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Measuring Mechanical Stress with Strain Gauges

Measure mechanical stresses and forces in assemblies quickly and reliably: Strain and compression measurements with strain gauges provide precise results on the forces acting on assemblies for structural tests, fatigue strength measurements and product and material testing.

In order to design components optimally, precise knowledge of the type, direction and magnitude of the forces acting on them is essential. In order to determine these, strain gauges are applied to the test specimen. CSM supports all common bridge types (quarter, half and full bridges) with its measurement modules.

Transducers

Crane booms, tie rods, or vehicle axles are applications where acting forces and mechanical loads must be frequently examined throughout the product development process. These are measured in road and field tests or on the test bench. The geometry of the object to be examined or the general space available does not always allow the installation of additional sensors for force or torsion measurement. In such cases, the object itself becomes the sensor. The strain gauges are attached directly to the component and calibrated without any load applied. The component is then reinstalled into the system where it is measured under operating conditions. This is done, for example, with a tie rod on which tensile and compression forces are measured.

CSM’s STGMM measurement modules for measurements with strain gauges allow a high resolution with 5 volt sensor excitation and a small measurement range. Measurements in operating conditions or on the test bench can thus be easily implemented.

In operational tests CSM’s ECAT STGMM strain gauge measurement modules are exposed to extreme conditions and precisely record the stresses occurring on the test object. Even strong vibrations do not impair the reliability of the measurement modules. According to the road to rig method, the measured values can then be easily transferred to a fatigue test rig. The same ECAT STGMM measurement modules are used on the test bench as previously in the road test, allowing easy comparison of the measured data. Using the CSMconfig software, the configuration settings from the road test are transferred to the measurement modules on the test bench (or vice-versa) in the form of .dBc or .a2l files. This speeds up the test considerably by shortening the set-up time.

With the HV STG4, strain gauge measurements can be easily implemented in high-voltage environments such as measuring the dynamic vehicle forces being transferred into an electric vehicle’s battery assembly..

Truck wheels on uneven road
Mechanical loads have an effect on all components. For a suitable design, forces must be measured during development - preferably under realistic conditions in road tests.

Experimental Stress Analysis

Experimental stress analysis with strain gauge rosette
A strain gauge rosette can be used to analyze stress curves for an unknown principal stress direction.

With strain gauges, calculated mechanical stresses in assemblies can be validated quickly and reliably. Quarter bridges are often used for this purpose (Wheatstone bridge circuit with one active strain gauge and three resistors), as these can be implemented quickly and cost-effectively.

If the main direction of the principal stress is known, a quarter bridge is sufficient.

If the direction of the principal stress is unknown before the measurement, two to three quarter bridges are attached to the test specimen as a rosette. The three individual strain gauges of the rosette can each be complemented to a half-bridge with the CSM quarter bridge completion cable (K356) and thus easily be integrated into the STGMM measurement module. Thanks to the high measurement range of the STGMM, very small as well as very large strains can be measured.

On large objects, such as construction machinery, the required measurement points are often far apart. Using the ECAT STGMM this is no problem: The measurement points can be up to 100 meters apart.

Measurement of Mechanical Loads with Sensors

If conditions permit, mechanical loads can also be measured with sensors. Most of the available sensors emit the signal without amplification or modification by integrated electronics. The very small signal emitted by the sensor places special demands on the measurement technology used. The STGMM meets these requirements by precisely detecting even small signal voltages and offering the required sensor excitation.

Heavy duty truck
If there is sufficient space, sensors can also determine the mechanical loads. In this way, vehicles are optimally designed for demanding usage.

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