Well-designed composite structures have high strength-to-weight and high stiffness-to-weight ratios, are fatigue and corrosion resistant, and can be structurally optimized for specific applications. Designing parts that will be made from composite materials is often more involved than designing parts from metal. Metals are generally isotropic, meaning they have the same properties in all directions, which simplifies design and analysis. Composites however, are anisotropic and have properties that vary based on the orientation of fibers in the material. Anisotropic material properties, as well as the weaknesses of composite materials must be taken into account in the design process.