Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
2000-04-20
2001-12-25
Noori, Max (Department: 2856)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
C073S081000
Reexamination Certificate
active
06332364
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The invention relates to a universal testing device for determining certain material properties of a sample.
(b) Description of Prior Art
Material testing refers to the evaluation of mechanical properties of solid materials by simultaneously measuring material deformation (displacement) and stress (force). The technical area is mature and highly developed with respect to industrial sized objects with dimension of centimeters or larger. When specimen dimensions encroach upon millimeters instrumentation and methods are less well developed, due to precision and control difficulties. When materials are soft in addition to small, technical difficulties also arise in eliminating noise from force signals.
Material testing systems are often developed with precise goals in mind. Thus some systems provide mechanical configurations appropriate for adhesion and tack tests (U.S. Pat. No. 5,438,863) for extrusion of thermoplastics in rheological testing (U.S. Pat. No. 4,680,958) and others for hardness and bonding tests of pharmaceuticals (U.S. Pat. Nos. 4,780,465, and 5,140,861). Common technical hurdles in these specific applications are precise control of displacement and low noise acquisition of force and displacement. These problems are overcome to varying degrees but generally insufficiently so in modern instruments. Also in spite of the underlying commonality in all material testing which is control and acquisition of force and displacement, instruments are often conceived and designed for the application of a limited number of tests where, for example, only one type of displacement is applied to obtain a certain force response upon which a particular analysis yields one characteristic material parameter. The limited flexibility of such systems is evident since proper mechanical and electrical design combined with algorithmic computer control of tests can in principle provide a universal system capable of executing the full range of material tests on small samples, as has been achieved for industrial sized objects. For example common measures of adhesion, tack, hardness, strength, modulus, viscoelasticity, plasticity etc. can all be obtained by parametric control of a limited number of fundamental tests such as ramp, stress relaxation, dynamic sinusoidal and creep tests.
In the biomedical domain of material testing, a particular need for testing samples in aqueous solutions under controlled environments of atmospheric gas composition and humidity arises. In the absence of material testing needs, these environments are generally provided by cell or tissue culture incubators. In the past, the need to perform material tests under these controlled environments has been addressed by developing testing chambers specific to the material testing apparatus to provide environmental control, since the material testing device is usually much too large to be placed in an incubator.
It would thus be highly desirable to be provided with a material testing instrument that would allow testing of these small specimens and that could be designed so as to fit inside a standard tissue culture incubator, thus adding to the universality of the device by including biomedical applications in their most standard format.
SUMMARY OF THE INVENTION
One aim of the present invention is to provide a precise and controlled material testing device for testing small specimens.
Another aim of the present invention is to provide a material testing device that could be designed so as to fit inside a standard tissue culture incubator, thus adding to the universality of the device by including biomedical applications in their most standard format.
Another aim of the present invention is to provide a material testing device for performing stress relaxation test, ramp-release test, Creep test, dynamic sinusoid measurements, long sinusoids, using an actuator for moving a sample at a constant speed, in which the actuator is so controlled as to mimic sinusoidal or other displacement, when needed.
Another aim of the present invention is to provide a material testing device for testing for unconfined or confined compression test, indentation test, tension test, and bending test.
In accordance with the present invention, there is provided a universal material testing device comprising:
a) a frame;
b) an actuator mounted on the frame for controlling a displacement of a sample to be tested;
c) a load cell movably mounted on the frame and adapted to abut against the sample for detecting a force applied thereon by the actuator, the load cell producing a signal corresponding to the force detected; and
d) a signal conditioning unit for reducing input noise and for processing of the signal and executing specific tests by coordination of displacement control and load signals received for processing from the load cell.
In one embodiment of the invention, the signal conditioning unit is a force sensing amplifier device.
In a variant on the invention, the frame may further comprises a crossbar for receiving the load cell, the crossbar having a minimal mass and minimal vertical deflection for not increasing device compliance while still exerting minimal resting force on an attached load cell, to avoid damaging of the latter.
The crossbar is preferably slidably adapted onto the frame for sliding in a vertical direction, the crossbar being removably fixed at a given height on the frame by manual retention means. The retention means may be for example butterfly bolts.
The device may also further comprising means for attaining fine vertical alignment with a sample fixed to the actuator. The means for attaining fine vertical alignment may comprise for example an enlarged bore hole through the crossbar, two rigid washers on each side of the bore hole and a bolt traversing the hole attached to the load cell, whereby in use fine vertical alignment with the sample is achieved visually by sliding the bolt and washers across the crossbar using the tolerance provided by the enlarged bore diameter.
The device may further comprise a test chamber for unconfined compression of a sample. The test chamber is mounted on the device for allowing the load cell to access within.
The device may alternatively further comprise a test chamber for confined compression of a sample, the test chamber being mounted on the actuator and provided with a bore adapted in size to receive in a fit-tight manner the load cell for measuring confined compression on a sample placed within the bore.
The load cell may be provided with an indentor for testing indentation of a sample.
The device may also comprise a test chamber for tension testing of a sample attached therein, the load cell being provided with grips for retaining and pulling on one end of the sample.
The device may also further comprise a test chamber attached to and suspended from the load cell, the load cell being connected to the actuator supported by the crossbar, wherein the crossbar is mounted on the frame for vertical movement, the actuator, the load cell and the chamber being aligned in one axis.
The device may also comprise a test chamber having a floor and being adapted for bending tests, the test chamber being provided with supports for supporting a sample above the floor of the chamber.
Still in accordance with the present invention, the device may also comprise a test chamber provided with microelectrodes incorporated into the test chamber to detect electrical events caused by compression induced streaming potentials within the sample during testing.
The device may further comprise a detachable chamber designed to be autoclave sterilized and to accept sterile specimens within an aseptic environment for testing in a sterile environment. The detachable chamber may further comprise a humidifying media for humidification of the sample environment confined within the chamber and separated from the sample so as to avoid potential damaging effects of humidity on the sample or on the device.
The device may further comprise a programmable digitizing amplifier situa
Buschmann Michael D.
Garon Martin
Lavertu Marc
Ouellet Matthieu
Bio Syntech Canada Inc.
Crowell & Moring LLP
Noori Max
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