In this paper, the approximate analysis of the low aspect ratio wing is carried out, getting a new integral equation of the lifting surface being oblique in the plane of free stream in order to estimate the lift distribution on the wing with low aspect ratio.
The bound vortices are herein assumed to be distributed over the wing surface that is considered as the lifting surface and hence the induced free vortex filaments extend over the infinite down. stream having reasonable small angle to the wing surface.
Applying this integral equation to the extreme case of the lifting surface, it is shown that Munk's Integral Equation is derived in case of the infinite span, and on the other hand, in case of the infinite chord wing the same result is given as that being obtained by Newton's momentum theory. The integral equation identical with that by Prandtl is further derived from the author's equation, putting aspect ratio high as the approximate treatment.

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This paper deals with the kind of ship hull forms, whose generating source is undulatorily distributed amidship through the ends of a ship.
So-called μ-correction (a kind of reduction factor for the source strength partially applied, i. e. just for wave-making, not for hull generating), shows a better coincidence between tank results and calculation.

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Hitherto the wave analysis has been applied mainly to the direct determination of the total wave-making resistance component and not to the improvement of either the current wave-making resistance theory or the hull form design procedure. To obtain full understanding of the actual wave-making phenomena, the analysis of the bow wave alone, not of the resultant wave, particularly the detection of the inherent wave amplitude is most indispensable.
This paper presents the first example to analyze the wave amplitude function from the measured bow free wave (not from the resultant free wave). Asymptotic expansion of the exact expression for the free wave elevation was applied.
A 2.5 m Wigley model was adopted to measure the bow wave, where a capacity-typed wave recorder was applied. The analyzed bow wave amplitude is compared with the calculation assuming that the equivalent singularity distribution is given by Michell's thin ship approximation. Noticeable is the reduction of the actual wave amplitude not only at the higher θ range but also at the lower θ range. The former may be attributed to the extremely steep wave slope there as is easily expected from the working limit of the linearized theory. However it is very important to clarify the real cause for the inconsistency at the lower θ range. Presently the authors suppose that this may come from the so-called “blocking effect” of ship hull.
To determine this, further approach is urgently desired both from experiment and from theory.

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This paper is the second report on the subject that the authors studied and reported at the Society in 1966. The previous paper deals with the tank experiments of three symmetrical models, UU-, VU- and VV-types, all of which are derived from a certain prescribed sectional area curve with block coefficient C_B=0.55. The present paper deals with the further symmetrical models, newly envisaged, UU- and ∧U-types, under the same configuration with block coefficient C_B=0.52.
The main object of this second report is to appraise the validity and usefulness of the slender ship theory which is to be applied to the preliminary stage of the hull form design procedure, i. e., the determination of the sectional area curve. The effectiveness of the so-called “Pienoid” method is also verified concerning the final stage of the determination of the detailed hull form characteristics such as the waterline-and frameline-forms.
In this connection, the authors prepared some mathematical tables to be applied to the slender ship theory calculation of the wave-making resistance.

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In the previous report the authors discussed a few problems involved in the Newman-Sharma's method, a method of wave analysis, and exhibited some examples of application of this method. The examples of application which are reported in the previous paper and the prevent paper are likely to show effectiveness of this method. The real wave-making characteristics of a ship are obtained by calculating the spectrum and the amplitude functions of free wave from the measured wave profiles. The authors study here the problem of determination of the equivalent source distribution from the amplitude function of free wave.

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The main aim of this report is to make clear the effects of finite water depth and finite water channel width on ship manoeuvrability both qualitatively and quantitatively.
For this object, the forced yawing technique, by which the author has measured the coefficients of the equations of motion in last four years with enough accuracy, was used to measure the effects of the restricted waters on each coefficient, to say, acceleration, static and rotary derivatives. Besides these coefficients, the two more coefficients which are representative of the effectiveness of the presence of the channel walls, are measured by the straight tow test with variation of the position of the ship in the water channel. In the following, they will be called as the asymmetric hydrodynamic iorce coefficients.
From these results of experiments, the manoeuvrability of ships, specially the course keeping quality, are discussed in detail. According to them, it can be said that in certain circumstances even a ship which is stable in deep water, becomes unstable in a specific range of water depth, but in more shallow water, the ship returns to be more stable rather than in deep water.
The asymmetric hydrodynamic force coefficients play a significant role on determination of the course keeping quality in narrow water channels. In the most wide and deep channel that was examined in this investigation, that is W/B=6 and H/d=1.9, the ships are unstable in the course keeping quality. But it can be concluded that the unstable quality can be improved by simple automatic steering-by directional control system.

