Glass fiber reinforced polyester laminates (GRP) have recently found a wide industrial application and the mechanical properties of the laminates have often been reported. However, few are really studied based on a well-organized experimental method.
The purpose of our investigations is to study the following effects using the orthogonal array table type L₈₁.
(1) The effects of the kinds of base materials in each layers on mechanical properties of GRP.
(2) The effects of the molding conditions on mechanical properties of GRP.
The test samples were prepared by the hand lay-up molding method with three kinds of base materials which are shown in Table I and Fig. 3.
Using the test pieces from the samples, tensile strength, tensile modulus, flexural strength, flexural modulus and thickness were measured in the atmosphere of 20±°C, 65±2% R.H. and the following results were obtained.
(1) The force applied to a tensile test piece seems to be uniformly distributed into each layer of the laminates.
(2) When the laminates is used as a bent member, the effects of the kinds of base materials are scarcely influenced by the adjacent base materials, and the farther the base material is located from the central layer, the larger become the effects. In ten plies of laminate, the effects of the kinds of the interior four base materials can be neglected.
(3) It is advisable not to use woven roving on compression side of bent members.
(4) The slower the rate of resin curring is, the stronger products can be obtained.
(5) Differences of breaking stresses and moduli are not noticeable between the samples molded by the man of experience and one of inexperience.
(6) The screw roller brought a good result in lamination of satin-like weavings, and mohair and wool rollers brought good results in lamination and resin impregnation of the woven rovings. The washer roller gave only bad result for all base materials.
(7) After-curring of the sample caused lower tensile strength and modulus with higher flexural strength and modulus. After-curring of the test pieces subsequent to machining caused higher strength and modulus than curring prior to machining.
(8) Wider specimens improve apparent breaking stress and modulus.

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The carbon fiber and the glass fiber reinforced epoxy resin can be understood as a kind of hybrid composite and this material is now attracting attention of many engineers for it's excellent properties. This report describes the mechanical properties of the material. The characteristic properties as follows:
(1) The Young's modulus of glass fiber reinforced epoxy resin is increased remarkably by the carbon fiber.
(2) The strength of hybrid composite is shown by two peak stress.
(3) The existence of both optimum modulus ratios and volume fraction of the fibrous reinforcements is suggested considering the energy absorption.

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The 1st FRP symposium were held on 27-28, March, 1972 at the Osaka Science and Technical Center. This record summarizes the note of the panel discussion. The theme of the discussion was "Reliability of the Strength of FRP and it's Design" chaired by Dr. S. Shimamura. Also the following members were nominated as panellers:
Dr. T. Hirai, Mr. K. Komaki, Mr. T. Tanaka, Mr. Y. Hatogai, Mr. H. Kida.

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This paper presents a numerical and experimental analysis of the influence of wire strain gage on strain for materials with low modulus of elasticity. A numerical analysis was made using two-dimentional model and the finite element method was applied. The results were compared with those obtained by the photoelastic analysis and the bending test.
The results are as follows
(1) When the strain of materials with low modulus of elasticity is measured by the wire strain gage, the wire strain gage stiffens the base materials.
(2) This stiffning effect increases with an increasing stiffness ratio, E_g/E_m, where E_g and E_m are modulus of elasticity of the wire strain gage and the base material, respectively.
(3) For example, in the case of plastics, the strain measured by the wire strain gage is about 80% of true strain.

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In our previous paper, the dynamical mechanical model under the uni-axial load has been established and the theoretical analysis showed good agreements with the experimental results. This paper presents the multi-axial model which is developed to analyze the behavior of composite materials. As a result of the study Poisson's ratio was found to be the stress dependent and a new concept regarding composite materials was suggested. Furthermore, the behavior of fracture mechanism for composite materials became clear using the mechanical model presented here.

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The objective of this study is to investigate the mechanical properties of fiber reinforced plastics subjected to an arbitrary stress.
To analyze the mechanical properties of FRP mathematically, the author set up a mechanical model composed of four elements; i.e. two springs, one dashpot and one slider. Assuming the material as a visco-plasto-elastic body, these elements were combined in order to give a reasonable explanation for the mechanical behavior of FRP.
Thus, we can express the property of the material by setting up a differential equation regarding stress, strain and the time. If either stress or strain was determined as the function of the time, the other can be mathematically solved and the relation of the stress and the strain can be defined.
Based on the experimental stress-strain diagram of FRP observed at the tensile test of the constant loading velocity, the approximate value of the modulus of the each parameter in the model could be estimated. When the repeated stress was given to the material as the function of the time elapsed, by comparison of the experimental results with the calculated results obtained from the differential equation and by repeating the same operation several times in this way, the accuracy of the estimated moduli could be increased. In this method, the numerical calculation and the automatic graph drawing were operated by the electronic computer.
As the results of this investigation to determine the characteristic equation of FRP, the behavior of the material at the stress which is supposed to occur can be estimated beforehand.

