This article discusses some preliminary studies dealing with the mechanical characteristics of a new type of reinforced composite material. The reinforcing members used differ from conventional reinforcements, and consist of two components, a core and an outer sheath. The sheath is bonded to the composite structure using conventional techniques but the shear strength of the core/sheath interface does not have a fixed value and is reduced as the tensile load carried by the core element is increased. The mechanism of stress transfer is arranged so that the reinforcing members are progressively decoupled from the rest of the structure where and when they are experiencing unacceptably high tensile stresses. This action is reversible and decoupling can be arranged to occur at any desired stress value. Decoupling would normally occur at a stress level rather less than the ultimate tensile strength of the core or alternatively at rather less than its fatigue endurance limit. By this means it can be arranged for the core members not to fracture whatever the tensile loads or displacements applied to the composite structure. Because the core elements do not fracture they bridge any transverse matrix crack which may be generated and inhibit its propagation in various ways. In addition they provide a residual tensile load bearing capability and absorb large amounts of energy under overstrain conditions.