Method for estimating fracture life of rubber composition

Abstract

To provide a technique for more simply estimating the fracture life of a rubber composition.SOLUTION: A method for estimating a fracture life of a rubber composition includes a step of acquiring a material constant of a test piece of a target rubber composition, a step of acquiring a repeated strain condition or a repeated stress condition, and an estimation step of calculating a crack growth rate of the test piece or a number of times at fracture indicating the number of times of the repeated load at which the test piece fractures, by using the material constant and the strain condition or the repeated stress condition, assuming that the repeated load acts on the test piece of the target rubber composition in a repeated tensile test.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for estimating the fracture life of a rubber composition. [Background technology]

[0002] In rubber products such as tires made of a rubber composition, cracks occur and grow due to repeated deformation during use, but it is difficult to grasp the deterioration state of rubber products during use. Therefore, various methods have been proposed for evaluating the wear resistance and fatigue properties of rubber products or rubber materials based on actual measurements obtained by performing tests such as tensile tests on rubber test pieces that repeatedly apply loads.

[0003] The following Patent Document 1 discloses a method for estimating the tensile fatigue life of a vulcanized rubber material with desired specifications for an arbitrary tensile strain energy density W, by creating a life estimation line with the vertical axis representing strain energy density W and the horizontal axis representing the number of times a tensile force is applied n, based on data obtained by measuring the crack growth rate and conducting a tensile test on the rubber material. Patent Document 2 listed below discloses a method for evaluating the abrasion resistance of vulcanized rubber by applying a predetermined strain a predetermined number of times to a test piece having a V-shaped portion with a predetermined interior angle and a notch of a predetermined length made at the apex of the interior angle, and then measuring the amount of crack growth in the notch of the test piece. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-85701 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-255741 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is still room for improvement in existing evaluation methods. For example, the evaluation method disclosed in Patent Document 2 requires the preparation of a specific test piece having a V-shaped portion and the measurement of the crack growth amount through an actual test, and therefore there is room for improvement in terms of evaluation time and labor. The present invention has been made in view of the above circumstances, and provides a technique for more simply estimating the fracture life of a rubber composition. [Means for solving the problem]

[0006] According to the present invention, there is provided a method for estimating the rupture life of a rubber composition, which includes: a first acquisition step of acquiring material constants of a test piece of a target rubber composition; a second acquisition step of acquiring repeated strain conditions or repeated stress conditions; and an estimation step of calculating, using the material constants and the strain conditions or the repeated stress conditions, the crack growth rate of the test piece or the number of times to rupture indicating the number of repeated loads at which the test piece ruptures, assuming that repeated loads act on the test piece of the target rubber composition in a repeated tensile test.

[0007] Furthermore, according to the present invention, there is also provided a tire manufacturing method, which includes a selection step of selecting one rubber composition from among a plurality of rubber compositions having mutually different component formulations based on the relationship information obtained by applying the above-mentioned method for estimating fracture life, and a manufacturing step of manufacturing a tire using the selected rubber composition, wherein in the selection step, a rubber composition is selected for which the repeated strain condition or the set repeated stress condition, or the calculated value of these, at a set value of the number of fractures indicated by the relationship information, exceeds a set threshold value.

[0008] Furthermore, according to the present invention, it is possible to provide an information processing device that includes at least one or more memories and one or more processors and that is capable of executing the above-described fracture life estimation method. Furthermore, according to the present invention, there can also be provided a computer program stored in one or more memories and executed by one or more processors, which causes one or more computers equipped with the one or more memories and the one or more processors to execute the above-mentioned fracture life estimation method, and a recording medium on which the computer program is recorded. [Effects of the Invention]

[0009] According to the present invention, a technique for more simply estimating the fracture life of a rubber composition can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flowchart showing a specific example of a method for estimating the rupture life of a rubber composition according to the present embodiment (the present method). [Figure 2] FIG. 2(a) is a conceptual diagram showing a cyclic test performed on a strip-shaped rubber test piece, and FIG. 2(b) is a conceptual diagram showing a cyclic test performed on a pure shear rubber test piece. [Figure 3] 1 is a graph illustrating the relationship between tear energy and crack growth rate. [Figure 4] 1 is a graph showing an example of an SN curve. [Figure 5] FIG. 1 is a diagram conceptually illustrating an example of the hardware configuration of an information processing device capable of executing the present method. [Figure 6] 1 is a flowchart showing an example of a tire manufacturing method (the present manufacturing method). DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described. Note that the following embodiments are merely examples, and the present invention is not limited to the configurations of the following embodiments.

[0012] [Outline of the method for estimating the rupture life of a rubber composition (this method)] First, an outline of the method for estimating the breaking life of a rubber composition according to this embodiment (hereinafter sometimes abbreviated as this method) will be described. This method includes a first acquisition step of acquiring material constants of a test piece of a target rubber composition, a second acquisition step of acquiring repeated strain conditions or repeated stress conditions, and an estimation step of calculating the crack growth rate or number of breaks of the test piece using the material constants and strain conditions or repeated stress conditions, assuming that repeated loads are applied to the test piece of the target rubber composition in a repeated tensile test.

[0013] The test specimen is made of the rubber composition to be estimated (target rubber composition), and as described below, is assumed to be, for example, a rectangular vulcanized rubber sheet that is longitudinal (uniaxial extension) or transverse (pure shear, uniaxial extension, uniaxial restraint). Hereinafter, such a test specimen may also be referred to as a rubber test specimen. Then, a repeated load is applied to such a rubber test specimen, causing repeated deformation (repeated strain) to the rubber test specimen. There are no particular limitations on the rubber composition that can be estimated by this method.