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The strip method is generally used to calculate pitch and heave of ships in regular waves, but this method is not the perfect method.
The author has already obtained the vertical component of flow velocity by applying the thin ship theory, in this report, however, he also shows the vertical component will be determined by the slender ship theory different from the strip method. He obtained, furthermore, the new formulae of calculating pitch and heave of ships by the strip method, using the vertical component 'obtained above with the Takagi's method.
By using four methods, such as Watanabe's (ordinary), modified Watanabe's, Takagi's or modified Takagi's method, the pitch and heave of several ships are numerically obtained and compared each other.
Comparison between the new method and the ordinary method shows that maximum amplitudes of heave obtained by the new method become generally less than those by the ordinary method, and maximum amplitudes of pitch become larger in the former than those of the latter.

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As the speed of ships becomes higher and the size becomes larger, the problem of traffic control in inland sea or near the port becomes more acute. An automatic device to set the course of ships and the auto- pilot equipped on a ship herself will prevent many traffic accidents in confined waters.
But the auto-pilot in present use is so designed that it controls ships in oceans mainly, it is not suitable for ship's control in inland sea or in confined water course. In order that the ship should follow the course in narrower region the control device should be proportional to the deviation of ship's position besides being proportional to the deviation of heading angle from the directed course.
The authors of this paper, therefore, assumed the following type of ship's steering in which
δ=k₁ (θ_i-θ₀) +k₂ (η_i-η₀)
θ_i, η_i : Values denoting the angle and the position of the directed course respectively
θ₀, η₀ : Values denoting the actual angle and position of the ship respectively
δ : Rudder angle
In other words the rudder angle is proportional to the error of both angle and position of ship. k₁ and k₂ are suitably selected to make the system stable, so that the ship follows the directed course. This paper describes the conditions to be fulfilled for the automatic steering system assumed by the authors.

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This paper deals with experimental results of three types of rudders with flap i. e. flap ratio =0.5, 0.25 & 0.165. Their dimensions are 200 mm in chord, 40 mm in thickness and the aspect ratio is unity. They were tested at a speed of 0.69 m/s with a recirculating water channel whose dimensions at the test section are 1.2 m × 0.8 m.
The results are as follows;
(1) Increment in lift coefficient is almost linear with respect to flap angles.
(2) Separation depends only on the angle of the main part and is independent from the flap angle.
(3) Change of the centre of pressure is a function of the ratio between main part and flap angles.
(4) The twisting moment of the rudder stock of a main part can be decreased by selecting the position of a rudder stock suitably.
(5) The moment of the rudder stock of the flap becomes larger according to the area of the flap.
(6) Best performance is shown by a rudder of flap ratio =0.25 and of rudder angle ratio (=flap angle/main part angle) =2, which is twice as good as that of an ordinary rudder without flap.

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It it often said that the position of the pivoting point of any ship moves to the stem along with the progress of its turning motion, or that it moves with the ship's situation in the course of its turning motion.
But when an ordinary ship is steered in a calm sea without external forces, her pivoting point is fixed, and settled regardless of her speed or rudder angle.
So any ship has her own proper turning quality which depends on the position of her pivoting point at any given time. If we divide the turning quality of this ship into two kinds, that is, the steering and the rotating, each has also a special quality of its own. So these qualities of any ship can be shown by indices which are comparable with those of other ships.

