Stress and strains

Stress and strains occur when a load is applied to a structure or component. The stresses and strains are in a stress-strain relationship. This depends on the modulus of elasticity of the building material and is described by Hooke's law (σ = E · ε).

These relationships are generally determined by a tensile test. This is a standardized method for material testing. This is one of the destructive test procedures in which a sample of the material is taken up to the breaking load. This enables the yield strength, tensile strength, elongation at break and other material properties to be determined.

The test setup for the tensile test on an elastomer sample is shown in the right figure. The specimen is clamped between 2 abutments. A laser optical measuring sensor is installed to measure the strains. During the test the sample is pulled apart at the plates with a continuous speed. The test is run up to the breaking load. The stress-strain relationship can then be determined from the stresses entered and the measured strains.

Experimental setup for a tensile test on an elastomer sample

Strain gages

So-called strain gauges can be used for the direct measurement of strain. These must be attached directly to the samples, which requires surface preparation. This is one of the reasons why they are used less frequently.

Other direct measuring methods are: 

  • Laser extensometer
  • Laser Speckle Extensometer
  • Videoextensometer
  • Gray value correlation

Often, laser optical measurement sensors sensors are used to determine the strains, which offer a high resolution and can be used several times.

Strain gages on a tensile test

Services

SKI Ingenieurges. mbH offers the following services in the field of strain measurements:

  • Test accompanying and monitoring activities
  • Construction and calibration of numerical models for recalculation
  • Recalculation of test results in the static, dynamic and transient range
  • Evaluation and interpretation of measurement results, as well as comparison of numerically supported test methods
  • Creation of measurement concepts, reports and expert opinions
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