Hardness test method and program

A hardness test method performed by a controller of a hardness tester includes a first measurement process measuring an indentation curve (indentation history curve) for a plurality of times under a same condition with respect to a test specimen for verification in a predetermined environment; a setting process setting an acceptable range of variation in a load loading curve based on load loading curves (load loading history curves) of the plurality of the indentation curves obtained by the first measurement process; a second measurement process measuring an indentation curve under a same condition as the first measurement process with respect to the test specimen in an actual usage environment; and a judging process judging whether a load loading curve of the indentation curve measured by the second measurement process is within the acceptable range of variation in a load loading curve set by the setting process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 of Japanese Application No. 2010-238718, filed on Oct. 25, 2010, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hardness test method and a program.

2. Description of Related Art

Conventionally, as a material tester, a test method called an instrumented indentation test (nano-indentation test) is known in which, during a process of forming an indentation by pressing an indenter loaded with a predetermined load against a surface of a test specimen, a test force (force loaded on the indenter) and an indentation depth (amount of displacement of the indenter) are continuously measured, and a mechanical property of the material is determined by analyzing an obtained indentation curve (for example, see Japanese Patent Laid-Open Publication No. 2009-47427).

For an instrumented indentation test like this, to what extent a test can be performed at a small indentation depth without being influenced by a disturbance is important in evaluating performance of a tester. For example, fused silica (silica glass) is often used to perform a performance evaluation test. However, silica glass is less susceptible to disturbance due to its high elastic deformability in a small indentation range, so that a result of a performance evaluation test using silica glass may not be applicable to an actual installation environment. Thus, in general, as a verification method of an installation environment of an instrumented indentation tester, measurement of floor vibration is used.

However, an instrumented indentation test may be influenced not only by floor vibration but also by noise in an installation room and wind due to air conditioning and the like. Further, with respect to the floor vibration, its impact varies widely depending on the frequency of the vibration, and thus cannot be judged based on only a numeric value indicated by a vibration meter. Therefore, as it stands now, an experiment is conducted after performing, for example, inspection of an indenter, measurement of floor vibration, and the like that can be done, and validity of an obtained test result is judged based on empirical values.

SUMMARY OF THE INVENTION

A purpose of the present invention is to provide a hardness test method and a program that are capable of quantitatively verifying influence of an installation environment.

To achieve the above purpose, one aspect of the present invention is a hardness test method performed by a controller of a hardness tester. The hardness test method includes a first measurement process forming an indentation by pressing an indenter loaded with a predetermined load with respect to a test specimen for verification in a predetermined environment, and measuring for a plurality of times under a same condition an indentation history curve detecting an amount of displacement of the indenter and a test force loaded on the indenter during the formation of the indentation; a setting process setting an acceptable range of variation in load loading history curves based on load loading history curves, formed during load loading of the plurality of the indentation history curves obtained by the first measurement process; a second measurement process measuring an indentation history curve under a same condition as the first measurement process with respect to the test specimen for verification in an actual usage environment; and a judging process judging whether a load loading history curve of the indentation history curve measured by the second measurement process is within the acceptable range of variation in a load loading history curve set by the setting process.

According to another aspect of the present invention, in the hardness test method, the indenter is a cone-shaped indenter. The setting process includes fitting the load loading history curves of the plurality of the indentation history curves using quadratic functions; selecting two curves having maximum and minimum slope values; and setting a range between the two selected curves as the acceptable range of variation in the load loading history curve.

According to another aspect of the present invention, in the hardness test method, the slope values of the two selected curves are multiplied by a safety factor to set the acceptable range of variation in the load loading history curve.

According to another aspect of the present invention, in the hardness test method, the indenter is a cone-shaped indenter. The setting process includes fitting the load loading history curves of the plurality of the indentation history curves using quadratic functions; calculating a correlation coefficient; and setting a minimum of the calculated correlation coefficient or above as the acceptable range of variation in the load loading history curve.

According to another aspect of the present invention, in the hardness test method, the minimum of the calculated correlation coefficient is multiplied by a safety factor to set the acceptable range of variation in the load loading history curve.

