Research On Impact Monitoring Method Of Aircraft Structure Based On Beam Focusing Theory

Low-speed impact is one of the several common damages to aircraft.When the aircraft encounters low-speed external impact,it is easy to cause invisible matrix damage inside the structure,the continuous accumulation of damage causes material performance degradation,which is a safety issue during aircraft service.Therefore,it is necessary to monitor the impact damage of aircraft.It is essential to detect the localization of the impact in time and focus on this area to ensure the safety of the aircraft.In this paper,the beam focus localization algorithm is used to conduct impact experiments on metal materials and composite materials.And the more accurate impact localization of the structure is achieved through the beam focus localization algorithm combined with the probability-based tomography method.This paper first introduces the principle of linear array beam focusing and localization algorithm,and proposes a multi-dimensional array beam focusing algorithm for its existing localization blind areas and low localization accuracy.At the same time,the sensitivity of one-dimensional linear arrays to different angles is explored,and the optimal number of arrays is determined by combining factors such as localization accuracy and economy.Secondly,passive tomography technology is introduced by introducing lamb wave tomography technology,and the influence of uncertainty of wave speed on the localization result is introduced.The wave velocity of metal materials and composite materials are measured respectively to obtain probability distributions.Probabilistic imaging is combined with tomography to realize the imaging of the shock source.In order to achieve a more scientific description of impact damage,the intuitive probability map is used to describe the impact source,which means that a small area is used to describe the possible location of the real shock source,and the degree of proximity of the damage location to the real shock source is described from the perspective of probability.Finally,four commonly signal processing methods are introduced:wavelet decomposition,Empirical Mode Decomposition(EMD),Variational Mode Decomposition(VMD,)and cross-correlation methods.Through repetitive experiments,three signal decomposition methods are used to decompose the measured impact signal,and then the cross-correlation algorithm is used to extract the time delay characteristic parameters between the signals,and the cross-correlation method is used to calculate the time difference between the signals arriving at different sensors.The degree of dispersion is used as the evaluation standard,and the three signal decomposition methods are experimentally verified.Compared with the other two decomposition methods,the time delay obtained by VMD is the most dense,so VMD and cross-correlation algorithm are dopted as the feature parameter extraction method.Currently,the main constituent materials of aircraft are consist of aluminum alloy and composite materials.Monitoring aircraft structure need to take into account the different characteristics of these two materials.Due to the anisotropic characteristics of composite materials,the wave speeds of different azimuths are not consistent.The array sensor is used to scan to determine the azimuth information of the impact source,and the wave speed information of this azimuth is substituted into the beam focus localization algorithm.The final impact source localization map can be obtained through different array beam focus localization algorithms and tomographic imaging algorithms.In this paper,experimental studies are carried out on the metal material flat plate and the composite material flat plate respectively,and the results show the effectiveness and practicability of this method.