Dynamic Stress & Strain Measurement

Understanding the origin of the stress and strain distribution is crucial to increasing the durability of components under dynamic load. Numerical simulations based on finite element (FE) models help with this understanding but must be validated by real component data. Polytec’s 3-D Scanning Laser-Doppler Vibrometer with StrainProcessor provides an advanced, non-contact optical test solution.

Polytec’s StrainProcessor is a measurement extension developed for easy FE model updating and for comparisons to calculated stress and strain distributions. It comprises a set of hardware and software components enabling a PSV-400-3D Scanning Vibrometer – a well established tool for full-field non-contact vibration mapping – to measure and analyze the dynamic strain and stress distribution on surfaces with high resolution and low noise.

The Scanning Vibrometer makes a series of non-contact deflection measurements on a predefined grid using the laser probe to characterize strain at each point instead of attaching individual strain gauges. Thus, the test set-up is fast and very repeatable with no mass loading from an attached transducer. Tests are fast and avoid the high cost of preparing and instrumenting the sample with strain gauges.

Benefits

Full-field method: direct visual comparison to FE results
Safe method: high spacial distribution to measure the location of maximum strain
Quick setup and fast results
Non-contact probe
No mass loading, stiffening and damping
High spatial resolution at no additional cost
Variable field-of-view for different object sizes
Measure using arbitrary points or FEM geometry for model validation

The Strain Extension consists of a set of hardware and software accessories to enable a PSV-400-3D or PSV-400-3D-M Scanning Vibrometer to precisely measure the raw data (displacement) and post process this data into a full-field strain distribution.

The StrainProcessor

Simply put, the PSV-400-3D acts as a full-field vibration measurement system. The Scanning Vibrometer PSV Software calculates the three-dimensional vibration vector from the raw data. Strain is processed from the displacement data using the StrainProcessor software package, a stand-alone software with a direct data interface to PSV software.

Strain is calculated by placing virtual strain gauges at each edge of a triangulated measurement grid. The distribution of the strain values is displayed and animated as a color-coded map. Stress distributions are calculated from the strain distributions for isotropic materials.

In order to achieve good quality input data, the Strain Extension supports the operator with specially designed accessories:

Software Option for PSV Software (version 8.6 or higher) optimizing the measurement point geometry with the PSV-400-3D and PSV-400-3D-M by image processing. Boosts the accuracy of the geometry measurement of the Geometry Scan Unit PSV-A-420 especially for small objects, for high-frequency measurement and for strain measurement. With small objects and in conjunction with the optional external A -CAZ-1000 high-resolution video camera the performance is high enough to replace the Geometry Scan unit.

The precision of the PSV-400-3D and PSV-400-3D-M is determined not only by the precision of the sensor, but also by a precise definition of the position of the three sensor heads in space. The procedure to acquire this specific information, called 3-D alignment, is supported for high-precision or high-frequency measurements by this reference object. It features a tripod adapter for VIB-A-T02 tripods for convenient positioning and adjustment in front of the actual measurement object.

Precisely machined and marked reference points with known coordinates and a well-balanced distribution of these marks in space allow a precisely defined basic alignment of the PSV-3D measurement system for perfect results.

External digital camera with macro zoom lens for the PSV-400-3D and PSV-400-3D-M. Allows precise measurement point definition on small samples. Provides higher resolution than the internal camera of the PSV-I-400 for small objects and short working distances.

Resolution 1034 x 779 pixels
monochrome
C-mount
1/4" thread adapter for tripod mounting

Includes a 1/3" C-mount macro zoom lens

Focal length 8.5 mm - 90 mm
Minimum working distance 178 mm
Smallest field-of-view 6 x 8 mm

Mounting adapters are provided also for the tripod systems PSV-A-T31 and PSV-A-T34 tripod systems.

Rigid support for three PSV-I-400 scan heads. The angle between the scan heads is optimized and balanced for resolution of all vibrational components (in-plane and out-of-plane). Support for A-CAZ-1000 camera.

The tripod is an essential accessory for the measurement of small parts and very helpful for dynamic strain measurements with the PSV-400-3D.