JP3456588B2 - Energy absorbing member - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy absorbing member, and more particularly to the structure of an energy absorbing member made of a composite material of resin and reinforcing fibers.

[0002]

2. Description of the Related Art For example, an energy absorbing member that absorbs impact energy is used for a seat around an aircraft, a seat around an automobile, a bumper, and various structural members (JP-A-60-109630). 62-17
No. 438, etc.). In addition to the ability to absorb impact energy well, this energy absorbing member is generally lightweight,
Since high rigidity is required, a composite material of a resin and reinforcing fibers, so-called fiber reinforced plastic (hereinafter sometimes referred to as FRP), especially carbon fiber reinforced plastic (hereinafter also referred to as CFRP) There is) is said to be suitable. In such an energy absorbing member, an energy absorbing mechanism may be considered in which local destruction is caused from a certain portion of the energy absorbing member, for example, a member end portion, and the energy is absorbed by utilizing the local destruction.

[0003]

However, conventional energy absorbing members made of a composite material of resin and reinforcing fibers still have insufficient energy absorbing ability. For example, when reinforcing fibers are laminated in layers, delamination is likely to occur and a small amount of energy leads to breakage, so that a large amount of energy cannot be absorbed in the end and it is not practically used in practice. is there.

It is an object of the present invention to provide an energy absorbing member which does not cause delamination, can exhibit substantially uniform and high strength over the entire thickness direction of the member, and can exhibit high energy absorbing ability. To do.

[0005]

The energy absorbing member of the present invention which meets this object is an energy absorbing member made of a composite material of resin and reinforcing fibers, wherein the reinforcing fibers are:
It consists of short fibers with a length of 100 mm or less, and is oriented in a random direction, and the breaking elongation of the resin is 30% or more.
The breaking elongation of the reinforcing fiber is 1.5% or more,
And, the shear strength at the interface between the resin and the reinforcing fiber,
The resin has a ratio to the shear strength of 0.8 to 1.2 .

In such an energy absorbing member, for example, as shown in FIG. 1 as a cylindrical energy absorbing member 41, a member 41 made of a composite material 43 of resin and reinforcing fibers 42 has a length of 100 mm or less. Reinforcing fibers made of short fibers are three-dimensionally oriented in a random direction. When the energy absorbing member 41 absorbs impact energy in the direction of the energy absorbing axis 44, for example, in the compressing direction, as shown in the enlarged view of the member 41 in FIG. When it is destroyed, the member 41
The member 41 tries to open in such a manner that the member 41 tears in the thickness direction at the end. However, since the reinforcing fibers 42 are oriented in a random direction, this composite material 43 has no layers,
So-called delamination does not occur. Therefore, the member 41
Can exhibit a substantially uniform strength in the thickness direction, and the member 4
In fact, the end portion of 1 is difficult to spread and break as shown in FIG. 2, and an extremely large load P is required to break the member 41.
Will be needed. In other words, this energy absorbing member 41 can absorb a large amount of energy.

Further, once the breakage is started, the reinforcing fibers 42 are oriented in a random direction, so that they are entangled between the both side portions 43a and 43b of the member end portion expanded as shown in FIG. The reinforcing fiber 42a is in the intervening state. Reinforcing fiber 42 interposed between the expanded portions 43a and 43b
The a exerts a large resistance force when the both portions 43a and 43b try to further expand. As a result, the energy release rate of this composite material is increased and the energy absorbing member 4
The specific absorbed energy amount of 1 is further increased.

The reinforcing fiber has a length of 100 mm or less,
It is preferably 5 to 100 mm. If the length exceeds 100 mm, a layer may be locally generated, which is not preferable. When the length is shorter than 5 mm, the effect of reinforcement in the composite material becomes small and the reinforcing fiber 4 extending between the expanded portions 43a and 43b as shown in FIG.
2a reduces the effect of increasing the amount of specific absorbed energy.

