Defects in composite laminates are difficult to detect because of the conductive and paramagnetic properties of composite materials. Timely detection of defects in composite laminates can improve reliability. This research illustrates the preliminary analysis and detection of delaminations in carbon fiber laminate beams using a single layer of magnetostrictive particles and noncontacting concentric magnetic excitation and sensing coils. The baseline analytical models also begin to address the intrusive nature of the magnetostrictive particles as well as relate the applied excitation field with the stress and magnetic flux densities induced in the magnetostrictive layer. Numerical methods are used to begin to characterize the presence of magnetostrictive particles in the laminate and the behavior of the magnetostrictive particles in relationship to the magnetic field used during sensing. Unidirectional laminates with embedded delaminations are used for simulations and experimentations. A novel, yet simplified fabrication method is discussed to ensure consistent scanning and sensing capabilities. The nondestructive evaluation scanning experiments were conducted with various shapes and sizes of damages introduced into carbon fiber-reinforced polymeric composite structures. The results demonstrate high potential for magnetostrictive particles as a low-cost, noncontacting, and reliable sensor for nondestructive evaluation of composite materials.

The overall purpose of this research is to characterize the affects of imbedding magnetostrictive particles (MSP) in a CFRP laminate for the purpose of nondestructive evaluation. This paper details an investigation using an analytical and experimental approach. At the time of this publication, both the analytical and experimental investigations are in a preliminary stage and the results have not yet converged. The analytical investigation utilizes fundamental equations for the magnetomechanical properties of the MSP and classical laminate theory for the strength and stiffness of the CFRP laminate to obtain a model of the combination. It is assumed that the magnetomechanical relationship of the MSP layer is a function of the prestress acting on the layer. This relationship is nonlinear in nature but is broken down into a number of linear sections to facilitate analysis. This prestress acting on the MSP layer is a result of the CFRP laminate’s stiffness resisting the induced strain of the MSP layer. Classical laminate theory is used to obtain the value of the prestress as a function of this induced strain. As would be expected, this analysis becomes an iterative process. The induced strain is calculated based on a prestress level of zero. This strain is then used to calculate the amount of stress in the CFRP laminate which becomes the prestress value, and the process is repeated until convergence is reached. Unidirectional CFRP laminates are used in this analysis. The experimental approach involved testing a collection of composite beams imbedded with MSP using a scanner that surrounded the beams. The scanner was composed of an excitation coil and a sensing coil. A detailed schematic of the scanner is included in the paper showing the slide along which the scanner apparatus moved, and the sensing coil surrounded by the excitation coil. The samples used in this analysis were constructed from unidirectional prepreg carbon fiber with varying internal delaminations, ply orientations, and number of plies. A program was constructed that allowed the user to control the signal being output to the excitation coil as well as record data from the sensing coil. The results presented in this paper are not final and will be used to create a foundation for continuation of this research.

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 mod...