Tapered patch for predictable bonded rework of composite structures

A bonded rework of an inconsistent area in a composite structure, comprising:

• a tapered edge on the composite structure surrounding the inconsistent area, the tapered edge comprising a first tapered surface and a second tapered surface respectively having a first scarf angle and a second scarf angle, the second scarf angle being steeper than the first scarf angle, the first scarf angle configured to carry a higher load than the second scarf angle and aid a prediction of performance of the bonded rework over time;
• and,
• a tapered composite laminate patch covering the inconsistent area, the patch comprising an edge comprising a first tapered portion and a second tapered portion respectively bonded to the first and second tapered surfaces and forming a scarf joint between the composite structure and the composite tapered laminate patch, the first tapered portion corresponding to a first boundary of a first control region, the first control region configured to reduce a peak probability of a crack in the first region from extending beyond the first control region, the second tapered portion corresponding to a second boundary of a second control region, the second control region configured to elevate a total fatigue threshold strain energy release rate of the bonded rework;
• and
• an adhesive layer configured to bond the tapered composite laminate patch to the tapered edge on the composite structure, the adhesive layer being sectioned corresponding to each control region of the tapered composite laminate patch such that each section of the adhesive layer comprises a respective tailored rate of release strain energy.

A patch for reworking an inconsistent area in a composite aircraft structure, comprising:

• a composite laminate patch adapted to cover the inconsistent area and including first, second and third groups of composite plies respectively defining first, second and third regions of differing fracture toughness, the first, second and third groups of composite plies having edges respectively tapered at first, second and third angles, the first region configured to exhibit favorable in-plane adhesive stresses, the second region substantially contiguous and concentric about the first region and configured to indicate a need for reworking the inconsistent area, the third region substantially contiguous and concentric about the second region and configured for domination by in-plane shear and peeling moments;
• a first surface, a second surface, and a third surface formed on an edge of the composite structure surrounding the inconsistent area and respectively having scarf angles generally matching the first, second and third angles;
• and,
• a layer of adhesive configured to bond the edges of the plies to the first surface, the second surface, and the third surface of the edge on the composite structure;
• the layer comprising a first adhesive section, a second adhesive section, and a third adhesive section, corresponding to the first region, the second region, and the third region respectively, and each adhesive section tailored to at least one of:
• a desired thickness between the patch and the composite aircraft structure, a desired rate of release strain energy, and a desired fracture toughness.