Experimental study of the effects of pin geometry, advancing speed and D/d ratio on the mechanical and microstructural properties of 6061 aluminum alloy under the friction stir processing

The aim of this research is to investigate the effect of different pin geometries, the ratio of shoulder diameter to pin diameter, and advancing speed on the mechanical and microstructural properties of the specimens fabricated from 6061 aluminum sheet by friction stir processing. Cylindrical, frustum and prisms with triangular section (in three sizes), square and hexagonal cross-sections pins were prepared. The diameter of the shoulder was considered 18 and the diameter of the peripheral circle of all the pins was considered 6 mm. Advancing speeds of 14, 20, and 28 mm/min and rotational speed of 1000 rpm were considered. The smallest grain size was obtained using a pin with square cross-section. As the advancing speed increased, the average grain size decreased and its lowest value was observed at the advancing speed of 28 mm/min. In addition, the best mechanical properties were observed in the specimens fabricated by square cross-section pin and frustum pin. As the advancing speed increased, the ultimate strength of all specimens and the yield stress of most specimens increased. The highest hardness was observed in the specimens fabricated by square cross-section pin and the lowest hardness was observed using cylindrical pin. Also, in specimens fabricated by triangular cross-section pins, by decreasing the ratio of the shoulder diameter to the pin diameter, the ultimate strength and hardness increased and the elongation decreased

Experimental and numerical investigation of hole and edge radius effect on collapse properties of cylindrical absorbers under axial impact loading

In this paper, the collapse properties of aluminum cylindrical tubes that hole or curvature is created on their edges or their mid is studied in experimental and numerical methods. The tubes were put under axial impact of a rigid mass-block of 30.405 kg by an initial velocity of 6 or 7 m/s. In experimental exams, first the type of aluminum alloy and mechanical properties of tubes were determined, and then four samples in order to validating the numerical results were analyzed under Impact collapse. An explicit FE code, LS-Dyna, was used to implement numerical investigation and a total of 13 specimens were examined. In results and discussion it was found that in impact loading, creating hole and curvature in edge and mid of cylindrical shells while keeping energy, decreases maximum force significantly and increasing crush force efficiency. In general, by increasing the number of holes, the less maximum force and more crush force efficiency. It was observed that in impact loading, establishment of curvature at the edges, reduces the maximum force and absorption energy and raises the crush force efficiency so that by raising edge curvature radius, maximum force and absorption energy decrease but crush force efficiency increase. Finally samples with optimal performance for each type of perforated and curved edge energy absorbers were introduced. These absorbers can be an appropriate alternative for usually types

Numerical analysis of the effect of tubes distance on the mechanical behavior and energy absorption of nested thin-walled tubes

In this paper, the effect of tubes distance on the mechanical behavior and energy absorption characteristics of nested thin-walled tubes is investigated using LS-DYNA. Thin-walled cylindrical tubes made of aluminum and steel. Axial impact load is carried out and by increasing the distance between the tubes the absorbed energy is calculated. Finally, the optimum distance to maximize this parameter is determined. Results showed that aluminum tubes in both material models used in the analysis, in an almost identical and the same distance (about 4 to 5 mm) from each other had the highest amount of absorbed energy. Steel pipes in both material models, at different distances showed the highest amount of energy absorption, although the number of folds in different distances was the same. Furthermore, the overall crushing and behavior of the steel tubes were different than those of aluminum tubes

A parametric study of the mechanical behavior of nested multi tube structures under quasi-static loading

Mechanical behavior of nested aluminum structures under lateral and quasi-static loadings has been investigated in current paper. These structures consist of two nested tubes in which the inner tube is located vertically in the horizontal outer tube. The research has been done numerically and experimentally. In the numerical section, the LS-DYNA software has been used while experimental results are implemented to validate the FE outcome. The well correlated numerical results show that increasing the diameter of the inner tube leads to a decrease in the maximum force and the specific energy absorption. Later, employing the optimization by response surface method in Minitab software, the energy absorber's characteristics has been optimized and introduced as new set of specifications. High crush force efficiency is the main criterion in current research