According to another aspect of the present invention, the hardness test method further includes an estimation process estimating a type of disturbance in the actual usage environment based on the indentation history curve measured by the second measurement process.

According to another aspect of the present invention, in the hardness test method, the test specimen for verification is copper, aluminum, or gold.

Another aspect of the present invention is a program that causes a computer to act as a first measurer forming an indentation by pressing an indenter loaded with a predetermined load with respect to a test specimen for verification in a predetermined environment, and measuring for a plurality of times under a same condition an indentation history curve detecting an amount of displacement of the indenter and a test force loaded on the indenter during the formation of the indentation; a setter setting an acceptable range of variation in load loading history curves based on the load loading history curves, formed during load loading, of the plurality of the indentation history curves obtained by the first measurer; a second measurer measuring an indentation history curve under a same condition as the first measurer with respect to the test specimen for verification in an actual usage environment; and a judger judging whether a load loading history curve of the indentation history curve measured by the second measurer is within the acceptable range of variation in a load loading history curve set by the setter.

According to the present invention, the hardness test method includes a first measurement process forming for a plurality of times under a same condition an indentation by pressing an indenter loaded with a predetermined load with respect to a test specimen for verification in a predetermined environment, and measuring for a plurality of times under a same condition an indentation history curve detecting an amount of displacement of the indenter and a test force loaded on the indenter during the formation of the indentation; a setting process setting an acceptable range of variation in load loading history curves based on the load loading history curves, formed during load loading, of the plurality of the indentation history curves obtained by the first measurement process; a second measurement process measuring an indentation history curve under a same condition as the first measurement process with respect to the test specimen for verification in an actual usage environment; and a judging process judging whether a load loading history curve of the indentation history curve measured by the second measurement process is within the acceptable range of variation in a load loading history curve set by the setting process. Therefore, after a measurement is performed with respect to the test specimen for verification in the predetermined environment and an acceptable range of variation in the load loading curves is set, the same measurement is performed with respect to the same test specimen for verification in an actual usage environment; and, based on whether the obtained load loading history curve is within the set acceptable range, whether the influence of disturbance in the actual usage environment is large can be determined. Therefore, the influence of an installation environment can be quantitatively verified.

DETAILED DESCRIPTION OF THE INVENTION

In the following, with reference to the drawings, a hardness test method according to the present invention is explained in detail. The hardness test method according to the present invention is performed for verifying whether influence of disturbance is large with respect to an installation environment (actual usage environment) of a hardness tester when performing a hardness test. The hardness tester according to the present invention is a hardness tester having a function for using the hardness test method.

First Embodiment

A hardness tester100according to the present embodiment is an instrumented indentation tester capable of continuously monitoring a test force applied to an indenter3and an indentation depth of the indenter3. The hardness tester100includes, for example, asFIGS. 1 and 2illustrate, a controller10and a hardness tester body1in which component members are arranged. The tester body1is configured to include an XYZ stage2moving a test specimen S in X, Y, and Z directions; a load lever4having on one end thereof the indenter3forming an indentation on the test specimen S; a load loader5loading (applying) a predetermined load (test force) to the load lever4; a displacement meter6detecting an amount of displacement of the indenter3; an image capturer7capturing an image of an indentation formed on a surface of the test specimen S and the like; a display8; an operator9; and the like.

The XYZ stage2is configured to move in the X, Y, and Z directions (that is, horizontal and vertical directions) according to a control signal input from the controller10. The test specimen S is moved back and forth, left and right, and up and down by the XYZ stage2so as to adjust a location relative to the indenter3. The XYZ stage2holds the test specimen S using a test specimen holding stage2aso as to keep the test specimen S mounted on an upper surface thereof in alignment during a test measurement. Here, the test specimen S is a test specimen for verification that can be favorably used in the hardness test method according to the present embodiment. For example, a plastically easily deformable metallic material such as copper, aluminum, gold, and the like is used.

