Title of Invention

"A TWO-DIMENSIONAL STRESS RELAXATION TESTING DEVICE"

Abstract A two dimensional stress relaxation testing device by two pairs of juxtaposed grippers, mutually perpendicular to each other for holding the test specimen, each gripper being provided with a thimble to eliminate any slackness while testing, the grippers being driven over four slideways, away from each other, through forearm linkage mechanism, each arm displacing one gripper slide in horizontal plane, while the drive being fed by a shaft from a driving source and the force generated thereby being detected by four force detectors mounted on a clamp, displaying the output in an output device, connected to an interface.
Full Text The present invention relates to a two-dimensional stress relaxation testing device.
This device has potential industrial application for selecting right kind of materials by analysing their behaviour under different simulated stress-strain conditions while producing various value added products. It has thus enormous potential for the purpose of quality control as well as materials management in respect of such prominent industries as leather products, footwear, textile, polymeric industry to name but a few.
Several sheet materials like polymeric materials, leathers , textiles, engineering composite materials etc. are being widely used in several engineering environments. As reported by Ramanathan et al (Journal of the Indian Leather Technologists Association, 16 , 293, 1968), these materials undergo various stresses in mutually perpendicular directions while in use for different applications. For example, the upper leather of a shoe is subjected to force in all directions. Ramanathan et al (Proceedings of the International Southern Biomedical Engineers Conference, Shrevepor, Louisiana, USA , 1982) reported that the force on the surface of the upper portion of the leather is enormous while walking. Moreover, with the advent of fashions several combination of materials are being used in shoe manufacture. It is therefore necessary to understand the mechanical properties, stress relaxation, hysteresis and mechanism of failure of these materials by simulating the user conditions for efficient use of these materials.
Presently the viscoelastic nature of the materials are analysed using unidirectional testing by Universal Testing Machines (UTM), where a dumbbell shaped sample

gripped by two jaws is pulled apart using motorised crosshead till the sample fails. As reported by Ridge and Wright (Biorheology, 2 ,67,1964), Muthiah et al (Biorheology, 4 ,185,1967), the force generated per unit area during the deformation, which eventually leads to the fracture of the sample, is usually taken as a measure of the tensile strength of the material under consideration. In addition, the gradual decrease in the force, developed during deformation, to a given strain level, viz., stress relaxation, provides information on the rearrangements of the molecular structure, which depends on the viscous nature of the samples, as reported by Arumugam et al (Handbook of Advanced Materials Testing , Edited by N P Cheremisinoff and P N Cheremisinoff, Marcel Dekker Inc., New York, p 909, 1995). Similarly repeated deformations upto a certain strain level and back provide information about the plasticity of the sample, as reported by Vogel (Bioengineering and Skin , 4, 75,1988). As reported by Arumugam (Studies on the structural and mechanical properties of collagenous materials, Ph.D. Thesis submitted to the University of Madras, 1989) and Arumugam et al (Journal of Biosciences, 19, 307,1994), all these characteristics depend on the rate at which the experiments are performed.
The use of unidirectional sample and the failure in one direction does not simulate the application conditions. This is because of the fact that the high Poisson's ratio of many viscoelastic materials does not permit deduction of realistic information about these materials from such tests. For example, there is tremendous amount of lateral contraction due to the high Poisson's Ratio of the leather while testing the sample in the conventional UTMs. Therefore, the extension and the breaking load observed for the sample under uni-directional test conditions are very different from those in a shoe

