JP7370515B2 - Indentation test device - Google Patents

Description

The present invention relates to an indentation testing device capable of measuring the softness of a subject.

BACKGROUND ART Conventionally, an indentation test device as described in Patent Document 1 below has been proposed as a device for detecting the softness of an article.

Such an indentation test device includes an indenter with a hemispherical tip, a casing that holds the tip of the indenter in a protruding state, and a load cell provided between the casing and the indenter. When detecting the softness by pressing an indenter into a test object, the amount of push into the test object Δx, the load F acting on the indenter during pushing, the diameter φ of the hemispherical surface of the indenter, and the test object. The Young's modulus E of the subject can be measured using the following formula using the Young's modulus E of the subject and the Poisson's ratio ν specific to the subject.

According to such a device, it is possible to measure the softness of a subject by pushing an indenter into the subject. It becomes possible to quantify the condition of objects and the feel of objects.

Japanese Patent Application Publication No. 2019-132623

However, when measuring the softness of a subject using such an indentation test device, there are the following problems.

In other words, when such an indentation test device is pressed into a test object to measure the softness, the above equation 1 is used to measure the softness, but the measured Young's modulus E is Since the measurement is performed assuming that the indenter is pressed in the normal direction from the surface of the specimen, it is not possible to accurately measure the Young's modulus E if the indenter is actually pressed in an oblique direction.

Specifically, when the indenter is pressed diagonally against the specimen, the surface of the specimen will be in a state of bulges and depressions as shown in Figure 3, and the indenter will be pressed from complicated directions. Pressure loads and tensile loads will occur. Furthermore, when the indenter is pressed diagonally, the amount of displacement with respect to the indenter is smaller than when it is actually pressed vertically, but in Equation 1, the amount of displacement remains large. Therefore, when the indenter is pressed obliquely, the measured value changes greatly, making it impossible to accurately measure Young's modulus E.

Therefore, the present invention has been made with attention to the above problem, and is an indentation test that enables accurate measurement of the softness of a test object even when an indenter is pressed against the test object from an oblique direction. The purpose is to provide equipment.

In order to solve the above-mentioned problems, the present invention provides an indenter that is pushed into a subject whose softness is to be measured, a casing that houses the indenter, and an indenter that protrudes from the casing when pressed against the subject. , and a triaxial load detection sensor for detecting the load acting on the indenter, the angle between the longitudinal direction of the casing and the pressing direction acting on the test object is adjusted along the three axes. Calculated using each acting load component , and according to the calculated angle, the load by the load detection sensor, the diameter of the tip of the indenter that can come into contact with the subject, and the amount of depression of the indenter. The apparatus includes a measurement section that measures the softness of the subject using parameters including the following.

With this configuration, when the indenter is pressed diagonally against the test object, the pressing direction is estimated based on the triaxial loads, and the angle between the pressing direction and the longitudinal direction of the casing is detected by the load detection sensor. In addition, the load detection sensor can detect the pressing force on the subject.

Furthermore, when measuring softness, the softness is measured by multiplying by a correction value according to the angle.

With this configuration, the amount of depression and the contact area of the indenter can be corrected depending on the angle, and the softness can be measured accurately.

According to the present invention, there is provided an indenter that is pushed into a subject whose softness is to be measured, a casing that houses the indenter, and an indenter that acts on the indenter when the indenter protruding from the casing is pressed against the subject. In an indentation test device comprising a three-axis load detection sensor for detecting a load, the angle between the longitudinal direction of the casing and the pressing direction acting on the test object is determined by each load component acting on the three axes. and, according to the calculated angle, using parameters including the load by the load detection sensor, the diameter of the tip portion where the indenter can contact the subject, and the amount of depression of the indenter. Since it is equipped with a measurement part that measures the softness of the specimen, when the indenter is pressed diagonally against the specimen , the pressing direction is estimated by the three-axis loads, and the pressing direction and the longitudinal direction of the casing are calculated. The load detection sensor can detect the angle with respect to the object, and the load detection sensor can also detect the pressing force on the subject.

