JP2014163783A - Fatigue testing method of viscoelastic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new fatigue testing method which reproduces shearing fatigue received by a viscoelastic material under compressive deformation due to vehicle weight.SOLUTION: Test pieces 11A, 11B which are a viscoelastic material used for a tire are deformed by applying a compressive load, and simultaneously keep being periodically deformed in a direction perpendicular to a compression direction. The time for the test pieces to be destroyed is set as an index. The viscoelastic material is vulcanized rubber used for an inner liner. A pressure of 200-500 kPa is applied in the compressive deformation. Shearing strain amplitude is 5-20% and a shearing strain period is 20 Hz or less at room temperature, in the periodic deformation.

Description

The present invention relates to a fatigue test method for viscoelastic materials.

Conventionally, as a fatigue test method for viscoelastic materials, a test using a dematcher tester has been the mainstream. In this test method, a groove is put in a test piece, and bending deformation is repeatedly applied to the groove. The main deformation mode is tensile deformation (elongation deformation) applied to the groove bottom. Actually, the fatigue failure of the viscoelastic material is finally caused by a crack generated at the groove bottom propagating in the groove direction.

On the other hand, focusing on viscoelastic materials (rubbers) used for tires, the members that undergo tensile deformation are the only members that are subject to tensile deformation among the rubbers used for tires. Subject to deformation and shear deformation. For this reason, in the dematcher test in which the tensile deformation is the main deformation, the fatigue resistance characteristics when actually used in the tire may not be accurately expressed.

On the other hand, R.D. Klauke et al. Established a fatigue test method in which simple shear deformation is applied to a test piece by using rotational deformation. Their test method is to give a simple shear deformation by torsion to a test piece under a shear deformation applied in the direction perpendicular to the axial direction, which occurs in an actual tire much more than a conventional tensile deformation. There is an advantage that it can be measured in the deformation mode close to the deformation. However, this method does not take into account the compressive deformation due to the vehicle weight that should be received in an actual tire, and it cannot be said that the actual deformation of the tire is completely reproduced.

Among the tire components, the inner liner is placed under a high compression force due to the vehicle weight at the tire edge, so the viscoelastic material (rubber) used for the inner liner is a fatigue test that takes into account the effects of compressive deformation. A method needs to be built and evaluated.

R. Klauke, T .; Alshuth, J. et al. Ihlemann, Lifetime prediction of rubber materials under simple samples shear load with rotating axes, Kautsch Gummi Kunstst 63 (7/8) 286-290

An object of the present invention is to solve the above-mentioned problems and to provide a new fatigue test method that reproduces the shear fatigue experienced by a viscoelastic material under compression deformation due to vehicle weight.

The present invention is a viscoelasticity used for a tire, which applies cyclic deformation to a test piece while continuously applying cyclic deformation in a direction perpendicular to the compression direction and uses the time until the test piece is broken as an index. The present invention relates to a fatigue test method for materials.

It is preferable that the viscoelastic material is a vulcanized rubber used for an inner liner.

In the compression deformation, it is preferable to apply a pressure of 200 to 500 kPa.

In the periodic deformation, the shear strain amplitude is preferably 5 to 20% and the shear strain cycle is preferably 20 Hz or less at room temperature.

According to the present invention, while applying compressive deformation to a test piece, it continues to give periodic deformation in a direction perpendicular to the compression direction, and is used for a tire using the time until the test piece is broken as an index. Since this is a fatigue test method for viscoelastic materials, it is possible to provide a new fatigue test method that reproduces the shear fatigue experienced by viscoelastic materials under compression deformation due to vehicle weight. Therefore, by evaluating the viscoelastic material by the test method, it is possible to evaluate the properties of the viscoelastic material against shear fatigue under compressive deformation due to vehicle weight, and fatigue resistance characteristics when the viscoelastic material is used for a tire. Can be predicted.

It is a schematic diagram for demonstrating an amplitude. It is a schematic diagram which shows an example of the sample for a test. It is a schematic diagram which shows an example of the compression deformation | transformation and periodic deformation | transformation added to the test sample.

The fatigue test method of the viscoelastic material used in the tire of the present invention is to apply cyclic deformation to the test piece while applying compressive deformation until the test piece is broken. Time is used as an index.

