Tinius Olsen have introduced the next generation of extensometry technology – their new video extensometer, the VEM Series.
The instrument, which is available in both single and multi camera systems, is designed to measure low levels of strain from 0.01% in tensile, compression, shear and flexural modes. It utilises high resolution monochrome cameras, with advanced high-speed image processing, which added to the inclusion of cool lighting, allows point to point real-time video processing capable of exceeding ASTM E83 Class B1 and ISO 9513 Class 0.5 accuracy.
“The system works by acquiring an image of the test sample with the VEM’s pattern recognition technology locking onto two targets creating a gauge length, which can be set as required by the user,” said Martin Wheeler, Director of Sales and Business Development.
“As the specimen is tested, software tracks the point to point movement of the two targets from camera frame to camera frame, allowing the strain data to be calculated in real time. Multiple gauge lengths are possible in both longitudinal and transverse directions, allowing the determination of r and N values.”
The required high resolution of the VEM system needed to calculate these results is achieved through sub-pixel interpolation algorithms, allowing the system to resolve to micron levels of movement. All measurements and outputs are time stamped and can be archived for later reference. The uncompressed video output can be recorded for post-test measurements and analysis.
An integral lighting strip guarantees repeatability in tests regardless of lab conditions yet requires no special light sources or red colours, being easily regulated by the user modifying intensity as required, to guarantee a stable light environment.
These adaptable extensometer modules are available in a range of different performance configurations each compatible with Tinius Olsen’s Horizon and VSS materials testing software, whether the Basic, Standard, or Advanced option.
The VEM is available in two different versions for either low or high extension materials, which is achieved by the selection of specific high resolution lenses. The low extension system utilises a small field of view lens, which is designed specifically for low strain measurements, whereas the high extension version is supplied with a general purpose lens, giving a field of view of up to 1,000 mm.
This range of technology provides video extensometry for almost every type of application, including composites, metals inclusive of thin wire, textiles and plastics.
“The precise camera, lens and data acquisition technology delivers zero gauge length error every time and rapid application of gauge marks, including for the measurement of rotation (to monitor specimen alignment) during testing. Calibration is digitally embedded but, for reassurance, can be verified at any time using the standard traceable gauge block supplied,” continued Mr Wheeler
Further enhancement of the system can be achieved by utilising multiple cameras for more demanding applications, such as thin wire and composites. The system software can track patterns from up to eight individual cameras, with eight different lenses.
Tinius Olsen Horizon software utilises data from the materials testing lens for the initial linear section of the stress/strain graph then switches to the camera with the general purpose lens for the rest of the test. This ensures the highest possible quality data to be used.
The VEM Series is also directly compatible with the entire range of Tinius Olsen testing machine frames. It is mounted using a stabilised carbon fibre arm with integrated X, Y and Z fine positioning adjustment for optimum measuring performance.
“The units are completely combined with the testing machine and result-reporting software, supporting strain rate control, many gauge length click-and-drag placements, and real-time results during and throughout the test.”
“Where the new system really excels however, is by the optimising of productivity through speed of use, thus enhancing repeatability as well as aiding traceability via the embedded strain data video stored as part of the results data set.”