The concepts or the definitions of composite materials and material design, the constraints which must be considered in the material design process, and the development of material design methodology are described with the focus on the material design in the new era. The ideas for creating intelligent materials and easy-to-dispose materials are presented.
The author has been working for Hitachi, one of the leading manufacturers of electrical machinery in Japan. He specializes in electrical insulation. Insulation systems are typically composed of resins and reinforcements, which are glass fibers, mica flakes, inorganic fillers, organic fibers, etc. Nowadays, insulation systems are being expected to withstand severer stresses, mechanical as well as electrical, than before. The author, as an insulation systems designer, has experienced several chances to estimate mechanical properties of reinforced plastics, that is, mica flake reinforcement theory, interlaminar shearing test methods, tensile properties and thermal contraction at cryogenic temperature, glass/resin interface, etc.
The author says that he has given up his investigation halfway, since, he says, he does not specialize in mechanical material systems engineering. In this paper are described some notes on mechanical properties of some FRPs, which he is expecting some mechanical researchers should investigate further.
The material design of fibrous composite materials are composed by the design on mechanical properties of elemental specimen and structural members.
The mechanical properties mean the elastic modulus, stiffness and strength. These items are almost completed about various topics under the condition of static load.
The future trend of material design is considered as the following items, time and atomspher dependent design and interfacial design fiber orientation design, etc.
Recently, in the Japanese FRP boat industry, a marked tendency to construct still more larger boats or higher speed small boats is seen. The forward bottom shell of these boats has the tendency to be exposed to higher water impact pressure and suffer shell delamination damage or breaking of bottom stringers.
In this paper, special design considerations on the bottom shell of high speed boat are summerized from the “Standard FRP boat construction method”, which is recently published by the standards drafting committee of the Japan Ship and Boat Manufacturer's Association. The basic FRP laminating process and secondary bonding method of joints are related in detail.
The optimum design techniques for mechanical structures are composed of the methods changing a boundary shape of structure and the material properties such as the specific gravity and the Young's modulus. In this paper, the survey for these methods is presented by using the simple truss design models. From the result two important problems are pointed out. One is on the design techniques to determine an optimum layout of mechanical structure and other on the formulation techniques of material design problem. On these problems some ideas from the author's papers presented previously are proposed and discussed.
The fiber reinforcements to improve the strength are discussed by use of fiber reinforced plastics. The strength laws of unidirectional fiber reinforced plastics of carbon fibers and Kevlar are formulated on the basis of the experimental results of the strengths under combined stress state. By combining the unidirectional strength laws and the laminated plate theory, the strength of angle ply laminated plates are obtained under combined stress states. Using the strength laws of various ply angles, the optimum fiber orientations are determined for given combined stress states. The specific strength of fiber reinforced plastics with the optimum fiber orientations are compared with metal specific strength and the superiority of fiber reinforced plastics are shown.
As an application of fiber reinforced plastics to machine elements, fiber reinforced plastic gears are presented. The gear teeth are reinforced along the teeth configurations by carbon or glass cloths. The bending strength of the reinforced tooth is investigated by the stress analysis. The effects of reinforcing material constitutions on the bending strength are discussed. It is shown that the fiber reinforcement is effective to improve the tooth strength of plastic gear.
Composite materials containing two or more different types of fibers are called “hybrid” composite materials. The importance of hybrid composites is related to (1) the wider range of spectrum on materials properties, (2) the good balance between strength, rigidity and toughness of composites, and (3) the possibility of obtaining a more complicated multi-load-path structure.
In this paper, a materials design guideline of hybrid composites is described from three viewpoints of interdisciplinary, integration and interface and some typical examples are given including the effect of interfacial strength on fracture toughness of composites. The characterization of the so-called “hybrid” effect are reviewed in terms of first failure strain enhancement, modified rule of mixture and condition of multiple fracture. A new simulation model is introduced in order to discriminate the difference between failure process due to hybrid constitutions, in which the interfacial debonding between fibers and matrix is taken into consideration as well as the fiber fracture.
Recently the design of composite materials has received much consideration ; particularly metallic, organic and inorganic materials. These composite materials are considered easy to design because they are made primarily of artificial materials. Fiber reinforced plastics made through the molding method are even more easily designed. Design for impact on these materials, however, is not as simple a process as that for other properties.
This paper considers the impact properties of composite materials and how they relate to the designing of the structure of materials used in many industrial products. Follwing this, the relationship between impact properties and the constitution of composite materials is examined as well as material properties which are relevant in designing composite materials for impact.
This paper is concerned with the optimization of laminated composite flat plates and circular cylindrical shells for buckling. The plates and shells are composed of N orthotropic layers. Each layer is assumed to have the same thickness and an equal number of fibers in the + αi, and －αi directions with respect to the reference axis. The directions of the fibers in all layers are sought which give the highest buckling load. A mathematical optimization technique (Powell's method) is applied to this problem. The numerical calculation is made for boron/epoxy composite.
