Physico-mechanical, thermal and biodegradation performance of random flax/polylactic acid and unidirectional flax/polylactic acid biocomposites

Fully biodegradable flax/polylactic acid (PLA) thermoplastic composites were fabricated by using random (nonwoven mat) and aligned (unidirectional yarn) flax fiber as reinforcements (39% flax by volume) and Polylactic acid (PLA) as matrix. Results revealed that the aligned flax fibers have a greater reinforcing effect due to the uniform distribution of load axially along the fiber length in the composite. The aligned flax/PLA and random flax/PLA showed the tensile strength of (83.0 ± 5.0) and (151.0 ± 7.0) MPa respectively and flexural strength of (130.0 ± 5.0) and (215.0 ± 7.2) MPa respectively. Young’s modulus of (9.3 ± 1.5) and (18.5 ± 2.0) GPa and flexural modulus of (9.9 ± 1.0) and (18.8 ± 1.0) GPa was attained for the random and unidirectional fiber composites, respectively. It was also found that both composite constituents, fiber and matrix, were degradable if buried in compost soil (ready soil after composting process), which is a distinctive advantage of the new composite structures. Remarkably, the biodegradation property of aligned flax fiber composites was significantly lower than random mat composites, possibly due to the less water swelling behavior of the aligned fiber composites. After 120 days burial test, the aligned flax/PLA composite displayed the reduction of 19% mass, residual flexural strength and modulus decreased by 57 and 50% respectively, while the random mat composites exhibited the loss of 27% mass, residual flexural strength and modulus declined by 80% at the same period.</jats:p

Compressible flow characteristics around a biconvex arc airfoil in a channel

Shock wave-boundary layer interactions (SWBLI) are observed in several practical high-speed internal flows, such as compressor blades, turbine cascades, nozzles and so on. Shock induced oscillations (SIO), aerodynamic instabilities so-called buffet flows, flutter, aeroacoustic noise and vibration are the detrimental consequences of this unsteady shock-boundary layer interactions. In the present study, a numerical computation has been performed to investigate the compressible flow characteristics around a 12% thick biconvex circular arc airfoil in a two dimensional channel. Reynolds averaged Navier-Stokes equations with two equation k-ω shear stress transport (SST) turbulence model have been applied for the computational analysis. The flow field characteristics has been studied from pressure ratio (ratio of back pressure, pb to inlet total pressure, p01) of 0.75 to 0.65. The present computational results have been compared and validated with the available experimental data. The results showed that the internal flow field characteristics such as shock wave structure, its behavior (steady or unsteady) and the corresponding boundary layer interaction are varied with pressure ratio. Self-excited shock oscillation was observed at certain flow conditions. Moreover, the mode of unsteady shock oscillation and its frequency are varied significantly with change of pressure ratio