Mostafa Yakout, M.A. Elbestawi, S.C. Veldhuis and S. Nangle-Smith
Residual stresses are induced during selective laser melting (SLM) because of rapid melting, solidification and build plate removal. This paper aims to examine the thermal cycle…
Abstract
Purpose
Residual stresses are induced during selective laser melting (SLM) because of rapid melting, solidification and build plate removal. This paper aims to examine the thermal cycle, residual stresses and part distortions for selected aerospace materials (i.e. Ti-6Al-4V, stainless steel 316L and Invar 36) using a thermo-mechanical finite element model. The numerical results are validated and compared to experimental data.
Design/methodology/approach
The model predicts the residual stress and part distortion after build plate removal. The residual stress field is validated using X-ray diffraction method and the part distortion is validated using dimensional measurements.
Findings
The trends found in the numerical results agree with those found experimentally. Invar 36 had the lowest tensile residual stresses because of its lowest coefficient of thermal expansion. The residual stresses of stainless steel 316L were lower than those of Ti-6Al-4V because of its high thermal diffusivity.
Research limitations/implications
The model predicts residual stresses at the optimal SLM process parameters. However, using any other process conditions could cause void formation and/or alloying element vaporization, which would require the inclusion of melt pool physics in the model.
Originality/value
The paper explains the influence of the coefficient of thermal expansion and thermal diffusivity on the induced thermal stresses using experimental and numerical results. The methodology can be used to predict the part distortions and residual stresses in complex designs of any of the three materials under optimal SLM process parameters.
Details
Keywords
Dawa Dolma Bhutia, Yeka Zhimo, Ramen Kole and Jayanta Saha
The purpose of this paper was to determine the antifungal activities of different solvent extracts of common plants in vitro and in vivo against banana anthracnose fungus…
Abstract
Purpose
The purpose of this paper was to determine the antifungal activities of different solvent extracts of common plants in vitro and in vivo against banana anthracnose fungus Colletotrichum musae (Berk & M.A. Curtis) Arx, and to investigate its effects on the pathogen and identify the bio active component(s).
Design/methodology/approach
Extracts were obtained from leaves, tender shoots, rhizomes, bulbs, seeds and fruits of 42 naturally growing plant species following hot sequential extraction. Preliminary screening of the solvent extracts was done based on the inhibition of radial mycelial growth of C. musae following poison food technique and conidial germination inhibition by cavity slide technique. The selected extracts were assessed for their effect on harvested banana in reducing anthracnose during storage. The active components in the bio-active fractions of plant extract were identified by gas chromatography-mass spectroscopy.
Findings
Methanol extracted a larger quantity of material (between 6.9 and 12.5 per cent) than hexane or chloroform, and all its extracts were active against the test pathogen with mycelial growth inhibition ranging from 13.70 to 88.89 per cent. Zingiber officinale rhizome extract as well as Polyalthia longifolia and Clerodendrum inerme leaf extracts exhibited more than 80 per cent inhibition of mycelial growth. Total inhibition of spore germination of C. musae was recorded in Z. officinale and P. longifolia extracts at 0.3 per cent w/v and 0.5 per cent w/v concentration, respectively, while only 68 per cent spore inhibition was recorded in C. inerme at 0.5 per cent w/v concentration. Of the three plant species, Z. officinale had the best antifungal activity (18.0 per cent disease incidence; 2.2 disease severity scale) when banana fruits were dipped in the extract at a concentration of 0.5 per cent w/v at 5 days of storage in ambient condition (80-82 per cent R.H., 27 ± 1°C). The bio-active compounds in the extract of Z. officinale were identified as alpha-curcumene and zingerone.
Originality/value
Based on the antifungal activity, plant extract of Z. officinale can be used as an effective alternative to chemicals in controlling anthracnose pathogen in harvested banana.