JP5836745B2 - Indentation test equipment - Google Patents

Description

  The present invention relates to a novel indentation test method. The present invention also relates to a novel indentation test apparatus using the above indentation test method.

  Tensile tests used for investigating properties such as deformation of metal materials are common as objective evaluation methods. However, it is necessary to cut out test specimens from samples and the like. It is difficult to apply to other materials and living tissues.

  On the other hand, the indentation test that is generally used for measuring the hardness of materials similarly enables minimally invasive measurement because it is not necessary to cut out a test piece. In this indentation test, it is known that Hertz's elastic contact theory has high reliability for metal materials (for example, see Non-Patent Document 1).

  In addition, there are several examples in which the indentation test is used for measuring the compositional relationship of soft materials with large deformations such as biological soft tissues (for example, see Non-Patent Documents 2 to 5).

  However, in the measurement of the compositional relationship of soft materials with large deformation such as living soft tissue by the indentation test described above, the high reliability of Hertz's elastic contact theory is shown by Toshiyuki Sawa, but it is within the range of minute deformation. In addition, Osamu Takatani et al. Applied to soft biological tissues is a technique based on N value which is essentially equivalent to Hertz's elastic contact theory. In addition, the method of Yoshiki Arima, who identifies from the energy loss in the loading / unloading process together with the N value, assumes a semi-infinite body as well as Hertz's elastic contact theory, and does not consider the effect of thickness. . Regarding this thickness, there is a research report of N.E.WATERS, but it shows the effect, and has not yet been evaluated in association with the stress-strain relationship. Furthermore, although there is a report on application to polymer materials by Tatsuya Ishibashi and others focusing on irreversible behavior, there is a problem that application to soft materials with high reversibility is difficult.

  On the other hand, in recent years, progress on breast cancer and its medical technology has been rapid. Breast Cancer Progression and Treatment Breast cancer is a cancer that occurs in the mammary gland and surrounding breast tissue, and is a disease accompanied by tissue changes such as calcification and lump in the course of its progression. For this reason, visual examination, ultrasonic examination, and mammography examination using X-rays are performed in the medical treatment, and surgical treatment is given in more advanced cases.

  As seen in routine breast cancer screening, breast cancer has already undergone extensive medical examinations such as visual and palpation and ultrasonography, as well as all patients who are highly suspected of breast cancer regarding mammography. Some local governments are intensifying their efforts to apply them.

  However, even in such a situation, the rate of regular breast cancer screening is not necessarily high. This is because the accuracy of visual examination and ultrasound diagnosis is low, or expensive and sometimes painful mammography examinations are avoided. There are some points.

  Palpation is a method by which the operator can obtain various findings by sensing the subtle differences in the tissue with his fingertips, and is one of the most basic means of initial diagnosis because of its simplicity.

  The inventor has disclosed technical contents related to the present invention (see Patent Document 1 and Non-Patent Documents 6 to 11).

