An analyzing structure and method for determining properties such as elastic shear modulus and mechanical hysteresis of a material. A pair of mutually spaced holders hold the sample in such a way that the holders are interconnected by the sample, and these holders are in turn carried by driver and driven supports. A drive sets the driver support into vibratory motion so that the latter is transmitted through the sample to the driven support. By detecting the manner in which the driver and driven supports vibrate it is possible to determine properties of the sample. The sample is tested by cyclically generating substantially pure shear forces in the sample, with the power required to sustain the vibrations of the sample at a constant level being measured to determine the damping of the sample and the frequency of vibration being measured to determine the modulus of the sample.
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22. A method of dynamically analyzing a sample comprising the steps of:
cyclically moving the center of the mass of a sample along an arcuate path lying in a plane, and simultaneously moving spaced portions of said sample in opposite senses in said plane transverse to said arcuate path, thereby to create stresses in said sample, and sensing said stresses.
20. A method of dynamically analyzing a sample comprising the steps of:
securing said sample between a pair of spaced, dynamically decoupled, elongated support members, subjecting one of said support members and hence through said sample the other of said support members to in phase lateral vibratory motion, thereby to stress said sample with a vibratory motion in a sense transverse to the sense of said lateral vibratory motion, and sensing said vibratory motion.
14. Apparatus for dynamically analyzing properties of a sample comprising, in combination:
a rigid base member, a pair of sample holders adapted to grip said sample at spaced portions of said sample, a corresponding pair of elongated, spaced support means for said holders secured distant from said holders to said base member, drive means operatively connected to one of said support means for imparting lateral vibratory motion thereto, whereby said sample is subjected to vibratory motion transversely to said lateral vibratory motion, detecting means associated with one of said support means responsive to vibratory motion thereof.
1. In an analyzer, a pair of mutually spaced holding means for holding a sample which is to be analyzed with said sample extending between and interconnecting said pair of holding means, driver support means carrying one of said holding means to support the latter for vibratory movement and driven support means carrying the other of said holding means to support the latter also for vibratory movement, drive means operatively connected with said driver support means for setting the latter into vibratory motion which is transmitted through said one holding means to said sample and from the latter to said other holding means to vibrate the latter and said driven support means therewith, whereby said driver support means and said one holding means, on the one hand, and said driven support means and said other holding means, on the other hand, form driver and driven units which are set into vibratory motion when said drive means operates with a vibratory motion being transmitted to said driven unit through said sample, and detecting means coacting with at least one of said units for responding to vibratory motion thereof for determining properties of the sample which is under test.
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The invention relates to an apparatus Thus, for a given sample at a given temperature the drive means 20 drives the driver support means 16 at a fixed frequency.
The tines 16 and 18 as well as the clamps 12 and 14 are identical, and in order to maintain the identical relationship between this structure the tine 18 carries a compensating weight 42 which has the same mass as the armature 36. Furthermore, in order to reduce the influence of the carrying structure on the sample the tines and clamps may be cooled in any suitable way.
The detecting means 24 includes a light-chopping means 44 in the form of an opaque fin or plate which is fixed to and extends laterally from the tine 18 toward the tine 16. A regulated light-source means 46 also forms part of the detecting means 24. This light-source means 46 provides a beam of light which travels toward the light-chopping means 44 so as to be modulated thereby at a frequency equal to the frequency of vibration of the tine 18. A photosensitive means 48 is situated on the side of the light-chopping means 44 opposite from the light-source means 46 to receive the modulated light from the source 46 whenever the light-chopping means 44 is sinusoidally oscillated within the beam of light issuing from the source 46. In this way the photosensitive means 48 will receive a sinusoidal light signal at a frequency equal to the vibrating frequency of the tine 18, and at an amplitude proportional to the displacement so that this photosensitive means 48 forms a pick-up capable of transmitting a signal to oscillation amplitude control circuitry, as indicated schematically in FIG. 1.
The detecting means 26 is identical with the detecting means 24. Thus, the detecting means 26 includes a light-chopping means 50 which is identical with the light-chopping means 44. This light-chopping means 50 is thus in the form of a fin or plate which is fixed to and extends laterally from the tine 16 toward the tine 18. The detecting means 26 includes a light-source means 52 identical with the source means 46 and supplying a light beam which is modulated by the light-chopping means 50 at a frequency equal to the vibrating frequency of the tine 16. At the side of the light-chopping means 50 opposite from the light-source means 52 is a photosensitive means 54 which receives modulated light whenever the beam from the source 52 is sinusoidally obstructed by the chopper 50. Thus, the photosensitive means 54 also forms a type of photodetector which is capable of providing information with respect to the drive frequency required to drive the unit 12, 16, at its natural frequency and, as was pointed out above, it is also possible to use the detecting means for the purpose of achieving the feedback signal which controls the drive means 20 so as to maintain the bent vibrating at its natural frequency.
