DESC:FIELD OF THE INVENTION
The present invention relates to the durability evaluation of rubber compound. More particularly the present invention relates to a method of establishing the fatigue life of rubber compounds. More importantly the present invention relates to a method for preparation of a simple specimen which when loaded in unidirectional fatigue type loading, is able to provide accurate information on the material durability by utilizing the basic modules of commercially available simulation process and a basic testing capability of DMA material testing. Further the present invention relates to a method for evaluating the fatigue life of a polymer or rubber composition.

BACKGROUND OF THE INVENTION
It is difficult to establish the fatigue life of rubber compounds in an accurate manner. There is commercially available software, specially designed to cater to this more sophisticated technical evaluation of a rubber product. Such commercial software is expensive to acquire and maintain. Reference may be made to the following-

Publication No. WO2017208214A1 relates to a tyre for heavy duty vehicle wheels comprising a carcass structure; and a belt structure; and a tread band, wherein the belt structure comprises: a first belt layer incorporating reinforcing elements, oriented in one or more directions, and selected from cords made of non- metallic material; a second belt layer applied on the first belt layer and comprising: i) a pair of lateral reinforcing layers positioned at axially outer ends of said second belt layer, said lateral reinforcing layers incorporating reinforcing elements oriented along a substantially circumferential direction, and ii) a central belt layer axially interposed between said pair of lateral reinforcing layers and incorporating reinforcements oriented in one or more directions; optionally, a sheet of elastomeric material arranged between said at least a first belt layer and said second belt layer, a third belt layer, radially outer side of the second belt layer and incorporating inclined reinforcing elements; and a fourth belt layer, radially outer side of the third belt layer and incorporating inclined reinforcing elements at an opposite direction with respect to that of the third belt layer. The patent is for testing of composite materials used in construction of heavy duty vehicles.

Indian Publication No. 4054/DELNP/2013 provides prediction of an expected life of a pliable material. Some embodiments of a method include modeling by a computing device the pliable material and simulating strain on the pliable material wherein simulating strain on the pliable material includes creating a strain results file. Similarly some embodiments of the method include identifying from the strain results file a point of strain energy density on the pliable material accessing a life prediction curve associated with the pliable material to determine a material file and creating a strain material file by combining the strain results file and the material file. Still some embodiments of the method include executing software to predict the expected life of the pliable material and predicting the expected life of the pliable material.

The article entitled “Study on determination of durability analysis process and fatigue damage parameter for rubber component” developed a durability analysis process for vulcanized rubber components that can predict fatigue life at the initial product design step. The determination method of nonlinear material constants for FE analysis was proposed. Also, to investigate the applicability of the commonly used damage parameters, fatigue tests and corresponding finite element analyses were carried out and normal and shear strain was proposed as the fatigue damage parameter for rubber components. Fatigue analysis for automotive rubber components was performed and the durability analysis process was reviewed [Seong-In Moon, Il-Je Cho, Chang-Su Woo and Wan-Doo Kim; Journal of Mechanical Science and Technology 25(5):1159-1165, May 2011].

The article entitled “Durability Analysis Process for Vulcanized Rubber Component” developed the durability analysis process for vulcanized rubber components, which is applicable to predict fatigue lifetime at initial product design step. Fatigue lifetime prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter. In order to develop an appropriate fatigue damage parameter of the rubber material, a series of displacement controlled fatigue tests was conducted using three dimensional dumbbell specimens with different levels of mean displacement. Fatigue analysis procedure employed in this study could be used approximately for the fatigue design [C. S. Woo , H. Y. Park, W. D. Kim, S. I. Moon; ECCM15 - 15TH European Conference On Composite Materials, Venice, Italy, 24-28 June 2012].

The article entitled “Fatigue lifetime prediction methodology of rubber components” proposed fatigue lifetime prediction methodology of vulcanized natural rubber by incorporating the finite element analysis and fatigue damage parameter determined from a fatigue test. Nonlinear finite element analyses of the 3-dimensional dumbbell specimen and rubber component were performed using the Ogden hyper-elastic material model determined from the tensile, shear and biaxial tension tests of the natural rubber, and resulted in relationships between displacement and Green-Lagrange strain for both the dumbbell specimen and the rubber component. Fatigue life tests were performed using the 3-dimensional dumbbell specimen at different levels of mean displacement. The fatigue life curve of the natural rubber represented by the maximum Green-Lagrange strain was determined from the finite element analysis and displacement-controlled fatigue test of the dumbbell specimen. Predicted fatigue lives of the rubber engine mount agreed fairly well with the experimental fatigue lives [C. S. Woo & W. D. Kim; High Performance Structures and Materials IV 285, 2008].