As the indenter3, for example, a cone-shaped indenter can be used, such as a Vickers pyramid indenter (face angle is 136±0.5°), a Berkovich triangular pyramid indenter (angle between one face and an indenter axis is 65.03° or 65.27°), a conical indenter (apex angle is 120±0.35° and the like), a Knoop rhombic-base pyramid indenter (apical angles between opposite faces are 172°30′ and 130°, and the like. When such an indenter3is loaded with a predetermined load and is pressed against a surface of the test specimen S, an indentation is formed on the surface of the test specimen S.

The load lever4, for example, is formed in an approximately rod shape, and is fixed on a seating via a cross spring4anear its center. On one end of the load lever4, the indenter3is provided, which is freely movable above the test specimen S both toward and away from the test specimen S, and which is pressed against a surface of the test specimen S to form an indentation, the test specimen S being mounted on the test specimen holding stage2a. On the other end of the load lever4, force coils5aare provided, which constitute the load loader5.

The load loader5, for example, is a force motor, and is configured to include the force coils5aattached to the load lever4; a fixed magnet5bfixed so as to face the force coils5a; and the like. The load loader5, for example, rotates the load lever4according to a control signal input from the controller10, using as a driving force a force generated by electromagnetic induction of a magnetic field created in a gap by the fixed magnet5band an electrical current flowing in the force coils5aprovided in the gap. This allows the end of the load lever4on the indenter3side to tilt downwardly so as to press the indenter3against the test specimen S.

The displacement meter6, for example, is a capacitive displacement sensor, and is configured to include a movable electrode plate6aprovided on the end of the load lever4on the indenter3side, and a fixed electrode plate6bfixed so as to face the movable electrode plate6a. The displacement meter6, for example, detects an amount of displacement that the indenter3moved when forming an indentation on the test specimen S (indentation depth when the indenter3is pressed against the test specimen S) by detecting a change in a capacitance between the movable electrode plate6aand the fixed electrode plate6b, and outputs a displacement signal based on the detected amount of displacement to the controller10. As the displacement meter6, the capacitive displacement sensor is used as an example. However, it is not limited to this. For example, it may also be an optical displacement sensor or an eddy current displacement sensor.

The image capturer7includes, for example, a camera and the like, and captures, for example, an image of an indentation formed on the surface of the test specimen S by the indenter3, and the like, above the test specimen holding stage2a, according to a control signal input from the controller10.

The display8, for example, is a liquid crystal display panel, and performs display processing of a surface image of the test specimen S captured by the image capturer7, various test results, and the like, according to a control signal input from the controller10.

The operator9, for example, is a group of operation keys such as a keyboard and the like, and, when operated by a user, outputs an operation signal associated with the operation to the controller10. Further, the operator9may also include a pointing device such as a mouse, a touch panel, and the like, a remote controller, and the like, and other operation devices. The operator9is operated when a user performs directive input for performing a hardness test with respect to the test specimen S, when setting a test force, that is, a load, loaded on the indenter3, and the like.

The controller10is configured to include a CPU (Central Processing Unit)11, a RAM (Random Access Memory)12, a memory13, and the like, and is connected, via a system bus, to the XYZ stage2, the load loader5, the displacement meter6, the image capturer7, the display8, the operator9, and the like.

The CPU11, for example, performs various control processing according to various processing programs for a hardness tester stored in the memory13.

The RAM12, for example, includes a program storage area for deploying a processing program and the like executed by the CPU11; a data storage area storing input data and a processing result and the like generated when a processing program is executed; and the like.

The memory13, for example, stores a system program executable on the hardness tester100; various processing programs executable under the system program; data used when the various processing programs are executed; data of various processing results arithmetically processed by the CPU11; and the like. A program is stored in the memory13in the form of computer readable program code.

Specifically, the memory13stores, for example, a first measurement program131, a setting program132, a second measurement program133, a judging program134, an estimating program135, and the like.

