JP2012132840A - Strength evaluation method for layer structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strength evaluation method for a layer structure capable of easily and accurately evaluating interlayer strength in a layer structure having a curvature.SOLUTION: This strength evaluation method for a layer structure measures interlayer strength of a layer structure having a curvature. In this method: a test piece 12 having the curvature is cut out from the layer structure; the test piece is supported at support points 12a and 12b in between which the part having the curvature is held; and an interlayer stress of the test piece 12 is measured by applying a load (arrows A, B) between the two support points 12a, 12b of the test piece 12, acting in such a direction that makes the curvature smaller.

Description

  The present invention relates to a method for evaluating the strength of a laminated structure having a cylindrical shape or a spherical shell shape.

  In general, a laminated structure has a configuration in which a plurality of thin plate members are laminated and bonded between them with an adhesive member. However, foreign matter or air is mixed between the thin plate members, or an adhesive member pool or the like between the thin plate members. If there is any missing adhesive member, the degree of adhesion between the layers will be reduced, reducing the strength of the structure. Therefore, when evaluating the strength of the laminated structure, in addition to measuring the strength of the entire structure such as tensile stress and bending stress, measurement of interlayer stress such as interlayer tensile stress and interlayer shear stress is performed.

For example, Patent Document 1 (US Pat. No. 6,314,819) discloses a method for measuring the adhesive strength of a resin material. This method is configured to measure interlayer shear stress by applying two different loads between layers.
Patent Document 2 (Japanese Patent No. 2733134) discloses a method for measuring the shear bond strength of a laminate. In this method, the laminate is wound around a rotating roll to give a bending deformation to generate a shear stress, and the shear bond strength is measured.

  On the other hand, a structure having a curvature has been widely used as a laminated structure. For example, a laminated structure having a cylindrical shape or a spherical shell shape is formed by a filament winding (FW) molding method. The FW molding method is a molding method in which a composite tape impregnated with a resin is wound while applying tension to a rotating mandrel, and is demolded after the resin is cured.

However, in the FW molding method, depending on the tension of the composite material tape and the rotational speed of the mold material, undulation of the tape or a gap between the upper and lower tapes may occur. As described above, the gap causes generation of a resin pool between the layers, a resin dropout, a void, or the like. These are manufacturing defects and cause a reduction in product strength. Further, regarding the gap, even if it does not become a manufacturing defect, it can be a factor that lowers the degree of adhesion between the layers, and in particular, may affect the interlayer strength.
Therefore, evaluation of interlayer strength has been performed also in FW molded products. In this strength evaluation, a flat specimen was prepared, and the interlayer stress of the FW molded product was estimated by measuring the interlayer stress of the specimen.

US Pat. No. 6,314,819 Japanese Patent No. 2733134

However, it is considered that there is a difference in strength between the flat laminated structure and the laminated structure having a curvature like the FW molded product due to the difference in adhesion in the interlayer direction. In particular, a laminated structure with a curvature has a greater effect on the interlayer strength when a load is applied than a flat laminated structure, but the in-plane rigidity is reduced when an interlaminar fracture occurs. The impact on the must also be considered.
In addition, in a laminated structure having a curvature, a flat specimen is prepared, and the interlayer strength is measured using, for example, a method such as Patent Document 1 or Patent Document 2, and an allowable value is set for this measurement result. Although it is set and used as the strength evaluation result of the actual structural member, it is difficult to set the allowable value, and anxiety remains in the evaluation accuracy.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a strength evaluation method for a multilayer structure that can easily and accurately evaluate interlayer strength in a multilayer structure having a curvature.

  In order to solve the above-described problems, a strength evaluation method for a multilayer structure according to the present invention is a strength evaluation method for a multilayer structure that measures the interlayer strength of a multilayer structure having a curvature. A specimen including the curvature is cut out, the specimen is supported at two support points sandwiching a portion where the curvature exists, and the curvature decreases between the two support points of the specimen. It is characterized in that an interlayer load of the specimen is measured by applying a load acting in the direction.

According to the present invention, the specimen including the curvature is cut out from the laminated structure that is the object of strength evaluation, and the interlaminar stress is directly measured. Therefore, compared to the case of newly producing and measuring a flat specimen. Thus, it is possible to perform strength evaluation easily and with high accuracy.
In addition, since the load is applied between the two support points of the specimen in a direction in which the curvature decreases, it is less affected by stresses other than the interlayer stress and generates the interlayer stress most effectively. Thus, the interlayer strength can be reliably evaluated.

