Piezoelectricity has proved effective in capturing changes in structures caused by various damage mechanisms. In one approach, piezoelectric wafer active sensors (PWAS) are mounted on the surface of the host structure and utilized as both actuators and sensors to interrogate the structure and monitor its health. This is achieved by subjecting the PWAS to a transient electric pulse and reading the resulting voltage. Changes in the stiffness of the substrate due to structural damage affect the response of the PWAS, which could be correlated to integrity of the structure. Applying this technique to fibrous composite laminates encounters particular challenges due to the presence of multiple damage mechanisms in one or more plies. Simulation of the procedure using advanced computational techniques and material models helps in understanding the reliability of PWAS in sensing damage in fibrous laminates.
This paper combines the finite element method and micromechanical modeling of composites to simulate damage detection using surface mounted PWAS. The finite element solution is obtained by the ABAQUS code with user defined material properties, which reflect the underlying damage modes. The latter are obtained in a preprocessing exercise in which the composite laminate is first subjected to a given mechanical load level and the damage mechanisms in the plies are identified using transformation field analysis, TFA (Bahei-El-Din el al., 2010). In the present work, the Mori-Tanaka averaging model is utilized within the TFA and local failure modes, which are a function of the matrix average stresses were specified. Material properties of the individual plies, which correspond to the damage mechanisms introduced at the given load level are then determined numerically in terms of the overall moduli and utilized in the finite element solution of the laminate using ABAQUS.
The methodology is applied to a quasi-isotropic, symmetric laminated beam subjected to bending. In the finite element simulation, each fibrous composite ply of the laminated beam is modelled using shell elements while the surface mounted PWAS are modeled with 3D solid elements. The bending moment is applied to the beam intermittently to allow interrogation of the laminate by applying a transient electric pulse to the PWAS and allowing the beam to vibrate for a very short period of time, which is followed by reading the voltage response. The voltage readings are correlated to the damage mechanisms in the plies.