The first measurement program131, for example, is a program that causes the CPU11to form an indentation by pressing the indenter3loaded with a predetermined load with respect to the test specimen S in a predetermined environment, and measure for multiple times under a same condition an indentation history curve (indentation curve) detecting an amount of displacement (indentation depth (h)) of the indenter3and a test force (F) loaded on the indenter3during the formation of the indentation.

Here, the predetermined environment is a nearly ideal environment in which various disturbances that interfere with measurement are nearly absent, the various disturbances including sudden vibrations such as opening and closing of a door, operation sound of a machine, falling sound, and the like; relatively high frequency disturbance of the order of several 100 Hz such as voice and the like; relatively low frequency disturbance such as wind and the like; and the like. A user installs the hardness tester100in such a predetermined environment and performs measurement. When a user performs a directive input with respect to the operator9for performing a hardness test with respect to the test specimen S, in response to this, the CPU11executes the first measurement program131, performs the instrumented indentation test with respect to the test specimen S in the predetermined environment, and performs measurement of a test force (F) versus indentation depth (h) curve (indentation curve) (the first measurement process). The instrumented indentation test in this first measurement process is performed for multiple times under a same test condition. It is desirable that the indentation depth (h) be as small as possible for ease of confirming the influence of an installation environment. For example, it is desirable that the indentation depth (h) be 100 nm or less. The number of tests is set by a user in advance.FIG. 3(a) is an example illustrating an indentation curve measured by the first measurement process.

Specifically, for the measurement of the test force (F) versus indentation depth (h) curve (indentation curve), each time the following process is performed. First, after the test specimen S is mounted on the test specimen holding stage2a, when an operation signal is input from the operator9instructing the CPU11to perform measurement, the CPU11controls the load loader5to apply a predetermined test force to the test specimen S. Then, the CPU11continuously measures an indentation depth (h) [nm] of the indenter3on the test specimen S during formation of an indentation and a test force (F) [mN] during the formation of the indentation to measure a test force (F) versus indentation depth (h) curve.

More specifically, when the test specimen S is mounted on the test specimen holding stage2aand an operation signal is input, the CPU11outputs a control signal to the load loader5, and uses as a driving force a force generated by electromagnetic induction of a magnetic field created in a gap by the fixed magnet5bof the load loader5and an electrical current flowing in the force coils5aprovided in the gap, to rotate the load lever4. Thereby, the end of the load lever4on the indenter3side tilts downwardly to allow the indenter3to form an indentation on the test specimen S. During the formation of the indentation, the load loaded on the indenter3is gradually increased until a set maximum test force is reached (load loading process). In this load loading process, as a load loading history curve (load loading curve) inFIG. 3(a) illustrates, by increasing the test force loaded on the indenter3, the indentation depth of the indenter3on the test specimen S also increases. The indenter3is a cone-shaped indenter. Therefore, the load loading history curve is a quadratic curve. Next, when the CPU11judges that the load loaded on the indenter3has reached the maximum test force, the CPU11operates the load loader5by controlling supply of the electrical current to the driving coils to gradually decrease the load loaded on the indenter3(load unloading process). In the load unloading process, as a load unloading curve inFIG. 3(a) illustrates, by decreasing the test force loaded on the indenter3, the indentation depth of the indenter3on the test specimen S also decreases.

By executing such a first measurement program131, the CPU11acts as a first measurer (also referred to as a “first scale”).

