The characteristics of the waves in the vicinity of the stern and the mechanism of wave resistance reduction by stern-end-bulb are experimentally investigated. Observation of stern waves, measurement of disturbance velocities, wave height, momentum loss and pressure on hull surface are carried out, and they show that waves in the vicinity of the stern have nonlinear properties and that the effect of stern-end-bulb considerably consists in the attenuation of nonlinear stern waves. The problems of scale effect in wave making and wave reduction by stern-end-bulb and those of the design for the improved stern-end-bulb are also studied.

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Bow wave breaking phenomena around full ship models are studied by velocity field measurements and by a flow visualization technique. By use of dye particles placed in front of the bow of full form, the authors find that there exists a shear flow on the free surface. Then it is shown that the shear flow has a significant effect on the formation of breaking bow waves. Namely an artificially strengthened shear flow affects considerably to the extent of breaking of bow waves and as a result, the resistance of ship model is increased. On the contrary, by the acceleration of the free surface toward ship model, i.e. by the reduction of shear, wave breaking phenomenon and ship resistance are reduced. Thus, the authors consider that the bow wave breaking is regarded as a kind of separation at the free surface in front of the full bow forms.

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The measurement and the analysis of the unsteady waves generated by a ship model making sway, yaw and roll motions and simultaneously running with a constant forward velocity are proposed for getting the energy flux of the waves and deriving the wave damping coefficients for those motions. The damping coefficients derived do not include the damping effects caused by the dissipation of energy due to the viscosity of water. Accordingly they can be directly compared with the predictions by the Strip theory.
Some examples are presented for the damping coefficients obtained by the wave measurements. The wave damping coefficient for roll is confirmed to be independent of forward speed for greater Ω=Vω/g. and can be predicted fairly well by the Strip theory. The accuracy of the theoretical predictions are revealed, however, to be questionable for the damping coefficient of yaw.

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Any wave generator of model basins has always a limitation of generating capability concerning with both wave frequency and amplitude. So, it is only practically possible in tanks to generate a truncated spectra waves in some frequency range.
Meanwhile, the model experiments in irregular waves to keep the specific values of H and T are oftenly demanded by customers. In these cases, the realization of specific H and T should have priority over the realization of spectra shapes.
Therefore, we introduce the “Modified Truncated Wave Spectra” to keep the specified values of T and H, and the following items are investigated in this paper.
1) Calculating methods on the modified truncated spectra are induced for P-M type and JONSWAP type.
2) Practical usefulness of these spectra is checked by the experiments.

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In order to simplify the technique of ship motion model tests in oblique waves, it is proposed to carry out towing model tests using a measuring apparatus of 5 degrees of freedom which supports sway and yaw motions with linear springs. This technique enables the model tests in oblique waves to be performed more efficiently comparing with the tests using a free running model. Moreover, phase lag measurements with regard to encounter waves have a good accuracy because the surge motion is fixed in this guidance system.
Meanwhile, towing conditions in these tests are similar to the assumptions of the theoretical calculation based on the Strip Method. Therefore this test is suitable for the direct comparson between experiments and calculations.
Though it is unavoidable for measured data to be affected by this guidance system, it is possible by some pre-calculations to estimate the degree of its influence and to select a optimum guidance system. Accordingly the guidance system which is planned appropriately has a very small influence for measurements. In conclusion, this guidance system is recommended to be used routinely.
Using this guidance system, model tests in oblique waves were executed for a container ship model which was adopted as the ship form for the comparative calculations of the ITTC. Successful experimental data about ship motions and 5 components of wave-induced loads were obtained. The results of comparison between model tests and theoretical calculations revealed that there were some discrepancies and that further investigations on details of the Strip Method should be carried out.

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The second-order potentials, pressures and forces are calculated by the Boundary Integral Equation Method, which was proposed in previous report (1), in two-dimensional radiation problems.
The second-order forces are decomposed into each non-linear terms and the quantitative comparison is made and dismissed. The experiments in forced heave and sway motions are carried out and compared with the calculations.
Results obtained are as follows :
(1) The numerical results by the present method agree fairly well with existing results and experimental results in first and second-order radiation problems.
(2) In radiation problems, the non-linearity of the body-boundary condition is dominant and the second-order forces are nearly proportional to the wave-number of the motion.
(3) Total second-order forces show good coincidence with the experimental results.

