Dynamic Mechanical Spectroscopy Using the Autovibron DDV-III-C

Abstract

This-document has been approved for public release; its distribution is unlimited. The Autovibron DDV-IIIC (IMASS, Inc.) is a forded vibration unit capable of operating at several constant frequencies for the determination of the dynamic mechanical response of a system. The automation provides a programmed heatine rate, continuous sample tensioning, and acquisition and reduction of data. Recently a generally similar adaptation has been introduced, based on the hydraulically operated Rheovibron DDV-III-C. Automation of a resonance-type (7) and a different constant frequency instrument(8) have also been described. DISTRIBUTION STATEMENT (of the abstract enteredWhile a full critical analysis of the operation of the Autovibron DDV-III-C has not yet been possible, it is appropriate to describe our experience with this new instrument, and to make preliminary recommendations with respect to operation and future improvement. Since the instrument is the first of its type, the observations reported should be helpful to other investigators. Results obtained in our laboratory using an automated DDV-II are also described for comparison. Temperature programming is effected through the calculator in conjunction with a platinum resistance thermometer. From -140 0 C to -45 0 C the temperature is allowed to increase without regulation at a rate of ,I*C/ min. At -45 0 C, power is supplied to the heaters and the temperature is controlled by programming the application of power. The temperature use can also be controlled at rates other than 1C/min. through changes in the operating program. For temperatures above 175 0 C, the high-temperature chamber must be used.Phase-angle measurements using the lock-in analyzer were incorporated to simplify automation of the measurements, improve resolution of small angles, and increase the range of tan 6 measurements (4). The calculator alternately switches the load (P) and displacement X) signal through the multiprogramler to the lock-in analyzer. After a programmed delay for setting of the signal, the in-phase and quadrature components of the respective signals are measured with respect to a reference signal from th= Autovibron. The complex Young's modulus, E*, is calculated using Equaticn 1. •With E* and 6 from Equations I and 2, respectively, the storage modulus, E', and loss modulus, E", can be calculated.E' =IE*/cos 6 (3)E" -/E*/sin 6 (4)The data acquired are displayed while the program is running and stored on magnetic-tape cartridges for further reduction. Results can be printed or plotted during the run with appropriate programming; programs for data reduction and plotting from tape are available. EXPERIMENTALProblems and their correction. During start-up and subsequent trials using the DDV-III-C, several significant problems have been encountered.Much of our recent work has been conducted using an automated DDV-II because of problems with the DDV-III. Preliminary work with the large load capacity unit has shown problems in sample tensioning, load control, measurement of small phase ang...