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INNOVATION IN COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping, G. Montero, R. Montenegro
Adaptive Impact Absorption
J. Holnicki-Szulc, G. Mikulowski, A. Mroz and P. Pawlowski
Smart-Tech Centre, Institute of Fundamental Technological Research, Warsaw, Poland
J. Holnicki-Szulc, G. Mikulowski, A. Mroz, P. Pawlowski, "Adaptive Impact Absorption", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Innovation in Computational Structures Technology", Saxe-Coburg Publications, Stirlingshire, UK, Chapter 24, pp 517-539, 2006. doi:10.4203/csets.14.24
Keywords: adaptive impact absorption, controlled shock-absorbers, optimal design, structural control, real-time load identification.
This paper demonstrates progress in the adaptive impact absorption (AIA) research field obtained recently by our research group and is based on previously published conference contributions. The monograph , under preparation, will present more detailed discussion of the problems under consideration in the near future.
Motivation for the undertaken research is in response to the requirement for high impact energy absorption in areas such as: structures exposed to risk of extreme blast and light; thin-walled tanks with high impact protection; vehicles with high crashworthiness; protective barriers. Typically, the suggested solutions focus on the design of passive energy absorbing systems. These systems are frequently based on the aluminium and/or steel honeycomb packages characterised by a high ratio of specific energy absorption. However high the energy absorption capacity of such elements they still remain highly redundant structural members which do not carry any load in an actual operation of a given structure. In addition, passive energy absorbers are designed to work effectively in pre-defined impact scenarios. For example, the frontal honeycomb cushions are very effective during a symmetric axial crash of colliding cars but are completely useless in other types of crash loading. Consequently, distinct and sometimes completely independent systems must be developed for specific collision scenarios.
In contrast to the standard passive systems the proposed approach focuses on active adaptation of energy absorbing structures (equipped with sensor systems detecting and identifying impact in advance and controllable semi-active dissipaters, so called structural fuses) with a high ability to adapt to extreme overloading . The following characteristic cases of adaptive impact absorption (AIA) problems can be identified:
The first case corresponds to smoothing down the impact effect (such as for reduction in fatigue effect, as in adaptive landing gear ) and coming from service loads, while the second one corresponds to the impact absorption (for example, from critical environmental loads) with minimal cost of induced distortions. In both cases a semi-active or fully active solution can be applied depending on constant or time-dependent modifications realised via controllable dissipative devices. Note, these devices are dissipaters (with no need for a significant power supply) rather then actuators. Feasible, dissipative devices (structural fuses) under consideration in the application discussed below can be based on the following technologies; adaptive dissipaters based on MR fluids, adaptive dissipaters based on (hydraulic or pneumatic) piezo-valves, and adaptive dissipaters based on SMA alloys.
Multi-folding microstructures - the paper presents the concept of Multi-folding structures providing additional energy dissipation, due to the synergy of the repetitive use of active elements (equipped with so-called structural fuses), according to the pre-design optimal distribution of yield stress levels, triggering the desired sequence of local collapses.
Adaptive wind turbines - one of the major technological limitations of up-scaling modern wind turbines is the load bearing capacity of blade materials. Connection between blade and hub has to withstand very large bending moments in particular during high winds. An alternative for developing new blade materials is to introduce a semi-actively controlled connection between blade and hub with controllable characteristics. The paper demonstrates the idea of controlling the value of peak dynamic force that is transferred to the support by means of a pneumatic system with a controllable on/off piezo-valve.
Dynamic mass identification under impact loading - optimal strategy of structural adaptation depends on the impact load, which has to be identified in real time. In some cases (for example, when the dropping mass is known in advance) the impact velocity measurement is sufficient to perform the desired structural adaptation. However, in many cases (for example, an unknown hitting object) on-line determination of the impact velocity as well as the mass of the hitting object is the real challenge. The main objective for the study was determination of the time delays in the mass identification procedure, when we assume that the process is being performed at the beginning of the impact phenomena.
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