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A new multi-body-type floating breakwater, which consists of an infinite array of slender bodies with regular interval, is proposed and the two proto-types are examined in a model basin. A mathematical model is obtained in order to estimate the performance. This mathematical model is useful to design this breakwater to meet user's requests.
The velocity potential for the water motion due to this floating breakwater is obtained by using Newman's unified slender ship theory and Isshiki's expression for a periodic source in a rectangular channel. This is used as a basis for the mathematical model.

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This paper describes about both analysis of performance of wave power absorbers, and prediction of absorbed wave power.
The authors clear up the diffinition of absorbed wave power spectrum, and calculate the expected value of absorbed wave power around Japan by making use of the data of long term wave frequency. Salters Duck is used as one of examples of wave power absorbers.
The conclusions are as follows :
1) Absorbed wave power spectrum consists of two components, the one is the spectrum which indicates the constant component of absorbed wave power, and the other means the varying component. These spectra can be estimated theoretically by use of the present method.
2) The long term expected value of absorbed wave power around Japan correspons to about twenty or thirty percents of the power supply in Japan in 1975.

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Model tests in a cavitation tunnel are necessary to predict cavitation erosion of ship propellers. Several erosion test methods have been developed such as paint test, aluminum erosion test etc. Paint test is usually used to predict the risk of erosion at many research institutes. In spite of its simplicity, the test results are affected much by slight change of testing procedures.
This paper describes two new erosion test methods, which are aluminum plate erosion test and “Prescale” test. At the aluminum plate erosion test, a thin plate of pure aluminum is glued on a blade surface and its surface roughness increase is measured after erosion test at a cavitation tunnel. Impact pressure caused by cavity collapse can be measured using a pressure detecting film “Prescale” which was recently developed by a film company in Japan. Those two test methods were applied to five foil sections. From these experimental results, a close correlation between erosive intensity and fluctuation of cavity length was verified.

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Linearized theories on a supercavitating hydrofoil are not suitable for the foil with a rounded nose where a sheet cavity does not generate from the leading edge of the foil. The theoretical result gives a negative infinite pressure at the leading edge because of singularity.
Furuya proposed a new theoretical method to remove the singularity by applying the singular perturbation method. But it can not give a definite position of cavity tip for a given cavity end. Developing Furuya's theory, the authors propose a new iterative method in which the position of cavity tip agrees with the laminar separation point.
Cavitation experiment was made for a hydrofoil with parabolic section. The test result was modified to remove wall effects of tunnel, using a newly developed method by the authors.
The calculated results by the proposed theory agreed with the experimental results on the pressure distribution as well as the cavity shape.

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Authors planned theoretical and experimental research on Highly Skewed Propeller (HSP) in order to establish advanced HSP design method which enables remarkable decrease of vibratory propeller forces, high propulsive efficiency and no problem related to blade strength.
First, simplified method to calculate wake adapted skew distribution and non-linear lifting surface method to estimate propeller open characteristics were developed. These outlines are presented in this paper.
Then, propeller open test (1 st, 3 rd and 4 th quadrants), self-propulsion test and cavitation test (cavity extent and thickness) were performed by using following three propellers designed for a container ship.
Convensional Propeller (CP) of MAU type (MPNO. 80-3)
Convensional HSP (MPNO. 80-4)
Theoretically designed HSP (MPNO. 80-5) (Wake adapted skew distribution is adopted, and blade section and rake etc. are determined from the result of non-linear lifting surface calculation in order to get high propeller open efficiency.)
The test results obtained are as follows;
(1) Thrusts of MPNO. 80-4 and MPNO. 80-5. at astern condition are lower than that of MPNO. 80-3.
Propeller open efficiency and propulsive efficiency of MPNO. 80-5 at propeller design point are about same as those of MPNO. 80-3, even though propeller open efficiency of MPNO. 80-4 at propeller design point is about 2% lower than that of MPNO. 80-3.
(2) The effect of skew on cavitation characteristics related to surface force (time variation of cavity volume) was quantitatively confirmed.
This research continues.
The sequent reports will inform the other model test results like measurement of pressure fluctuation on a hull and measurement of stress on propeller blade etc.

