JP7492681B2 - How to measure the strength of tempered glass - Google Patents

Description

The present invention relates to a method for measuring the strength (particularly the drop strength) of tempered glass.

Conventionally, glass plates that have been chemically strengthened by ion exchange have been used as cover glass for electronic devices such as smartphones and tablet PCs. Such strengthened glass plates are generally manufactured by chemically treating a glass plate containing an alkali metal as a component with a strengthening liquid to form a compressive stress layer on the surface. Strengthened glass plates are designed to have high strength by appropriately adjusting so-called strengthening properties such as surface compressive stress and internal tensile stress.

When a portable electronic device is dropped to the ground, the cover glass may break. One type of breakage that can occur in the cover glass (strengthened glass) is one in which a deep scratch that penetrates the compressive stress layer is the starting point, and the strengthened glass breaks at a relatively slow speed (slow cracking) (see, for example, Patent Document 1). Another type is one in which a shallow scratch (fracture starting point) that does not penetrate the compressive stress layer is formed in the cover glass, and then the crack progresses due to the action of a large stress, leading to breakage (non-slow cracking).

Various destructive tests are carried out to confirm the fracture strength and fracture mode of tempered glass. Patent Document 1 discloses a sandpaper ball drop test and a bending strength test as examples of destructive tests.

In the sandpaper drop ball test, sandpaper is placed on top of tempered glass placed on a base, and a sphere is collided with the sandpaper to destroy the tempered glass. In the bending strength test, an indenter is driven into the tempered glass to form an indentation, and then the tempered glass is destroyed by a three-point bending test.

International Publication No. WO 2013/088856

In addition to the sandpaper drop ball test and bending strength test described above, a drop strength test may be performed in which a test specimen with tempered glass attached is dropped onto an electronic device housing or a pseudo housing that mimics an electronic device, destroying the tempered glass. In a drop strength test, for example, the test specimen is dropped onto sandpaper placed on a surface plate, causing the tempered glass to collide with the sandpaper. The drop height of the test specimen when the tempered glass is destroyed can be regarded as the drop strength of the tempered glass.

This drop strength test is important for analyzing and evaluating the fracture strength of tempered glass because it can reproduce the fracture behavior of cover glass caused by dropping an electronic device more accurately than sandpaper drop tests or bending strength tests.

However, with conventional drop strength tests, it was difficult to determine whether the mode of breakage of the tempered glass was due to a scratch deeper than the depth of the compressive stress layer, or due to a scratch shallower than the depth of the compressive stress layer.

The present invention was made in consideration of the above circumstances, and has as its technical objective the estimation, when measuring the strength of tempered glass, of whether breakage of the tempered glass is caused by a scratch deeper than the depth of the compressive stress layer, or by a scratch shallower than the depth of the compressive stress layer.

The present invention is intended to solve the above problems, and is a method for measuring the strength of reinforced glass having a compressive stress layer, comprising a drop strength measurement step of dropping a measurement structure including the reinforced glass to break the reinforced glass and measuring the drop height as the drop strength, and a failure mode estimation step of estimating whether the breakage of the reinforced glass belongs to a first failure mode or a second failure mode based on the measured drop height, characterized in that the first failure mode is a failure mode caused by a scratch formed in the reinforced glass that is deeper than the depth of the compressive stress layer, and the second failure mode is a failure mode caused by a scratch formed in the reinforced glass that is shallower than the depth of the compressive stress layer.

According to this configuration, the fracture mode estimation process can estimate whether the fracture of the tempered glass belongs to the first fracture mode or the second fracture mode, based on the drop height of the tempered glass measured in the drop strength measurement process. This makes it possible to estimate whether the fracture of the tempered glass in the drop strength measurement process is caused by a scratch deeper than the depth of the compressive stress layer, or is caused by a scratch shallower than the depth of the compressive stress layer.

The strength measurement method according to the present invention may include a first preparation step of creating a first estimation formula for calculating a first expected drop height that estimates that the breakage of the tempered glass belongs to the first breakage mode. The first preparation step may include a drop breakage step of dropping a test structure including a first test tempered glass having a first compressive stress layer, and breaking the first test tempered glass by forming a scratch deeper than the depth of the first compressive stress layer in the first test tempered glass, and a collision breakage step of colliding a first impactor with the first test tempered glass that has not been subjected to the drop breakage step, and breaking the first test tempered glass by forming a scratch deeper than the first compressive stress layer in the first test tempered glass.