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Testing ship models in transient water waves is considered to one of the useful methods which measures or predicts the ship frequency response functions in waves. On ship-wave-systems, testing or calculating techniques of transient water waves have been discussed by some authors. In this paper, the properties of wave-wave system and wavemaker-wave system in transient water waves are investigated by experiments and analysises.
Transient water waves used in this experiments are classified two groups. First group are called concentrating transient waves, these waves are generated in conditions that the wave frequency are uniformly swept from high to low. The concentrating transient wave produces the pulsive water wave at some position of the model basin. Second group are called diffusing transient waves, these waves are formed in case that wave frequency are inversely swept from low to high.
In consequence of the present investigation, next properties on these transient water waves ware obtained.
1) So-called linear response system can be applied to next cases.
a). diffusing transient waves, b). concentrating transient waves before the concentration, c). wavemaker-wave systems in the cases a) & b).
2) Concentrating transient waves after the concentration can not be explained by the linear response system.
3) wavemaker-wave system are also considered to one of the linear system. But the phase lag between motions of the wavemaker and the generating waves at the position of wavemaker is complex. The amplitude ratio calculated from the transient experiments coincides with that measured from regular wave tests.

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This paper gives a general description of a new ship model experiment tank, “Mitaka No.2 Ship Model Experiment Tank”, built at the Ship Research Institute. The principal dimensions of the tank are 400m × 18m × 8 m with the breadth and depth largest in the world. Because of this huge size of the tank, it took four years to complete all the facilities.
In this report are given design considerations and general descriptions of the construction of the tank, which includes the tank itself, the rails, the carriage, the trolley wires, the wave absorbers, the wavemaker, the measuring instruments, the data processor, the building to house facilities, and the workshop and the office.
The main features of the experiment tank are as follows ;
1. large cross section of the tank.
2. deep and shallow trimming tanks with watertight doors.
3. four kinds of brake systems for the carriage.
4. air-conditioned room on a side part of the carriage.
5. accurate speed control of the carriage.
6. rigid trolley wires.
7. movable wave absorbers at the both sides of the tank wall.
8. measuring instruments of digital type with remote control system.
9. on-line data processing system.

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A method of predicting the short term probability of deck wetness and the long term probability of “wet-deck navigation” is presented, along with results of its application to cargo ships operating on the North Atlantic.
Relative bow motions have been evaluated theoretically for geometrically similar ships of various sizes at different headings to regular and irregular waves, based upon the linear strip theory and the linear superposition technique. According to those results, the relationship between the short term probability of deck wetness related to bow freeboard and the significant wave height of irregular sea has been determined in correlation to average wave period, heading angle and ship speed. Then, the long term probabilities of “wet-deck navigation”, where the short term probability of deck wetness will be larger than 1/10, are predicted for different seasons and for various wind forces by the aid of long term wave statistics on the North Atlantic.
The following trends of deck wetness related to bow freeboard are concluded from the predicted results :
(a) The probability of deck wetness is large in head and bow seas, and small in following, quartering and beam seas.
(b) The probability of deck wetness decreases with decrease of ship speed, but the influence of ship speed is rather small in higher speeds beyond 10 knots.
(c) A large sized ship has small probability of deck wetness.
(d) A full ship has small probability of deck wetness.
(e) The long term probability of “wet-deck navigation” is large in winter and small in summer on the North Atlantic.
(f) The long term probability of “wet-deck navigation” increases with increase of wind force on the North Atlantic, but this trend is not so remarkable in extremely heavy weather.

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The determination of the elastic-plastic stresses and strains ahead a sharp notch should be required in the study of the criteria on the initiation and propagation of fracture. Some kinds of modifications of elastic solutions on stress distribution around a notch have been used in the field of fracture mechanics to assess the behaviour of brittle and fatigue failures because of the difficulty of elastic-plastic analysis.
Elastic-plastic analysis of stresses and strains ahead a notch is usually investigated with using deformation theory of plasticity, which could not be considered as the exact representation of the physical phenomena. Recent development of high speed digital computer, however, has made it possible to solve numerically elastic-plastic problems with the flow theory of plasticity.
In the present paper non-linear system of equations is derived based on flow theory for linearly strain hardening square thin plates with side notches, which are slit shaped and 90°-V shaped notches. The load was increased in increments, and for each increment of load non-linear partial differential equations were solved numerically by using finite difference and iterative methods. The distributions of stresses and strains all over the plates and their changes were studied in this way.
The distributions of strains calculated numerically were compared with the values of strain in experiment, and as the result it is concluded that the solution of numerical analysis approximates closely the stresses and strains in the finite plate with sharp side notches.

