Strain gauges for composite material use

Strain gauges for composite material testing

Strain gauges are used to measure mechanical strain in composite materials such as carbon-fibre-reinforced plastics (CFRP) and glass-fibre-reinforced plastics (GFRP). They support material testing, structural analysis and product development, where understanding deformation under mechanical loading is essential.

Unlike many metals, fibre-reinforced composites are often anisotropic: their mechanical properties depend on the direction of the reinforcing fibres. This makes strain gauge orientation, configuration and installation particularly important.

Why is strain measurement on composites challenging?

The strain response of a composite component depends on its fibre orientation, laminate structure and loading conditions. Strain can differ considerably between the longitudinal, transverse and shear directions. Temperature changes may also produce direction-dependent thermal expansion and apparent strain.

Accurate measurements therefore require a suitable gauge configuration, reliable strain transfer through the adhesive layer and careful consideration of temperature effects.

When should you use strain gauges for composite materials?

Typical applications include:

• Tensile, compression and bending tests on composite specimens.
• Mechanical testing of CFRP and GFRP components.
• Research and development of lightweight composite structures.
• Structural testing under static or cyclic loading.
• Validation of numerical models and finite element analysis (FEA).

What should you consider when selecting a strain gauge for composites?

• Fibre orientation: Align the measuring grid with the required strain direction. For multi-directional measurements, consider a suitable strain gauge rosette.
• Gauge length: Choose a measuring length appropriate for the laminate structure, local strain gradients and test objective.
• Surface preparation: Prepare the surface without unnecessarily damaging reinforcing fibres or the laminate.
• Bonding and strain transfer: Select an adhesive and installation procedure compatible with the composite matrix and test conditions.
• Temperature effects: Consider the material's direction-dependent thermal expansion and the need for temperature compensation.
• Measurement conditions: Check the expected strain range, loading frequency, operating temperature and environmental exposure.

Always consult the individual strain gauge datasheet and the composite material specifications before selecting the measurement setup.