High-strain gauges for large deformation measurement

High-strain gauges for large deformation measurements

High-strain gauges, also known as post-yield strain gauges, are designed to measure mechanical strain beyond the range of conventional strain gauges. They are particularly useful in material testing and deformation analysis where the test specimen undergoes significant plastic deformation.

Althen offers YEF, YF and YHF Series strain gauges for different large-strain measurement requirements, with selected models suitable for strains up to 40%.

What is the difference between elastic and plastic strain?

Elastic strain is deformation that is largely recovered when the load is removed. Plastic strain is permanent deformation that remains after unloading. During tests that extend beyond a material's yield point, the total strain may become much larger than the range normally measured with standard strain gauges.

High-strain gauges are designed to follow these larger deformations, provided the gauge, adhesive and measurement setup are suitable for the application.

Can high-strain gauges measure repeated loading?

Not every high-strain gauge is suitable for repeated large deformations.

• YEF Series: Designed for large strains of approximately 10–15%. Selected models can withstand repeated loading within a specified small elastic-strain range, but not repeated large plastic-strain cycles.
• YF Series: Designed for approximately 15–20% strain. Not intended for repeated strain measurements in the elastic or large-strain range.
• YHF Series: Designed for very large strains of approximately 30–40%. Not intended for repeated strain measurements.

Always distinguish a gauge's maximum strain limit from its fatigue performance. A gauge capable of measuring a large strain once is not necessarily suitable for repeated cycles at that strain level.

What should you consider when selecting a high-strain gauge?

• Expected maximum strain: Choose a gauge with a strain limit appropriate for the test.
• Loading conditions: Determine whether deformation occurs once or repeatedly, and whether the strain remains elastic or becomes plastic.
• Bonding adhesive: Select an adhesive approved for the gauge series and expected deformation.
• Time between installation and testing: Consider adhesive aging, particularly when large-strain testing takes place several days after bonding.
• Gauge length and configuration: Select the measuring length and grid arrangement appropriate for the specimen and strain direction.
• Temperature and environment: Check the operating temperature and environmental limits of the complete measuring point.

Consult the individual product datasheet for the strain limit, fatigue characteristics, approved adhesives and installation requirements.