiently high the bolt can be overloaded and subsquently fail. The BOLTCALC program determines the load being sustained by the bolt and checks if the resulting stress will exceed the bolt's minimum yield strength.

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Bolt fatigue issues

The program can assist in solving bolt fatigue issues. Fatigue is typically quoted as the commonest reason for bolts to fail in service. In the vast majority of applications, the most effective way to ensure that the bolt is fatigue resistant is to ensure that it is tightened sufficiently. The BOLTCALC program checks for this condition as well as determining the alternating stress in the critical thread section and compares with the bolt's endurance limit determined by the program.

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Thread stripping issues

Thread stripping, sometimes referred to as thread shearing, is when the shear stress acting on the threads is such that the threads either shear completely so that the nut becomes detached, or partially, in which case the strength of the thread is severely impaired. The program will determine the force to shear both the nut (internal) thread and the bolt (external) thread. Thread stripping can be a problem in many designs where tapped holes are required in low tensile material.

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Excessive bearing stress

If the bearing pressure under the nut face exceeds the compressive yield strength of the joint material, plastic deformation will occur. The preload loss from embedding determined by the program, assumes that the compressive yield strength is not exceeded. If it is, then such preload loss can increase uncontrollably. The program checks that the bearing pressure is within acceptable limits and if it is not, recommends a number of design alternatives.

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Insufficient bolt preload

The bolt preload provides a clamp force that prevents gaps from occurring at the joint faces, or lateral movement, when external forces are applied. It provides the loading that generates the frictional force between the joint faces to prevent slippage and the load to ensure that any gasket within the joint, seals effectively. If the bolt preload is not sufficient to resist the external forces, loosening, fatigue or wear problems can be anticipated. BOLTCALC will establish if such a condition is likely to arise.

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