The setting program132, for example, is a program that causes the CPU11to set a predetermined acceptable range of variation in load loading history curves (load loading curves) based on the load loading history curves (load loading curves), formed during load loading, of the plurality of the indentation history curves (indentation curves) obtained by executing the first measurement program131. Specifically, first, the CPU11perceives the shape of the load loading history curves of the plurality of the indentation history curves obtained by executing the first measurement program131. In the present embodiment, it is perceived that the load loading history curves are quadratic curves. Next, the CPU11uses quadratic functions to fit the load loading curves of the plurality of the indentation curves obtained by executing the first measurement program131to select two curves having maximum and minimum slope values, and sets a range between the two selected curves as a predetermined acceptable range of variation in a load loading curve (setting process). Here, the acceptable range of variation in a load loading curve is a range specifying an acceptable measurement error range in a case where a measurement is performed with respect to the test specimen S, which is a test specimen for verification, under the same test condition as that for the above described first measurement process. That is, in the case where the installation environment of the hardness tester100is changed and a measurement is performed with respect to the test specimen S under the same test condition as that for the first measurement process, when a load loading curve is within the acceptable range, the installation environment can be judged as being close to the predetermined environment, having small influence of disturbance. At this time, it is also possible to multiply by a predetermined safety factor the slope values of the two curves selected by fitting the above described load loading curves using quadratic functions to set an acceptable range of variation in a load loading curve. For example, by performing operations of a maximum slope value×2 and a minimum slope value×½, an acceptable range is set. For the safety factor, values set by a user in advance are used. This allows adding a certain degree of margin to a set acceptable range.FIG. 3(b) is an example illustrating an acceptable range set by the setting process. By executing such a setting program132, the CPU11acts as a setter.

The second measurement program133, for example, is a program that causes the CPU11to measure an indentation history curve (indentation curve) under the same condition as that for the first measurement program131(first measurement process) with respect to the test specimen S in an actual usage environment. Here, the actual usage environment is an actual installation environment of the hardness tester100. As compared to the nearly ideal predetermined environment, the actual usage environment is an environment susceptible to various disturbances. A user moves the hardness tester100from the predetermined environment where the first measurement process was performed to such an actual usage environment, and performs a measurement. When a user performs a directive input with respect to the operator9to perform a hardness test with respect to the test specimen S, in response to this, the CPU11executes the second measurement program133, and performs the same control as during the execution of the above-described first measurement program131to measure an indentation curve in the actual usage environment (the second measurement process).FIGS. 4(a) and4(b) are each an example illustrating a load loading curve of an indentation curve obtained as a result.FIG. 4(a) illustrates an example in which a load loading curve is within an acceptable range.FIG. 4(b) illustrates an example in which a load loading curve is outside an acceptable range. By executing such a second measurement program133, the CPU11acts as a second measurer (also referred to as a “second scale”).

The judging program134, for example, is a program that causes the CPU11to judge whether a load loading history curve (load loading curve) of an indentation history curve (indentation curve) measured by executing the second measurement program133is within an acceptable range of variation in a load loading history curve (load loading curve) set by the setting program132. Specifically, the CPU11judges whether a part of or the whole of a load loading curve measured in an actual usage environment is within a set acceptable range (judging process). Then, for example, the CPU11displays a message and the like on the display8to inform a user of a judged result. According to the judged result, the user can recognize whether the influence of disturbance is large or small with respect to the actual usage environment. That is, in a case where the whole of a load loading curve measured in the actual usage environment is within the acceptable range, it can be recognized as that the influence of disturbance is small; and in a case where even a part is not within the acceptable range, it can be recognized as that there was influence of some kind of disturbance. By executing such a judging program134, the CPU11acts as a judger.

The estimating program135, for example, is a program that causes the CPU11to estimate a type of disturbance in the actual usage environment based on the indentation curve (indentation history curve) measured by executing the second measurement program133. Specifically, for example, the CPU11estimates a type of disturbance by comparing a shape of the indentation curve (behavior of the indentation curve) measured by the second measurement process with types of disturbance stored in advance (estimation process). The estimation process can be performed not only in the case where it is judged based on the result of the judging process that the influence of disturbance is large, but also in the case where it is judged that the influence of disturbance is small. That is, regardless the degree of the influence of disturbance, in a case where the shape of the indentation curve is disturbed, the type of disturbance in the installation environment can be estimated. For example, asFIG. 5(a) illustrates, in a case of an indentation curve in which displacement rapidly changes during indentation, it is estimated that a sudden vibration has occurred (load has changed in a case of a displacement controlled tester) such as opening and closing of a door, an operation sound of a machine, a falling sound, and the like. AsFIG. 5(b) illustrates, in a case of an indentation curve in which large displacement appears, it is estimated that a relatively high frequency disturbance of the order of several 100 Hz such as a voice that does not appear as fluctuation of the curve has constantly occurred. AsFIG. 5(c) illustrates, in a case of an indentation curve in which fluctuation appears, it is estimated that a relatively low frequency disturbance has been constantly shaking the tester. By executing such an estimation program135, the CPU11acts as an estimator.

