A minicomputer-controlled all-digital tensile test system

Abstract

This paper presents the design, construction, and evaluation of an all-digital programmable tensile test system, superior in several ways to other systems presently available for testing yarns. However, the basic system concepts can be applied to tensile test systems for other materials. The system is capable of performing three standard yarn tests: constant rate of extension, constant rate of loading, and fatigue. Extension rates range from 1 mm/s to 420 mm/s. Loading rates of up to 700 g/s and above are possible. Fatigue testing allows sinusoidal loading of yarn at frequencies from 0.88 to 5.2 Hz. A minicomputer is used for direct digital control, data acquisition, and on-line analysis. A digital tension mechanism incorporating a variable-reluctance step motor was designed and constructed. A "fractional stepping" scheme is presented where the computer software is used to improve the displacement resolution for slow-speed breaks. A unique indirect digital force transducer was designed for the system employing transistor-transistor logic integrated circuits. The interrogation rate is 7 kHz, the load range is 0-700 g, and resolution for the present design is 4 g. Final testing of the digital system involves the comparison of test results with those from a proved programmable analog tester. The three types of tests produced good results and show that the digital test system does characterize yarn break strength for different types of yarn. It overcomes many disadvantages of analog systems and performs certain tasks which these systems are unable to perform.