JPH04198842A - Stress relaxation measuring apparatus - Google Patents

Abstract

PURPOSE:To accurately measure a minute change by detecting the change of the internal stress at the center part of a test piece as the change of the double refraction of light. CONSTITUTION:A laser 18 is started and measuring polarized light (j) modulated in phase is incident to a test piece 1. Next, a stretching part 7 is operated and the test piece 1 is instantaneously stretched by grips 5, 6 and the tensile displacement of the test piece 1 is held as it is. After the stretching of the test piece 1 is completed, plastic deformation is generated in the test piece 1 so that the tensile stresses in respective parts become uniform and the tensile stress at the center part of the test piece 1 is relaxed with the elapse of time and the double refraction of transmitted light is also successively reduced in a state almost proportional to tensile stress. The change state of this double refraction is inputted to a computer 4 as the change of the AC component Iw outputted from a lock-in amplifier 27 at each time when a reference signal (h) is inputted to the amplifier 27 that of the DC component IDC not passed through an AC amplifier 26 and these signals are analyzed to repeatedly calculate the value of double refraction phase difference at every definite time interval and, further, the value of stress corresponding to each value of double refraction phase difference is calculated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an apparatus for measuring the stress relaxation phenomenon caused by plastic deformation of a polymer material such as plastic when it is stretched, and in particular, an apparatus having high measurement sensitivity and The present invention relates to a stress relaxation measuring device that can quickly follow minute changes in the internal state of a material and accurately grasp the state of stress relaxation.

[Prior Art] In the as-manufactured state of polymer materials such as polymer films and polymer fibers, the molecules are unoriented or almost isotropic, and their inherent advantages as polymer materials are That is, it does not have the following characteristics: 1) high resistance to stretching in the direction of the molecular chain, and 2 easy bending but difficulty in cutting. Therefore, in order to impart these properties to a material, it is necessary to stretch the material to form molecular orientation during the manufacturing process of the product.

However, in order to cause molecular orientation by stretching, it is necessary to set the amount of stretching, ambient temperature, etc. that matches the properties of the material (for example, when the ambient temperature is below the glass transition point Tg of the material, molecular orientation is tests are being conducted to obtain information on the molding conditions and physical properties of the material. A stretching machine, which is a typical conventional testing machine, will be described below.

As shown in Figure 3, this stretching machine has upper and lower grips b and c that grip both ends of a ribbon-shaped test piece a, and the grips b and c are pulled in the vertical direction to cause plastic deformation of the test piece a. a stretching section d that causes the test piece to maintain its deformed state; a load cell e that detects the tensile load acting on the specimen a after stretching and outputs it as an electric quantity; and an electric current sent from the load cell e over time. This stretching machine includes a calculation device g that calculates the tensile stress inside the test piece based on signals, and can measure the stress relaxation phenomenon that occurs inside the test piece a immediately after stretching.

[Problems to be Solved by the Invention] However, the above-mentioned stretching machine had the following problems.

(i) Since the sensitivity of the load cell e is low, it is necessary to set the time interval for detection to be long (information is taken in at most several seconds, and usually at intervals of tens of seconds to several minutes).

(iii) As a result of the previous section, it was difficult to measure the physical properties of a polymer film during high-speed stretching, that is, how the stress relaxation phenomenon occurs at the molecular level, at a speed equivalent to or higher than high-speed stretching.

In view of the above-mentioned problems, the present invention has good measurement sensitivity, and can quickly follow minute changes in the internal state when a material is deformed at high speed to accurately and precisely grasp stress relaxation phenomena. An object of the present invention is to provide a stress relaxation measuring device.

[Means for Solving the Problems] The means of the present invention for solving the above problems include a stretching machine that pulls both ends of a test piece to rapidly deform it plastically and maintain the deformed state, and a measurement method that modulates the phase. The value of birefringence generated inside the test piece is measured over time by irradiating polarized light onto the center of the test piece and detecting the polarization state of the light that has passed through the test piece. This is a stress relaxation measuring device equipped with a high-speed birefringence measuring device that determines the value of tensile stress relaxation inside a test piece from each refraction.

[Effect]

(Since changes in internal stress at the center of the il test piece are detected by replacing them with changes in birefringence, accurate data can be measured.

(ii) Since phase-modulated measurement light is used to measure birefringence, changes in birefringence caused by the test piece can be interpreted as changes in the ellipticity of the measurement light, improving measurement sensitivity. (The sensitivity of the birefringence value Δn is 10-
', which is 103 to 10 the sensitivity of conventional load cells.
).