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The strength of a heavily loaded propeller for a high arctic class ship-more than class 7- has been studied.
At first, ice impact and ice milling model test have been carried out. Sequentially, statical loading test also has been conducted, and the measurement results have been analysed by FEM technique. In impact and milling test, 320 mm dia. NiA1Br 4-bladed model propellers have been used. Ice blocks for test have been specially prepared, saline ice and paraffin wax blocks. This 1st report mainly describes details of the model tests of impact and milling tests. From this study, the authors have made clear an interactive behavior of propeller blades and ice blocks, namely bending moment, thrust, and torque of propeller blades and shafts during impact and milling condition.

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In our previous report, the authors developed a calculation method of the ultimate strength of square plates subjected to compression and shear. In order to get more practical solutions, in this paper, the previously developed analytical method is applied to rectangular plates subjected to compression and shear.
At first, buckling analysis is carried out using the energy method as to rectangular plates with aspect ratio β=2 and 3. Secondly, post buckling elastic analysis is conducted on the basis of the knowledge of buckling strength and mode. And finally, the ultimate strength of rectangular plates is obtained by using collapse condition which is introduced by the plastic hinge line method.
The following conclusions are obtained.
(1) As the result of the buckling analysis based on the energy method, the buckling strength and mode of rectangular plates, which are subjected to various kinds of combination of compression and shear, are obtained. (Table 1)
(2) As the result of the post buckling elastic analysis, approximate equations for loadmaximum deflection curves are obtained. These equations can be applied to various kinds of combination of load. (eqs. 17 and 18)
(3) Interaction curves of the ultimate strength of rectangular plates with aspect ratio β=2 and 3 are obtained. According to the above mentioned curves, it is clarified that ultimate strength and collapse modes depend largely upon the load ratio σ/τ. (Figs. 17 & 19)

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The collapse behaviors of wing tanks in ore carriers are investigated experimentally using large scale models. Then the behaviors of ore pellets, struts and curved girders are idealized using the results of the previous reports (Reference 5-8). Finally the collapse behaviors of wing tanks are analized with the aid of those idealizations by the elastic finite element method. The comparisons are shown between the experiments and the calculations.

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A small cargo boat of 48 m suffered from serious damages among rough seas, and its main hull was bent at S. S. 7 by hogging moment. The ship under consideration was in ballast condition, and was carrying a large amount of ballast water in the fore-peak tank. If slamming impact pressure occurs at S. S. 7, a large hogging moment may appear at the section. In the first report, the analysis based on the hydroelasticity shows that this damage is caused by hogging moment due to bottom slamming, although, in the case of conventional ships, slamming causes a large sagging moment in the mid-part. Elastic responses are calculated step by step for the ship idealized as a Timoshenko beam, taking account of slamming impact force, which are determined with respect to instantaneous configurations. It is shown that slamming response gives hogging moment enough for the damage in an unlucky condition of waves corresponding to the sea state reported. In the second report, the collapsing strength of the ship will be estimated by the help of experiments.

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In the first report, it is clarified that a small cargo ship of length 48m in ballast condition is subjected to large hogging moment due to bottom slamming. In this report, the strength of the ship at S. S. 7 against hogging moment is estimated with the help of experiments for a structural component. The collapsing strength of S. S. 7 is significantly reduced by the existence of bottom corrugations which may be caused by slamming previously. Bottom corrugations reduce the effective stiffness of the bottom plates and also the section modulus I/y for bottom. Compared with the value of hogging moment caused by slamming, the strength of the ship may be insufficient for preventing the structural failure of the ship, although it is much larger than the required strength against the bending moment expected by the linear conventional theory.

