Method of manufacture of a composite material

A method of joining together multiple layers of pre-preg, comprising the steps of:

• providing a first layer of pre-preg, said layer having a surface and a plurality of edges;
• providing a second layer of pre-preg, the second layer having a surface and a plurality of edges;
• laying-up the first and second layers of pre-preg such that an edge of the second layer is adjacent a surface of the first layer of pre-preg, but such that the edges of the first and second layers of pre-preg do not terminate in the same place, the difference in positioning of said edges forming an edge drop;
• and
• applying pressure and vibrational energy to the edge of the second layer of pre-preg to thereby smooth the ply drop at the edge of the second layer of prepreg;
• wherein the step of applying pressure and vibrational energy to the edge of the second layer is carried out at a first position and wherein the method comprises a further step of applying pressure and vibrational energy to the second layer at a second position, the second position being offset in a direction normal to the edge of the second layer with respect to the first position;
• wherein the pressure applied is between 20 kPa and 500 kPa;
• and wherein
• the second layer defines an undulating formation having a plurality of protrusions having triangular or curved edges.