Research On Static,Dynamic Characteristics And Constrained Buckling Response Of Variable-Length Composite Slender Structures

The variable-length structures are widely used in engineering practice.The static and dynamic analysis of variable-length beams under different working conditions are fundamental scientific researches and are of great significance to practical engineering.Besides,the problem of constrained buckling on variable-length slender structures is often encountered in engineering or medical applications.Although the current research on variable-length structures has attracted the attention and attention of domestic and foreign scholars,the research on static buckling,vibration characteristics,and the constrained buckling of composite variable-length structures are still needed to be further explored and improved.The static buckling,dynamic characteristics,and constrained buckling behaviors of the variable-length composite slender structures are investigated.The effects of extension velocity,hygrothermal effects,fiber lay-up angle,and spinning velocity on the critical buckling load and vibration characteristics of the variable-length structures are discussed.And the dependences of the constrained buckling behavior of the variable-length structures on the constraint gap,the stiffness of the spring-supported constraint,hygrothermal effects,and fiber lay-up angle are presented.Based on the Euler-Bernoulli beam theory and Rayleigh beam theory,the nonlinear dynamics models of the variable-length composite beams incorporated hygrothermal effects are established with the aid of the extended Hamilton principle.On the other hand,the constrained buckling model of the variable-length composite beam is established based on the Lagrange method and the principle of minimum potential energy.Compared with the existing models,the correctness of those models is verified.The free vibration of a deploying laminated beam in the hygrothermal environment with a constant axial velocity is studied,especially focus on the effect of the hygrothermal environment on critical buckling loads and frequencies of the variable-length beam.The numerical calculations are performed to illustrate the effects of varying extension velocities,temperature,moisture,and ply angles on critical buckling loads and frequencies.The motion stability of the beam is also discussed by the system energy and the response of the beam in the process of extension and contraction.The results reveal that the axial extension velocity,fiber lay-up angle,and temperature effect have effects on the critical buckling loads and the vibration characteristics of the system,and the energy and frequency of vibration decrease and increase monotonically during extension and reaction,respectively.On the contrary,the amplitude of vibration increases during extension.The Eigenvalue method and Newmark method is used to analyze the static buckling and free vibration of a variable-length composite cylinder with spinning motion in the hygrothermal environment.The traveling wave frequency in both the rotating reference frame and the inertial reference frame are analyzed,respectively.The beat phenomenon of this system in the inertial reference frame is also studied.The effects of extension velocity,spinning velocity,hygrothermal effects,and fiber lay-up angle on the critical buckling loads,the forward and backward traveling wave and the sensitivity of each parameter to the frequency variation are discussed.The results show that there are significant differences between the forward and backward traveling waves in the rotating reference frame.The extension velocity,spinning velocity,fiber lay-up angle,thickness diameter ratio,and hygrothermal effects can cause the critical buckling load and frequency to decrease.The frequency is the most sensitive to the deploying speed and the least sensitive to the moisture.The beat phenomenon occurs in both v and w directions,and the period and amplitude of vibration increase with the increasing time.The post-buckling response of a variable-length composite beam with the unmovable and movable bilateral constrained boundary under an axial compression force is studied.The geometrical segmentation method and the perturbation method are used to solve the asymptotic solution of each segment.The buckling evolution process and the buckling path of the beam are obtained.The differences of the post-buckling response and path of the beam under rigid constraint and movable constraint are discussed,and the effects of different constraint gap,fiber lay-up angle,hygrothermal effects,the geometry of the beam,the stiffness of the spring-supported constraint on the post-buckling response of the system are analyzed in detail.Finally,the research contents and the results of this work are summarized up,and a brief plan for future work is given.