In material mechanics and structural testing, strain measurement is always a critical step. Conventional resistance strain gauges are mature, but they are often constrained in scenarios such as flexible materials that are difficult to bond, wiring challenges on complex structures, noise amplification under dynamic loading, and measurement points that are hard to adjust once fixed. Research and engineering need not just data, but efficient, flexible, reliable, and repeatable solutions.

What is a "virtual strain gauge"

The virtual strain gaugeBased on digital image correlation (DIC) algorithms rather than a physical sensor. The system performs high-precision displacement/strain calculations on images before and after loading and generates "virtual measurement points" at any location on the specimen surface; strain and displacement results can be extracted in real time or in post-processing.

Core value:A single set of image data captured in one experiment supports multi-point reuse; even after the experiment is over, measurement points can be flexibly added on the same data to meet secondary and tertiary analysis needs.

Why choose virtual strain gauges (vs. conventional strain gauges)

Typical application scenarios

Flexible and composite materials: tension/bending/interlaminar shear of films, honeycomb/sandwich structures, fabrics/prepregs, etc.

Complex structures and confined spaces: irregular components, welded/bonded zones, stiffener transition regions, and areas near holes/notches.

Dynamic and transient events: vibration, impact, rotation, collision, and fatigue crack initiation and propagation.

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Application cases

(1) Poisson's ratio test of composite materials

The front of the specimen was sprayed with a speckle pattern for DIC, and resistance strain gauges were bonded on the back for comparison; virtual strain gauges were placed in the images, corresponding one-to-one with the resistance strain gauge positions.

Results:The virtual strain gaugeThe computed Poisson's ratio agrees closely with the resistance strain gauges, and the further derived elastic modulus of ≈48 GPa matches the theoretical value of the material, verifying its reliability.

Calculation:Poisson's ratio = transverse strain / longitudinal strain

Value range:Take the average of the ratio over the 1500–2500 data range 

2）Real-time vibration measurement

Under dynamic loading and vibration conditions, virtual strain gauges capture strain evolution in real time and reduce the noise amplification introduced by contact chains, providing stable support for high-speed and transient testing.

(3) Tensile comparison of composite plates

Comparing the virtual strain gauge with an adjacent resistance strain gauge: the two curves follow highly consistent trends, with fluctuations during the static loading stage within an acceptable range and a very small maximum deviation, accurately reflecting the evolution of the strain curve.

When to "directly replace" contact strain gauges?

For tasks involving flexible materials, complex geometry, dynamic/high-speed loading, or measurement points that need repeated adjustment or traceability, virtual strain gauges offer clear advantages in efficiency, stability, and reusability. In many laboratory and engineering scenarios, Haytham virtual strain gauges can directly replace contact strain gauges as the preferred solution: faster preparation, more complete data, a more stable process, and a longer value cycle.

Frequently Asked Questions (FAQ)

Q1: Do virtual strain gauges require bonded sensors?

A: No. A virtual strain gauge is a "virtual measurement point" computed from images, with no bonding or wiring required.

Q2: Can measurement points still be added after the experiment is over?

A: Yes. Virtual measurement points can be added or moved on the same image data at any time, supporting multiple rounds of recalculation and audit.

Q3: Is it suitable for dynamic/high-speed testing?

A: Yes. The system captures strain evolution in real time under conditions such as vibration and impact; image and mechanical data can be analyzed in sync.