With this configuration, the drop destruction process and the impact destruction process in the first preparation process can perform the measurements necessary to estimate the first destruction mode.

The first estimation formula may be created based on a linear function of the test drop height of the test structure measured in the drop destruction process and the fracture energy when the first test tempered glass is broken in the impact destruction process.

The method for measuring the strength of tempered glass according to the present invention may include a second preparation step of creating a second estimation formula for calculating a second expected drop height that estimates that the fracture of the tempered glass belongs to the second fracture mode. The second preparation step may include a scratching step of forming a scratch shallower than the depth of the second compressive stress layer in a second test tempered glass having a second compressive stress layer, and a bending fracture step of applying a bending stress to the second test tempered glass after the scratching step to fracture the second test tempered glass.

With this configuration, the damage process and bending fracture process in the second preparation process can perform the measurements necessary to estimate the second fracture mode.

The second estimation formula may be created based on a linear function of the damage energy imparted to the second test tempered glass by the damage process and the fracture bending stress imparted to the second test tempered glass by the bending fracture process.

The failure mode estimation process may include a drop height comparison process that compares the first expected drop height with the second expected drop height.

By comparing the first predicted drop height with the second predicted drop height in the drop height comparison process, it is possible to estimate whether the breakage of the tempered glass belongs to the first breakage mode or the second breakage mode.

In the collision destruction process, the first collision body may be caused to collide with the first test tempered glass in a state where a damage member for forming the damage deeper than the first compressive stress layer of the first test tempered glass is placed on the first test tempered glass. This makes it possible to reproduce the destruction of the first test tempered glass in the first destruction mode.

In the scratching process, a scratching member for forming the scratch shallower than the second compressive stress layer of the second test tempered glass may be placed on the second test tempered glass, and a second impact body may be collided with the second test tempered glass. This ensures that a scratch shallower than the second compressive stress layer of the second test tempered glass is formed in the second test tempered glass.

In the bending fracture process, the bending stress may be applied to the second test tempered glass by a four-point bending tester. This makes it possible to reproduce fracture of the second test tempered glass in the second fracture mode.

In the collision destruction process, the damage member superimposed on the first test tempered glass may be pressed by a first pressing member surrounding the collision site of the first collision body against the first test tempered glass. This allows stable contact between the damage member and the first test tempered glass.

In the scratching process, the scratching member superimposed on the second test tempered glass may be pressed by a second pressing member surrounding the impact site of the second impact body against the second test tempered glass. This allows stable contact between the scratching member and the second test tempered glass.

In the collision destruction process, the impact of the first impact body may be applied to the first test tempered glass via a first buffer member. This makes it possible to adjust the impact applied to the first test tempered glass by the first impact body.

In the damage application process, the impact from the second impact body may be applied to the second test tempered glass via a second buffer member. This makes it possible to adjust the impact applied to the second test tempered glass by the second impact body.

The test structure may include a support to which the first test tempered glass is fixed. This allows the test structure to mimic an electronic device such as a smartphone.

According to the present invention, when measuring the strength of tempered glass, it is possible to estimate whether the breakage of the tempered glass is caused by a scratch deeper than the depth of the compressive stress layer, or by a scratch shallower than the depth of the compressive stress layer.

FIG. 2 is a cross-sectional view of tempered glass. 1 is a flowchart of an intensity measurement method. FIG. 11 is a side view showing the drop destruction step of the first preparation step. FIG. 11 is a side view showing the collision destruction step of the first preparation step. 11 is a graph created in a first preparation step. FIG. 11 is a side view showing the scratching step of the second preparation step. FIG. 11 is a side view showing a bending breaking step of the second preparation step. 11 is a graph created in a second preparation step. 1 is a graph created in a second preparation step. FIG. 4 is a side view showing a drop strength measurement process. FIG. 11 is a side view showing a testing device used in the scratching step of the second preparation step. FIG. 11 is a side view showing another example of the scratching step of the second preparation step.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Figures 1 to 10 show one embodiment of the method for measuring the strength of tempered glass according to the present invention.

Figure 1 shows a cross-sectional view of glass chemically strengthened by ion exchange (hereinafter referred to as "strengthened glass"). The strengthened glass 1 is configured, for example, in a rectangular plate shape, has a compressive stress layer CSL on the surface, and has a tensile stress layer TSL inside. The surface of the strengthened glass 1 includes a first main surface MS1, a second main surface MS2, and an end surface ES. The first main surface MS1 and the second main surface MS2 are main surfaces that are located on the front and back of each other.