[0014] The material constants of the rubber test specimen are characteristic values ​​inherent to the rubber composition that constitutes the rubber test specimen. In the first obtaining step, the material constants may be calculated based on data actually measured in a specific test, as will be shown in the example described later, or may be obtained as known information. As a method for obtaining the material constants, the material constants may be obtained based on information input by a user via a user interface in the computer that executes the estimation step, or may be obtained via communication from another computer or the like.

[0015] The cyclic strain conditions that can be acquired in the second acquisition step are setting information used in the estimation step, and are strain conditions assumed (set) for the cyclic load acting in each cyclic test. The cyclic strain conditions may be set as a strain (ε) that is the ratio of the deformation amount to the size (length) before deformation, or as a ratio (λ = ε + 1) of the size (length) after deformation to the size (length) before deformation (hereinafter referred to as the elongation ratio). The repeated stress conditions that can be acquired in the second acquisition step are setting information used in the estimation step, and are stress conditions that are assumed (set) to occur in response to the repeated load acting in each repeated test. The value of stress (σ) is set as the repeated stress condition.

[0016] The crack growth rate refers to the speed at which a crack in a rubber test piece grows, and is expressed, for example, as the length that a crack grows under the action of a single repeated load in a cyclic test. The crack growth rate can be obtained by conducting a cyclic test in which strain is applied to a rubber test piece of a predetermined width having an initial crack of a predetermined length in the width direction.

[0017] Then, in the estimation step, the material constants of the rubber test specimen and the set information of the cyclic strain conditions or cyclic stress conditions are used to calculate the crack growth rate or the number of breaks of the rubber test specimen under the assumption that cyclic loads are applied in a cyclic tensile test on a test specimen of the target rubber composition. Note that in this estimation step, both the crack growth rate and the number of breaks may be calculated. Such an estimation step is executed by one or more computers. The number of times to break means the number of times a load is repeatedly applied or the number of times a test is repeated until a crack reaches the entire width of a rubber test piece of a predetermined width and the rubber test piece breaks. In addition, in the estimation process, it is preferable to assume a rubber test piece in a state where there is no initial crack, but even if a rubber test piece in a state where there is an initial crack is assumed, the crack growth rate or the number of breaks can be calculated.

[0018] According to this method, by using the material constants of the rubber test specimen and varying the cyclic strain conditions or cyclic stress conditions assumed for the cyclic test of the rubber test specimen, the crack growth rate or the number of times to break can be calculated for each condition, thereby making it possible to more simply and accurately estimate the rupture life of the rubber composition constituting the rubber test specimen in actual use.

[0019] [Details of the method for estimating the rupture life of a rubber composition (this method)] The present method will be described in detail below with more specific examples. FIG. 1 is a flowchart showing a specific example of the method for estimating the rupture life of a rubber composition according to this embodiment (the present method). This method consists of a preparation step and an analysis step. The preparation step is a step of preparing information required for the calculations performed in the analysis step. In the example of Figure 1, steps (S10) to (S19) correspond to the preparation step, and steps (S21) and after correspond to the analysis step. The processing contents of each step will be described in detail below.

[0020] Step (S10) is a step of repeatedly conducting tensile tests on a test piece of the target rubber composition without an initial crack, and obtaining strain data and stress data as actual measured values ​​in each repeated test. The strain data refers to the measured value of the strain generated in the rubber test piece, and may be the strain (ε), the elongation ratio (λ), or both. Note that the strain (ε) can be replaced with the elongation ratio (λ). The stress data refers to the actual measured value of stress when strain occurs in the rubber test piece. The actual measured value of stress can also be calculated by dividing the tensile load on the rubber test piece by the cross-sectional area of ​​the rubber test piece. That is, the strain (ε) and stress (σ) are obtained as actual measured values ​​by the tensile test in step (S10).

[0021] The rubber test specimen used is a rectangular, vertically elongated vulcanized rubber sheet with a width of 5 mm to 20 mm. For example, a vulcanized rubber sheet with a width of 10 mm, a length (between the chucks) of 5 cm, and a thickness of 2 mm is used. Hereinafter, this type of rubber test specimen may be referred to as a rectangular rubber test specimen. When this test specimen is stretched, the stress state becomes uniaxial tension.

[0022] Another example of a target rubber test specimen is a vulcanized rubber sheet that is horizontally rectangular and has a width-to-length ratio of 8 or more. One example is a vulcanized rubber sheet that is 15 cm wide, 1.5 cm long (between the chucks), and 2 mm thick. Hereinafter, this type of rubber test specimen may be referred to as a pure shear rubber test specimen. When this test specimen is stretched, the stress state becomes uniaxially constrained biaxial tension.

[0023] Step (S11) is a step of repeatedly conducting tensile tests on a test piece of a target rubber composition, which is a test piece of a predetermined width and has an initial crack of a predetermined length in the width direction, and at least obtaining an actual value of the crack growth rate in each repeated test. As the rubber test piece, for example, the above-mentioned strip-shaped rubber test piece or pure shear rubber test piece is used, and it is preferable to use a rubber test piece of the same type as the rubber test piece used in step (S10), but a rubber test piece of a different type may also be used. When a strip-shaped rubber test piece is used, an initial crack having a length of, for example, 0.5 mm or more and 3.0 mm or less is provided in the center of one of the vertical sides (long sides) of the vulcanized rubber sheet of the test piece. When a pure shear rubber test piece is used, an initial crack having a length of, for example, 1 mm or more and 30 mm or less is provided in the center of one of the vertical sides (short sides) of the vulcanized rubber sheet of the test piece. The initial crack is formed so as to penetrate the vulcanized rubber sheet of the test piece in the thickness direction. However, the length of the initial crack provided in each rubber test piece is not limited to these lengths. In addition, in order to calculate the strain energy density (W) to be used in step (S15), strain data and stress data may be obtained as actual measured values ​​by a repeated tensile test using a rubber test piece having an initial crack in step (S11).