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In this paper, the behaviour and the compressive strength of long rectangular plates (aspect ratio α=3 and 4) with four clamped edges under increasing compression and constant hydrostatic pressure, are studied theoretically and experimentally following the previous papers.
Results obtained in this study are summarized as follows :
1) The basic equations for pursuing the elastic behaviour of the plate with four clamped edges under such combined loads, are led by means of the energy method. Carrying out the analyses based on these equations, characteristics of behaviours including buckling phenomena are clarified.
2) The compressive strength of such a plate is calculated in the same way as the previous paper, and characteristics on the compressive strength and the collapse mode of the plate with four clamped edges are clarified. From these results, it is found that the tendency of the variation of the compressive strength due to hydrostatic pressure is generally similar to that obtained for plates with simply supported edges.
3) Performing tests for thin plates (α =3) having comparatively large value of (b/t) √σ_Y/E, the obtained results on behaviours including buckling phenomena and compressive strength are in good agreement with theoretical results.

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It is important to estimate accurately the maximum values of sloshing load in cargo tanks of membrane type LNG carriers in order that their reliability and safety may be maintained even in their severe service condition.
Usually, model tests are carried out in order to estimate the sloshing load. But it is well known that measured impact pressure fairly scatters even in the case of harmonic oscillation. Then, we performed the statistical analysis by using both three parameter weibull distribution and Gumbel extreme distribution with upper limit in order to deal with the scattering of impact pressure. As the results, it is turned out that the application of Weibull distribution is useful to fit the experimental values and to estimate extreme values. Remarks in statistical analysis are also discussed in this paper.

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In order to apply fracture mechanics to hull designs, a new design method using unique models is proposed.
This method has following characteristics.
1) Ordinary hull designers, who have no special knowledge in fracture mechanics, can estimate,
2) both crack initiation life N, and crack propagation life N_p,
3) using only the stress distribution in the condition without cracks,
4) without troublesome analysis of K Value,
5) without a computer,
6) with enough accuracy.
This paper represents the theoretical background of the new method, verification of the accuracy of K Values estimated by the method and application examples.

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In order to make the fracture mechanics analysis readily applicable at design levels with efforts normally required in design for stress analysis, this paper proposes its simplified application procedure. The key point of this procedure is the estimation of the crack propagation path and K value from the stress analysis results on crackless model.
The proposed crack path estimation criteria are based on the study of the relationship between the direction of principal stress in a flat plate as well as the K value when the crack reaches a normal crossing member and the crack propagation path. The proposal also includes simplified K value estimation methods by grouping actual forms of cracking into several typical patterns, so that the designer can estimate the K value for almost any type of structural members which he will face in his design. To verify the validity of the proposed procedure, the bottom transverse damage of a large tanker was analyzed for comparison with the actual cracks. The analysis results are consistent in explaining the actual damage phenomena and this procedure has been proved quite practical through examination of the design measures taken.

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Verification for the cargo tank of the liquefied gas carrier that it is of safe life, type B design which presupposes a limited fracture calls for analysis of fracture mechanism of the tank structure.
There is a move, as well, towards performing the similar analysis for ships other than the liquefied gas carrier to assure their structural safety.
When analyzing the fracture mechanism, in what manner to calculate the stress intensity factor K is one of important consideration. This problem has been explored by No. 3 Standardization Research Committeel) and No. 169 Research Committee of the Shipbuilding Research Association of Japan, etc., but these researches contain not all members of hulls.
The author carried out fatigue tests on some types of tank structural members, to obtain data on the initiation and propagation of fatigue cracks. Propagation of the fatigue crack can be defined by the Paris' law which employs K as parameter. Based on these data, as well as using the ordinary methods of K and stress concentration calculations by finite element method, etc., the author devised an approximation formula to obtain K for each of the following four types of tank structural members.
1) Crack at the bracket end jointed in “T”, “L”, or overlapped form to the longitudinal.
2) Crack at the end of stiffener reinforcing the bracket.
3) Crack at the end of web stiffener in corner R of girder joints.
4) Crack at the snipped end of the built up type of the girder.

