Studies On The Dynamic Counterintuitive Behaviour Of Elastic-Plastic Structures Subjected To Impact Loading

Dynamics of elasto-plasticity studies the dynamic strength, rigidity and stability of subject under impact load. These issues have important influence on industries, civil constructions and national defence engineering. As an important research field, the dynamic response of structures is getting increasing interests. Counterintuitive behavior is a unusual dynamic response, which refers that permanent deflection is in the opposite direction of the load. In this paper, detailed numerical analysis and experiment investigations on dynamic counterintuitive response of beams and plates subjected to short pulse loading have been studied. The main works are as follows:1. Summarized and reviewed the current situation and analyzing methods of counterintuitive response ,and put forward suggestions for future studies.2. By analyzing the counterintuitive response of beams subjected to impulsive loads in detail, it is found that there exist two minimal loading ranges, called slots. One slot(the second slot) was given in literature[l] by Symonds et al. Now in our investigation the first slot, which is an asymmetric counterintuitive response in symmetric structures, has been revealed.3. Tracing the developing of deformation during the response found that: if the structure is in plastic deformation, further plastic dissipation after unloading is one of the important reasons that makes counterintuitive response occur. This means that only when elasto-plastic recovery happens, can counterintuitive response occur. This could be considered as the coupling of material nonlinearity and geometry nonlinearity .4. As the impulsive load increases, the dynamic response of circle plate transits from elastic to elasto-plastic. And the structure goes through three stages, i.e. loading, recovering after unloading and final free vibration. It is found that characteristic diagrams which describe the envelope of the final elastic vibration as a function of loading strength shows non-stable zone just can be found in some slots, and the finalslot must be accompanied with the change of final equilibrium position from negative side to positive. This transformation is a continuous process.5. Tracing the process of counterintuitive response, it is shown that axial force first reaches the limit value in loading phase, then bending moment also reaches the limit value as the plate swings negative direction. In this case, dissipation developing leads to too little energy left to snap positive direction. That is a character of counterintuitive phenomenon.When the plate goes back to negative side after unloading, further plastic deformation in the low layer of structures leads to energy dissipation once again.6. In the vicinity of slots, a small variation of loads and structural parameters, etc. can lead to much different dynamic behaviors. The dynamic behavior shows intense to these factors.7. Investigation of elasto-plastic square plate subjected to short transverse pulse load shows the similar response model as that of circular plates. Furthermore, common characteristic of anomalous behavior have been confirmed in plates .The effect of materials hardening is also considered.8. Based on numerical analysis, which has provided valuable guide and reference to experiments, a quantity of impulsive tests have been carried out on aluminum alloy circular plates of different diameters and thickness. And for the first time, the dynamic counterintuitive response of circular plate has been found in our experimental investigation. Different response modes and a range of velocity at which counterintuitive response occurs are obtained for plate structures. Experimental results confirmed the results of numerical analysis. This shows the objectivity of dynamic counterintuitive behavior and indicates that counterintuitive behavior may happen under certain circumstances.