Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Reexamination Certificate
2001-09-11
2004-01-06
Noori, Max (Department: 2855)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
C073S012010
Reexamination Certificate
active
06672141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method of measuring viscoelastic characteristic values such as Young's modulus, a loss factor, and the like of a viscoelastic material such as synthetic resin, crosslinked rubber, and the like. More particularly, the present invention is intended to measure viscoelastic characteristic values of a soft viscoelastic material accurately by using a so-called split Hopkinson's bar.
2. Description of the Related Art
In recent years, to analyze the deformation and behavior of an object to which an impact is applied, simulation is used rather than measurement. In the simulation, it is necessary to perform substitutions of the viscoelastic characteristic values (parameter) such as the Young's modulus, the loss factor, and the like of the object. The parameter is classified into a static parameter and a dynamic parameter. Because the deformation and behavior of the object is dynamic, the dynamic parameter measured in a state close to the deformation and behavior is effective for the simulation. The measurement of the dynamic parameter is also important for apprehending the characteristic of the object.
As means for measuring the dynamic parameter, an apparatus using the split Hopkinson's bar is known. The split Hopkinson's bar is used in the field of a metal material (see page 173-183 of “Impact Engineering” published by Nikkan Kogyo Newspaper Ltd. on Oct. 28, 1989) or the like. In the apparatus using the split Hopkinson's bar, a impact bar, an input bar, and an output bar all made of metal are arranged in a straight line, with a specimen held between the rear end of the input bar and the front end of the output bar, and a strain gauge is installed on each of the input bar and the output bar (the input bar and the output bar may be hereinafter referred to as stress bar). In measuring the viscoelastic characteristic of the specimen, the impact bar is brought into collision with the front end of the input bar. A strain wave generated at this time propagates from the input bar to the specimen and the output bar. The following three waves are measured with the strain gauges installed on the input bar and the output bar to compute the viscoelastic characteristic value of the specimen: An incident strain wave progressing in the input bar to its rear end, a reflected strain wave reflected from the rear end of the input bar to the front end thereof and a reflected strain wave reflected from the rear end of the specimen to the front end thereof after the incident strain wave passes through the specimen, and a transmitted strain wave which advances from the input bar to the rear end of the output bar through the specimen.
It is to be noted that in description made below the incident strain wave, the reflected strain wave, and the transmitted strain wave are abbreviated as a “strain wave” as necessary.
The measuring apparatus is capable of measuring the characteristic value of a metal material but has difficulty in measuring the viscoelastic characteristic value of a polymer such as synthetic resin, crosslinked rubber, and the like. When the specimen is made of the polymer, there is a large difference between the characteristic impedance of the specimen and that of the stress bar made of metal. Consequently the reflected strain wave is generated. Thus in measuring the viscoelastic characteristic value of the polymer, it is necessary to select the stress bar made of a material whose characteristic impedance is not different much from that of the specimen.
A viscoelastic characteristic value-measuring apparatus using the stress bar made of polymethyl methacrylate is disclosed by Nakagawa of Hiroshima University and others on pages 25-29 of lecture thesis of 16th series of Chugoku Branch of Japan Design Engineering Society Association. It is possible to reduce the difference between the impedance of the specimen made of the polymer and that of the stress bar by composing the stress bar of the polymer such as polymethyl methacrylate. Thereby it is possible to measure the viscoelastic characteristic value of the specimen made of the polymer.
Unlike the stress bar made of metal, the strain wave generated in the stress bar made of the polymer attenuates greatly. For example, the incident strain wave progressing to the specimen from the input bar is measured with a strain gauge installed on the input bar and attenuates a little before it reaches the rear end of the input bar. Thus, it is impossible to correctly measure the incident strain wave at the rear end of the input bar. Similarly, it is impossible to correctly measure the reflected strain wave reflected from the rear end of the input bar to the front end of the input bar and the reflected strain wave reflected from the rear end of the specimen to the front end of the input bar after the incident strain wave passes through the specimen, and the transmitted strain wave which passes through the output bar from the rear end of the specimen.
In the viscoelastic characteristic value-measuring apparatus disclosed by Nakagawa and others, two strain gauges are installed on each of the input bar and the output bar to solve the problem of the damp of the stress bar made of the polymer. That is, a transmission function is derived from the incident strain wave, the reflected strain wave, and the transmitted strain wave measured with the two strain gauges. From the transmission function, the strain amount of each of the incident strain wave at the rear end of the input bar, the reflected strain wave at the rear end of the input bar, and the transmitted strain wave at the front end of the output bar are estimated. The viscoelastic characteristic value-measuring apparatus is capable of measuring the viscoelastic characteristic value of the specimen when the specimen deforms greatly at high speed (maximum strain speed: 100-8000 per second) and in a large amount (maximum deformation amount is in the range from 0.1%-30%).
The viscoelastic characteristic value-measuring apparatus is capable of correctly measuring the viscoelastic characteristic value of a comparatively hard polymer, but has a large error in measuring the viscoelastic characteristic value of a particularly soft viscoelastic material. That is, the viscoelastic characteristic value-measuring apparatus is incapable of obtaining a correct viscoelastic characteristic value. The error is attributed to the fact that as the specimen becomes softer, the difference between the propagation speed of a strain in the specimen and that of a strain in the input bar and the output bar disposed forward and rearward from the specimen respectively becomes increasingly large.
That is, in the case of the specimen made of the particularly soft viscoelastic material, the reflected strain wave (reflected from the rear end of the input bar to the front end thereof and reflected from the rear end of the specimen to the front end of the input bar after the incident strain wave passes through the specimen) interferes with the second reflected strain wave (the incident strain wave reflected from the rear end of the input bar to the front end thereof from which it is reflected again). Thus, it is difficult to measure the reflected strain wave.
More specifically, in the case where the specimen is made of a soft material particularly, of the above-described reflected strain waves which are measured with the strain gauge installed on the input bar, before the damp of the reflected strain wave (hereinafter referred to as third reflected strain wave) which is reflected from the rear end of the specimen to the front end of the input bar after it passes through the specimen does not terminate, the strain gauge installed on the input bar measures the second reflected strain wave. That is, the second and third reflected strain waves interfere with each other. Thus it is difficult to measure the second and third reflected strain waves correctly.
In the case where the specimen is made of a very soft material
Maruoka Kiyoto
Nishibayashi Jun
Birch & Stewart Kolasch & Birch, LLP
Noori Max
Sumitomo Rubber Industries Ltd.
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