The stress measurement by X-rays is based on the variation of lattice spacings of metallic crystals due to stress. It has been noted as a unique method of measuring nondestructively the local stress, especially residual stress. Recently, this X-rays stress measurement has been applied in a very wide field of engineering studies in consequence of development of X-ray equipments as well as improvement in measuring devices. On the other hand, the stress measurement with a brittle lacquer coating is based on the crack development perpendicular to the tensile strain when the loading exceeds a certain value. In this method, the direction of principal stress and the position of stress concentration can be determined directly from the crack patterns on the specimen surface. In comparison with other stress measuring methods, however, the lacquer coating technique has not been widely employed in engineering because of its lower strain sensitivity and the susceptibility to the influence of lacquer ingredients, drying techniques, or conditions of temperature and humidity. In this paper, the authors report the practical usefulness of infrared rays baking device for brittle lacquer of baking type. Moreover, the stress values on plain carbon steel plates determined by the lacquer coating were compared with those by the X-ray method in their elastic range during bending tests. The results obtained are as follows: (1) The measured temperature of a specimen coressponded well with the preset temperature of the baking device, showing the practical usefulness of the device. (2) The stresses obtained by using the lacquer coating and the X-ray techniques at any stage of bending tests in the elastic region agreed well each other in the range from 4kg/mm2 to 20kg/mm2. It seems easy to make a reliable stress measurement by X-ray even on the complex machine parts or structures, if the direction of principal stress and the pattern of stress distribution are preliminarily analysed by the brittle lacquer coating method.
In the Marshall test, the percentage of air voids has been used as a basis to determine the asphalt content. But, it is not easy to determine accurately the value of air voids of a compacted asphalt mixture. According to the author's experience, it is not rare to have the case that the calculated value of air voids content becomes negative. In this paper, in order to clarify the reason why the value of air voids content sometimes becomes too small an attempt was made to determine the effects of the following three factors on the calculated value of air voids content: (1) Method of measuring the volume of specimens, (2) method of measuring the specific gravity of aggregates, and (3) difference between the specified and the true asphalt content of compacted test specimens. From the results of the investigation, the following conclusions were drawn. (1) The method of measuring the volume of compacted specimens affects the calculated value of air voids content. A minimum value was obtained when the volume was measured with paraffin coating. (2) The method of measuring the specific gravity of aggregates also affects the value of air voids content. A minimum value was obtained when the bulk specific gravity was used. (3) When a large amount of asphalt is used, some of it adheres to the mixing and molding apparatus during the preparation of specimen. As the result, the value of air voids content calculated using the specified asphalt content is smaller than the true air voids.
Three selected rigid plastics, namely polymethyl-methacrylate, polyvinyl chloride and glass-cloth reinforced polyester, were subjected to fatigue tests with four different fatigue testing machines. The results showed the following effect of the fatigue tester on the fatigue strengths of these materials. (1) The effect of testing machine on the fatigue strength is appreciable. Therefore, a careful comparison of fatigue data resulting from the tests with different fatigue testers is necessary. (2) The difference in the type of fatigue testing machines employed (constant stress-amplitude or constant strain-amplitude) as well as the difference in the method of holding specimens may affect the fatigue strength.
In the present paper, the relationship between the strength of PIC and the total exposure dosage of gamma-rays was discussed for the mortar specimens containing MMA monomer cured by the irradiation at the dose rate of (1.25, 2.5, 5 and 10)×105 Roentogen/hr. In addition, the effects of the turning irradiation, wrapping and annealing were examined, and the strength of PIC polymerized by the radiation method was compared with that of PIC polymerized by the thermal catalytic initiation method. The results show that the total radiation dosage for polymerization to obtain the desirable MMA-PIC strength is 4MR at 106R/hr dose rate, 3MR at 5×105R/hr, about 2.5MR at 2.5×105R/hr and 2MR at 1.25×103R/hr. These values change depending upon the ambient temperature in the radiation cave. If the polymerization is carried out under an appropriate condition, the characteristics of PIC, obtained by both the thermal catalytic initiation method and the radiation polymerizing method, are the same. The effect of annealing on PIC strength is negligibly small in the temperature range lower than 100°C. Therefore, it is necessary to make the annealing temperature higher than 100°C. No effect of the turning irradiation was found out.