In the present invention, since the deformation actually received by the tire is disassembled into elementary deformation elements and the corresponding deformation elements are given to the test piece, a fatigue test method that is more faithful to actual tire deformation can be provided. Specifically, for compression by vehicle weight, pressure (compression load) is applied to the test piece as compression deformation, and for cyclic deformation received from the road surface, periodic shear strain is applied to the compression direction as periodic deformation. Apply to the test piece in the vertical direction. Thus, by evaluating the viscoelastic material using the test method, it is possible to evaluate the fatigue resistance characteristics of the viscoelastic material in a deformation mode closer to the actual tire fatigue, and when the viscoelastic material is used for a tire. It is possible to make a more precise prediction of the tire life. For example, when a group of samples (viscoelastic material) that does not show a significant difference in a test using a dematcher testing machine is tested by the test method of the present invention, a significant difference is observed in the results of each sample. A more accurate prediction can be made with respect to the life of the tire when the (viscoelastic material) is used for the tire.

In the compression deformation, the applied pressure (compressive load) is not particularly limited, but is preferably a pressure corresponding to the vehicle weight, specifically 200 to 500 kPa. This is because when the weight of a light vehicle is equivalent to 200 kPa and the weight of a heavy truck is equivalent to 500 kPa, the applied pressure is within the above range, and the measured viscoelastic material is used for a tire. It is possible to predict the fatigue resistance of the steel. In addition, what is necessary is just to set the said pressure according to the weight of the vehicle which plans use of a tire. Here, that the applied pressure is 500 kPa means that a compressive load of 500 kPa is applied to the test piece.

In the cyclic deformation, the shear strain amplitude (the amplitude of the cyclic deformation) is not particularly limited, but it preferably corresponds to the amplitude of the periodic strain that the tire actually receives from the road surface. % Is preferred. By setting the amplitude within the above range, it is possible to suitably predict fatigue resistance characteristics when the measured viscoelastic material is used for a tire. In the present invention, the shear strain amplitude means the ratio of the strain amount in the shear direction to the sample thickness (strain amount in the shear direction / sample thickness × 100 (%)) (see FIG. 1).

The shear strain period (period of periodic deformation) is not particularly limited, but when measured at room temperature, it is preferably set to 20 Hz or less (corresponding to 200 km / h), which is the maximum value of the tire rolling period at room temperature. . Although the minimum of this period is not specifically limited, When measuring at room temperature, Preferably it is 0.5 Hz or more, More preferably, it is 1 Hz or more. By setting the cycle within the above range, it is possible to suitably predict the fatigue resistance when the measured viscoelastic material is used for a tire. The set range of the cycle can be converted to a set range at an arbitrary temperature using a so-called time-temperature conversion rule.

The measurement temperature (the temperature of the thermostatic chamber in which the test piece is placed during the measurement) is preferably 10 to 130 ° C., more preferably 10 to 110 ° C., because the influence of the thermal deterioration and embrittlement of the rubber can be reduced. .

The shape of the test piece is preferably a disk shape having a diameter of 3 to 25 mm and a thickness of 1 to 10 mm.

The viscoelastic material is not particularly limited, and general materials such as vulcanized rubber (composition), thermosetting plastic, and thermoplastic plastic can be used. Among these, vulcanized rubber that is often used for tires can be preferably used. Among vulcanized rubbers, the tire edge portion is placed under a high compressive force due to the vehicle weight, so the fatigue test method of the present invention can be used to predict fatigue resistance characteristics when used in tires. Vulcanized rubber used for the liner is preferred.

The vulcanized rubber used for the inner liner is preferably one containing butyl rubber, natural rubber (NR) and carbon black. Thereby, the fatigue resistance characteristic at the time of using the measured viscoelastic material (vulcanized rubber) for a tire can be estimated suitably.

Examples of the butyl rubber include halogenated butyl rubbers such as butyl rubber (IIR), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR), and fluorinated butyl rubber (F-IIR).

The content of butyl rubber in 100% by mass of the rubber component is preferably 70 to 90% by mass. The content of NR in 100% by mass of the rubber component is preferably 10 to 30% by mass. The content of carbon black with respect to 100 parts by mass of the rubber component is preferably 10 to 150 parts by mass, more preferably 50 to 90 parts by mass.

The measuring apparatus capable of performing the fatigue test method of the present invention is an apparatus capable of continuously applying cyclic deformation in a direction perpendicular to the compression direction while applying compressive deformation (compression load) to the test piece. If it is, it will not specifically limit, For example, the viscoelasticity measuring apparatus as described in Unexamined-Japanese-Patent No. 2006-177734, the large-sized fatigue testing machine by Yoshimizu, the large deformation viscoelasticity testing apparatus by Yoshimizu, etc. can be used.

Next, an example of a test sample used for the fatigue test method of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic diagram illustrating an example of a test sample. The test sample 1 is composed of a pair of test pieces 11A and 11B made of a viscoelastic material, an intermediate support body 12 in which the test pieces 11A and 11B are arranged on both end faces, and the intermediate support body 12 with the test pieces 11A and 11B interposed therebetween. It consists of a pair of both-sides support body (one side support body 13 and the other side support body 14) which are arrange | positioned at both sides and are arranged on a straight line and the straight line.