[0024] FIG. 2(a) is a conceptual diagram showing a cyclic test performed on a strip-shaped rubber test piece, and FIG. 2(b) is a conceptual diagram showing a cyclic test performed on a pure shear rubber test piece. As shown in Figures 2(a) and 2(b), in cyclic tests on strip-shaped rubber specimens or pure shear rubber specimens, both ends of the rubber specimen in the longitudinal direction are gripped and each of the ends is repeatedly pulled in opposite longitudinal directions, or one end is repeatedly pulled in the longitudinal direction. In cyclic tests on strip-shaped rubber specimens, both short sides of the specimen are gripped and both short sides or one short side is repeatedly pulled, while in cyclic tests on pure shear rubber specimens, both long sides of the specimen are gripped and both long sides or one long side is repeatedly pulled. When a strip-shaped rubber test piece with an initial crack is used, the initial crack is provided on one of the long sides of the test piece, and when a pure shear rubber test piece with an initial crack is used, the initial crack is provided on one of the short sides of the test piece.

[0025] Step (S13) is a step of calculating the material constants of the rubber test piece using the actual measurement values ​​acquired in step (S10). Specifically, the actual measurement values ​​are applied to a strain energy density function equation to calculate the material constants of the rubber test piece. The strain energy density function equation is a relationship between the material constant, the strain or extension ratio, and the strain energy density. The strain energy density (W) is the strain energy per unit volume generated inside a rubber test piece during each deformation in a cyclic test, and can be calculated using stress (σ) and strain (ε). There are various known strain energy density function formulas, such as the Neo-Hookean formula, the Mooney-Rivlin formula, the Ogden formula, etc. The strain energy density function formula may be appropriately selected depending on the shape of the target rubber test specimen, the method of repeated testing, etc.

[0026] For example, when a strip-shaped rubber test piece is used, the material constants are calculated using the Neo-Hookean equation shown below. In the following equation, C 10 indicates the material constant, λ1 indicates the elongation ratio, and W(λ1) indicates the strain energy density when a strain of λ1 is applied. The material constant C can be calculated by substituting the elongation ratio and strain energy density of each cycle of the repeated test, which are obtained as actual measured values, into the following formula and obtaining an approximate curve using a known method such as the least squares method. 10 is calculated.

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[0027] When a strip-shaped rubber test piece is used, the material constants may be calculated using the Mooney-Rivlin equation shown below. In the following equation, C 10 and C 01 indicates the material constant, λ1 indicates the elongation ratio, and W(λ1) indicates the strain energy density when a strain of λ1 is applied. In this case, as in the above case, the material constant C can be calculated by applying the measured values ​​to the following equation: 10 is calculated. Note that the material constant C 01 can be determined by an existing known method.

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[0028] When a pure shear rubber specimen is used, the material constants are calculated using the Neo-Hookean equation shown below. In the following equation, C 10indicates the material constant, λ1 indicates the elongation ratio, and W(λ1) indicates the strain energy density when a strain of λ1 is applied. As with the case of using a rectangular rubber test piece, the material constant C can be calculated by applying the measured values ​​to the following equation: 10 is calculated.

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[0029] Additionally, the material constants may be calculated using the Mooney-Rivlin equation shown below, using the measured values ​​obtained when a pure shear rubber test specimen is used. 10 and C 01 indicates the material constant, λ1 indicates the elongation ratio, and W(λ1) indicates the strain energy density when a strain of λ1 is applied. In this case, as in the above case, the material constant C can be calculated by applying the measured values ​​to the following equation: 10 is calculated. Note that the material constant C 01 can be determined by an existing known method.

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[0030] In this way, in the present method illustrated in Fig. 1, the material constants of a rubber test piece without an initial crack are calculated using the measured values ​​obtained by repeated tensile tests on the test piece of the target rubber composition. This allows the material constants to be calculated more accurately than when a test piece with an initial crack is used.

[0031] Step (S15) is a step of calculating the tear energy corresponding to the actual measurement value acquired in step (S10) or step (S11). Specifically, when a strip-shaped rubber test piece (with an initial crack) in which the stress state is uniaxial tension is used in step (S11), the tear energy for each iteration of the repeated tensile test is calculated by substituting the initial crack length, the strain obtained as the measured value, and the strain energy density obtained from the stress into the following (Equation 4-1). In the following (Equation 4-1), T represents the tear energy for each iteration of the repeated tensile test, W represents the strain energy density for each iteration of the repeated tensile test, c represents the initial crack length, and ε represents the strain for each iteration of the repeated tensile test. In other words, the following (Equation 4-1) is a formula for calculating the tear energy of a strip-shaped test piece in which the stress state is uniaxial tension. On the other hand, when a pure shear rubber test piece in which the stress state is uniaxially constrained biaxial tension is used in step (S10) or step (S11), the following (Equation 4-2) is used. That is, the following (Equation 4-2) is a formula for calculating the tear energy of a pure shear rubber test piece in which the stress state is uniaxially constrained biaxial tension. In the following (Equation 4-2), T represents the tear energy in each cycle of the repeated tensile test, W represents the strain energy density in each cycle of the repeated tensile test, and h represents the longitudinal length of the test piece under no load (the distance between the chucks).

