An incorrectly loaded specimen* or aligned load string** can induce bending in a specimen. This misalignment will have an effect on the results generated.
The Instron averaging axial extensometer measures strain on both sides of the specimen to provide more accurate determination of material properties particularly modulus of elasticity.
* Instron recommend specimen alignment fixtures are used where possible
** Instron supply alignment fixtures and cells to enable adjustment of specimen bending in the load string
If a material is stressed in the axial direction it is highly likely to show contraction in the transverse direction. In many materials, Poisson's ratio has been used to improve engineers understanding of the mechanical properties to aid in the manufacture of components.
The difficulty with Poisson's ratio is ensuring your device has the accuracy and resolution to measure very small changes in transverse strain. This is evident in today’s unidirectional composite materials.
The Instron biaxial extensometer can either average strain from two sides of the specimen or produce two independent axial strains along with measuring transverse strain to determine either Poisson's ratio and in-plane shear modulus.
These biaxial and averaging axial clip-on extensometers use strain gauges for measurement and are constructed from high-strength aluminum, titanium, and stainless steel. All of the extensometers feature simple, single-handed operation.
The extensometer incorporates automatic electrical calibration and transducer recognition including a unique digital serial number.
All of the extensometers measure the axial strain on both sides of the specimen. Versions are available that provide either a single averaged axial strain output or two independent axial strain outputs. In all cases, the use of average axial strain corrects for any specimen bending due to misalignment for the consistent and accurate determination of modulus. The independent output versions allow simultaneous monitoring of both; the average axial and the bending strain.
Additionally, the biaxial versions measure transverse strain that allows for the determination of Poisson’s ratio and the in-plane shear modulus.
Conical points are provided as standard with the extensometer and are recommended for most composite materials.
A range of contact options are available: line contacts, which are recommended for use with soft materials, such as thermoplastics; and vee profiles, which are most suitable for thin section test pieces.