A Two-step Inverse Method for Quantitative Damage Evaluation of Plate-like Structures Using Vibration Approach

This study presents a novel two-step approach to assess plate-like structural laminar damages,particularly for delamination damage detection of composite structures.Firstly,a 2-D continuous wavelet transform is employed to identify the damage location and sizes from vibration curvature data.An inverse method is subsequently then used to determine the bending stiffness reduction ratio along a specified direction,enabling the quantification of the delamination severity.The method employed in this study is an extension of the one-dimensional inverse method developed in a previous work of the authors.The applicability of the two-step inverse approach is demonstrated in a simulation analysis and by an experimental study on a cantilever composite plate containing a single delamination.The inverse method is shown to have the capacity to reveal the detailed damage information of delamination within a constrained searching space and can be used to determine the effective flexural stiffness of composite plate structures,even in cases of complex delamination damage.

The Effect of Internal Delamination Damage on the Tensile Strength of Aeronautical Composites

For aeronautical composite materials,the appearance of internal delamination has a fatal impact on their mechanical properties and may even seriously threaten aircraft flight safety.In this study,the effect of internal delamination damage with different sizes and depths on the tensile strength of aeronautical composites was investigated.Firstly,based on carbon-fiber-reinforced composites commonly used in aircraft,laminate specimens with internal delamination damages of different depths and diameters were fabricated,and tensile tests of composite materials were carried out.Then,the finite element model for the carbon-fiber-reinforced laminate specimens was established,and the validity of the model was verified by comparing its simulation results with the experimental data.Furthermore,by changing the geometric parameters of the internal delamination damage model,the influence of delamination damage on the tensile strength of carbon-fiber-reinforced composites was analyzed and summarized.The results show that,on the one hand,for the internal delamination damages of the same area,the closer is the delamination damage to the surface layer,the lower is the tensile strength.In particular,the closer is the delamination damage to the surface layer,the greater is the decrease in tensile strength,which exhibits an obvious nonlinear relationship.On the other hand,for the internal delamination defects of the same depth,the difference in delamination area has little effect on the tensile strength.This law provides a reference for the damage detection and maintenance focus of aeronautical composite structures,which is of great significance to ensure the safe use of aeronautical composites.

Computational Study of the A0 Scattered Field Due to an Edge Delamination

Delamination detection presents a pertinent problem for SHM be no visible signs of the damage on the surface of the structure. （structural health monitoring）, as in most cases, there may This study investigates the scattering of a zeroth-order anti-symmetric （A0） Lamb wave mode by an edge delamination using the commercial FE （finite element） package ABAQUS. The Ao Lamb mode is chosen because the corresponding stress distribution is more sensitive to delamination than is the case for symmetric modes. The paper presents results for the scatter field for various angles of incidence, and for varying defect sizes. The regime of small defect size relative to the incident wavelength is of particular interest for SHM as it corresponds to early damage detection. It is shown that, in this regime the scattered field appears to originate from a point source at the origin of the delamination, and the corresponding amplitude is linearly proportional to area of the delamination. These results can be used to guide the use of Lamb waves to detect and quantify edge delamination in plate-like structures.