The kinds of resin and reinforcing fiber of the composite material constituting the energy absorbing member of the present invention are not particularly limited,
The tensile strength of the reinforcing fiber is preferably 350 kgf / mm ² or more, more preferably 450 kgf / mm ² or more. Tensile strength of reinforcing fiber is 350kgf
When it is / mm ² or more, the amount of energy required for breaking the fiber is large with respect to the impact energy applied to the energy absorbing member made of the composite material, so that a large amount of energy can be absorbed for the same amount of breaking. When the tensile strength is less than 350 kgf / mm ² , the reinforcing fiber is likely to break with a small amount of energy. in this way,
Since the strength and rigidity of the composite material as a whole can be improved by the reinforcing fiber having high tensile strength, the energy absorbing member has higher energy absorbing ability and is more difficult to break.

Further, in the present invention, it is preferable that the surface roughness of the reinforcing fiber is 1.08 or more. When the surface undulation degree of the reinforcing fiber is 1.08 or more, the so-called anchor effect due to the undulation of the surface is improved, so the adhesiveness between the reinforcing fiber and the resin is improved, and an interface that is extremely difficult to peel or break can be achieved. . By improving the adhesiveness, the strength of the reinforcing fiber in the composite material can be utilized very effectively, and the rigidity of the composite material as a whole can be improved,
Can absorb a large amount of energy. If the surface undulation degree is less than 1.08, the anchor effect as described above cannot be expected, or even if there is, it is slight.

Further, in the present invention, when the reinforcing fiber is made of carbon fiber, the amount of surface functional group (O), which is the atomic number ratio of oxygen (O) to carbon (C) on the surface of the reinforcing fiber.
/ C) is preferably 0.08 or more. When the amount of surface functional groups (O / C) is 0.08 or more, the activated O enhances the adhesiveness of the surface of the reinforcing fiber and enhances the adhesive strength between the resin and the reinforcing fiber, and the composite material as a whole. It can exhibit extremely high rigidity and energy absorption capability. If the amount of surface functional groups (O / C) is less than 0.08, the adhesiveness between the resin and the reinforcing fiber becomes insufficient, and peeling or breakage easily occurs at the interface between the resin and the reinforcing fiber during energy absorption. , The energy absorption capacity is reduced accordingly.

[0012] resin in the composite material constituting the energy absorbing member of the present invention, the elongation at break is 30% or more
It When the elongation at break is less than 30%, it becomes difficult to achieve a high energy absorption capacity. In the present invention,
High toughness resin having this high breaking elongation, breaking elongation,
By using a composite material with a reinforcing fiber having a high tensile strength, an excellent energy absorption capacity can be exhibited and a high specific absorbed energy amount can be achieved. Further, by increasing the surface roughness of the reinforcing fiber, or by increasing the surface functional group amount (O / C) when the reinforcing fiber is carbon fiber, the adhesion between the resin and the reinforcing fiber The property is enhanced, and a composite material that is resistant to peeling and destruction at both interfaces can be realized, and an excellent energy absorption capacity can be achieved. That is, in the energy absorbing member of the present invention, by using a composite material in which a resin having high toughness and a reinforcing fiber having high strength and / or high adhesiveness are combined, excellent energy absorbing ability can be exhibited and a high ratio can be obtained. The amount of absorbed energy can be achieved.

In the present invention, the reinforcing fiber has a breaking elongation of 1.5% or more . Breaking elongation of reinforcing fiber is 1.5%
If the above is the case, the part of the energy absorbing member made of the composite material, which is expected to break, actually breaks,
Can absorb a large amount of energy. If the breaking elongation is less than 1.5%, the reinforcing fiber is broken by a small amount of deformation of the energy absorbing member, and large energy cannot be absorbed when the reinforcing fiber is broken. Will be reduced.

