Recently solid-type crankshafts for 4-stroke diesel engines are required to have higher fatigue strength to increase output of marine and power generator engines and make them more compact. Due to these requirements, surface treatment methods that can induce residual stresses have been well-studied. To study the effect of surface treatment methods on fatigue strength, fatigue tests, under mean stress, were conducted using fatigue specimens, namely artificial defects with different sizes. The result found that in the compressive mean stress region, fatigue strength of the specimens corresponded well with modified Goodman equation and that in the tensile mean stress region, their fatigue strength matched well with Gerber equation. Moreover, it was found that fatigue strength of the specimens with artificial defects, can be evaluated with the square root of defect area.
The purpose of this study is to elucidate effects of manufacturing errors on static and dynamic characteristics of multi-lobe hydrodynamic journal bearings. The study is also intended to come up with a proposal for guidelines about the optimized design for multi-lobe hydrodynamic journal bearings. This paper analyzed and examined changes in the dynamic characteristics of a four-lobe hydrodynamic journal bearing, such as oil film spring coefficients and oil film damping coefficients between the bearing and journal, and the stability characteristics of a rotor supported by bearings when the position of the bottom lobe at the sliding surface is shifted from where it should be due to manufacturing errors. The main results of the study show that when the position of the bottom lobe is moved inside of the bearing from the original location due to manufacturing errors, the dimensionless stability threshold speed becomes greater in comparison with the situation in which the lobe stays at the original location. On the other hand, manufacturing errors should not cause a shift in the position of the bottom lobe in outer direction of the bearing from the original location, and this should be included in design guidelines for four-lobe hydrodynamic journal bearings.
Torque wrenches driven by hydraulic, pneumatic or electric power are commonly used to tighten large bolts. Bolt tightening operations based on the torque control method are generally performed by applying the target torque to the outer surface of the nut. However, torque can sometimes be applied to the bolt head, due to the geometric limitations of the joint. It has been reported that during the tightening process with powered wrenches, the bolt side tightening sometimes produces lower bolt preload compared to the nut side tightening. This is caused by contact between the bolt cylindrical body and bolt hole surface, which can occur during tightening operations, and this friction consumes a part of the tightening torque. This paper is intended to identify critical conditions for the bolt body contact and slip at the bolt head bearing surface in a mathematical form. The slip phenomenon may lead to shortage of bolt preload. An equation that relates torque with bolt preload, which takes into account the effect of bolt body contact, is given in a similar form to the ordinary bolt-nut tightening. This paper aims to substantiate the validity of the proposed equation by conducting tightening experiments using a pneumatic wrench.