  Further, the laminated structure has a certain curvature, and the two support points of the specimen are each supported by a rotatable support member, and both the support points are supported by the support member between the two support points. It is preferable to measure the interlaminar tensile stress or interlaminar shear stress of the specimen by applying a tensile load acting on a straight line passing through the support point.

In this configuration, since there is a curvature between two support points of the specimen, an interlayer stress can be generated by applying a tensile load between the two support points. Therefore, it is possible to easily measure the interlaminar tensile stress or interlaminar shear simply by applying a tensile load between the two support points. Further, when a tensile load is applied at this time, the bent specimen is extended and the support point is rotated. However, in this configuration, the two support points are supported by the rotatable support members, respectively. Even if it rotates, a tensile load can be applied on a straight line passing through both support points.
In this configuration, the laminated structure having a certain curvature is a structure having a cylindrical shape or a spherical shell shape, for example.

Furthermore, it is preferable that the angle range between the two support points with respect to the center of curvature of the specimen is 90 ° or more and 180 ° or less.
By setting the angle range between the two support points as described above, an interlayer stress can be effectively generated between the two support points. Here, when the angle range between the two support points is less than 90 °, the tensile stress of the specimen itself is more dominant than the interlayer stress, and it is difficult to obtain an effective measurement result regarding the interlayer stress. On the other hand, if the angle range between the two support points exceeds 180 °, other stresses such as bending stresses are generated in addition to the interlayer stress, and it is difficult to obtain an effective measurement result regarding the interlayer stress.

Further, the laminated structure has a certain curvature, and the specimen is placed in a convex state on two support members that are spaced apart in the horizontal direction, and the two support members It is preferable to measure the interlaminar tensile stress of the specimen by applying a bending load vertically downward from the two operating points between the two supporting points supported by the above.
This configuration uses a four-point bending method. The specimen is placed on two support members in a convex state, and the load in the vertical direction is lowered by two action points between the support points of the specimen. Is added. Thus, an interlayer stress can be generated by applying a bending load between two support points on the support member, and the interlayer tensile stress can be easily measured.
The laminated structure having a certain curvature is, for example, a cylindrical or spherical shell structure.

The laminated structure is preferably a cylindrical or spherical shell-shaped structure formed by filament winding using a composite material in which reinforcing fibers are dispersed in a matrix resin.
Thereby, compared with the conventional method which produced the flat specimen and evaluated strength, it is possible to perform strength evaluation easily and with high precision.

Furthermore, it is preferable that the specimen is manufactured by cutting out a portion including the artificial defect from the laminated structure in which the artificial defect is inserted between layers.
In this way, by inserting an artificial defect between the layers at the time of stacking the laminated structure and performing a strength evaluation on the specimen including the artificial defect, it is likely that defects will occur during the production of the laminated structure. It is possible to evaluate the soundness of the laminated structure even when the strength is reduced due to the above, and it is also possible to evaluate and confirm allowable defects in the structure.
For example, a Teflon film (Teflon: registered trademark) is used as the artificial defect.

As described above, according to the present invention, the specimen including the curvature is cut out from the laminated structure that is the object of strength evaluation, and the interlayer stress is directly measured. Therefore, a new flat specimen is prepared. Compared to the case of measurement, it is possible to perform strength evaluation easily and with high accuracy.
In addition, since the load is applied between the two support points of the specimen in a direction in which the curvature decreases, it is less affected by stresses other than the interlayer stress and generates the interlayer stress most effectively. Thus, the interlayer strength can be reliably evaluated.

It is a figure which shows an example of the measuring object in embodiment of this invention, (A) is a perspective view which shows a cylindrical laminated structure, (B) is a perspective view which shows a test body. It is a figure which shows another example of the measuring object in embodiment of this invention, (A) is a perspective view which shows a spherical shell-shaped laminated structure, (B) is a perspective view which shows a test body. It is a figure explaining the strength evaluation method concerning a 1st embodiment of the present invention. It is a figure explaining the interlayer stress in 1st Embodiment of this invention, (A) is a figure which shows interlayer tensile stress, (B) is a figure which shows interlayer shear stress. It is a graph which shows an intensity | strength evaluation test result, (A) is a graph which shows the interlayer tensile stress in a plate | board thickness direction, (B) is a graph which shows the interlayer tensile stress in the circumferential direction. It is a graph which shows an intensity | strength evaluation test result, (A) is a graph which shows the interlayer shear stress with respect to a sheet thickness direction, (B) is a graph which shows the interlayer shear stress with respect to the circumferential direction. It is a figure explaining each dimension of the test body in a strength evaluation test. It is a figure which shows the modification of the intensity | strength evaluation method which concerns on 1st Embodiment of this invention. It is a figure explaining the strength evaluation method concerning a 2nd embodiment of the present invention. It is a figure explaining the interlayer tensile stress in 2nd Embodiment of this invention. It is a graph which shows an intensity | strength evaluation test result, (A) is a graph which shows the interlayer tensile stress in a plate | board thickness direction, (B) is a graph which shows the interlayer tensile stress in the circumferential direction.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.
The measurement object in the embodiment of the present invention is a laminated structure having a curvature. For example, FRP (fiber reinforced plastic) is used as the laminated structure. The object to be measured may or may not have a constant curvature.