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This paper deals with the significance of the crack exisitng in the stress concentrated region from a view point of brittle fracture.
The relation between the J-integral of the cracks existing in the stress concentrated regions and the local strain is investigated experimentally and theoretically with the aid of elasticplastic finite element analysis.
The finite element analysis and test results lead to the following conclusions :
(1) A non-dimensionalised J, JE/ (σ_Y²a), computed in a plane stress condition for several kinds of stress concentrated regions with a short crack under tension gives a reasonably compact group of data, when plotted against the averaged strain across the assumed cracked area, e. The upper bound of a J design curve is defined as follows :
JE/ (σ_Y²a)=4 (e/e_Y) ² for e/e_Y <1
JE/ (σ_Y²a)=4 (e/e_Y) fore/e_Y≥1
where E : Young's modulus, σ_Y : yield stress
a : half length of crack, e_Y : yield strain (=σ_Y/E)
(2) Use of this curve provides a good estimation for the brittle fracture from a crack existing in the stress and strain concentrated region.

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In this study, the characteristics was investigated of brittle crack propagation in mild steel. And it was experimentally obtained as the material property in relation to the crack velocity and the temperature and the dynamic fracture toughness K_D of common hull steel.
Next, it was tried to forecast the crack propagation behavior in plates and beams structure. Using the double tension type large size specimen with stiffener, simplified procedure by modifying the L. B. Freund's solution was experimentally verified to be useful to predict the brittle crack velocity fluctuations.
The procedure is based on the theory of the stationary crack propagation, and extended to the non-stationary crack. So when the boundary load makes no displacements during the crack propagation, that is, no additional works this method is seemed to be considerably promising.

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The problem of a slightly non-collinear, quasi-static crack growth is considered. Problems of this kind have been treated by a first-order perturbation method, in the contex of Mushkelishvili's complex potentials, by Banichuk, and Goldstein and Salganik. Recently, Cotterell and Rice have employed the same method and obtained a rather simple first-order expression for the stress intensity factors, which are then used to examine the crack growth path of a semi-infinite crack in an infinitely extended region.
In the present paper we consider a solution method, which takes into account the effects of the geometry of the domain, i. e. finite outer boundaries, as well as the finite crack length. For this purpose we first calculate the first-order perturbation solution for a semiinfinite straight crack with a slightly branched and curved extension, which will be used as a fundamental solution of the problem. When a loading condition is given, the stress intensity factors at the extended crack tip can be deduced from its near tip field solution. Then we use an alternating solution scheme to establish the effect of the geometry of the domain, where the far field behavior of the fundamental solution plays an essential role. The first-order expressions for the stress intensity factors are obtained for a slightly branched and curved crack extension in a finite domain. The geometrical effect due to the crack extension, which appears in the expression of the stress intensity factors, is proportional to the length of the crack extension.
An initial prediction of the crack growth path is obtained under a slightly non-symmetric loading condition. For this purpose we assume a locally symmetric deformation ahead of the crack tip; i. e. the Mode II stress intensity factor vanishes along the crack extension path. As a simple analytical example we consider the slightly slanted Griffith crack under the biaxial loading condition. The small inclination of the crack with respect to the principal stress directions, is considered as the imperfection (which causes a non-collinear crack growth), and the stability of the crack growth path is examined. Numerical applications of the present formulation to more complex problems will be made in subsequent works.

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It is important to investigate characteristics of the vibration of jack up type oil rig foi its successful design. FEM is available to calculate natural frequencies accurately, but there are a few uncertainty to be studied, such as, virtual mass of leg vibrating in water, supporting condition of the sea bed and others.
This paper, first of all, tries to find the most suitable model for FEM, and after obtaining experimental virtual mass of leg with model tests, the authors calculated the natural frequencies and the mode shapes by the idealized model composed of beam elements and plate ones, supported elastically at the sea bed. Those calculated natural frequencies in the first three order are found to be in good agreement with the experimental ones obtained by vibration tests using the actual oil rig.
Main conclusion are as follows.
1) It may be practically acceptable that virtual mass coefficient of leg composed of circular cylinders, C_V, equals 1.0.
2) On calculating natural frequency of oil rig in jacked up condition, spring effect of the sea bed should be taken into account.
3) In estimating dynamic response of oil rig, the lowest three natural frequencies govern the dynamic response due to wave force. Then the higher frequencies than those can be disregarded for dynamic response.

