JP6045390B2 - Rubber abrasion test method - Google Patents

Description

  The present invention relates to a rubber wear test method for evaluating the wear characteristics of a rubber material.

  Conventionally, in order to evaluate the wear characteristics of rubber materials used in rubber products such as automobile tires, various rubber wear tests that simulate actual vehicle running on test courses and public roads have been performed using test equipment installed indoors. It has been implemented. In such a test, it is important to improve the evaluation accuracy to reproduce the wear mode close to the condition in actual vehicle running.

  By the way, in actual vehicle running, there are a process in which rubber is fatigued due to input of unevenness on the road surface, and a process in which rubber is worn by frictional force with the road surface. Rubber fatigue is accompanied by changes in the physical and chemical properties of the surface layer, causing a decrease in physical properties such as breaking strength. Moreover, in tires used for actual vehicle travel, rubber fatigue increases due to various disturbances such as environmental changes, and rubber wear tends to be promoted.

  For this reason, it is considered effective to reproduce the wear mode in consideration of fatigue even in the rubber wear test simulating actual vehicle running. However, in the conventional tests, the severity (severity) in actual vehicle driving was not fully taken into account, and rubber fatigue was not properly taken into account, so there was room for improvement in the reproducibility of the wear mode. It was.

  Patent Document 1 below discloses a device that includes a disk-shaped member A that wears a rubber test piece and a disk-shaped member B that fatigues the rubber test piece, and independently controls them. The disk-shaped member A is made of a material suitable as a wear material such as a grinding wheel or a crushed stone, and the disk-shaped member B is made of a material that does not cause wear, such as stainless steel or plastic. Thus, when the characteristics of the simulated road surface are different between wear and fatigue, it is considered that the wear mode close to the condition in actual vehicle running cannot be reproduced sufficiently.

JP2011-153865A

  It is an object of the present invention to provide a rubber wear test method excellent in reproducibility of wear modes in consideration of rubber fatigue.

  The above object can be achieved by the present invention as described below. That is, in the rubber abrasion test method according to the present invention, the rubber test piece is rolled under a condition that does not cause wear while pressing the rubber test piece against the simulated road surface, and the rubber surface is input by inputting the unevenness of the simulated road surface. A fatigue process for fatigue the test piece, and a wear process for wearing the rubber test piece by rolling while pressing the rubber test piece that has undergone the fatigue process against a simulated road surface with a second load, The same simulated road surface is used in the fatigue process and the wear process.

  In this rubber wear test method, the wear mode that takes into account the fatigue of rubber can be reproduced by using the rubber test piece that has undergone the fatigue process in the wear process. In addition, since the fatigue process is performed under conditions that do not cause wear on the rubber test piece, the surface layer of the rubber test piece whose properties have changed is prevented from being worn out by the fatigue process, ensuring accurate evaluation in the wear process. it can. In addition, since the same simulated road surface is used in the fatigue process and the wear process and approaches the conditions in actual vehicle travel, the reproducibility of the wear mode is excellent.

  The use of the same simulated road surface in the fatigue process and the wear process is not limited to the case where the simulated road surface used in the fatigue process is continuously used in the wear process, but substantially the same properties as the simulated road surface used in the fatigue process. The case where another simulated road surface is used in the wear process is also included. For example, a simulated road surface formed by an asphalt road surface is used in a fatigue process, and another simulated road surface formed by an asphalt road surface having properties (for example, surface roughness) substantially the same as the simulated road surface is used in an abrasion process. May be.

  In the fatigue step, the rubber test piece is worn by covering the surface layer portion of the rubber test piece with a thin protective sheet or by making the first load smaller than the second load. It can be prevented from occurring. According to this method, wear of the rubber test piece in the fatigue process can be easily prevented, and an accurate evaluation in the wear process can be secured satisfactorily.