In the strength evaluation method for a laminated structure according to an embodiment of the present invention, first, a specimen including a curvature is cut out from the laminated structure.
FIG. 1 is a diagram showing an example of a measurement object in an embodiment of the present invention, (A) is a perspective view showing a cylindrical laminated structure 10, and (B) is a perspective view showing specimens 11 and 12. is there. A part of the cylindrical laminated structure 10 as shown in FIG. 1 (A) is cut out in a ring shape, and as shown in FIG. 1 (B), an annular specimen 11 may be used. Furthermore, it is good also as a circular-arc shaped specimen 12 cut out in circular arc shape.
FIG. 2 is a view showing another example of the measurement target in the embodiment of the present invention, (A) is a perspective view showing a spherical shell-shaped laminated structure 20, and (B) shows a specimen 21. It is a perspective view. A part may be cut out from the spherical shell-shaped laminated structure 20 as shown in FIG. 2 (A) to form an arc-shaped specimen 21 as shown in FIG. 2 (B).

Next, the specimen is supported by the support member at two support points sandwiching the portion where the curvature exists. And the load which acts in the direction where a curvature becomes small is added between the two support points of a specimen, and the interlayer stress of a specimen is measured. Here, interlayer stress includes interlayer tensile stress or interlayer shear stress.
Specifically, a load acting in a direction in which the curvature decreases between the two support points of the specimen is added, and the load when delamination occurs due to interlayer stress is measured. Then, using this load, the interlayer stress is obtained based on the relationship between the load and the stress obtained in advance. The relationship between the load and the stress may be obtained, for example, by a theoretical formula disclosed in Patent Document 1 or the like, or may be obtained by simulation.

According to the present embodiment, the specimen including the curvature is cut out from the laminated structure that is the object of strength evaluation, and the interlayer stress is directly measured. Therefore, when a flat specimen is newly measured and measured. Compared to this, it is possible to easily and accurately perform strength evaluation.
In addition, since the load is applied between the two support points of the specimen in a direction in which the curvature decreases, it is less affected by stresses other than the interlayer stress and generates the interlayer stress most effectively. Thus, the interlayer strength can be reliably evaluated.

In the present embodiment, the specimen may be manufactured by cutting out a part including the artificial defect from the laminated structure in which the artificial defect is inserted between the layers.
In this way, by inserting an artificial defect between the layers at the time of stacking the laminated structure and performing a strength evaluation on the specimen including the artificial defect, it is likely that defects will occur during the production of the laminated structure. It is possible to evaluate the soundness of the laminated structure even when the strength is reduced due to the above, and it is also possible to evaluate and confirm allowable defects in the structure. For example, a Teflon film (Teflon: registered trademark) is used as the artificial defect.
Below, the specific aspect of this embodiment is demonstrated.

(First embodiment)
FIG. 3 is a diagram for explaining the strength evaluation method according to the first embodiment of the present invention.
The measurement object of the first embodiment is a laminated structure having a certain curvature, and the specimen shown in FIG. 1 or 2 is preferably used. Here, as an example, a description will be given using an arc-shaped specimen 12 shown in FIG. In this specimen 12, the angle between two support points with respect to the center of curvature is 180 °.

  In the strength evaluation method according to the first embodiment, support points 12a and 12b are set at both ends of the specimen 12 cut out from the laminated structure 10, and the support points 12a and 12b are supported by the support members 5 and 5, respectively. To do. Each of the support members 4 and 5 is configured to be rotatable. At this time, the support members 4 and 5 rotate around the rotation axes 4a and 5a perpendicular to the plane passing through the three points of the support points 12a and 12b of the specimen 12 and the central portion 12c between the support points. It is preferable. Although the support method by the support members 4 and 5 is not particularly limited, the support points 12a and 12b may be bonded and supported, or the support points 12a and 12b may be gripped.