undergoing a similar kind of stress during usage. Moreover, intermediate conditions of testing and the formation of surface cracks and their role in hastening or delaying failure during application cannot be studied. In addition, there are inherent inhomogeneities in certain materials like leather, textiles etc., which necessitates performing uniaxial testing in more than one direction to get a complete understanding of the material properties.
No prior art is available on the use of a device to analyse stress relaxation behaviour of a material in two mutually perpendicular directions.
The main objective of the present invention is to provide a two-dimensional stress
relaxation testing device, which obviates the drawbacks stated above.
Another objective of the present invention is to provide a device to analyse stress
related behaviour of materials simultaneously in two mutually perpendicular
directions.
Yet another objective of the present invention is to provide a device to perform
dynamic testing of materials
Still another objective of the present invention is to reduce the number of test
sample and time as well as labour while analysing the stress related properties of
materials.
Yet another objective of the present invention is to to provide a device study the
mechanical properties of sheet materials without any lateral contraction.
Still another objective of the present invention is to to provide a device study and develop theoretical model for stress relaxation when the lateral contraction is not present.
In the drawings accompanying this specification,
Fig.l represents the elevation of the device of the present invention and
Fig.2 represents the plan of the device of the present invention
Various components, as shown with numerals in the Figure 1 as well as Figure 2 of
the drawings accompanying this specification are the following.
1 refers to the driving source.
2 refers to the shaft connected to the driving source.
3 refers to the grippers.
4 refers to the slide ways, on which the grippers slide away from each other.
5 refers to the arms connecting the shaft and the grips.
6 refers to the specimen to be tested.
7 refers to the force detector and
8 refers to the attached output device.
Thus the device of the present invention comprises essentially of a forearm mechanism which gets the drive from a driving source to move two pairs of grippers away from each other on slide ways.
Accordingly, the present invention provides a two dimensional stress relaxation testing device, which comprises of two pairs of juxtaposed grippers(3), mutually perpendicular to each other for holding the test specimen (6), each gripper being provided with a thimble to eliminate any slackness while testing, the grippers being driven over four slideways (4), away from each other, through forearm linkage mechanism, each arm (5) displacing one gripper slide in horizontal plane, while the drive being fed by a shaft (2) from a driving source(l) and the force generated thereby being detected by four force detectors (7) mounted on a clamp, displaying the output in an output device (8), connected to an interface. In an embodiment of the present invention, the driving source may be such as D.C.(Direct Current) motor, hydraulic drive, pneumatic drive.
In another embodiment of the present invention, the speed of separation of grips may be in the range of 0.01mm to 1000 mm per second.
In yet another embodiment of the present invention, the gauge length used along two perpendicular axes may be at least 5 mm.
In still another embodiment of the present invention, the grips used may be selected from the group consisting of mechanical, electrical, pneumatic grips.
In still another embodiment of the present invention, the control mechanism for the movement of the grips may be selected from gear assembly, hydraulic drive, pneumatic drive In yet another embodiment of the present invention, the force detectors may be selected from force transducers, strain gauges
In still another embodiment of the present invention, the output device used may be selected from the group consisting of a computer interface, digital display, analog output, chart recorder.
The device has two pairs of juxtaposed grippers(3), mutually perpendicular to each other for holding the test specimen. The grippers are designed to move away from each other on mutually perpendicular linear motion slideways. Each gripper slide is provided with a thimble to eliminate any slackness in the specimen before initiating the experiment. The test sample (6) is held by the grippers (3) and is stretched at a rate ranging from 0.01mm to 1000 mm per second in equal amounts along two mutually perpendicular directions. The drive to the gripper slides is provided by a driving source (1) through a vertical shaft (2) and a forearm linkage (5) mechanism, each arm displacing one gripper slide in the horizontal plane. The force generated is detected and measured by the force detectors (7), which send the output to output device. The simultaneous measurement of the force in the two mutually perpendicular directions gives the two dimensional stress relaxation. The loss of energy owing to the repeated stress or strain cycling of the sample can also be computed from the hysteresis loop obtained on the output device.
The novelty of the present invention lies in using two pairs of juxtaposed grippers, mutually perpendicular to each other for holding the test specimen , thereby enabling the simultaneous measurement of stress related properties, especially stress relaxation of materials, avoiding the factor of Poisson's ratio, in mutually perpendicular directions while simulating the near exact application conditions of different materials of multifarious characteristics.
The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
Example -1
A plus shaped test sample of length 20 mm in both the mutually perpendicular directions was cut with a die from a cow upper leather and the same was gripped to the device with the help of four mechanical grippers. The test sample was strained at 1 mm/min speed by using a DC motor as the driving source to 20% level and then the machine was switched off. The sample was allowed to relax for a period of 3 hours, while continuously monitoring the force, which was displayed on the monitor of a computer terminal in graphical form.
Example-II
A plus shaped test sample of length 40 mm in both the mutually perpendicular directions was cut with a die from a goat upper leather and the same was gripped to the device with the help of four mechanical grippers. The test sample was strained at 5mm / min speed by using a hydraulic drive to 30% level and was again brought back immediately to the original condition of 0% strain at the same speed. Again the sample was strained at same speed and the process was repeated for 100 times. Finally the machine was switched off at the 0% strain level of the sample. Hysteresis loops of all the cycles were obtained on the recorder.
Example - III
A plus shaped test sample of length 50 mm in both the mutually perpendicular directions was cut with a die from a polyethylene film and the same was gripped to
the device with the help of four mechanical grippers. The test sample was strained at 50mm / min speed by using a DC motor as the driving source to 80% level and then the machine was switched off. The sample was allowed to relax for a period of 2 hours, while continuously monitoring the force on the sample which was displayed on the monitor of a computer terminal in graphical form.
Example - IV
A plus shaped test sample of length 70 mm in both the mutually perpendicular
directions was cut with a die from a textile material and the same was gripped to the
device with the help of four pneumatic grippers. The test sample was strained at
1000mm / min speed by using a pneumatic drive to 20% level and then the machine
was switched off. The sample was allowed to relax for a period of 5 hours, while
continuously monitoring the force on the sample which was displayed on the monitor
of a computer terminal in graphical form.
The main advantages of the present invention are the following.
I.It is possible to study the stress relaxation behaviour as well as hysteresis of
different materials in two mutually perpendicular directions simultaneously, thereby
reducing the number of test samples and testing time required thereof.
2. Stress relaxation experiments can be carried out without subjecting the test sample
to lateral contractions, thereby overcoming the limitation encountered in the materials
with high Poisson's ratio in connection with the simulation to the actual working
conditions.
3.It is possible to study the role of fiber orientation in the stress relaxation and
dynamic testing conditions, especially in materials having no or very little Poisson's
ratio.
4.It is also possible to study the fatigue and flexing properties of sheet materials,
polymeric materials and leather.
5. The shape deformation in sheet materials, biological materials and leather for a
given stress can be studied in this instrument.



