A composite material is essentially heterogeneous in which at least two raw materials are combined. This heterogeneity distinguishes composites from other conventional materials. Thus composite properties such as stiffness and strength should be discussed from the properties of each constituent materials. A micromechanics deals with the above problem. A so-called rule-of-mixture may be classified to the micromechanics, although it is too primitive.
It is well known that the strength of each individual fiber is not uniform. If a tensile load is applied to a unidirectional composite, the weakest fiber will break first and the stress redistribution will take place in the composite. Hence the failure process of composites must be discussed statistically. This is the primary subject of the micromechanical approach. In a composite material, failure can occur at fiber, matrix, and/or fiber-matrix interface which makes the failure process more complicated. This is also a subject of the micromechanics.
This paper reviews recent developments of the above micromechanical strength theory of continuous fiber composites, short fiber composites, and hybrid composites.
A paper survey was performed with respect to Materials system. The keywords which are used to collect the abstracts of papers concerned with the concept of materials system engineering are :
1) nonferrous metal
4) composite material
6) inorganic material
8) clad metal
9) fiber reinforced plastic (FRP)
The results of paper survey were tabulated in order to material and methodology. It will be suggested from the results where the new concept of material system engineering is located.
Many studies have been made of optimum reliability design of structural systems. However, they are limited to simple types of structures. This main reason is no efficient methods are available for calculating failure probability of structures. Another reason is due to the fact that, in spite of the high development of structures for making structural analysis by using digital computers, they make their effectiveness decrease for complex structures.
In the present paper, a design method of calculation to solve these problems have been proposed and incorporated into the optimum reliability design. The optimum reliability design problem was treated to determine a structure having a minimum weight or cost under the constraint on the allowable probability of each structural elements.
In this approach, a stochastic finite element method is applied to structural analysis and a reliability analysis of composite materials accounts for statistical variation of material strengths. In addition, numerical examples are presented to demonstrate the validity of the proposed method.
This paper deals with influence of the reinforcements on the variation of tensile strength of the glassfiber reinforced unsaturated polyester resin laminate with U type notch. The reinforcements treated in this experiment are plain cloth and chopped strand mat. The main results obtained are summarized as follows;
1) The mean value of tensile strength of the specimen with notch is lower than that of the flat specimen, and the strength degradation ratio of Cloth FRP is smaller than that of Mat FRP.
2) The coefficient of variation of tensile strength of the specimen with notch is larger than that of the flat specimen. This tendendy is remarkable in Mat FRP.
3) The mean value and the coefficient of variation of the strength degradation ratio were obtained by applying the first order second moment method.
This paper is concerned with the residual stress and deformation of thermosetting resin strip produced by rapid cooling under three cooling conditions, that is, both sides cooling, single side cooling without constraint and single side cooling with constraint on warp. These are the most simplified models for expressing the cooling process of resin molding. First, the theoretical value of the residual stress and deformation of the thermosetting resin strips under the three cooling conditions were obtained by the liner viscoelastic theory. The specimens were then actually subjected to rapid cooling in the three cooling conditions. After rapid cooling, the residual stresses and deformations were measured by the layer removal methed. The experimental and theoretical results are then compared and discussed.
Laminated composite materials which have symmetrical stackings and of which plies are not orthotropic materials shows coupled deformation between bending and twisting. Such a coupling is considered unfavorable in the designing of structural members so far. Novel performances not available with conventional materials, however, can be produced when the coupling is introduced appropriately.
In this paper, designing method of laminated fibrous composite materials with required bending-twisting coupling is proposed. The method is based on the graphical representation of the feasible design region on the flexural and coupling lamination parameter diagrams introduced newly in this paper. The stacking construction of the laminate whose flexural and torsional properties are satisfied with given conditions can be obtained by the proposed design procedure.
To investigate the time and temperature dependences of the flexural strength of cross-ply laminated CFRP, three-point bending tests were conducted at various temeperature and strain rates. The flexural strength of cross-ply laminated CFRP showed a remarkable dependence upon time and temperature. The master curve for this strength was constructed based on the thermo-rheologically simple properties. The time and temperature shift factors were quantitatively in good agreement both for the flexural strength of cross-ply laminated CFRP and the tensile strength of matrix epoxy resin.
The fracture of cross-ply laminated CFRP under three-point bending was classfied into the two modes ; a) breaking on only the compression side at the loading point of specimen and b) microbuckling of fibers on compression side in the region of high temperature.
A general framework is presented for a development of data processing and management information system in materials testing. The design process of all major structural system is dependent on the design target which is a controlling factor in the decision making process within the constraints of economy and quality assurance. In this decision making process, the information from the materials test plays a role to evaluate the response of structural element as one of the simulation for the situation to which the structural system will be subjected actually, since a structural system is subjected to various environment condition.
This paper deals with the new system development which consists of:
1) materials testing system with laboratory automation system,
2) data processing and information network system, and
3) data-base and management information system.
The system is developed in order to construct the multi-purpose data management system. The feature of the present system is in the idea that the information communication network combines the fatigue test machine with personal computer which collects and arranges the materials testing data, and computer center which has the data-base for the information management. In the paper, the organization of total system and the methodology of network and data management system are also demonstrated.