Papers by Author: Qun Zhao

Abstract: Multiple site damage (MSD) usually occurs in the form of some small fatigue cracks at several sites within aging aircraft structures. It is very important to study the fatigue life of this kind of structure. This paper used testing method to observe the phenomenon of crack propagation, to analysis the result of the crack propagation. It provides testing reference for the study on fatigue life of MSD structures. According to the analysis of fatigue life of typical structures, a series of valuable conclusions are obtained.

Abstract: This paper introduced compounding method to calculate the SIF of typical MSD configurations. Complex function method was proposed to calculate the modification coefficient of the adjacent holes. Combining the method with compounding method, the SIF calculation of typical MSD configurations was achieved. The calculation process is easy to operate and the results are reliable which can be verified by FEM calculation. By studying the SIF results of typical MSD configurations, a series of conclusions with practical value in engineering can be obtained.

Abstract: In this paper, a kind of material compactor was designed beginning with the recognition of energy conservation and low cost. Through the study of the influence factors and the mechanization of the material compaction at normal temperature, the author found out better parameters of influencing factors. The improved material compactor consists of a compression roller, backspin rolls, supporting device and other auxiliary devices. The eccentric block inside the compression is driven by the motor to generate exciting force. After the material enters the feeding inlet, it will be squeezed between the compression roller and the backspin rolls. Under the action of both extrusion pressure and vibration, the purpose of material compaction is achieved.

Abstract: This paper introduces a finite element analysis software FRANC2D/L to calculate the stress intensity factor (SIF) and simulate the crack growth. Samples with infinite plate containing center crack, one hole-edge crack and two symmetrical hole-edge cracks were analyzed by this software. Comparing the SIF calculation results of the three samples based on displacement correlation method, J-integral method and virtual crack closure integral method, the results show that the three methods are all suitable for calculating the SIF problems, and the calculation precision of J-integral method and virtual crack closure integral method are better. Comparing the three crack growth criterion of maximum circumferential stress, maximum strain energy release rate and minimum strain energy density, the calculation velocity and precision of maximum circumferential stress criterion and minimum strain energy density criterion are prior to maximum strain energy release rate criterion. The calculating time and angle error of maximum strain energy release rate criterion is larger than that of the other two criterions．

Abstract: On the basis of the powerflow theory and four-end parameter analysis method, the responses and the powerflow characteristics of the vibration transfer path system are examined. The sensitivity of non-linear damping is employed as measurement criterion. The powerflow and powerflow sensitivity are obtained and the effect on powerflow and powerflow sensitivity of dry friction damping, fluid damping and structural damping is studied. Numerical results are also presented and discussed. It is supposed to study the sensitivity of these parameters, to estimate the effect of the change of parameters, to improve the design performance.

Abstract: Multiple site damage (MSD) is the occurrence of small fatigue cracks at several sites within aging aircraft structures. Focusing on this typical structure, an analytical method for calculating the stress intensity factor (SIF) of an infinite plate containing multiple holes was introduced in this paper. The properties of complex variable functions are used to evaluate the stress function. The approximate superposition method is applied to solve SIF problems on multiple holes. Some numerical examples of radial cracks appearing at the boundary of two circular holes are examined by this method. By comparing the analytical and finite analysis results it was realized that the analytical results are accurate and reliable. This modified analytical method is easier to apply than traditional analytical method and can provide SIF solutions for an infinite plate containing multiple holes.