Research And Development Of Structural Defects Identification Method With Phase Diagram Geometric Feature

With the continuous development of human society,a lot of materials with different properties have been developed,and constitute a variety of engineering structures,which greatly promotes social production.However,no matter what kind of material,with the increase of service time,there will inevitably be damaged.If the damage is not found in time and the corresponding measures are not taken,the damage to the structure will be more and more serious,and even cause significant economic damage and casualties.Therefore,the identification of structural damage is a very practical research topic.In this paper,the truss core sandwich beams with skin breathing cracks and core defects and homogeneous beams with breathing cracks are studied.The dynamic characteristics of the two beams are analyzed from the perspective of vibration.The relevant identification indexes are defined by the geometric characteristics of the phase diagram to identify the different damage parameters of the beams.The content of this paper can be summarized as follows:Through finite element simulation,the change of natural frequency of pyramid truss core sandwich beam with different positions and different numbers of core member missing is analyzed.Then,the natural frequency of truss core sandwich beam with core layer defect under different member radius conditions is studied by changing the member radius,and the function expression is fitted to calculate the natural frequency of the beam under the condition of selected member radius and core layer defect.The breathing crack in the skin of the sandwich beam is equivalent to a nonlinear spring oscillator,and the mathematical expression of the natural frequency of the beam with the defect location is fitted.The stiffness change of the beam is described by the function varying with the time period,and the dynamic equation of the sandwich beam with skin crack and core layer defect is derived by combining the additional flexibility.The phase diagram with different damage parameters is segmented,and the area of each part of the phase diagram is calculated.The contour map and three-dimensional scatter diagram is drawn by using the area of the phase diagram,and the identification index is defined.The feasibility of this method is verified by an example.Nonlinear energy sink(NES)is used to assist crack identification of structures in view of its characteristics of vibration reduction and indirectly signal amplification.The equation of a cracked simply supported beam with a NES is derived,and the influences of the crack properties on the dynamics of the system are investigated.The pixel method is applied to estimate phase diagram areas and the crack parameters are identified based on the geometric features of phase diagram.The results show that the phase diagram of the NES varied significantly with crack parameters due to the NES usually generate larger amplitude than the primary structure as the NES absorb energy.Secondly,the NES can reduce the amplitude of cracked beam without reducing the identification effect.Thirdly,through introducing the NES,the system can produce a strongly modulated response which can be utilized to detect cracks conveniently.Two sets of crack identification index are defined respectively when the system generates single-period response and strongly modulated response.Contour maps of identification indexes based on area of phase diagram by varying crack location and depth are obtained.The crack parameters are identified through the intersection of contour lines.