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Preload control. Amount of the no-load tension in the bolted joint ( preload) greatly affects the reliability of the joint. Multiple techniques exist for preload control to ensure that the tension in the bolt is close to the one specified in the design (some bolt-to-bolt statistical variations are inevitable): [1] torque-controlled tightening ...
The applied torque causes the bolt to "climb" the thread causing a tensioning of the bolt and an equivalent compression in the components being fastened by the bolt. The preload developed in a bolt is due to the applied torque and is a function of the bolt diameter, the geometry of the threads, and the coefficients of friction that exist in the ...
The most common usage is to describe the load applied to a fastener as a result of its being installed, i.e., before any external loads are applied (e.g., tightening the nut on a bolt). Preload in such cases is important for several reasons. First, a tightened bolt experiences only a small fraction of any external load that will be applied ...
The bolt was qualified to a preload (F p*) of 19,300 lbf (85,900 N), actuated by torque (τ) from an actuator (3) having a maximum sustained output of 1,600 lb⋅in (180,000 mN⋅m). [105] The effective preload can change (F cte ) after berthing by the difference between coefficients of thermal expansion of bolts and flanges.
In critical fastener joints, embedment can mean loss of preload. Flattening of a surface allows the strain of a screw to relax, which in turn correlates with a loss in tension and thus preload. In bolted joints with particularly short grip lengths, the loss of preload due to embedment can be especially significant, causing complete loss of preload.
Rockwell scale. The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). [1] There are different scales, denoted by a single letter, that use different loads or ...
Multi-jackbolt tensioners (MJT) are an alternative to traditional bolted joints. Rather than needing to tighten one large bolt, MJTs use several smaller jackbolts to significantly reduce the torque required to attain a certain preload. MJTs range in thread sizes from in (19 mm) to 32 in (810 mm) and can achieve 20 million pounds-force (89 × ...
It is therefore beneficial in high-frequency high-load situations with a higher risk of fatigue related failure, like a bolted down cylinder head, to use torque to yield bolts. [ citation needed ] The torque applied to the fastener must be determined such that it does not contribute to a service condition where the fastener enters a low-cycle ...