International Publication No. WO / 2010/084840

T. Sawa, Practical Material Mechanics, (2007), pp.258-279, Nikkei Business Publications, Inc. (in Japanese) O. Takatani, T. Akatsuka, The Clinical Measurement Method of Hardness of Organism, Journal of the Society of Instrument and Control Engineers, Vol.14, No.3, (1975), pp.281-291. (In Japanese) Y. Arima, T. Yano, Basic Study on Objectification of Palpation, Japanese Journal of Medical Electronics and Biological Engineering, Vol.36, No.4, (1998), pp.321-336. (In Japanese) N. E. Waters, The Indentation of Thin Rubber Sheets by Spherical indentors, British Journal of Applied Physics, Vol. 16, Issue 4, (1965), pp.557-563. T. Ishibashi, S. Shimoda, T Furukawa, I. Nitta and H. Yoshida, The Measuring Method about Young's Modulus of Plastics Using the Indenting Hardness Test by a Spherical Indenter, Transactions of the Japan Society of Mechanical Engineers, Series A, Vol .53, No.495, (1987), pp.2193-2202. (In Japanese) M. Tani, A. Sakuma, M. Ogasawara, M. Shinomiya, Minimally Invasive Evaluation of Mechanical Behavior of Biological Soft Tissue using Indentation Testing, No.08-53, (2009), pp.183-184. M. Tani, A. Sakuma, Measurement of Thickness and Young ’s Modulus of Soft Materials by using Spherical Indentation Testing, No. 58, (2009), pp. 365-366. A. Sakuma, M. Tani, Spherical Indentation Technique for Low-invasive Measurement for Young ’s Modulus of Human Soft Tissue, No.09-3, (2009), pp.784-785. M. Tani and A. Sakuma, Evaluation of Thickness and Young's Modulus of Soft Materials by using Spherical Indentation Testing, Transactions of the Japan Society of Mechanical Engineers, Series A, Vol.75, No.755, (2009), pp.901 -908. (In Japanese) A. Sakuma, Softness Evaluation of Human Skin by Spherical Indentation imitating Palpation, The 36th Annual Meeting of Japan Cosmetic Science Society, Vol.36, (2011), p.79. (In Japanese) A. Sakuma, K. Tanabe, K. Kawagoe and M. Ogasawara, Evaluation of Thin Soft Tissues by Indentation System imitating Palpation, JSME Annual Meeting, Vol.2011, No.11-1 (DVD-ROM edition), p.J022054 (in Japanese)

  As described above, palpation is a method in which the operator can obtain various findings by sensing the difference in the delicate state of the tissue with the fingertip, and the most basic of the initial diagnosis is one of means because of its simplicity. On the other hand, it is a problem to be solved that different diagnoses can be made even for the same symptoms due to differences in the experience of the surgeon.

  Therefore, it is desired to develop an objective and quantitative measurement method and apparatus by mathematically processing the measurement data obtained in the process of deforming the inspection object by pressing such as palpation. Further, development of a method and apparatus that can be applied not only to the above-described breast cancer medical technique but also to quantitative measurement when a foreign substance is present in a sample is desired.

The present invention has been made in view of such problems, and an object thereof is to provide a novel indentation test method.
Another object of the present invention is to provide a novel indentation test apparatus using the above indentation test method.

According to one aspect of the present invention, in an indentation test apparatus for detecting the presence or absence of foreign matter in a sample, a horizontal for positioning the ball indenter at a plurality of positions of the sample by relatively moving the sample and the ball indenter. Actuator, vertical actuator that pushes the ball indenter into the sample, control unit that controls the indentation load and indentation amount at multiple positions, and calculation of Young's modulus and sample thickness at multiple positions based on the indentation load and indentation amount And a storage unit that stores values of Young's modulus and thickness at a plurality of positions calculated by the calculating unit, and the difference between the plurality of positions of the Young's modulus and the calculated Based on the change of the thickness value between a plurality of positions, the presence of an object having different hardness in the sample and the position of the object in the pushing direction are estimated.

It is a figure which shows the contact state of a spherical indenter and a plane sample. It is a figure which shows the relationship between a load and pushing amount. (a) It is a figure which shows the relationship between a ball indenter indentation coefficient, and the amount of indentation, (b) It is a figure which shows the relationship between a sample thickness and the second derivative of a ball indenter indentation coefficient. It is a figure which shows the compression area | region of an ellipsoid shape. It is a figure which shows the relationship between a sample thickness and the second derivative of the Young's modulus at the time of contact. It is a figure which shows the outline of an indentation testing machine. It is a figure which shows the structure of an indentation test apparatus. (a) It is a conceptual diagram of an indentation test to a sample with a uniform thickness with the position of the indenter to be pushed in. (b) Indentation test to a sample with a change in the thickness with the position of the indenter to be pushed in FIG. It is a conceptual diagram of the measurement with respect to the sample which has a lesion part in a bottom. (a) The measurement result of the distribution of the thickness h of the sample and the distribution of the initial Young's modulus E ₀ , and (b) the identification result of correcting the thickness h of the sample. It is a conceptual diagram of the measurement with respect to the sample which has a lesioned part on the surface. (a) Measurement result of distribution of thickness h of sample and distribution of initial Young's rate E ₀ , (b) Identification result of correcting initial Young's rate E ₀ of sample. It is a conceptual diagram of the measurement with respect to the sample which has a lesion part in the middle. (a) The measurement result of the distribution of the sample thickness h and the distribution of the initial Young's modulus E ₀ , and (b) the identification result of correcting the sample thickness h and the initial Young's modulus E ₀ .

