Digital Image Correlation (DIC)

Capture random speckle patterns on the surface of an object through a high-resolution camera, compare the differences in images before and after loading, and calculate displacement and strain fields.

3D measurement: At least two cameras are required to simultaneously capture images from different angles and reconstruct 3D deformations using stereo vision technology.

Optical interferometry

Like the multi-channel heterodyne interferometry method, which uses the principle of laser interference to measure small displacements, it has high sensitivity and anti-interference ability.

Multi degree of freedom decoupling: By designing the optical path and analyzing the phase, different degrees of freedom deformations (such as axial translation and angular deflection) can be distinguished.

System Composition

Hardware: laser light source, optical components (beam splitter, reflector), high-precision camera, image acquisition card.

Software: Speckle matching algorithm, phase processing program, 3D reconstruction and visualization module.

2、 Deformation judgment method

The system determines the type and degree of deformation through the following steps:

Threshold setting and anomaly detection

Set displacement/strain thresholds based on material properties or safety standards, and trigger alarms when real-time monitoring data exceeds the threshold.

Dynamic threshold adjustment: Combining historical data with machine learning algorithms, adaptively optimizing thresholds to adapt to complex working conditions.

Multi degree of freedom decoupling analysis

Geometric modeling: Establish a mathematical model of the measured object and clarify the coupling relationship between each degree of freedom.

Decoupling algorithm: Separate independent deformation components such as translation and rotation through simultaneous equations or matrix operations.

Example: In telescope mount testing, the system needs to distinguish the axial translation (Δ z), lateral offset (Δ y), and rotation (Rx) of the primary and secondary mirrors to avoid coupling errors.

pattern recognition

Using spectral analysis or wavelet transform to identify deformation characteristics (such as vibration frequency, modal shape).

Fault diagnosis: Compare normal and abnormal deformation patterns to determine the structural health status (such as crack propagation and loosening).

3、 Deformation calculation method

The system achieves accurate calculation of deformation parameters through the following process:

data preprocessing

Image denoising: Gaussian filtering or non local mean denoising is used to improve the clarity of speckle patterns.

Speckle optimization: Enhance speckle characteristics through sub-pixel interpolation or morphological operations.

Displacement field calculation

DIC algorithm: based on zero normalized cross-correlation (ZNCC) or iterative least squares method, matches speckle sub regions.

3D reconstruction: Combining binocular vision principles, convert 2D displacement into 3D spatial coordinate changes.

Strain field calculation

Numerical differentiation: Using displacement field data, calculate the strain tensor through least squares method or local weighted regression.

Principal strain analysis: Extract the maximum/minimum principal strain and direction to assess the risk of material failure.

Multi degree of freedom coupling correction

Error compensation: Combining finite element analysis (FEA) to estimate coupling errors and correcting measurement results through backpropagation algorithm.

Real time calibration: dynamically adjust optical parameters (such as lens focal length and light source intensity) during the testing process to ensure measurement accuracy.

Result visualization and output

Deformation cloud map: Display displacement/strain distribution in pseudo color, visually showing deformation hotspots.

Time history curve: Record the changes in key point deformation over time and analyze dynamic responses (such as vibration attenuation and impact response).

4、 Application scenarios and limitations

Typical Applications

Aerospace: wing aerodynamic elasticity testing, rocket engine thermal deformation monitoring.

Civil Engineering: Modal Analysis of Bridge Vibration, Slope Stability Assessment under Earthquake Simulation.

Biomechanics: Compression testing of articular cartilage, biocompatibility evaluation of implants.

Limitations and improvement directions

Environmental interference: Temperature fluctuations and air disturbances may introduce measurement errors.

Solution: Adopt vibration isolation platform, temperature control cabin or environmental compensation algorithm.

Computational complexity: Massive amounts of data (such as high-speed videos) require high-performance computing resources.

Optimization direction: GPU acceleration, distributed computing, or edge AI processing.

Surface requirements: Smooth or reflective surfaces require additional treatment (such as spraying matte paint).

Alternative solution: Utilize natural texture of materials or laser-induced speckle.

The multi degree of freedom full field deformation testing system achieves high-precision and full field measurement of complex deformations through optical measurement and intelligent algorithms. Its judgment and computing capabilities rely on advanced optical path design, speckle matching technology, and multi degree of freedom decoupling algorithms, which are widely used in scientific research and industrial fields. In the future, with the integration of computational optics and AI technology, the system will further enhance automation and measurement efficiency, providing stronger support for structural health monitoring under working conditions.