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The relation between the maximum holding power ratio and the shear strength of the sea bed is discussed on the basis of experimental results of anchoring and sounding tests. Sounding tests have been performed with the device which is proposed in the present paper to measure the strength of the bed as the N-value.
If the bed is in loose state as N<0.6, Danforth anchor is embedded deeply in it, and therefore its maximum holding power ratio becomes very large. On the contrary, Hall's anchor performs in the vicinity of the surface in any case and its maximum holding power ratio increases as the N-value. It should be noted that, when Hall's anchor moves on the bed, its holding power decreases suddenly because of its unstableness.
In case of deep sea mooring, the anchor is dragged by wire or hawser with large scope angle. In order to prevent the anchor from lifting by large upward forces, a certain length of chain is commonly attached at the anchor shackle. In the present paper, behaviors of the chain are analyzed on the basis of experiments, and a chart is proposed for calculating the weight of chain necessary for satisfactory performances.

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Low-temperature, low-cycle fatigue strength of aluminum alloy welded joints were investigated, carring out deflection controlled repeated bending fatigue tests at room temperature and at -196°C on the following four materials : 5083-O plate, 5083/5183 butt weldments with and without reinforcement, and Tee-fillet weldments made by MIG welding process.
The results showed the fatigue properties at -196°C to be superior to those at room tem..' perature, except for the butt weldment with reinforcement machined off in the fatigue life range less than 100 cycles. The fatigue strength ratio at both temperatures increased with increasing fatigue life up to about the ultimate tensile strength ratio at both temperatures.
The strain-basis fatigue strength reduction factor due to the reinforcement of the weld K_f., as difined by the ratio of the fatigue strength of the weldment to that of the 'plate, was found to be essentially the same at both temperatures and to become greater than or equal to the elastic stress concentration factor at the weld toe. The above mentioned factor K_f., was reasonably evaluated by Stowell's equation.
From these observations it is concluded that the application of the fatigue strength at'room temperature as an allowable stress in the fatigue design of LNG tanks will be on the conservative side.

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In our previous paper, assuming that phenomenon of fatigue crack propagation is continuous fatigue crack initiation at crack tip and crack initiation a life is used up when damage caused by cyclic strain near crack tip is accumulated and reached to a certain critical value during ΔN cycles, authors proposed a law- on the fatigue crack propagation rate under fully reversed loading neglecting the crack closure phenomenon.
In this report, effect of mean stress on the fatigue crack propagation is discussed quantitatively. It is assumed that main factors of mean stress which affect the crack propagation rate are phenomena of cyclic creep and crack closure, and a new law on the crack propaga-tion rate is proposed.
In order to prove the validity of the law, crack propagation rate curve calculated by the law were compared with experimental results obtained by several investigaters and fairly good agreements between them were found.

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Completely reversed bending fatigue tests were carried out on fillet welded cruciform joints with no penetration of mild steel and the effects of the ratio of a fillet size, h, to a main plate thickness, t, on their fatigue strength were examined with the aim of fracture mechanics method. The main conclusions obtained are as follows :
(1) It can be assumed that the fatigue crack initiation life, N_c, is equal to the fatigue failure life, N_f, in a toe of weldment since the thickness of the main plate is thin on fillet welded cruciform joints used in this study. The N_f at the toe failure may be estimated using the relation between N_f and a stress-strain function, D, obtained from the results of reversed bending fatigue test conducted by the smooth plane specimens of a base metal.
(2) In the reversed bending fatigue tests, a weld failure occurs at any stress amplitude on the fillet welded cruciform joints with h/t of below 0.3, while a toe failure takes place on those with h/t of over 0.5. On the fillet welded cruciform joints with h/t of 0.3 to 0.5, which correspond to critical weld size, the weld failure occurs at higher stress ranges, and the toe failure at lower stress ranges.
(3) The fatigue crack growths from the tip of a lack of penetration are observed with optical microscope when the variations of stress intensity factor, ΔK, which are obtained by identifying the lack of penetration as an initial crack, are more than the variation of threshold stress intensity factor, ΔK_th, in a weld metal.

