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The damping performance of lightweight steel/polymer/steel sandwich composites has been typically studied without considering the interface between the heterogeneous materials. Herein, the interface between the steel and polymer layers was investigated experimentally for various steels and polymers. Impact hammer tests revealed that the interfacial adhesion strength between steel and polymer did not significantly affect the loss factor of the sandwich cantilever beam composites. However, although very thin, the adhesive layer itself greatly influenced the vibration-damping performance of the composite. As such, previous three-layered (skin-core-skin) sandwich model without considering the properties of adhesive layer predicted different results from experiments. To accurately predict the loss factor of the sandwich, a five-layered sandwich model consisting of two skins, two adhesives, and a core layer was proposed and validated with experiments.

Due to their high specific strength, specific stiffness, and toughness, aramid fabrics have been used in various applications, especially those involving bulletproofing. The bulletproof capability and mechanical properties of aramid fabrics can be enhanced at the mesoscale with shear thickening fluid (STF) coatings; however, little is known about the microscale characteristics of STF-coated aramid fabrics. This study aimed to investigate the microscale rate-dependent behavior of STF-coated single aramid fibers inside aramid yarns using a newly proposed testing method, in which a high shear rate is applied to STF-coated yarns and fibers in a single-fiber pull-out test.

Steel-polymer sandwich composites are relatively strong and lightweight materials. However, accurately predicting the mechanical properties of these materials has been challenging, presumably due t...

The structure of lead-free (1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 (BNT-STx) ceramics was analyzed by the Rietveld method, using X-ray diffraction and neutron scattering data. The structural refinement results suggest that the crystal structure successively changes with SrTiO3 concentration, x, from the rhombohedral phase (x = 0.00) to rhombohedral and tetragonal (x = 0.10–0.30), tetragonal and cubic (x = 0.40–0.60), and finally cubic (x = 0.80–1.00) phases. Correlation between the charge sensor constant (d33) and the weighted off-center value (dw) was observed, which may be attributed to the increased dipole motion in the unit cell due to an increased tendency to respond to external stimulation. Furthermore, an improved charge sensor constant (d33) of 140 pC/N was observed for BNT-ST0.20, and a large strain of 0.25% and a d33* value of 443 pm/V were observed from x = 0.30.

This study reports on the prediction of the delamination of steel-polymer composites. To characterize the adhesive properties from peeling tests, a simple model was derived based on peeling mechanics, in particular considering plastically dissipated energy of polymer film due to bending. Peeling tests were performed at two angles so that the adhesive properties were determined in both normal and tangential directions. Then, peel strength at arbitrary angle was predicted and compared with experiments, showing that the peel strength at only two angles and peeling mechanics considering the bending of polymer film can accurately describe the adhesive properties of steel-polymer interface. Finally, finite element simulations based on the cohesive zone model were performed to predict the delamination between steel-polymer sandwich composites, demonstrating the validity of cohesive zone model equipped with necessary properties determined using peeling tests and the developed model in this study.

Shear-thickening fluid-impregnated aramid (STF-im-AR) fabrics have been manufactured for advanced soft body armor applications for which they provide improved ballistic and stab resistances. It is not yet clear whether or not such improvements can be attributed solely to the STF. In this study, the rate-dependent behavior of an STF-im-AR fabric was investigated at the fabric level, using uniaxial tensile, bias-extension, and picture-frame tests. Rate-dependent behavior of the STF-im-AR fabric was observed during uniaxial tensile testing; however, the effect of the STF treatment was slight and consistent with only the inherent effect of the polymeric nature of its constituent fibers. The shear rigidity of the STF-im-AR fabric increased, due to the presence of the STF and the sensitivity of the fabric's shear stiffness to changes in the shear strain rate also increased slightly. This rate-sensitive shear stiffness of STF-im-AR fabrics may contribute to improved ballistic and stab resistances.

Steel-polymer composites have low density, high specific flexural stiffness and vibration damping properties over other metal materials. However, the weak interfaces between steel and polymer sheet are the typical locations where the failure occurs. Furthermore, interfacial failure is a fatal reason of the degradation of mechanical properties. Therefore, predicting interfacial failure of the final product is an important technology in commercialization of steel-polymer composites. In this study, we built forming limit diagram (FLD) based on two different failure modes: failure of the bottom skin steel and interfacial failure between the skin steel and core polymer. Acoustic emission (AE) technique was conducted to observe the interfacial failure moment. Peak frequency was found to be the key feature to distinguish interfacial failure. Peak frequency band that indicates interfacial failure was from 300 kHz to 500 kHz. This peak frequency band made it possible to build FLD considering the interfacial failure.

Recently, hybrid composites of carbon fiber reinforced plastics (CFRP) and steel have attracted great attention from automotive engineers due to their high potential for lightweight and multi-materials structures. Interestingly, such hybrid composites have demonstrated increased breaking strain, i.e., the breaking strain of CFRP in the hybrid was larger than that of single CFRP. As such the mechanical properties of hybrid composites could not be calculated using the rule of mixture. In addition, such increase is strongly dependent on the adhesion between CFRP and steel. In this study, a numerical analysis model was built to investigate the mechanism behind increased breaking strain of CFRP in the hybrid structure. Using cohesive zone model, the adhesion between CFRP and steel was effectively considered. The numerical results showed that the simulated mechanical behavior of the hybrid composites did not change as much as observed in experimental as the interfacial adhesion varied. We will investigate this ...

Various properties of electrowetting such as reversibility, reproducibility and mobility have been investigated experimentally. A conductive water drop on a thin hydrophobic film of amorphous fluropolymers coated on the counter electrode showed unexpectedly the poor reversibility under the discontinuous voltage, so called the contact angle hysteresis. The hysteresis could not been completely suppressed by inserting additionally a thick parylene-C film which has the high dielectric constant and no pinholes. However, both the reversibility and the reproducibility have been enhanced under the continuous voltage starting from the highest absolute electric potential.