  With the specimen 12 supported by the support members 4 and 5, a tensile load acting on the straight line L passing through the two support points is applied between the two support points 12a and 12b by the support members 4 and 5. Specifically, the support point 12a and the support point 12b may be pulled in the directions of arrows A and B by the support members 4 and 5, respectively, or the other support may be performed while holding either one of the support points 12a or 12b. The point 12b or 12a may be pulled in the arrow B direction or the arrow A direction.

  When a tensile load is applied, an interlayer tensile stress and an interlayer shear stress are generated in the specimen 12. As shown in FIG. 4, the interlaminar tensile stress is mainly generated at the center between the two support points 12a and 12b, and the stress is generated in the direction of separating the layers as indicated by arrows in the figure. As shown in FIG. 5, the interlaminar shear stress is mainly generated in the vicinity of both support points 12a and 12b, and the stress is generated in the direction in which the interlamellar is shifted as indicated by arrows in the figure. Delamination occurs when either one of the stresses exceeds the interlaminar strength of the specimen. Based on the position or state where the delamination occurs, it is determined whether it is an interlaminar tensile stress or an interlaminar shear stress, and the load at that time is measured.

  Then, using the measured load, the interlayer stress is obtained based on the relationship between the load and the stress obtained in advance. At this time, the relationship between the load and the stress is selected according to the type of interlayer stress (interlayer tensile stress or interlayer shear stress), and the interlayer stress is obtained.

  Here, FIG. 5 and FIG. 6 show the strength evaluation test results. FIG. 5 is a graph showing the strength evaluation test results, (A) is a graph showing the interlayer tensile stress in the sheet thickness direction, and (B) is a graph showing the interlayer tensile stress in the circumferential direction. FIG. 6 is a graph showing the strength evaluation test results, (A) is a graph showing the interlaminar shear stress in the thickness direction, and (B) is a graph showing the interlaminar shear stress in the circumferential direction. In addition, FIG. 7 is a figure explaining each dimension of the test body in a strength evaluation test. Here, the radius of curvature of the outer peripheral surface of the specimen 12 is r0, the radius of curvature of the inner peripheral surface is ri, the radius of curvature at an arbitrary point in the plate thickness is r, and the plate thickness is t.

  As shown in FIGS. 5A and 5B, the interlayer tensile stress is highest in the central portion in the plate thickness direction and highest in the circumferential direction. As shown in FIGS. 6A and 6B, the interlaminar shear stress is highest at the center in the thickness direction and highest at the end in the circumferential direction. Therefore, when the type of interlayer stress is specified from the delamination position, if delamination occurs at the center of the specimen 12, it is determined as interlayer tensile stress, and delamination occurs at the end of the specimen 12. In such a case, it is preferable to determine the interlaminar shear stress.

  In the first embodiment, since a curvature exists between two support points of the specimen, an interlayer stress can be generated by applying a tensile load between the two support points. Therefore, it is possible to easily measure the interlaminar tensile stress or interlaminar shear simply by applying a tensile load between the two support points. Further, at this time, when a tensile load is applied, the bent specimen extends and the support point rotates, but in the first embodiment, the two support points are supported by the rotatable support members. Even if the point rotates, a tensile load can be applied on a straight line passing through both support points.

In the first embodiment, the angle range between the two support points with respect to the center of curvature of the specimen is preferably 90 ° or more and 180 ° or less.
By setting the angle range between the two support points as described above, an interlayer stress can be effectively generated between the two support points. Here, when the angle range between the two support points is less than 90 °, the tensile stress of the specimen itself is more dominant than the interlayer stress, and it is difficult to obtain an effective measurement result regarding the interlayer stress. On the other hand, if the angle range between the two support points exceeds 180 °, other stresses such as bending stresses are generated in addition to the interlayer stress, and it is difficult to obtain an effective measurement result regarding the interlayer stress.

FIG. 8 is a diagram showing a modification of the strength evaluation method according to the first embodiment of the present invention.
In this method, the annular specimen 11 shown in FIG. 1B is used. The supporting members 4 ′ and 5 ′ are brought into contact with the inner peripheral surface of the specimen 11, and a tensile load is applied by pulling in the directions of arrows A and B in the drawing.
In the annular specimen 11, an interlayer tensile load can be easily applied to the specimen 11 by using the above method.