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Fatigue crack growth under random loading has been extensively studied since nearly a decade in relation with the design of offshore structures, ship hulls, pressure vessels and so on.
For the sake of simplicity, random loads in service conditions are often simulated by block programmed loads in laboratory fatigue tests. However, very few studies have been conducted on the difference of fatigue crack growth behaviour between random loads and block programmed loads.
The authors previously presented an experimental study on fatigue crack growth under block programmed loads, and discussed on the effect of block size on fatigue crack growth life. A proposed model gave a good prediction of fatigue crack growth life in block programmed loading tests. In the present paper, fatigue crack growth tests were performed under three different types of block or random loads. Experimental results show that fatigue crack growth behaviour under random loads is very similar to that under block programmed loads with short periods. Miner's rule gave a non-conservative estimation for crack growth life under both random and short block loads. Life estimation by the model previously proposed agreed well to the experimental results.

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This paper describes a further study on the problem of transient phenomena such as transverse forces acting on tack welds and deformation behavior of groove resulting from butt weld of thin mild steel plates.
A series of tests on the transient behavior of butt welded joints is performed and experimentally obtained results are compared with those of theoretical calculations in which unsteady heat conduction analysis and uncoupled thermal elastic-plastic analysis are carried out by use of the finite element method as described in the previous report. The calculated results are fairly in good agreements with_ the experimental results.
In the initial stage of butt welds, transverse forces acting on tack welds and deformation behavior of groove differ with presence of root gap significantly. However, as the weld progresses, the difference decreases gradually because influence of trailing stress field at the rear of the moving weld heat source becomes more predominant. Special attention is made to clear effect of welding speed closely relating with weld heat input on the transient behavior of butt welded joints.
It is shown that, as a weld heat source approaches to end of weld, in case of slow speed welding transverse compressive force is generated on the end tack weld and the groove of the welded joint closes, while in case of high speed welding tensile force is generated on the end tack weld and the groove of the welded joint opens, and that closing or opening behavior of groove of butt welded joints may be specified by a parameter β representing shapes of isothermal lines around a Moving weld heat source.

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The role of adequate non-destructive inspections and following repairs of detected flaws is essential in order to continue the integrity of welded structures. It is, however, pointed out that catastrophic failures sometimes happen due to insufficient repairs having no regard for unfavorable effects of repair.
In case of welded joints, when a detected flaw is repaired by renewed welding, the fracture toughness of a flaw which is not discovered and adjacent to the detected flaw becomes smaller because of so-called the Hot Straining Embrittlement. Therefore, if such effect mentioned above is not taken into account, the reliability of the welded joint must be overestimated.
The purpose of the research is to investigate the effect of the Hot Straining Embrittlement giving rise to serious deterioration of fracture toughness and evaluate the optimum range of repair in order to prevent an unexpected failure with the aid of reliability analysis.
This report, at first, describes deterministic or probabilistic factors which should be adopted in the reliability analysis, a model and formulations of the analysis, and then, presents the comparison between estimated reliabilities of various cases, i. e., no repair, repair with or without the Hot Straining Embrittlement (HSE).
From the results of numerical examples, it is shown that, 1) the probability of failure of repair with HSE is extremely larger than that of repair without HSE, 2) when the detected flaw is small, the probability of failure of no repair becomes smaller than that of repair with HSE, and 3) the important results are obtained on the range of repair with HSE.

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It is known as “Liquid Metal Embrittlement (LME)” that elongation and reduction of area can be markedly reduced when a solid metal is coated with a certain liquid metal and then immediately deformed in tension. There are several reports on the LME cracking of steel structures by molten zinc occured while hot dip zinc galvanizing.
In this study, first of all, LME of SM 50 A and STK 55 steels contacting with molten zinc was examined by both tensile and bending tests using a special testing apparatus. The elongation and the reduction of area in molten zinc were reduced to 0.21 and 0.170.20 at the same temperature in air, respectively. However, the tensile strength was almost the same as that of in the air. LME of welded steel joints was also examined in molten zinc. In the second place, the thermal strain variations of a steel pipe which was dipping into molten zinc were measured by using capsule type high temperature strain gages, and the data obtained were converted into thermal stresses. On the other hand, the temperature distributions of the steel pipe which was dipping into molten zinc were analyzed sequentially by using heat equation, and quasi-static thermal stresses were analyzed sequentially by using “Finite Element Method (FEM)”. The thermal stresses measured by using capsule type high temperature strain gages were similar to the analyzed stresses by FEM. The higher the dipping speed in molten zinc becomes, the smaller the thermal stresses are, which occur in the steel pipe while dipping. Therefore, quick dipping is one of the useful countermeasures to prevent the crack occurence in the steel members which are galvanized.

