DEVELOPMENT OF CRITERION FOR STRENGTH RESIDUAL PREDICTION OF COMPOSITE STRUCTURES DAMAGED BY IMPACT

Abstract

Structural health monitoring is an area of growing interest using innovative approaches. Other hand, the maintenance and repair tasks represent about one quarter of the operating costs of commercial aircraft. Therefore, SHM system installed in the structure not only provides greater airworthiness, but also maximizing the numbers of suitable inspection periods for airplanes. Thus, SHM system can replace the traditional maintenance plan, reducing the airplane operational costs and preventing needless maintenances. The SHM system should inform, all the time, during the structure life, a diagnostic of the material state as well as the structure condition, which should be in agreement with specified by the initial structural project. However, the material state and the structure condition modify in function of the time due to aging, environment effects and loadings in service. Based on the complete history occurred, the SHM system can also perform a prognostic of the structure, for example, a prediction of residual strength. Considering this scenario, the main objective of this work consists on developing residual strength criterion for composite structures damaged by impact loading. For the development of the criterion, it will be necessary: to identify and to localize damage, as well as to calculate the severity of the damage and to estimate the residual strength of the composite structure. To achieve these goals, it is used to research Methodology based on three main groups of activities: (1) Before Impact Test; (2) During Impact Test (real-time) and (3) After Impact Test. In the first group (Before Impact Test), consists of literature reviews related to mathematical model used for SHM systems, which use sensors/actuators piezoelectric. Then, theoretical dynamic analyses of composite structure will be carried out by program ABAQUS, aided by "macro" in Python language. Piezoelectric sensors/actuators are attached on suitable positions of intact composite plates. After that, experimental analyses (modal tests) will be performed in intact composite specimens with attached piezoelectric sensors/actuators. The consistency of the computational models is evaluated comparing numerical results with experimental results for intact structures. If the consistency is acceptable, then move into the second group of activities. In this group (During Impact Test), finite element analyses of composite structures under low velocity impact will be carried out, using program ABAQUS and UMAT and/or VUMAT subroutines in Fortran language. After that, composite plates with attached piezoelectric sensors/actuators will be impacted under low velocity. In the third group (After Impact), there will be a comparison between numerical and experimental results in order to verify the consistency of the computational models for damaged structures. Thus, a method to localize and to evaluate damage severity will be proposed, using experimental and numerical results from intact and damaged composite structures. Finally, the results provided by the proposed method will be used to evaluate the residual strength of damaged composite structures. This criterion consists on determining the 4-point bending maximum loading, which will be supported by damaged plate by impact test.