s. h. nourbakhsh

Severe plastic deformation processes are used as a method to increase the mechanical strength of metals. One of the new deformation methods is twist channel angular pressing (TCAP). TCAP has been developed based on a combination of twist extrusion processes (TE) and Equal Channel Angular Pressing (ECAP) process. In this paper, the effect of TCAP die geometry on the grain size distribution and plasticity properties using simulation in DEFORM software is investigated. For this reason, dies with internal angles of 90◦, 100◦ and 110◦, external (corner) angles of 0◦, 10◦ and 20◦ and twist angles of 30◦, 45◦, 60◦ are used. In addition, the location of the twist channel is examined before and after the ECAP location. The distribution of plastic strain, grain size distribution, and the required punch force for the TCAP process on Aluminum alloy 7050 are extracted in all conditions. The results showed that locating the twist section after ECAP location led to a better microstructure in the billet. Also, die with a twist angle of 45◦, an internal angle of 110◦, and a corner angle of 0◦ created the best results; therefore, the grain size decreased from 100µm to 3.67µm.

In this paper, energy absorption of aluminum thin-walled combined geometry, including a cylinder and a hemisphere under axial and oblique loading, is investigated using numerical simulation. The aim of this research is optimizing the dimensions of the combined geometry in order to increase the energy absorption capacity and comparing it with an equal weight thin-walled simple cylinder. Numerical simulations were performed at 0, 7, 14, and 21 degree of loading using ABAQUS software. The results showed that with increasing the radius of curvature and decreasing the height of the combined geometry, energy absorption parameters increase, and in general the combined geometry has better performance than the simple cylinder especially in oblique loading. The SAE and CFE of the optimum combined geometry with dimensions of R = 25mm, h = 25mm, H = 181:92mm, and D = 50mm in the 0 and 7 degree of loading is similar and in the 14 and 21 degree of loading increased 300% and 200% respectively in comparison with an equal weight thin-walled simple cylinder.

Twist extrusion is a novel method for severe plastic deformation of materials. Severe plastic deformation in metals creates small and uniform grain size and therefore increases their mechanical strength. In this study, the effect of die angle in twist extrusion and cross-section of extruded parts on plastic properties and microstructures of Aluminum 7050 alloy was investigated using DEFORM 3D finite element software. Samples were simulated using dies with die angles of 20, 37, and 56 degrees with square, rounded-rectangular, and elliptical cross-sections. The aspect ratios of rectangular and elliptical cross-sections were also changed while keeping the cross-section area constant in order to investigate the effects of dimensions. Plastic strain distribution, gain size distribution, and the force needed for extrusion were extracted under all conditions. The results indicate that increase in die angle significantly reduces grain size and increases the force necessary for extrusion. Removing sharp corners in cross-section also results in more uniform plastic strain distribution and reduction in extrusion force. The elliptical cross-section with dimensions of 9×6mm which had the lowest dimension ratio can reduce grain size from 100ffm to 6ffm in a single pass and requires the lowest extrusion force.

Biology of Scaeva albomaculata (Macquart) was investigated on Brachycaudus amygdalinus (Schouteden) as a prey in laboratory conditions (20 ± 2 ºC and 45 ± 5 % RH). Developmental times were 2.57 ± 0.098, 1.57 ± 0.072 and 4.3 ± 0.085 days for the first, second and third instar larvae, respectively. The first and second instar larvae of syrphid fly consumed 21.7 ± 0.87 and 35.1 ± 1.25 the first and second nymphs, respectively, whereas the third instar larvae consumed 613.2 ± 18.43 alate nymphs of B. amygdalinus. Adults of syrphid flies mostly emerged in early morning. Population dynamics of eggs and larvae and larval behavior were studied from emergence time (early March) to late October during 2001-2004 in two regions (Shahrekord and Shorab-Saghir). In natural conditions, the larvae that completed their growth left the almond twigs and pupated at a depth of 3-5 cm below the soil surface. The most important natural enemies of S. albomaculata larvae were identified as Diplazon laetatorius (Fabricius) (Hym.: Ichneomonidae) and Dotriothorax sp. (Hym.: Encyrtidae), which parasitized 34% and 5% of the larvae, respectively. These parasitoids emerged from pupae of S. albomaculata. Another mortality agent was an unknown pathogen, which caused the body content of the pupae to become a milky liquid.