Global load path adaption in a simple kinematic load-bearing structure to compensate uncertainty of misalignment due to changing stiffness conditions of the structure’s supports

Abstract

Load-bearing structures with kinematic functions enable and disable degrees of freedom and are part of many mechanical engineering applications. The relative movements between a wheel and the body of a car or a landing gear and an aircraft fuselage are examples for load-bearing systems with defined kinematics. In most cases, the load is transmitted through a predetermined load path of a host structure to the structural support interfaces. However, uncertainty due to unexpected load peaks or varying health condition, e.g. changes in stiffness or damping parameters over time of the structure’s components may require an adjustment of the load path for safety reasons. Load paths transmitted through damaged or weakened components can be the reason for reduced comfort or even failure. For example, reduced support stiffness can lead to uncertain and undesirable misalignment in the structure. In this paper, a two mass oscillator, a translatoric moving mass connected to a rigid beam by a spring-damper system, is used to numerically investigate the capability of load path adaption due to controlled semi-active guidance elements with friction brakes. The mathematical friction model will be derived by the LuGre approach. The rigid beam is embedded on two supports and is initially aligned with evenly distributed loads in beam and supports by the same stiffness condition. However, if uneven support stiffness occurs, e.g. by damage or fatigue, the beam becomes misaligned. One sided lowering of the beam may follow. Two auxiliary kinematic guidance elements are used to redirect the load path depending on the beam’s alignment condition. With the semi-active auxiliary kinematic guidance elements it is possible to provide additional forces to relieve one of the beam’s support if it changes its stiffness. The beams’s misalignment is calculated numerically for varying stiffness parameters of the supports and is compared with and without semi-active auxiliary kinematic guidance elements. The structure is loaded with a force according to a step-function and a simple signal-based feedback PID-controller is designed to induce additional forces in the auxiliary guidance elements to bypass portions of loading away from supports with decreasing stiffness. Thus, uncertainty due to unacceptable misalignment caused by varying stiffness conditions of the structure’s supports can be reduced by shifting load between the supports during operation.