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The deck is a main strength member of a ship structure. When the strength of the deck is considered, the contribution of plate elements which are subdivided by stiffeners and girders is important. For this purpose, precise evaluation of compressive strength of the plate elements is necessary.
In this paper, as a series of research, the ultimate strength of a rectangular plate under thrust is theoretically investigated taking into account of the welding residual stresses, in addition to welding deformation, which was dealt in the previous report. The main conclusions obtained in this study are presented in the following.
(1) The existence of residual stresses tends to maintain the mode of the minimum buckling strength and decrease the effect of other modes of the initial deflection. In this way, the critical ratio of the components of the initial deflection is influenced by the residual stresses, though this effect is small.
(2) The welding residual stresses reduce the secondary buckling strength. For this reason, secondary buckling sometimes takes place, which reduce the ultimate strength.
(3) The effective coefficient of initial deflection is more precisely discussed, and it was found that this coefficient decreases as the magnitude of initial deflection increases. For this relation, simple formula is proposed.
(4) Simple formulae are proposed for the compressive ultimate strength of a rectangular plate with consideration of the effects of welding residual stresses and initial deflection.

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Welding deformations and reisdual stresses are major factors which control the collapse strength of externally pressurized vessels. Problems of circumferentially welded cylindrical shell and spherical shell welded along the equator have already been investigated by some of the authors.
There are many cases that a penetrator or a partial sphere is welded circumferentially to a spherical shell in actual structures. In this case, the spherical shell near the weld line and the penetrator tend to sink toward the center of spherical shell. Few researches on this problem, however, have been reported.
In this report, the deformations of a spherical shell caused by the welding of penetrator or partial sphere are investigated. Experiments are carried out in order to clarify the characteristics of welding deformations and the effects of shell and penetrator dimensions and welding procedure on them.
The results obtained in this research are as follows :
The deformation in a spherical shell is mainly caused by welding thermal shrinkage. Its profile resembles to that in butt-welded cylindrical or spherical shell, and it is approximated by the deflection of spherical shell of which radial load is applied to the weld line. On that basis, two parameters which correlate dimensions and rigidity to welding deformations of spherical shell are proposed, and their effectiveness are confirmed by comparing with the experimental results.

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The residual stresses and deformations due to circumferential welds of spherical shells are one of the most important problems concerning to collapse strength of pressure vessels. Nevertheless it can be said that few researches have been carried out with regard to these problems.
In this paper, one dimensional thermal elasto-plastic analysis using Rayleigh-Ritz method is applied to the axi-symmetric thermal stress problems of comparatively thin spherical shells as was done to the cylindrical shells in the previous paper.
It is clarified that the parameter (Q/h) ·β is the most important factor to describe the dimensions of shell and welding heat input. Therefore welding deformations and residual stresses can be described by this parameter. To be available for practical purpose, design charts are proposed.

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The pressure hull for deep submersible has to cope with the trade-off subject of load carrying capacity and minimum weight at the same time. For this reason, spherical shell has been normally adopted for the pressure hull. Besides this, high yield strength materials and high-precision manufacturing are indispensable for it.
The authors have already confirmed that GTA welding is effective for the pressure hull of 6, 000 m class of 10 Ni-8 Co steel. However recently, electron beam welding, which has the possibility to reduce welding distortion in comparison with GTA welding, has come to withstand this objective.
The authors, in this paper, have estabilished the effectiveness of EBW for the pressure hull of 6, 000 m class of 10 Ni-8 Co steel.

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