JP2010002289A - Evaluation testing method of peeling in multilayer structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a testing method for reproducing a mode I load and a mode II load in any combination relative to a crack by a uniaxial loading. <P>SOLUTION: In a test piece 1 of foam core sandwich panel having a crack 5 generated, an auxiliary plate 7 is adhered to the whole area of the test piece 1 outside an upside crack piece 6a having a smaller bending rigidity on the upper side of the crack 5 so that the bending rigidity gets substantially equal to each other, in upper and lower portions of the crack 5 to obtain a reinforced crack piece 6A. The reinforced crack piece is mounted on struts 32, 33. A downside crack piece 6b on the lower side of the crack 5 is rotatably fixed to the strut 32, while the reinforced crack piece 6A on the upper side of the crack 5 is rotatably fixed to the strut 33. In this condition, a load is applied to a loading point 39 of a lever section 37 using a chip of a leg section 36 of a tool 34 as a fulcrum 38. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a peel evaluation test method for a laminated structure, and more specifically, a peel evaluation test for a laminated structure having a structure in which laminated materials are laminated in the vertical direction and having an interlaminar crack in an asymmetric position vertically. Regarding the method.

  The delamination in the mixed mode in the laminated structure such as the FRP laminated plate in which the interlayer crack is generated is evaluated by the opening load and the shear load. That is, as shown in FIGS. 12A to 12C, an opening load (hereinafter referred to as “mode I load”) shown in FIG. And a shear load shown in FIG. 12B (hereinafter sometimes referred to as “mode II load”).

  Further, as shown in FIG. 12 (c), an MMB (Mixed Mode Bending) test method is known as a test method for applying a mode I load and a mode II load in an arbitrary combination by a uniaxial load (for example, as shown in FIG. 12C). Non-Patent Document 1). In the MMB test method, as shown in FIG. 13, a test piece 30 made of an FRP laminated plate or the like in which a crack 31 is formed in advance is placed on support columns 32 and 33, and the lower portion 30 b of the crack 31 is a support column. The leg portion 35 of the jig 34 is fixed to the upper portion 30a. A load is applied to the load point 39 of the lever portion 37 with the tip of the leg portion 36 as a fulcrum 38. The force acting on the test piece 30 in this case can be expressed as shown in FIG. In the MMB test method, a mode I load and a mode II load can be applied in any combination by a uniaxial load, and the ratio between the mode I load and the mode II load is the distance between the fulcrum 38 and the load point 39. It can be changed by changing c.

  In the MMB test method, a load of the same magnitude is given as the opening load in the opposite direction of the crack, and a load of the same magnitude is given as the shear load in the same direction of the crack. Therefore, in order to create only mode I from the opening load and only mode II from the shear load, the position of the crack 31 in the test piece 30 is the center in the thickness direction of the test piece. Must be in the department. In other words, the MMB test is established because the rigidity of the lower portion 30b and the upper portion 30a of the crack 31 is equal. This makes it possible to create a combination of mode I and mode II at an arbitrary ratio by simply changing the distance C from the fulcrum 38 to the load point 39. However, if the position of the crack 31 is not at the center in the thickness direction of the specimen, not only mode I but also mode II is generated from the opening load, and not only mode II but also mode I is generated from the shear load. Thus, the range in which the combination ratio can be changed is limited.

On the other hand, a laminated structure such as a foam core sandwich panel has a structure in which the upper and lower sides of a resin foam core are sandwiched between face plates, and a crack generated between the foam core and the face plate is As shown in FIG. 3, it is not at the center of the laminated structure, and therefore, the lower portion 30b and the upper portion 30a of the crack 31 have extremely different rigidity. Therefore, even if the MMB test method shown in Fig. 13 established for FRP laminates is used for specimens of laminate structures that crack at asymmetric positions, any combination of mode I load and mode II load is reproduced. It is impossible to do.
Arai, et al., “Evaluation of Interlaminar Fracture Toughness of CFRP Cross-Laminated Plates by MMB Test”, Transactions of the Japan Society of Mechanical Engineers (A), October 2004, Vol. 70, No. 698, p. 1356-1363

  The present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to apply a mode I load and a mode II load to a single axis load instead of applying loads from a plurality of directions. Thus, it is to provide a test method capable of reproducing a mode I load and a mode II load in an arbitrary combination with respect to a crack.

  In the laminate structure peeling evaluation test method of the present invention, in a laminate structure in which planar laminates are laminated in the vertical direction, a test piece in which an interlayer crack is formed at an asymmetrical position in the vertical direction of the laminate structure is used. A test method for evaluating the peeling of a laminated structure, wherein the test piece is placed over the entire surface of the test piece on the outer side of the crack piece having the lower bending rigidity among the crack pieces located above and below the interlayer crack. The auxiliary plate is coupled, and a uniaxial load is applied to the test piece coupled with the auxiliary plate.