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[0032] Step (S17) is a step of identifying an inflection point of the crack growth rate. Specifically, in step (S17), relationship information is generated between the tear energy (T) for each cycle of the tensile test calculated in step (S15) and the crack growth rate obtained in step (S11) as an actual measurement value for each cycle of the tensile test, and the inflection point of the crack growth rate is identified from this relationship information.

[0033] FIG. 3 is a graph illustrating the relationship between tear energy and crack growth rate. It is known that the crack growth rate of a rubber composition increases as the tear energy increases, and accelerates further when the tear energy exceeds a certain value, as shown in Figure 3. The point at which this crack growth rate jumps (tear energy value) is referred to as the inflection point of the crack growth rate. In step (S17), the combination of crack growth rate and tearing energy obtained as actual measured values ​​or calculated from actual measured values ​​is plotted on a graph, thereby identifying the inflection point of the crack growth rate.

[0034] As shown in FIG. 3, the crack propagation speed of the rubber composition slows as the tear energy decreases, and cracks do not propagate below a certain level of tear energy. The level of tear energy at which cracks do not propagate is determined by the graph plotting method described above, and this is the lower limit of the tear energy (T th ) is identified as

[0035] The method for identifying the inflection point of the crack growth rate and the lower limit of the tear energy in step (S17) is not limited to such a method based on a graph plot, and can also be automatically calculated by obtaining an approximate curve or an approximate straight line using a known method such as the least squares method. In the latter method, for example, an approximate curve or an approximate straight line is obtained from the tear energy for each predetermined energy range using the group of tear energies calculated in step (S15), and the point at which the slope changes beyond a predetermined value is identified as the inflection point of the crack growth rate, and the asymptotic value at which the tear energy becomes constant is identified as the lower limit of the tear energy.

[0036] Step (S19) is a step of calculating various constants in the formula for calculating the crack growth rate based on the actual measurement values ​​obtained in step (S10) or step (S11) or numerical values ​​calculated from the actual measurement values. As shown below, two types of formulas are provided for calculating the crack growth rate: a first formula (function f(a) below) used when the tear energy is equal to or less than the inflection point of the crack growth rate, and a second formula (function g(a) below) used when the tear energy is greater than the inflection point of the crack growth rate. In the following formula, T represents the tear energy for each cycle of the tensile test, T2 represents the tear energy corresponding to the inflection point of the crack growth rate, da / dN represents the crack growth rate, C1 and C2 represent material constants, m1 and m2 are exponents, and T th indicates the lower limit of the tear energy.

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[0037] In step (S19), the exponents m1 and m2 in the above-mentioned function formulas f(a) and g(a) are calculated. Specifically, by comparing the tear energy of each cycle of the repeated test calculated in step (S15) with the inflection point, either function formula g(a) or function formula f(a) is selected, and the tear energy (T) and crack growth rate (da / dN) of the same cycle, as well as the material constant (C1 or C2) calculated in step (S13) and the lower limit value of the tear energy (T) specified in step (S17) are added to the selected function formula. th ) are substituted to calculate the indices m1 and m2. Since the indices m1 and m2 are calculated multiple times from the combination of tear energy and crack growth rate for each cycle of the test, they may be calculated by averaging them, for example.

[0038] In this way, by obtaining a measurable crack growth rate using a test piece with an initial crack, it is possible to identify the inflection point of the crack growth rate and further to determine the constants of the two calculation formulas corresponding to the inflection point, thereby improving the accuracy of estimating the fracture life of the target rubber composition in the analysis step.

[0039] The above steps are the preparation step, and the analysis steps from step (S21) onwards are carried out on the rubber test piece to be analysed using the information acquired in this preparation step (material constants, inflection point, lower limit of tear energy, various constants (indexes m1 and m2) in the calculation formula for crack growth rate). In this embodiment, a test piece made of the target rubber composition and free of initial cracks is assumed to be the analysis target.

[0040] In step (S21) of the analysis process, first, a repeated strain condition or repeated stress condition (represented as a set repeated condition in FIG. 1) is acquired. The repeated strain conditions and repeated stress conditions are as described above. For ease of understanding, an example will be given here in which the strain (ε) acting on the rubber test piece to be analyzed in each repeated test is obtained as the set repeated condition.

[0041] Step (S23) is a step of calculating the tear energy corresponding to the set repetition conditions acquired in step (S21). In step (S23), for example, (Equation 4-1), which is a formula for calculating the tear energy of a strip test piece in which the stress state is uniaxial tension, is used. (Equation 4-1) includes the initial crack length (c), and the analysis step is performed assuming that a latent crack (referred to as a latent crack) exists in the rubber test piece without an initial crack to be analyzed. Therefore, in this case, the initial crack length (c) in (Equation 4-1) corresponds to the latent crack length. Here, a "latent crack" is a crack that is assumed to potentially exist in a test piece without an initial crack, and its dimension, i.e., the latent crack length, can be determined from the crack length at which mechanical properties such as fracture elongation are consistent between a test piece without an initial crack and a test piece with an initial crack. More specifically, in step (S23), the strain energy density (W) for each cycle of the cyclic test is calculated by substituting the material constants obtained in the preparation step and the elongation ratio (λ) obtained from the set cyclic conditions (strain) obtained in step (S21) into any of the equations for calculating the material constants described above. Then, this strain energy density (W), the strain (ε) as the set cyclic conditions, and the potential crack length (initial crack length) (c) are substituted into the tear energy calculation formula (Formula 4-1) to calculate the tear energy (T) for each cycle of the cyclic test.

