No abstract

In this paper, the fretting wear properties of 20CrMnTi steel, a common material for a rocker bracket, was discussed for the first time after it was suffered carburizing treatment. Subsequently, the fretting wear behaviors of virgin, quenched, and carburized states were studied. The effect of loads (corresponding to different engine power output) and reciprocating frequencies (corresponding to different engine speed) on wear behaviors and mechanisms of carburized specimen were further discussed. The results showed that the coefficient of friction (CoF) and wear volume loss (WVL) of the carburized specimens were significantly lower than that of virgin and quenched states. During the wear test, the surface CoF decreased gradually with the increase of applied load, while the linear correlation trend was not observed with the increase of fretting frequency as it showed an increase first and then a decrease. It was observed that the WVL increased gradually with the increase of load and frequency. With an increase of the load, the wear mechanism gradually deteriorated from the initial adhesive wear to the mixed wear mechanism. When the load was high, the oxidative wear became more severe. However, no significant effect of frequency was observed on the wear mechanism.

The selection of biomimetic prototypes mostly depends on the subjective observation of a designer. This research uses TRIZ to explore some inferential steps in bionic design of the heavy machine tool column. Conflict resolution theory of TRIZ is applied to describe improved and deteriorated parameters and a contradiction matrix is used to obtain recommended inventive principles. A reference table of solutions corresponding to the biological phenomenon and TRIZ solutions is formed to expedite retrieving the biomimetic object. Based on the table, herbaceous hollow stem is selected to imitate column structure. Four kinds of plant are chosen from the biological database. To select the best from four candidates, a bionic ideality evaluation index is proposed based on similarity analysis and ideality evaluation theory in TRIZ. Thus, the bionic effect can be described and compared quantitatively. Bionic configuration is then evolved concerning manufacturing requirements. Size optimization of stiffener thicknesses is implemented finally, and satisfactory results of the lightweight effect is obtained.

Thermal load has a vital influence on the normal operation and service life of diesel engines. In this study, the thermal load and oil-cooling effect on diesel engine pistons were investigated by means of computational fluid dynamics. In particular, the flow and heat transfer characteristics of the cooling gallery were determined during the oscillation of the piston. Moreover, the temperature field distribution of the piston with and without the cooling gallery were compared. The results revealed that the cooling gallery has a prominent effect on reducing the thermal load on the piston crown and piston lands. To fully understand the oscillating heat transfer effect related to the cooling gallery and verify the accuracy of the calculation, the numerical results were also compared with temperature values experimentally measured at key positions of the piston. The measurements were found to be consistent with the calculation results within an acceptable error range, which proves the rationality and accuracy of the mathematical and numerical models used.

The STAR-CCM + software is used to investigate the flow inside a cooling water jacket of an in-line six-cylinder diesel engine. The results show that the average flow velocity of the cooling water inside the jacket is 1.669 m/s while the flow velocity distribution is not uniform for each cylinder. Moreover, the fluid velocity in proximity to the cylinder head is too low, thereby affecting the cooling performances of the water jacket. Two corresponding structural optimization schemes are proposed to mitigate this issue and the post-optimization performances of the water jacket are discussed in detail.