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In the series studies with the same subject, several kinds of elasto-plastic problems have been treated hitherto.
One of them was the plastic strength of framed structures, especially structures subjected to combined loading such as bending and torsion, or biaxial bendings and torsion.
In this paper, as one of the examples of such structures, bipod-type masts were analyzed by using matrix displacement method.
Although only the collapse loads and mechanisms of the masts were calculated by using upper bound theorem in the previous studies, in this paper successive formation of plastic hinges from the first hinge to the last one was traced and the complete load-displacement curves wered obtained.
The numerical results were compared with the previous experimental and theoretical results and showed a satisfactory agreement with them.
This method may easily be extended to biaxial bendings and torsion problems in the same way.

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Recently, the matrix method has become a powerful tool for structural analysis in conjunction with the rapid development of digital computers and the method of elastic analysis of framed structures is almost established. While, the plastic analysis on the structures is performed with the aid of the mechanism method, the moment distribution method or the linear programming method. However, it is impossible by these methods to analyze the elastic-plastic behavior of the framed structures for the entire process of loading.
Jennings and others studied on the elastic-plastic strength of plane frames subjected only to bending and showed a method to analyze the frames by inserting hinges at the yielded sections. This kind of method is not satisfactory to the analysis for framed structures, especially, for space frames, since the interaction is not taken into account and this may produce a serious error in the result of the analysis. The authors contrived a new mechanism of plastic hinge based on the plastic flow theory and established a new method of elastic-plastic analysis of framed structures in two and three dimensions with full consideration of the interaction.
The result of analysis approaches to the exact solution when the increment of external load becomes infinitesimal.
The analysis was made on several kinds of structures including plane frames under combined axial forces and bending and space frame.
The following important informations are obtained.
(1) The new mechanism of plastic hinge is characterized by that the continuity is maintained at yield section through the entire process of elastic-plastic behavior, and the rigidity is reduced automatically by plastification of the section. It should be also noted that a combination of forces and bending (twisting) moment is possible to change at the plastic hinge without violating the yield, condition.
(2) By the new method of analysis, the elastic-plastic behavior of framed structures is investigated, taking into account of the interaction. And the deformation is obtained at each step of loading and the plastic collapse load is evaluated.

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In the present paper, the matrix methods are developed for elastic-plastic analysis of plane framed structures subjected to proportional loading on the basis of the plastic hinge concept :
After the bending moment at a joint reaches the fully plastic moment, the joint behaves as a hinge for the further increase of load. In the case of the force method, the number of redundant forces decreases corresponding to the formation of plastic hinges, and the flexibility matrix for the structure should be modified. The structure collapses when any redundant force cannot be eliminated for the new formation of a plastic hinge. In the case of the displacement method, it is easy to modify the stiffness matrix of the structure by the use of the member stiffness matrix corresponding to the formation of plastic hinges. The structure collapses when the structure stiffness matrix ceases to be positive definite.
The present method can easily be modified to be effective for structures which may yield by axial forces. For a structure subjected to a prescribed loading program, the stress analysis may be conducted by the present method by taking unloading process of plasticity into account.

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Subsequent to the previous study on the ultimate strength of girder structures, the author has investigated into the mechanism and the plastic behavior of frame-type structures composed of a deep transverse and vertical webs with round corner at their ends.
A theoretical method is presented of analysis on the plastic failure of the structures subjected to a concentrated load at the center of the transverse. In this analysis, the effect of both axial thrust and shear on the plastic failure of the girder structure is taken into consideration. A discussion is made on the development of yield zones in the girders, and a general method is suggested to determine the location of the plastic hinge at the round corners.
Model tests have also been carried out to examine the collapse mode of the girder structures, where an extensive measurement has been made on the strain distributions in the components. The results of the tests have shown that the ultimate strength of such girder structures can be well predicted by the theoretical analysis which has been reported in this paper.

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The first container fleet in Japan is coming into view as a part of containalization of this country.
This paper gives the result of our study on the torsional strength and rigidity which is the most serious problem in the structural design of container ship.
First, the twisting moment acting on hull was obtained in static and the values of moment were compared with those by De Wilde's or Vedeler's theory.
Second, distortion of hatch opening and nominal bending and shear stress acting on the ends of cross deck in actual ship were studied and the effect of reinforcement at cross deck, was investigated.