The thickness t of the tempered glass 1 is preferably 0.05 to 1.2 mm, but is not limited to this range. In addition, in the tempered glass 1, the depth DOL of the compressive stress layer CSL from the surface (principal surfaces MS1, MS2) is preferably, for example, 100 to 250 μm, but is not limited to this range.

In this method, when tempered glass 1 is dropped and broken, the drop height is measured as the drop strength, and it is possible to estimate whether the breakage belongs to the first or second breakage mode.

The first fracture mode is a fracture mode that occurs when a scratch deeper than the depth DOL of the compressive stress layer CSL is formed in the strengthened glass 1. The second fracture mode is a fracture mode that occurs when a scratch shallower than the depth DOL of the compressive stress layer CSL is formed in the strengthened glass 1 and the scratch progresses due to bending stress acting on the strengthened glass 1.

As shown in FIG. 2, this method includes a first preparation step S1 for performing measurements necessary to estimate a first failure mode, a second preparation step S2 for performing measurements necessary to estimate a second failure mode, a drop strength measurement step S3 for dropping a measurement structure including a test tempered glass and measuring the drop height when the test tempered glass is broken as the drop strength, and a failure mode estimation step S4 for estimating whether the breakage of the test tempered glass in the drop strength measurement step S3 belongs to the first failure mode or the second failure mode.

The first preparation process S1 includes a drop destruction process in which a test structure including a first test tempered glass is dropped to destroy the first test tempered glass, and an impact destruction process in which a first impact body is caused to impact the first test tempered glass to destroy the first test tempered glass.

As shown in FIG. 3, the test structure 2 used in the drop fracture process includes a first test tempered glass 3 and a first support 4 that supports the first test tempered glass 3. The first test tempered glass 3 has the same structure as the tempered glass 1 shown in FIG. 1. Hereinafter, the compressive stress layer CSL of the first test tempered glass 3 is referred to as the "first compressive stress layer." The conditions of the first test tempered glass 3, such as the dimensions and the depth DOL of the first compressive stress layer CSL, are the same as the conditions of the second test tempered glass measured in the second preparation process S2 described below, and the conditions of the measurement tempered glass measured in the drop strength measurement process S3.

The first test tempered glass 3 is fixed to the first support 4 via an adhesive layer 5. The first support 4 is formed in a plate shape from, for example, polycarbonate or other resin or metal.

In the drop destruction process, the test structure 2 is dropped and struck against a base plate 6, forming a scratch deeper than the depth DOL of the first compressive stress layer CSL on the first main surface MS1 of the first test tempered glass 3. This causes the first test tempered glass 3 to be destroyed. The base plate 6 may be, for example, a stone base plate or a metal base plate. Sandpaper is placed on the base plate 6 as the first scratching member 7.

In the drop destruction process, the test structure 2 is dropped from above the first damaging member 7 while changing (increasing) the drop height in a stepwise manner. In the drop destruction process, the height of the test structure 2 when the first test tempered glass 3 is destroyed is measured and recorded as a first test drop height _H1 .

In the impact destruction process, multiple pieces of first test tempered glass 3 that have not been subjected to the drop destruction process are prepared. As shown in FIG. 4, in the impact destruction process, a first impact body 9 is collided with the first test tempered glass 3 in a state where a second scratching member 8 for forming a scratch DW deeper than the first compressive stress layer CSL is placed on the first test tempered glass 3.

The first test tempered glass 3 is supported on a base plate 10. Sandpaper is placed on the first main surface MS1 of the first test tempered glass 3 as the second scratching member 8. The second scratching member 8 has the same grain size as the first scratching member 7 (sandpaper) used in the drop breakage process.

The second scratching member 8 is placed on the first test tempered glass 3 with the abrasive surface having the abrasive grains in contact with the first main surface MS1 of the first test tempered glass 3.

A first buffer member 11 is placed on the upper surface of the second scratching member 8. The first buffer member 11 is made of a resin plate such as polycarbonate or acrylic, but is not limited to this material.

