Polymer impregnation and pyrolysis (PIP) process-based C/SiC composites are fabricated using the in-house synthesized methyl-polycarbosilane (PCS). Two-level factorial design matrix is employed to carry out experiments to study the effect of four factors on flexural strength of the composite. Total sixteen sets of composite samples are fabricated. Response table, normal probability plot, ANOVA and regression analysis are carried out to determine the statistical significant factors. Composite density (ρ), fibre volume fraction (V f) and pyrolysis temperature (T) are found to be statistically significant, while softening point (SP) of the PCS and interaction of these four factors are found insignificant. Higher levels of the density and V f have shown positive effect, while the pyrolysis temperature has negative effect on the flexural strength of the composites. Flexural strength was found to be in the range of 374-592 MPa depending on the process parameters. The mechanical behaviour of the composites at different process conditions was explained with the help of their microstructures.

No abstract

No abstract

Treating Kevlar fabric with silica nanoparticles is known to augment its mechanical properties, especially under shear deformation. Silica nanoparticle-treated Kevlar (SNK) fabric could therefore display improved ballistic performance. In this study, the ballistic performance of SNK with various percentages by weight of nanoparticle addition and number of layers is evaluated using compressed air gun experiments. A colloid-based treatment procedure is used to impregnate dry silica nanoparticles into the fabric. Addition of nanoparticles provided about 17.3% mass advantage (due to three fewer layers) for the 40 wt.% SNK vis-à-vis neat Kevlar for the non-penetrative case. SEM imaging reveals that at higher treatment levels the nanoparticles tend to agglomerate in the interstitial spaces of yarn crossover points, which helps better engage secondary yarns away from the impact location of the projectile. A semi-empirical model is developed to capture the influence of treatment level and number of layers on the kinetic energy absorbed by SNK. The flexibility of SNK is tested using a fixed cantilever test that avoids the sliding of the sample between flat plates used in standardized tests, which tends to dislodge the nanoparticles. The measured tip deflection angle decreases from 33o for the neat fabric to 19o for the 40 wt.% SNK. The flexural rigidities educed using digital image analysis range from 48.9 μNm2 for the neat fabric to 113.7 μNm2 for the 40 wt.% case. SNK could potentially enable multifunctional structural solutions in applications related to personal protective gear, military vehicle hulls and impact shielding of space structures.

Meta-acoustic barriers (MABs) that are inspired by acoustic metamaterials (AM) offer opportunities to defy mass law-driven sound transmission loss (TL) performance that is characteristic of conventional acoustic barriers. In this analytical parametric study, the TL behavior of MABs that incorporate various local oscillator configurations are analyzed using an effective-mass modeling approach. Resonant, damped and inertant local oscillator configurations and combinations thereof that result in negative and complex effective-mass for the meta-acoustic barrier are considered. The influence of the local configuration’s orientation, oblique incidence and the presence of multiple oscillator types are examined using nondimensionalized metrics and compared to the performance of static mass and volume-equivalent limp mass and double wall barriers. It is shown that due to their anomalous effective-mass, such barriers display tunable TL bandwidths exceeding that of mass-equivalent conventional barriers indicating new device implications. The effective-mass modeling approach can easily be adapted to account for the presence of different dynamic features within various types of inclusions considered and is thus an efficient tool to evaluate meta-acoustic barrier designs. Inasmuch as these meta-acoustic barrier structures can be realized using recent advances in additive and hybrid manufacturing techniques, opportunities exist to create lightweight barriers for tonal and broadband acoustic applications.