Further, in the present invention, at least the breaking elongation of the reinforcing fiber is 1.5% or more, and the ratio of the shear strength at the interface between the resin and the reinforcing fiber and the shear strength of the resin is 0.8. The range is from 1.2 to 1.2. By setting the breaking elongation of the reinforcing fiber to 1.5% or more, the above-described actions and effects can be obtained, and by setting the shear strength ratio in the range of 0.8 to 1.2 (that is, the resin and the reinforcing fiber). The adhesive strength between the resin and the reinforcing fiber can be increased to a desired degree and as much as necessary by setting the shear strength at the interface between and to a value equal to or close to the shear strength of the resin. Due to the high breaking elongation of the reinforcing fibers and the high adhesiveness between the resin and the reinforcing fibers, it becomes possible to realize an energy absorbing member having a high energy absorbing ability even with reinforcing fibers other than carbon fibers.

Examples of the resin having a breaking elongation of 30% or more include polyamides such as nylon 6, nylon 66, nylon 11, nylon 610 and nylon 612, copolyamides of these polyamides, polyethylene terephthalate and polybutylene. Polyesters such as terephthalate, or copolyesters of these polyesters, and further polycarbonates, polyamideimides, polyphenylene sulfides, polyphenylene oxides, polysulfones, polyether sulfones, polyether ether ketones, polyetherimides, polyolefins, etc., and polyester elastomers. , Thermoplastic elastomers typified by polyamide elastomers, and the like.

However, the resin forming the matrix of the composite material of the present invention is not limited to the above resins, and examples thereof include epoxy resin, unsaturated polyester resin, polyvinyl ester resin, phenol resin, guanamine resin, and bismaleimide. Examples include polyimide resins such as triazine resins, furan resins, polyurethane resins, polydiallyl phthalate resins, and thermosetting resins such as amino resins such as melanin resins and urea resins. Further, rubber such as acrylic rubber, acrylonitrile butadiene rubber, urethane rubber, silicone rubber, styrene butadiene rubber, and fluoro rubber can be used. Furthermore, a resin obtained by blending a plurality of the above-mentioned thermosetting resins, thermoplastic resins, and rubber may be used.

Examples of the reinforcing fiber that can be used in the present invention include carbon fiber, glass fiber, aromatic polyamide fiber, alumina fiber, silicon carbide fiber, boron fiber and the like.

The shape of the energy absorbing member made of the composite material of the present invention is not particularly limited, and may be cylindrical, columnar, or
Various shapes such as a plate shape can be adopted. Representative shapes or applicable shapes are illustrated in FIGS. 3 to 12.

As a typical shape of the energy absorbing member, first, a cylindrical shape can be mentioned. The most typical shape as a cylindrical shape is a cylinder 1 as shown in FIG. The direction of the arrow in the figure is the compressive load acting direction as impact energy. Further, as shown in FIG. 4, a cylinder 2 in which the top of the cylinder is formed in a conical shape or a spherical shape can also be applied. Further, although not shown in the drawings, a prism, a cone, a pyramid, a truncated cone, a truncated pyramid, or a cylinder having an elliptical cross section, and further, as shown in FIG. A tubular shape 4 such as a tube) can also be adopted.

The shape is not limited to the cylindrical shape, but may be a columnar shape. For example, a columnar shape or a prismatic shape can be mentioned.

Further, it is possible to adopt a plate shape. For example, a corrugated plate-shaped member can be used as an energy absorbing member because it is strong against buckling. Also,
As shown in FIG. 6, for example, a cross section T having a rib 5 is provided.
The shape 6 may be a V shape, or may be a shape 7 having a U-shaped cross section as shown in FIG. 7. In the shape 7 having a U-shaped cross section shown in FIG. 7, the lid member 8 can be provided as shown by a two-dot chain line. Further, as shown in FIG. 8, a cross-shaped cross section 9 may be used.

Furthermore, it is also possible to adopt a structure in which members of various shapes are combined. For example, FIG. 9 and FIG.
As shown in FIG. 0, small elongated cylinders 12 and 13 are put in a large cylinder 10 and a large truncated cone 11 and are made of a composite material, so that an energy absorbing member that is less likely to buckle can be obtained. it can.