The intermediate support body 12, the one-side support body 13, and the other-side support body 14 are made of a cylindrical metal material and have the same diameter.

The test pieces 11 </ b> A and 11 </ b> B are cut into a disk shape having the same diameter as the intermediate support 12, the one-side support 13, and the other-side support 14. The test pieces 11A and 11B are attached to both end faces of the intermediate support 12 and are sandwiched between the one side support 13 and the other side support 14 from both sides.

As described above, in the test sample shown in FIG. 2, the pair of test pieces 11A and 11B are sandwiched between the intermediate support 12 and the one side support 13, and the intermediate support 12 and the other side support 14, respectively. ing.

In this example, the intermediate support body 12, the one-side support body 13, the other-side support body 14, and the test pieces 11A and 11B have the same diameter and cross-sectional shape. Thereby, the fatigue resistance characteristic at the time of using the measured viscoelastic material for a tire can be estimated suitably.

In this example, the diameter of the intermediate support body 12, the one side support body 13, the other side support body 14 and the test pieces 11A and 11B is 3 to 25 mm, and the thickness (height) of the test pieces 11A and 11B is 1 to 10 mm. The height (thickness) of the intermediate support body 12, the one side support body 13, and the other side support body 14 is 3 to 50 mm. Thereby, the fatigue resistance characteristic at the time of using the measured viscoelastic material for a tire can be estimated suitably.

It is possible to perform the fatigue test method of the present invention by setting the test sample shown in FIG. Specifically, as shown in FIG. 3, the test piece 11 </ b> A is obtained by pressing the one side support 13 and the other side support 14 toward the intermediate support 12 side in the cylinder axis direction (X direction in FIG. 3). , 11B, compression deformation is applied from both sides. Furthermore, periodic shear deformation is applied to the test pieces 11A and 11B by periodically reciprocating (vibrating) the intermediate support 12 in the direction perpendicular to the cylinder axis direction (Z direction in FIG. 3).
As described above, compression deformation corresponds to deformation due to vehicle weight, and periodic shear deformation (periodic deformation) corresponds to deformation received from the road surface.

The viscoelastic material having the same composition as the test pieces 11A and 11B is used for the tire by continuously applying compression deformation and shear deformation to the test pieces 11A and 11B and measuring the time until the test pieces 11A and 11B break. It is possible to predict the fatigue resistance of the tire when it is worn. In the present invention, the time until destruction is not limited to the time until the test piece is completely destroyed, but is a concept including the time until the test piece is cracked.

In the test sample shown in FIG. 2, the test piece is fixed to the support (intermediate support 12, one-side support 13, and other-side support 14) in the cylinder axis direction (X direction in FIG. 3). However, in order to prevent peeling between the metal and the viscoelastic material (rubber), it is preferable to use a chemical substance that bonds the metal and the viscoelastic material. Thereby, the fatigue resistance characteristic at the time of using the measured viscoelastic material for a tire can be estimated suitably. The chemical substance is not particularly limited as long as it is usually used as an adhesive. For example, an epoxy adhesive, a urethane adhesive, a vulcanized adhesive, and the like can be used.

In the test sample shown in FIG. 2, the case where the intermediate support body and the both side support bodies are cylindrical has been described. However, in the present invention, the intermediate support body and the both side support bodies may have a prismatic shape. In this case, it is preferable that the test piece has the same cross-sectional shape as the support.

As a test sample, a pair of test pieces made of a viscoelastic material, an intermediate support on which the test pieces are arranged on both end faces, and arranged on both sides of the intermediate support with the test piece in between, on a straight line with the intermediate support Applying pressure (compression load) to the test piece from both sides using a test sample consisting of a pair of side supports arranged in a row, and applying periodic shear strain to the test piece in a direction perpendicular to the compression direction. Can evaluate the fatigue resistance characteristics of viscoelastic materials (particularly vulcanized rubber used for inner liners) in a deformation mode closer to the fatigue of actual tires. More accurate predictions for lifespan.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Natural rubber: TSR # 20
Chlorobutyl: Chlorinated butyl rubber HT1066 manufactured by JSR Corporation
Recycled butyl: Muraoka Rubber Industrial Co., Ltd. Butyl Tube Recycled Rubber Carbon Black: Mitsubishi Chemical Co., Ltd. Dia Black N660
Aroma oil: JOMO process X140 manufactured by Japan Energy Co., Ltd.
Anti-aging agent RD: ANTAGE RD manufactured by Kawaguchi Chemical Industry Co., Ltd.
Stearic acid: Zinc stearate manufactured by NOF Corporation: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Ouchi Shinsei Chemical Industry Co., Ltd. ) Noxeller DM made

(Preparation of vulcanized rubber composition and test tire)
According to the formulation shown in Table 1, using a Banbury mixer, materials other than sulfur and the vulcanization accelerator were kneaded for 4 minutes at a discharge temperature of 140 ° C. to obtain a kneaded product. Sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 2 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was vulcanized at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition (vulcanized rubber sheet).
Next, the obtained unvulcanized rubber composition was molded into an inner liner shape on a tire molding machine, and bonded to another tire member to produce an unvulcanized tire. A test tire was manufactured by vulcanizing an unvulcanized tire at 180 ° C. for 10 minutes.

