Factors Affecting Strain Measurements: Short Notes (Strain Gauges & Indirect Influences)

Strain measurements (commonly with strain gauge-based systems) are affected by both sensor-specific behavior and system/installation conditions. Key influences include temperature effects, mechanical installation (bonding/alignment), gauge non-idealities, and electrical measurement errors such as lead resistance and noise. These factors determine the final measurement accuracy, repeatability, and drift over time.3

A useful mental model is:

Key terms

• temperature compensation
• gauge factor
• transverse sensitivity
• creep

1) Temperature effects (thermal strain + gauge self-heating)

Temperature changes can produce apparent strain in two ways:

1. Direct gauge resistance change (material property changes of the foil/gauge) even with no mechanical strain.
2. Thermal expansion of the substrate: when the specimen expands/contracts, strain gauges experience strain due to the structural temperature gradient.

Mitigation usually relies on temperature compensation using matched gauges, dummy gauges in a bridge, and proper bridge configuration/excitation control.2

What to watch in practice

• Temperature gradients across the gauge area (not just absolute temperature).
• Variation in ambient vs specimen surface temperature.
• Gauge self-heating from excitation (especially at higher current).

2) Installation and bonding effects (adhesive and mounting stiffness)

Bonding and mounting determine how faithfully the gauge follows the specimen surface strain:

• Bond thickness and uniformity: variations lead to local strain transfer errors.
• Adhesive cure effects: mismatch in cure temperature and final operating temperature can introduce residual strain.
• Mounting stiffness / bending of the backing: can distort how strain is transmitted to the foil.
• Surface preparation (roughness, cleanliness, corrosion): affects adhesive integrity and long-term stability.

These are usually grouped under strain transfer quality and installation workmanship.2

Key terms

• strain transfer
• adhesive creep
• bond line stiffness

3) Gauge geometry and alignment errors (directionality + transverse sensitivity)

Strain gauges are designed to respond primarily to strain along the gauge axis, but real behavior includes:

• transverse sensitivity: strain components perpendicular to the grid can cause output.
• Misalignment between gauge axis and principal strain direction: converts shear/other components into measured longitudinal strain.
• Curvature effects: gauges on curved surfaces experience a different strain distribution than flat approximations.

These effects are especially important near stress concentrators, bending regions, and complex stress states.2

4) Non-ideal gauge behavior: gauge factor variation, hysteresis, and aging

Real gauges do not behave perfectly linearly over all conditions.

• gauge factor not constant with temperature and sometimes with strain range.
• Hysteresis: repeated loading/unloading can yield different outputs at the same strain due to mechanical and adhesive effects.
• Aging drift: gradual change in zero output over time due to material and adhesive relaxation.

These contribute to measurement drift and reduced reproducibility, particularly for long-duration monitoring.2

5) Creep and relaxation (time-dependent strain transfer)

Creep and stress relaxation in:

• the specimen (e.g., polymers/creep-sensitive metals),
• the adhesive layer,
• and the gauge backing

cause output change even if the applied mechanical load is constant.

This is often modeled as time-dependent strain error and is critical for:

• sustained loads,
• proof testing,
• and structural health monitoring.2

6) Electrical system and instrumentation errors (bridge, wiring, excitation, noise)

Even with perfect strain transfer, the electrical measurement chain can introduce error:

• Wheatstone bridge balance: incomplete balancing causes sensitivity to lead resistance and offset.
• Lead wire resistance/temperature: causes apparent strain/offset if not accounted for (often using 3-wire/4-wire arrangements).
• Excitation voltage instability: scales the output directly with bridge excitation.
• Electrical noise: EM interference, grounding issues, and bandwidth limitations.
• ADC resolution and sampling strategy: affects quantization and dynamic measurement fidelity.

These are commonly discussed under strain-gauge instrumentation and bridge circuit error sources.2