  Hereinafter, embodiments for carrying out the invention relating to the indentation test method and the indentation test apparatus will be described.

  The indentation test method is an indentation test method in which a ball indenter is indented into a sample. The sample thickness is identified, the equivalent indentation strain of the sample is calculated using the sample thickness, and the Young's sample of the sample is calculated using the equivalent indentation strain. This is a method for calculating the rate.

  The indentation test apparatus includes a sample thickness identification unit for identifying a sample thickness and an equivalent indentation strain calculation unit for calculating an equivalent indentation strain of the sample using the sample thickness. And a Young's modulus calculator that calculates the Young's modulus of the sample using the equivalent indentation strain.

  In the text of this specification, “(English character symbol) hat” refers to an English character symbol with a hat symbol, and “(English character symbol) overline” refers to an English character symbol with an overline. And the one with a secondary differential coefficient appended to an English letter symbol is described as “(English letter symbol) secondary differential coefficient”.

The indentation test evaluation method will be described. First, contact deformation of a finite sample will be described.
When a sufficiently hard ball indenter is pushed into a semi-infinite body sample and Hertz's elastic contact theory is used, the relationship between the pushing load F and the pushing amount δ shown in FIG. 1 is expressed as follows.

  However, the coefficient A has the following relationship.

  Here, φ, E, and ν are the diameter of the ball indenter, the Young's modulus of the sample (hereinafter also referred to as “Young's modulus”), and the Poisson's ratio (hereinafter also referred to as “Poisson ratio”), respectively. Furthermore, by assuming a load distribution indicated by p (r) in the radius r direction on the load surface of the sample with respect to the contact surface of radius a in FIG. Expressed.

  Further, as a function of the indentation load F and the strain ε, the Young's modulus E is derived from the equation (3) and Hooke's law σ = Eε as follows:

  Here, from the relationship between these equations (1) and (4), the strain due to the contact between the semi-infinite sample and the hard sphere is expressed by the following equation depending on the indenter diameter φ and the indentation amount δ:

Can be obtained uniquely. This ε _H overline is referred to as a Hertz strain.

When considering the indentation test of a spherical indenter on samples of various thicknesses hi (i = 1,2,-, ∞) placed on a rigid body, the effect of the rigid body opposite to the load surface of the indenter A load F-push-in amount δ curve as shown in Fig. 2 is obtained. In the indentation test for a semi-infinite body sample with infinite thickness h _∞ , a load F curve indicated by a broken line as explained by Hertz's elastic contact theory can be obtained, but in general a load F hat is semi-infinite for a finite body sample. The result of the following relationship is greater than that of the body sample.

  Assuming that Hertz's elastic contact theory can be applied to the effect on the load F hat due to the difference in the sample thickness hi, from Equation (1)

Therefore, the following relationship can be obtained for the coefficients A and A hat related to the indentation amount δ.

  Furthermore, if there is no change in the indenter diameter φ and the Poisson's ratio ν of the sample, the relationship of the following equation can be obtained from Equation (2), so Hertz's elastic contact theory to the indentation test result of the finite body sample The Young's rate E hat obtained by application is higher than the original value E.

  The Young's modulus E hat obtained in this way is referred to as a spherical indentation modulus.

  Applying Hertz's elastic contact theory equation (1) assuming a semi-infinite sample to a finite sample, as shown in equation (9), shows the effect of the thickness hi on the spherical indenter indentation coefficient E hat. Therefore, consider the identification of the sample thickness hi using this phenomenon.