[iii] By detecting the measured value using the modulation signal etc. when phase modulated, it is possible to quickly follow changes in the internal state of the test piece and perform measurements, making it possible to perform measurements on the order of lO microseconds. Data can be captured at time intervals of

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. 1st
Figures 1 and 2 show an embodiment of the present invention, and the main part of the apparatus of this embodiment is a stretching method that pulls both ends of a test specimen 1 to rapidly deform it plastically by a predetermined amount and maintain the deformed state as it is. A device 2 is used to detect birefringence generated inside the test piece 1 by irradiating phase-modulated measurement light onto the center of the test piece 1 and detecting the polarization state of the light transmitted through the test piece 1. The device is comprised of a high-speed birefringence measurement device 3, etc., which measures the value of the birefringence over time, and further obtains a value of tensile stress relaxation from the measured birefringence.

As shown in FIG.
is the test piece, and the upper and lower grips 5.6 grip both ends of the test piece 1, leaving the central part 30■, and the grips 5 and 6 are simultaneously separated by the same stroke amount at high speed [maximum When the stroke amount is 3011II11 (up and down total), the stretching part 7 is stretched for about 0.1 seconds], and the tensile load and tensile displacement applied to the test piece 1 are adjusted in small increments according to the type of material of the test piece 1. It consists of a stretching section controller 8, a constant temperature bath 9 (temperature adjustment range of about 25 to 360'C) surrounding the test piece 1, grips 5, 6, stretching section 7, etc., and the stretching section controller 8 includes: The tensile load applied to test piece 1 was divided into five stages from 0.02 kgf to 5 kgf.
In addition, the tensile displacement was increased from 0.01mm to 30mm by 0.01mm.
It can be set in mm units.

In the figure, 10 is a heater that raises the atmospheric temperature in the constant temperature bath 9, 12 is a temperature controller, 13 is a thermocouple that detects the atmospheric temperature in the constant temperature bath 9, 14 is a thermometer, and 15 is the extension part 7. A load cell (or strain gauge) 16 is a load cell amplifier that is incorporated in the test piece 1 and generates an electric signal by detecting the tensile load applied to the test piece 1. It serves to check whether the tensile load matches the tensile load set by the extension section controller 8.

The high-speed birefringence measuring device 3 includes a laser power source 17 and an H
A laser 18 that generates an e-Ne (helium-neon) laser beam, and a polarizer (Glan-Thompson prism) 19 that converts the laser beam sent from the laser 18 into linearly polarized light.
For example, 50K is applied as a modulation signal to a crystal having a crystal axis.
By applying an alternating current electric field of Hz and continuously and periodically changing the birefringence phase difference when light passes through the inside of the crystal from zero to 1/4 wavelength, the polarizer 19
A phase-modulated measurement light j is created by continuously changing the linearly polarized light sent from the An optical phase modulator (for example, a photoelastic modulator) 20 to be made incident, and an analyzer (Glan-Thompson prism) that receives the light that has passed through the test piece 1 and is birefringent inside the test piece 1 and converts it into linearly polarized light. 22, a photodetector (photodiode) 23 that photoelectrically converts the light incident from the analyzer 22, and converts the electric signal sent from the photodetector 23 into AC components (phase difference changes of the modulated measurement light and (including the phase difference change generated inside the test piece) and a DC component (components such as dark current other than the phase difference change), and amplify the phase difference change from the AC component and extract it over time. An electric circuit and an AC signal I output from this electric circuit. The optical phase modulator 20 includes a computer 4, etc., which calculates the birefringence phase difference And using the DC signal 111C and the birefringence value, and further calculates the tensile stress value from the birefringence value.
4.

The electric circuit includes a preamplifier 25 that amplifies the electrical signal sent from the photodetector 23, an AC amplifier 26 that extracts and amplifies the AC component in the signal sent from the preamplifier 25, and a signal sent from the AC amplifier 26. A lock-in amplifier 2 performs synchronous detection (phase detection) on the received signal using the modulation signal for the optical phase modulator as a reference signal.
Consists of 7th magnitude.