  As described above, in the present invention, among the crack pieces positioned above and below the crack formed on the test piece of the laminated structure, the crack piece having the lower bending rigidity is reinforced by the reinforcing plate. Thus, the bending rigidity can be made substantially equal, and in the conventional MMB test method, the mode I load and the mode II load can be reproduced in any combination.

In the above, among the crack pieces positioned above and below the interlaminar crack of the test piece, the bending rigidity of the crack piece having a small bending rigidity and the auxiliary plate combined is B ₁ , and the bending rigidity of the crack piece having a large bending rigidity is B ₁ . As B ₂
0.5 ≦ B ₁ / B ₂ ≦ 2
It is preferable to use the auxiliary plate.

  Thereby, in the said invention, the combined load of an opening load and a shear load generate | occur | produces with the said uniaxial load.

  The peeling evaluation test method according to the invention can be suitably used in the case where the laminated structure is a foamed core sandwich panel obtained by laminating a prepreg on the top and bottom of a foam, and applying pressure and heating.

  In the peel evaluation test method for a laminated structure according to the present invention, the reinforcing plate is coupled to the crack piece positioned above and below the crack formed on the test piece of the laminated structure, so that the bending plate has a smaller bending rigidity. It is possible to evaluate the laminated structure in which the bending rigidity is substantially equal between the upper and lower sides and a crack is generated at an asymmetric position in the laminating direction using the MMB test method.

  The present invention will be described below using a foam core sandwich panel as an example of a laminated structure. FIG. 1 is a cross-sectional view of a test piece 1 of a foam core sandwich panel. In this test piece 1, face plates 3b and 3a made of CFRP (carbon fiber reinforced plastic) are formed on both upper and lower surfaces of a foam core 2. The face plates 3b and 3a are formed by stacking a plurality of prepregs and heating and press-molding together with the foamed core 2, and the adhesive layer 4 is formed of a resin that has oozed out of the prepreg during pressurization. Further, a crack 5 is formed in the foamed core 2 by forming a Kapton film (made by Toray DuPont) made of polyimide between the face plate 3a and the foamed core 2 in advance. .

  In this specification, the face plate 3a and the adhesive layer 4 on the upper side of the crack 5 are collectively referred to as an upper crack piece 6a, and the face plate 3b, the adhesive layer 4 and the face plate 3b on the lower side of the crack 5 are collectively shown. It will be referred to as the lower crack piece 6b. When the bending rigidity of the upper crack piece 6a and the lower crack piece 6b is compared, the bending rigidity of the upper crack piece 6a is small. Therefore, as shown in FIG. The auxiliary plate 7 is bonded to the entire surface using, for example, an adhesive. Although the test piece 1 is not specifically limited, the aluminum plate was used in this embodiment. In the present specification, the portion where the auxiliary plate 7 is bonded to the upper crack piece 6a as described above is referred to as a reinforcing crack piece 6A.

In the present embodiment, the thickness of the auxiliary plate 7 has a bending stiffness B ₁ of the reinforcement-out lobes 6A, and bending rigidity B ₂ of the lower-out lobes 6b is of _{0.5 ≦ B 1 / B 2 ≦} 2 relationship It is decided to satisfy. FIG. 3 illustrates the relationship between the thickness of the auxiliary plate 7 and the value of B ₁ / B ₂ . In this example, it can be seen that a suitable thickness of the auxiliary plate 7 is 6.46 mm.

  If the bending rigidity of the reinforcing crack piece 6A and the lower crack piece 6b positioned above and below the crack 5 is made substantially equal as described above, the conventional MMB test method can be applied. FIG. 4 is a schematic diagram showing an MMB test method using the test piece 1 of the foam core sandwich panel to which the auxiliary plate 7 shown in FIG. 2 is bonded. As shown in the figure, the test piece 1 in which the crack 5 is formed in advance is placed on the pillars 32 and 33, and the fixing block 42 is attached to the lower crack piece 6b below the crack 5. The fixed block 42 is rotatably fixed to the support column 32 by a rotating shaft 43. A fixed block 45 is attached to the reinforcing crack piece 6 </ b> A on the upper side of the crack 5, and this fixed block 45 is rotatably fixed to the leg portion 35 of the jig 34 by a rotating shaft 46. Then, a load is applied to the load point 39 of the lever portion 37 with the tip of the leg portion 36 of the jig 34 as a fulcrum 38. Here, in FIG. 4, the distance between the center of the support column 32 and the center of the support column 33 is 2L, and the fulcrum 38 is located at a distance L from the center of the support column 32. The distance between the fulcrum 38 and the load point 39 is C. It is assumed that the crack 5 is formed from a position a distance a from the center of the support column 32 to the end surface 1 a of the test piece 1.