Methods for designing laminated composites which have required in-plane and/or flexural stiffness or have the maximum buckling strength are reviewed.
The characteristics of the parameters which were first introduced by Tsai and Hahn as geometric factors to evaluate the stiffness of composites and are referred to as lamination parameters in this paper are examined and it is shown that these parameters can play an important role in material design problem as well. The key feature of the method lies in the clarification of the feasible region of the lamination parameters. Design specifications or constraints in material design problem can be graphically represented in this feasible region, and optimum fiber orientation angle and stacking sequence can be obtained easily by using lamination parameter diagram.
Among many outstanding characteristics of modern composites that can be exploited for structures, the superior strength of a laminated construction remains one characteristic that deserve critical evaluation. Bidirectional laminates will be examined from the st ength standpoint. Design options and the relative strength of composite laminates with respect to an aluminum construction will be presented.
A series of research works on the analytical approach for estimating the burst strength and on the optimum design of filament-wound(FW) pressure vessels are summarized.
The mechanical behaviors and the structural optimum design are discussed from the two viewpoints of (ⅰ) initial failure and (ⅱ) ultimate fracture, taking account of the four kinds of fundamental failure mechanisms of unidirectional composites. The ultimate fracture after initial failure is analysed by considering the degradation of stiffnesses corresponding to the initial failure modes. The two types of vessels, that is, the helical-wound cylindrical ones and the filament-wound ones which are wound together with domes en bloc are discussed.
The experiments on such FW vessels showed good agreements with the analytical predictions not only of the burst pressures but also of the burst behaviors or the pressure-strain curves up to ultimate fracture. Based on these strength analyses and experimental evidences, the optimum winding angles, lamination ratios and dome shapes are proposed.
Several kinds of rocket chambers were developed based on the above-mentioned structural analyses and optimum designs. Some of them were launched successfully giving a considerable weight reduction compared with the previous metal chambers.
A method to calculate the divergence speed of a swept-forward wing made of cover skins of fiber reinforced composite materials as an eigen-value problem of differential equation is proposed. The deformation of the wing under the concentrated force and moment in an aerodynamic chord is calculated, and a concept of a pseudo elastic axis is derived as a result. The two-dimentional approximation yields a simplified formula of the divergence speed which is expressed in the use of the position of the pseudo elastic axis. It is concluded that the optimum constitution of lamination for the prevention of divergence should be selected taking the position of the pseudo elastic axis as a target. A numerical example using carbon-expoxy composites shows that until 30° of swep-forward angle it is easy to prevent divergence by the selection of optimum constitution of lamination.
The presented study is concerned with the probabilistic design method for the strength of the fiber reinforced composite materials under the plane stress state. This method is established by applying the advanced first order second moment (AFOSM) method to the tensor polynomial theory proposed by Tsai and Wu. The laminate composite is treated as a homogeneous and orthotropic material. The tensor polynomial theory is adopted as the failure criterion becauce of covering various theories based on the maximum work criterion. The proposed theory requires only the mean values and the coefficients of variation of both the principal strength components and the applied load by using of AFOSM method. Safety index is used as the scale of reliability in stead of the probability of survival. It is shown that the Lagrange multiplier formulation can be used to evaluate the safety index and the location of the design point. The numercal results by AFOSM method are compared with those by the first order second moment method. Thus, it is obvious that the probabilistic design with AFOSM method is excellent and effective enough for practical use.
This paper deals with the natural vibration characteristics of laminated composite plates. The vibration frequencies of laminated plates are analyzed based upon the classical lamination theory.
In the first part of this paper, it is shown that the vibration frequencies are lower in the laminated plates than the ones of the orthotropic plates due to the coupling effects. It is also shown that the vibration modes of the off-axis plates are quite different from the ones of the orthotropic plates.
In the second part, the optimal laminate configuration to maximize the fundamental frequency is investigated for the orthotropic laminated plates. It is shown that an angle-ply laminate gives the optimal laminate configuration for the simply-supported plates, while a cross-ply laminate gives it for the clamped plates.
Such the mechanical properties, which are dependent upon the time and temperature, as the transversal relaxation modulus, the longitudinal and transversal tensile, compressive and flexural strengths, of unidirectional CFRP are investigated in connection with epoxy resin of its matrix. These mechanical properties of CFRP show thermo-rheologically simple behaviors in same manner as the mechanical properties of matrix resin. And them the obvious quantitative relations between these mechanical properties of CFRP and that of matrix resin are obtained.
Based on these results, new selection rule of the matrix resin for unidirectional CFRP which have required mechanical properties at arbitrary time and temperature are proposed.