A METHOD OF HEAT TREATMENT AND/OR INSPECTION OF FUNCTIONAL MECHANICAL PROPERTIES, PARTICULARLY TRANSFORMATION STRAIN AND/OR STRENGTH, OF SHAPE MEMORY ALLOY FILAMENTS AND APPARATUS FOR THE APPLICATION OF THIS METHOD

摘要

This invention introduces a method and equipment for nonconventional thermo-electro- mechanical treatment of continuous and discontinuous SMA filaments, particularly NiTi, allowing for setting their functional mechanical properties, particularly transformation strain and/or strength, as required by the user. Heat treatment of continuous SMA filaments is realized on an apparatus consisting of respooling system with driving units for feeding and taking spools and at least two electrical contacts allowing conductive for electrical contact of the respooled filament and electric current source. When applying the method, an effective filament temperature is first evaluated from the interpolated experimentally determined dependence of transformation strain and/or strength of the filament achieved by range of heat treatments characterized by various effective filament temperatures and tensile stress. Heat treatment is then performed by supplying the electric power calculated from this effective filament temperature to the segment of the treated SMA filament. Heat treatment can also be performed utilizing on-line control of the supplied electric current in a feedback to the on-line measured filament temperature and/or change of electric resistance before and after the treatment. Compared to currently used conventional heat treatment of SMA filaments in environmental furnace, the filament treated by the present method is exposed to much higher temperatures for much shorter time allowing for efficient, less energy consuming and compact heat treatment of continuous SMA filaments for applications in technical textile production. Functional mechanical properties different from those achievable by conventional heat treatment can be given to the treated SMA filaments. In addition, this invention introduces a method for inspection of the homogeneity of continuous SMA filaments consisting in measurement of the electrical resistance, temperature and/or characteristics of the ultrasonic signal passing through the filament during respooling. The homogeneity of the SMA filament is evaluated as the deviation of the actually measured value of one of these quantities from the expected value. The method is realized on apparatus with respooling system and sensors of the above introduced signals.