FIG. 6is a flowchart illustrating a hardness test method using the hardness tester100. The following step S1and step S2are performed in a state in which the hardness tester100is installed in a predetermined environment, and step S3-step S5are performed in a state in which the hardness tester100has been moved to an actual usage environment.

First, at step S1, in response to an operation of the operator9, the CPU11executes the first measurement program131, and measures a plurality of indentation curves with respect to the test specimen S in the predetermined environment (first measurement process). Next, at step S2, the CPU11executes the setting program132, and sets an acceptable range of variation in load loading curves based on load loading curves of the plurality of the indentation curves obtained by the first measurement process (setting process).

Next, at step S3, the CPU11executes the second measurement program133, and measures an indentation curve under the same condition as the first measurement process with respect to the test specimen S in the actual usage environment (second measurement process). Next, at step S4, the CPU11executes the judging program134, and judges whether a load loading curve of the indentation curve measured by the second measurement process is within the acceptable range set by the setting process (judging process). Next, at step S5, the CPU11estimates a type of a disturbance (estimation process), and terminates processing.

As describe above, the hardness test method according to the present embodiment includes the first measurement process measuring an indentation curve for a plurality of times under the same condition with respect to the test specimen S in the predetermined environment (step S1); the setting process setting an acceptable range of variation in load loading curves based on the load loading curves of the plurality of the indentation curves obtained by the first measurement process (step S2); the second measurement process measuring an indentation curve under the same condition as the first measurement process with respect to the test specimen S in an actual usage environment (step S3); and the judging process judging whether the load loading curve of the indentation curve measured by the second measurement process is within the acceptable range of variation in a load loading curve set by the setting process (step S4). Therefore, after a measurement is performed with respect to the test specimen S in the predetermined environment and an acceptable range of variation in a load loading curve is set, the same measurement is performed with respect to the same test specimen S in an actual usage environment, and, based on whether the obtained load loading curve is within the set acceptable range, whether the influence of disturbance in the actual usage environment is large can be determined. Therefore, for example, the influence of an installation environment that cannot be determined by measurement of floor vibration alone can be quantitatively verified.

According to the hardness test method of the present embodiment, the indenter3is a cone-shaped indenter. In the setting process (step S2), the load loading curves of the plurality of the indentation curves are fitted using quadratic functions; two curves having maximum and minimum slope values are selected; and the range between the two selected curves is set as an acceptable range of variation in a load loading curve. Therefore, an acceptable range of variation in a load loading curve that can be used as a reference during a test in an actual usage environment is set from two load loading curves having maximum and minimum slope values obtained by the first measurement process.

Further, according to the hardness test method of the present embodiment, an acceptable range of variation in a load loading curve is set by multiplying the slope values of the two selected curves by a safety factor. Therefore, a certain degree of margin can be added to a set acceptable range, which allows an unexpected measurement error in an actual usage environment to be absorbed.

The hardness test method of the present embodiment further includes an estimation process (step S5) estimating a type of a disturbance in an actual usage environment based on the indentation curve measured by the second measurement process (step S3). Therefore, what type of disturbance is occurring can be estimated from the behavior of the indentation curve measured in the actual usage environment. This allows a user to easily take measures to reduce the disturbance.

According to the hardness test method of the present embodiment, the test specimen S is copper, aluminum, or gold. Therefore, a measurement is performed using the test specimen S that is susceptible to plastic deformation and for which the influence of disturbance is easy to appear in an indentation curve, and thus a more accurate verification result can be obtained.

Second Embodiment

Next, a second embodiment of the present invention is explained. The second embodiment is different from the first embodiment in how to set an acceptable range of variation in a load loading curve in the setting process S2. Therefore, the explanation will be focused on this point. Constituents that are the same as in the first embodiment are indicated using the same reference numerals, and the explanation thereof is omitted.