[0042] The potential crack length (c) in (Equation 4-1), which is the formula for calculating the tear energy used in step (S23), is preferably 0.1 mm or more and 0.5 mm or less. This is because, when the breaking strains of dumbbell-shaped rubber test pieces with and without an initial crack were measured and compared in a tensile test, the test pieces with an initial crack of such a length had similar breaking strains. For this reason, in this embodiment, an initial crack having a length of 0.1 mm or more and 0.5 mm or less is regarded as a latent crack, and the tearing energy is calculated using (Equation 4-1). As a result, even when assuming a rubber test piece without an initial crack, it is possible to calculate with high accuracy the tear energy for each cycle of the repeated test using (Equation 4-1), and to estimate the fracture life of the target rubber composition.

[0043] Step (S25) is a step of selecting a formula for calculating the crack growth rate based on the tear energy corresponding to the set repetition conditions calculated in step (S23). Specifically, either the first calculation formula (function f(a)) or the second calculation formula (function g(a)) is selected as the formula for calculating the crack growth rate based on the magnitude relationship between the inflection point identified in step (S17) and the tear energy calculated in step (S23). Here, a formula for calculating the crack growth rate is selected for each cycle of the cycle test based on the tear energy calculated for each cycle of the cycle test.

[0044] Step (S27) is a step of calculating the crack growth rate corresponding to the set repetition conditions using the calculation formula selected in step (S25). At this time, the exponents m1 and m2, material constants C1 and C2, and the lower limit value T of the tear energy in the calculation formula of the crack growth rate are th have already been obtained in the preparation process, and by using these, the crack growth rate for each cycle of the cycle test expected under the set cycle conditions can be calculated. The above has been explained using an example in which strain (ε) is obtained as the set repetition condition, but even when stress (σ) is obtained as the set repetition condition, the crack growth rate can be obtained using the same process as described above, because stress (σ) and strain (ε) or elongation ratio (λ) are mutually interchangeable.

[0045] Step (S29) is a step of calculating the number of times the rubber test piece breaks based on the crack growth rate calculated in step (S27) and the width of the rubber test piece without an initial crack to be analyzed. In step (S29), the number of times the rubber test piece breaks is calculated using the following formula: In the following equation, a0 is the potential crack length, and a F indicates the width of the rubber test piece, and Δa indicates the crack length a i From a i+1 The crack propagation length (Δa = a i+1 -a i ) A constant (for example, 0.01 mm) may be set to Δa. (da / dN) i indicates the crack growth rate at that time, and ΔN i indicates the number of repeated tests required for the crack to progress by the unit crack progression length (Δa) (hereinafter referred to as the number of crack progressions). F‐1 indicates the crack propagation length just before fracture, the number of repeated tests required for the crack to propagate, and N f indicates the number of times the test was repeated until the rubber test piece broke.

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[0046] Step (S30) is a relational analysis step of acquiring information on the relationship between the number of breaks calculated in step (S29) and the set repetition conditions used to calculate the number of breaks or the calculated values ​​thereof. By executing the above-described steps (S21) to (S29), the number of breaks corresponding to the set repetition conditions (repeated strain conditions or repetitive stress conditions) acquired in step (S21) is calculated in step (S29). To acquire the relevant information in step (S30), although not shown in Fig. 1, first, the set repetition conditions are changed while steps (S21) to (S29) are repeatedly executed, and the number of breaks for each of the plurality of set repetition conditions is acquired.

[0047] Next, the number of times to break N and the cyclic strain conditions (strain (ε) or elongation ratio (λ)) or cyclic stress conditions (stress (σ)), or their calculated values, used to calculate the number of times to break N are plotted on a graph to obtain the relationship information, which can be called an SN curve.

[0048] Fig. 4 is a graph showing an example of an SN curve. In the example of Fig. 4, the horizontal axis shows the number of times to break N, and the vertical axis shows the product (MPa) of stress (σ) and elongation ratio (λ). By plotting the product of stress (σ) and elongation ratio (λ) versus the number of times to break, N, an SN curve can be generated, as shown in FIG. The method for generating such an SN curve is not limited to the method based on such a graph plot, and an approximate curve can also be automatically obtained using a known method such as the least squares method. Furthermore, the SN curve is not limited to the example of Figure 4, and the vertical axis may be set to stress (σ), strain (ε), the product of stress and strain, or a calculated value using multiple of stress, strain, and elongation ratio.

[0049] Here, when the product of stress (σ) and elongation ratio (λ) is used as the relationship information of the number of times to break, 5A rubber composition in which the product of the stress (σ) and strain (ε) is 12 (MPa) or more is suitable for tire products. 5 A rubber composition having a product of 6 (MPa) or more when the number of times is 100 is suitable for tire products. The relationship information (SN curve) acquired in step (S30) can be used to determine whether the rubber composition in question is suitable for use in tire products.

[0050] [Implementer of the method for estimating the rupture life of a rubber composition (this method)] At least some of the steps of the above-described method are executed by one or more processors included in one or more information processing devices. FIG. 5 is a diagram conceptually illustrating an example of the hardware configuration of an information processing device 10 capable of executing this method. The information processing device 10 is a so-called computer, and includes a CPU 11, a memory 12, an input / output interface (I / F) 13, a communication unit 14, etc. The information processing device 10 may be a desktop PC (Personal Computer), or may be a mobile terminal such as a portable PC, a smartphone, or a tablet.