The present invention circumvents the requirement of expensive softwares and utilizes the basic modules of commercially available simulation process and a basic testing capability of DMA material testing machine. Accordingly, there exists a need for a simple specimen design to provide accurate feedback on the material’s fatigue life.

OBJECTS OF INVENTION
It is the primary object of the present invention to utilize the basic modules of commercially available simulation software (ABAQUS) and a basic testing capability of DMA material testing machine to provide accurate feedback on the material’s fatigue life.

It is another object of the present invention to provide fatigue testing of compound at lab level.

It is another object of the present invention to provide a method that uses one single loading level.

It is another object of the present invention to utilize basic unidirectional loading capability of DMA machine.

SUMMARY OF THE INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.

It is the primary aspect of the present invention to provide a method for evaluating the fatigue life of a polymer or rubber composition, comprising:
providing a polymer or rubber composition;
manufacturing test specimens from the polymer or rubber composition;
loading of specimen/component on fatigue testing fixture of dynamic mechanical analysis (DMA) material testing machine to decide maximum strain; and
conducting of fatigue tests at one level of strain on the specimen/component and fitting of specimen on to the vehicle and testing for durability,
wherein the specimen/component reflects the number of cycles the real product withstands during its real test,
wherein the criterion of evaluation of fatigue life is strain energy, and
wherein the design of specimen is done in a manner to match the strain energy of the vulnerable areas in the product to the specimen strain energy.
It is another aspect of the present invention, wherein the fatigue testing of specimen is provided at lab level.

It is another aspect of the present invention, wherein the strain magnitude is applied repeatedly on the specimen throughout the test and the response of the specimen over a finite number of cycles evaluates its durability characteristics.

It is another aspect of the present invention, wherein the sample is subjected to standard unidirectional loading on a dynamic mechanical analysis (DMA) machine.

It is another aspect of the present invention, wherein the polymer or rubber test specimen comprises of NR/SBR/PBR blend rubber composite (TRD-A), SBR/PBR blend rubber composite (TRD-B), NR/SBR/PBR blend rubber composite (TRD-C), NR/PBR blend rubber composite (TRD-D) and the like.

It is another aspect of the present invention, wherein the fatigue testing fixture comprises:
a rubber compound specimen/component; and
a texting fixture clamp,
wherein the rubber compound specimen/components comprises of NR/SBR/PBR blend rubber composite (TRD-A), SBR/PBR blend
rubber composite (TRD-B), NR/SBR/PBR blend rubber composite
(TRD-C), NR/PBR blend rubber composite (TRD-D) and the like and is fixed to the testing fixture clamp and subjected to strain energy.

BRIEF DESCRIPTION OF THE DRAWINGS:
So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawing, which form a part of this specification. It is to be noted, however, that the drawing illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of the invention's scope as it may admit to other equally effective embodiments.
Figure 1 illustrates line diagram of fatigue testing fixture with specimen in accordance to the present invention.
Figure 2 illustrates images of the actual specimen stand alone and as fitted on the fatigue testing fixture in accordance to the present invention.
Figure 3 illustrates Image of groove crack noticed on tire using TRD-B as the tread compound.
Figure 4 illustrates the graphical representation of the Lab test data for fatigue testing of tread compounds.

DETAILED DESCRIPTION OF THE INVENTION
It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

The present invention relates to the durability evaluation of rubber compound. More particularly the present invention relates to a method of establishing the fatigue life of rubber compounds. More importantly the present invention relates to a method for preparation of a simple specimen which when loaded in unidirectional fatigue type loading, is able to provide accurate information on the material durability by utilizing the basic modules of commercially available simulation process and a basic testing capability of DMA material testing.

The method uses one single loading level. The fatigue tests are conducted at one given level of strain on the specimen. The same strain magnitude is applied repeatedly on the specimen throughout the test. The response of the specimen over a finite number of cycles is captured to evaluate its durability characteristics.

