Interfacial Damage of Fiber/Matrix Composite under Mechanical and Physical Loading

Varbinka Valeva, Jordanka Ivanova, Ana Yanakieva

In this paper on the base of representative volume element (RVE) the modified shear lag model was used to investigate the stress state, stress transfer and interface fracture energy of nanofiber/matrix composite. The RVE is subjected to static mechanical and physical load, e.g. temperature and moisture excitation. The solution of the problem is considered for the cases of perfect bond of the interface, perfect bond  and break of the fiber, perfect bond and partially interface debonding and break of the fiber as well. The obtained in closed analytical form results for axial stress and shear interfacial stress as well as the debond length are illustrated in figures. As a numerical example, the carbon nanofiber (CNF)/epoxy composite is considered. Three cases are studied: elastic with static mechanical loading, elastic with static mechanical loading and temperature and elastic with static mechanical loading with temperature and moisture. All three cases are compared in respective figures. The presence of the initial partial debond leads to smaller values of the respective fiber axial and interface shear stresses as well as to the magnitude of the plateau of the axial fiber stress. As a consequence, the progressive interfacial debonding is considered as well. The influence of the temperature excitation (20^o–30^oC) at given characteristics of the chosen CNF composite on the interface debond length is negligible, while the influence of moisture is significant especially for the case of progressive interface debonding. It is shown that the influence of the moisture on CNF is bigger at smaller volume fraction. At smaller aspect ratio (AR) the values of the stress transfer function (STF) are smaller when the influence of the moisture is taken into account and further it increases with the increasing of the mechanical load. The influence of the temperature and moisture on the debonding length is also estimated and some conclusions and recommendations are done.