Further, the energy absorbing member may be composed of one member, or may be composed of a plurality of members stacked or combined. For example, in FIG.
As shown in FIG. 12, the energy absorbing members 16 and 17 may be configured by vertically stacking members 14, 15a, 15b and 15c made of a composite material having the same or similar shapes. In the configuration of FIG. 12, each member may be alternately laminated inside and outside.

In the energy absorbing member as described above, it is desirable to form a trigger shape for sequentially destroying the energy absorbing member from the end, and this trigger is a pressing member for pressing the energy absorbing member. It may be provided on the side.

[Characteristic Measuring Method and Effect Evaluation Method] The characteristic measuring method and effect evaluating method in the present invention will be described below. (1) Energy release rate of resin G _IC compact test (CT test) Standard: ASTM-E-39
It measured based on 9.

(2) Elongation at break and tensile strength of fiber Measured according to the resin-impregnated strand test method specified in JIS-R7601. The resin formulation and curing conditions used in the test are shown below. Resin Formulation: "Bakelite" ERL-4221 100 parts of 3 boron trifluoride monoethylamine (BF ₃ · MEA) ₃ parts acetone 4 parts Curing conditions: 130 ° C., 30 minutes

(3) Surface relief The composite material is cut perpendicularly to the fiber direction, and the cut surface is mirror-polished by metal phase polishing. Here, the cross-sectional shape of the single fiber perpendicular to the polishing surface was measured by a scanning electron microscope (JSM manufactured by JSM Co., Ltd.).
-T300 type) is used to photograph a backscattered electron composition image at an accelerating voltage of 15 kV and a photographing magnification of 10,000 times on a film. The backscattered electron composition image photograph thus obtained was further stretched to 2 times at the time of printing, that is, the magnification was 2 in total.
It is taken as a photograph for surface undulation analysis with a magnification of 0000. Here, from the photograph for surface undulation analysis, the area S (m
m ² ) and the outer peripheral length L (mm) are measured. The surface undulation degree is obtained according to the following formula as a ratio of the above L and the outer peripheral length of a virtual perfect circle having the same S. Surface relief = L · (πS) ^−1/2 / 2 L is measured at 20000 times. After accurately sticking a non-stretchable cotton thread on the outer periphery of the single fiber cross-sectional image in the photograph, Can be removed and the length of the straight line can be measured. Further, S was measured by placing a trace paper of known weight per unit area on a photograph printed at 20000 times, accurately tracing the outer periphery of the single fiber cross-sectional image, and accurately cutting the trace line. The weight can be converted from the weight of the cut single fiber cross-sectional image and the weight per unit area of the trace paper. The measurement is carried out on 10 monofilaments, and the average value is taken as the surface relief. There is no limitation on the method of measuring L and S as long as it can be accurately measured, and an image analyzer can be used in addition to the above method.

(4) Amount of surface functional group (O / C) It was determined by the following procedure by X-ray photoelectron spectroscopy. First, carbon fiber (bundle) from which sizing agents have been removed with a solvent
After cutting and arranging them on a copper sample support, the photoelectron escape angle was set to 90 °, and MgKα1, X-ray source was used.
2 is used and the sample chamber is kept at 1 × 10 ⁻⁸ Torr. The kinetic energy value (KE) of the main peak of C _1S is set to 969 eV as a correction of the peak associated with charging during measurement. The C _1S peak area was calculated as K. E. As 958-97
It is obtained by drawing a linear baseline in the range of 2 eV. The O _1S peak area was measured by K.K. E. As 714-726
It is determined by drawing a straight baseline in the range of eV. Here, the amount of surface functional groups (O / C) is calculated as an atomic number ratio from the ratio of the O _1S peak area and the C _1S peak area using a sensitivity correction value specific to the apparatus. The inventors of the present invention used a model ESCA-75 manufactured by Shimadzu Corporation.
0 was used to measure the ratio of the O _1S peak area to the C _1S peak area, and the ratio was divided by the sensitivity correction value of 2.85 to obtain the surface functional group amount (O / C).