A diagram showing the configuration of the indentation test device of the present invention Diagram showing measured values when changing the pushing speed in the same form Diagram of state when pushed diagonally Diagram showing the contact area of the indenter when pressed in an oblique direction Comparative example showing measured values when changing the pushing angle

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

The indentation test device 1 in this embodiment is capable of measuring and outputting an index of the softness of the test object 6 as Young's modulus, and as shown in FIG. It includes an indenter 4 that is pressed by the specimen 6, a pressing section 3 for pressing the indenter 4 against the specimen 6, and a load detection sensor 5 that detects the load of the indenter 4 pressed by the pressing section 3. configured. Characteristically, when pressing the indenter 4 against the subject 6, the angle between the pressing direction and the axis CL along the longitudinal direction of the casing 2 is measured. This makes it possible to measure the Hereinafter, the indentation test device 1 in this embodiment will be described in detail with reference to the drawings. In addition, in the description, the longitudinal direction of the casing 2 is assumed to be the Z axis, and the directions orthogonal to this are assumed to be the X axis and the Y axis.

First, the structure of this indentation testing apparatus 1 will be explained using FIGS. 1 and 2.

A casing 2 constituting this indentation test device 1 has a pressing part 3, a load detection sensor, an indenter 4, etc. therein, and has a hollow interior. A planar contact portion 21 for pressing the indenter 4 perpendicularly to the subject 6 is provided at the tip of the casing 2 . The contact part 21 here has a ring shape with an outer diameter larger than that of the upper grip part 20 so that it can be contacted with the longitudinal axis CL of the indentation test device 1 in the normal direction of the test object 6 as much as possible. . Here, the contact part 21 has a ring shape, but it may have a rectangular shape larger than the grip part 20, and the lower end surface thereof is made into a relatively large planar shape. Then, such a casing 2 is held by a human hand and the contact portion 21 is pressed against the subject 6, or the grip portion is fixed to a jig or the like and the contact portion 21 is pressed against the subject 6. I am making it possible to do so.

A pressing section 3 provided inside the casing 2 is capable of pressing an indenter 4 against the subject 6, and is constructed of a servo motor here. By driving the servo motor, it is possible to measure vertical displacement according to the amount of rotation, and the subject 6 is pressed while measuring the amount of displacement of the indenter 4. Note that here, the pressing section 3 is constituted by a servo motor, but the indenter 4 may be pressed by a spring or manual pressing. At this time, a displacement sensor or the like is provided so that the vertical displacement of the indenter 4 can be detected.

The load detection sensor 5 is capable of detecting the load that acts when the indenter 4 is pressed against the subject 6, and is provided between the upper end portion of the indenter 4 and the pressing portion 3. Here, as the load detection sensor 5, a load cell capable of detecting loads in three axial directions (loads in orthogonal XYZ axes directions) is used. As is well known, this load cell has strain-generating parts made of thin metal plates installed in four directions, which are erected toward a central action part, and the load applied to the strain-generating parts is transferred by electricity. It is configured so that it can be detected as a change in the signal. When detecting a load based on a change in this electric signal, a Wheatstone bridge attached to the strain-generating portion detects a voltage change that occurs as the strain-generating portion deforms as a load. Note that when such a load detection sensor 5 is provided, the axis CL along the longitudinal direction of the casing 2 can be detected as the Z axis, and the directions perpendicular to this can be used as the X and Y axes to detect the respective loads. Let's do it like this.

The indenter 4 to which the load detection sensor 5 is attached has a hemispherical end portion 41, and is configured to move up and down on a sliding portion 42 provided on the inner wall of the casing 2 with a small gap. As shown in FIG. 2, the indenter 4 is pressed against the subject 6 so that the softness of the subject 6 can be measured. Note that, before measurement, the indenter 4 is housed inside the casing 2 as shown in FIG. 1, and the hemispherical surface 41 at the tip thereof is kept from protruding from the contact surface 21 of the casing 2. Then, at the stage when measurement is started, the indenter 4 is made to protrude from the contact surface 21 of the casing 2 via the pressing part 3.

With this configuration, the softness of the subject 6 is measured by pressing the indenter 4.

