The flow properties were measured on two specimens of high density polyethylene (SHOLEX 4250H) mixed with 50 and 60wt% gypsum by use of a capillary type rheometer, and the results were compared with that for pure polyethylene. The temperature dependence of the flow properties was very slight for all the materials tested. The apparent viscosity, the non-Newtonian flow-behavior index, and the viscosity coefficient in the power law equation were obtained from the flow curve. All of the parameters increased with the mixing of gypsum. The increase of non-Newtonian flow-behavior index may be associated with the shape of gypsum particles.
The spiral flow tests have been carried out on high density polyethylene (SHOLEX 4250H) and the same polymer mixed with 50wt% gypsum by use of a vertical type injection molding machine with a spiral cavity. The results obtained are as follows: (1) For both of the materials, the spiral flow length is expressed by a polynominal whose variables are injection pressure, resin temperature, mold temperature and injection rate. (2) The spiral flow length measured for both of the materials is affected primarily by injection pressure and secondarily by mold temperature. For the high density polyethylene mixed with gypsum, the spiral flow length is affected by resin temperature more strongly than by injection rate. (3) The range of the combination of injection pressure and resin temperature in which injection molding of the mixture is possible, shifts to the high pressure side as compared with that for the pure high density polyethylene at the same temperature. But the extent of the range is almost equal for both of the materials.
Compressive creep tests were carried out using some injection molded cylindrical specimens of polycarbonate filled with 30wt% glass-fiber and unfilled. Creep properties under various conditions of temperature and compressive stress were discussed. The results obtained are as follows: (1) At the condition of temperature under about 60°C, the maximum stress below which creep compliance does not depend on stress is 3∼6kg/mm2 on filled polycarbonate and 1kg/mm2 on unfilled. (2) Creep compliance D(t) is shown in the following equation, when the conditions are not very severe. logD(t)=alogt+b (1) where t is time. Creep compliance D(t) after a long time is able to be estimated by using the values of a and b obtained from short period creep tests under conditions being considered. (3) The value of a in equation (1) increases with temperature, and b is constant. The reinforcement with glass-fiber brings so low values of a and b as to be effective for an increase of dimensional stability under load.
It has been established that an aluminum single crystal having <100> tensile orientation shows initial rapid hardening. After about two to three percent elongation, the tensile stress-strain curve becomes flat until the necking point. It has been reported that the prominent cross slip which does not usually occur in aluminum but does, for example, in α-brass, was observed in this flat region of the curve. However, many problems pertaining to the relation between the deformation mode and the stress-strain curve of the <100> oriented single crystal have remained unsolved. In the present paper, the <100> oriented aluminum single crystals were tested in tension at room temperature and the deformation mode was examined by observation of slip lines and the changes of orientation of tensile axis. Initially, the flow stress of the <100> oriented single crystals increased rapidly due to multiple slips. After about 2% elongation, clustered slips accompanied by the prominent cross slips were formed and the deformation proceeded by the propagation of these clustered slips, likely as the Lüders band deformation. Therefore, the flow stress of the single crystals became constant. After about 20% elongation, the tensile orientation of the single crystals deviated from <100> axis, due to the deformation by the clustered slips, and suitable slip systems for the deviated tensile orientation which were not accompanied by the prominent cross slips were activated. The occurrence of the prominent cross slips in aluminum crystals primarily depends on the ratio of shear stress on the cross slip system to that of the primary slip system, and in a crystal having a large value of this ratio, i. e., a tensile orientation near <100> axis, the prominent cross slip occurs.
The effect of pre-deformation on the martensitic transformation induced plasticity (TRIP) in austenitic Fe-Ni-C alloys (their Ms temperatures are below room temperature) was studied by tensile tests between -196°C∼80°C. Pre-deformation up to 65% in reduction was given by rolling at 200°C. Since the rolling temperature was above Md temperature, all the specimens consisted of a single austenitic phase even after rolling. The TRIP was observed in the pre-deformed specimens as well as in the non-deformed ones, showing the maximum elongation at a certain temperature between Ms and Md. The value of maximum elongation (εmax) decreased with the degree of pre-deformation. The amount of the increase in elongation by TRIP (ΔεA), which was defined as the difference between εmax and the elongation of austenite itself (εA), was found to be independent on the degree of pre-deformation in alloys having less than 0.2% carbon, but in an alloy with 0.4% carbon, the ΔεA was decreased by pre-deformation. When εA, εmax, and the elongation of martensite (εM) which was obtained by the subzero treatment, were compared with each other, the εM was scarcely decreased by pre-deformation. So, both the strength and elongation of martensite formed from pre-deformed austenite by cooling the specimen to a temperature below Ms temperature were higher than those of pre-deformed austenite itself (without TRIP). The difference (ΔεM) between εmax and εM decreased with pre-deformation even in 0.2% C alloys, being different from the trend of ΔεA. Finally, the Lüders type deformation, which appeared in heavily pre-deformed specimens, was observed in detail and discussed in comparison with other phenomena caused by the stress induced martensitic transformation.