This paper is concerned with the time- and temperature dependences of the bending properties of the plain fabric glass cloth reinforced laminates (GRP) and the unsaturated polyester resins which are the matrices of the GRP. The results obtained are summarized as follows: (1) The creep compliances of the matrix and the GRP show the remarkable time- and temperature dependences; that is, they have so called viscoelastic behaviors. (2) The master curves of the creep compliances for both the matrix and the GRP can be constructed, using their thermo-rheological simple properties. As for the time- and temperature shift factors, they are in good agreement quantitatively. (3) It was found that the relation between the creep compliances of the matrix and the GRP is uniquely determined by the rule of mixture for viscoelastic materials, independent of the conditions of their circumstance such as time and temperature. This was also confirmed experimentally.
For the purpose of quantitatively distinguishing the influences of temperature (t), humidity (h), leaf position in a tobacco stalk (p) and direction in a leaf, upon the tensile characteristics or equilibrium moisture content of tobacco (Y), statistical calculations were carried out with many data on typical varieties in Japan, that is, Flue-cured (v1) and Domestic variety (v2). And the following formula to estimate Y was analyzed (Table III). Y=C0+C1t+C2h+C3h2+C4p+C5p2 After that, the relation between tensile characteristics and equilibrium moisture content (w) was searched with the formula Y. The important results obtained were as follows: (1) Tensile strength (Pm) The Pm of v1 was greater than that of v2. The Pm of v1 was decreased when the h(w) or t was increased, but the Pm of v2 did not show any notable tendency with the h (w) or t. In every variety the Pm was decreased toward the lower position in a stalk (Fig. 3 and 4). (2) Elongation percentage (ε) The ε of v1 was higher than that of v2. In every variety the ε was increased when the h (w) or t was increased, and toward the upper position in a stalk (Fig. 3 and 4). (3) Elastic modulus (E) and Elasticity per unit dry weight (EG) The E of v1 was smaller than that of v2. In every variety the E was decreased when the h (w) or t was increased. In the variety v1 the E became minimum at the upper or middle position of a stalk, and was increased toward the lower position. This tendency was shown in the variety v2 too, but the degree of change with the stalk position in the v2 was smaller than that in the v1. The appearance of the change in the EG was very similar to the above-mentioned results in the E (Fig. 5 and 6). (4) The influence of w on tensile characteristics (Pm, ε, E or EG) was very much greater than that of t (Fig. 4 and 6).
The conventional moiré interfringe spacing-strain relation does not contain a factor for determining the strain sign. Therefore, in the case of complex strain fields, this equation can not give exact strain values. In this paper, new equations for the fringe-strain relation are derived. These expressions contain new factors Mii and Mij (±1) for determining the strain sign. The factors can easily be determined by shifting the master grid in the direction perpendicular to the grid lines. When the crossed grid is used, the discrimination of two kinds of fringes produced by X and Y grid is generally difficult. However, it is proposed that the above mentioned shifting method is also an effective means for the discrimination of both fringes.
The authors previously pointed out that when measuring small strains by the moiré method the lowest measurable limit inherent in this method must be taken into consideration. On the contrary, in applying this method to the measurement of large strains, one should consider the highest measurable limit of strain. This paper deals with the property of the moiré fringes studied from the physiological view point to clarify the highest measurable limit of strain that exists inherently in this method. In our theory, the highest measurable limit of normal strain εi(i=x or y) can be expressed as 2cosαi/3(1+λ)cosθ-1<εi<3cosαi/2(1+λ)cosθ-1 where αi are shear strain components, λ and θ are values of mismatch and misalignment, respectively. The highest measurable limit mentioned above can be avoided in the practical measurement by selecting the value of λ properly.
A method was devised to determine the fiber volume content (Vf) in FRP by the ultrasonic wave technique. When the ultrasonic wave length was shorter than the diameter of the fiber, Vf could be easily determined by this method. However, when the ultrasonic wave length was longer than the diameter of the fiber, Vf could not be determined by the ultrasonic wave method only, but it was necessary to use an approximate solution for the transverse rigidity of FRP under the test. The fiber volume contents of glass FRP and carbon FRP determined by this non-destructive method were in good agreement with those determined by the commonly-used destructive method.