This paper aims to present evidences for the changes of work hardening phenomena that can occur in tensile pre-strained coppers when they are subjected to fatigue combined stresses.
The present author believes that the phenomena are the result of the origination and propagation of micro-crack. From the fact that the intrusions are found along the slip bands, the author surmises that they develop into persistent slip bands and fissures, and that these bands and fissures are kinds of micro-cracks.
Changing the grade of tensile pre-straining (K), the fatigue stage of the first origination of slip band was studied in connection with the generation of the intrusion, and that of the first origination of the persistent slip band was investigated in relation to the occurrence of the micro-crack.
The main conclusions from this study are as follows:
(1) In the case of uniaxial tensile pre-strained copper the changes of the work hardening phenomena appeared slowly during the fatigue test. These results differ remarkably from that obtained by Professor Wood with regard to the fatigue of complex pre-strained copper.
(2) In the case of the fatigue of the tensile pre-strained copper the work hardening was saturated at an early stage of the fatigue test, and the appearance of the stage of saturation was delayed by the increase of pre-strained grade K. Concerning the fatigue of annealed copper, the saturated fatigue stage was about 20 to 30% of its life.
(3) The occurrence of the initial and decisive fatigue damages was delayed by pre-straning and also by the increase of the normal stress σ_x caused in the longitudinal direction of the specimen.
(4) In view of the fact that in the case of the pre-strained copper the number of cycles from the origination of the micro-crack to the failure of the specimen is less than in the case of the annealed copper, it is believed that the micro-crack in the former case propagates faster than in the latter.

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The tests were carried out of specimens of specially prepared medium carbon steels which were designated as A1, A2 and B2. A1 and A2 steels contained respectively Mn-silicate and Al-silicate inclusions. B2 steel was the top part of ingot, and had a number of large flaws. The fatigue limits due to rotary bending for these materials were obtained after the specimens were preworked by statical tensile deformations beyond the yield point.
As the supplementary test, the torsional fatigue machine was stopped at intervals after additional cycling in order to investigate the initiation and propagation of fatigue cracks for annealed specimens, and photomicrographs were taken in the same area on the surface of the specimen
The results obtained are as follows.
(1) Comparing with the results for annealed states, the fatigue limits in A1 and A2 materials decrease few percent for small strains, and increase for large strains of preworking. This tendency is similar to that obtained previously for 0.15% C steels, and the effect of the presence of inclusions can not be found.
(2) In B2 steel, however, the above-mentioned tendency is not found, and also the scatter of fatigue test results for S-N curves is obtained. It should be pointed out that the influence of the large flaws on the fatigue strength is much more than that of the structural variation of metal by tensile preworking.
(3) The specimens made of B2 steel contained a number of large flaws as longitudinal directed inclusion lines parallel to the specimens axis, but these flaws had no harmful influence on the fatigue life of specimens.
(4) The surface of specimens not broken at 10⁷ torsional stress cycles was found a large number of small cracks, but the number of small cracks in B2 specimens was much less than that in A1 and A2 specimens.

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Either with the aim of studying the effect of the pre-strain on the fatigue strength of materials, or for the purpose of increasing fatigue strength, there have been investigators so many who have tested many materials with various amounts of pre-strain under repeated stresses, such as push-pull, rotary or reversed bending, and reversed torsion with some of those having mean stress, and the results from these tests indicate that fatigue limit is generally increased by pre-strain. On the other hand, there have been reports that the fatigue limit of specimens that have been subjected to a small amount of pre-strain (just above yield point) drops below that of the original material.
The above-mentioned facts are ascertained in this paper by the experiments with 7:3 brass specimens with electro-polished and pre-strained surface. The amounts of pre-strain are 1.3, 5.3 and 8.7%. With 1.3% pre-strain, the fatigue limit decreases 8.3%. This phenomenon is explained by the fact that slips occurred in relatively weak grains on the surface of the specimen. The damage is retained and there is no artificial strengthening of the material. On the other hand, in the largely pre-strained state, the improvement by artifice is greater than the damaging effect due to the slip, and the fatigue limit is increased. By this consideration, the same phenomenon about notched prestrained specimens can also be explained.