To study the behavior of cracks in the earlier stage of fatigue in copper, observations were made on both longitudinal sections and fracture surfaces using optical and scanning electron microscopes. The observation on longitudinal sections showed that transcrystalline crack paths along the slip bands were predominant at low fatigue stresses, but intercrystalline crack paths were frequent at high fatigue stresses. Two kinds of fracture surfaces were observed beneath the specimen surface; one is lying in a slip band and the other along a grain boundary. The former was usually said to be featureless, but steps of about one micron in the direction of crack growth as well as clear slip traces were found on the flat surface. Matching of the steps on mating fracture surfaces was fairly good in such manner that hills on one surface fit into valleys on the other, but matching of the slip traces was not good. On the smooth fracture surfaces lying along grain boundaries, slip traces were observed in most areas, but clear and regular striations were found in some cases. Such topography observed on the fracture surface of intercrystalline crack was similar to that observed within the interior. The observations above suggest that both unslipping and the local plastic blunting process are responsible for the growth of the crack lying in the slip bands, and that intercrystalline cracks grow in tensile mode even in the earlier stage.
The authors have carried out the low-cycle torsional fatigue tests under multiple repeated loads by using annealed carbon steel S45C, and investigated experimentally the applicability of the fatigue fracture criterion 1/C0∫N0γpadn=1 based on varying plastic strains, which was introduced instead of the linear damage criterion Σ(n/N)=1 based on stresses. Furthermore, the applicability of the above fracture criterion has been also discussed on the basis of the experimentally determined correlation between the equivalent stress amplitude and the equivalent plastic strain amplitude. The main conclusions obtained are summarized as follows: (1) The present test results were similar to the ones that the authors carried out previously under the periodical 2-step or 3-step multiple repeated loads by using 0.84%C piano wires. The values of fatigue life obtained from the fatigue fracture criterion based on varying plastic strains were slightly closer to unity than those calculated from the linear damage criterion. Therefore, when used for predicting the fatigue life under the stress control test, the fatigue fracture criterion based on varying plastic strains is better than the linear damage criterion. (2) From the test results, a log-log straight line relationship was found to hold between the equivalent stress amplitude and the equivalent plastic strain amplitude.
The crack propagation of a center notched plate specimen in tensile creep under the plane stress condition was simulated by means of a finite element method on the finite strain theory. In the analysis, the restriction force of a nodal point in the triangular elements at the crack tip was removed whenever the strain at the point reached a critical value (i.e., the fracture strain). The distributions of creep stress and strain ahead of the propagating crack, the shape of the crack, and the relations between the crack propagation rate and the crack length, the crack tip stress, the net section stress or the elastic stress intensity factor were calculated. And the effects of the values of creep exponent, α, and fracture strain, ε*f, on the above quantities were clarified. The crack propagation rate was found to be proportional to the creep rate at the crack tip and inversely proportional to the slope of tangent of the creep strain distribution curve at the crack tip. The history of creep deformation made the slope of strain distribution ahead of the crack flat with the crack growth, resulting the acceleration of crack propagation rate especially in the region of relatively short crack length. The crack propagation rate changed approximately linearly against the net section stress, σnet, or the stress intensity factor KI, in a log-log diagram. For a given value of σnet/σg or KI/σg, the crack propagation rate was in proportion to the creep rate under the gross stress, σg, and in inverse proportion to the fracture strain of the material.
The experiments on crack propagation in tensile creep were conducted using the center notched thin plate specimens of an 18Cr-8Ni stainless steel (SUS304) at the test temperature of 650°C. The material was highly ductile and the wedge-shaped crack was propagated in the contracted section in nearly plane stress state. The crack propagation rate was given as a function of the crack length, the net section stress or the elastic stress intensity factor. It was found that the crack propagation rate changed approximately linearly against the net section stress for the true net section area, σnet', or against the elastic stress intensity factor, KI, in the log-log diagram, and the non-dimensional relationship: dl*/dt/Bσgα/ε*f=An'(σnet'/σg)α or AK(KI*/σg)α was obtained, where l*=2l/W0, l is the half crack length, W0 is the initial specimen width, Bσgα is the creep rate under the gross section stress, σg, ε*f is the fracture strain and is about constant for the same fracture mode, α is the stress exponent of creep in smooth specimens and is nearly equal to αloc or the exponent of stress in the stress-rupture life relation, KI*=KI/√πW0/2=σg √l*sec(πl*/2), and An' and AK are material constants. The experimental results substantiated the validity of the result of the finite element analysis based on the finite deformation theory reported in the previous paper. The result of the finite element analysis suggested that the crack propagation rate would be proportional to the αloc'th power of the net section stress, σnet=σg/(1-l*), in the material with low ductility or in the state of plane strain. Double edge cracks in the plate specimens and circumferential cracks in the bar specimens of a 1Cr-1Mo-1/4V steel at 600°C exhibited the grain boundary fracture with little reduction of area, and their propagation rates were expressed by the following non-dimensional relation. dl*/dt/bσgαloc=An(σnet/σg)αlocor AK'(KI*/σg)αloc' where bσgαloc is the mean rate of fracture under σg, being equal to 1/tr; tr is the time to rupture the smooth specimens, and the value of αloc' is a little smaller than αloc. The results on two kinds of materials tested indicated the possibility of application of the net section stress or the elastic stress intensity factor for the made I crack propagation in creep.