  Regarding the identification of the ball indenter indentation coefficient E hat, it is considered that the influence of the difference in the sample thickness hi is small at the moment of contact when the deformation amount is very small. That is, at the moment of contact, the relationship of the following equation can be considered from the application condition of equation (1) for an arbitrary thickness hi.

  On the other hand, as the sample thickness hi is smaller, the influence of the rigid body under the sample appears earlier, and as shown by the solid line in Fig. 3 (a), the identification result of the ball indenter indentation coefficient E hat accompanying the indentation increases. Become prominent. This increase is expressed by the following relationship when the thickness of the sample has a relationship of hi <hi + 1.

  From this, the relationship between the sample thickness hi and the second derivative of the ball indenter indentation coefficient E hat and second derivative is given by

If the function f (E hat · second derivative) shown in FIG. 3 (b) can be obtained, the sample thickness hi can be deduced from the information at the start of contact.

  The indentation deformation evaluation method will be described. In the indentation process of the soft material, a phenomenon in which the deformation region in the sample is remarkably changed by the indenter indentation is observed like a large change in the surface shape on the load surface. From this, it is considered that the indentation deformation is superimposed on the contact deformation by the ball indenter with the effect of the compression deformation.

At this time, the following relationship is defined on the assumption that the contact effect is first expressed by the Hertz strain ε _H overline, and further the compression is expressed by the rate of change ε _V of the region volume of the compressive deformation due to softness.

This ε _I overline is an attempt to express the three-dimensional strain distribution that occurs in the sample in the indentation process with an equivalent uniaxial strain, which is called the equivalent indentation strain. .

  In the indentation process of a soft material with a ball indenter, a compression region V accompanied by deformation due to a significant load is considered in the sample. For this region V, as shown by the shaded portion in FIG. 4, an ellipsoid that is orthogonal to the surface of the indenter sphere on the intermittence line between the initial surface and the indenter surface and also orthogonal to the lower boundary surface of the sample is considered. At this time, the function of the ellipse expressed using the distance β from the load axis z to the intersection line at the lower boundary surface and the height α of the ellipsoid

Is used, the volume V of the compression region can be expressed by the following equation.

  Although the strain generated in the compression region can be obtained from the region change dV, a method of simply expressing this region change dV by the amount of movement dδ of the upper surface of the compression region will be examined. At this time, the region change dV can be expressed by the following equation using the movement amount dδ.

Furthermore, the change rate ε _V overline increment dε _V overline of the compression region V can be defined by the following equation.

Therefore, the strain ε _V overline generated in the compression region can be expressed by the following equation.

From this, the equivalent indentation strain ε _I overline of the equation (13) becomes the following equation.

This equivalent indentation strain ε _I overline is obtained when the indenter diameter φ is infinite.

Thus, the nominal strain is uniaxial. On the other hand, if the thickness h is infinite,

Which is consistent with the Hertz strain ε _H overline.
From these facts, it can be seen that the equivalent indentation strain ε _I overline expressed by the equation (19) has a characteristic capable of expressing both contact deformation and compression deformation.

If the equivalent indentation strain ε _I overline in equation (19) can equivalently express uniaxial deformation, the following equation can be assumed in relation to the stress σ generated in the sample.

Furthermore, if Equation (3) is established by the relationship between the stress σ and the load F hat at the contact portion, the Young's modulus E of the sample can be derived from the following equation using the equivalent indentation strain ε _I overline.

By combining this equation (23) with equation (19) representing the equivalent indentation strain ε _I overline and the method for obtaining the sample thickness hi described above, the diameter φ of the ball indenter, the load F hat, the indentation amount δ In principle, the Young's modulus E of the sample can be evaluated.

  Next, regarding the phenomenon shown by the solid line in FIG. 2 where the slope of the load curve increases as the sample thickness hi decreases, by taking this into account as a function of the indentation amount δ or an apparent Young's modulus E hat, Hertz's Consider the following equation, which is an extension of theoretical equation (1).