  If the simulated road surface used in the fatigue process and the wear process is formed of an asphalt road surface, the simulated road surface has substantially the same properties as the actual road surface, so that the evaluation accuracy is effectively approached to the conditions in actual vehicle running Enhanced. Such a simulated road surface can be formed, for example, by fixing a hard aggregate with an adhesive to a surface against which a rubber test piece is pressed.

Schematic configuration diagram showing an example of a rubber abrasion tester Schematic configuration diagram when a protective sheet is attached to a rubber test piece Graph showing the relationship between the rolling time of rubber test pieces and the amount of wear during the wear process A close-up of the start stage of the graph of FIG. Schematic configuration diagram showing another example of rubber abrasion test equipment

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a rubber wear test apparatus used in this embodiment. In this test apparatus, the outer peripheral surface of the rotating drum 2 is a simulated road surface 20, and the rubber test piece 1 is rolled on the simulated road surface 20. The rubber test piece 1 is formed of a columnar rubber material, but may be a rubber material of other shapes such as a disk shape, or a tire product itself such as a pneumatic tire assembled with a rim may be used as a rubber test piece. Is possible.

  A rotary drive unit such as a servo motor is connected to the rotary shafts 11 and 21 arranged in parallel to each other, and the rubber test piece 1 and the rotary drum 2 rotate independently of each other. Further, the distance between the rotary shaft 11 and the rotary shaft 21 can be adjusted by a known actuator mechanism, and the rubber test piece 1 can be pressed against the simulated road surface 20 with a desired load. Although not shown, this test apparatus includes a detector for detecting a load, a longitudinal force, a lateral force and the like acting on the rubber test piece 1 and a control unit for controlling the operation of the rotary shafts 11 and 21. Prepare.

  The simulated road surface 20 is formed of an asphalt road surface so as to approach the conditions in actual vehicle travel. The simulated road surface may be formed of a concrete road surface according to the purpose, or may be in a wet state. Even if it is other than the above, the simulated road surface 20 is brought close to the properties (for example, surface roughness) of the actual road surface by laying aggregate on the outer peripheral surface of the rotating drum 2 or performing surface treatment such as thermal spraying. It is desirable.

  In the present embodiment, a fatigue process for fatigue the rubber test piece 1 is provided before the wear process for wearing the rubber test piece 1. In the fatigue process, the rubber test piece 1 is caused to roll by rolling under conditions that do not cause wear while pressing the rubber test piece 1 against the simulated road surface 20 with a first load, and inputting the irregularities of the simulated road surface 20. . In the surface layer portion of the rubber test piece 1, the properties change due to the distortion caused by repeated input in the compression direction, and physical properties such as breaking strength are lowered. In order to improve the evaluation accuracy of the wear characteristics close to the conditions in actual vehicle running, it is necessary to consider such property changes due to fatigue.

  As described above, in the fatigue process, the rubber test piece 1 is rolled under conditions that do not cause wear. This is because if the surface layer portion of the rubber test piece 1 is worn in the fatigue process, the evaluation in the wear process may be affected. As an example of the condition that does not cause wear, the first load is set to be smaller than the second load. For example, the first load is set to 80% or less of the second load. As will be described later, the second load is a load when the rubber test piece 1 is pressed against the simulated road surface 20 in the wear process.

  Another example of the condition that does not cause wear is that the surface layer portion of the rubber test piece 1 is covered with a thin protective sheet 3 as shown in FIG. The protective sheet 3 of the present embodiment is formed of rubber, and when the rubber test piece 1 is fatigued without being worn, the thickness is preferably 0.3 to 1.0 mm. When the protective sheet 3 is used, it is preferable to set the first load higher than the second load, for example, set the first load to 80 to 120% of the second load. This compensates for a decrease in input to the rubber test piece 1 and is advantageous in that the test time can be shortened.

