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Embedded polymeric insert for increased toughness of adhesive bonded joint

3D printingAdhesive bondingBridging su larga scalaCFRPToughening

Introduction

The invention concerns the use of an architected polymeric insert to impart toughening and damage tolerance in adhesive bonded carbon-fiber reinforced polymers (CFRPs). The insert is embedded within the joint bondline during manufacturing. During fracture the polymeric strands of the insert bridge the crack and enable large scale bridging, extensive energy dissipation and a remarkable increase of fracture toughness.

Technical features

Toughening of adhesive joints with composite adherents has a fundamental role for many applications in the field of automotive and aerospace, including filed repair. The long standing issue with adhesive bonding of composites is the relatively brittle response and corresponding sudden failure under mechanical loading. To tackle this problem various toughening strategies have been deployed. In this patent a 3d printed ductile thermoplastic film is embedded within the joint bondline to enable toughening through large scale bridging of polymeric strands. The efficiency of the toughening strategy depends on the film architecture (a-c) and the ability to trigger the formation of polymeric strands bridging the crack faces and resisting crack propagation. The proposed strategy and ensuing methods enable remarkable increase in energy dissipation and fracture toughness. Toughening strategies for adhesive joints comprise the use of advanced surface preparation techniques and/or the use of toughened epoxy adhesives. These strategies provide step changes in fracture toughness but are unable to delay or arrest incoming cracks. Through large scale bridging, the proposed technology not only allow to increase fracture toughness but can significantly delay crack growth and extend service life before repair.

Possible Applications

  • Automotive parts, including body in white, aerospace structures, and other lightweight components that make use of CFRPs.
  • The proposed technique allows for an improved bonding of CFRPs and may have important implications in the field of damage repair/patching in the above mentioned fields.

Advantages

  • It allows to increase the resistance to fracture;
  • Significantly delay the growth of cracks and extend the service life before repair.