Investigations on Interlaminar Fracture Toughness of T300/914 Composite and Severe Plastic Deformation of C70600 Alloy

Abstract

Experiments were conducted to investigate Interlaminar fracture toughness of carbon epoxy composite T300/914. carbon epoxy composite T300/914 has wide range of applications in aerospace industry as a structural material. For measuring inter-laminar fracture toughness, laminates with a thickness of 4.6 mm comprising of 48 layers of T300/914 are used. Hand layup technique were used to create these specimens, which were then cured in an autoclave machine. Double Cantilever Beam (DCB) test for Mode I and End Notch Flexure (ENF) test for Mode II were carried out in line with ASTM standards. The findings of pulse-echo tests and C-Scan pictures of the specimens were used to pinpoint specific locations of delamination. During early testing, it was discovered that the interlaminar fracture toughness varied due to release of film's bonding to laminate's sides. Mode I and Mode II fracture toughness values of T300/914 laminate composites were determined to be 0.090 kJ/m2 and 0.542 kJ/m2, respectively, using Modified Beam Theory. Fracture toughness of identical laminate specimens changed depending on degree of compaction. Copper-Nickel alloy, C70600, because of its superior anti-corrosion and anti-fouling properties, was used in sea water pipe line applications, C70600 was subjected to severe plastic deformation process by equal channel angular pressing (ECAP) technique. Material were pressed at room temperature along route BC for 8 passes. Microstructural analysis, mechanical characterization and corrosion properties of the alloy was done for each of the ECAP processed samples. Initial homogenized material having equiaxial grains of average grain size 74µm was reduced to 20µm after 8 ECAP passes. Electron backscatter diffraction (EBSD) data presented an increase in low angle grain boundaries with increase in number of ECAP passes. Initially ultimate tensile strength (UTS) and hardness showed an increase of nearly 60% and 90% respectively. After 5th ECAP pass, drastic reduction in UTS and ductility was witnessed. Fractured surface revealed ductile type of facture with reduced ductility. Corrosion study showed improvement in corrosion resistance at higher ECAP passes.