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The major problem in designing a ship with wide and long hatch openings, such as a container ship, is to clear her torsional behaviour.
Many investigations have been done in regard to this problems. But these are all restricted themselves within rather a simple hull structure. It is, therefore, difficult to clear the torsional behaviour of above mentioned ship by applying the results of investigations published before.
In this paper, the authors try to establish the method of theoretical calculation for the torsional behaviour of the ship holding her structural characteristics and then to verify the reliability of the method of calculation by the torsion test on models. The results of the torsion test are analyzed according to above mentioned method and the following items are found conclusively.
(1) The torsional behaviour of such a ship can be well characterized and estimated by the method of theoretical calculation developed here.
(2) The distortion component of hatch opening due to warping of the cross section can not be neglected comparing to the ones due to change of the transverse displacement at the deck level.
(3) The corner stress due to distortion of hatch opening reaches its maximum at the end of the cross deck where the opening is changing its width from wider opening into narrower one.

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On designing of full container ship with cell constructions, new peculiar problems concerning torsional strength and vibration of ship's hull have been brought out due to the necessity of large hatch openings for handling containers, which were not required for designing of ordinary ships so far built.
In this connection, we have synthetically carried out theoretical and experimental investigations so as to clarify these problems in Mitsubishi Heavy Industry, Ltd.
This report describes some results of our experimental studies on the strength at hatch corner induced by torsional deformation of hatch opening.
In these studies, the following two experiments were carried out.
(1) Experiments using three dimensional steel models made similar to actual structure.
(2) Experiments using two dimensional photo-elastic models.
And, the conclusions obtained are as follows.
(1) The effects on the stress concentration of several types of hatch corner can be estimated by this investigation.
(2) The hatch corner structure of the designed ship has sufficient strength for the torsional deformation of the ship.

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The reason of the damage which would often appear on the bottom shell of forebody is simply because of the large impulsive pressure acted thereon, and it is known, in general, that when the angle between the bottom surface and the surface of oncoming waves becomes nearly zero the water pressure becomes very high, and the air is also entrapped between both surfaces.
In order to get damage phenomena reasonably, which would often appear on the bottom shell plate panel surrounded by stiffeners at all sides, the author is now concerned with the elasto-plastic response of long rectangular plates developed by impact on the water surface, from the view-points of both theory and experiment ; where the aspect ratio of used plates was chosen beyond about two times by scaling similarly compared with the plate panels of both destroyers and torpedo boats.
First, the damping effect being induced by air entrapped between the plate and the water surface is introduced into the theoretical treatment, and this will be approximately determined by putting the theoretical deflections of the plate equal to the experimental data, applying the try-and-error method to the nondimensional damping coefficient. After inserting the magnitudes of the damping coefficient determined as above into the theoretical equation again, we shall be able to obtain the so-called experimental formula of response due to only the first impact.
Second, supposing that concavities developed on bottom shells of ship are the accumulation of each permanent set induced by the slam load, the experimental test due to repetition of the same loads is continued until reaching the saturated concavities. The multiplier is then determined by dividing the concavities developed due to only the first impact with the saturated concavities reached after many impacts.
Applying such damping coefficient and multiplier determined as above to the actual cases, we discuss the comparison between computed results given by numerical analysis and measured data of concavities developed on bottom shells, by which reasonable coincidences are obtained between them.
If we substitute concavities developed on plate panels, the impulsive loads with which ships would have encountered during slamming are reversely determined. Then, so as to resist obtained loads, the determination of plate scantlings is further pursued either from elastic or elasto-plastic view-point.
Judging from our results, the plastic design which permits small amount of concavities is reasonably recommended rather than the elastic design, because we can prevent largely the increase of already developed concavities and also diminish newly spreading of concavities to the neighboring parts.

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The normal stress distribution in the mid-surface of the stiffened plate at vibration is investigated theoretically, and using these results, the effective breadth for the typical vibrating modes are made clear. The normal stress distribution of the simply supported rectangular plate stiffened by a inverted angle on its center line is investigated theoretically and experimentally. The experimental results agree fairly well with theoretical ones. In general, the formulas of the effective breadth of vibrating stiffened plate are same as the ones of the stiffened plate subjected to the statically distributed sine load, but in the case of mode that all the stiffeners do not laterally deflect, but rotate torsionally about the intersection at vibration, the effective breadth takes the indeterminate form.

