The DOE/MSU Fatigue Database has been expanded Delamination is a dominant failure mode in composite to include a number of matrix resins of potential interest material structures, leading to the breakdown of structural in wind turbine blades. The main considerations in resin integrity in areas such as the tra iling edge, spars, and root selection have been to increase the structural integrity connections. Experience in aerospace composites [1] (such as delamination resistance) in blades while indicates that the toughness of the matrix resin, as well as maintaining or improving other mechanical properties, the design of details controls interlaminar fracture particularly under hot, wet conditions. The resins resistance and structural performance, as well as f acewise included in the study are also appropriate for the wind impact resistance [2]. The low cost matrix resins (general turbine blade application in terms of cost and processing purpose polyesters, vinyl esters, and epoxies) used in characteristics (all materials were prepared by resin most turbine blades are relatively brittle, and so the transfer molding). Resins included unsaturated delamination resistance of most blade materials is polyesters, vinyl esters, epoxies, and a urethane. relatively low. Tougher versions of these and other resins Mechanical properties have been obtained for wet and dry are investigated in this study. A sec ond type of resin, specimens tested at temperatures from -20 to 70 C. thermoplastics, also have high toughness, but their high Fatigue, delamination resistance (Mode I and II crack viscosity limits their use in conventional blade growth), and performance in stiffened substructure manufacturing techniques. Tougher resins which bond sections have been evaluated for selected cases. well to the fiberglass also tend to give higher strengths in Significantly improved performance relative to baseline off-axis directions relative to the fiber reinforcement. polyester is shown for several resins. A second concern with matrix resins is that if their