(5) Tensile breaking elongation of resin Measure according to ASTM-D-638.

(6) Shear strength of resin Measure according to ASTM-D-732.

(7) Interfacial shear strength It is measured by the so-called "single yarn embedding method" based on the Kelly-Tyson rule in the Cox model. For example, one monofilament (single yarn) of a reinforcing fiber is linearly placed between two upper and lower (or more) matrix resin films, and this is heated and pressed to fuse and solidify the upper and lower films to form reinforcing fibers. The single yarn of and the resin are integrated (the single yarn is embedded in the resin). Cut a strip having an appropriate width centering on the single yarn in the direction parallel to the embedded single yarn to obtain a test piece. When both ends of this test piece are gripped and a tensile load is applied, the tensile load is transmitted from the matrix resin to the single yarn in the resin through the interface between the resin and the fiber, and the single yarn is cut at a certain length. When the load is further increased and the load exceeds a certain value, the single yarn cannot be cut further. At this time, the cut length of the reinforcing fiber was measured, the average value was Lav, and the tensile strength of the reinforcing fiber was σ.
_{If f is} the single yarn diameter and d _f is the single yarn diameter, the interfacial shear strength τ between the fiber and the resin is calculated by τ = (3 · σ _f · d _f ) / (8 Lav). Since this interfacial shear strength matches the shear strength τ _{m of the} resin if the fiber and the resin are completely bonded, the ratio τ / τ _m of both represents the degree of adhesion at the interface between the fiber and the resin. It can be an index. In addition, when a force in the fiber direction is acting in the normal direction of the fiber surface due to the curing shrinkage of the resin, the interfacial shear strength τ is the resin even if the fiber and the resin are not completely bonded. The shear strength may be a value close to or higher than the shear strength τ _m , and in any case, it can be an index showing the degree of adhesion at the interface between the fiber and the resin.

(8) There is no standard for specific absorbed energy amount or standardized method. As shown in FIG. 13, when a compressive load P is applied to the energy absorbing member 21 via the pressing member 22 to destroy the member 21, generally a load-displacement (displacement of the pressing member) diagram as shown in FIG. Is obtained. In this load-displacement diagram, displacements x ₁ to x ₂
The energy absorbed during is calculated as the area of the shaded area in the figure. The weight of the energy absorbing member destroyed during that period is calculated (if the members have the same cross section, the cross sectional area and (x
₂ −x ₁ ) and specific gravity)), and the value obtained by dividing the absorbed energy amount by the weight is taken as the specific absorbed energy amount. x ₁ , x
The setting of ₂ , the speed of displacement of the pressing member, and the like can be set appropriately.

[0033]

Example 1 Carbon fiber T300 manufactured by Toray Industries, Inc. was used as a reinforcing fiber, nylon 6 was used as a matrix, and the inner diameter was 70 mm and the wall thickness was 2.3.
The mm-sized cylinder was preheated to 280 ° C. with a composite plate (fiber length 25 mm) obtained in JP-A-2-143810, charged into a mold at 250 ° C., and compression-molded.

The cylindrical composite material thus obtained was machined to an inner diameter of 70 m as shown in FIG.
m, a wall thickness 2.3 mm, a length 70 mm, and an inclination angle of the upper end of 45 degrees, an energy absorbing member 31 made of a cylindrical composite material was obtained.

The energy absorbing member 31 is mounted on the universal testing machine 32 as shown in FIG.
A compression load was applied to the energy absorbing member 31 from 3 through the load cell 34 and the pressing member 35, and the displacement of the cross head 33 was used as the displacement of the pressing member 35 to measure the load-displacement characteristics. The displacement speed was 10 mm / min. When the specific absorbed energy amount was calculated from the obtained load-displacement diagram (FIG. 16), it was 90 kJ / kg.

