This article addresses possible sources of error when strain gauges are used in experimental stress analysis and shows how to successfully assess measurement uncertainty already in the design stage
The aim of this article is to point out the many (often avoidable) sources of error when strain gauges are used in experimental stress analysis and to provide assistance so that measurement uncertainty can be assessed already in the design stage.
Signs of fatigue in the strain gauge measuring grid appear during dynamic loading of the component that are expressed in a zero drift (apparent strain in the material). The greater the alternating strain amplitude and the greater the number of load cycles, the greater the effect (Fig. 5).
The installation and the arithmetic mean of the strain also affect the zero drift. If the average is negative, the fatigue life improves. If the value is positive, it deteriorates. Practically no zero drift may be expected for alternating strains with an amplitude up to 1000 μm/m. Greater amplitudes are more critical. A zero error of 10 μm/m may be expected for:
1500 μm/m and approx. 2 mil. load cycles
2000 μm/m and approx. 100,000 load cycles
2500 μm/m and approx. 4000 load cycles
3000 μm/m and approx. 100 load cycles
Note that the test specimen also undergoes fatigue. If its resistance to alternating loads is greater than that of the foil strain gauge, use of optical strain gauges should be considered (fiber Bragg grating).