laserXtens HP Extensometer Offers High-Precision Measurement

laserXtens consists of two measuring heads with digital cameras and laser light sources mounted on motorized slides. 

  • The distance between the cameras can be varied, allowing different initial gage-lengths to be set.
  • laserXtens systems feature a resolution of 0.11 µm, making measurements on small specimen geometries easy.
  • Flexibility and ease of operation make laserXtens equally suitable for classical quality assurance applications or for use in research and development.
  • The specimen is illuminated with laser light, generating a speckle pattern on the surface.
  • Tunnels of different lengths are used to minimize environmental influences (e.g. air currents). 
laserXtens + laserXtens HP Extensometer

Overview of laserXtens Systems

Application description

Extensometers using laserXtens systems provide non-contact measurement of deformations on a wide range of materials.

The measuring principle eliminates the need to apply gage marks, giving laserXtens systems a wide range of application.

  • Tensile, flexure and compression tests on metals and plastics.
  • Tests on components.
  • Tests on specimens where specimen contact is undesirable or not possible due to specimen condition or properties.
  • Deformation measurements on specimens prone to whipping at break which might damage a contact-type measuring system.
  • Testing possible in temperature chambers and at high temperatures.
  • Applications requiring biaxial deformation measurement.

With laserXtens high-resolution systems, measurements on small specimen geometries are easy. Flexibility and ease of operation make laserXtens equally suitable for classical quality assurance applications or for use in research and development.

Advantages and features

  • High precision and resolution
  • laserXtens possesses high precision in the micro and macro measurement ranges.
  • laserXtens HP satisfies the requirements of Class 0.5 of ISO 9513 (Class B2 of ASTM E83).
  • Even the smallest specimens can be measured
  • Specimens from 1 mm in width/diameter can be tested; smaller specimens may also be possible following pre-testing.
  • In contrast to contact-type extensometers or pure video instruments, laserXtens can measure strain on short specimens (gage lengths from 1.5mm) with high accuracy.
  • No specimen contact - no specimen marking
  • laserXtens has no contact with the specimen; measurement is not influenced by the laser light.
  • Specimen marks are not required. This saves time, especially with high specimen throughput.
  • laserXtens can be mounted at varying distances from the specimen. One advantage of this is that it can be used in temperature chambers, where application of gage marks can be very difficult due to environmental conditions.
  • Easy to use in automated systems also - no manual specimen preparation required.
  • laserXtens can also measure transverse strain with no need for additional markings; biaxial measurement is possible.
  • Unrivaled functions and options
  • laserXtens HP can be used for strain-rate-controlled tests to ISO 6892-1 Method A1 (closed loop) (for gage lengths ≥ 50 mm).
  • laserXtens Array HP can be used for strain-rate-controlled tests to ISO 6892-1 Method A1 (closed loop) (for gage lengths ≥ 30 mm).
  • Optional upgrade for determination of r & n-values to ISO 10113 and ISO 10275.
  • laserXtens is integrated into testXpert II testing software. Use of a separate monitor is recommended to enable the live image from laserXtens to be observed parallel to the testXpert II display.
  • Matrix option allows two-dimensional measurement at up to 100 measuring points distributed arbitrarily or in matrix form over a planar specimen surface. This enables determination of local strains and specimen inhomogeneities.
  • Another software option allows determination of strain distribution at multiple measuring points along the specimen gage-length. It is also possible to determine strain at break as per Annex H of ISO 6892-1 (laserXtens Compact and laserXtens Array HP only).
  • Specimen deflection can optionally be deternined in 3 and 4-point flexure tests. Measurement can be carried out at one or three points (with a maximum measurement base of 15 mm).

Specimen range

laserXtens
  • The following specimen types can be tested using laserXtens:
  • All types of flat specimens made of plastic and rubber with a thickness of 0.5 to 12 mm
  • Flat specimens made of metal with a thickness of 0.1 to 30 mm
  • Round specimens made of metal with a diameter of >1 mm to 30 mm

laserXtens systems consist of measuring heads with digital cameras and laser light sources.
The specimen surface is recorded by full-frame digital cameras. The specimen is illuminated with laser light. The laser light is dispersed on the specimen surface. the specimen surface appears with a speckled pattern in the video frame of the camera.

An evaluation window is positioned within the overall image (= field of view) of a camera. The speckled pattern within this evaluation window is like a type of fingerprint of the specimen surface. It is known as a virtual gauge mark. When a load is applied to the specimen, the virtual gauge marks move. The laserXtens tracks these virtual gauge marks using the highly developed correlation algorithm. This process is known as speckle tracking.

laserXtens' software calculates the strain on the specimen from the relative displacement of the virtual gauge marks.

Important notes

laserXtens was developed for use with a majority of the classical materials and testing requirements.

Various physical considerations mean that reliable operation of laserXtens requires observance of a greater number of general conditions than when using contact-type extensometers.

