Tensile Testing and Non-destructive Evaluation Scanning of Varied Ply CFRP Laminates with Embedded Magnetostrictive Particles

One method for Nondestructive Evaluation (NDE) of Carbon Fiber Reinforced Polymers (CFRP) is the integration of magnetostrictive particles (MSP) into CFRP laminates. In order to ensure that integration of MSP would be a feasible method of nondestructive evaluation, the structural intrusiveness of the particles must be investigated. Since one of the major benefits of CFRP is its strength to weight ratio, the inclusion of a foreign material must be minimally intrusive on the material properties of the laminate. This paper details several analyses meant to quantify the affect of integrating MSP into unidirectional CFRP laminates on the quasi-static tensile properties. First, the material properties of both the MSP and CFRP laminate were used in conjunction with the constitutive equations to estimate the ultimate tensile strength of symmetric laminates with and without MSP. Once a prediction of the failure stress had been determined, laminates were fabricated and tested under quasi-static tension. Finally, the experimental tests were correlated with a Finite Element Model. The laminates tested ranged from two plies to ten plies with a single layer of MSP embedded in the center of laminates. The results from experimental testing of carbon fiber-reinforced polymer composite beams with and without a layer of magnetostrictive particles showed that the particle layer was minimally intrusive on the quasi-static tension properties of the beam. Analysis of the results revealed that the addition of a layer of MSP caused a slight increase in the ultimate tensile strength of the beams, while the modulus saw an equivalent drop. Based on the number of samples tested, the amount of change seen in both the tensile strength and the modulus was statistically negligible. An investigation using scanning electron microscopy shed light on the change in the material properties. It was seen that during the curing process the epoxy matrix flowed into the voids between particles in the particle layer, which caused an increase in the fiber volume in the ply region. Previous research has shown that an increase in fiber volume in fiber reinforced composites leads to an improvement in ultimate tensile strength. This is because tensile strength is a fiber-dominated property. The microscopy analysis also showed that while there was flow over of epoxy resin into the particle layer, there were still large voids present. The presence of voids inside a laminate would reduce the incubation time for matrix cracks, limiting the matrix’s ability to transfer stress between fibers and reducing the stiffness of the laminate. The results from the analytical model proved to overestimate both the ultimate tensile strength and the modulus. The analytical model was based on equations and material properties for ideal laminates. Experimental testing tends to encounter issues such as material flaws, fabrication inconsistencies, and testing inconsistencies, which cause the results to deviate from the analytical model. While the experimental results and analytical model did not completely agree, the difference was not an order of magnitude in size. On the other hand, the results from the finite element analysis were in close agreement with the experimental data. For laminates with ply numbers of fewer than the data was statistically equivalent to the FEA model, with the higher laminate numbers seeing a slight overestimation in the ultimate tensile strength. The overestimation was likely the result of a