Papers by Keyword: Dynamic Components

Abstract: In an effort to improve the reliability and reduce the operating costs of helicopter structure, an increasing emphasis is being placed on the damage tolerant approach for life management of helicopter structure. Corrosion damage of helicopter dynamic components and life reliability prediction approach has been systematically analyzed. Based on the conclusion of fatigue life under normal environment, the model for life reliability analysis of helicopter dynamic components has been established. A hybrid approach based on a mixture of the traditional safe-life and damage tolerance techniques can be used as an optimal strategy for ensuring helicopter structural integrity; the life of a helicopter main rotor blade under corrosion environment has been obtained according to flaw-tolerance method. According to probabilistic fracture mechanics theory, the analytical model of structures with initial corner cracks has been established. Thus the service life and inspection intervals according to the request of reliability can be determined; it is very valuable in engineering for life prediction and monitoring of helicopter dynamic components under corrosion environment.

Abstract: A new method for evaluation of adhesion in cutting is proposed. Adhesion of chip induces fluctuation in chip flow or stick-slip movement of chip, so that dynamic component of cutting forces depends on the cutting conditions and properties of the work materials. In this investigation continuous turning of a medium carbon steel was carried out and dynamic components of cutting forces are measured by piezoelectric dynamometer. Fluctuation in dynamic force on rake face of the tool is considered at a range of cutting speeds under dry condition and oil-mist lubrication. Surface profiles of machined surfaces and sticking of chip on tool face were also investigated. In cutting of medium carbon steel, the dynamic components below 500Hz increased under the condition of build-up edge (BUE) formation, and gradually decreased as increase of cutting speed. Tool-edge geometry well transferred onto the machined surface when the dynamic components were low level. Smoothness of chip flow on rake face is strongly associated with good surface finish.

Abstract: Using of a safe life approach is necessitated by the small critical crack sizes and rapid crack growth rates resulting from the severe vibratory environment of rotorcraft. However Based on the success of damage tolerance initiative for airframe structure, a crack growth based on damage tolerance approach is being examined for implementation into the design and management of dynamic components. In this paper the crack growth behavior in low cycle fatigue (LCF) and high cycle fatigue (HCF) are compared and the accuracy of several damage tolerance analysis methods in determining the crack growth life from an initial detectable crack size 1.25 mm to 12 mm for a rotorcraft main rotor yoke are investigated. The real rotorcraft materials measured by experiment and the fatigue load mean frequency spectrum based on statistical usage spectrum are adopted. The crack growth equations used in the programs are discussed to provide a basis for understanding the results. The results show that the load less than the safe fatigue limit has an important effect on crack growth life and it is reasonable for the material that the cut-off stress ratio for the threshold stress intensity factor range is set 0.7.