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The fatigue limits due to rotary bending for specially prepared mild steels containing silicate inclusions were obtained after the specimens were preworked by statical tensile deformations beyond the yield point.
The results obtained are as follows;
(1) Comparing with the results for annealed states, the fatigue limits decrease few percent for small strains, and increase for large strains of preworking. This tendency is similar to that obtained previously by Fukui and Sato for ordinary carbon steels, and the effect of the presence of inclusions can not be found.
(2) Accordingly, in the preworked soft steels studied in this investigation, the presence of inclusions appears to have little influence on the fatigue strength.
(3) 196-1 steel contains greater quantity of inclusions than the other steels. The fatigue limit of this steel, preworked to about 2% tensile strain by applying the tensile stress of 27.0kg/mm², falls by 10% as compared with that for the annealed state, and then recover the same value for preworking of 40kg/mm² stress and approximately 7% tensile strain.
(4) Since the fatigue cracks initiate at inclusions, the fracture surface of a specimen which was subjected to a high stress level is very rough, and numerous micro-cracks are found on the outer smooth surface of many specimens near the fractured section.

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High load levels are sometimes observed in randomly varying loads applied to some structures or machine parts, owing to sudden accidents or some other causes. Recently, furthermore, materials are being used under severe loading conditions and often subjected to stresses comparable to the range. In case of designing, it is dangerous to neglect such high load levels.
The purpose of the present study is to investigate the effect of high tensile loads (in plastic range) on rotating bending fatigue strength of carbon steel. In this paper, as the first step, in order to obtain the fundamental data, the fatigue tests were carried out on smooth specimens of 0.33%C carbon steel subjected to a static high tensile load prior to stress cycling. The results were discussed on the basis of hardness change, residual stress change, surface observation during the fatigue tests and the effect of heat treatments.
The conclusions obtained are summarized as follows:
(1) In many cases, the tensile pre-load lowers the rotating bending fatigue strength. Especially, in the case of the lower yield point pre-load, the decrease of fatigue strength is more pronounced and in the case of the highest pre-load just under the tensile strength, the fatigue strength increases slightly above that of a virgin specimen.
(2) As the reasons of change in fatigue strength by the tensile pre-load, it is necessary to consider the stress concentration due to non-uniformity of work hardening as well as the residual stress and work hardening.
(3) By the heat treatments after pre-load, the fatigue strength of pre-loaded specimens increases, because the annealing effect by the heat treatment reduces the stress concentration due to non-uniformity of work hardening.

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This investigation has been conducted to make clear the effect of strain rates on the internal structure and the mechanical properties of rapidly stretched stainless steels. The 18%Cr-8%Ni stainless steel and 17%Cr-4%Ni PH stainless steel specimens have been used in this study.
The main results obtained are as follows:
(1) The yield strength and the tensile strength of these stainless steels in rapid tensile testing are larger than those in static tensile testing. The strain rate gives a remarkable effect on the resistance in deformation of these stainless steels.
(2) The yield strength, the tensile strength and the hardness of rapidly pre-stretched 18%Cr-8%Ni stainless steel are larger than those of statically pre-stretched sort. It was recognized that this fact is mainly due more to the promoting martensite transformation by rapid pre-stretching than by static one.
(3) The yield strength, the tensile strength and the hardness of statically pre-stretched 17%Cr-4%Ni PH stainless steel are larger than those of rapidly pre-stretched sort. It seems that this fact is mainly due more to the promoting aging by static pre-stretching than by rapid one.
(4) From the above mentioned results, it is recognized that the mechanical properties of prestretched stainless steels are remarkably affected by the internal structure caused by the strain rate in pre-stretching.

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  Effect of pre-strain on tensile and fatigue properties was investigated in a ferritic spheroidal graphite cast iron which was applied tensile pre-strain from 0 to about 14 %. Density decreases nearly linearly with increasing pre-strain. Graphite nodules of the pre-strained specimens are observed as ovals whose major axes correspond with the direction of tension. From these facts, it seems that the voids are produced around graphite nodules by appling pre-strain. Proof stress (σ_0.2) increases largely and elongation decreases monotonously with increasing pre-strain. Both fatigue strength at 2×10⁶ cycles or less and fatigue limit of the pre-strained specimens decreased compared with the specimen which is not pre-strained. However, the decrease of these values is little or small with increasing pre-strain. Fatigue crack growth rate was hardly influenced by pre-strain. It is considered from the results that the decrease of fatigue strength due to pre-strain is mainly caused by the voids which made the initiation of fatigue crack easy.

