Analysis Of Loading Characteristics During Object Collisions At Medium-low Velocity

Collision is a common phenomenon in nature and practical engineering.Understanding the local impact load characteristics of object collisions is the basis and premise for utilization of collision phenomenon,product safety protection design,analysis and evaluation of response.At present,there is a lack of systematic analysis and summary of the characteristics of local impact loads during object collisions.This thesis mainly deals with two kinds of collision problens and systematically analyzes the characteristics of the local impact loads:rigid-flexible collision and collision of flexible bodies under elastic constraints with clearances in which the collision materials do not penetrate each other and the solid material does not undergo phase transformation plasticity.For the rigid-flexible collision problem,the local deformation behavior and the structural characteristics of the flexible body are phenomenologically represented as various force-displacement relationships to establish the simplified discrete dynamic model of the system.This thesis combines the advantages of discretization modeling and continuous contact force modeling of multi-body collision dynamics,and avoids their shortcomings.It condenses the commonality and main contradiction of the rigid-flexible collision problem from the perspective of phenomenology.The established model not only reflects the essence and typical characteristics of the rigid-flexible collision,but also greatly improves the analysis efficiency.Based on the simplified dynamic model,the characteristics of the local impact load due to the rigid-flexible collision are obtained.The influence of the local deformation of the flexible body and the stiffness effect of the flexible body structure on the characteristic parameters such as the spectral shape,peak value,pulse width,impulse and work done by the local impact load is analyzed systematically.And the accurecy of the modeling methodology and the results are qualitatively verified briefly by the finite element method.The analysis of the rigid-flexible collision problem shows that:in the case that the stiffness of the flexible body structure and the local deformation stiffness of the collision are weak,the coupling between the two will have a significant effect on the local impact load of the rigid-flexible collision,and neither can be ignored;in the case that the mass/momentum/kinetic energy of the rigid body is small,the mass of the flexible body is large and the stractural stiffness of flexible body is strong,the local impact load characteristics of rigid-flexible collision are dominated by the local deformation of flexible body collision.In the collision problem between the flexible bodies under elastic constraints with clearances,for the simply supported beam system with unilateral constraints under harmonic excitation,the Rayleigh-Rita basis function discrete system is adapted to establish nonlinear discrete dynamic equations of the system.The dynamic response characteristics of the system are analyzed by numerical method,and the understanding of the clearance impact effect and its local impact load is obtained.The study showed that the local collision caused by the gap of the nonlinear dynamic system will cause the system vibration energy transfer between the various modes of the system,especially if it is transmitted to the higher-order mode beyond the excitation frequency band,which makes the linear equivalent method invalid.Even in nonlinear analysis,it is necessary to consider the mode in which the natural frequency of the system is much larger than the upper limit of the excitation band.The obtained results of this thesis are of great importance in the following aspects:understanding and research on the mediul-low speed collision of objects,utilization of collision phenomenon,object/product safety protection design,and response analysis and evaluation as well.