JPS6224039A - Leaf spring made of fiber-reinforced resin - Google Patents

Abstract

PURPOSE:To reduce the weight of an FRP leaf spring by forming a groove in the longitudinal direction of a beam, in the direction of plate width on the tension side, and forming said groove to have the sectional form for which a numerical equation is satisfied. CONSTITUTION:The surface onto which the compression stress of a beam is applied is formed flat, and a groove which has the width alpha.b in the direction of the plate width and the depth beta.t in the direction of length of the beam is formed on the side onto which a tensile stress is applied, and alpha and beta on the sectional form satisfy the following equation: 3beta<2>.alpha-4beta.alpha+1=0. Therefore, the design stress having the superior efficiency is generated on the side onto which the tensile stress is applied and on the side onto which a compression stress is applied, and the weight can be reduced.

Description

[Detailed description of the invention] Industrial applications The present invention relates to improvements in leaf springs made of fiber-reinforced resin.

Conventional technology A spring plate with a mouth shape to increase rigidity was developed in 1973.
No. 19809.

In addition, leaf springs made of fiber reinforced resin (hereinafter referred to as FRP) are
Compared to steel plates, it has the advantages of being lighter, has excellent corrosion resistance, and high tensile strength, but on the other hand, it has the disadvantage of low compressive strength. In order to eliminate this drawback, the neutral axis of bending of the FRP leaf spring is moved to the side where compressive stress is generated, so that the maximum compressive stress during one bending load is smaller than the maximum tensile stress.
However, the optimal ratio of tensile stress to compressive stress was not known at all.

Problems to be Solved by the Invention In the above-mentioned conventional FRP springs, how can the tensile stress on the tension side and the compressive stress on the compression side be balanced when the shape of the cross section perpendicular to the longitudinal direction is configured? Moreover, no particular consideration is given to whether or not the weight of the FRP board can be reduced.

The object of the present invention is to obtain a cross-sectional shape perpendicular to the longitudinal direction of an FRP plate in which the tensile stress on the tension side and the compressive stress on the compression side are balanced and the weight is reduced.

Means/Function for Solving All Problems In order to achieve all of the above objects, the present invention provides a beam having a width b and a thickness t to which a bending load is applied with fibers reinforced in one direction. The surface of the cross section perpendicular to the longitudinal direction of the beam is made flat, and the side that receives the tensile stress has a width α・b and a depth β・t in the length direction of the beam. A groove or notch is provided so that the above α and β are 3β
The cross-sectional shape satisfies 2・α−4β・α+1=0.

When bending stress is applied to the unidirectional reinforcing fibers, the bending strength is 9f/mj and the compressive strength σ is 120 to 130. =55
~65 kg f/a Therefore, approximately σt/σ. Ki 2
．． 0, so this σt/σ. Basic calculations were performed to obtain a cross-sectional shape perpendicular to the longitudinal direction of the strength member so that the strength was 2.0.

In Figure 4, the plate width b and the plate thickness t in a cross section perpendicular to the longitudinal direction of the beam to which a bending load is applied with fibers reinforced in one direction.
ll1 receives compressive stress when a bending load is applied.
l CS 'f < plane, groove width α・b, groove depth β, all centered on the center line in the plate width direction of the side TS receiving tensile stress
・L and tensile stress? Assuming that the distance from the receiving surface to the neutral axis of bending is k i+ + the distance k12 from the neutral axis to the surface receiving compressive stress, the beam's second moment of area I, tensile stress σa, and compressive stress σc8 is calculated using the following formula.

Therefore, if the neutral axis is moved to the side C8 receiving compressive stress so as to satisfy the equation 3β2・α+1=00, both the side TS receiving tensile stress and the side C8 receiving compressive stress will have efficient design stress. Therefore, it is possible to reduce the weight.

Embodiment FIGS. 1 to 3 show embodiments of the FRP leaf spring of the present invention, in which 1 is an FRP leaf spring, 2.2 is a center spacer, and 2.2 is a center spacer. lj: Fixed by center bolt 3. 4 is a plate, and 5 is an eyepiece. 6
is the groove or notch determined by the above formula,
As shown in FIG. 3, the shape of the groove or notch is such that in a cross section perpendicular to the longitudinal direction of the spring plate 1, the groove 6 is centered on the center line A-A in the plate width direction ( Fig. 3 (a)) has a narrow plate thickness part 7 with the same thickness as the plate thickness centered on the center line A-Ak in the plate width direction, and has grooves 6.6'e symmetrically provided on both sides thereof. Cross-sectional shape (Figure 3 (b)),
A plate thickness part 7' having the same thickness as the plate thickness is provided at the center of the center line A-Ak in the plate width direction, and notches 8 are symmetrically formed on both sides of the plate thickness part γ'.
. Tapered portions 9 facing downward from both ends,
9''e is formed to form cutout portions 8, 8' in cross section (as shown in FIG. 3).

Now, assuming that the straight span l, plate width b, and spring constant k are the same for the conventional rectangular cross-sectional beam and the beam having the cross-sectional shape of the present invention, the weight, stress, and plate thickness of both are assumed to be the same (see the following table). When compared, each is expressed by the following formula.

At 0.75, the stress increase rate is the smallest, and the weight reduction is 3
It becomes 2.9%. The values of α and β are determined depending on which of the weight W, plate thickness t, and stress is considered to be the most important.

Specific example: When comparing stress, weight, and plate thickness between a conventional beam with a rectangular cross section and a beam with a metal cross-sectional shape according to the present invention, with straight span, plate thickness, and spring constant, The cross-sectional beam has a board width of 70m+n and a board thickness of 24mm, and the beam with the cross-section according to the present invention has a board width of 70m+n and a board thickness of 33wn.
The groove width was 56mm, and the groove depth was 16.5+n+n. The results are shown in the table below.

(Left below) Effects of the Invention The present invention provides a beam having a width b and a thickness t on which a bending load is applied using fibers reinforced in one direction, the compression side being flat, and the tension side being flat. By forming all grooves or notches in the length direction of the beam with width α・β and depth β・t in the width direction, the values of α and β are 3β2・α−4β・
This is because it is an FRP leaf spring with a cross-sectional shape that satisfies α+l=Q.

The shape is determined with optimal efficiency in terms of stress, weight, etc., and the weight of the FRP leaf spring is particularly reduced.

In addition, the leaf spring may be a stacked leaf spring made by overlapping several spring boards, and the corners of the spring boards may be slightly chamfered.
Chamfering such as eight chamfers may be applied.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and Figure 1 shows an example of FRP.
FIG. 2 is a side view of the leaf spring, FIG. 2 is a plan view thereof, and FIGS. Fig. 4 is an explanatory diagram of each part of the calculation formula that is the basis of the present invention, and Fig. 5 shows the straight span, plate width, and spring constant of a beam with a conventional rectangular cross section and a beam with the cross-sectional shape of the present invention. This is a comparison diagram that compares the weight, stress, and plate thickness of the two, assuming that they are equal. 1: FRP leaf spring 6: Groove 8.8': Notch 1st I

Claims (1)

[Claims] Plate width b where bending load is applied with fibers reinforced in one direction
, in a beam with plate thickness t, the surface on the side receiving compressive stress in the cross section perpendicular to the longitudinal direction of the beam is flat, and the side receiving tensile stress has a width α・b and a depth in the plate width direction. β・
By providing a groove or notch in the longitudinal direction of the beam t, the above α
, β approximately satisfies 3β^2・α−4β・α+1=0. A fiber-reinforced resin plate spring.