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The added virtual mass and the added virtual mass moment of inertia induced by the vibration of a ship are defined as the equivalent mass and the equivalent mass moment of inertia deduced from the effects of water surrounding a vibrating ship. These equivalent mass and the equivalent mass moment of inertia can be estimated either from the inertia force (or moment) concept or from the kinetic energy concept as long as the ideal fluid is concerned, and the solution of the Laplace's differential equation is required in both cases.
This paper, dealing with the problem by the use of the inertia force (or moment) concept, shows that the so-called “finite element method” can be applied, with the aid of a high speed digital computer, to obtain the approximate solution of the Laplace's differential equation with any arbitrary boundary condition. In order to examine the accuracy of this method, the inertia coefficients C_v, C_H and C_T of vertical, horizontal and rotational vibrations of bars of circular and rectangular cross section are computed first by this method. Then, as an application of this method, the effects on the inertia coefficients of the restricted water and of the bilgekeel are shown numerically.

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Experiments were made to investigate the effect of prior strain history on the fracture stress curve and notch toughness of a killed mild steel.
Various types of pre-straining were subjected to the steel plate, i.e., compressive straining by 10% or 20%, tensile straining by 10% in oblique direction, tensile straining by 5% after 10% compressive straining and straining at lower temperatures. Fracture stress curves were measured on those pre-strained steels. At the same time, standard V-notch impact tests were also performed.
It was revealed after analysing the test results that the difference in strain history gave no appreciable effect on the fracture stress curves. Also it was known that the same correlation was found between the height of fracture stress curves and Tr₁₅ in those pre-strained steels, as reported for usual structural steels.

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When strength of a structure is discussed, amount of stress and strain concentration at discontinuous portion would be considered as one of the most important factors.
As an example, strict stress analysis around an elliptical portion of different material and different thickness in infinite plate has been carried out.
The problem of an elliptical boundary is a simple one. In this analysis, however, boundary conditions required for continuity in displacements and stresses are all satisfied. Therefore, some additional methods to usual analytical way have to be used.
As for more complicated boundaries and loading conditions, this analytical way would be similarly applied.

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At present it is a controversial problem how to formulate the mechanical condition for the onset of brittle crack propagation especially when it is accompanied by “large scale yielding”. A proper engineering and macroscopic fracture criterion is essential for any effective fracture-safe design.
Crack opening displacement (COD) concept seems to be promising as one of the possible fracture criteria for yielding materials. But satisfactory experimental checks on its validity and the limitation of its applicability have not been available.
As the first step in a series of investigations intended to establish a comprehensive engineering fracture criterion, the authors carried out an experimental study to clarify fundamental characteristics of critical COD value as the fracture-controlling material parameter. Several kinds of fracture tests were performed, using “double notched specimen” and microscope technique for the determination of critical COD values.
It was found that critical COD values were affected by various parameters such as temperature, specimen size, stress system, notch depth and plastic constraint. Some of these parameters were related to critical COD in terms of the effect of strain rate at the notch root.

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In the previous reports, the authors applied fracture mechanics approach to the problem of brittle crack propagation-arrest and of the quantitative evaluation of effectiveness of several types of crack arrester model.
This report contains the experimental and theoretical considerations on the “stiffener-plate type arresters”, in which crack arresting is effected by arresting force of the stiffener to restrain the open-up displacement propagating crack. Analysis of the effectiveness of the stiffener-type crack arresters is made on the basis of fracture mechanics concept. Results of large-sized brittle crack propagation test using the double tension specimens with several kinds of stiffener-type arrester are described as well as the comparison with calculated results.
The stiffener-plate type crack arresters are considered to be of much practical importance because their configurations are similar to the stiffening members often used in many welded steel structures such as ships, etc., But the method of quantitative estimation for the effectiveness of such crack arresters has not yet been available. Thus the authors carried out experiments and some approximate calculations to clarify the fundamental and practical aspects of the Stiffener plate-type crack arresters.

