---

In this paper, with the aim of providing a new test pattern for empirical prediction of FLD of 304 stainless steel tube, firstly numerical investigation of hydro-bulging process with various load paths and die geometries has been performed on strain path and plastic instability. Study on geometry of dies has been performed by varying die corner radius (R) and bulging length (W). Here, effect of axial feeding on strain ratio (β) has been studied. In this condition, by increasing of W, strain ratio (β) tends to value of zero that this situation is independent to boundary condition. By increasing of die corner (R) in free loading condition, reduction of β occurs and the strain path approaches to plane strain state; while in loading with axial feeding condition, increasing of R has neglect able effect on strain path and ratio. In loading with axial feeding condition, increase in axial feeding strain ratio (β) is reduced drastically. From the simulated tests, number of 10 tests with distributed loading path on strain diagram was selected for empirical study. Meshed tubes are loaded controllably until tearing and the FLCs have been drawn using strains which were obtained near tearing locations.

---

In recent years, rubber pad forming process have many advantages, such as high flexibility, good surface quality and lower manufacturing costs; RPF have been widely used in automotive, aerospace and military industries. In present research, numerical and experimental analysis of free bulging 304 stainless steel seamed tube, using a polyurethane elastic pad has been studied. Firstly, 3D simulation of seamed tube bulging using the finite element ABAQUS/Explicit 6.12 software by several frictional conditions has been performed. An incompressible hyperelastic pad has been modeled by Mooney-Rivlin constitutive equation and the elastic-plastic behavior as more as progressive ductile damage criterion FLD for steel tube were assumed. In the experimental activity, compression test of rubber was carried out according to ASTM D575-91 standard and compressive stress-strain curve and the Mooney-Rivlin constants were determined. Forming of meshed tubes by using elastic pad with different lubricating systems have been conducted up to onset of bursting in the seam weld and longitudinal, hoop and thickness strains were measured. Results showed that friction, especially between rubber and tube plays the main role in controlling wrinkles, increasing the bulge depth, reducing the forming load and friction dissipation energy of the process. Also observed that the intact parts without any wrinkles formed by using nylon lubricant between tube and rubber and drawing oil between tubes and die.

---

This paper puts forward a novel numerical-experimental method for calculation of constants of advanced anisotropic yield criterion BBC2003. Calculation of the eight constants of this yield criterion, demands experimental determination of eight mechanical properties of the material. These properties include; axial-yield stresses in 0, 45 and 90 degree with respect to the rolling direction, anisotropic parameters in the directions mentioned and plane strain yield stresses for 0 and 90 degree orientations. However, determination of the equi-biaxial yield stresses and anisotropic coefficients is relatively expensive. In the method presented in this paper, using a simple technique, the constants of the yield criterion are calculated based on plane strain yield stresses in 0 and 90 degree to the rolling direction. The system of equations involving the contestants of the yield function, is solved numerically through defining an error function and minimizing it using steepest descent method. In two case studies, the constants of BBC2003 yield criterion for anisotropic sheets of aluminum alloys AA3105 and AA6061-O, were calculated using this method. Subsequently, the accuracy of predicting of axial-yield stress and anisotropic coefficient in different directions as well as the coincidence of yield surface with experimental results for BBC2003 and Hill48 yield criteria have been investigated. The results show that the proposed method has good accuracy and stability in calculating of advanced yield criterion constants and consequently the mechanical properties of anisotropic sheets in different directions.

---

Bulging with elastomer tool has been used in the production of integrated hollow parts as one of flexible forming methods. Nowadays, most industries such as Aerospace and military are using flexible die forming methods due to their flexibility, high quality and lower cost. In this research, finite element simulation has been implemented by ABAQUS software to investigate the behavior of stainless steel 304 tube bulging process using elastomer tool. By comparing the geometry of deformed tubes in experimental tests and simulation results, the FEM model was verified. The aim of this study is to determine the process factors and their effects on the average thickness and depth of bulged tube. In this regard, design of experiment (DOE) was performed using a full factorial method and the results were interpreted using analysis of variance (ANOVA). Also a regression model was presented to predict these responses. Results showed that among the studied factors, friction (between tube and rubber), rubber height, punch displacement and tube axial feeding have significant effects on the process. Finally, the optimal values for significant factors were presented.

---

The aim of this study is to improve the strength properties of glass-aluminum multilayer hybrid composite using AA1050 aluminum sheets processed by the accumulative roll bonding (ARB) process. Also, the effect of different cycles of ARB process on the strength properties of hybrid composite has also been investigated. At first, the ARB process was applied on the AA1050 sheet. Afterwards, the microstructure and tensile properties of the ARB deformed sheets were investigated. Then, the ARB processed AA1050 sheets were used to make glass reinforced aluminum laminate (GLARE). In the end, the tensile properties of the GLARE composite were examined. By the progress of the ARB process, the hardness and strength of the sheet increased. The elongation of the first cycle processed specimens dropped drastically. But, by increasing the process cycles, the elongation increased gradually. The use of the ARB processed aluminum sheet in the manufacture of GLARE composite significantly improved the tensile strength of the GLARE. In the GLARE made of annealed aluminum, most of the elongation of the aluminum layer occurred after the breaking of the glass fibers and in conditions outside the GLARE composite; as a result, the reduction of the sheet elongation during the ARB process caused the simultaneous failure of the metal layers and the glass fibers during the tensile test of the GLARE. Hence, this event did not reduce the ductility of the composite. In other words, the total energy absorption and fracture toughness of the aluminum layers occurred when the GLARE had not failed.

---

The ECAP-Conform is one of the newest and less known processes that improve mechanical properties. In the present study, the effective parameters of the ECAP-Conform process for AA7075 have been investigated. Influence of parameters such as roller radius, bending angle, die channel angles, rod/roll friction coefficient, rod/die friction coefficient, and the aspect ratio of the die groove on the torque, the applied force on the die, the stress, and the effective plastic strain, the output rod curvature, and the strain distribution uniformity have been investigated. The design of experiments was carried out based on the response surface method by the Minitab software, and simulations were performed using the ABAQUS software. To validate the FEM, the ECAP-Conform process of AA7075 rod was performed and the comparison of experimental and numerical results have acceptable compliance (7.5% error). It was found that the die channel angles and the rod/die friction coefficient have a more significant effect on all responses. Moreover, to maximize the imposed strain and strength, and to minimize the process torque and curvature, as well as achieving a uniform distribution of strain, the optimal output parameters have been obtained.