  Here, the following relationship is established between the original Young rate E and the apparent Young rate E hat.

As shown in FIG. 3 (a), the original Young's rate E and the apparent Young's rate E hat are the same value E ₀ at the start of contact, whereas the apparent Young's rate E as the push-in progresses. This represents a phenomenon in which the hat is measured higher than the original Young's rate E.

  It is known that the relationship between the sample thickness h of this phenomenon and the second derivative E hat and the second derivative of the Young's modulus at the time of contact can be approximated by an exponential relationship as shown in Fig. 5. Represented by

  Here, G is a coefficient for making the second derivative of the Young's modulus dimensionless, and H is a coefficient for the sample thickness.

Accordingly, the sample thickness h is obtained from the Young's modulus second derivative E-hat and the second derivative at the time of contact according to the equation (26), thereby obtaining the equivalent indentation strain ε _I overline of the equation (13). Furthermore, from this and the indentation load F hat, the Young's modulus E of samples having various thicknesses can be obtained by the equation (23).

  The Young's modulus obtained by this equation (23) has been confirmed to be independent of thickness from experimental verification on samples of various thicknesses [1]. Furthermore, if applicability to various hardnesses and shapes can be confirmed, it is possible to evaluate samples having complicated deformation characteristics and shapes such as biological soft tissue by this measurement method.

  Next, verification of the evaluation method will be described. First, the indentation test apparatus and its conditions will be described. The indentation tester shown in Fig. 6 is used to verify the evaluation method. In this indentation tester, a vertical actuator 1 is attached to a horizontal actuator 2, and a stage 3 is attached to the vertical actuator 1. A load shaft 5 is attached to the stage 3, and the position of the load shaft 5 is controlled by operating the vertical actuator 1 and the horizontal actuator 2 with a personal computer (PC). The load acting on the ball indenter 6 attached to the tip of the load shaft 5 is acquired from the load cell 4 attached to the load shaft 5, and the pushing amount is the amount of movement of the stage 3 to which the load shaft 5 is attached. And from the horizontal actuator 2.

  As shown in FIG. 7, the indentation test system 20 has a Young's modulus based on the load value F sent from the load cell 4 of the indentation tester 19 and the indentation amount δ sent from the vertical potentiometer 9 in the vertical actuator 1. At the same time, the movement of the indentation tester 19 is also controlled by the indentation position / indentation amount control unit 18. At this time, the sample thickness is identified from the indentation amount δ sent and the calculated Young's modulus, and the strain considering the effect of the sample thickness based on the identified and calculated sample thickness. Is calculated, and the Young's modulus in consideration of the influence of the sample thickness is calculated. Further, the sample thickness and Young's modulus information obtained by the sample thickness identifying unit 12 and the Young's modulus calculating unit 14 are obtained by using the information on the indentation position obtained from the horizontal potentiometer 10 in the horizontal actuator 2. It is corrected in the initial Young's modulus correction unit 15. The position of the lesioned part is identified by the lesioned part position identifying unit 16 from this correction information. All the data handled by the CPU unit 11 is recorded in the storage unit 17.

  A test in which the position where the indenter is pushed is changed will be described. In the test method, a ball indenter is pushed into the object to be inspected, and the relationship between the push-in amount and the reaction force when pushed in is mathematically processed. As described above, this push-in test apparatus has a mechanism for pushing the ball indenter into the sample, a part for measuring the reaction force, and a part for calculating, and further a mechanism for changing the position of the ball indenter to push. (FIG. 8 (a)).

Using the test method in which the indentation position of the ball indenter shown in FIG. 8 (a) is changed, the distribution of the sample thickness h and initial Young's modulus E ₀ can be obtained as shown in the graph in FIG. 8 (a). Can do. Further, if the thickness of the sample varies even if the surface is flat, the distribution of the sample thickness h and the initial Young's modulus E ₀ can be obtained as shown in the graph of FIG. 8 (b).