The measurement unit first estimates the direction of the load that actually acts using the load components in the XYZ axis directions that act on the load detection sensor 5, and compares the direction of the load with the longitudinal direction (Z axis direction) of the casing 2. Calculate the angle of When calculating this angle, the composite vector is estimated to be the direction of the load that actually acts from the load components acting in the X-axis direction, Y-axis direction, and Z-axis direction, and the angle between the composite vector and the Z-axis direction is calculated. Calculate. This calculated angle includes a roll angle around the X-axis and a pitch angle around the Y-axis, and each angle is calculated in advance. Note that when calculating the angle with respect to the Z-axis direction from such load components in the XYZ-axis directions, the angle of the casing 2 with the Z-axis direction may not match. Specifically, when the indenter 4 is pushed diagonally into the specimen 6, as shown in FIG. A tensile load is applied. These pressing loads and tensile loads make it impossible to accurately calculate the inclination angle of the casing 2 with respect to the Z-axis direction. Therefore, a correction coefficient is multiplied in consideration of the influence on the load due to bulges, depressions, etc. of the subject 6. As for such a correction coefficient, it has been found through experiments that an accurate angle can be detected if it is set within the range of 1.5 to 2.0 within the inclination range of 0 degrees to 20 degrees.

Next, from the angle thus calculated, the amount of displacement Δx along the load direction (direction of the composite vector) when the indenter 4 is actually pressed is determined. At this time, if the indenter 4 is pressing along the Z-axis direction, the displacement according to the amount of rotation by the servo motor will be the displacement that presses the subject 6, and for example, if the indenter 4 is tilted at 45 degrees from the Z-axis direction If it is, the value is a value that is 1/√2 of the displacement caused by the servo motor.

Further, using the displacement Δx in the direction of the resultant vector calculated in this manner, the pushing speed in the direction of the resultant vector is also calculated from the rotational speed of the servo motor and the like.

Furthermore, the area of the pressing surface of the indenter 4 is also corrected based on the thus calculated inclination angle with respect to the Z axis. When the indenter 4 is actually pressed in the Z-axis direction, the contact surface with the subject 6 is circular, but when it is pressed at an angle, the contact surface has a shape as shown in the shaded area in FIG. , the contact surface area S becomes smaller. Therefore, the contact surface area S is corrected according to this inclination angle. The contact surface area S is calculated by subtracting the area of the non-contact portion from the surface area of the hemisphere depending on the inclination angle.

Then, using the pushing amount Δx, pushing speed, contact surface area S, etc. corrected in this way, the measuring section measures Young's modulus E using the following equation 2.

Here, the known quantities are the corrected displacement Δx, the load F in the Z-axis direction, the corrected contact surface area S of the indenter, the Poisson's ratio ν, and the corrected speed (differential value of Δx). On the other hand, since the unknown quantities are the Young's modulus E and the speed correction coefficient c, it is not possible to measure the Young's modulus E and the speed correction coefficient c using Equation 2 alone. Therefore, the equation 3 obtained by differentiating the equation 2 with respect to time is used.

Here, the amount of displacement when pressing the test object 6 is very small, and assuming that it is pressed at a constant velocity, the second differential term (acceleration term) of the displacement is zero, and the following equation 4 is obtained. Become.

Since the differential term of this F is a value obtained by dividing the load by the sampling time, it becomes a known quantity, and using Equation 4 and Equation 2, the Young's modulus E and the speed dependence coefficient c are calculated.

Then, the Young's modulus E, the velocity dependence coefficient c, etc. thus measured are outputted in a displayable manner, and the pushing speed at that time can also be displayed.

FIG. 5 shows the results of Young's modulus when using Equation 1 and Equation 4 when the test object was pressed at various angles using the indentation testing apparatus having such a configuration.

In FIG. 5, the upper diagram shows Young's modulus E measured when the indenter 4 is pressed perpendicularly to the specimen 6 (0 degree inclination), and the middle diagram shows the measurement with the indenter 4 pressed at a 10 degree inclination. The Young's modulus E was measured when the product was pressed in at a 20-degree angle. In the experiment, Young's modulus E was measured using three types of samples in order to investigate errors due to samples.

