The application of advanced composite materials is only limited in aerospace field, sports and leisure goods under present conditions. What to do, technologically and politically, for the purpose of spreading out the application into infrastructural field, industrial and public use from this time is proposed.

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In this paper first the features of offshore structures which the author handled while he was working for Hitachi Zosen are introduced. They are jack-ups, semi-submersibles, jackets and the floating airport. Then the problems relating to materials of offshore structures are explained. They are problems regarding the materials of legs of jack-ups and those of high strength steel used for offshore structures.

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In this report, researches on hydrogen embrittlement of iron and low strength steels are reviewed. The characteristic features of the fracture due to hydrogen embrittlement of commercial steels, the influnce of hydrogen on the plastic deformation and fractographic approaches are discussed. Recent progress of the studies has made possible to get the solution for some important problems and to understand the kinetics of hydrogen embrittlement. Its mechanism is, however, still under the discussion. Further researches especially giving the direct evidence are needed. As the fracture process of hydrogen embrittlement depends on the conditions such as hydrogen charging, stress conditions, temperature of testing, etc., it may not be explained with a unique mechanism.

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A fracture criterion based on the concept of linear notch mechanics (LNM) for predicting the fracture load of rigid plastics bars and FRP plates containing stress concentrations is subjected to further experimental scrutinization. An experimental program is presented which the effect of notch-root radius on the fracture. This is accomplished by obtaining experimental data on several thermoplastics and a glass-fiber/epoxy laminate containing stress concentrations for a wide range of notch geometries. The experiment shows that the maximum elastic stress at the notch root when the specimen fails is governed by the notch-root radius only. On the basis of the concept of LNM, the experimental results can be clearly explained, and a limiting condition for the fracture of rigid plastics and FRP containing notches is determined.

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High strength type CF/Epoxy composites have been applied to many aircraft and spacecraft structures. The composite laminate, however, has week point at interlamina strength. It is well known that the plates easily delaminate by low velocity impact such as tool drop and fatigue loading. Therefore, there are many studies to evaluate the delamination resistance. In those, stick-slip phenomena has been reported in mode I delamination resistance measurements. In this study, the stick-slip phenomena was examined in detail with CF/Epoxy unidirectional lamia by changing loading speed of mode I delamination tests. Additionally, crack configurations were observed by using a scanning acoustic microscope during testing. The observation made it clear that nonlinearity between load and displacement relations reveals directly the beginning of the delamination crack propergation. Based on many experimental results, models of source of fiber bridging and delamination toughness were proposed and successfully verified by experiments.

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Fatigue tests on FRP (SMC) were made on the tensile-tensile conditions under two-step loading and the effects of stress change on stiffness ratio were investigated. The results obtained were as follows: (1) It was found that the degradation behavior of SMC due to cyclic loading is not able to estimate using Miner's law because the fatigue life is usually widely scatter on about a three-digit number. The new method of the estimation of degradation curve was proposed using the linear-properties of them recoggized from the statistical analysis. (2) The experimental curves of the stiffness ratio before and after change of stress were good fit to the estimated curves except the specimen being relatively weak in the case of the stress increase. Remarkable degradation of stiffness ratio at first cycle after the stress increase is found on the weak specimen. (3) It was found that the degradation phenomenon on the weak specimen depended on the crack growth phenomena observed on the surface of specimen.

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A series of titanium carbide (TiC)-graphite (C) composites was sintered by hot-pressing with condition of 2000℃ for 2h in Ar gas atmosphere under a pressure of 40 MPa. Monolithic TiC exhibited a grain growth with an average size of 15 times larger than that of the starting particles, whereas dispersed graphites well prohibited the grain growth of TiC grains in the composites. The graphites lay in the boundaries or their triple points of the TiC grains, and the graphites delaminated occasionally to overlay the TiC grains, which implied a good sliding properties due to solid lubricant action of the graphite. Although the relative density of the composites increased at 5 wt% graphite addition, it gradually decreased with the increase in graphite addition due to low sinterability of graphite. Room temperature flexural strength was improved by adding graphite, which would have been resulted by the inhibiting effect of grain growth by graphite dispersion. Fracture toughness was also improved mainly through the crack deflection caused by the dispersed graphite phase. Addition of graphite resulted significant improvement in sliding properties of TiC against copper in dry air. The wear of Cu occurred by adhesion, wheres that of the TiC-C composites was minimized by delamination of graphite phase.

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The present paper deals with the identification problem of materials properties using measured deflections in a symmetric laminated plate under a concentrated force. The bending stiffnesses of symmetric laminated plates are evaluated from the measured values of bending deflections, which leads to the estimation of the material properties of constitutive unidirectional composites and also the estimation of the lamination parameters governing the laminate configurations. The present identification method makes use of the Fourier series representations of the bending deflections. The bending stiffnesses as well as the loading location can be evaluated precisely by the present method. It is shown that the identified material properties rapidly converge to the exact ones with the increase of the number of measured deflections.

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In fracture problems, stress intensity factors obtained theoretically or by experimental analysis have been effectively utilized in analytical evaluation of the effect of cracks. Use of the caustics method to determine the stress intensity factors of two-dimensional cracks has been established theoretically and experimentally. However, relatively few experimental analysis concerning the three-dimensional crack by using caustics method have so far been conducted. In this study, a combination of the optical method of caustics and photoelastic stress freezing technique for measuring the stress intensity factor K_Ⅰ, K_Ⅲ of three-dimensional cracked-body problems is presented. The mixed mode stress intensity factors, K_Ⅱ and K_Ⅲ for three-dimensional crack under the complex stress condition are separately determined by using the caustics and photoelastic methods.

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The axial impact of two finite length rods of unequal cross-sectional area and dissimilar material was studied experimentally and theoretically. With the help of the strain gages fixed on the curved surface from the impact end, the time history of the strain was measured. The wave speeds and impact stresses of incidence, transmission and reflection were calculated using this strain history. These experimental values were nearly equal to the theoretical values.

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