do fasteners fail, and how to eliminate fastener failure.
The factors that cause a
fastener to loosen.
The impact load causes
the assembly to resonate.
Focused on the first
engaged thread of the fastener, cyclic plastic deformation
The torsional energy is
The bearing surface
Once the loosening starts at a given pre-load the pre-load will progressively reduce. Once the pre-load is reduced the rate of loosening will increase until the failure occurs.
Therefore, it is prudent in the design to eliminate the possibility of any loosening.
Unalock eliminates this problem.
initial pre-load torque value for the fastener is too low.
The pre load torque value is greater than the yield stress of
Choosing the right material for the fastener
One of the reasons
fasteners fail is when the yield stress of the fastener
material is the wrong choice for the application.
the proper grade, strength material for the fastener is
Installation Pre-Load is
critical to preventing failures.
Force should be appropriate for the fastener material and
eliminating fastener failure (clampforce).
- Determine the needed
clamping load for the fastener.
- Achieve the proper
clamp-load in the assembled joint.
- Eliminate uneven
surfaces in the assembled joint.
- Minimize the number
of joint elements and materials in the assembled joint.
- Minimize the hole
clearances in the assembled joint.
- Use Fine threads in
assembled joints that will experience vibration.
- Make a tighter
tolerance fit, by reducing thread clearance.
Friction Coefficient is a
very important factor.
- Torque values are strictly based on
the friction present in the joint
assembly. Variances in the friction will lead to variances
in the amount of clampload/tension attained at a specified
- Controlling the friction
coefficients, in both the
thread and under-head regions, will result in more
consistent and predictable clamp load values.
- Increasing the pitch torque by
lowering the friction coefficients will cause an
increase in clamp load.
Each variable listed below has an effect on clampforce.
- Coefficient of friction-underhead
- Coeffcient of friction-threads
- hole clearance
- head or nut diameter
- thread pitch
Friction coefficient testing helps
obtain maximum clampforce in assembled joints.
Know the environment your fasteners will be
Temperature, Pressure, Moisture, and Vibration.
Temperatures that cause weakness in the fastener.
Fasteners can be manufactured
to withstand extreme temperature.
Vibration causing the fastener to loosen.
stress amplitudes above the endurance limit.
Vibration forces reduce the friction force
on the threads, allowing the fastener to slide in a loosening
Suggestions to eliminate fastener
failure in assembled joints.
- By using Unalock fasteners, you can
sustain the initial level of bolt tension that is higher
than the tension where self loosening occurs.
- Unalock creates an extra spring in the
joint which increases the overall strength of the assembled
Using rolled threads
instead of cut threads provides greater fatigue resistance.
assembly design should be individually tested and evaluated
using specific guidelines, to reduce fastener failure.
® fasteners minimize the amplitude of alternating
Unalock fasteners reduce
stress concentrations, which reduces fatigue on the bolt and the
increase the ability of
the joint to capture, retain, and deliver energy back to the
us for direct
consultation regarding your fastener application needs.