[0051] The CPU 11 is a so-called processor, and may include not only a general CPU (Central Processing Unit) but also an application specific integrated circuit (ASIC), a DSP (Digital Signal Processor), a GPU (Graphics Processing Unit), etc. The memory 12 is a RAM (Random Access Memory), a ROM (Read Only Memory), an auxiliary storage device (such as a hard disk), etc. The input / output I / F 13 can be connected to user interface devices such as a display device 15 and an input device 16. The display device 15 is a device, such as an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube) display, that displays a screen corresponding to drawing data processed by the CPU 11 or the like. The input device 16 is a device, such as a keyboard or a mouse, that accepts input of user operations. The display device 15 and the input device 16 may be integrated and realized as a touch panel. The communication unit 14 communicates with other computers via a communication network and exchanges signals with other devices such as a printer. A portable recording medium or the like can also be connected to the communication unit 14.

[0052] The hardware configuration of the information processing device 10 is not limited to the example in FIG. 5. The information processing device 10 may include other hardware elements not shown. Furthermore, the number of each hardware element is not limited to the example in FIG. 5. For example, the information processing device 10 may have multiple CPUs 11. Furthermore, the information processing device 10 may be realized by multiple computers each having multiple housings.

[0053] The information processing device 10 can execute at least some of the steps of the present method by having the CPU 11 execute a computer program stored in the memory 12. This computer program is installed from a portable recording medium such as a CD (Compact Disc) or a memory card, or from another computer on a network, via the input / output I / F 13 or the communication unit 14, and stored in the memory 12.

[0054] The information processing device 10 (CPU 11) may execute all the steps exemplified in Fig. 1. In this case, in step (S10) and step (S11), the CPU 11 may acquire the actual measurement value from the measurement device via communication, or may display an input screen on the display device 15 and acquire the actual measurement value by a user input using the input device 16 on the input screen. In step (S21), the CPU 11 may acquire the repeated strain condition or repeated stress condition via user input, similar to the acquisition of the actual measurement value, or may acquire it from another computer via communication. In step (S17), the CPU 11 may acquire information on the inflection points of the crack growth rate through user input, similar to acquiring actual measured values, or may automatically identify the inflection points of the crack growth rate using the calculation method described above.

[0055] Furthermore, the information processing device 10 (CPU 11) may execute only the analysis process (process (S21) and subsequent processes) among the processes illustrated in Fig. 1. In this case, the preparation process (process (S10) to process (S19)) may be executed manually by a person. Furthermore, among the steps illustrated in FIG. 1, the calculation processes (e.g., step (S13), step (S15), step (S19), step (S23), step (S27), and step (S29)) may be performed by the information processing device 10 (CPU 11), and the other steps may be performed manually by a person. In this way, the present method can be executed using the information processing device 10 as appropriate.

[0056] [Tire manufacturing method] This method can be used in the quality testing and manufacturing of rubber products. An example of how this method is used in a manufacturing method of a tire as a rubber product will be described below. FIG. 6 is a flowchart showing an example of a tire manufacturing method (hereinafter, sometimes referred to as this manufacturing method). As shown in FIG. 6, this manufacturing method includes a step (S61) of preparing multiple types of rubber compositions, steps (S10) to (S30) in this method illustrated in FIG. 1, a step (S63) of selecting a rubber composition, and a step (S65) of manufacturing a tire.

[0057] In step (S61), a plurality of rubber compositions having different component blends are prepared. Specifically, rubber test pieces are prepared for each rubber composition. Then, for each of the multiple types of rubber compositions prepared in step (S61), the above-described method is applied to generate an SN curve (information on the relationship between the number of breaks and the set repetition conditions or the calculated values ​​thereof).

[0058] In step (S63), one rubber composition is selected from the plurality of rubber compositions based on the relationship information (SN curves) of the plurality of rubber compositions. Specifically, the rubber composition is selected such that the repeated strain condition or the repeated stress condition at the set number of times to break, or the calculated value of these, indicated by the SN curve (relationship information), exceeds a set threshold. For example, when the product of stress (σ) and elongation ratio (λ) is used as the relationship information for the number of breaks, 5 It is preferable to select a rubber composition in which the product of stress (σ) and strain (ε) is 12 (MPa) or more (set threshold value) when the number of times to break is 10. In addition, when the product of stress (σ) and strain (ε) is used as the relationship information with the number of times to break, it is preferable to select a rubber composition in which the product of stress (σ) and strain (ε) is 12 (MPa) or more (set threshold value) when the number of times to break is 10. 5 It is preferable to select a rubber composition in which the product of the number of times (set value of number of times to break) is 6 (MPa) or more (set threshold value).

[0059] In step (S65), a tire is manufactured using the rubber composition selected in step (S63). Any existing method may be used as a specific method for manufacturing a tire from the rubber composition in step (S65). By using this method in a tire manufacturing method, it is possible to manufacture a tire product that can achieve a desired breaking life, and also to shorten the manufacturing process.

[0060] This manufacturing method may be executed by the information processing device 10 (CPU 11) in the same manner as the above-described method. 5The number of times) and the set threshold value (for example, 12 (MPa)) are stored in the memory 12, and the CPU 11 can execute the step (S63) by referring to them. Then, the CPU 11 may display the information on the rubber composition selected in the step (S63) on the display device 15, or may output it in another form.

