Bi-Axial Field Structured Magnetoelastomer Coupons for Magnetostrictive CFRP Delamination Density Detection

Abstract Due to the low strain degradation characteristics of Carbon Fiber Reinforced Polymer (CFRP), a wide variety of damage can be sustained by CFRP without any appreciable change to its physical structure. This damage suffered by the energy transfer from high-stress levels appears in microporosity, crazes, and delamination in the matrix material before any severe laminate damage is observed. The CFRP component’s capacity and overall life cycle highly depend on the composite’s delamination density progression. Magnetoelastomers are a type of smart material that can change their shape in response to a magnetic field. These materials are made of a magnetic filler, such as Terfenol-D sensors, embedded in an elastomeric matrix. Magnetostrictive carbon fiber reinforced polymer (MagCFRP) is a self-sensing structural health composite material that is magnetically activated by an external magnetic field. MagCFRP composite constituents are carbon fiber, resin matrix, and Terfenol-D sensors. The magnetically activated Terfenol-D sensors are embedded between the lamina of the composite. These magnetostrictive embedded sensors respond to their surrounding stress field, allowing them to be used as damage sensors. Using magnetoelastomer field structuring techniques, highly-ordered “fibrous” b-stage Terfenol-D sensor coupons can be produced for laminate stacking sequence deposition. Producing and subsequently embedding the magnetoelastomer coupons throughout a structural laminate would allow highly structured Non-Destructive Evaluation (NDE) Terfenol-D sensors to be embedded with superior fidelity at damage-sensitive regions (i.e., high-stress-strain regions). These field-structured fibers are formed using a bi-axial magnetic field to orient the Terfenol-D sensor in a-stage elastomers. A fiber-structured Terfenol-D sensor b-stage coupon for MagCFRP can be produced using a high-purity bisphenol A two-part epoxy resin. Since this bisphenol A-Terfenol-D slurry does not cure at room temperature, the solution was first introduced to a magnetic field for structuring. Once the Terfenol-D sensors were structured, the magnetic field was removed, and the silicone mold was placed in an oven for b-stage curing. Using this magnetoelastomer field method and micro X-ray CT scanning, there was an observed reduction of localized Terfenol-D sensor cross-sectional area consolidation of 97% (more than one order of magnitude).