Thermochemical characterisation of straws and high yielding perennial grasses

The research is concerned with thermochemical characterisation of straws and high yielding perennial grasses. Crops selected for this study include wheat straw (Triticum aestivum), rape straw (Brassica napus), reed canary grass (Phalaris arundinacea) and switch grass (Panicum virgatum). Thermogravimetric analysis (TGA) was used to examine the distribution of char and volatiles during pyrolysis up to 900 °C. Utilising multi-heating rate thermogravimetric data, the Friedman iso-conversional kinetic method was used to determine pyrolysis kinetic parameters. Light and medium volatile decomposition products were investigated using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) up to 520 °C. The 22 highest yielding identifiable cellulose, hemicellulose and lignin biomass markers were semi-quantified taking into consideration peak areas from GC chromatograms. Notable differences can be seen in butanedioic acid, dimethyl ester (hemicelluloses decomposition products), 2-methoxy-4-vinylphenol (lignin marker) and levoglucosan (intermediate pyrolytic decomposition product of cellulose) content when comparing perennial grasses with straw. From results presented in this study, perennial grasses such as switch grass, have the most attractive properties for fast pyrolysis processing. This is because of the observed high volatile yield content of 82.23%, heating value of 19.64 MJ/kg and the relatively low inorganic content.

Serrated yielding and the localized shear failure mode in aluminium alloys

A study has been made of serrated yielding in two commercial Al-Zn-Mg alloys in the as-quenched condition. The different serration types produced in the two alloys and the shear failure mechanism observed in both notched-bend and tensile testing are related to the mechanisms of dynamic strain ageing occurring during the test. An estimate of 19.7 kJ/mole for the activation energy for exchange of a solute atom and a vacancy in Al-6.2 wt% Zn, 2.5 wt% Mg has been made. © 1981.

Characterization of viscoplastic yielding of asphalt concrete

A temperature and strain rate dependent yield surface model was proposed to characterize the viscoplastic yielding of asphalt concrete. Laboratory tests were conducted on specimens that have two binders, two air void contents, and three aging periods. Strain decomposition was performed to obtain viscoplastic strain and stress-pseudostrain curves were constructed to determine the model parameters accurately and efficiently. Results indicate that a stiffer asphalt concrete has greater cohesion and strain hardening amplitude, both of which decline as temperature increases or strain rate decreases. The temperature and strain rate factors of the yield surface can be accurately determined solely by the peak stress of the strength tests. © 2013 Elsevier Ltd. All rights reserved.