Peak value, force–time or force–displacement: which recording do you need?

A spring that builds up slowly to 100 N behaves differently from a connection that suddenly breaks at 100 N. The same maximum force can therefore tell a very different story in two tests. Decide beforehand which recording you need for your decision.

Three ways to describe a force test

A SAUTER FH force gauge has a peak value mode and a live measurement mode. That is often enough if you only want to compare against a limit value. If you want to analyse the progression, the data must be stored during the test or sent to a PC.

When do you choose a force–time curve?

A force–time curve plots the force in N against time in seconds. It shows you, for example, how long a load was held and when the force dropped away. The manufacturer intends the SAUTER AFH FAST software for force–time measurements with suitable force gauges, including the FH series.

Note the difference between the internal measuring frequency of a gauge and the number of points the software records. For the FH 500, KERN states a measuring frequency of 2 kHz; for AFH FAST, a transfer rate of up to 20 values per second with the gauges listed. You will therefore not necessarily see a fast event on the PC with the same time resolution. With very short peaks, check which part the instrument itself holds and which data is actually stored.

When do you need force–displacement?

With a spring, foam, seal or press-fit process you sometimes want to know how much force is needed at a given displacement in mm. A force gauge on its own does not measure distance. For a force–displacement curve you also need a suitable length measuring instrument, mounting, data connection and matching software. KERN describes the AFH LD for force–displacement measurements in combination with a SAUTER LD length measuring instrument; the manufacturer lists the FH series, among others, as a suitable force gauge.

Our range also includes the TVO 500N500S-LD as a version with displacement measurement. Before ordering, check the complete set, including the chosen force gauge, grips and interconnections. Moreover, the travel of a test stand is not automatically the same as the deformation of the test piece: play and flexing in the set-up can play a part. How to build the set-up itself is explained in measuring tensile and compressive force reliably.

Five items that belong in a useful test report

1. Test piece, identification and the number of samples tested.
2. Instrument, measuring range, calibration status and chosen unit.
3. Test stand, grips, starting position and set speed.
4. Result and decision rule: peak, value at an agreed time or force at an agreed displacement.
5. Remarks on slipping, breakage and deviations during the test.

Frequently asked questions about force recording

Can I create a force–displacement diagram with AFH FAST alone?

AFH FAST is intended for force–time recording. For force against displacement you also need a displacement measurement and a suitable software combination, such as the AFH LD with a SAUTER LD as described by KERN.

Is the peak value sufficient for a spring test?

Only if the maximum answers the question. For the behaviour at a given compression you need a force–displacement recording or a fixed measuring point at a known displacement.