(Second Embodiment)
FIG. 9 is a diagram for explaining a strength evaluation method according to the second embodiment of the present invention.
The measurement object of the second embodiment is a laminated structure having a certain curvature, as in the first embodiment.

In the strength evaluation method according to the second embodiment, the specimen 12 is placed in a convex state on the two support members 6 and 7 that are spaced apart in the horizontal direction. Here, the portions supported by the two support members 6 and 7 of the specimen 12 become the two support points 12 c and 12 d of the specimen 12. At this time, the specimen 12 may be fixed to the support members 6 and 7 so that the support points 12c and 12d of the specimen 12 are rotatable. Thereby, the position shift of the specimen 12 can be prevented.
Between the two support points 12c and 12d supported by the two support members 6 and 7, a bending load is applied vertically downward from the two action points 8 and 9 as indicated by an arrow C in the figure. The load applied from the two action points 8 and 9 is the same.

  When a bending load is applied, an interlayer tensile stress is generated in the specimen 12. As shown in FIG. 10, the interlayer tensile stress is mainly generated at the center between the two support points 12c and 12d, and the stress is generated in the direction of separating the layers as indicated by arrows in the figure. Delamination occurs when the interlayer tensile stress exceeds the interlayer strength. The load at this time is measured, and using this load, the interlaminar stress is obtained based on the relationship between the load and the stress obtained in advance.

Here, the strength evaluation test results are shown in FIG. FIG. 11 is a graph showing the strength evaluation test results, (A) is a graph showing the interlayer tensile stress in the sheet thickness direction, and (B) is a graph showing the interlayer tensile stress in the circumferential direction. The dimensions of the specimen in the strength evaluation test are as shown in FIG.
As shown in FIGS. 11A and 11B, the interlayer tensile stress is highest in the central portion in the plate thickness direction and constant in the circumferential direction. Therefore, if delamination occurs at any position in the circumferential direction, it is determined as an interlayer tensile stress.

  In the second embodiment, a four-point bending method is used, and a specimen is placed on two support members in a state of being convex upward, and is perpendicular to the support points of the specimen by two action points. A downward load is applied. Thus, an interlayer stress can be generated by applying a bending load between two support points on the support member, and the interlayer tensile stress can be easily measured.

In the first embodiment or the second embodiment, the laminated structure is a cylindrical or spherical shell-shaped structure formed by filament winding using a composite material in which reinforcing fibers are dispersed in a matrix resin. It is preferable that it is a body.
Thereby, compared with the conventional method which produced the flat specimen and evaluated strength, it is possible to perform strength evaluation easily and with high precision.

4-7 Support members 8, 9 Action point 10 Laminated structure (cylindrical shape)
11, 12 Specimens 12a to 12d Support point 20 Laminated structure (spherical shell shape)
21 Specimen

Claims (6)

A strength evaluation method for a laminated structure for measuring an interlayer strength of a laminated structure having a curvature,
Cut out the specimen containing the curvature from the laminated structure,
The specimen is supported at two supporting points sandwiching a portion where the curvature exists, and a load acting in a direction in which the curvature decreases is applied between the two supporting points of the specimen. A method for evaluating the strength of a laminated structure, comprising measuring an interlaminar stress of a specimen. The laminated structure has a certain curvature,
The two support points of the specimen are each supported by a rotatable support member, and a tensile load acting on a straight line passing through both support points is applied between the two support points by the support member, The method for evaluating the strength of a laminated structure according to claim 1, wherein an interlayer tensile stress or an interlayer shear stress of the specimen is measured.   The method for evaluating the strength of a laminated structure according to claim 2, wherein an angle range between the two support points with respect to the center of curvature of the specimen is 90 ° or more and 180 ° or less. The laminated structure has a certain curvature,
The test specimen is placed in a convex state on two support members that are spaced apart in the horizontal direction, and has two actions between the two support points supported by the two support members. 2. The method for evaluating the strength of a laminated structure according to claim 1, wherein a bending load is applied vertically downward from the point, and the interlayer tensile stress of the specimen is measured.   The laminated structure is a cylindrical or spherical shell-shaped structure formed by filament winding using a composite material in which reinforcing fibers are dispersed in a matrix resin. The strength evaluation method for a laminated structure according to one item.   The laminate according to any one of claims 1 to 5, wherein the specimen is manufactured by cutting out a portion including the artificial defect from the laminated structure in which the artificial defect is inserted between layers. Structural strength evaluation method.

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