A first pressing member 12 is placed on the upper surface of the first buffer member 11. The first pressing member 12 is preferably a member having a mass or structure capable of pressing the second damaging member 8 and the first buffer member 11 to an extent that the movement of the second damaging member 8 during a collision can be suppressed. The first pressing member 12 is formed, for example, of a rectangular metal frame having a mass of 5 to 300 g, but is not limited to this shape or material. The first pressing member 12 has an opening 12a through which the first impact body 9 can pass. The first pressing member 12 is arranged to surround the impact site of the first impact body 9 against the first test tempered glass 3.

As shown in FIG. 4, the first impact body 9 used in the impact destruction process is formed of a sphere, but is not limited to this shape. The first impact body 9 is formed of, for example, stainless steel or other metal, but is not limited to this material. The first impact body 9 impacts the first buffer member 11 within the range of the opening 12a of the first pressing member 12.

When the first impacting body 9 collides with the first buffer member 11, the impact is transmitted to the first test tempered glass 3 via the second scratching member 8 (sandpaper). This causes a scratch DW deeper than the depth DOL of the first compressive stress layer CSL to be formed on the first main surface MS1 of the first test tempered glass 3. The first test tempered glass 3 is destroyed starting from this scratch DW.

In the collision destruction step, the height of the first impactor 9 when the first test tempered glass 3 is destroyed is measured and recorded as a second test drop height _H2 (m). Then, the energy applied to destroy the first test tempered glass 3 (hereinafter referred to as "destruction energy") E1 (J) is calculated and recorded from the product of the second test drop height _H2 of the first impactor 9, the mass m (kg) of the first impactor 9, and the gravitational acceleration g (9.8 m/ ^s2 ) _{( E1} = _mgH2 ).

Next, based on the first test drop height _H1 measured in the drop failure step and the fracture energy _E1 of the first test tempered glass 3 measured in the impact fracture step, a first estimation equation is created to estimate that fracture of the test tempered glass in the drop strength measurement step S3 described later belongs to the first fracture mode (first estimation equation creation step).

5 is a graph showing a relationship between a first test drop height _H1 of the first test tempered glass 3 measured in the drop breakage process and a fracture energy _E1 of the first test tempered glass 3 measured in the impact breakage process. FIG. 5 illustrates a measurement result in the case where seven pieces of the first test tempered glass 3 are broken.

From the measurement results, the following relational expression (1) is created:
H ₁ = aE ₁ (1)
Here, the coefficient a is a positive number.

Based on the above relational expression (1), the following first estimation expression (2) is created.
H _E1 = a E ... (2)

Here, H _E1 is a first expected drop height (m) serving as a reference for estimating the first fracture mode, and E is a fracture energy (J) of the test tempered glass measured in a drop strength measurement step S3 described later.

In this way, the first estimation formula (2) is created based on a linear function of the first test drop height _H1 measured in the drop fracture process and the fracture energy _E1 when the first test tempered glass 3 is broken in the impact fracture process.

In the second preparation step S2, multiple pieces of second test tempered glass are prepared. The second test tempered glass has the same structure as the tempered glass 1 shown in FIG. 1. Hereinafter, the compressive stress layer CSL of the second test tempered glass is referred to as the "second compressive stress layer." The conditions of the second test tempered glass, such as the dimensions and the depth DOL of the second compressive stress layer CSL, are the same as the conditions of the first test tempered glass 3 in the first preparation step S1 described above and the conditions of the test tempered glass in the drop strength measurement step S3 described below.

The second preparation process S2 includes a scratching process for forming scratches in the second test tempered glass that are shallower than the depth DOL of the second compressive stress layer CSL, and a bending fracture process for applying bending stress to the second test tempered glass after the scratching process to fracture the second test tempered glass.

As shown in FIG. 6, in the scratching process, sandpaper serving as a third scratching member 15 is placed on the first main surface MS1 of the second test tempered glass 14 supported by the base plate 13, and a second impact body 16 is collided with the third scratching member 15 and the second test tempered glass 14.

The third scratching member 15 is placed on the second test tempered glass 14 so that the abrasive surface containing the abrasive grains contacts the first main surface MS1 of the second test tempered glass 14. The third scratching member 15 has a smaller grain size than the sandpaper used for the first scratching member 7 and the second scratching member 8 used in the first preparation step S1.

A second buffer member 17 is placed on the upper surface of the third scratching member 15. The second buffer member 17 is made of a resin plate such as polycarbonate or acrylic, but is not limited to this material.

