JPS6113006A - Joint structure of composite material product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a joint structure for attaching a composite product made of a composite material in which reinforcing fibers are impregnated with a resin to another structure. In particular, in the present invention, a composite material made of resin-impregnated fibers whose fiber directions are aligned in one direction is folded back into a U-shape to form a loop portion, and a fastener such as a bolt is inserted into this loop portion. Regarding the joint structure of composite material products.

(Prior art) When a product made of a composite material in which reinforcing fibers are impregnated with resin is drilled with a drill or the like for attachment to another structure, one of the reinforcing fibers is cut, resulting in a decrease in strength. , it is not possible to construct an effective joint structure. Therefore, for joint structures that require high strength and high reliability, such as the attachment part of the rotor blade of a helicopter or the strut force of an artificial guard, composite materials made of resin-impregnated fibers with fibers aligned in one direction are used. A joint structure in which a loop portion is formed by folding back into a letter shape and a fastener such as a bolt is inserted into the loop portion is disclosed in, for example, U.S. Pat.
No. or German Patent No. 1, S-θls,! ; It has been proposed in No. 73, etc.

(Problems to be Solved by the Invention) In the above-mentioned joint structure having the loop portion, there are two types of breakage mode: a fiber breakage mode in which the fibers break, and an interlayer shear breakage mode in which the resin peels off in layers. Usually, the glabellar shear breaking mode is weaker, so the problem is that the high strength of the fibers is not fully utilized. In the conventional structure described above, the loop part has a shape in which a unidirectional resin-impregnated fiber is rolled in a semicircular shape and folded back. However, when a tensile force is applied to this type of joint structure, the composite material forming the loop part Since the cross section of the material is not rotated in accordance with the curved shape of the loop portion, but is aligned in the tensile direction, a bending force acts on the composite material, and this bending causes a bending between the fibers due to the force. Interlaminar shear stress occurs. This interlaminar shear stress is maximum on the radially inner side of the loop portion on both sides, and interlaminar shear rupture occurs here.

An object of the present invention is to solve the above-mentioned problems of the conventional composite product joint structure having a loop portion, and to provide a joint structure that can greatly reduce interlaminar shear stress.

(Means for Solving the Problem) In order to solve the above object, the present invention provides a joint structure for a composite @ product having a loop portion as described above, in which the radius of curvature of the loop portion is minimized near the apex, and the radius of curvature of the loop portion is minimized near the apex. The radius of curvature gradually increases from the apex toward both sides, and the radius of curvature is maximized at the two sides. It is preferable that the rate of change in the radius of curvature of the loop portion is maximum near the apex, and that the rate of change gradually decreases toward both sides. For example, the loop portion may have an elliptical shape with the long axis oriented in the longitudinal direction of the loop portion and the short axis oriented in a direction perpendicular to the longitudinal direction.
In this case, the ratio of the major axis to the minor axis of the elliptical shape constituting the loop portion is preferably %1.3 to 1.7.

(Effects of the Invention) In the present invention, since the loop portion of the composite material constituting the joint structure has a large radius of curvature on both sides,
When tensile force is applied to the composite material.

On both sides, the rotational displacement of the 11 horizontal planes of the composite material is small υ
, so the bending force acting on the composite material becomes smaller;
Interlaminar shear forces are reduced. In particular, by appropriately determining the change in the radius of curvature of the loop portion, the stress on the inner side of both sides of the loop portion, where the interlaminar shear stress conventionally was maximum, can be made equal to the stress on other portions. Effective use of material strength can be achieved.

(Explanation of an Embodiment) FIG. 1 shows an embodiment of the present invention, in which the joint structure 1 is made of a composite material 10 made of resin-impregnated fibers with fiber directions aligned in the length direction. 10 is a metal bushing 9
It has a loop portion 10g that is wound around the body. The bushing 9 has a seat hole 9a, and in the space formed between the side parts 10b of the composite material 10 behind the bushing 9, there is an insert 11 in which chopped fibers are impregnated with resin and hardened. is inserted and adhered to the composite material 10.

Although not shown in the drawings, the '61 composite material 10 is formed integrally with a composite product, such as a rotor blade of a helicopter, by a known method. The joint structure formed in this way is inserted into the metal fitting 12 of the counterpart structure,
Multiple connections are made to bolts 13 and nuts 14.

As shown in FIGS. 1 and 1, the bush 9 inside the loop portion 10a has a shape obtained by dividing an ellipse by a short (-), with the long axis of the ellipse extending in the longitudinal direction of the joint.

