JPS6350571B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a leaf spring made of composite material that can be used in leaf springs for vehicles and vibration devices.

Composite material leaf springs are attracting attention because they have superior stress resistance, can take larger displacements, and are lighter in weight than conventionally used steel leaf springs. There are high hopes for something that can replace. Considering the required properties of the leaf springs made from composite materials that have been developed in the past, it has been said that the reinforcing fiber volume content (hereinafter referred to as VF) must be as high as 50 to 70%. In leaf springs made of composite materials with a large VF, residual stress occurs at the prepreg lamination interface during molding, and when repeated bending stress is applied to the leaf spring, delamination occurs, which is thought to be based on this residual stress. , the phenomenon of destruction has finally been recognized, and there has been a demand for an immediate solution to this problem.

In addition, when attaching a leaf spring made of composite material to a mechanical device, the fixed part of the leaf spring is usually drilled and connected with bolts, etc., but by drilling holes in the leaf spring, the part concerned can be An inconvenient phenomenon has also been observed in which the strength of the reinforcing fibers is significantly reduced due to the cutting of the reinforcing fibers.Therefore, there is a strong demand for the development of a leaf spring having a fixing part structure that does not cause such inconveniences.

Therefore, the present inventors conducted studies with the aim of developing a leaf spring that could satisfy the above two demands, and found that the spring constant of the leaf spring was EI [where E is the bending modulus of elasticity and I is the moment of inertia of the area]. is proportional to 1/12 x (width of the leaf spring) x (thickness of the leaf spring)], and the shear stress distribution when bending is applied to the leaf spring is
As shown in the figure (in Figure 1, y is the thickness direction, Z is the width direction, is the magnitude of interlayer shear stress, and h is the thickness of the leaf spring), the center layer of the leaf spring By utilizing the fact that the distribution is maximum and zero on both surface layers, there is no destruction due to delamination phenomenon.
The present invention has been completed, which consists of a composite material leaf spring having a special structure that does not require drilling in the fixing part of the leaf spring.

The gist of the present invention is that, as shown in the cross section in FIG.
An intermediate layer A with a V.F of 40% or less is provided at a thickness equivalent to 90%, and a layer with a thickness equivalent to the remaining board thickness divided into two equal parts is provided on both surface layers to form a V.F of 40~ The leaf spring has a structure in which a composite material layer B of 70% is provided, and a fixing part with an uneven pattern is provided at the part where the leaf spring is fixed to the equipment.

As the reinforcing fibers used in carrying out the present invention, organic and inorganic fibers such as carbon fibers, glass fibers, aromatic polyamide fibers, silicon carbide fibers, and boron fibers can be used, but composite materials containing 40 to 70% VF can be used. By forming the layer B as a reinforcing fiber layer mainly composed of carbon fibers, a leaf spring having excellent performance can be obtained.

Furthermore, as the matrix resin constituting the composite material, any synthetic resin can be used as long as it has a breaking elongation of 2% or more, such as thermosetting resins such as epoxy resins, unsaturated polyester resins, and polyimide resins. Examples include thermoplastic resins such as resins, polyester resins, polyamide resins, polyetheretherketones, polycarbonate resins, and ABS resins.

The reinforcing fibers may be in the form of unidirectionally aligned fiber sheets, woven fabrics, or prepregs impregnated with matrix resin, and the matrix resin may be in the form of films, sheets, etc. Various forms such as pellets and powders can be used, but sheets and films are particularly preferred since they are easy to handle.

To carry out the present invention, a reinforcing fiber prepreg sheet impregnated with a matrix resin and a matrix resin sheet are usually prepared, and a laminated molded material having the configuration shown in FIG. 2 is formed. The gas in the molded material is removed by reducing pressure while heating, and a spacer corresponding to the thickness of the leaf spring is inserted.
The leaf spring of the present invention can be obtained by press-forming the end portion of the leaf spring by placing it in a hot press machine with a concave-convex pattern as shown in 2 in FIG. can.

