The drilling conditions to obtain a good shape and fine accuracy in dimension of drilled holes in metallic sheets of mild steel (S35C), brass (6/4 brass) and duralumin (2017) as well as in nonmetallic sheets of bakelite, vinyl and acryl with conventional standard twist drills or a fishtail point special drill were examined. The results obtained are as follows: In the case of drilling metallic sheets with conventional standard drills of different point angles, the drillled hole shows more enlarged hole diameter, more distorted shape and larger pile-up at the hole-inlet as the drill point angle becomes wider. In the case of drilling nonmetallic sheets, the influence of the point angle is little and a circular hole is easily obtainable. And if the point angle is obtuse, the burr at the hole-outlet is little even in metallic sheets, but the cracks tend to appear at the hole-outlet in nonmetallic sheets. In the case of drilling with a special drill, the enlargement of hole diameter is smaller compared with the case with a standard drill and a circular hole is obtainable. But, in drilling nonmetallic sheets, large cracks tend to appear at the hole-outlet and the burr at the hole-outlet is smaller compared with the case of standard drill. For the drilling of bakelite, it has been proved that a good drilled holes is obtainable by drilling after placing bakelite on top of aluminium sheet. The drilled hole shows no cracks, little enlargement of hole diameter and little pile-up or burr.
The ion-exchange reactions of mixed-alkali lead silicate glasses with molten lithium nitrate were carried out for 1 to 5 hours at 380°C. The results obtained are summarized as follows: (1) In the ion-exchange reaction of a mixed-alkali glass containing two different kinds of alkalis, the diffusion of one type of alkali ion occurs independently of the other. (2) For the mixed-alkali glasses containing Na2O and K2O, the amount exchanged becomes minimum at the molar concentration ratio (βK) of about 0.5. (3) For the simple alkali glasses containing Na2O or K2O, the amount exchanged decreases remarkably with increasing PbO content. But, for the mixed-alkali glasses, it varies very little with PbO content.
There have been hitherto many studies on the crystallite size and the lattice distortion of the ground zinc oxide powder by X-ray diffraction method. However, it seems that the thermal analysis is as effective for the study on the lattice distortion of the ground powder as the X-ray diffraction method. For this reason, the zinc oxide ground by a ball mill was studied by the thermal analysis, and the results were compared with the results obtained by the X-ray diffraction method. Moreover, the effects of heat-treatment of the ground zinc oxide on the disappearance of lattice distortion and on the growth of crystallite were also studied. As a result, an exothermal peak was found between 220° and 260°C in the heating process of the differential thermal analysis, but no change of the weight could be found at those temperatures. As the grinding time became longer, this exothermal peak shifted to a higher temperature and became larger. This exothermal peak in the heating process may be attributed to the discharge of lattice distortion energy. The lattice distortion increased with grinding time up to 200 hours, but after 200 hours it increased little. Such lattice distortion diminished or disappeared easily by heating at 200°C, and gradually diminished even at room temperature after a long time. On the other hand, the crystallite size increased gradually by heating above 200°C and rapidly above 700°C.
Specimens of annealed 7-3 brass were subjected to constant loads in a corrosive environment of gaseous ammonia. The crystal deformation caused in the process of stress corrosion cracking was examined by two diffraction methods, viz., the X-ray profile analysis and the X-ray microbeam diffraction method, and the progress of stress corrosion cracking was discussed in terms of microscopic parameters supplied by these X-ray methods and by optical microscopic observations. The following is the summary of the results obtained: (1) The half-value breadth of the diffraction profile is little changed in the early period, increases gradually in the middle stage and increases sharply near the final fracture in the process of stress corrosion cracking. This change is similar to the change in specimen elongation. (2) The microscopic stress obtained from the half-value breadth by Hall's analysis increases and the particle size decreases as the stress corrosion cracking progresses. The results obtained by the Fourier analysis of the (311)-reflection profile after Garrod are similar to those by Hall's analysis. (3) Slight changes in micro-lattice strain, total misorientation and subgrain size, which are determined from X-ray microbeam diffraction patterns, are observed of the unnotched specimens. The X-ray microbeam diffraction patterns at the stress corrosion fractured surfaces of the notched specimens differ from those at the mechanical brittle or ductile fractured surfaces. It can be surmised, therefore, that cracks mainly propagates mainly by electrochemical attacks. (4) It seems from the optical microscopic observations near the notch roots of specimens that initial cracks are formed by the joining of microcracks which appear mainly along grain boundaries. The main crack, which is also intergranular, propagates by the joining of microcracks which have been formed in front of the main crack.
In order to clarify the effect of cyclic loading during the tempering on the temper brittleness of Ni-Cr steel, the transition temperatures of specimens which had been tempered under various loading and cooling conditions were examined, and the precipitation and the grain boundary etching in each tempered specimen were observed by the electron microscope. The summarized results are as follows: (1) In all cases of the cooling methods, such as water cooling, furnace cooling A (cooling rate: 4°C/min), furnace cooling B (cooling rate: 1°C/min) and furnace cooling A with loading, the effect of cyclic loading during the tempering on the transition temperature clearly exists and the transition temperature rises with the increase of stress amplitude. And the effect of cyclic loading on the transition temperature is more remarkable at higher cooling rate. The transition temperatures in both conditions of the furnace cooling A and the furnace cooling A with loading are nearly the same value at all stress amplitudes. (2) The grain size and the hardness in the tempered specimens under the various conditions are almost constant, that is, the grain size is about 40μm in diameter and the hardness is about 20HRC. There are no effects of cyclic loading during the tempering on the grain size and the hardness in the tempered specimens. (3) There is a slight correlation between the volume of precipitation and the transition temperature. The transition temperature has a tendency to rise with the increase of the volume fraction of precipitation, but this tendency is not so clear. There is a clear correlation between the extent of boundary etching and the transition temperature. When the cyclic load during tempering increases, the extent of boundary etching increases and the transition temperature move to the higher side in temperature. In other words, when the cyclic load during tempering increases, the diffusion of some component or the micro precipitation on the grain boundary might be facilitated and the temper brittleness might be promoted.
