• What is needed to make a proper assembly?
• Why use bolted joints?
• What is pre-load and tensile force?
• What is friction?
• How does the pre-load influence the bolt?
• What is torque?
• When we have oil on threads?
• When we have a corroded bolt?
• When we add a washer?
• Loctite, locknut, paint in threads, damaged threads, weld slag, bolt finishing
Clamping force - Compressive force that the bolt exerts on the joint materials, also called clampload
Preload - Tension force that is generated in the bolt
Axial load - Applied force in the same direction as the axis of the bolts
Transverse load - Applied force to the joint that is perpendicular to the bolts
Friction - Resistant force to materials moving against each other
Torque - Resistant force to materials moving against each other
Prevailing torque - The amount of torque required to run down a screw or bolt, typically associated with a lock-nut or thread forming screw
Residual torque - The amount of torque remaining in the joint after tightening
Static breakaway torque - The amount of torque remaining in the joint after tightening
Relaxation - A loss of clampload in a joint after tightening
Embedment - A cause of relaxation attributed to high surface pressure in hard surfaces, most apparent in hard joint with multiple hard layers Relaxation associated with embedment typically stabilizes quickly (less than 0.2 seconds)
Creep - A cause of relaxation attributed to soft materials under high pressure that slowly flow material away from the joint. Can take longer periods of time than embedment losses
Stress - Force per unit area e.g. Newtons per square millimeter or pounds per square inch
Strain - Change in length compared to original length
Elastic area - The region of the angle-torque curve in which the material returns to the undeformed state when applied forces are removed
Plastic area - The area in which the material deforms permanently
Yield point - The point separating the elastic from the plastic area
Snug - The point at which the components of a bolted joint are contacted together and torque starts to build
Hard joint - The plates and material between the nut and bolt bearing surfaces have a high stiffness. Usually defined as hard if the bolt is tightened to its full torque and it rotates through an angle of 30 degrees or less after it has been tightened to snug
Soft joint - The plates and material between the nut and bolt bearing surfaces have a low stiffness. This usually has to be tightened by two or more complete turns, after it has been torqued to snug