Electric field induced extrinsic strains in BaTiO3-epoxy nanocomposite: a contact-less mechanical property tailoring smart material

Epoxy is an important class of thermosetting material which have been used in many fields such as aerospace, automobile, and energy sectors. Cured epoxy, however, exhibits poor resistance to crack initiation and growth, thus exhibiting low toughness and brittleness at failure. To improve the mechanical properties, epoxy matrix in polymer composites has been modified by various techniques such as the inclusion of a second phase (e.g., core-shell rubber, thermoplastics or nanofillers) which has demonstrated improved toughness and impact resistance. Very few studies have focused on offering an ‘active toughening’ mechanism in which an increase in toughness and strength is achieved via remote field stimulation such as magnetic, electric or electromagnetic forces. In this study, aerospace grade epoxy resin modified with tetragonal barium titanate (BaTiO3) nanoparticles has been prepared, and its mechanical response has been studied under electric field stimulations. The BaTiO3 nanoparticles have been functionalised with silane coupling agents and dispersed uniformly in epoxy Araldite LY1564 at different content loads (1, 5, 10 wt.%), a diglycidyl ether of bisphenol A (DGEBA) associated with its curing agent Aradur 3487. Several test coupons have been fabricated from such modified epoxy. Real-time in-situ Raman spectroscopy measurement has been conducted on the nanocomposites equipped with electric fields. The results provide a quantitative description of Raman peaks and their intensity variations under the electric field application. The variation of mechanical properties under the application of such fields has also been investigated and analysed alongside the Raman data. The failure stress and strain in the nanocomposites at all BaTiO3 contents examined have been improved in the presence of such fields. The tensile modulus has been increased with the increasing field strength in the 1 wt.% nanocomposites while reduced in the case of 5 and 10 wt.% in the presence of the field. The Raman data have shown a consistent trend of increasing intensity and peaks broadening under the increasing electric field strength and BaTiO3 contents, which is attributed to the softening effect by BaTiO3’s dipolar displacement in the high-content nanocomposites (i.e., 5 and 10 wt.%) which dominates the stiffening trend induced by the electric fields, and observed in the 1 wt.% samples. The mechanism provides an effective route for remote mechanical property tailoring.