As in the previous report1), it has been considered that the direction of stress wave propagation during “impact load” has to be taken into account in order to clarify the intrinsic nature of the impact strength of bolts. Consequently, the impact load was applied on bolts from both the bolt-head side and the nut side, and the intrinsic nature of the high-speed impact tensile characteristic of bolts was investigated. It has been found that the impact tensile characteristic of bolts not only depends on the inherent strength of the material used, but also it varies greatly with such factors as the screw thread, shank, screwed-in position of a nut and acting direction of impact load. For example, in the case that the shank diameter is equal to the outside diameter of thread, the shank is elongated and acted as the so-called“damper”when impact load is applied on the bolt-head side. This fact reveals the intrinsic nature of the impact tensile characteristic of bolts. Accordingly, in such case, the direction of stress wave propagation is important and it is deemed advisable to apply impact load on the bolt-head side. Further, as for the bolt itself, if the shank is made slender, the screw part does not break but the shank elongates, resulting in a remarkable increase of energy absorption. In addition, the longer the length of shank between a bolt head and a nut becomes, the greater the energry absorption becomes. On the other hand, it was found effective from the viewpoint of energy absorption to leave a part of screw idle when a nut is screwed in.
The linear viscoelastic constitutive equation of the unidirectional fiber reinforced plastics of rectangular array has been theoretically derived for the plane stress state. By applying the correspondence principle, the constitutive equation was obtained by the inverse Laplace transformation of the constitutive equation for elastic body in which elastic fibers were embeded. The linear viscoelastic failure criterion was also determined on the basis of the following two considerations, (1) the proportional limit stress for fiber, and (2) the stress causing the debonding between fiber and matrix. Experimental works of creep tests, stress relaxation tests, constant load rate tensile tests and constant strain rate tensile tests were conducted by using copper fiber-epoxy resin composite having various fiber volume fractions and fiber directions. A good agreement between the results calculated by the constitutive equation and the experimental results was observed in the low stress region where the linear viscoelastic behavior predominates. The experimental results of linear viscoelastic failure criterion show an analogous tendency to the calculated ones.
Experiments on fatigue of polycarbonate subjected to a push-pull loading were carried out at the speed of repetition of 3cpm or lower at room temperature. Careful observations of the processes of the appearance of deformation bands and the fracture were made in conjunction with the measurements of the change of load and hysteresis loop. The fatigue behavior and its fracture surface appearance were studied over a range of strains yielding the specimen lives from 10 to 2×103cycles. The fatigue behavior in the low cyclic-life range of polycarbonate was interpreted by taking into account of the behaviors and mechanical properties in the static tension tests. It has been confirmed that the transition of the fatigue fracture mode from the deformation band type to the brittle fracture type exists and the strain of this transition depends more on the maximum strain than on the strain amplitude. Beyond 4% of the maximum strain, the deformation bands appear at 40-50% of the cyclic-life. As the deformation bands grow, the load per cycle decreases and the hysteresis energy per cycle increases. On the fracture surface of the deformation band type, the plastically deformed zone accompanying numerous microscopic deformation bands is observed. Below 4% of the maximum strain, the appearances of the fatigue surface have a number of features in common with fatigue fractures in metals, and the conditions for the onset of catastrophic failure appear to be in accord with the Griffith criterion for brittle fracture. The fracture surface energy of polycarbonate has been evaluated to be 6.77×105erg/cm2 in the cyclic loading.
This study was firstly undertaken to ascertain the formation of microcracks in cement paste (hereafter called paste cracks) under compressive load, and secondly to obtain the information concerning these cracks. The tests were made on cylindrical mortar specimens of 5×10cm. The materials used in this test were normal portland cement and river sand, and they were mixed in the proportion of 1 to 2.09 with a water-cement ratio of 0.5. The cylinders were cured for one day in mold, then placed in water for 28 days and finally stored in the room atmosphere. The age of the specimens at test was about three months old. The cylinders were loaded statically until they received the strains of 0.6, 3.0, 6.8, 8.5, 12.3 or 15.8×10-4. After removal of the load, each specimen was soaked in red ink for 24 hours to stain the cracks and then dried in air. The same treatment was also given to broken specimens. Thin slices were made from the stained near-surface portion of the specimens and microcracks were examined with a microscope using 150×(sometimes 600×) magnification. The results obtained are as follows: (1) The paste cracks appear even by application of very small stress. (2) The paste cracks can be divided into two types, viz., the hair-shaped cracks and the void-shaped cracks. (3) The magnitude of strain has little effect on the number and length of the hair-shaped cracks. (4) On the contrary, the void-shaped cracks propagate with increasing strain, and good agreement exists between the strain beyond which the rate of deformation increases rapidly and the strain beyond which the total area of void-shaped cracks increases rapidly.