NONCONTACT MICROSTRAIN MEASUREMENTS IN ORTHODONTIC WIRES

A technique is presented that allows for highly sensitive and highly a ccurate measurements of microstrain in biomaterials. It is particularl y useful for measuring strains in materials where the use of conventio nal extensometers or strain gauges is impracticable, such as in reinfo rcement fibers and orthodontic wires and in hostile environments. The technique is based on the well known technique of observing translatin g laser speckle with a linear-array charge-coupled device (CCD) camera . However, it employs a relatively new data processing algorithm invol ving a two-dimensional frequency transform of the data. Advantages of the technique include: insensitivity to slow surface microstructure ch anges, insensitivity to zero-mean noise processes, compact design, mod est resolution requirements, and the fact that it is truly noncontact. Strain rate measurements were made on an 0.028-gauge round stainless steel orthodontic wire as an example of this technique. The Young's mo dulus of the wire based on the speckle technique was 2.04 x 10(11) Nm( -2), which is very close to the textbook value. (C) 1995 John Wiley & Sons, Inc.