Sadao Amijima

Microscopic fatigue processes in a plain-weave glass-fibre composite

Abstract This paper focuses on the microscopic damage and progressive failure of a composite reinforced by plain-weave glass cloth under tensile fatigue loading. The fatigue process was divided into three stages like that of multi-directional laminates. It was found that the internal damage at each stage (matrix cracks, debonds in the weft, successive debonds in the warp and ‘metadelaminations’ between warps and wefts) occurred near the cross-over point of the fabric. The modulus decay mechanism was explained by considering the progression of this internal damage. From the end of the first stage to the beginning of the middle stage, a characteristic damage state (CDS) (called a ‘meta-CDS’) was observed. It was found that woven composites have a unit area of damage accumulation (called a ‘unit cell’) and the damage of each unit cell and its distribution control the total fatigue damage of the material.

Nonlinear Stress-Strain Response of Laminated Composites:

This paper presents a simplified method of predicting the nonlinear stress-strain curves upt to the tensile and compressive failures for an unidi rectionally orthotropic lamina, symmetric biaxial and triaxial laminates. The analytical procedure is based on the classical Laminated Plate Theory (L.P.T.). With applying L.P.T. to the small sress or strain increments of the stress-strain curve, nonlinear stress-strain curve is continuously predicted for various laminates. Comparisons are made between analytical predic tions and experimental results. As the results, the nonlinear stress-strain curves for various cases could be estimated and the results have consider ably good agreement with experimental ones.

Progressive Nature of Fatigue Damage of Glass Fiber Reinforced Plastics

The progressive nature of fatigue damage due to cyclic loading on glass fiber reinforced plastics was studied. The residual strength of the specimens subjected to fluctuating tension with a given number of cycles was measured, and the number of cracks developed in the samples were counted by means of a microscope. From our test results, the progression process of fatigue damage in the composite materials can be divided into three stages.

Study on Strength and Nonlinear Stress-Strain Response of Plain Woven Glass Fiber Laminates under Biaxial Loading

Strength and stress-strain properties are investigated for plain woven glass fiber laminates using thin tubular specimens under biaxial static and cyclic loadings. Some composites show large distortion and fiber reorientation close to failure under biaxial load ing. For such composites the usage of the 2nd Piola-Kirchhoff stress instead of the nominal stress is proposed for strength evaluation. The experimental result reveals that the Tsai-Wu criterion fits the biaxial strength expressed by the 2nd Piola-Kirchhoff stress much better than the strength expressed by the nominal stress. Strong interaction between axial and shear deformations is found beyond the knee/yield points while, within the elastic range no interaction is found between the axial and shear stiffness. Fiber misalignment with the loading axis affects the observed stress-strain behavior under cyclic loading. More than two S-S curves are distinguishable when the fiber misalignment is higher than 2°. Such stress-strain relations are successfully simulated using an incremental method in conjunc tion with updating fiber orientation. Good agreement between the calculated result and ex perimental one confirms that the proposed model which considers fiber misalignment can explain the observed stress-strain response under biaxial fatigue loading.

Fatigue Behavior of Plain Woven Glass Fiber Laminates under Pulsating Tension/Pulsating Torsion Combined Loading.

Fatigue Strength and stress-strain response of plain woven glass fibric laminates subjected to pulsating tension/pulsating torsion combined loading were studied in this paper. In order to evaluate the biaxial fatigue failure strength, the normalized fatigue strength that a cyclic biaxial stress is divided by the static strength was used in S-N curves. According to the test results, it is found that all data locate in a slightly wide band on the S-N plot in spite of different biaxial stress ratios, but the tendency that the slope of the S-N curve becomes low in case of a high shear stress component, can be distingushable. The tendency of modulus decays in both tension and shear even under combined loading is almost the same as those under uniaxial tension and pure torsion loadings, respectively. The direction of matrix cracking seems dependent on the principle stress direction under pulsating tension/pulsating torsion combined loading although it is also strongly influenced by fiber orientation.

Study on the V ribbed belt (Rib deformation and mechanism of force transmittion.

リブ付Vベルトの場合,ベルト抗張帯とプーリ間の力の伝達はリブおよびリブと抗張帯をつなぐ底ゴムを通してなされる.この点に注目して,本研究はベルト抗張帯からプーリへの力の伝達機構を明らかにした.すなわち,ベルト微小長さ部分について抗張帯に作用する力と抗張帯-プーリ間の相対変位(リブ変形)との関係の理論式を導いた.理論の有効性は実験により確かめた.また,リブの変形は荷重履歴依存性のあることもわかった.

On the Tensile and the Bending Strength of the Glass Fiber Reinforced Laminated Composite Materials

Recently we have seen many experimental data published on the static properties of the glass fabric reinforced plastics (F. R. P.), but there have been few reports so far which have treated the influence of environmental temperature and the glass content of the specimen.It is intended in this paper to describe (the influence) of the glass content and the environmental temperature on the static behaviour of F. R. P. in which satin woven, plane woven and roving woven fablics are used for reinforcement. On the other hand we made analysis to predict the elastic moduli in flexure of composite laminates and determined their flexure strength by the use of these calculated moduli with the assumption that the F. R. P. materials will keep their elastic properties till the moment of fracture.