The method for evaluating the fatigue life of a polymer or rubber composition, comprises the following steps. A polymer or rubber composition is provided. The test specimens are manufactured from the polymer or rubber composition. The specimen/component is loaded on fatigue testing fixture of dynamic mechanical analysis (DMA) material testing machine to decide maximum strain. The fatigue tests are conducted at one level of strain on the specimen/component; and fitting of specimen on to the vehicle and testing for durability. The specimen/component reflects the number of cycles the real product withstands during its real test. The criterion of evaluation of fatigue life is strain energy. The design of specimen is done in a manner to match the strain energy of the vulnerable areas in the product to the specimen strain energy.

The fatigue testing fixture [100] comprises a rubber compound specimen/component [10] and a texting fixture clamp [20]. The rubber compound specimen/components [10] comprises of NR/SBR/PBR blend rubber composite (TRD-A), SBR/PBR blend rubber composite (TRD-B), NR/SBR/PBR blend rubber composite (TRD-C), NR/PBR blend rubber composite (TRD-D) and the like and is fixed to the testing fixture clamp [20] and subjected to strain energy.

Fatigue tests were performed using the designed sample on four different compounds viz NR/SBR/PBR blend rubber composite (TRD-A), SBR/PBR blend rubber composite (TRD-B), NR/SBR/PBR blend rubber composite (TRD-C) and NR/PBR blend rubber composite (TRD-D). The same compounds were utilized in the tread section of the tires on a scooter size. The tires were fitted on to the vehicle and tested for durability. The data from the fatigue tests in the lab is shown in Figure 2, Table 1 shows the mileage achieved from each of the compounds during outdoor testing of tires. And Figure 3 shows the image of tire tested with TRD-B that was observed to fail due to groove crack.

From the data, it is observed that the lab tests are able to very accurately capture the on-field durability characteristics of different compounds.
TABLE: 1
Distance (km) Remarks
TRD-A 18000 Test stopped, no failure
TRD-B 9000 Groove crack, Test stopped
TRD-C 18000 Test stopped, no failure
TRD-D 18000 Test stopped, no failure

Although the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention. ,CLAIMS:WE CLAIM:
1. A method for evaluating the fatigue life of a polymer or rubber composition, comprising:
providing a polymer or rubber composition;
manufacturing test specimens from the polymer or rubber composition;
loading of specimen/component on fatigue testing fixture of dynamic mechanical analysis (DMA) material testing machine to decide maximum strain; and
conducting of fatigue tests at one level of strain on the specimen/component and fitting of specimen on to the vehicle and testing for durability,
wherein the specimen/component reflects the number of cycles the real product withstands during its real test,
wherein the criterion of evaluation of fatigue life is strain energy, and
wherein the design of specimen is done in a manner to match the strain energy of the vulnerable areas in the product to the specimen strain energy.

2. The method for evaluating the fatigue life of a polymer or rubber composition as claimed in claim 1, wherein the fatigue testing of specimen is provided at lab level.

3. The method for evaluating the fatigue life of a polymer or rubber composition as claimed in claim 1, wherein the strain magnitude is applied repeatedly on the specimen throughout the test and the response of the specimen over a finite number of cycles evaluates its durability characteristics.

4. The method for evaluating the fatigue life of a polymer or rubber composition as claimed in claim 1, wherein the sample is subjected to standard unidirectional loading on a dynamic mechanical analysis (DMA) machine.

5. The method for evaluating the fatigue life of a polymer or rubber composition as claimed in claim 1, wherein the polymer or rubber test specimen comprises of NR/SBR/PBR blend rubber composite (TRD-A), SBR/PBR blend rubber composite (TRD-B), NR/SBR/PBR blend rubber composite (TRD-C), NR/PBR blend rubber composite (TRD-D) and the like.

6. The method for evaluating the fatigue life of a polymer or rubber composition as claimed in claim 1, wherein the fatigue testing fixture [100] comprises:
a rubber compound specimen/component [10]; and
a texting fixture clamp [20],
wherein the rubber compound specimen/components [10] comprises of NR/SBR/PBR blend rubber composite (TRD-A), SBR/PBR blend
rubber composite (TRD-B), NR/SBR/PBR blend rubber composite

(TRD-C), NR/PBR blend rubber composite (TRD-D) and the like and is fixed to the testing fixture clamp [20] and subjected to strain energy.