Interleaf Material Research Articles

Fracture behaviour of interleaved fiber-resin composites

Interleaving, the technique of inserting a tough material into the composite laminate as extra interlaminar layers, has been used successfully to enhance the damage tolerance of brittle composites. Both carboxyl-terminated butadiene acrylonitrile (CTBN) and polyurethane (PU) were used to modify various epoxy resins. These modified epoxy resins were then chosen as interleaf materials for toughening graphite/epoxy composites. The effects of adding a thin interleaf phase on the microstructure and the fracture resistance of the resulting laminates were investigated. The results obtained from double cantilever beam (DCB) tests and end notched flexure (ENF) tests demonstrate that the tensile opening mode (Mode I) and the shear mode (Mode II) critical strain energy release rates of a graphite/epoxy laminate can be improved considerably by the technique of interleaving. The damage tolerance of interleaved composites, as assessed by the impact fatigue tests, is much greater than that of the control sample. The critical stress intensity factor, K lc , of interleaved materials was also measured by use of compact tension specimens and was correlated with the mechanical properties of the corresponding interleaved composites.

Analysis and Experimental Characterization of the Center Notch Flexural Test Specimen for Mode II Interlaminar Fracture

The interlaminar Mode II critical strain energy release rates of unidirec tional graphite/epoxy, graphite/polyetheretherketone (PEEK), and graphite/epoxy with interleaf material were characterized using the End Notch Flexural (ENF) and Center Notch Flexural (CNF) test specimens. The CNF test method was developed specifically for this study. Compliance and strain energy release rate expressions of the CNF are derived and are in good agreement with finite element results for a wide range of crack lengths. Mode II critical energy release rates for both test methods were found to be in quite good agreement.

Solid-state diffusion bonding of tungsten-25 rhenium alloy

Nickel has successfully been used as an interleaf material to join W-25Re between 900 and 1400° C. The bond strength was found to depend on the temperature and stress at which the bonding process was conducted. It was also found that nickel reacts with the parent metal and forms a Ni-W-Re ternary alloy. The formation of the alloy causes significant embrittlement in the parent material. The alloy first nucleates at the grain boundary and then grows into the grain. Quantitative studies of the growth kinetics of the ternary alloy and its effect on the bond strength are discussed. Joining of W-25Re by self-diffusion bonding has also been successfully demonstrated at temperatures above 1500° C. The effect of surface conditions will be correlated with the quality of the joint.