Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
1999-06-16
2001-05-08
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S295400, C428S297100, C428S299100, C428S301400
Reexamination Certificate
active
06228473
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fiber-reinforced composite material and more particularly relates to a plate- or beam-like fiber-reinforced composite material suitable for use in leaf springs, bodies for trucks and passenger cars, parts for artificial satellites, structural members for aircraft, robot arms, ski boards, and others.
BACKGROUND OF THE INVENTION
Fiber-reinforced composite materials (or FRP) are widely used in many applications such as various industries, sporting goods and equipment for leisure time amusement as well as space and aviation fields. Owing to its properties characterized by light weight, high strength, and high elastic modulus, a carbon fiber-reinforced material (or CFRP) is used in a large amount for parts, which need to be light and highly rigid, among fiber-reinforced composite materials made by using fibers such as glass fibers, aramid fibers, boron fibers, and the like. For example, in industrial fields such as printing machines and film making machines, increase in productivity has been made possible by the use of a composite roll which is prepared by metal- or resin-plating the surface of a CFRP core and whose weight is 20 to 40% less than that of a conventional aluminum alloy roll.
Excellent strength and impact resistance are indispensable for a fiber-reinforced material. In the field of automotive parts, use of FRP for truck bodies and use of CFRP for leaf springs have been hither promoted. In these applications, in order to protect the persons in the vehicle in case an accident should happen, it is very important to impart excellent strength and impact resistance to the structural members of bodies and it is also very important to impart excellent impact resistance to the leaf springs and others which are subjected to the repetition of impact load in order to ensure long-pending reliability of automobiles. Conventionally, automotive parts have been made lighter by use of the above-described FRP in comparison with automotive parts made of metal. However, automotive parts using FRP cannot be said to be satisfactorily light because these automotive parts made of FRP need to maintain the same strength and impact resistance as those of automotive parts made of metal.
Moreover, lowness of elastic modulus, namely excellence in flexibility, is also one of the very important properties of a fiber-reinforced composite material depending on applications. In particular, the flexibility of sporting goods is said to exert a significant influence on the feeling of the players. For example, a golf club using a flexible shaft is said to be beneficial to beginners and female golfers. This is because, although their swing speed is slow, the use of such a club enables them to increase the head speed of the club so that a longer flying distance of ball can be expected due to the pliant suppleness of the shaft. Similarly, flexible ski boards are said to be suitable to beginners or women playing golf because turns utilizing the flexibility of boards become possible.
Conventionally, in order to obtain the above-mentioned shaped articles having low rigidity, glass fibers have often been used. However, the use of glass fibers is associated with disadvantages. For example, since the density of glass fiber is larger than that of carbon fiber or the like, the use of glass fiber brings about increase in weight of the shaped articles. Further, since the compressive strength of glass fiber is low despite its high tensile strength, a shaped article made of a glass fiber-reinforced composite material does not exhibit sufficient strength. Furthermore, in the aspect of vibration characteristics, since the vibration damping characteristics of glass fibers are inferior to those of carbon fibers, a shaped article made of a glass fiber-reinforced composite material exhibits a feeling inferior to that of a shaped article made of a carbon fiber-reinforced composite material.
Meanwhile, when designing FRP, it must be taken into account that FRP has anisotropy. That is, although high strength and elastic modulus are exhibited in the direction of orientation of the reinforcing fibers, both of strength and elastic modulus are extremely low in the direction at a right angle to the direction of orientation of the reinforcing fibers because the tensile strength of the matrix resin and the bonding strength in the interface between the matrix resin and the reinforcing fibers dominate the characteristics in that direction.
Further, caution must be exercised to the fact that delamination is liable to occur in FRP laminated materials. For example, in the case of FRP used for aircraft, a flying body such as a bird may collide with the body of the aircraft during flight or otherwise a member of maintenance staff may inadvertently drop a tool such as wrench, spanner, or the like on the body of the aircraft during maintenance service on the ground. These impacts cause serious delamination inside the FRP laminated materials and a significant reduction in mechanical properties, in particular compressive strength, thus presenting a big problem.
On the other hand, since repeated impact takes place in leaf springs of automobiles, it is very important to increase interlayer fracture toughness. As to structural members of bodies, it is also important to inhibit the delamination in order not to aggravate the mechanical properties by impact caused by, for example, an accident.
Heretofore, various methods have been employed to increase interlayer fracture toughness of FRP by making the matrix resin more tenacious or by using thermoplastic resins particles or short fibers between the layers of an FRP laminated material. However, these methods have been necessarily associated with disadvantages such as increase of process steps.
OBJECTS OF THE INVENTION
An object of the present invention is to solve the problems of the prior art and to provide a fiber-reinforced composite material which is lightweight and has excellent strength, impact resistance, and flexibility.
Another object of the present invention is to solve the problems of the prior art and to provide a fiber-reinforced composite material which has excellent interlayer fracture toughness and mechanical properties less vulnerable to impact load.
SUMMARY OF THE INVENTION
First, the present invention provides a plate- or beam-like carbon fiber-reinforced composite material having carbon fibers aligned nearly parallel to the longitudinal direction, characterized in that the carbon fibers have a tensile elastic modulus of 5 to 160 GPa, a strain at compressive break of 1.7 to 5%, and a density of 1.5 to 1.9 g/cm
3
and further in that the composite comprising said carbon fibers exhibits a mode I interlayer fracture toughness G
IC
(at 5% offset in accordance with JIS K 7086) of 0.15 to 4.5 kJ/m
2
, a mode II interlayer fracture toughness G
IR
(at propagation in accordance with JIS K 7086) of 0.20 to 5 kJ/m
2
, a mode II interlayer fracture toughness G
IIC
(at 5% offset in accordance with JIS K 7086) of 0.45 to 9.5 kJ/m
2
, and a mode II interlayer fracture toughness G
IIR
(at propagation in accordance with JIS K 7086) of 0.5 to 10 kJ/m
2
, and the composite produces no delamination by an impact energy of less than 1.4 J/mm in the test of compression after impact in accordance with JIS K 7089.
Second, the present invention provides a sandwich-structured plate- or beam-like carbon fiber-reinforced composite material made up of at least one plate- or beam-like fiber-reinforced composite material comprising carbon fibers having a tensile elastic modulus of 200 to 1000 GPa such that additional carbon fibers are disposed on the front and back faces or the front and back outermost faces of the composite material, characterized in that said additional carbon fibers have a tensile elastic modulus of 5 to 160 GPa, a strain at compressive break of 1.7 to 5%, and a density of 1.5 to 1.9 g/cm
3
and further in that the composite comprising said additional carbon fibers exhibits a mode I interlayer fracture toughness G
IC
(at 5% offset in ac
Arai Yutaka
Nakanishi Tomohiro
Ohno Hideyuki
Soda Yoshio
Takemura Shinichi
Copenheaver Blaine
Nippon Mitsubishi Oil Corporation
Scully Scott Murphy & Presser
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