A second pressing member 18 is placed on the upper surface of the second buffer member 17. Like the first pressing member 12, the second pressing member 18 is composed of a rectangular metal frame having a mass of, for example, 5 to 300 g, but is not limited to this shape and material. The second pressing member 18 has an opening 18a on its inside. The second pressing member 18 is positioned so as to surround the impact site of the second impact body 16 against the second test tempered glass 14.

The second impact body 16 used in the damage process is composed of a metal sphere, similar to the first impact body 9, but is not limited to this shape or material.

When the second impact body 16 is collided with the second buffer member 17, the second buffer member 17 presses the third scratching member 15 (sandpaper). As a result, a scratch SW smaller than the depth DOL of the second compressive stress layer CSL is formed on the first main surface MS1 of the second test tempered glass 14. In this case, the scratch SW formed on the second test tempered glass 14 does not penetrate the second compressive stress layer CSL. Therefore, the second test tempered glass 14 is not destroyed in the scratching process.

In the damaging process, the height _H3 (m) of the second impactor 16 (hereinafter referred to as the "third test drop height") is varied to damage each of the second test tempered glasses 14. That is, in the damaging process, the energy _E2 (J) imparted to each of the second test tempered glasses 14 (hereinafter referred to as the "damage energy") is varied. The damage energy _E2 is calculated by the product of the mass m (kg) of the second impactor 16, the third test drop height _H3 of the second impactor 16, and the gravitational acceleration g ( _E2 = _mgH3 ).

As shown in FIG. 7, for example, a four-point bending tester 19 is used in the bending breaking process. Not limited to this, a three-point bending tester may be used in the bending breaking process. In the bending breaking process, the bending stress applied to break the second test tempered glass 14 is measured by the four-point bending tester 19. For example, a method conforming to JIS-R1601 can be used as the four-point bending test. Specific conditions for the four-point bending test can be, for example, a pressure jig width of 20 mm, a support jig width of 40 mm, and a crosshead descent speed of 3 mm/min.

Hereinafter, the bending stress when the second test tempered glass 14 is broken in the bending breaking process is referred to as the "breaking bending stress." The action of the breaking bending stress causes a crack to propagate from the scratch SW formed in the second test tempered glass 14 as an initiation point, and the second test tempered glass 14 is broken. The measured breaking bending stress of each second test tempered glass 14 is recorded in association with the damage energy _E2 .

8 is a graph showing the measurement results of the scratching process and the bending fracture process, that is, the relationship between the scratching energy _E2 in the scratching process and the fracture bending stress _σ1 in the bending fracture process. FIG. 8 illustrates the measurement results when six second test tempered glasses 14 are broken.

Based on the measurement results, a relational expression is created between the damage energy _E2 and the fracture bending stress σ1. This relational expression is formed by a linear function of the damage energy _E2 and the fracture bending stress _{σ1 ,} as shown in the following formula (3).
σ ₁ =−bE ₂ +σ _C ... (3)
Here, the coefficient b is a positive number.

In the second preparation process S2, a second estimation equation is created based on the above relational expression (3) to estimate that the breakage of the tempered glass to be measured in the drop strength measurement process S3 described below belongs to the second breakage mode (second estimation equation creation process).

To create the second estimation formula, the injury energy _E2 measured in the injury process is converted into the expected drop height H _E (m) by the following conversion formula (4). This conversion formula (4) is created based on the above relational formula (1).
H _E = a E ₂ ... (4)

Next, the predicted drop height H _E of each second test tempered glass 14 converted by the conversion formula (4) is associated with the fracture bending stress σ _1. Fig. 9 is a graph showing the relationship between the converted predicted drop height H _E and the fracture bending stress σ _1. In Fig. 9, the fracture bending stress σ ₁ is displayed as the predicted fracture bending stress σ _E.

Based on the relationship between the expected drop height H _E and the expected fracture bending stress σ _E , the following relational expression (5) is created.
σ _E = -dH _E +σ _C ... (5)
Here, the coefficient d is a positive number.

Next, the following relational expression (6) is prepared. This relational expression (6) is prepared based on a straight line (calibration curve) connecting the origin of the graph in Fig. 9 and the point indicating the second test tempered glass 14 broken by the smallest fracture bending stress σ _min . This relational expression (6) is formed as a linear function of the expected drop height H _E and the expected fracture bending stress σ _E.
σ _E = eH _E (6)
Here, the coefficient e is a positive number.

