Through-the-thickness mechanical properties of smart quasi-isotropic carbon/epoxy laminates

Abstract

Integrating smart materials such as fibre optic sensors or actuating shape memory alloy (SMA) wires with the host composites during manufacturing is one of the most fundamental aspects in the technology of smart structures. Sensing or actuating needs often dictate at what depth and how many sensors or wires should be embedded in the host composites. Thus manufacturing defects like resin pockets or poor interfacial bonding occur and could affect interlaminar shear (ILS) and flexural mechanical behaviour of smart composite structures. Limited information on these through-the-thickness mechanical properties is available from smart quasi-isotropic (QI) laminates of less than 8-ply thick, but no such data exists for thicker smart QI laminates. Therefore in the present research, both ILS and flexural mechanical properties of smart QI carbon/epoxy beams have been determined by using short beam shear (SBS) and Iosipescu methods as well as three-point and four-point bending methods. While SMA wires were embedded at selected interfaces of two different lay-ups in the longitudinal direction, optical fibres (OFs) were embedded at six different ply interfaces in both the longitudinal and transverse directions. It was found that neither ILS properties nor flexural modulus was affected, irrespective of the smart materials, their orientation, or through-the-thickness location. The flexural strengths did not suffer any noticeable degradation when the OFs or SMA wires were embedded either in the longitudinal direction or in the transverse direction in the tensile region. It was shown that the flexural strength degraded significantly when the OFs embedded in the transverse direction were in the compressive region.