Experimental Study On The Vibration Characteristics Of Cantilever Beams In Steel And Composite Structures

Vibration is a common physical phenomenon in life.Vibration needs to be considered in almost all major engineering designs and operations of bridges,buildings,airplanes,automobiles,ships,engines,rockets,satellites,etc.Theoretical analysis,numerical calculation and vibration testing are three methods to solve the vibration problem.Compared with theoretical analysis and numerical calculation,there are fewer experimental studies related to vibration testing.The 21 st International Ship and Offshore Structures Congress(ISSC: International Ship and Offshore Structures Congress)set up a Benchmark research project in 2019: "Experimental research on the vibration characteristics of cantilever beams of steel and composite structures",11 universities or research institutions worldwide The work was carried out according to their respective conditions.After 2021,a summary and comparative analysis became one of the contents of the conference publicly published conference materials,which provided a reference for experimental vibration research.According to the Benchmark project of ISSC,the thesis takes the vibration characteristics of a simple structure cantilever beam as the research object.The structure is made of three materials: steel,glass fiber composite and carbon fiber composite.It uses two methods of electrical and optical experiments to conduct research and analyze different test methods,Sensor type,number of measuring points,excitation methods,etc.on the test results,the specific research content and conclusions are as follows:(1)Theoretical analysis and numerical calculation methods are used to calculate the low-order natural frequencies and mode shapes of a steel cantilever beam with a length of 500 mm,a width of 25 mm,and a thickness of 5 mm,and two composite material cantilever beams.First,the Euler-Bernoulli beam theoretical formula was used to calculate the low-order natural frequency of the cantilever beam of the steel structure.Based on the Timoshenko beam theory,the superposition stiffness method and Hamilton principle were applied to derive the vibration of a cantilever beam suitable for composite laminated structures.Equation,from which the low-order natural frequencies of two composite laminated structures cantilever beams are calculated.Finally,the numerical simulation method is used to calculate the low-order natural frequencies of two composite laminated structures cantilever beams based on ABAQUS software.Comparative analysis of research results provides a reference.(2)In the structural laboratory of Wuhan University of Technology,the electrical test method is used.The acceleration sensor model is B & K4519-003,the data acquisition model is B & K 3560-B-010,and the exciter model is DH40200.Research on step excitation and hammering.The influence of working conditions such as method excitation,exciter excitation,different pick-up point positions and numbers,and different excitation points on test results of cantilever beam vibration characteristics.Experimental research shows that the error of measuring the vibration parameters of the cantilever beam by the hammer method is the smallest.(3)In the laboratory of Ningbo Shunyu Optical Technology(Group)Co.,Ltd.and Wuhan University of Technology,two kinds of optical measurement experiment methods,laser and fiber grating,were used to conduct vibration test experiments of cantilever beams,and different laser vibration measurements were studied.The influence of different operating conditions such as instrument type,vertical distance between different laser vibrometer probes and measuring points,different sampling times,different number of measuring points,and different sampling frequency bands on the test results of cantilever vibration characteristics.Experimental research shows that the error of measuring the vibration parameters of the cantilever beam using the laser vibrometer is the smallest,and the method has better measurement results than any of the experimental methods in the electric measurement method.(4)Comprehensively compare all the cantilever beam vibration test methods in the electrical and optical measurement methods.The study shows that the method of measuring the cantilever beam vibration parameters using the laser vibrometer has the smallest experimental error.The fiber laser vibrometer and vibrometer are used in the experiment.The vertical distance between the optical head and the test piece is 0.5m,and the transient excitation method is hammering,and the sampling time is 5s.