Search

Tensile test pieces of aluminium bi-crystal were obtained by the strain annealing method from commercial aluminium plate. Orthogonal grids of 20lines/mm were printed on the surfaces of the specimens. The plastic deformation of these specimens were measured by the usual moire technique. The amount of deformation obtained experimentally almost agrees with that calculated on the basis of slip of crystal plane, but it becomes small near the grain boundary. That is, the grain boundaries tend to restrict deformation of crystals. The distribution of elongation in the neighborhood of grain boundaries is similar to the result obtained by Urie and Wain4). The effect of grain bondaries reaches to 2∼5mm from grain boundary. It seems that the extent of such region is related to the Schmidt's factors of bi-crystals and their slip direction.Next, to examine the rotation of crystal lattice induced by plastic deformation, Laue photographs were taken. For this purpose, about ten slits of 4cm in length and 0.45mm in diameter were set in a row. This slits system makes it possible to take Laue patterns around the grain boundary on a X-ray film. It was observed that the amount of rotation of crystal lattice and the direction of its rotation axis are abnormal in the neighborhood of grain boundary.

A moire method is described for measuring partial slope contours of flat surfaces of transparent plates. A reference grating is projected by means of a collimated light beam on the surface of a specimen. The light beam passing through the specimen forms a distorted image of the reference grating on the surface of an identical grating, and produces moire fringes which yield partial slope contours of the specimen.A formula for obtaining the slope contour from the inclination and the spacing of the moire fringe is introduced theoretically. Experiments made with a straight line grating of 0.025 mm spacing show that this method has nearly the same precision as the optical interference method.In this paper few applications are shown. As an example, the slope contours are calculated from moire pattern produced by an acrylyte plate which is supported at both ends and loaded at mid point. And also a moire pattern produced by the fractured surface of acrylyte plate is shown.The method described in this paper is applicable for the transparent materials, but for the reflecting materials their slope contours are derived by the somewhat different moire technique.

Fatigue crack propagation in epoxy resins containing 0 wt% to 45wt% plasticizer was examined. In this experiment, double-cantilever type specimens were used. The stress intensity factor was adopted to express the stress near the crack tip. When specimen was cyclically loaded, not only the range of stress intensity factor ΔK but also the maximum stress intensity factor Kmax or the mean stress intensity factor Kmean were taken into consideration. Under the assumption of dl/dN=A(Kmax)α1(ΔK)α2 or dl/dN=B(Kmean)β1(ΔK)β2(dl/dN means the fatigue crack propagation rate) as the fatigue crack propagation law, dl/dN was measured for several combinations of ΔK and Kmax or Kmean and the values of constants A, α1, α2, B, β1 and β2 were evaluated from the values of log(ΔK) and log(Kmax) or log(Kmean) by means of least squares analysis.As the results, it was found that as the percentage of plasticizer increases, A and B increase by two orders, α1 and β1 decrease by 40%, and α2 and β2 decrease slightly. For the specimen without any plasticizer, both α1 and α2 are equal to about 5, and for the specimen with 40 wt% of plasticizer, both β1 and β2 are equal to about 4. It is interesting that the exponent of ΔK remains constant in spite of the decrease in exponent of Kmax or Kmean. The mechanical properties vary widely from the brittle fracture type to the ductile fracture type as the percentage of plasticizer increases, and it seems that the above interesting results about the fatigue crack propagation behavior in epoxy resins containing plasticizer are principally attributed to the difference in their mechanical properties.

Polymethyl methacrylate specimens were fractured by the static bending, and the speed of the crack propagation was measured by the speed of breaking of the electro-conductive coatings on the surface of the specimens. The rate of crack propagation speed obtained by our method is found to be greater than that which has been obtained by any other investigator.It is found that the fracture morphology is roughly divided into three main classes: (1) the glassy fracture surface containing a number of geometric figures resembling parabolas, (2) the fracture surface having the semicircular“ribs or scallops”of great roughness, and (3) the fracture surface of the greatest roughness at low temperature. It seems that the concentric scallops observed on the fracture surface of the notchless specimens have been produced by the dilatational wave based on the stress release as the crack spreads over the plate.

Fatigue failure mechanism in polymers was examined by using a fatigue testing machine of constant deflection type. The fatigue tests were carried out both on polycarbonate and polyamid, and the effect of the difference of their structure on fatigue behaviors was investigated. Moreover, the effect of temperature on a fatigue crack propagation was also investigated.The state of stress in the specimen during crack propagation was theoretically analyzed and compared with the experimental value. From the relation between the rate of fatigue crack propagation and the applied stress the fatigue life of polymers was discussed.The following results have been obtained:(1) The results obtained from the stress analysis are qualitatively consistent with the experimental value. The rate of fatigue crack propagation is found to be proportional to 2-3 power of applied stress in polycarbonate, and it has decreased with an increase of the testing temperature.(2) It has been found from fractographic examination that: (a) the fatigue crack in polycarbonate has initially propagated, forming striation markings on the fracture surface, but this marking of striation has not necessarily corresponded to each cycle, (b) the spherulite structure in polyamid seems to have had great influence on the failure mechanism.