Materials Mechanics
Monocular 3D Video Extensometer
I. What Is an Extensometer?
An extensometer is a dedicated sensor in material testing that measures deformation/strain within the specimen gauge length. It converts the tiny displacements during tension, compression, bending and torsion into recordable data, used to compute key indicators such as stress-strain curves, elastic modulus, yield strength and r-value/n-value.
II. Mainstream Classification by Measurement Method
1) Contact extensometers
Clamp-on knife-edge (Clip-on):Clamped on the specimen by knife edges; displacement is converted by mechanical structures/strain gauges/LVDT, etc.
Advantages: high precision, wide adaptation to standard metal materials; limitations: moderate friendliness to thin/brittle/soft materials, susceptible to installation force, friction and alignment; dedicated models needed for high temperature.LVDT / inductive contact extensometer:a movable iron core converts displacement into voltage change; advantages: good linearity, anti-interference; limitations: requires stable clamping and alignment, frequency response affected by the mechanism.
Transverse/bidirectional extensometer:Adding transverse gauge measurement (e.g. Poisson's ratio, reduction of area), mostly used for evaluating the plastic stage of metals.
2) Non-contact extensometers
Laser extensometer:：A laser tracks the relative displacement of two markers.
Advantages: non-contact, friendly to fragile/high-temperature surfaces; limitations: sensitive to surface reflection, smoke and window interference, mainly point measurement.video extensometer（DIC）：A camera captures images, tracks speckles/markers through the digital image correlation (Digital Image Correlation) algorithm, and computes displacement and strain.
Advantages: non-contact, few restrictions on specimen shape; simultaneous axial and transverse multi-gauge measurement, expandable to full-field displacement/strain contour maps; mature solutions for high/low temperature, large strain, fatigue and other conditions.
Common forms: 2D, 3D (single-camera 3D or stereo 3D), high-temperature video extensometers, and dedicated models for high-speed/fatigue scenarios.
Summary: for standard metal tension at room temperature with ordinary frequency, both contact and non-contact types are viable; for high/low temperature, soft/thin/brittle materials, complex curved surfaces, large strain and cross-cycle fatigue, non-contact types (especially video extensometers/DIC) offer better adaptability and scalability.
III. Segmentation by Application Environment/Working Conditions
High/low-temperature extensometer:For tests inside environmental chambers, consider window material/size, thermal radiation interference, filtering treatment and marker heat resistance.
Large strain/rubber and films:Traditional clamp-on types fall off or scratch easily; DIC or laser types are more suitable; pay attention to gauge length selection and speckle pattern quality.
Fatigue/high-frequency loading:Focus on sampling frequency, synchronization method, filtering and cross-cycle data capture capability.
Irregular/multi-axis deformation:DIC can perform joint multi-gauge and full-field evaluation, assisting failure mechanism analysis (crack initiation/propagation, necking-area strain concentration, etc.).
IV. Selection Key Points and Practical Checklist
Specimen and gauge length:Thick/thin, brittle/soft, width and expected necking; gauge length and fixture interference.
Strain range and accuracy:Elastic-stage accuracy, plastic-stage stability, and whether class 0.5 regulatory compliance is needed.
Environment:Whether it is high/low temperature, whether observation through a window is needed, and whether there is strong radiation/smoke.
Frequency:Static/quasi-static/fatigue, sampling and communication delay requirements.
Measurement dimensions:Axial/transverse/multi-gauge/full-field; whether r-value/n-value and reduction of area are needed.
System integration:Force-displacement-strain synchronization with the testing machine, communication protocols, and software output (curves/reports).
V. Product Introduction: Haytham Video Extensometer
The Haytham video extensometerBased on single-camera 3D DIC technology, it is a non-contact video extensometer. It supports laser focusing, embedded software and delay-free communication, and can output stress-strain curves synchronized with the testing machine force; it also supports axial and transverse multi-gauge measurement, with an optional full-field displacement/strain module. It is compatible with most materials and shapes (plates, rods, films, soft materials, etc.), suitable for high/low-temperature environments and cross-cycle fatigue data acquisition; it meets the JJG762-2007 class 0.5 accuracy requirement and covers multiple models from 2D to 3D and high-temperature scenarios.
(For specifications, gauge lengths and compatible window sizes, match the corresponding model and optical configuration according to specific test conditions.)
VI. Frequently Asked Questions (FAQ)
Q1: How to choose between a video extensometer and a laser extensometer?
Laser leans toward point-to-point displacement measurement with simple installation; beyond point measurement, the video extensometer can extend to multi-gauge and full-field contour maps, and is more flexible in complex surfaces, large strain, high/low temperature and fatigue scenarios.
Q2: Can a Video Extensometer Measure Poisson's Ratio / Reduction of Area?
Yes. Through combined axial plus transverse measurement and multi-gauge schemes, Poisson's ratio and reduction of area can be obtained; the full-field module also helps locate strain concentration and crack propagation.
Q3: Do high- and low-temperature environments affect measurement?
Yes, but stability can be ensured through temperature-resistant speckle/markers, filtering and imaging path optimization, and window size matching; high-temperature dedicated video extensometers also integrate radiation-resistant optics and image processing modules.
Q4: Is Calibration Needed? How to Synchronize with the Testing Machine?
A mature video extensometer solution provides a standardized measurement process and delay-free communication with the testing machine; at selection, just confirm the synchronization method, data interface and software reporting requirements.
VII. Applicable Scenarios at a Glance
Testing inside high/low-temperature environmental chambers (tension, compression, bending, torsion)
r-value/n-value, Poisson's ratio,Reduction of areaand crack propagation analysis
Mechanism research requiring multi-gauge/full-field contour maps
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