We claim:
1. A two dimensional stress relaxation testing device characterized by two pairs of juxtaposed grippers(3), the said juxtaposed grippers (3) being placed mutually perpendicular to each other for holding the test specimen (6), each of the said gripper being provided with a thimble to eliminate any slackness while testing, the said grippers being driven over four slideways (4), away from each other, through forearm linkage mechanism, each of the said arm (5) displacing one gripper slide in horizontal plane, while the drive being fed by a shaft (2) from a driving source(l) and the force generated thereby being detected by four force detectors (7) mounted on a clamp, displaying the output in an output device (8), connected to an interface. 2.A device, as claimed in claim 1, wherein the driving source is D.C. motor , hydraulic drive, pneumatic drive.
3. A device, as claimed in claim 1, wherein the speed of separation of grips is in the
range of 0.01mm to 1000 mm per second.
4. A device, as claimed in claim 1, wherein the gauge length used among in two
mutually perpendicular axes is minimum 5 mm.
5. A device, as claimed in claim 1, wherein the grips used are mechanical, electrical,
pneumatic.
6. A device, as claimed in claim 1, wherein the control mechanisms for the
movement of the grips are gear assembly, hydraulic drive, pneumatic drive.
7. A device, as claimed in claim 1, wherein the force detectors are selected from force
transducers, strain gauges.
8. A device, as claimed in claim 1, wherein the output devices used computer
interface, digital display, analog output, chart recorder.
9. A two dimensional stress relaxation testing device substantially as herein described with reference to the examples.

Documents:

137-del-1999-abstract.pdf

137-del-1999-claims.pdf

137-del-1999-correspondence-others.pdf

137-del-1999-correspondence-po.pdf

137-del-1999-description (complete).pdf

137-del-1999-drawings.pdf

137-del-1999-form-1.pdf

137-del-1999-form-19.pdf

137-del-1999-form-2.pdf

137-del-1999-form-3.pdf

137-del-1999-petition-138.pdf


Patent Number 215617
Indian Patent Application Number 137/DEL/1999
PG Journal Number 11/2008
Publication Date 14-Mar-2008
Grant Date 28-Feb-2008
Date of Filing 25-Jan-1999
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001,
Inventors:
# Inventor's Name Inventor's Address
1 SANJEEVI RAMASWAMY CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600020, INDIA.
2 NARESH MANDYAM DEIVASIGAMANI CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600020, INDIA.
3 ARUMUGAM VISWANATHAN CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600020, INDIA.
4 SOMANATHAN NARAYANA SASTRI CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600020, INDIA.
5 MUTHUKRISHNAN SUBRAMANIAM CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600020, INDIA.
6 KALAIARASU KRISHNASWAMY CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600020, INDIA.
PCT International Classification Number G01N 3/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA