National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Hygrothermal Effects on RT-Cured Glass-Epoxy Composites in Immersion Environments. Part B: Degradation Studies

Abstract: The degradative effects of artificial seawater and distilled water immersion at 333° K on the mechanical properties (ILSS, compression strength) of BID glass/epoxy composite materials has been studied. Experimental results showed that the composite degradation trends were similar in both the media. It was found that the composite specimens exhibited a higher compressive and ILSS retention when immersed in the artificial seawater than when immersed in distilled water. This is attributed to the moisture absorption levels being higher in specimens immersed in distilled water than those immersed in artificial seawater (Part A). Further, it was found that the measured and predicted mechanical strength retention ratios (compression and ILSS) were in fairly good agreement with each other for both the immersion conditions.

Forbidden reflections from the aramid PPTA - A novel correlation with stacking faults

Abstract: The occurrence of space group forbidden reflections in the X-ray diffraction patterns from the aramid PPTA has been correlated with the presence of stacking faults. The fraction of sample affected by the presence of such faults has also been estimated.

Effect of Cross-linking Density on Creep and Recovery Behavior in Epoxy-Based Shape Memory Polymers (SMEPs) for Structural Applications

Abstract: Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature (T g) was measured for these SMEPs using advanced rheometric expansion system, and from the T g measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures.

Structural transformation, thermal endurance, and identification of evolved gases during heat treatment processes of carbon fiber polymer precursors focusing on the stereoregularity

Abstract: Structural transformations of polyacrylonitrile microstructure with varying degrees of stereoregularity during the thermal-oxidative degradation and pyrolysis reactions were investigated employing coupled thermal techniques namely pyrolysis–gas chromatography–mass spectrometry, evolved gas analysis–mass spectrometry, and thermal gravimetric analyzer-FT infrared spectrometry (TG-FTIR) in the temperature range of 200–600 °C. More number of intense peaks with large ionic abundances in the thermal curves and pyrograms indicate that atactic-rich polyacrylonitrile copolymers undergo thermal cleavage, fragmentation and cyclization reactions more readily than isotactic polyacrylonitrile. The mass loss accompanying the thermal reactions was accounted for the evolution of hydrogen cyanide, ammonia, and homologous of alkyl nitrile having molar mass between 47 and 224 m/z; their most probable structures were identified. Thermal analysis results confirm that nitrile cyclization reactions proceed preferentially at isotactic triads leading to a steady and stable thermal-oxidative degradation reactions as compared to atactic-rich polyacrylonitrile. The simultaneous TG-FTIR results of evolved gas analysis also validate the pyrolysis experiments.