Analysis of an Embedded Sensor in a Composite Laminate for Enabling Damage Detection

A study of the influence of embedding sensors to detect damage within a composite laminate is conducted. A variety of sensors are considered along with several encapsulation materials. Encapsulation is required to aid in interfacial adhesion and to provide an electrical isolation from the graphite fiber composite laminate. This study is conducted to down-select the options for the sensor and encapsulant. A parametric global and local finite element models are developed to perform multiple runs corresponding to a design of experiments (DOE). The parameters that are varied are the sensor thickness, sensor length, encapsulant thickness, sensor modulus and coefficient of thermal expansion (CTE), and encapsulant modulus and CTE. Each parameter is varied based on the initial selection of sensors and encapsulants and considered at three levels for a quadratic transfer function. The DOE selected is a face centered CCD resulting in a total of 143 runs. The required output from each run is the effective axial and bending stiffness and the normal and shear stresses at the material interfaces. For each of these outputs from all of the runs, a transfer function is developed to identify the major contributors to the results. The resulting transfer functions indicate that the influence of the sensor and encapsulant parameters do not significantly affect the effective composites stiffness. However, they do contribute significantly to the material interfacial stresses, with the modulus of the sensor and encapsulant contributing the most to the variation of these stresses.