Notched plates of 3%Si-Fe, 0.04%C steel and 7075-T6 Al alloy were stretched, and the distributions of longitudinal and in-thickness strains, εy and εz, were measured in the vicinity of notch tips. The results of strain distributions were explained using the analytical results of near-tip deformation for non-linear elastic materials, combined with a simple model of the plastic state under a mixed plane stress and plane strain condition. The main results were, summarized as follows: (1) The distribution of in-thickness strain, εz, ahead of the notch tip was divided into three regions designated by region I, II and III. In region I, the width of the plane strain region decreased linearly with the distance, x, from the notch tip. The strain distribution in region II had a singularity of -1/(1+n) th power of x. (2) The distribution of longitudinal strain, εy, ahead of the notch tip was divided into region I, II, III and IV. The strain value in region I was under a direct influence of the notch. The strains in region II and IV were proportional to -1/(1+n) th power of x. The region III was identified as a transition region from region II to IV.
Polycarbonate was subjected to static tests under several loading conditions (simple tension and compression, bi-axial tension, and torsion under hydrostatic pressure) at room temperature at a constant low strain rate. Simultaneous readings of longitudinal and circumferential strains of a specimen were obtained continuously during the loading period until the onset of instability or necking appeared. Particular attention was given to the importance of the anelastic component of strains for ductility of polycarbonate. Careful observations were made on the anelastic deformation of solid bars during uniform tensile or compressive deformation, and of thin-walled tubes subjected to various combinations of axial tension and internal pressure. The stress-strain relations of all the tests were compared each other in terms of maximum shear stress and maximum shear strain. There was no consistency in the stress-strain curves for all the tests, owing to the effect of mean normal stress (hydrostatic pressure) on the stress-strain relation for polymeric solids. From these stress-strain curves, plots of the maximum shear stress versus the mean normal stress at corresponding strain in each test were produced, and it was observed that the maximum shear stress increased linearly with hydrostatic compression up to the yield point but decreased rapidly under hydrostatic tension.
The glass forming regions in the mixed-alkali borate systems with high-alkali contents were determined. The densities of the resultant glasses at room temperature were measured by the buoyancy method, from which the apparent molar volumes were calculated. The relationships between these properties and compositions of glasses were investigated. The main results obtained were: (1) The effectiveness of alkali ions for the glass formation in the single- and mixed-alkali borate systems is in the order of Li>Na>K. (2) The apparent molar volume-composition curve is nearly linear for the Li-K glasses. On the other hand, the curve has a negative deviation from linearity for the Li-Na glasses and a positive one for the Na-K glasses. The experimental results were discussed in terms of the theory of field strength.
Recently, thermo-setting plastic composites containing micro-balloons have been investigated frequently as a potential buoyant material for the ocean exploration. However, these investigations have been almost limited to their mechanical and physical properties. In view of the need for other properties, the following investigations have been undertaken. Four kinds of composite materials were prepared by the vacuum infiltration method with epoxy resin as the matrix and glass, carbon, phenol or shirasu balloons as the filler. The relation between acoustic and mechanical properties was investigated under the soaking condition in water. The results showed that the composite with carbon balloons is much better than others from the view point of its smallest acoustic transmission loss and smallest decrement of mechanical properties under the soaking condition in water.
The polarization behavior of austenitic stainless steels in hot concentrated caustic soda with and without sodium chloride was investigated by means of the potential sweep and the potential step methods. Iron, nickel, chromium, and molybdenum were also examined as reference. The austenitic stainless steels, Types 304 and 316, showed reproducible potential vs. current density curves when the potential sweep was repeated in pure caustic in the potential range between hydrogen evolution and oxygen evolution (ca. -1.3v to 0.6v vs. Hg/HgO). In solutions containing sodium chloride, on the other hand, the current increased greatly due to pitting when anodically polarized beyond the critical potential. Incident on the surface of specimen was well repaired at the protection potential during potential scan in the cathodic direction. The protection potential moved gradually to less noble values as the chloride concentration increased, and the stable region of passivation diminished.