The short axis is oriented perpendicular to it. Therefore, in the loop portion 108, the composite material 10 is also curved into an oval shape. FIG. 3 shows the action of this joint structure. When a tensile force P is applied to the composite material 10, the cross section A of the side portion of the loop portion 108 is displaced to the point indicated by B in FIG. This displacement is a combination of the displacement δ in the direction of the tensile force P and the rotational displacement I caused by the curvature of the loop portion. As a result, the side part 101) of the composite material tries to displace from the position shown at A' in Figure 1 to the position shown at P, but since the direction of the tensile force P remains unchanged, it ends up at position C'. , bending force often acts on the composite material 10 on both sides of the loop portion 10a. However, since the joint structure in this example is 8% elliptical and the short axis of the ellipse is uniformly oriented as described above, the radius of curvature is large on both sides (therefore, the rotational displacement θ is smaller than before). Since the bending force acting on the composite material 10 becomes smaller as the rotational displacement θ decreases, the lv4 shearing force is also reduced accordingly.

Fig. 7 and Fig. S show the results obtained by finite element analysis of the interlaminar shear stress in the composite material in the conventional joint structure and the joint structure according to an embodiment of the present invention. The line represents the magnitude of shear stress. As is clear from FIG. 7, in the conventional joint structure, fAII in am of the loop portion shown as θ0 in the figure.
The maximum Lc force occurs at D and gradually decreases towards the longitudinal end of the joint structure, i.e. the apex shown as 00 in the figure. On the other hand, in a joint structure having an elliptical loop part,
As shown in FIG. S, a large stress is generated on the side E at a certain angle from the apex, in this example, at a position of approximately λ0.

FIG. 6 shows the relationship between the interlayer shear stress and the ratio of the major axis to the minor axis of the ellipse. As can be seen from the figure, as the ellipse becomes longer, the interlaminar shear stress at the side ε decreases, but conversely, the 230 position lower force increases. When the length/breadth ratio is approximately 1.5, the stress at the above-mentioned position becomes equal. The stress at this time is about % of the stress when the length ratio is l and θ, that is, when the shape is circular. When the length/breadth ratio is between about 1.3 and 1.7, a significant decrease in stress is observed compared to the case of a circular shape. Figure 7 shows the conventional joint structure and the long/short axis ratio of 1.
．． This figure shows the test results of joint fatigue strength in an example of the present invention with lI. As is clear from the figures, the embodiment of the present invention achieves a significant improvement in fatigue strength compared to the conventional joint structure.

As mentioned above, when the loop part is elliptical, a large area of interlaminar shear stress occurs at a portion approximately 25' from the apex of the loop part, but this is due to the non-ideal shape of the joint. By selecting an appropriate curve, it is possible to make the distribution of interlayer shear stress inside the wadding uniform over the entire loop portion.

That is, in the above-mentioned joint structure, due to elongation of the composite material due to external force, a difference in shape from the inner bushing occurs, and this difference in shape causes generation of interlaminar shear stress. Therefore, when the loop portion is circular, as shown in FIG. 4, the interlayer shear stress is small in areas other than the sides of the loop portion. Taking this into consideration, the interlayer shear stress can be reduced as follows. That is, since the elongation displacement of the composite material is close to zero near the apex of the loop portion and gradually increases as it moves toward the sides, the change in the shape of the joint, that is, the rate of change in the two radii of curvature also changes. It is preferable to change the thickness so that it is thickest near the apex, gradually becomes smaller toward the sides, and becomes finer around 900. A cubic curve is suitable to satisfy this condition, but strictly speaking, the optimal shape is achieved by making the amount of elongation of the composite material equal to the amount of change in one radius of curvature from the vertex to both sides. can be set.

[Brief explanation of drawings]

Fig. 1 is an exploded perspective view showing an embodiment of the joint structure according to the present invention, Fig. 1 is a plan view thereof, Fig. 3 is a schematic diagram for explaining the generation of bending force, and Fig. 4 is a conventional joint structure. A diagram showing the distribution of glabella shear stress in the structure, Figure S is a diagram showing the distribution of interlayer shear stress in an example of the present invention, and Figure 6 is II!
Figure 1 is a diagram showing the relationship between the peak value of inter-shear stress and the ratio of major to minor axis of the ellipse of the loop portion, and Figure 2 is a diagram showing the results of a fatigue test. DESCRIPTION OF SYMBOLS 1... Joint structure, 9... Bush %10... Composite material, 10a... Loop part. Part 1: Toshiaki Toshiaki - 3:

Claims (4)

[Claims] (1) A joint of a composite material product in which a composite material made of resin-impregnated fibers whose fiber directions are aligned in one direction is folded back in a U-shape to form a loop portion, and a fastener is inserted into this loop portion. In the structure, the loop portion has a minimum radius of curvature near the apex, gradually increases in radius from the apex toward both sides, and has a maximum radius of curvature at both sides. structure (2) In the joint structure of item (1) above, the loop portion has an elliptical shape with its major axis oriented in the longitudinal direction of the loop portion and its minor axis oriented in a direction perpendicular to the longitudinal direction. Characteristic joint structure (3) The joint structure according to item (2) above, wherein the dimensional ratio of the major axis to the minor axis of the elliptical shape constituting the loop portion is 1.3 to 1.7. (4) In the joint structure of item (1) above, the loop portion has a maximum rate of change in the radius of curvature near the apex, and the rate of change gradually decreases toward both sides, reaching the minimum rate of change at both sides. A joint structure characterized by having