Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
1998-11-24
2001-03-27
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
C073S808000
Reexamination Certificate
active
06205862
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an instrument for measuring the static viscoelasticity and/or dynamic viscoelasticity of a material.
A known invention of this kind is an instrument for measuring the relation between the stress and strain in a material as described in Patent Publication No. 57-40963 (hereinafter referred to as the first prior art). Also, as described in Patent Laid-Open No. 63-139232 (hereinafter referred to as the second prior art instrument), an improved instrument is available. The mechanisms of this instrument are simplified to increase the mechanical strength and to decrease the weight of the vibrating system. Thus, the effects of the mechanical resonance are mitigated. Hence, the dynamic viscoelasticity of the material can be measured. In addition, as described in Patent Laid-Open No. 3-82934 (hereinafter referred to as the third prior art instrument), another improved instrument applies an alternating force to a material. A DC current is added to the alternating force. The DC strain component of the strain developed in the material is mechanically compensated. The dynamic viscoelasticity of the material can be measured only from the AC component by the pulling system.
In all of these prior art instruments, a force is applied to a sample via a detection rod. The strain in the sample is detected by a displacement detector placed between the detection rod and an external support. The detection rod of these instruments needs to be supported by a support within the instrument of some form. In the first prior art instrument, a balance support mechanism is used. In the second and third prior art instruments, leaf springs are mounted to the supports.
In each prior art instrument described above, the friction between the detection rod and the support must be small (i.e., the viscous resistance between the detection rod and the support is small). This is a characteristic generally required for each system for holding the detection rod.
In addition, in order to measure the static viscoelasticity of the sample, the elastic coupling constant (spring constant) between the detection rod and the support) is required to be small.
To measure the dynamic viscoelasticity of a sample, the mass of the vibrating portion including the detection rod must be small, forminimizing the measurement error due to inertia. Furthermore, the resonant frequency of the vibrating portion determined by the ratio of the elastic coupling constant to the mass of the vibrating portion needs to be higher than the measured frequency and so it is necessary that the elastic coupling constant between the detection rod supports be considerably large.
In particular, measurement of the static viscoelasticity of a sample and measurement of the dynamic viscoelasticity are common in that the relation between a stress and a strain produced in the sample is measured. However, where the detection rod is held as in the prior art technique described above, conflicting requirements take place concerning the elastic coupling constant between the detection rod and the support. Consequently, any instrument capable of accurately measuring both static and dynamic viscoelasticities of a sample has not existed.
In practice, the static viscoelasticity can be measured, using the first prior art instrument. However, measurement of the dynamic viscoelasticity is limited to quite low frequencies of less than 1 Hz due to the large mass of the balance mechanism.
On the other hand, in the second and third prior art instruments, it is possible to measure dynamic viscoelasticity up to higher frequencies such as hundreds of Hz. In measuring the static viscoelasticity of a sample, it is difficult to separate the contribution of the spring constant of leaf springs when the stress and strain vary at the same time.
In consequence, sufficient measuring accuracy cannot be obtained.
SUMMARY OF THE INVENTION
The present invention has been developed to solve the problems described above. The invention comprises:a sample holder for supporting at least one end of a sample; a sample chuck for supporting a part of said sample; a detector support capable of moving relative to said sample holder; a detection rod coupled to said sample chuck and elastically held to said detector support; a displacement detector for sensing variations in longitudinal position of said detection rod relative to said detection support; a force generator fixedly mounted to said detection support and acting to apply a longitudinal force to one end of said detection rod to thereby apply stress to said sample via said detection rod and via said sample chuck; a function generator connected with said force generator and acting to establish a DC component and an AC component of a stress applied to the sample; a mechanical feedback control means for varying the position of said detector support relative to said sample holder so that a DC component output from said displacement detector approaches zero; negative feedback control means for varying the DC output from said force generator so that the DC component output from said displacement detector approaches zero; recording means for recording the output from said force generator and amount of movement of said detector support relative to said sample holder; and an arithmetic unit for Fourier-transforming periodic function components of the periodic function signal from said periodic function generator and periodic function components of a displacement signal sensed by said displacement detector.
In the operation of the structure described above, at least one of a DC force and an AC force is applied to the sample via the detection rod from the force-generating portion. The sample is held to the sample holder and to the sample chuck. At this time, reflecting the linear viscoelasticity between the sample and the elastic support, a DC-like strain is induced in the DC force, and an AC-like strain is induced in the AC force. Both are sensed by the displacement detector.
The AC-like strain sensed by the displacement detector is compared with the applied AC force and is thus detected as a composite dynamic viscoelasticity of both sample and elastic support. If the sample and the elastic support are coupled parallel, the dynamic viscoelasticity of the sample can be determined by subtracting the elastic modulus of the elastic support from the composite dynamic viscoelasticity.
The applied DC force and the DC component of strain sensed by the displacement detector can be measured by passing the displacement signal through a low-pass filter or continuously applying DC waves and intermittently applying AC waves and then measuring the displacement when no AC wave is applied. At this time, the detector support is moved or the DC force is varied according to the measured value so that the measured value of the DC component of the displacement signal approaches zero. At this time, the amount of movement of the detector support represents the deformation of the sample. The elastic support is not deformed. Accordingly, the applied DC force is fully distributed to the sample. That is, the applied DC force and the amount of movement of the detector support represent the static stress and the static strain, respectively, in the sample oand, therefore, the static viscoelasticity of the sample can be measured.
REFERENCES:
patent: 3699808 (1972-10-01), Ford et al.
patent: 4719804 (1988-01-01), Maruyama
patent: 4967601 (1990-11-01), Teramoto
patent: 5182950 (1993-02-01), Takeda
patent: 5287749 (1994-02-01), Nakamura
patent: 2238879 (1979-02-01), None
patent: 3240666 (1984-05-01), None
patent: 4306119 (1994-09-01), None
patent: WO9102235 (1991-02-01), None
Patent Abstracts of Japan, vol. 006, No. 034 (P-104) Mar. 2, 1982.
Nakamura Nobutaka
Take Masafumi
Takeda Haruo
Adams & Wilks
Noori Max
Seiko Instruments Inc.
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