  As still another example of the condition that does not cause wear, a shearing force such as a longitudinal force (a force along the vertical direction in FIG. 1) or a lateral force (a force along the axial direction of the rotating shaft 11) is used. It may be less than 0.05 times the load of 1. Thus, substantial wear of the surface layer portion of the rubber test piece 1 can be prevented by reducing the force in the shear direction. Combination with the load setting and the method using the protective sheet as described above is also possible. Since the simulated road surface 20 having unevenness is used, when viewed microscopically, although a shearing force acts on the rubber at each of the minute convex portions and the concave portions, such a shearing force is a force in the shearing direction described above. Shall not be included.

  In the above, in order to bring the shearing force close to 0, it is preferable to roll the rubber test piece 1 without applying any slip ratio, slip angle, or camber angle. On the other hand, depending on the conditions, it is conceivable to provide a slip ratio or the like in order to reduce the force in the shear direction. In particular, if the rubber test piece is a pneumatic tire, a braking force is generated by rolling resistance, which may cause a longitudinal force and a lateral force. In such a case, the longitudinal force and the lateral force are offset. What is necessary is just to roll the rubber test piece 1 after giving a slip ratio etc. to the direction which can be obtained.

  In the fatigue process, it is preferable to fatigue the rubber test piece 1 in accordance with test conditions set in advance based on actual vehicle travel. That is, it is preferable to include a step of setting a test condition for the fatigue process based on actual vehicle travel before the fatigue process. The test conditions in the fatigue process include the magnitude of input to the rubber test piece 1 (first load) and the number of repetitions of the input (rolling time). When the heat history due to the ambient temperature is given to the rubber test piece 1 in the fatigue process, the ambient temperature may be included in the test conditions.

  In the step of setting the test conditions for the fatigue process based on actual vehicle travel, the input from the road surface during actual vehicle travel is predicted or estimated by tests, experiments, or simulations. In the fatigue process, an input having the same size and number of repetitions as the input in the actual vehicle travel is applied to the rubber test piece. Specific methods for setting the fatigue process test conditions based on actual vehicle running include the methods described below.

  For example, a method may be considered in which changes in the physical properties of rubber in actual vehicle travel are measured and conditions that cause equivalent physical property changes in the fatigue process are employed. That is, this is a technique for finding a condition in which physical property degradation occurs in the surface layer portion of rubber due to actual vehicle traveling, and in which physical property degradation equivalent to that occurs in traveling on a simulated road surface. Physical properties to be measured include breaking strength or breaking elongation, which can be measured by carrying out a tensile test according to JISK6251.

  Specifically, first, a rubber piece is cut out from the surface layer portion of a tire that has been actually driven, and its physical properties are measured. In addition, the rubber test piece is rolled under the condition that the simulated road surface is used and the ambient temperature is close to that of the actual vehicle and is not worn, and the load and rolling time at that time are appropriately changed. For example, the load is constant and the number of rotations of the rubber test piece is changed from 0 to 1 million. And a rubber piece is cut out from the surface layer part of each rubber test piece, the physical property is measured, and the condition which corresponds with the physical property of a real vehicle driving | running | working is made into the test condition of a fatigue process.

  As another example, a method may be considered in which conditions are set by simulation using a computer so that the maximum strain due to input from the road surface in actual vehicle travel matches the maximum strain due to input from the simulated road surface during the fatigue process. . Specifically, first, an evaluation thickness w (for example, 0.2 to 1 mm) of a rubber test piece to be tested is determined. In addition, a finite element model is created from the representative road surface shape in actual vehicle travel (one to several points on the road surface where the road surface input is large and dominant), and a finite element model is also created for tires.

  Next, a contact analysis is performed in consideration of the contact pressure during running, and the input to the tread rubber of the tire (distortion input distribution) is obtained. A finite element model is also created for the simulated road surface and rubber test piece used in the fatigue process, contact analysis using the finite element model is performed by changing the load, and the input to the rubber test piece is obtained. Further, the road surface and the load condition are determined so that the maximum strain level at the evaluation thickness w is equivalent. On the other hand, the travel distance per evaluation thickness w of an actual tire and the number N of rolling tires at the travel distance are obtained.