[0061] [Variations] The above-described embodiment is merely an example, and the above content can be modified as appropriate within the scope of the spirit thereof. For example, although the present method in the example of Fig. 1 includes the preparation step and the analysis step, the preparation step may not be included. In this case, it is sufficient if the material constants, inflection points, and various constants (such as indexes m1 and m2) in the formula for calculating the crack growth rate for the target rubber composition are previously obtained by some method (such as obtaining known information). Furthermore, this method is sufficient as long as it can estimate information indicating the rupture life of the rubber composition, and may end with the step (S27) of calculating the crack growth rate, and may not include the step (S29) of calculating the number of ruptures and the step (S30) of generating the SN curve, or may end with the step (S29) of calculating the number of ruptures, and may not include the step (S30) of generating the SN curve.

[0062] The following examples are provided to further support the above, but the above-described embodiments and modifications are not limited to the following examples. [Example]

[0063] In this example, eight types of rubber compositions (Examples 1 to 5, Reference Examples 1 to 3) shown in Table 1 were prepared, and SN curves were generated for each rubber composition by applying the method illustrated in FIG. 1. To calculate the material constants of the rubber compositions of Reference Examples 1 to 3 and Examples 1 to 3, pure shear rubber test specimens were used in steps (S10) and (S11) of FIG. 1, and the Neo-Hookean equation for pure shear rubber test specimens was used in step (S13). To calculate the material constants of the rubber compositions of Examples 4 and 5, strip-shaped rubber test specimens were used in steps (S10) and (S11) of FIG. 1, and the Neo-Hookean equation for strip-shaped rubber test specimens was used in step (S13).

[0064] Table 1 shows the component blends (parts by mass) for each rubber composition in Examples 1 to 5 and Reference Examples 1 to 3, and the number of breaks in 10 5 The graph shows the product of the stress (σ) and the elongation ratio (λ) at which the strain is generated. [Table 1]

[0065] The types of raw materials shown in Table 1 are as follows: "SBR Nipol 1502": Styrene butadiene rubber: Nipol 1502 manufactured by Nippon Zeon "NR RSS#3": Natural Rubber: RSS#3 "Hydrogenated SBR": Hydrogenated aromatic vinyl-conjugated diene copolymer "Acid anhydride-added PE": Polyethylene with acid anhydride added: Admer NF518 manufactured by Mitsui Chemicals "Acid anhydride-added PP": Polypropylene with acid anhydride added: Umex 1001 manufactured by Sanyo Chemical Industries "CB": Carbon Black: Seast N, manufactured by Tokai Carbon "Silica": ZEOSIL1165MP manufactured by Solvay "Silane coupling agent": Si69 manufactured by Evonik "Stearic acid": Stearic acid 50S, manufactured by Nisshin Rika "Zinc oxide": Three types of zinc oxide manufactured by Seido Chemical Industry "Oil": Diana Process NH-70S manufactured by Idemitsu Kosan "Sulfur": Oil-treated sulfur manufactured by Hosoi Chemical Industry Co., Ltd. "Vulcanization accelerator": Noccela CZ-G manufactured by Ouchi Shinko Chemical Industry

[0066] As described in the embodiment, the rubber composition for tires has a breaking frequency of 10 5 Since a rubber composition in which the product of stress (σ) and elongation ratio (λ) when the test cycle is repeated is 12 (MPa) or more is preferable, it can be seen that the rubber compositions of Examples 1 to 5 of the eight rubber compositions in Table 1 are suitable for tire manufacturing. In other words, for the rubber compositions of Examples 1 to 5, an SN curve was generated by plotting the number of times to break and the product (σ·λ) of the number of times to break and the number of times to break while changing the cyclic strain condition and the cyclic stress condition in the above-mentioned method. 5 It can also be expressed as a rubber composition in which the product (σ·λ) is 12 (MPa) or more. However, if the threshold value for selecting rubber compositions for tires or other uses is set to another value (a value other than 12 (MPa)), Reference Examples 1 to 3 may also be selected.

[0067] Some or all of the above-described embodiments and modifications can be specified as follows: However, the above-described embodiments and modifications are not limited to the following descriptions.