Thus, by injecting energy into the bent at its resonant frequency, in the manner described above, shear stresses are cyclically generated in the sample 10. These shear stresses are the type of stresses considered best for thermomechanical analysis. Under such cyclic stresses and their associated strains the sample 10 will dissipate or transfer the injected energy according to the hysteresis of the material, so that through the detecting means 24 it is possible to determine a property such as the hysteresis of the material.
In addition to changing the hysteresis or clamping effect, altering the temperature will cause the stiffness of the sample to change, and this temperature regulation can be brought about by the temperature-regulating means 30. The change in the stiffness resulting from temperature regulation manifests itself as a change in the resonant frequency of the bent. Thus, by altering the temperature with the regulating means 30 it is possible through the detecting means 26 to detect the change in resonant frequency of the bent and thus achieve in this way additional information with respect to the characteristics of the sample. It is to be noted that in the limiting case where the sample has zero stiffness the frequency of the bent approaches that of either tine with additional mass added to the top equal to one half the sample mass.
The manner in which shear forces are generated in the sample with the structure and method of the invention is illustrated in detail in FIGS. 2A and 2B which respectively illustrate the upper region of the bent at its extreme left and right positions. As is apparent from FIGS. 2A and 2B the clamps 12 and 14 remain at all times at a constant distance from each other. These clamps however shift angularly and in elevation with respect to each other so that at the extreme left position shown in FIG. 2A the left portion of the sample has been displaced upwardly while the right portion has been displaced downwardly, while in FIG. 2B the left portion of the sample has been displaced downwardly and the right portion of the sample has been displaced upwardly. In the neutral position shown in FIG. 1, where the upper portion of the bent is midway between the positions respectively shown in FIGS. 2A and 2B, the sample is in a horizontal attitude, assuming a straight configuration.
Thus, the driver support means 16 and driven support means 18 cooperate with the holding means 12 and 14, respectively, for maintaining them at a constant distance from each other.
The result of this method and apparatus of the invention is that the sample is cycled about a point of zero stress situated at the center of the body which forms the sample. In this way it is possible to prevent large distortions of the sample by unidirectional forces (tensile or compressive) in the event that the material 10 becomes plastic or taffy-like in its behavior. Furthermore, with the method and apparatus of the invention very little energy is required to maintain the oscillation of the driven unit 14, 18. This type of operation thus results in an extremely small tensile stress component and, in effect, places the sample in almost pure shear. This behavior can be illustrated by the fact that a material may be analyzed at a temperature above the softening point with the method and apparatus of the invention without being pulled apart.
Control of the oscillating tines and measurement of the stiffness and loss parameters are achieved by way of the chopped light beams, as described above. Each beam is modulated by the chopping means carried by one of the tines with the amplitude of the resulting signal being proportional to the excursions of the associated tine.
The photodetector activated by the driver support means 16 functions in connection with the feedback means 28 to utilize the driver tine 16 as a frequency control element for the oscillator from which the signal is transmitted to the electromagnetic drive means 20, so that in this way it is possible to control the entire system. Thus with the method and apparatus of the invention the bent is always excited by energy having a frequency equal to the natural frequency of the bent. The frequency of the applied power is continuously read out so as to yield the required stiffness output data.
The remaining photodetector 48 is of course activated by the vibration of the driven tine 18. Inasmuch as the tines are kept cool during a test their physical characteristics are maintained constant. As a result all of the energy required to sustain the oscillation of the driven tine 18 at a constant amplitude must be transmitted through the sample 10. This operation renders the loss of energy generated by the sample proportional to the power required by the electromagnet 38, 40 to maintain the oscillation of the driven tine 18, and thus of the entire bent, at a constant value. Continual readout of this power level is all that is required to achieve the necessary loss data of the sample.
It is to be noted that it is not essential to have a pair of detecting means respectively coacting with the driver and driven units to detect the vibration thereof. Thus, the construction shown in FIG. 1 may be modified by eliminating the source 46 and pick-up 48 and all of the circuitry connected thereto. This latter circuitry can instead be supplied with signals from a single pick-up 26 which would form the only detecting means of the entire structure with the source 52 forming the only light source for the entire structure. Components 42 and 44 would be retained only to maintain the driven unit identical with the driving unit. All signals and controls would thus be derived from the single detecting means 54. This can be done because when the bent vibrates the driven unit vibrates synchronously, in phase with the driver unit, so that both units have identical vibrations, thus eliminating all except shear stresses in the sample. Because of the identical, in-phase vibrating movements of the driver and driven units it is possible to derive all data and controls with the single detecting means which coacts with the driver unit.
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| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Jul 17 1975 | Chemical Instruments Corporation | (assignment on the face of the patent) | / |
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