As can be seen from FIG. 5, when the indentation force is measured using Equation 1, the Young's modulus E is measured to be smaller as the inclination angle increases, whereas the Young's modulus E is measured using Eq. When measured, it can be seen that the change is small. From this, it can be seen that the Young's modulus E can be accurately measured even when the inclination angle changes.

In this way, according to the above embodiment, the indenter 4 that is pushed into the subject 6 whose softness is to be measured, the casing 2 that accommodates the indenter 4, and the indenter 4 that protrudes from the casing 2 are inserted into the subject 6. In the indentation testing apparatus 1, which is equipped with a triaxial load detection sensor 5 that detects the load acting on the indenter 4 when the indenter 6 is pressed, the load acting on the longitudinal direction (CL) of the casing 2 and the test object 6 is applied. The angle with the pressing direction is calculated using the respective load components acting on the three axes , and the load F by the load detection sensor 5 and the indenter 4 Since the Young's modulus E of the specimen 6 is measured using parameters including the contact surface area S based on the diameter of the indenter 4 that contacts the indenter 6 and the indentation amount Δx of the indenter 4, it is possible to can be estimated, and the angle between the pressing direction and the longitudinal direction of the casing 2 can be detected by the load detection sensor 5, and the pressing force on the subject 6 can be detected by the load detection sensor 5. become.

Note that the present invention is not limited to the above embodiments, and can be implemented in various forms.

For example, in the above embodiment, the Young's modulus E is measured in consideration of the pushing speed, but the Young's modulus E may be measured without considering the pushing speed. In this case, it is calculated using Equation 1 based on the corrected displacement and contact surface area.

Furthermore, in the above embodiment, when calculating the inclination angle, the angle between the composite vector and the Z-axis direction using the triaxial load detection sensor 5 is calculated. The angle between the normal direction and the longitudinal direction of the casing 2 may be calculated. In this case, when calculating the angle, a method is used in which the distance between the casing 2 and the surface of the subject 6 is measured using a separate distance sensor, etc., and the inclination angle of the casing 2 is calculated according to that distance. be able to.

Furthermore, in the above embodiment, the contact surface area S of the indenter 4 is corrected according to the inclination angle, but the indenter 4 is configured to be very small, and even if it is pressed in an inclined state, the entire hemispherical surface will not be able to press. In such a case, the contact surface area S may not be corrected.

1... Indentation test device 2... Casing 21... Contact surface 3... Pressing part 4... Indenter 41... Hemispherical surface 42... Sliding part 5... Load detection sensor 6 ...Subject

Claims (4)

An indenter that is pushed into the subject whose softness is to be measured,
a casing that accommodates the indenter;
a triaxial load detection sensor that detects the load acting on the indenter when the indenter protruding from the casing is pressed against the test object;
In an indentation test device comprising:
The angle between the longitudinal direction of the casing and the pressing direction acting on the subject is calculated using the respective load components acting on the three axes , and the load detected by the load detection sensor is determined according to the calculated angle. and a measurement unit that measures the softness of the subject using parameters including the diameter of the tip of the indenter that can come into contact with the subject, and the amount of depression of the indenter. Indentation test equipment. The indentation test device according to claim 1, wherein the measuring section measures by multiplying by a correction value according to the angle. An indenter that is pushed into the subject whose softness is to be measured,
a casing that accommodates the indenter;
a triaxial load detection sensor that detects the load acting on the indenter when the indenter protruding from the casing is pressed against the test object;
In an indentation test method using an indentation test device comprising:
The angle between the longitudinal direction of the casing and the pressing direction acting on the subject is calculated using the respective load components acting on the three axes , and the load detected by the load detection sensor is determined according to the calculated angle. and an indentation test characterized in that the softness of the subject is measured using parameters including the diameter of the tip of the indenter that can come into contact with the subject, and the amount of indentation of the indenter. Method. 4. The indentation test method according to claim 3, wherein the measurement is performed by multiplying a correction value according to the angle.

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