The high-speed birefringence measurement device 3 is disclosed in Japanese Patent Application Laid-Open No. 63-82345 (Patent Application No. 63-82345), which was proposed by the same inventor as the present application.
1-228814), but in this application, since it is used in combination with a stretching machine, the structure of rotating and tilting the test piece 1 may be omitted (if the tensile direction of the test piece is the direction of the molecular chain). Since they match, the optical principal axis, fast axis, etc. of the test piece 1 are determined by themselves, and there is little need to detect them).

Next, the handling procedure and operation of the device of this embodiment will be explained. First, the test piece 1 is attached to the grips 5 and 6, and the temperature controller 12 is operated to maintain the atmospheric temperature in the thermostatic chamber 9 at a desired temperature. The preparation for the test is completed by setting the tensile load and tensile displacement for test piece 1, and activating the laser 18 to make the measurement light j enter the test piece 1.

When the stretching section 7 is activated, the grips 5.6 instantaneously stretch the test piece 1 and maintain the tensile displacement as it is. On the other hand, after completion of stretching, the test piece 1 undergoes plastic deformation so that the tensile stress in each part becomes uniform, and the tensile stress in the central part (measurement part) of the test piece 1 is relaxed over time, and The birefringence of the light transmitted through the piece 1 also gradually decreases in approximately proportion to the tensile stress (stress and birefringence are in a proportional relationship during plastic deformation and at the same time as during elastic deformation).

The state of change in birefringence is caused by, for example, a change in the AC component I8 output from the lock-in amplifier 27 each time a 50 KHz reference signal is input to the lock-in amplifier 27, and a change in the AC component I8 that does not pass through the AC amplifier 26. These signals are input to the computer 4 as changes in the DC component IDC, and the computer 4 analyzes these signals and calculates the birefringence phase difference value Δnd at a fixed time interval Δt(10
The stress value corresponding to the multi-value Δnd of the birefringence phase difference is further calculated.

Furthermore, as mentioned above! Since the means for determining birefringence by analyzing w and Inc is well known, the explanation thereof will be omitted.

Since the stress relaxation state at the center of the test piece is measured by replacing it with the change in birefringence, it is possible to accurately grasp the change in tensile stress immediately after stretching.

Furthermore, since the measurement data is captured using a modulated signal or the like, it is possible to perform measurements while quickly following changes in the internal state of the material.

Furthermore, birefringence measurement uses phase-modulated measurement light, and the measurement results are photoelectrically converted and processed electrically, making it possible to increase the S/N ratio and improve measurement sensitivity. can.

Note that the present invention is not limited to the above-described embodiments; for example, instead of using a modulation signal, the reference signal input to the lock-in amplifier may be generated using another signal generated independently. It goes without saying that various other modifications may be made without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, the present invention exhibits the following excellent effects.

[1] Since changes in internal stress at the center of the test piece are detected by replacing them with changes in birefringence of light, minute changes inside the test piece can be measured as accurate data.

[11] Since phase-modulated measurement light is used to measure birefringence, it is possible to interpret changes in birefringence due to the test piece as changes in the ellipticity of the measurement light, improving measurement sensitivity. (The sensitivity of the birefringence value Δn is 10-
8, and the sensitivity of conventional load cells is 103 to 10.
(equivalent to 4 times).

[Mountain] Since the measured value is detected using the modulation signal obtained when phase modulation is performed, it is possible to quickly follow changes in the internal state of the test piece and perform measurements, and it is possible to perform measurements on the order of 10 microseconds. Data can be captured at time intervals.

C1v) As a result of the above items [i) to [i11], it becomes possible to accurately and precisely grasp the stress relaxation phenomenon when stretching polymeric materials, etc. Quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a device that is an embodiment of the present invention. 2 is an explanatory diagram of measurement results, and FIG. 3 is a block diagram of a conventional device. 1... Test piece 2... Stretching machine 3... High speed birefringence measuring device 4... Computer 18... Laser 19...
- Polarizer 20... Optical phase modulator 22... Analyzer 23... Photodetector 24... Optical phase modulator drive circuit 27... Lock-in up

Claims (1)

[Claims] A stretching machine that pulls both ends of a test piece to rapidly deform it plastically and maintain the deformed state, and a stretching machine that irradiates the center of the test piece with phase-modulated polarized light for measurement and the light that passes through the test piece. A high-speed birefringence measuring device that detects the deflection state, measures the value of birefringence generated inside the test piece over time, and further calculates the value of tensile stress relaxation inside the test piece from each measured birefringence value. A stress relaxation measuring device characterized by comprising: