Chen Chuanyao

An impedance analysis for crack detection in the Timoshenko beam based on the anti-resonance technique

An alternative technique for crack detection in a Timoshenko beam based on the first anti-resonant frequency is presented in this paper. Unlike the natural frequency, the anti-resonant frequency is a local parameter rather than a global parameter of structures, thus the proposed technique can be used to locate the structural defects. An impedance analysis of a cracked beam stimulated by a harmonic force based on the Timoshenko beam formulation is investigated. In order to characterize the local discontinuity due to cracks, a rotational spring model based on fracture mechanics is proposed to model the crack. Subsequently, the proposed method is verified by a numerical example of a simply-supported beam with a crack. The effect of the crack size on the anti-resonant frequency is investigated. The position of the crack of the simply-supported beam is also determined by the anti-resonance technique. The proposed technique is further applied to the “contaminated” anti-resonant frequency to detect crack damage, which is obtained by adding 1–3% noise to the calculated data. It is found that the proposed technique is effective and free from the environment noise. Finally, an experimental study is performed, which further verifies the validity of the proposed crack identification technique.

Transversely isotropic damage around conducting crack-tip in four-point bending piezoelectric beam

A static damage constitutive model was proposed on basis of the electrical enthalpy density, and then some characteristics of transversely isotropic damage were discussed. Finally, the effects of both crack depth and applied loads on damage distributions were investigated through numerically analyzing transversely isotropic damage in a four-point bending PZT-PIC151 beam with a central conducting crack. Some conclusions were given: 1) Crack depth and mechanical loading have great influence on both mechanical and electrical damages. With their increment, the damages at crack-tip obviously increase and their region sizes also expand. 2) Effects of electrical loading on the two kinds of damages are obviously different. Electrical loading monotonously changes magnitude but region size of mechanical damage, whose effect on electrical damage is very complex.

DYNAMIC ANALYSIS OF FLEXIBLE BODY WITH DEFINITE MOVING ATTITUTE

The nonlinear dynamic control equation of a flexible multi-body system with definite moving attitude is discussed. The motion of the aircraft in space is regarded as known and the influence of the flexible structural members in the aircraft on the motion and attitude of the aircraft is analyzed. By means of a hypothetical mode, the deformation of flexible members is regarded as composed of the line element vibration in the axial direction of rectangular coordinates in space. According to Kane’ s method in dynamics, a dynamic equation is established, which contains the structural stiffness matrix that represents the elastic deformation and the geometric stiffness matrix that represents the nonlinear deformation of the deformed body. Through simplification the dynamic equation of the influence of the planar flexible body with a windsurfboard structure on the spacecraft motion is obtained. The numerical solution for this kind of equation can be realized by a computer.

The maintenance economy and economic life of structures

Abstract Up to now, fatigue life analysis has been essentially based on the safety and/or the functional requirements of structures. To prevent structures with slow-growing cracks from suffering fatigue failure, a maintenance proramme is usually needed in modern fatigue design methods. In this paper, a quantitative criterion to evaluate the maintenance economy of structures in service is proposed, and it is found that there is an economic repair period for the service time of structures. The definition of the economic life of structures is then discussed on the basis of maintenance economy. Finally, the formulae for the above analysis and a simple example are given.