Measuring and testing – Vibration – Hardness or compliance
Reexamination Certificate
1999-03-01
2001-09-18
Kwok, Helen (Department: 2856)
Measuring and testing
Vibration
Hardness or compliance
C073S081000, C073S575000
Reexamination Certificate
active
06289734
ABSTRACT:
THE FIELD OF THE INVENTION
The present invention generally relates to a test system for in-situ, non-destructive identification of a visco-elastic or rubberlike material. The test system employs a unique method for identifying the visco-elastic material or identifying non-homogenous insertions or flows in the visco-elastic material.
BACKGROUND OF THE INVENTION
Visco-elastic or rubberlike materials occupy a special place in today's .engineering because of the unique property of resilience. Every year scientists are reporting about new rubberlike polymers with exciting properties and potential applications for automobile, marine and aerospace industries. Despite the fact that the dynamics of rubberlike materials has been investigated intensively since early 1940s, the number of non-destructive testing methods is still limited mainly because rubberlike materials are acoustically weak, i.e., conventional ultrasonic testing is hardly applicable. Todays users are left to rely on the specification provided by a maker or manufacturer of the material.
Available non-destructive test methods are classical hardness testing and x-ray examination. Such test methods typically require large size test instruments or test instruments which are not portable and must be used in a laboratory environment. Crucial disasters due to the failure of rubberlike materials, some which have involved many casualties, illustrate a need for the highly reliable non-destructive test methods and devices. Such disasters include the explosion of the space shuttle Challenger in 1986, caused by failure of “O” rubber rings at the liquid oxygen tank and the sinking of the Estonian ferry boat in the Baltic Sea in 1995, caused by non-functioning of rubber isolation seals at the front door. It is obvious that new standards and methods for non-destructive testing of rubberlike parts in-situ should be developed in order to reliably test these materials.
SUMMARY OF THE INVENTION
The present invention provides a new test system for nondestructive identification of visco-elastic (i.e., rubberlike) materials. The system is based on simultaneous contact impedance and compliance testing, and signal processing which integrate simple rheological models into a sophisticated experimental data fitting process. Further, the test system in accordance with the present invention provides for in-situ testing, using a small, portable probe-like test member which is connectable to a portable controller or laptop computer.
The test system employs a method which may be used for both identification of visco-elastic materials and locating non-homogeneous insertions or flows in a visco-elastic material.
In one embodiment, the present invention provides a portable test system for in-situ, non-destructive identification of the visco-elastic material. The system includes a probe-like test member and a controller, wherein the controller is responsive to an output signal from the test member for determining properties of the visco-elastic material. The test member includes a longitudinally extending housing. A transducer mechanism is operably positioned within the housing. The transducer mechanism includes an indentation tip member, wherein the indentation tip member is extendable through the housing. A load mechanism is provided for loading the transducer mechanism with a desired constant load, causing the indentation tip member to extend through the housing to perform an indentation. A force calibration mechanism is provided for calibrating the application of a fixed force between the indentation tip member and the visco-elastic material. A mechanism is provided for applying an audiosonic signal to the visco-elastic material via the transducer mechanism, wherein in response to the audiosonic signal the transducer mechanism provides an output signal representative of identification properties of the visco-elastic material.
The system may further include a thermosensor which can be operably coupled to the visco-elastic material, wherein the thermosensor has an output which is representative of the temperature of the visco-elastic material at the time of the test. The force calibration mechanism may include a load pad and a spring mechanism, when the load pad is operably coupled to the probe via the spring mechanism. The load pad includes a major surface for contacting the visco-elastic material. In one aspect, the force calibration mechanism further includes a force calibration sensing mechanism. The force calibration sensing mechanism includes a proper load indicator. In another aspect, the system further includes a thermosensor, wherein the thermosensor is coupled to the load pad and is capable of measuring the temperature of the visco-elastic material at the time of the test.
In one aspect, the transducer mechanism includes a PZT actuator, a PZT sensor and a waveguide. The indentation tip member is operably coupled to a cantilever mechanism. In one preferred embodiment, the indentation tip member extends through a sidewall of the housing, and is substantially oriented perpendicular to the cantilever mechanism.
The load mechanism may include a loading plate, a mechanical linkage and a DC motor, wherein the DC motor is operably coupled to the loading plate via the mechanical linkage for controllably transferring a desired load to the loading plate. In one aspect, the mechanical linkage is a CAM system. The load mechanism may include a strain gauge, wherein the strain gauge is calibrated to the desired loading-force of the loading plate.
The controller may further include means responsive to the output signal for determining a set of material values, and a set of threshold material values corresponding to a type of visco-elastic material. In one aspect, a comparing mechanism is provided which compares the set of material values to the set of threshold material values to identify the visco-elastic material. In another aspect, a comparing mechanism is provided which compares the set of material values to the set of threshold material values to identify non-homogeneous insertions within the visco-elastic material.
In another embodiment, the present invention provides a method of identifying a visco-elastic material, including rubbers or elastomers. The method includes the step of performing an indentation on a visco-elastic material. A contact compliance test and impedance test is simultaneously performed during the indentation. A dynamic response signal is generated, wherein the dynamic response signal is representative of properties of the visco-elastic material. The dynamic response signal is filtered with a digital low-pass filter to generate an output signal waveform having a normalized amplitude. A set of test constants is determined from the output signal waveform. A table of material constants are defined for visco-elastic materials. The test constants and the set of material constants are compared to identify the visco-elastic material.
The method may further include the step of determining the temperature of the visco-elastic material during the indentation, wherein the table of visco-elastic materials includes a temperature constant for each material.
The step of determining the set of test constants may include the step of fitting the output waveform with piece-wise polynomials. The step of fitting the output signal waveform with piece-wise polynomials may include steps of fitting a first order polynomial to a first portion of the output signal waveform to obtain a first constant, fitting a second order polynomial to a second portion of the output signal waveform to obtain a second constant and a third constant, and fitting a first order polynomial to a third portion of the output signal waveform to obtain a fourth constant.
As used herein, the term “visco-elastic” refers to rubber, rubber-like, polymers, elastomers or materials exhibiting similar characteristics.
REFERENCES:
patent: 3153338 (1964-10-01), Kleesattel
patent: 3302454 (1967-02-01), Kleesattel
patent: 3308476 (1967-03-01), Kleesattel
patent: 3421364 (1969-01-01), Moneypen
Dicke, Billig & Czaja P.A.
Hysitron Incorporated
Kwok Helen
LandOfFree
In-situ non-destructive audiosonic identification system for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with In-situ non-destructive audiosonic identification system for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and In-situ non-destructive audiosonic identification system for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2491307