FIG. 5 shows the principle of the MMB test when the test piece 1 of FIG. 4 is used. As shown in the figure, in the mixed mode, P · (C + L) / L is applied to the load point 39, P · (C + L) / 2L is applied to the support 33, and the upper crack piece 6b (support 32) is directed upward. The upward load P · C / L is applied to the load P · (C−L) / 2L and the reinforcing crack piece 6A (leg portion 35). Such a load is expressed as the sum of a mode I load and a mode II load. Here, in the mode I load, as shown in FIG. 5, the lower crack piece 6b has a downward load P · (3C-L) / 4L, and the reinforcing crack piece 6A has an upward load P · (3C-L). / 4L will be added respectively. In mode II load, P · (C + L) / L is applied to the load point 39, P · (C + L) / 2L is applied to the support 33, and the upward load P · (is applied to the lower crack piece 6b and the reinforcing crack piece 6A. C + L) / 4L will be added respectively. Here, assuming that the energy release rates of the crack 5 in the mode I load and the mode II load are G _I and G _II , respectively, the mode ratio G _I / (G _I + G _II ) is expressed by Equation 1.

In order to confirm the effect of joining the auxiliary plate 7 to the test piece 1, numerical calculation is performed using the test piece 1 shown in FIG. 4 as a model to obtain the energy release rates G _I and G _II at the tip of the crack 5, The ratio of the combination of mode I load and mode II load was confirmed. Specifically, it was confirmed that the ratio of the combined load was changed by changing the distance C between the fulcrum 38 of the leg portion 36 and the load point 39 of the jig 34. The results are shown in FIG. As shown in the figure, it can be seen that in the peel evaluation test method of the present invention in which the auxiliary plate 7 is coupled, the ratio of the energy release rate can be arbitrarily set from 0 to 100%. On the other hand, when the auxiliary plate 7 is not coupled (conventional test method), it can be seen that the ratio of the energy release rate hardly changes. In addition, as shown in FIG. 7, it can be seen that the energy release rate can be set to an arbitrary ratio by the peeling evaluation test method of the present invention even when the length a of the crack 5 is changed. Furthermore, from the relationship between the thickness t of the metallic auxiliary plate 7 to be combined and the ratio of the combined load (see FIG. 8), the combination depends on the difference in the thickness t of the auxiliary plate 7, that is, the rigidity of the auxiliary plate 7 to be combined. It can be seen that the load ratio is affected. As shown in FIG. 8, when three types of auxiliary plates 7 having a thickness t are used, it can be seen that in this example, a plate thickness of 7 mm can change the combination ratio most greatly. From the results of FIGS. 6 to 8, according to the test method of the present invention, it was possible to confirm the usefulness of the test method of the present invention for creating a combined load ratio by uniaxial load.

  Hereinafter, peeling evaluation of the test piece of the foam core sandwich panel was actually performed using the test method of the present invention. The used foam core sandwich panel was produced using the materials shown in Table 1. FIG. 9 is a view showing a laminated structure of a foam core sandwich panel. Table 2 shows plain weave prepregs used for the layers P1 to P4 in FIG. The plain weave prepregs shown in Table 2 correspond to those listed in Table 1. Here, the orientation angle in Table 2 is an angle between the fiber direction and the specimen longitudinal direction.

  The size of the upper surface of the test piece used was 50 mm in width, 300 mm in length, and an aluminum plate having a thickness of 5 mm was bonded as an auxiliary plate 7 (FIG. 4), on which an aluminum fixing block 45 for load application was attached. Glued. An aluminum fixing block 42 for load application was bonded to the face plate 3b on the lower surface of the test piece 1. As shown in FIG. 10, the positions of the fixed blocks 42 and 45 were 24 mm from the tip of the Kapton film 48 at the center. Further, in all the test pieces, a pre-crack 51 of about 5 mm was made from the tip of the Kapton film 48 in a static opening mode before the test.

(1) Test apparatus The test apparatus used in the present Example is as follows.

Testing machine: Instron (5kN capacity) electric / hydraulic servo type fatigue testing machine
Instron 8501 type load cell: Instron load cell (5kN capacity)
Reading microscope: x50 magnification Measuring instrument: Kyowa EDX1500 (recording of load and displacement of the testing machine).

