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On The Use of Multifunctional Z-Pins for Sensing Internal Damage in Composite Laminates Based on Electrical Resistance Measurements



Experimental studies have demonstrated that multifunctional z-pins can significantly improve structural damage resistance while also providing a sensitive response to damage. While TTRs have been commonplace in the composites world for decades, multifunctional TTRs with self-sensing capabilities are a relatively unexplored area. This paper focuses on investigating the feasibility of leveraging the inherent electrical conductivity of carbon-fiber and metallic z-pin reinforcements for sensing internal damage in composite laminates. The study utilizes finite element models in ABAQUS to analyze the electrical resistance of the z-pins during progressive failure of pins subjected to combined pullout and shear failure. The electrical finite element models were utilized to understand the interaction between impact-induced mechanical damage and electrical responses for these multifunctional reinforcements. The finite element simulations were conducted in two phases. Initially, the damage was evaluated using continuum shell elements with damage evolution. Next, the damaged elements from the mechanical analysis were incorporated into electrical models of the z-pins, and the influence of mechanical damage on electrical response was studied. The results of this study indicated that carbon fiber z-pins provide a stronger response to damage compared to titanium zpins. The stronger damage response of the carbon fiber was attributed to the inherent electrical anisotropy of the carbon fiber composite. The results from this paper will be used to inform the development of multifunctional through-thickness reinforced composite laminates that demonstrate improved damage tolerance and have smartsensing capabilities.


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