AsFIG. 7illustrates, a hardness tester200according to the present embodiment includes a controller10A. The controller10A is configured to include a CPU11A, a RAM12A, a memory13A, and the like.

The CPU11A, for example, performs various control processes according to various processing programs for a hardness tester stored in the memory13A. The RAM12A, for example, includes a program storage area for deploying a processing program and the like executed by the CPU11A; a data storage area storing input data and a processing result and the like generated when a processing program is executed; and the like.

The memory13A, for example, stores the first measurement program131, a setting program132A, the second measurement program133, the judging program134, the estimating program135, and the like.

The setting program132A, for example, is a program that causes the CPU11A to set an acceptable range of variation in load loading history curves (load loading curves) based on the load loading history curves (load loading curves) of the plurality of the indentation history curves (indentation curves) obtained by executing the first measurement program131. Specifically, first, the CPU11A perceives the shape of the load loading history curves of the plurality of the indentation history curves obtained by executing the first measurement program131. In the present embodiment, it is perceived that the load loading history curves are quadratic curves. Next, the CPU11A fits the load loading curves of the plurality of the indentation curves (seeFIG. 8(a)) obtained by executing the first measurement program131using quadratic functions to calculate a correlation coefficient (r), and sets the minimum of the calculated correlation coefficient (r) or above as an acceptable range of variation in a load loading curve (seeFIG. 8(b)) (setting process). For example, asFIG. 8(b) illustrates, in a case where correlation coefficients (r) of three load loading curves are respectively 0.999, 0.996, and 0.998, the acceptable range can be set as r>0.990. At this time, it is also possible to multiply the calculated correlation coefficient by a safety factor to set an acceptable range of variation in load loading curves. For example, by performing an operation of a minimum correlation coefficient×½, an acceptable range is set. The safety factor is registered by a user in advance. By executing such a setting program132A, the CPU11A acts as a setter.

FIGS. 9(a) and9(b) are each an example illustrating an indentation curve in a case where the second measurement process is performed after the setting process.FIG. 9(a) illustrates an example in which a load loading curve is within an acceptable range.FIG. 9(b) illustrates an example in which a load loading curve is outside an acceptable range. Similar to the first embodiment, in the case where a load loading curve is within an acceptable range, it is judged that the influence of disturbance is small; and in the case where a load loading curve is outside an acceptable range, it is judged that the influence of disturbance is large.

As described above, according to the present embodiment, the indenter3is a cone-shaped indenter. In the setting process (step S2), the load loading curves of the plurality of the indentation curves are fitted using quadratic functions to calculate a correlation coefficient, and the minimum of the calculated correlation coefficient or above is set as an acceptable range of variation in a load loading curve. Therefore, an acceptable range of variation in a load loading curve that can be used as a reference during a test in an actual usage environment is set based on a correlation coefficient calculated from the plurality of the load loading curves obtained from a test performed in a predetermined environment.

In the above described first and second embodiments, the judging process (step4) and the estimation process (step S5) are explained as being executed by the CPU11or CPU11A. However, these may also be performed by a user.

Further, in the above described first and second embodiments, it is also possible that the first measurement process (step S1) and the setting process (step S2) are performed by a manufacturer of the hardness tester at a factory of the hardness tester prior to shipment, and a set acceptable range is stored in the hardness tester. In this case, a user actually performing a hardness test executes from the second measurement process (step S3) to the estimation process (step S5) in a state in which the hardness tester is installed in actual usage environment, and, according to the results, verifies the influence and type of the disturbance in the actual usage environment.

Further, in the above described first and second embodiments, a case was explained as an example in which a cone-shaped (cone or pyramid) indenter was used as the indenter3and the load loading history curves were quadratic. However, as the indenter3, besides this, it is also possible to use, for example, a ball indenter, a planer indenter, and the like. In this case, an acceptable range of variation in a load loading history curve may be set by fitting using a function having a shape that fits a load loading history curve of an indentation history curve.