  • The specimen surface must reflect enough laser light to generate sufficiently well-formed speckle patterns. This is the case with most metals and plastics. If necessary simple aids can be used to improve conditions on the specimen surface.
  • The specimen must be fixed firmly in the center of the test axis in order to minimize movement out of the measurement axis.
  • A low-vibration environment is necessary for safe, reliable, accurate operation (laboratory conditions).

All specimen gripping systems which hold the specimen firmly in the center of the test axis are suitable, e.g. hydraulic, pneumatic and screw grips.

In the case of plastics, pre-testing is necessary to determine the reflective properties of the material.

Pre-testing also allows the Zwick Testing Laboratory to assemble the optimum configuration for your particular application. The properties and condition of the specimen surface (reliable measurement signal, resolution), the specimen grips in use (elimination of out-of-plane movement) and the measurement travel required are all checked. Zwick guarantees reliable operation of laserXtens on the basis of pre-tested specimens and testing conditions (= process reliability).

Notes on use with temperature chambers and high-temperature furnaces

When laserXtens HP and laserXtens Array HP are used in conjunction with temperature chambers and high-temperature furnaces it should be noted that the change in optical conditions for testing will have a negative effect on the measurement signal. This basically concerns air currents in the temperature chamber / furnace and outside on the viewing port / furnace port. To minimize these effects the air flow around the specimen must be smoothed and the air currents near the viewing / furnace port minimized by means of optical tunnels. These solutions are designed and produced on a custom basis. Due to the dimensions of the temperature chamber, laserXtens is in this case mounted at a greater distance from the specimen, with consequent changes in resolution and accuracy class (technical details available on request).

Technical Overview

laserXtens High Precision

laserXtens HP

  • laserXtens extensometers for mounting on an AllroundLine testing system
  • Measuring head with motorized gage-length adjustment (automatic L0setting), 2 digital cameras incl. f = 75 mm lenses, 2 red laser light sources, software for image acquisition, evaluation of cross-correlation and transfer to testXpert II, accessory case with calibration tools
  • 2 tunnels are additionally supplied with laserXtens HP to reduce external influences such as air currents (short/long tunnel: 226 mm/100 mm, clear path from end of tunnel to test axis).

Type

laserXtens HP

Item No.

1001638

Laser safety class

2[1]

Initial gage length

3 to 200

mm

Measurement travel with speckle tracking

  • 40 mm with gage length of 20 to 200 mm (max. 220 mm minus gage length)
  • 20 mm minus gage length of 3 to 20 mm

Measurement travel flow measurement

After measurement travel via speckle tracking, laserXtens switches to flow measurement.

Strain control as per ISO 6892-1 Method A1

from 50[2]

mm

Resolution

0.11[3]

µm

Accuracy

Class 0.5

to EN ISO 9513

Typical measurement frequency (adjustable)

70

Hz

Max. measurement speed at measurement point

500

mm/min

Specimen thickness

flat specimens, measured on the broad side

≤30

mm

flat specimens, measured on the specimen edge

>1[4]

mm

round specimens

1 to 30[4]

mm

  1. No protective measures required.
  1. testXpert II V 3.3 or above required
  1. At specimen distance 380 mm
  1. Pre-testing is required for specimens with thickness < 1 mm.

laserXtens HP operates with testXpert II (Version 3.2 onwards) and in combination with testControl/testControl II.

A free slot is required in testControl II.
The required INC module is already included in delivery.

Software Options for the laserXtens Extensometer

Strain distribution

The Strain Distribution option enables determination of local strains at multiple measuring locations along the specimen gage-length. Evaluation of up to 16 measuring locations is possible. This option also allows automatic real-time symmetrical adjustment of the initial gage-length around the necking (as per ISO 6892-1, Annex H).

Second measurement axis

This option allows local transverse strain to be measured simultaneously with determination of longitudinal strain.

2D dot matrix

This option allows two-dimensional measurement of dots on a planar specimen surface. This enables determination of local strains and inhomogeneities of the specimen under load. X and Y co-ordinates plus the distances between dots are available as measured values.
Up to 100 measurement dots can be measured in any desired arrangement or in matrix form. Display in testXpert II is limited to 15 channels.

Deflection

laserXtens also determines deflection in 3 or 4-point flexure tests. This can be measured at one point (displacement of one measurement location) or three points (relative displacement of the middle or two outer measurement locations) with a maximum measurement base of 15 mm (20 mm for laserXtens Array HP).

Siemens opts for optical strain measurement by Zwick

Siemens’ customers in the power generation sector have access to a complete spectrum of products, services and solutions for power generation and distribution. Key products in this area include steam turbines and steam-powered generators, together with gas turbines. The high operating temperatures and pressures involved place special demands on materials testing, for which Siemens relies on high-temperature testing solutions by Zwick.
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