[0036]

As described above, according to the energy absorbing member of the present invention, the reinforcing fiber of the composite material constituting the energy absorbing member is a short fiber of 100 mm or less,
Arrange them in a random direction so that no inter-layers are created in the composite material , and the breaking elongation of the resin is 30% or more.
If the breaking elongation of the reinforcing fiber is 1.5% or more,
So that it can absorb a large amount of energy before it breaks
And shear at the interface between the resin and the reinforcing fiber
The ratio between the strength and the shear strength of the resin is 0.8 to 1.2,
To improve the adhesion between resin and reinforcing fiber
Therefore, the composite material can be made to exhibit uniform and high strength in the thickness direction, and an energy absorbing member having high energy absorbing performance can be realized.

[Brief description of drawings]

FIG. 1 is a partial vertical sectional view of an energy absorbing member according to the present invention.

FIG. 2 is an enlarged partial vertical sectional view of the member of FIG.

FIG. 3 is a perspective view showing an example of the shape of the energy absorbing member of the present invention.

FIG. 4 is a perspective view showing another example of the shape of the energy absorbing member of the present invention.

FIG. 5 is a perspective view showing still another example of the shape of the energy absorbing member of the present invention.

FIG. 6 is a perspective view showing still another example of the shape of the energy absorbing member of the present invention.

FIG. 7 is a perspective view showing still another example of the shape of the energy absorbing member of the present invention.

FIG. 8 is a perspective view showing still another example of the shape of the energy absorbing member of the present invention.

FIG. 9 is a perspective view showing another structural example of the energy absorbing member of the present invention.

FIG. 10 is a perspective view showing still another structural example of the energy absorbing member of the present invention.

FIG. 11 is a vertical sectional view showing still another structural example of the energy absorbing member of the present invention.

FIG. 12 is a vertical sectional view showing still another structural example of the energy absorbing member of the present invention.

FIG. 13 is an exploded perspective view showing a method for measuring a specific absorbed energy amount.

FIG. 14 is a load-displacement diagram in the measurement of the amount of specific absorbed energy.

FIG. 15 is a partial front view of the universal testing machine showing the measurement of load-displacement characteristics in Example 1.

FIG. 16 is a load-displacement diagram in Example 1.

[Explanation of symbols]

1, 2 Cylindrical energy absorbing member 3 Flange portion 4 Cylindrical energy absorbing member having a flange portion 5 Rib 6 Energy absorbing member 7 having T-shaped cross section 7 Energy absorbing member 8 having U-shaped cross section 8 Lid member 9 Cross section Cross-shaped energy absorption member 10 Cylindrical energy absorption member 11 Frustum-shaped energy absorption members 12, 13 Elongated members 14, 15a, 15b, 15c Energy absorption member members 16, 17 Combination energy absorption Member 21 Energy absorbing member 22 Pressing member 31 Energy absorbing member 32 Universal testing machine 33 Cross head 34 Load cell 35 Pressing member

Continuation of front page (56) Reference JP-A-6-123322 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F16F 7/00 C08B 5/00 F16F 7/12

Claims (4)

(57) [Claims] 1. An energy absorbing member comprising a composite material of resin and reinforcing fibers, wherein the reinforcing fibers have a length of 10
It consists of short fibers of 0 mm or less, and is oriented in a random direction, and the breaking elongation of the resin is 30% or more.
The breaking elongation of the reinforcing fiber is 1.5% or more, and
Shear strength at the interface between the resin and the reinforcing fiber and the resin
The energy absorption member is characterized by having a ratio to the shear strength of 0.8 to 1.2 . 2. The tensile strength of the reinforcing fiber is 350 kgf.
/ Mm ² or more, the energy absorbing member according to claim 1. 3. The surface relief of the reinforcing fiber is 1.08 or more.
The energy absorbing member according to claim 1 or 2 , which is the above . 4. The surface of the reinforcing fiber is oxygen (O) and charcoal.
The amount of surface functional groups (O / C), which is the atomic ratio with the element (C),
The energy absorbing member according to any one of claims 1 to 3 , which is a carbon fiber of 0.08 or more .