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It is important to choose a suitable jointing method for the construction of FRP structure by jointing the parts of FRP. In this study, jointing was performed by means of adhesives. The selection of adhesives, the bonding condition and mechanical properties of bonded joint were examined using two types of substrates, FRP and SMC.
The effect of number of ply and adhesive pressure, interlaminar shear strength (ILSS), flexural strength and Izod impact strength of bonded beam were also studied. The results obtained are as follows.
(1) When non-bonding material is at or near the substrate surface, the surface preparation by sanding or cleaning causes the substrate failure and the bond strength becomes greater than the untreated one. On the contrary, when non-bonding material is with the substrate, it is necessary to choose the surface preparation method of substrate depending on the type of adhesives.
(2) Since the bond strength is greatly affected by the flexural rigidity of substrate, it seems to be necessary to refer to the flexural rigidity when the bond strength is compared.
(3) The strength and rigidity of bonded structure depend on the properties of substrate. In the case when the lateral load is worked on bonded structure, if suitable rigidity of substrate, adhesive pressure and number of ply for shearing force are chosen, the shearing failure does not occur on adhesive layer and the strength and rigidity of bonded structure does not decrease for flexural force.
(4) For impact, bonded structure is advantageous to unbonded one with respect to impact strength. Especially for the direction of impact, the strength of bonded structure remarkably increases if the volume of adhesives is increased.

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The effect of lamination on flexure behavior of Fiber-Reinforced Plastic Composites was described emphasizing flat laminate and the FRP-FRTP or CFRP-FRTP composites. Examined flexure test variables were layup sequences, span to depth ratio, number of plies and loading speed. At the bending rate of 0.1cm/min. to 1.8×10⁴cm/min., a correlation of statical flexure with Charpy impact was studied. Furthermore, remarkable improvements in properties of Plastic Composites were obtained. The results are as follows.
(1) The reinforced polyester laminated composites demonstrated an increase in ultimate flexural strength with increasing rate of bending. The Charpy impact strength per unit cross section area has remarkably increased with increasing laminate depth or number of plies. The effect of notch on flatwise Charpy impact strength was negligible.
(2) FRP-FRTP composite, fabricated with PVC-GF and Epoxy-GF layers, has shown great improvements in flexural and impact strengths. Flexural strength increases two times of that of FRTP only, and flexural modulus of elasticity increases to almost 1.5 times. Charpy impact strength also increases to two times.
(3) CFRP-FRTP composite, fabricated with Nylon 6-GF and Epoxy-Carbonfiber layers, shows higher distortion energy than FRP-FRTP composites. The flexural and impact strength and the flexural modulus are markedly improved by laminating with CFRP. Charpy impact strength increases more than 4 times, and flexural modulus increases almost 3.5 times of that of FRTP.

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This paper deals with the theoretical aspects of laminated composite materials subjected by torsional stress and the effect of the void in matrix on their static strength. Three kinds of internal resisting moments in the materials take place when the torque moment act on the laminated composite materials perpendicular to the direction of laminated layers.
(1) The moment caused by the inter-laminae shear stress.
(2) The moment due to the distortion of each layer.
(3) The moment due to the bending of the laminated layers apart from the center of torque moment applied on the materials.
The torsional strength and the torsional rigidity of the laminated materials are calculated by summing up these three moments.
The calculated results were compared and in good agreement with the observed ones.
An empirical formula to predict the internal damage of the materials subjected to the stress is given as the result of the water immersion tests in order to examine the effect of void upon the static strength.

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This paper describes the influences of the glass content and the environmental temperature on the static behavior of glass fiber reinforced plastics (FRP) subjected to compressive load in the direction perpendicular to the laminated layers. (See Fig. 1 (b))
Although several papers were reported associated with the compressive strength of FRP laminated materials, in most case, most of the studies have been confined to the compressive stress in the parallel direction of the laminated layers and few papers are reported regarding the compressive stress in the perpendicular direction (the case shown in Fig. 1 (b)).
A method developed for the theoretical analysis of anisotropic laminated materials was applied to the latter.

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