In situ biaxial mechanical testing systemIt is a mechanical testing device that can apply bidirectional independent loads to samples and simultaneously observe the microstructure evolution of materials. The core consists of a loading system, an in-situ characterization module, and a measurement and control system, suitable for studying the mechanical behavior of materials under complex stress states.
1、 Loading system: achieve bidirectional independent and precise force application
Drive structure
The system usually adopts a four column symmetrical layout, equipped with two independent servo drive units (servo motor+ball screw/hydraulic cylinder), which control the cross shaped sample fixture in X and Y directions respectively.
There are two types of dual axis loading modes:
Proportional loading: The load/displacement in the X and Y directions are synchronously applied according to the preset ratio, simulating the stress state of equibiaxial and eccentric biaxial;
Non proportional loading: Independent control of load/displacement in the X and Y directions, which can achieve complex paths such as sequential loading and cyclic loading, and restore the actual working conditions of the material under stress.
Fixture and Sample Design
The samples often adopt a cross shaped structure to avoid stress concentration at the clamping end of uniaxial samples and ensure that the testing area is in a uniform biaxial stress field. The fixture is equipped with a self-locking device to prevent slipping during the stretching process of the sample, while reducing the interference of fixture deformation on the test results.
2、 In situ characterization module: synchronous observation of microstructural changes
The core advantage of "in-situ" lies in the synchronization of mechanical loading and microscopic characterization. Common integrated modules include:
Optical observation module: equipped with high-speed cameras and digital image correlation (DIC) systems, by spraying speckle on the surface of the sample, the strain distribution, crack initiation and propagation trajectory of the test area are captured in real time, and the elastic modulus, Poisson's ratio and other parameters of the material are calculated.
Electron microscopy module: integrating scanning electron microscopy (SEM) or electron backscatter diffraction (EBSD) devices, loading the sample in a vacuum environment, observing micro behaviors such as grain slip, twinning evolution, dislocation motion, etc., and establishing the correlation between macroscopic mechanical properties and microstructural changes.
Special Environment Module: Optional high and low temperature chambers, constant temperature water baths, corrosion chambers, etc., simulate high and low temperatures, physiological environments, corrosive media and other working conditions, and study the influence of environmental factors on biaxial mechanical properties.
3、 Measurement and Control System: Ensuring Accurate and Controllable Testing
control unit
Adopting a closed-loop servo control system, real-time load, displacement, and strain data are collected through force sensors, displacement sensors, and extensometers. After comparing with preset target values, the output of the servo drive unit is automatically adjusted to achieve flexible switching between force control, displacement control, and strain control modes.
Data processing unit
The system is equipped with built-in data acquisition and analysis software, which can record real-time biaxial load displacement curves, strain distribution cloud maps, microstructure images and other data, and automatically generate test reports, supporting data export and further analysis.
4、 Core workflow
Clamp the cross shaped specimen, adjust the fixture position according to the test requirements, set the loading mode (proportional/non proportional), loading rate, and target load/displacement;
Start the in-situ characterization module (such as DIC, SEM) and complete the calibration before testing;
The measurement and control system drives the biaxial loading unit to apply force, synchronously collecting load, strain data, and microstructure images;
After the experiment is completed, the system automatically integrates data and outputs the mechanical performance parameters and microscopic evolution laws of the material under biaxial stress state.