When carrying out the above-mentioned invention, air and other substances contained in the molding material that easily turn into gas are removed at a temperature above the temperature at which the matrix resin exhibits fluidity, and in the case of a thermosetting resin, at a temperature below its curing start temperature.
In the case of other resins, the temperature must be below their decomposition temperature.

The leaf spring of the present invention is a conventionally developed leaf spring of V.F50~
10-40% VF compared to 70% composite leaf springs
Because of the extremely low carbon content, it is extremely easy to remove air and other gases that predispose to the generation of voids from the molding material during the molding process, and it is possible to make void-free leaf springs by simple press molding.
With conventionally developed materials for composite materials, it was extremely difficult to form uneven patterns on the ends of leaf springs, but by using the constituent materials of the present invention, it is extremely easy to form such patterns. be able to.

In addition to this wave-shaped uneven pattern, any uneven pattern with a difference of about 1 mm or more can be used as a fixing part for a leaf spring, and is a fixing part for leaf springs made of composite materials that have been developed in the past. Since there is no need to make holes in the leaf spring, the reinforcing fibers are not cut, and the properties of the leaf spring can be fully demonstrated.

In addition, the leaf spring of the present invention has V.F40 to 70 in its surface layer.
% reinforcing fiber composite material layer is formed, and the center layer is made of matrix resin with a V.F of 40% or less, so it exhibits extremely excellent spring characteristics and reduces internal strain. It can be used as an excellent leaf spring without any damage.

The leaf spring of the present invention can be attached to a mechanical device by using a washer as shown at 3 in FIG. 3 and fixing it with a U-bolt.

The present invention will be explained in more detail with reference to Examples below.

Example 1 A prepreg with a resin content of 37.5 wt% and a thickness of 0.15 mm and an epoxy resin film f with a thickness of 0.38 mm were prepared by impregnating a unidirectionally aligned carbon fiber sheet with epoxy resin, and an epoxy resin film f with a thickness of 0.38 mm was prepared. The leaf spring in the length direction is 0°, and the leaf spring in the right angle direction is 0°.
As 90°, 0°/0°/90°/0°/90°/0°/90°/f/0°/
f/
0゜／f／0゜／f／0゜／f／0゜／f／90゜／0゜／90
゜／
They were laminated to have a laminated configuration of 0°/90°/0°/0° and degassed at 100°C for 30 minutes under reduced pressure.

This defoamed laminated material is placed in a press molding machine having a concavo-convex pattern on the edges as shown in FIG. I created a structural leaf spring.

The obtained leaf spring was voidless and had a VF of 20% in the center layer and 55% in the surface layer.
Even when used as a leaf spring, no damage occurred due to internal strain.

Example 2 A 0.35 mm thick polycarbonate resin film and a 0.20 mm thick prepreg made by bonding a unidirectionally aligned carbon fiber sheet to the polycarbonate resin film were prepared, and the same lamination configuration as Example 1 and Example 1 were prepared.
A leaf spring having a concavo-convex pattern as shown in FIG. 2 was produced by press-molding at 250° C. and applying a pressure of 10 kg/cm ² using the same mold as above.

The VF of the surface layer of the leaf spring is 55%, and the VF of the center layer is 55%.
F is 20%, and the spring characteristics are extremely good.
Furthermore, internal strain failure was less likely to occur during use. Also, it was easy to attach to equipment using washers and U-bolts.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the interlayer shear stress distribution when bending is applied to a rectangular cross section of a leaf spring, FIG. 2 is a partial side view of the leaf spring of the present invention, and FIG. It is a state diagram when the fixing part of a spring is attached with a washer.

Claims (1)

[Claims] 1. An intermediate layer A with a reinforcing fiber volume content of 40% or less is arranged at the center in the thickness direction at a thickness corresponding to 20 to 90% of the board thickness, and on both surface layers there are layers equivalent to the remaining board thickness. A leaf spring having a structure in which a composite material layer B having a reinforcing fiber content of 40 to 70% is arranged, which is a layer with a thickness that is roughly divided into two, and the leaf spring is fixed to equipment. A leaf spring characterized by having a fixing part with a concavo-convex pattern on its part.