The coefficient e in the relational expression (6) is the ratio σ _min /H _EX of the minimum fracture bending stress σ _min to the expected drop height H _EX corresponding to this minimum fracture bending stress σ _min (e=σ _min /H _EX ).

The second estimation formula is composed of the above relational expressions (5) and (6). Based on the above second estimation formulas (5) and (6), the second expected drop height H _E2 , which is the basis for estimating the second failure mode, is calculated and recorded. The second expected drop height H _E2 is the solution of the second estimation formulas (simultaneous equations) (5) and (6), as shown in the following formula (7).
H _E2 =σ _C /(d+e) ... (7)

As shown in FIG. 10, in the drop strength measurement process S3, the measurement structure 20 is dropped to break the measurement tempered glass 21. The measurement tempered glass 21 has the same structure as the tempered glass 1 shown in FIG. 1. The dimensions of the measurement tempered glass 21, the depth DOL of the compressive stress layer CSL, and other conditions are the same as those of the first test tempered glass 3 and the second test tempered glass 14. In other words, in this specification, the measurement tempered glass, the first test tempered glass, and the second test tempered glass are distinguished for the sake of convenience, and the composition, thickness, and conditions related to the compressive stress layer of each tempered glass are the same.

The measurement structure 20, like the test structure 2 in the first preparation step S1, includes a second support 22 that supports the measurement tempered glass 21. The measurement tempered glass 21 is fixed to the second support 22 via an adhesive layer 23. The second support 22 is formed into a plate shape, for example, from polycarbonate or other resin or metal.

In the drop strength measurement process S3, the measurement structure 20 is dropped and struck against sandpaper as the fourth scratching member 25 placed on the base plate 24. The fourth scratching member 25 used in the drop strength measurement process S3 has the same grain size as the first scratching member 7 and the second scratching member 8 used in the first preparation process S1.

In the drop strength measurement step S3, the plurality of test structures 20 are dropped to measure the drop height _H4 (m) at which each test tempered glass 21 is broken as the drop strength. In the drop strength measurement step S3, the fracture energy E (J) of each broken test tempered glass 21 is calculated based on the drop height _H4 etc. (E= _mgH4 ).

In the failure mode estimation process S4, a first expected drop height H _E1 of each of the test tempered glass sheets 21 is calculated and recorded using the calculated fracture energy E and the above-mentioned first estimation formula (2).

In the failure mode estimation step S4, the first expected drop height H _E1 is compared with the second expected drop height H _E2 calculated in the second preparation step S2 (a drop height comparison step). In the drop height comparison step, if the first expected drop height H _E1 is smaller than the second expected drop height H _E2 (H _E1 <H _E2 ), it is estimated that the failure mode of the test tempered glass 21 is the first failure mode. On the other hand, if the second expected drop height H _E2 is smaller than the first expected drop height H _E1 ( _{H E2 < H E1 )} , it is estimated that the failure mode of the test tempered glass 21 is the second failure mode.

The various processes in steps S1 to S4 above, such as formula creation, graphing, and numerical calculation, may be performed, for example, by a calculation processing device (computer) or by the person making the measurement.

According to the strength measurement method of this embodiment described above, when measuring the strength of the test tempered glass 21, it is possible to estimate whether the fracture of the test tempered glass 21 is caused by a flaw DW deeper than the depth DOL of the compressive stress layer CSL (first fracture mode) or by a flaw SW shallower than the depth DOL of the compressive stress layer CSL (second fracture mode).

The present invention is not limited to the configuration of the above embodiment, nor is it limited to the above-mentioned effects. Various modifications of the present invention are possible without departing from the gist of the present invention.

In the above embodiment, a resin plate or metal plate is used as a pseudo-housing for the first support 4 supporting the first test tempered glass 3 in the test structure 2, but this is not limiting, and the main body of an electronic device such as a smartphone or tablet may be used as the first support. In this case, the first test tempered glass 3 may be laminated and attached to the surface of an electronic device that already has tempered glass, or the first test tempered glass 3 may be attached as part of an electronic device that does not have tempered glass.

In the above embodiment, sandpaper is used as an example of the scratching member, but the present invention is not limited to this configuration. In addition to sandpaper, the scratching member may be a base material coated with an abrasive, an abrasive cloth, a diamond indenter, or other members.

