How to Read a Load-Deflection Curve for a Vibration Isolator
What Does a Load-Deflection Curve Show?
A load-deflection curve relates applied load to isolator displacement.
For an ideal linear spring:
F = kδ
where F is force, k is stiffness and δ is deflection.
Real vibration isolators are not always linear. Rubber mounts may become progressively stiffer as compression increases. In wire rope isolators, cable geometry changes as the loops deform, while interaction between individual wires contributes to a nonlinear response.
This is why a single stiffness value does not always describe the entire operating range.
Find the Working Point First
Consider a 100 kg electronic cabinet supported by four equally loaded isolators:
100 kg ÷ 4 = 25 kg per isolator
Locate 25 kg on the load axis and find where it intersects the curve. The corresponding displacement is the approximate static deflection, and the intersection is the working point.
Equal loading, however, should not be assumed when a transformer, motor, battery pack or other heavy component shifts the center of gravity. HOAN's existing load calculation guide shows how an offset center of gravity can produce substantially different reactions at individual supports.
For this reason, equipment weight divided by the number of mounts is a starting point—not always the final load used for selection.
Read Stiffness Around the Working Point
The local slope of the curve provides an indication of effective stiffness:
k ≈ ΔF / Δδ
A steeper section means that more force is required to produce additional movement. A flatter section means greater displacement for the same increase in force.
|
Curve feature |
Engineering meaning |
|
Steeper slope |
Higher effective stiffness |
|
Flatter slope |
Lower effective stiffness |
|
Changing slope |
Nonlinear response |
|
Working point near travel limit |
Less movement remains |
|
Loading/unloading paths differ |
Hysteresis and energy dissipation |
This matters because stiffness influences the natural frequency of the isolated system:
fₙ = (1 / 2π) √(k / m)
For a nonlinear isolator, engineers should therefore pay attention to the curve around the actual operating region, rather than assuming one stiffness value applies everywhere.
Check the Remaining Dynamic Travel
Static deflection uses part of the isolator's available movement before the equipment starts operating.
A useful preliminary check is:
Remaining travel ≈ δmax − δstatic
This is not a replacement for shock or dynamic analysis. It simply shows how much physical movement remains beyond the static working point.
Consider a vehicle-mounted electronic cabinet. Its weight first establishes the static deflection. When the vehicle passes over an uneven road surface, additional travel is needed to accommodate the transient input.
If the working point is already close to the end of the available travel, the isolator may have little room left for that movement.
This is why maximum load capacity should not be treated automatically as the preferred operating point.
What Does a Hysteresis Loop Tell You?
When both loading and unloading are plotted, a wire rope isolator may show different force-deflection paths.
As the cable loops deform, relative movement and friction occur within the wire rope structure. The unloading path therefore may not exactly retrace the loading path.
The result is a hysteresis loop.
The area enclosed by the loop represents mechanical energy dissipated during that loading cycle.
This is an important characteristic of wire rope isolators because their structure provides both spring action and friction-based damping. However, a hysteresis loop measured under one test condition should not be used to claim a universal damping ratio for every load or displacement amplitude.
Check the Loading Direction Before Using the Curve
The curve must also match the way the isolator will actually carry the load.
Compression and shear loading can produce different stiffness, deflection and available travel. Rotating the isolator does not change equipment weight, but it changes how the isolator structure deforms.
A compression curve therefore should not automatically be used for a shear installation.
This is especially important when the mounting arrangement is changed late in a design to solve a space problem. The bolt pattern may still fit, while the original load-deflection data no longer represents the actual working direction.
Use the Curve as Part of the Selection
A load-deflection curve is most useful when it is connected to the real installation.
For preliminary selection, Xi'an Hoan Microwave Co., Ltd. recommends checking:
Equipment Weight + Number of Isolators + Mounting Layout + Vibration Frequency/RPM + Mounting Orientation + Shock Requirement + Available Installation Space
For uneven or space-limited equipment, a CAD, STEP file or mounting drawing can help determine the actual load distribution and working direction.
Need a load-deflection check for your application?
Send your equipment parameters and installation drawing to HOAN for model selection.
FAQ
What is the working point on a load-deflection curve?
It is the point corresponding to the load carried by the isolator after installation. It indicates the approximate static deflection and normal operating region.
Is maximum static load the best operating point?
Not necessarily. Remaining travel, effective stiffness and dynamic requirements should also be checked.
Can a compression curve be used for shear loading?