[0068] <1> a first acquisition step of acquiring material constants of a test piece of the target rubber composition; a second acquisition step of acquiring a cyclic strain condition or a cyclic stress condition; an estimation step of calculating a crack growth rate of a test piece of the target rubber composition or a number of times to break, which indicates the number of times of repeated loads that the test piece will break, by assuming that repeated loads are applied to the test piece in a repeated tensile test using the material constants and the strain conditions or the repeated stress conditions; A method for estimating the fracture life of a rubber composition comprising: <2> The first obtaining step a step of repeatedly conducting tensile tests on a test piece of the target rubber composition without an initial crack, thereby obtaining strain data and stress data as actual measured values; calculating the material constant of the test piece by applying the measured value to a strain energy density function equation; Contains <1> A method for estimating the breaking life of a rubber composition according to claim 1. <3> a step of repeatedly performing tensile tests on a test piece of the target rubber composition having a predetermined width and an initial crack of a predetermined length in the width direction, thereby obtaining an actual measurement value of the crack growth rate for each of the repeated tensile tests; Calculating the tear energy for each repeated tensile test; Calculating various constants in a formula for calculating the crack growth rate using at least the crack growth rate acquired as the actual measurement value and the calculated tearing energy; Further comprising: In the estimation step, the crack growth rate is calculated using the calculation formula in which the calculated various constants are set. <1> or <2> A method for estimating the breaking life of a rubber composition according to claim 1. <4> Identifying an inflection point of the crack growth rate based on the relationship between the crack growth rate acquired as the actual measurement value and the calculated tear energy; Further comprising: The estimation step includes: selecting either a first formula or a second formula as a formula for calculating a crack growth rate based on a magnitude relationship between the tear energy corresponding to the identified inflection point and the calculated tear energy; calculating the crack growth rate by applying the material constant and the cyclic strain condition or the cyclic stress condition to the selected calculation formula; Including, <3> A method for estimating the breaking life of a rubber composition according to claim 1. <5> In the estimation step, the tear energy for each repeated tensile test is calculated using at least the strain energy density and a predetermined potential crack length calculated from the repeated strain conditions or the repeated stress conditions and the material constants, and the number of times to break is calculated, indicating the number of repeated loads at which a crack reaches the predetermined width and the test piece breaks, assuming that repeated loads act in the repeated tensile test on a test piece of the target rubber composition having no initial crack and a predetermined width. <3> or <4> A method for estimating the breaking life of a rubber composition according to claim 1. <6> The potential crack length is 0.1 mm or more and 0.5 mm or less; <5> A method for estimating the breaking life of a rubber composition according to claim 1. <7> a relational analysis step of acquiring relational information between the number of times to break calculated in the estimation step and the repeated strain condition or the set repeated stress condition used to calculate the number of times to break, or a calculated value using these; Further includes <1> from <6> 10. A method for estimating the breaking life of a rubber composition according to any one of claims 1 to 9. <8> With respect to each of a plurality of rubber compositions having mutually different component formulations, <7> a selection step of selecting one rubber composition from the plurality of rubber compositions based on the relationship information obtained by applying the method for estimating the rupture life of a rubber composition described in the above item (1); a manufacturing step of manufacturing a tire using the selected rubber composition; Including, In the selection step, a rubber composition is selected in which the repeated strain condition or the set repeated stress condition at the set value of the number of times to break, or a calculated value thereof, indicated by the relationship information, exceeds a set threshold value. Tire manufacturing method. <9> An information processing device including at least one or more memories and one or more processors, <1> from <7> 10. An information processing device capable of executing the method for estimating the breaking life of a rubber composition according to any one of claims 1 to 9. [Explanation of symbols]

[0069] 10. Information processing device (breakage life estimation device) 11 CPU 12 Memory 13 Input / Output Interface 14 Communication Unit 15 Display device 16 Input Devices

Claims

1. a first acquisition step of acquiring material constants of a test piece of the target rubber composition; a second acquisition step of acquiring a cyclic strain condition or a cyclic stress condition; an estimation step of calculating a crack growth rate of a test piece of the target rubber composition or a number of times to break, which indicates the number of times of repeated loads that the test piece will break, by assuming that repeated loads are applied to the test piece in a repeated tensile test using the material constants and the strain conditions or the repeated stress conditions; A method for estimating the fracture life of a rubber composition comprising:

2. The first obtaining step a step of repeatedly conducting tensile tests on a test piece of the target rubber composition without an initial crack, thereby obtaining strain data and stress data as actual measured values; calculating the material constant of the test piece by applying the measured value to a strain energy density function equation; The method for estimating the breaking life of a rubber composition according to claim 1, comprising:

3. a step of repeatedly performing tensile tests on a test piece of the target rubber composition, the test piece having a predetermined width and an initial crack of a predetermined length in the width direction, and obtaining an actual measured value of the crack growth rate for each of the repeated tensile tests; Calculating the tear energy for each repeated tensile test; Calculating various constants in a calculation formula for the crack growth rate using at least the crack growth rate acquired as the actual measurement value and the calculated tear energy; Further comprising: In the estimation step, the crack growth rate is calculated using the calculation formula in which the calculated various constants are set. A method for estimating the breaking life of a rubber composition according to claim 2.

4. Identifying an inflection point of the crack growth rate based on the relationship between the crack growth rate acquired as the actual measurement value and the calculated tear energy; Further comprising: The estimation step includes: selecting either a first formula or a second formula as a formula for calculating a crack growth rate based on a magnitude relationship between the tear energy corresponding to the identified inflection point and the calculated tear energy; calculating the crack growth rate by applying the material constant and the cyclic strain condition or the cyclic stress condition to the selected calculation formula; Including, The method for estimating the breaking life of a rubber composition according to claim 3.

5. In the estimation step, the tear energy for each repeated tensile test is calculated using at least the strain energy density and a predetermined potential crack length calculated from the repeated strain conditions or the repeated stress conditions and the material constants, and the number of times to break is calculated, indicating the number of repeated loads at which a crack reaches the predetermined width and the test piece breaks, assuming that repeated loads act in the repeated tensile test on a test piece of the target rubber composition having no initial crack and a predetermined width. A method for estimating the breaking life of a rubber composition according to claim 3 or 4.

6. The potential crack length is 0.1 mm or more and 0.5 mm or less. The method for estimating the breaking life of a rubber composition according to claim 5.

7. a relational analysis step of acquiring relational information between the number of times to break calculated in the estimation step and the repeated strain condition or the set repeated stress condition used to calculate the number of times to break, or a calculated value using these; The method for estimating the breaking life of a rubber composition according to claim 1, further comprising:

8. a selection step of selecting one rubber composition from among a plurality of rubber compositions having mutually different component blends, based on the relationship information acquired by applying the method for estimating a rupture life of a rubber composition according to claim 7; a manufacturing step of manufacturing a tire using the selected rubber composition; Including, In the selection step, a rubber composition is selected in which the repeated strain condition or the set repeated stress condition at the set value of the number of times to break, or a calculated value thereof, indicated by the relationship information, exceeds a set threshold value. Tire manufacturing method.

9. An information processing device comprising at least one or more memories and one or more processors, and capable of executing the method for estimating the breaking life of a rubber composition according to claim 1.

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