In the above embodiment, the strength measurement is performed using the first pressing member 12 and the second pressing member 18, but if the desired strength data can be obtained, the strength measurement method may be performed without using these pressing members.

In the above embodiment, the strength measurement is performed using the first buffer member 11 and the second buffer member 17, but if the desired strength data can be obtained, the strength measurement method may be performed without using these buffer members.

In the above embodiment, the scratching process is performed using the second impact body 16 (metal sphere) and the third scratching member 15 (sandpaper), but other scratching methods may be used as long as the desired scratching is possible. For example, the scratching may be performed by pressing or scratching the surface of the second test tempered glass 14 with a sharp tip such as an indenter.

The damage process may also be performed by a test device (damage device) shown in Figures 11 and 12. The test device 26 includes a hammer as the second impact body 16. The hammer includes an arm portion 27 and a head portion 28. The arm portion 27 is an elongated member having a constant cross-sectional shape in the extension direction. Specifically, the arm portion 27 is an aluminum rod-shaped member or plate-shaped member having a predetermined length, but the material and shape of the arm portion 27 are not limited to this example. One end (upper end) of the arm portion 27 is supported by a support shaft 29. As a result, the arm portion 27 is configured to be rotatable around the support shaft 29.

The head portion 28 is provided on the side portion at the other end (lower end) of the arm portion 27. The head portion 28 is made of a metal such as a stainless steel alloy, but is not limited to this and may be made of resin, stone, etc. The head portion 28 has a collision surface 28a that collides with the second test tempered glass 14 via the third scratching member 15. The collision surface 28a is configured as a flat surface, but is not limited to this configuration and may be configured as a curved surface such as a spherical surface.

The second test tempered glass 14 is supported on a base plate 13 so that the first main surface MS1 is aligned vertically, in other words, facing horizontally. The base plate 13 may be a metal base plate, a stone base plate, or the like, but is not limited to these and may be made of a glass plate. The base plate 13 is configured to be position-changeable, and the angle of the first main surface MS1 of the second test tempered glass 14 can be changed. A third scratching member 15 (sandpaper) is fixed to the first main surface MS1 of the second test tempered glass 14.

In the scratching process, the test device 26 places the head 28 of the second impactor 16 at the third test drop height H ₃ , and then rotates the arm 27 toward the second test tempered glass 14 by the action of gravity, thereby causing the collision surface 28a of the head 28 to collide with the third scratching member 15 and the second test tempered glass 14. As a result, a scratch SW shallower than the depth DOL of the compressive stress layer CSL is formed on the first main surface MS1 of the second test tempered glass 14. Not limited to this, the second buffer member 17 and the second pressing member 18 may be overlapped on the third scratching member 15 as in the above embodiment. In this case, the second pressing member 18 may be fixed to the base plate 13 by a fixing member such as a bolt or a clamp.

1 Tempered glass 2 Test structure 3 First test tempered glass 4 First support 8 Second damage member 9 First impact body 11 First cushioning member 12 First holding member 14 Second test tempered glass 15 Third damage member 16 Second impact body 17 Second cushioning member 18 Second holding member 19 Four-point bending test machine 20 Measurement structure 21 Test tempered glass CSL Compressive stress layer DW Scratch deeper than the depth of the compressive stress layer E ₁ Breaking energy E ₂ Damage energy σ ₁ Breaking bending stress H ₁ First test drop height H ₄ Drop height of test tempered glass H _E1 First predicted drop height H _E2 Second predicted drop height S1 First preparation process S2 Second preparation process S3 Drop strength measurement process S4 Fracture mode estimation process SW Scratch shallower than the depth of the compressive stress layer

Claims (10)