(2) Test procedure With the arrangement shown in FIG. 4, the test was performed at a constant load point displacement speed (1.0 mm / min). When the crack grew stably, the load unloading was repeated. The crack length was measured from both end faces of the test piece using a reading microscope at the time of load unloading (operation of JIS K 7086 3.4 DCB test).

(3) Test conditions The test conditions were such that the distance C between the fulcrum 38 and the load point 39 was 15 mm, 20 mm, and 40 mm.

(4) Fracture toughness value calculation method Fracture toughness value is proportional to the square of the ratio of the test load P to the load P _FEM used in the analysis, that is, proportional to (P / P _FEM ) ² Asked to do. .

(4) Test Results FIG. 11 shows the results of arranging the fracture toughness values with the vertical axis representing the mode I component and the horizontal axis representing the mode II component. From this result, it can be seen that the ratio of the mode I and the mode II in the mixed mode can be greatly changed from the present embodiment.

  The laminate structure peeling evaluation test method of the present invention can be used in the field of composite materials used in aircraft, vehicles, and the like.

It is sectional drawing showing the laminated structure of the foam core sandwich panel which has produced the crack. It is sectional drawing which shows a mode that the auxiliary | assistant board was couple | bonded over the whole surface of the test piece of the foam core sandwich panel of FIG. Is a diagram illustrating the relationship between the value of the thickness of the auxiliary plate and (bending rigidity B ₁ of the reinforcement-out lobe 6A) / (flexural rigidity B ₂ of the lower-out lobe 6b). It is a schematic diagram which shows the test method of MMB using the test piece of the foam core sandwich panel which adhere | attached the auxiliary | assistant board shown in FIG. The principle of the MMB test at the time of using the test piece of FIG. 4 is represented. Figure 4 performs a numerical calculation of the test piece 1 as a model shown in, the ratio of the combination of a mode I load and mode II load was calculated from the energy release rate G _I and G _II of the tip portion of the crack 5, the fulcrum and the load It is a figure showing the relationship with the distance C with a point. Can the ratio of the combination of a mode I load and mode II load was calculated from the energy release rate G _I and G _II of the distal end portion of the crack 5 is a diagram showing a relationship between the length a of crack 5. It is a figure which shows the relationship between the thickness t of an auxiliary plate, and the ratio of a combined load. It is a schematic diagram showing the laminated structure of the foam core sandwich panel used in one Example of this invention. It is a schematic diagram showing the state of the test piece in the peeling evaluation test method of this invention. It is the figure which represented the fracture toughness value as the mode I component on the vertical axis and the mode II component on the horizontal axis. (A) is a schematic diagram showing the mode I load in the laminated structure which has produced the interlaminar crack, (b) is a schematic diagram showing the mode II load, (c) is a schematic diagram showing the mixed mode load. It is a schematic diagram showing the case where the MMB test method is applied to a test piece of a laminated structure having a crack in the center of a layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test piece 1a End surface 2 Foam core 3a Face plate 3b Face plate 4 Adhesive layer 5 Crack 6A Reinforcement crack piece 6a Upper crack piece 6b Lower crack piece 7 Auxiliary plate 32 Support pillar 33 Support pillar 34 Jig 35 Leg part 36 Leg part 37 Lever part 38 fulcrum 39 load point 42 fixed block 43 rotating shaft 45 fixed block 46 rotating shaft 48 kapton film 51 pre-crack

Claims (4)

In a laminate structure in which planar laminates are laminated in the vertical direction, a peel evaluation test method for a laminate structure using a test piece in which an interlayer crack is formed at an asymmetric position in the vertical direction of the laminate structure,
The auxiliary plate was bonded to the entire outer surface of the test piece on the outer side of the crack piece having the lower bending rigidity among the crack pieces positioned above and below the interlayer crack of the test piece, and the auxiliary plate was connected. A peeling evaluation test method characterized by applying a uniaxial load to a test piece. Of the crack pieces located above and below the interlaminar crack of the test piece, the bending rigidity of the crack piece having a low bending rigidity and the auxiliary plate combined is B ₁ , and the bending rigidity of the crack piece having a high bending rigidity is B _2. ,
0.5 ≦ B ₁ / B ₂ ≦ 2
The peeling evaluation test method according to claim 1, wherein the auxiliary plate is used.   The peeling evaluation test method according to claim 1, wherein a combined load of an opening load and a shear load is generated by the uniaxial load.   The peel evaluation test method according to any one of claims 1 to 3, wherein the laminated structure is a foamed core sandwich panel obtained by laminating a prepreg on top and bottom of a foam, and applying pressure and heating.

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