It is impossible to make a spring from carbon fiber. Carbon fiber has a high modulus of elasticity and low elongation. Therefore, it has low energy absorption. The largest energy absorption of fiberglass. Only you need to choose the right thickness and width. Poor manufacturing technology will cause fiberglass delamination.Laying up a flat leaf spring using glass and carbon would not be a particularly difficult process. Bend a sheet of aluminum or plastic to the shape or bend of the spring you want. Take some strips of wood, or foam, or clay and put them on this curved form 1.5 or 2 inches apart. Put a layer of glass in, then fill the trough with carbon strips or rods, then another layer of glass. Let it cure out in the sun inside a black garbage bag for several hours, then take it out of the mold and cut it to final length. Then post-cure it at a little warmer temperature.