A method for measuring the strength of tempered glass having a compressive stress layer, comprising the steps of:
a drop strength measurement step of dropping a test structure including the tempered glass, breaking the tempered glass, measuring a drop height as a drop strength , and calculating a fracture energy of the broken tempered glass based on the measured drop height ;
a failure mode estimation step of estimating whether the breakage of the tempered glass belongs to a first failure mode or a second failure mode based on the measured drop height;
A first preparation step of creating a first estimation formula for calculating a first expected drop height that estimates that the breakage of the tempered glass belongs to the first breakage mode;
A second preparation process includes creating a second estimation formula for calculating a second expected drop height that estimates that breakage of the tempered glass belongs to the second breakage mode,
The first fracture mode is a fracture mode caused by a scratch formed in the strengthened glass that is deeper than a depth of the compressive stress layer,
The second fracture mode is a fracture mode caused by a scratch formed in the strengthened glass that is shallower than a depth of the compressive stress layer,
The first preparation step includes:
a drop and breakage step of dropping a test structure including a first test tempered glass having a first compressive stress layer, and breaking the first test tempered glass by forming a scratch in the first test tempered glass that is deeper than a depth of the first compressive stress layer;
a collision and destruction step of colliding a first impactor with the first test tempered glass that has not been subjected to the drop and destruction step, and destroying the first test tempered glass by forming a scratch deeper than the first compressive stress layer in the first test tempered glass,
In the first preparation step, the first estimation formula is created based on a linear function of a test drop height of the test structure measured in the drop failure step and a fracture energy when the first test tempered glass is broken in the impact failure step,
The second preparation step includes:
A scratching step of forming a scratch shallower than a depth of the second compressive stress layer in a second test tempered glass having a second compressive stress layer;
A bending and breaking process of applying a bending stress to the second test tempered glass after the scratching process to break the second test tempered glass,
In the second preparation step, the second estimation formula is created based on a linear function of the damage energy imparted to the second test tempered glass by the damage step and the fracture bending stress imparted to the second test tempered glass by the bending fracture step, and the second expected drop height is calculated by the second estimation formula;
The failure mode estimation process includes a drop height comparison process of calculating the first expected drop height using the fracture energy calculated in the drop strength measurement process and the first estimation formula created in the first preparation process, and comparing the first expected drop height with the second expected drop height;
The method for measuring the strength of tempered glass, characterized in that, in the fracture mode estimation process, when the first predicted drop height is smaller than the second predicted drop height, it is estimated that the first fracture mode is caused by a scratch formed in the tempered glass that is deeper than a depth of the compressive stress layer, and when the second predicted drop height is smaller than the first predicted drop height, it is estimated that the second fracture mode is caused by a scratch formed in the tempered glass that is shallower than a depth of the compressive stress layer. the linear function related to the second estimation equation is configured by a simultaneous equation of a first relational equation and a second relational equation,
The first relational expression is an expression that shows a relationship between a plurality of the predicted drop heights and a plurality of the fracture bending stresses, the plurality of the fracture energies being measured by the fracture process for a plurality of the second test tempered glasses, the plurality of the second test tempered glasses being measured by the bending fracture process, and the plurality of the measured fracture energies being converted into predicted drop heights,
2. The method for measuring strength of tempered glass according to claim 1, wherein the second relational equation is created based on a straight line connecting an origin and a point representing the second test tempered glass broken by the smallest fracture bending stress when a relationship between the plurality of predicted drop heights and the plurality of fracture bending stresses is plotted on a graph . 3. The method for measuring the strength of tempered glass according to claim 1, wherein in the collision destruction step, a scratching member for forming the scratch deeper than the first compressive stress layer of the first test tempered glass is placed on the first test tempered glass, and the first collision body is collided with the first test tempered glass in a state where the scratching member is placed on the first test tempered glass. 4. The method for measuring the strength of tempered glass according to claim 3, wherein in the scratching step, a scratching member for forming the scratch shallower than the second compressive stress layer of the second test tempered glass is placed on the second test tempered glass, and a second impact body is collided with the second test tempered glass in a state where the scratching member is placed on the second test tempered glass. The method for measuring a strength of tempered glass according to claim 1 , wherein in the bending fracture step, the bending stress is applied to the second test tempered glass by a four -point bending tester. 5. The method for measuring strength of tempered glass according to claim 3, wherein in the collision and destruction step, the damaged member superimposed on the first test tempered glass is pressed by a first pressing member surrounding a collision site of the first collision body against the first test tempered glass. 5. The method for measuring strength of tempered glass according to claim 4, wherein in the scratching step, the scratching member superimposed on the second test tempered glass is pressed by a second pressing member surrounding a collision site of the second collision body against the second test tempered glass. The method for measuring strength of tempered glass according to claim 1 , wherein in the collision and destruction step, an impact from the first collision body is applied to the first test tempered glass via a first buffer member. The method for measuring strength of tempered glass according to claim 4 or 7 , wherein in the damaging step, the impact from the second collision body is applied to the second test tempered glass via a second buffer member. 10. The method of claim 1 , wherein the test structure comprises a support to which the first test tempered glass is fixed.

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