Laser Scan Micrometer Aids Fibre Testing

10 December 2004

Dia-Stron a developer of miniature, automated fibre-strength testing machines, uses a Mitutoyo laser scan micrometer system to help rapid evaluation of the tensile properties of Kevlar, cotton, hair, carbon fibre and other fibres as thin as 5um.

Testing the mechanical properties of various types of fibre is important for composite processing as it provides consistent, reliable data.

Dia-Stron's FDAS fibre dimensional analysis system provides a fully automated fibre-diameter measuring capability to submicron resolution and so allows an accurate Cross Sectional Area (CSA) to be calculated. Accurate tensile strength properties can be derived using the company's MTT175/675 Series miniature tensile testers.

The FDAS system uses the same method of premounting fibre samples in PVC-lined brass ferrules as is used with the tensile testers, allowing fibres to be directly transferred between the FDAS and the MTT675 tensile tester, resulting in a reduction in the batch processing time from days to just a few hours.

The huge increase in efficiency associated with automated sample handling and state of the art measurement systems is driving expansion into applications in the textile, polymer, renewable fibre and carbon fibre industries.

Key parts of the FDAS are a Mitutoyo LSM-500H laser scan micrometer measuring unit and associated LSM-6100 multifunction display unit. This is an automated, non-contact measuring system for measuring thin fibres and coatings.

The principle of operation is that a laser beam, rapidly swept through a 2mm-wide band, detects the size of any object obstructing the beam in the direction of sweep. The system can be configured to measure outside diameters, or gaps, to a resolution of 0.01um at an accuracy of 0.4um and transfer data to a PC via an RS-232C port. A fibre sample can be measured at just one point along its length, or divided up and scanned in 24 x 1mm slices.

An optional version of the FDAS has the sample suspended within a chemically inert tank so that it can be measured while immersed in various solutions to investigate changes in CSA over time due to chemical treatment.

A crucial ability of the FDAS is the sample rotation feature, which allows a more accurate measurement of CSA by rotating a sample in the laser beam while taking multiple measurements at predetermined angles. Dr Nigel Winsey, Dia-Stron Director, said that the individual human hair varies in diameter along its full length. The cross section is more or less elliptical depending on the ethnic origin of the fibre, resulting in a single reading not giving a true measurement of the cross sectional area. This measurement is only possible with a laser instrument, as a hair tends to rotate to the position of least diameter between the anvils of a conventional micrometer.

Once scanned in the FDAS, the sample is automatically transferred to an MTT175/675 machine for tensile testing.

Dia-Stron's UvWin PC software processes the FDAS data to determine the actual CSA of each sample and, combining this with the tensile breaking force-strain data, produces a complete stress-strain analysis report for the whole batch.

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