A method for evaluating a lesion according to the present invention will be described. First, measurement of a sample having a lesion on the bottom will be described.
When there is a lesion at the bottom of the sample as shown in FIG. 9 (a), the distribution of the sample thickness h and the initial Young's modulus E ₀ in FIG. 9 (a) is the same as in FIG. 8 (b). It can be measured as a result of the change in thickness h as shown in the graph.

Next, measurement of a sample having a lesion on the surface will be described.
When there is a lesion on the surface of the sample as shown in FIG. 10 (a), the distribution of the sample thickness h and the initial Young's rate E _{0 is} the initial Young's rate E as shown in the graph of FIG. 10 (a). _It can be measured as a result of a change in _zero .

The measurement of a sample having a lesion in the middle will be described.
When there is a lesion in the middle of the sample as shown in FIG. 11 (a), the distribution of the sample thickness h and the initial Young's modulus E ₀ is the thickness h as shown in the graph of FIG. 11 (a). It can also be measured as a result of changes in both the initial Young's rate E ₀ .

  Note that the sample thickness identification method is not limited to the above-described method. In addition, CT, MRI, ultrasonic image diagnosis, optical coherence tomography, and the like can be employed as a sample thickness identification method.

  The application of the present invention is not limited to the aforementioned breast cancer medical technique. In addition, cirrhosis, arteriosclerosis, inspection of foreign substances in food, inspection of defects in polymer materials, and the like can be employed as applications of the present invention.

According to the present invention, the following effects can be obtained.
It is possible to provide a simple, safe and inexpensive medical technique for breast cancer that is low in invasiveness such as pain.
Provided is a method and apparatus for objectively and quantitatively measuring the extent, position, and range of lesions by mathematically processing measurement data obtained in the process of deforming an inspection object by pressing such as palpation. be able to.
Since this effect is based on the characteristics of soft tissue that is sensitive to environmental changes, it can also be used for objective measurement of the location and extent of bruises, identification of areas of tension and stiffness seen in daily life. it can.

  It is to be noted that the present invention is not limited to the embodiment for carrying out the above-described invention, and various other configurations can be adopted without departing from the gist of the present invention.

[References]
[1] M. Tani and A. Sakuma, Evaluation of Thickness and Young's Modulus of Soft Materials by using Spherical Indentation Testing, Transactions of the Japan Society of Mechanical Engineers, Series A, Vol.75, No.755, (2009), pp.901-908. (in Japanese)

DESCRIPTION OF SYMBOLS 1 ... Vertical actuator, 2 ... Horizontal actuator, 3 ... Stage, 4 ... Load cell, 5 ... Load axis, 6 ... Ball indenter, 7 ... Sample, 8 ... Table, 9 ... Vertical potentiometer, DESCRIPTION OF SYMBOLS 10 ... Horizontal potentiometer, 11 ... CPU part, 12 ... Sample thickness identification part, 13 ... Strain calculation part, 14 ... Young's modulus calculation part, 15 ... Sample thickness / initial Young's modulus correction part, 16 ... lesion location identification part, 17 ... storage device part, 18 ... push position / push amount control part, 19 ... push test machine 20 ... push test system

Claims (2)

In the indentation test device to detect the presence or absence of foreign matter in the sample,
A horizontal actuator for relatively moving the sample and the ball indenter to position the ball indenter at a plurality of positions of the sample;
A vertical actuator that pushes the ball indenter into the sample;
At the plurality of positions, a control unit that controls the indentation load and the indentation amount;
A calculation unit for calculating the Young's modulus and the thickness of the sample at the plurality of positions based on the indentation load and the indentation amount;
A storage unit that stores values of Young's modulus and thickness at a plurality of positions calculated by the calculation unit;
Based on the difference between the plurality of positions of the Young's modulus and the change in the calculated thickness value between the plurality of positions, the presence of an object of different hardness in the sample and the position of the object in the indentation direction Indentation test device to estimate.   The indentation test apparatus according to claim 1, wherein the sample is soft tissue.

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