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In the study of this shearing test, Amsler testing machine, three kinds of round shearing tools of 10mm, 25mm and 50mm in diameter respectively and autographic recorder are employed.The autographic recording system consists of dial gauge with thin disc having fifty slits, photocell, photo-electric-current amplifier with relay, electromagnet with ratchet attached to Amsler recording drum. By these apparatus, approximate shearing curves of round blank are recorded on the drum. The test pieces are of mild steel sheet of 0.96mm in thickness.
The results are as follows.
1) Nominal shearing stress decreases gradually in proportion to the increase of the tool clearance.
2) Nominal shearing stress is 7580% of ultimate tensile strength.
3) The Minimum values of the specific work required in each tool being about 12kg-mm/mm², appear between 8 and 16% tool clearance,
4) And others.

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It is generally known that the fatigue strength of the materials is increased by the workhardening of the materials before fatigue tests. Some reports, however, have recently published concerning a state that the stress of pre-loading given to mild steels which has been made just above the yield stress of the steels decreases the endurance limit of the materials.
Therefore, we made experiments to ascertain this result and further to obtain the endurance diagram of the work-hardened mild steel in the case of torsional fatigue.
The summary of the results is as follows. In case a comletely reversed alternating stress is given to the materials subjected to a pre-loading just above the yield stress, the endurance limit is reduced by about 10%. The pre-loading stress above this value hardly affects the endurance limit and it remains at nearly the some value with the non-preloaded specimens.
But in case fatigue tests where the mean stress is given to the materials subjected to a moderately high pre-loading tress, the endurance limit is increased by the pre-loading if the mean stress is applied in the same direction as the pre-loading stress, and it is almost equal to that of the non-preloaded specimens if this direction is reversed.

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The fabrication of final products in sheet plastics are generally performed by means of vacuum and blow forming methods. Now it is considered that if the conventional process for sheet metal press working operations is applied to the forming of sheet plastics, the working cycle will become more efficient, and then it will contribute to the reduction of production costs. In recent years the studies on this subject have been made by some researchers.
The present study deals with the performance of the stretch and deep drawing operations for the hard PVC sheet by means of the similar tooling as is used in sheet metal pressing. For this purpose, first as the fundamental procedure of the forming condtions, several mechanical and forming characteristics were tested, such as the mechanical properties based on the uniaxial tensile testing, the flow and softening properties, using the Koka-type flow tester, the stretch formability, using the Erichsen testing machine provided with a heating unit, and the deep-drawability by means of the cupping apparatus having conical dies.
From the results obtained in these tests, when cylindrical shells are deep-drawn from a flat blank by means of a conical and a flat-formed dies respectively, the maximum successful drawing ratios achieved in a single pressing were examined. In warm press drawing, it was found that the deep-drawability of PVC sheet within the proper forming temperature range from a minimum value of 56°C to about 90°C was preferable. And also, the deformation mechanism in deep-drawing work of PVC sheet could readily be traced in a similar way to the plasticity analysis for sheet metal drawing, then, the forming limit calculated theoretically was shown in satisfactory agreement with the data given by the drawing experiment. In spite of the excellent drawing formabilty, high anisotropy on the radial draw deformation was generated at the cylindrical part, and as a result of the wide allowance of the thickness of PVC sheet the unsteady forming conditions freqently occurred.

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In this paper, a problem to determine the distribution of stresses in an infinite strip under pure tension applied at infinity, provided two circular holes of equal radii are placed in the strip on each side of its neutral axis symmetrically, is treated analytically with the aid of the stress functions obtained by Howland, however, it seems to the writer that they require somewhat correction. Considering the results obtained in the present research together with those of the photoelastic one published already by Prof. Shinji Fukui and Mr. Katsuhiko Ito, for the same problem above mentioned, in the Report of The Scientific Research Institute, 1948, some characteristic properties in regard to the distribution of stresses are pointed out and discussed somewhat in detail.

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