Browsing by Author "Wu, H. Felix"
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- Interfacial Adhesion Evaulation of Uniaxial fiber-Reinforced-Polymer Composites by Vibration Damping of Cantilever BeamGu, Weiqun (Virginia Tech, 1997-02-17)The performance of fiber-reinforced composites is often controlled by the properties of the fiber-matrix interface. Good interfacial bonding (or adhesion), to ensure load transfer from matrix to reinforcement, is a primary requirement for effective use of reinforcement properties. Thus, a fundamental understanding of interfacial properties and a quantitative characterization of interfacial adhesion strength can help in evaluating the mechanical behavior and capabilities of composite materials. A large number of analytical techniques have been developed for understanding interfacial adhesion of glass fiber reinforced polymers. Common adhesion tests include contact angle measurements, tension or compression of specially shaped blocks of polymer containing a single fiber, the single fiber pull-out test, single-fiber fragmentation test, short beam shear and transverse tensile tests, and the vibration damping test. Among these techniques, the vibration damping technique has the advantage of being nondestructive as well as highly sensitive for evaluating the interfacial region, and it can allow the materials industry to rapidly determine the mechanical properties of composites. In this work, we contributed a simple optical system for measuring the damping factor of uniaxial fiber-reinforced-polymer composites in the shape of cantilever beams. A single glass fiber- and three single metallic wire-reinforced epoxy resin composites were tested with the optical system. The fiber- (wire-) matrix interfacial adhesion strength measurements were made by microbond test. A reasonable agreement was found between the measured interfacial adhesion strength and micromechanics calculations using results from vibration damping experiments. The study was also extended to multi-fiber composites. The interfacial damping factors in glass-fiber reinforced epoxy-resin composites were correlated with transverse tensile strength, which is a qualitative measurement of adhesion at the fiber-matrix interface. Four different composite systems were tested. For each system, glass fibers with three different surface treatments were used at three different volume fractions. The experimental results also showed an inverse relationship between damping contributed by the interface and composite transverse tensile strength for all of the multi-fiber composites.
- Stiff and strong, lightweight bi-material sandwich plate-lattices with enhanced energy absorptionHsieh, Meng-Ting; Ha, Chan Soo; Xu, Zhenpeng; Kim, Seokpum; Wu, H. Felix; Kunc, Vlastimil; Zheng, Xiaoyu (Springer, 2021-08-17)Plate-based lattices are predicted to reach theoretical Hashin–Shtrikman and Suquet upper bounds on stiffness and strength. However, simultaneously attaining high energy absorption in these plate-lattices still remains elusive, which is critical for many structural applications such as shock wave absorber and protective devices. In this work, we present bi-material isotropic cubic + octet sandwich plate-lattices composed of carbon fiber-reinforced polymer (stiff) skins and elastomeric (soft) core. This bi-material configuration enhances their energy absorption capability while retaining stretching-dominated behavior. We investigate their mechanical properties through an analytical model and finite element simulations. Our results show that they achieve enhanced energy absorption approximately 2–2.8 times higher than their homogeneous counterparts while marginally compromising their stiffness and strength. When compared to previously reported materials, these materials achieve superior strength-energy absorption characteristics, making them an excellent candidate for stiff and strong, lightweight energy absorbing applications. Graphic Abstract: [Figure not available: see fulltext.]