EVALUATION OF POROSITY IN COMPOSITE AIRCRAFT STRUCTURES

In recent years the use of carbon fiber-reinforced organic composite m aterials for highly loaded military and civil aircraft components has continuously increased. Because of these applications it is becoming e ven more important to be able to predict the material properties of co mposite laminates with different levels of material anomalies. One of the most common defects found in continuous carbon fiber composite lam inate is porosity. The analytical techniques to determine porous lamin ate stiffness and residual strength are not available. Therefore, a va riety of expensive and time-consuming structural tests have to be perf ormed to include different laminate thickness and stacking sequence ef fects for each composite material. A new analytical approach to determ ine porous laminate stiffness for various levels of porosity which emp loys state of the art N.D.T. (nondestructive testing) techniques. and photomicrographic examination to determine the porosity/voids distribu tion through the thickness of the laminate, and a thermomechanical con stitutive theory for elastic composites with distributed damage is pro posed, originally proposed by Allen et al. (1987a, b) Int. J. Solids S tructs 23(9), 1301-1338. The model utilizes second-order tensor valued internal state variables to represent porosity. The equations for eng ineering constants are developed.