Estimating Surface Damage of Composite Panels with Inverse Analysis

Abstract

When composite structures are exposed to harsh environmental conditions or impacted by foreign objects, their surfaces may degrade or damage. Damage evaluations of composite panels often demand expensive tools and time-consuming processes. The aim of this work is to introduce a versatile inverse analysis based method that requires less measurement efforts than those of conventional techniques. In this procedure, first, strains are measured on a surface opposite to damaged surface. Then, general functions relating damage conditions to strain fields are established. These functions reduce computational efforts required during the damage identification. With the measured strains and functions, an error objective function is minimized via iterations to estimate the damage extent. To verify the effectiveness of this proposed procedure, a detailed simulation study is performed with cross-ply composite laminates possessing various damage. The results show excellent matches between the estimated damage fields and the specified conditions imposed on the models. Following this promising outcome, the proof of concept study is extended to several real cross-ply composite panels that are damaged by either sand-blasting or environmental exposure. In the latter case, the composites were exposed to combined ultraviolet radiation and moisture absorption. On composite specimens, spatial variations of strain fields are measured with strip strain-gauges. Then they are used to identify surface damage distributions with either the quadratic formulation or the B-spline method. The latter approach is suitable when the functional change of strains due to damage is not smooth. The results estimated the variation of damage extent in each specimen. This feasibility study clearly supports the possibility of using strain sensor-network or optical method to quantify surface damage.

Effective property of tooth enamel: Monoclinic behavior

“…To process the data, the singular value decomposition (SVD) method, which minimizes errors arising from the model discretization, is adopted. The method is a multi-variable leastsquare fit to generate the best estimates from available or known relations (Mottershead and Foster, 1991;Ramanujam and Nakamura, 2007). Here, the following procedure is established.…”

Methodology for assessing impact damage using integrated simulation and experimentation

“…Initially, the parameter that will be investigated is chosen (e.g. modal parameter [14][15][16], strain [17]). The parameter value should change in the presence of the defect, so that the change can be derived from the measurements and the FEM analysis of an undamaged and damaged specimen.…”

The Experimental Research of Delamination Damage Location Based on FBG Sensors Network in Solid Rocket Motor Shell

“…where U and σ the mean and standard deviation of all subregions strain energies in the shell. In hydraulic internal pressure, the strain energy was good linearity with the pressure, and the singularity strain energy would mean that the subregion was damaged [5]. G23 and Poisson's ratio ν23 are not evident in thin plate, the values of G23 and ν23 were assumed to be the same as G12 and ν12.…”