Hot quasi-static pressing and dynamic compaction of Al7075-B 4 C composite powder are studied in this work. Micron sized Al7075 and B 4 C particles were milled to obtain uniform dispersion of B 4 C reinforcing phase. Samples with relative densities up to 97.5, 99 and 100% were fabricated using gas gun, drop hammer and hot quasi-statically compactions respectively. The results showed that the increase of B 4 C content improved the hardness of the compacts but did not improve the compressive strength in the samples compacted by the gas gun. However, the ductility of the samples was reduced significantly. The samples compacted using the drop hammer and under hot quasi-static loading experienced ,25 and 11% enhancement in the compressive strength respectively. The investigation indicated that the dynamic compaction using the gas gun was more successful if it is performed after quasi-static pre-compaction and under warm compaction process. It was concluded that the quasi-static pressing is the best fabrication technique to achieve the highest density, microhardness and strength.
The finite element method has been used to obtain elastic stress data for simply-supported short beams with uniformly distributed loading and short built-in beams subjected to shear displacement (referred to as ‘sinking beams’). Length-to-depth ratios in the range 0.5–2.0 have been considered. In the case of the simply-supported beam, some results are compared with published data, while additional information on section warping and stress contours is presented. Similar results are presented for the sinking beam, for which alternative solutions are not currently published. Predictions are compared with estimates using simple theory for slender beams and modified theories which include transverse shear effects. It is apparent that these estimates can be significantly in error when length-to-depth ratios are less than 2.0.
The true stress–strain curve has a significant role in the analysis of deformation in theoretical plasticity and numerical simulations. Because of the triaxial state of stress in the neck zone, the relationship that is normally obtained from the engineering stress–strain curve is no longer valid and must be corrected. Various correction techniques have been proposed and can be found in the literature. In this study, a new semi analytical approach for the correction of the stress–strain curve for circular cross-section specimens (axisymmetric) is introduced and a relation for a correction factor is derived based on the theory of plasticity. The relation requires only a few experimental surface strain measurements which can easily be made using an image processing technique. In the new method, the neck zone is divided into a number of thin walled toroidal elements. The algorithm for the correction factor is obtained in terms of the initial specimen radius, the neck radius and the z-strain on the neck surface. In this work, the true stress–strain curve, that is obtained using the image processing, follows a power law trend before the onset of necking and a linear trend after necking. However, the method is not limited by the trend of the stress–strain curve and can accommodate any trend describing the stress–strain relationship. The proposed approach is compared with methods proposed by Bridgman–Leroy, Bridgman, Davidenkov and Spiridonova, Siebel and Schwaigere and also numerical simulations. The number of simplifying assumptions in the present work is less than that of the Bridgman approach and some of the other methods.
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