Showing 3 results for Maleki
M. Maleki,
Volume 27, Issue 1 (7-2008)
Abstract
In this paper, an elastoplastic constitutive model is presented for predicting sandy soil behavior under monotonic and cyclic loadings. The model is based on the CJS3 model that takes into account deviatoric and isotropic mechanisms of plasticity. The flow rule in deviatoric mechanism is non-associated and a kinematic hardening law controls the evolution of the
yield surface. In the present study, the critical state surface and history surface separating the virgin and cyclic states in the stress space are defined. Hardening modulus and stress-dilatancy law for monotonic and cyclic loadings are effectively modified. Taking the hardening modulus as a function of deviatoric and volumetric plastic strain, the model will be capable of predicting sand behavior once the history surface and stress reversal are defined. All model parameters have clear physical meanings and can be determined simply from laboratory tests. The results of homogeneous tests on Hostun sand are used to validate the model. The results of validation indicate the capability of the proposed model.
M. Khoobroo, A. Maleki, B. Niroumand,
Volume 36, Issue 3 (Journal of Advanced Materials-Fall 2017)
Abstract
Conventionally, alloying elements are being added to the whole melt; however, in this research in-situ surface alloying of gray cast iron was employed to improve surface properties of the castings. Wires of pure copper with diameters of 0.4 and 0.8 mm were inserted and fixed at bottom of sand molds before melting. Chemical composition analysis revealed the presence of copper from surface to a depth of 1 cm. Microstructural investigations indicated that graphite type changed from A to D and E. Moreover, the content of graphite phase decreased while that of pearlite increased at the surface. Hardness was higher at surface of copper added samples. Wear resistant of the in-situ surface alloyed samples was better than the no-copper added ones.
M. Lashani Zand, B. Niroumand, A. Maleki,
Volume 37, Issue 4 (Journal of Advanced Materials-winter 2019)
Abstract
Mechanical properties of the alloys are a strong function of the average silicon particles size and the secondary dendrite arm spacing (SDAS). Modified Hall-Petch equation expresses the effects of these two microstructural parameters on the yield strength and ultimate tensile strength of the Al-Si based alloys. These microstructural parameters depen on parameters such as chemical composition, cooling rate and melt treatment. In this study, the effect of cooling rate on the equation constants of the alloy were determined. For this purpose, the alloy was poured at 750 °C in three different molds including a sand mold, a preheated steel mold, and a water cooled steel mold. The Thermal and microstructural analysis showed that the cooling rate in the metal mold was 15.7 times higher than that of the sand mold, which resulted in a decrease of the SDAS from 54 micrometers to 17 micrometers. It was also found that by reducing the SDAS from 45 micrometers to 17 micrometers, the yield strength and tensile strength were increased by 16.5% and 6.5%, respectively. The modified Hall-Petch equation constants and the microstructure-mechanical properties relationships were then established by the microstructural and tensile test studies.
