Generally metallic materials possess high mechanical strength, but inferior to thermal or chemical erosion. On the other hand, for ceramics high thermal and chemical erosion resistance can be expected. Therefore, metallic materials of which surfaces are coated by ceramics, that is, coating materials are considered to unite the good qualities of both. By such reasons there exist many used instances of coating materials, but it is doubtful whether sufficient investigations for the materials have been performed not only theoretically but also experimentally. Under these circumstances, in this paper thermoelasticity taking place in a coating slab is dealt with analytically. Furthermore, in order to make clear the general tendency of the thermal stress induced in such a slab, some numerical results calculated based on the obtained analytically are shown by graph together with several explanations.
This paper describes a method of analysis of crankshaft temperature distribution by means of a new theoretical calculation. This method of analysis, not dependent on the results of experiments, is easily applicable to the analysis of temperatures of crankshafts of any size or material. Temperature distribution of the journal and the crank web at an early stage is given. Then, clearance or contact pressure between the journal and the crank web is calculated on the basis of the thermal expansion. The value of thermal resistance between these two parts is obtained from the value of the clearance or the contact pressure. Boundary conditions around the crankshaft are theoretically obtained as well. By application of these boundary conditions, analysis of temperatures by the finite element method is performed. Temperature distribution after the laps of a short period of time is thereby obtained. On the basis of the new temperature distribution thus obtained, new boundary conditions are calculated. Calculations are performed by repeating the aforementioned procedures. Good agreement was obtained between the theoretical results and experimental values. As a result, the practicability of this analysis method was verified.
The method of estimation of the corrosion fatigue strength was proposed on the occasion of loading the constant stress, or varying stress. As a result, the estimated corrosion fatigue strength was considerably corresponded to the experimental results under the experimental conditions within the limit of this paper. Especially, when the constant stress was loaded, it was founded that on the corrosion fatigue test by combination the low carbon steel with the 3% saline solution, in spite of the dimension of the specimen, loading condition, and repeated rate, the estimated corrosion fatigue strength was expressed by σac=σa/1+2.16×10-4⋅Nf0.75/f0.39 , when σa is the fatigue strength in air, f is the repeated rate (cpm) .
For estimation of the fatigue life of the combustion chamber walls, a study has to be made on the influence of various stress fluctuation on the fatigue strength of material. From this point of view, taking the cooling side of combustion chamber walls as the object of study, the fatigue tests on Cr-Mo cast steel were carried out through four types fluctuating stress wave patterns set on the basis of the measurement results of load on ship under service condition and stress analysis. The following results have been obtained: 1) It has been confirmed that the fatigue life under superimposed stress wave pattern decreases even when superimposed stress amplitude is below the fatigue limit of the material. 2) The fatigue life Nt by various fluctuating stress wave patterns is nearly within a range of 3 Ne - 1/3 Ne of the estimated life Ne by the modified Miner rule. This means that rough life estimation of the combustion chamber walls can be made by this method. 3) The influence of the stress change by cleaning work of turbo chargers and the engine starting/stopping in a harbor, the fatigue strength of cooling side of the combustion chamber walls is small. This can be neglected. 4) It has been clarified that there exists a linear relationship between number of superimposed stress cycle and fatigue life in log-log scale. Based on this result, we proposed an experimental equation on the influence of number of the superimposed stress cycle to the superimposed fatigue strength of material.
Cast iron materials are used, in many cases, for cylinder cover of small and medium bore diesel engines and thermal fatigue strength of these cylinder covers becomes an important consideration. The cast iron materials, however, are of complicated characteristics, and it is difficult to evaluate thermal fatigue strength of the materials under actual service conditions. Conclusions of this study are summarized as follows; (1) “Thermal fatigue parameter Lth”which was derived to evaluate thermal fatigue strength of the materials, can be used in the material selection. (2) When the thermal fatigue strength of cylinder cover materials was estimated by using“Thermal fatigue parameter Lth”and also by thermal fatigue tests, pearlitic ductile cast iron material have higher thermal fatigue strength than ferritic ductile cast iron materials, and the latter have customarily been used for cylinder covers by majority of diesel engine manufacturers. (3) By way of trial, the pearlitic ductile cast iron cylinder covers for engine with 450 mm in bore size were produced, and then are being successfully used on board 2 refrigeration ships for testing. The above suggests that pearlitic ductile cast iron cylinder covers have a possibility of practice marine application.
Fatigue failure in marine propeller blades of Ni-Al bronze was studied. i) First of all, the calculation of stress pattern and alternating stress imposed on propeller blades in service was carried out by the unsteady lifting surface theory. Results of the calculation indicate to be almost equal level in stress with that of actual measurements reported in the literature and therefore it is considered that the calculated results can be used for the study of fatigue behavior in propeller blades. ii) Fatigue test in sea water was carried out with large sized unnotched and notched (α=5.2, 9.7) specimens taken from actual propeller blades, and the fatigue life up to crack initiation was estimated with obtained fatigue curves and stress-frequency curve already known. It has been suggested, from the result of fatigue test, that there will be some possibilities of crack initiation within a year if very sharp flaw of α≥5.2 exists at the root of blade on the surface of pressure side under a probable stress-frequency. iii) Also fatigue crack propagation test was carried out in brine environment with W.O.L. type specimens taken from actual propeller blades, and fatigue life up to the failure after crack initiation was estimated on the actual broken propeller blade with a help of method of fracture mechanics. The formula of da/dN=3.37×10-14 (ΔK) 5.2 was obtained and the estimated fatigue life was 626 days. The formula showing the relationship between maximum allowable flaw size and alternating stress imposed on propeller blades was also obtained.
The strength design of crank shafts is generally based on fatigue test data obtained by subjecting specimens to testing under a constant stress amplitude which is different from actual stress patterns, so it is necessary to confirm the effects of this service load (stress) oil the fatigue strength of crank shaft steel materials. Actual bending stress patterns on crankpin fillets of all crankthrows were measured by FM telemeters during the shop trial of a six cylinder 4-cycle diesel engine, and then the selected stress patterns based on the wave analyses were used as the inputs to the push-pull fatigue testing machine of a servo-hydraulic type to carry out fatigue tests with plane carbon steel specimens. This results of the service load fatigue tests were compared with those of the rotating bending fatigue tests and the push-pull fatigue tests whose stress patterns are a constant stress amplitude to examine the influential factors such as wave areas of a tensile side, maximum tensile stresses, minor stress waves, mean stresses and stress amplitudes of primary waves, synthetic wave effects etc.
In respect to the stresses on the pin boss of a piston skirt which has vertical ribs, we carried out a series of analyses, namely, 3-dimensional stress calculation by the F.E.M, 3-dimensional photoelasticity, strain measurement under static load, and strain measurement under service condition. Through these analyses the following matters were clarified. (1) Suitable taper given to the inner surface of the pin boss is effective for reducing the tangential tensile stress, due to gas pressure, on the boss end. (2) It is possible to calculate the degree of stress reduction due to above mentioned taper processing, by suitably estimating the contact pressure distribution along the inner surface of the pin boss. (3) It is possible to change a load transmitting path by changing an intersecting angle between the vertical rib and the pin boss. Consequently, when attaching the ribs perpendicularly to the pin boss as well as increasing the thickness of boss wall, the tangential tensile stress on the boss end is reducible.