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Effects of Interfacial Defects on Properties of Laminated Composite Materials and Their Bonded Joints



Composite materials are widely used in a range of applications and their reliability depends on the quality of manufactured structure. Defects can be produced in composite materials during the manufacturing and can also evolve over the entire service life. A number of different defects can initiate during the manufacturing, adhesive bonding and repair process. For example, voids and interfacial debond can be very detrimental to the performance of the composite structure. Debond at bonded joints is often difficult to characterize (for example, “kissing bondâ€). Although progress has been made in detection of defects using popular nondestructive methods, there are still significant challenges remain in quantifying the distribution of defects and the corresponding property loss. The objective of this study is to explore effects of defects (micro-void and debond) at interlaminar locations within the laminate and also at adhesive joints. To study the effect of interlaminar defect, glass microspheres and Teflon inserts are used to create debond region between two carbon fiber plies. On the other hand, coatings of mold release agent and release films were used in the adhesive joint to mimic kissing bond between glass fiber substrates. We will use a new concept that heterogeneous charge polarization inside a material is related to the microstructural degradation and can be quantified using Broadband Dielectric Spectroscopy (BbDS) technique. Using both bulk and scanning mode, we can quantify the distribution of dielectric properties. Corresponding mechanical property loss due to defects in the material has been determined and related to changes in dielectric characteristics such as changes is complex permittivity. Results show that real permittivity captures the interfacial defect in both interlaminar and kissing bond experiments. A 3D X-ray microscope will be used to validate experimental observations. Details of experimental results and observations are documented in the paper.

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