The use of threaded fasteners is very extensive, and the problem that gives us a headache is the loosening of threaded fasteners during use. In response to this problem, inventors have been designing methods to prevent loosening of fasteners, and there are many mechanisms that cause fasteners to loosen.
The following is the prerequisite knowledge we share with you, I hope it will be helpful to you.
Rotating and non-rotating loosening
In most applications, threaded fasteners are to be tightened in order to apply pre-tightening force in the joint. Loosening can be defined as the loss of pre-tightening force after tightening is completed. This can happen in either of two ways. Rotation loosening, usually called self loosening, refers to the relative rotation of fasteners under external load. Non-rotational loosening means that there is no relative rotation between the internal thread and the external thread, but preload loss will occur.
Hex Flange Nut
Metric Hex Flange Nut
Fastener loosening caused by non-rotating loosening
After assembly, deformation of the fastener itself or the joint may cause non-rotational looseness. This may be the result of partial plastic collapse of these interfaces. When the two surfaces are in contact with each other, the asperities on each surface bear the pressure load of the supporting surface. Since the actual contact area of the bump may be much smaller than the macro area, even under moderate load, the stress of the protrusion due to the surface roughness will be greater than the yield strength of the material, and these protrusions will bear very high local stress, resulting in Plastic deformation.
This can cause partial collapse of the surface after the tightening operation is completed. This collapse is commonly referred to as embedding. The amount of clamping force lost due to embedding depends on the stiffness of the bolt and the connected part, the number of interfaces in the joint, the surface roughness and the applied contact stress. Under moderate surface stress conditions, the initial collapse usually results in a clamping force loss of about 1% to 5%, and half of these losses are lost within the first few seconds after the joint is tightened. When the joint is subsequently dynamically loaded by the applied force, the joint will be further reduced due to the pressure change that occurs on the joint interface.
Loosening due to embedding loss is problematic at joints consisting of several thin joints and small clamping lengths of bolts. If the surface load-bearing stress is kept below the compressive yield strength of the joint material, the embedded loss can be calculated, and the loss can be compensated by the joint design.