The following evaluation was performed about each vulcanized rubber composition of the mixing | blending A and B, and each tire for a test. The results are shown in Table 2.

(Example)
(Evaluation of vulcanized rubber composition by the method of the present invention)
<Preparation of sample piece>
A pair of test pieces cut out from the obtained vulcanized rubber composition (vulcanized rubber sheet) into a disk shape having a diameter of 10 mm and a thickness of 2 mm was applied to a brass column having the same diameter and a height of 10 mm with an adhesive (Henkel). A sample for test was prepared by using Loctite 407) manufactured in the same manner as in FIG.
<Test conditions>
Using the obtained test sample, compression deformation (compression load) is applied to the test piece using a large deformation viscoelasticity test apparatus manufactured by Yoshimizu under the conditions of a temperature of 23 ° C. and a relative humidity of 55%. Evaluation was performed using the time until the test piece was broken as an index while applying cyclic deformation in a direction perpendicular to the compression direction. The compressive load, shear strain amplitude (amplitude of cyclic deformation), and shear strain cycle (period of cyclic deformation) were performed under the conditions shown in Table 2.
In addition, the compressive load of Examples 1-4 is a load equivalent to the vehicle weight of a normal passenger car, a light vehicle, and a large truck, respectively.

(Comparative example)
(Evaluation of vulcanized rubber composition by demach bending crack test)
The obtained vulcanized rubber composition (compound A, blend B) was subjected to the conditions of a temperature of 23 ° C. and a relative humidity of 55% according to JIS K6260 “Method for Demach Bending and Cracking of Vulcanized Rubber and Thermoplastic Rubber”. For the vulcanized rubber specimen sample, the number of times until the crack growth reached 1 mm was measured. The test results were as follows: Formulation A was 230,000 times and Formulation B was 220,000 times, and no significant difference was found between Formulations A and B.

(Actual vehicle evaluation)
The obtained test tire is mounted on a normal passenger car so that the test tire of Formulation A and the test tire of Formulation B are freed, run 6000 km, and cracks on the tire inner surface (inner liner) after running The presence or absence of occurrence was confirmed. As a result, cracks could not be confirmed in the test tire of Formulation A, but multiple cracks could be confirmed in the test tire of Formulation B.

((Result of Formulation A / Result of Formulation B) -1)
About the result of each example, the value of (Result of Formulation A (New) / Result of Formulation B (Recycled Product))-1 was calculated. The larger the calculation result ((Result of Formulation A / Result of Formulation B) -1), the greater the difference between the results of Formulations A and B, and the clearer the difference in fatigue resistance (fatigue fracture resistance) between the new product and the recycled product It shows that it can be evaluated. When the value of (Result of Formulation A / Result of Formulation B) -1) was 0.5 or more, it was determined that there was a significant difference.

In the examples evaluated by the fatigue test method using the time until the test piece was destroyed as an index, the test piece was subjected to cyclic deformation in the direction perpendicular to the compression direction while applying compressive deformation. A significant difference was found in the results of A and B, and a correlation was found with the results of actual vehicle evaluation. On the other hand, in the comparative example evaluated by the demach bending crack test, no significant difference was found in the results of the blends A and B.

DESCRIPTION OF SYMBOLS 1 Test sample 11A, 11B Test piece 12 Intermediate support body 13 One side support body 14 Other side support body

Claims (4)

Fatigue test of viscoelastic materials used in tires, with the period of time until the test piece breaks as an index while applying compressive deformation to the test piece and continuously applying cyclic deformation in the direction perpendicular to the compression direction Law. The viscoelastic material fatigue test method according to claim 1, wherein the viscoelastic material is a vulcanized rubber used for an inner liner. The fatigue test method for a viscoelastic material according to claim 1 or 2, wherein a pressure of 200 to 500 kPa is applied in the compression deformation. The fatigue test method for a viscoelastic material according to any one of claims 1 to 3, wherein in the periodic deformation, the shear strain amplitude is 5 to 20% and the shear strain cycle is 20 Hz or less at room temperature.

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