  As for the contact analysis result on the actual road surface, in the internal cross section of w from the ground contact surface, a region where a strain of 0.9 times or more with respect to the maximum strain is generated (that is, when the maximum strain value is 100). The area of the region having a strain of 90 to 100) is obtained, and the area ratio Sr to the entire cross-sectional area is obtained for the area. As for the contact analysis result on the simulated road surface, the area of the region where the distortion of 0.9 times or more with respect to the maximum strain is found in the internal cross section of w from the ground contact surface, and the total cross-sectional area of the area is calculated. The area ratio St to is obtained. Then, the number of revolutions obtained by multiplying the ratio Sr / St by N is calculated and used as a test condition for the fatigue process.

  After the fatigue process is performed as described above, the wear process is performed. In the wear process, the rubber test piece 1 is worn by rolling while pressing the rubber test piece 1 that has undergone the fatigue process against the simulated road surface 20 with a second load. The surface layer portion of the rubber test piece 1 has changed in properties due to the fatigue process, and the change in properties due to rubber fatigue during actual vehicle travel is reproduced, so that wear characteristics can be accurately evaluated.

  In the wear process, the rubber test piece 1 is rolled under conditions that cause wear. Therefore, a force in the shearing direction may be input to the rubber test piece 1 rolling on the simulated road surface 20 together with the input in the compression direction by the second load. The force in the shear direction can be input by, for example, applying at least one of a slip ratio, a slip angle, and a camber angle. The wear process is preferably performed in consideration of the severity (traveling severity) in actual vehicle travel, and the shearing force may be set accordingly.

  In the wear process, the same simulated road surface as that in the fatigue process is used. In this embodiment, the simulated road surface 20 used in the fatigue process is continuously used in the wear process. However, the present invention is not limited to this, and another simulated road surface having substantially the same property (for example, surface roughness) as the simulated road surface 20 used in the fatigue process may be used. Thereby, it is useful for reproducing the wear mode close to the condition in actual vehicle running.

  The simulated road surface 20 preferably has an average protrusion width of 2 to 30 mm and an average protrusion height of 2 to 30 mm so that the unevenness of the simulated road surface 20 is appropriately input to the rubber test piece 1 in the fatigue process. The average protrusion width is the maximum width (maximum diameter) in a plan view of protrusions on the road surface, and is an average value for 10 randomly extracted protrusions. The protrusion average height is the protrusion height from the base surface of the protrusion, and is an average value for 10 protrusions extracted at random.

  FIG. 3 is a graph that predicts the change in the amount of wear of the rubber test piece in the wear process, and FIG. 4 shows a close-up of the starting stage. For convenience of explanation, in FIG. 4, the scales of the horizontal axis and the vertical axis are different from those in FIG. The specifications in each example are as shown in Table 1. The actual vehicle test example is a result of a tread rubber of a tire that has been actually driven. Comparative Examples 1 and 2 and Examples 1 and 2 are the results of a laboratory test using rubber test pieces, and the test conditions are the same except for the fatigue process method and the type of simulated road surface.

  In the actual vehicle test example and the comparative example 2, the fatigue process is not performed. In Comparative Example 1 and Example 1, the rubber test piece in the fatigue process is not worn by setting the load in the fatigue process (first load) to be smaller than the load in the wear process (second load). It is like that. In Example 2, the surface layer of the rubber test piece is covered with a thin protective sheet so that the rubber test piece in the fatigue process is not worn.

  As shown in FIG. 3, as a tendency common to each example, immediately after starting the wear process, the wear rate is fast because the rubber wears while fatigued, and when the fatigue eventually ends, the wear rate becomes slow. Become. In the actual vehicle test example and the comparative example 2, since the fatigue and wear of the rubber start at the same time, the wear amount changes linearly, and the inflection point (the point where the inclination changes) seen in other examples as shown in FIG. But these are not seen.