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The crack arresting characteristics of butt joint type welded crack arrester was investigated for Class E steel, which has been applied as the crack arrester in all-welded vessels, as well as that in the previous report.
The steel quality of Class E steel defined by the specification of ship classification society was evaluated from the viewpoint of crack arrester by using the large size crack arrester test specimens of 1, 300 mm wide. In addition, the steel quality as the crack arrester for a trially improved steel and an aluminum killed steel quenched and tempered were evaluated, too.
Then the design process how to determine the maximum distance between two adjacent arrester plates delivered was provided.
Finally, the crack arresting characteristics of stiffener type crack arrester was evaluated experimentally.

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Data are presented on the low cycle fatigue characteristics in the life between approximately 10 and 10³ cycles for a large number of steels including mild steels, high tensile strength steels, austenitic stainless steel, high carbon steels for rail and ultra high tensile strength steel.
In low cycle fatigue the power law relation between life and plastic strain range as proposed by Manson and Coffin has been amply verified, in more recent linear relationship were found when elastic strain range were separately plotted on log-log coordinates against life by Manson.
However these relationships were not correct with some high strength steels which consist of bainitic structure. This phenomena becomes remarkable with increasing the ultimate tensile strength, yield strength, and true fracture strength. The true stress at this turning point from linear relationship coincides approximately with ultimate tensile strength obtained by static tensile test.
The yield ratio, work hardening exponent are closely related with exponent of power law equation between life and plastic strain range.
These relations are predicted from micro-structural point of view, ferrite-pearlite or bainitic structure.

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Low cycle fatigue tests with plain specimens and circular-holed plate specimens were carried out under constant load pulsating tension. The materials used are mild steel (SM 41) and quenched and tempered high tensile strength steel (HT 60). The development of plastic strain around a circular hole was experimentally analysed by the Moiré method at successive stages of fatigue, and the following characteristics were clarified concerning the plastic behavior in the specimens under low cycle fatigue.
In the case of SM 41, the distribution of plastic strain is relatively even for both plain and circular-holed specimens through all the stages of fatigue. In contrast to SM 41, the tendency of localization of strain to narrow regions is remarkable in the case of HT 60.
It is seen that the generalized plastic strain which occurred in the specimens only fractured in ductile manner under pulsating tension shows nearly a constant value, irrespective of the number of cycles at fracture.
It is also found that the generalized plastic strain near the fracture initiation point shows the behavior of cyclic creep which generally consists of three stages. The second stage, the stationary stage, of it usually shows the minimum creep rate and occupied the major part of the whole fatigue life. The following relation is found to exist in this stage, irrespective of materials, size of specimens, existence of circular hole, and frequency of load cycle,
(Δε) · N_f=ε₀/2
where Δε is the minimum creep rate,
N_f is the number of cycles at fracture,
ε₀ is the generalized plastic strain at fracture in simple tension.

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Recently along the rapid growth of ship size, the use of large bore pipes have increased resulting in the increase in hot bending works and the use of bend pieces. This necessititated the rationalization and improvement in efficiency of the pipe bending method. Here high frequency induction heating pipe bending method was developed and applied mainly for bending of carbon steel pipes, which eliminated the use of bend pieces, shortened the time for bending method, and improved the quality of the bends produced. About the bending of alloy steel pipes and copper alloy pipes, various studies have been made. In high frequency induction heating pipe bending method water cooling treatment is applied immediately after bending in order to reduce the amount of deformation. Some alloy steel pipes which have high quench hardening properties are afraid to have bad effects at the bends by water cooling. But the effect by hardening due to water cooling for alloy steel pipe was hardly noticed in case of adoption of water-cooling system with a certain interval for air cooling. Mechanical properties of the alloy steel pipe bent by high frequency induction heating method compare favourably with those by the conventional hot bending works.

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Modernization of shipbuilding industry cannot be achieved without establishing such highly standardized and specialized production processes as those of mass production. Systematically 'composed mechanization of automatic welding, for example, attained by essential application of numerical control technique to the drawing, fabricating and assembling works, will show the most, effective way of modernization. On this basis, shipbuilding operations go on as smoothly as they do in mass production, with production control through electronic data processing.
The authors have established wide range of computer system, improving production system. The computer system in the field of production management, named “COSPAC”, involves overall production planning programs from master schedule to detail operation schedules. This paper relates with computer program for production planning, “LOTAS”, which is a part of COSPAC.
The authors lay great emphasis on repetitive computer simulation in order to increase reliability of production planning, efficiency of production and profitability of shipbuilding.

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