  In Comparative Example 1 and Examples 1 and 2 after the fatigue process, an inflection point where the wear rate immediately after the start of the wear process is relatively high as shown in FIG. This is because the surface layer portion of the rubber that has been fatigued in advance wears preferentially, and after the surface layer portion wears, the portion that is not fatigued (not receiving the input of road surface irregularities) wears. .

  In Comparative Example 1, different simulated road surfaces are used in the fatigue process and the wear process, and the abrasive cloth hardly imparts fatigue of the rubber, so the inclination of the wear amount after the inflection point is different from the result of the actual vehicle test example. . Further, since the fatigue of rubber due to actual vehicle running is not sufficiently reproduced only by the wear process in the laboratory test, in Comparative Example 2 where the fatigue process has not been performed, the wear rate at the start stage is slower than the actual vehicle test example. As a result, as shown in FIG. 3, in Comparative Examples 1 and 2, the difference in the amount of wear with respect to the actual vehicle test example is relatively large at the stage where wear has progressed.

  On the other hand, in Examples 1 and 2, since the wear rate immediately after the start of the wear process is fast and wear and fatigue progress simultaneously after the inflection point, the slope of the wear amount after the inflection point is an actual vehicle test example. Close to. As a result, as shown in FIG. 3, in Examples 1 and 2, the difference in the amount of wear with respect to the actual vehicle test example is smaller than that in Comparative Examples 1 and 2 at the stage where wear progressed. According to Examples 1 and 2, by sufficiently imparting the fatigue of the rubber in advance, the result equivalent to the wear test by actual vehicle running is obtained, and the evaluation of the wear characteristics reproducing the influence of the actual road surface can be obtained. It becomes possible.

  According to Examples 1 and 2, the rubber's susceptibility to fatigue can also be evaluated. As an index for that purpose, the thickness of the fatigue layer (the region fatigued at the surface layer portion) can be mentioned. For example, the thickness of the fatigue layer is determined by measuring the amount of wear for a certain period of time in the wear step after the fatigue step, calculating the total mass of the amount of wear until the inflection point appears, and calculating the thickness of the rubber test piece. It can be measured by converting to. Or measure the amount of wear when the wear step is performed after the fatigue step and the amount of wear when the wear step is performed under the same conditions without going through the fatigue step, and the ratio between them is an index of fatigue susceptibility. It can also be considered.

  In the present embodiment, an example in which a so-called lambone type test apparatus is used has been described, but a turntable type test apparatus may be used instead. As shown in FIG. 5, in the turntable type, the base of the rotating turntable 7 is a simulated road surface 70, and the rubber test piece 1 is rolled thereon.

  The present invention is not limited to the embodiment described above, and various improvements and modifications can be made without departing from the spirit of the present invention, and the configuration and control contents of the apparatus can be changed as appropriate. It is.

DESCRIPTION OF SYMBOLS 1 Rubber test piece 2 Rotating drum 3 Protective sheet 11 Rotating shaft 20 Simulated road surface 21 Rotating shaft

Claims (3)

A rolling process in which the rubber test piece is rolled while pressing the rubber test piece against the simulated road surface with a first load, and the rubber test piece is fatigued by inputting irregularities on the simulated road surface;
A wear process for wearing the rubber test piece by rolling while pressing the rubber test piece that has undergone the fatigue process against a simulated road surface with a second load,
A rubber wear test method using the same simulated road surface in the fatigue process and the wear process.   In the fatigue step, the rubber test piece is worn by covering the surface layer portion of the rubber test piece with a thin protective sheet or by making the first load smaller than the second load. The rubber abrasion test method according to claim 1, wherein the rubber abrasion test method does not occur.   The rubber wear test method according to claim 1 or 2, wherein a simulated road surface used in the fatigue step and the wear step is formed by an asphalt road surface.

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