مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 4 (تیر 1400)

In this paper, to investigate the effect of strain caused by biaxial stress on the mechanical properties of the sheet in a uniaxial tensile state, several metallic blank discs were bulge formed in the hydroforming process under different biaxial stress due to different fluid pressures. Then, the slotting process was done on bulge formed sheet to change the loading from biaxial stress to uniaxial tension. Again, these specimens were subjected to fluid pressure to determine their resistance to fluid pressure at uniaxial stresses. By using the results of this paper, the burst pressure of composite Rupture discs can be predicted in any size by numerical simulation with an error of about 8%. A Rupture disc is a safety device that burst as the fluid pressure increase and prevents damages due to excessive pressure on the equipment. In a composite Rupture disc, a nonlinear strain path occurs. If the type of load changes during sheet metal forming, e.g., the sheet forms under biaxial stress and then under uniaxial tension, the maximum failure strain and force will change. The burst pressure comparison of vacuum annealed specimens with similar non-annealed discs after work-hardening shows the possibility of increasing burst pressure more than 64% in proportion to created strain due to biaxial stress. Also, in this paper, by using analytical and numerical simulations, the equality of strain due to biaxial stress in the equal ratio of forming height to diameter (h/d) proved to be the same. 

Gypsum is one of the most inexpensive and widely used building materials. It is almost could be found in all buildings, in different shapes and forms. Despite having unique properties, low tensile and bending strength are the main weakness of the gypsum. This has limited the use of gypsum to the interior facades. Fibers, especially those obtained from agriculture wastes, are widely used for increasing gypsum strength. Long fibers have better performance on increasing the gypsum strength which is almost uncommon in short fibers. Unfortunately, providing long fibers from wastes is always harder and has more limitations than short fibers. In this research, short fiber gypsum composite with different lengths and weights percent were made. Then bending tests were performed for investigating the composites strength. The results show that in composites with shorter fibers and/or lower fiber percentage, the strength not only did not increase but rather decreased. It is noteworthy that regardless of fiber length, a composite with higher strength than pure gypsum is achievable. This would happen in composite with short fibers in higher fiber concentrations. In fact, fiber length and concentration both have the same impact on composite strength. Both can greatly reinforce each other and can make up for each other's shortcomings.

The silkworm cocoon is a hierarchical structure with multiple functions that have evolved over millions of years to create optimal metamorphosis conditions and preserve insect life against predators. In this paper, inspired by the structure of a silkworm cocoon, the cores of two types of lattice sandwich structures were redesigned. For this purpose, the straight struts in the body centered cubic structure and the kagome structure were replaced by curved struts. Due to the complexity of geometry and high dimensional accuracy, three-dimensional printing (digital light processing) was used to construct the designed lattice structures. In this method, the part is made directly from its surfaces' geometric data, which has been designed with the help of a computer, layer by layer, using optical curing resins. After the fabrication of the parts, a quasi-static pressure test was performed on the samples. The results showed that the modified structures are capable of larger deformation without failure, and their energy absorption is uniform. Although modified structures have a lower modulus of elasticity and energy absorption, larger elastic strain and gradual failure of these structures are important advantages that can be considered in various applications such as energy absorbers or nonstructural medical implants.

Three-layer aluminum/polymer/aluminum laminate sheets are one of the new materials used to decrease the weight and air pollution of vehicles. Using the conventional methods for joining these sheets have lots of challenges. In this paper, the jointability of the three-layer aluminum/polymer/aluminum to a single-layer 1-mm-thick aluminum sheet is investigated, using the clinching process, which is a joining by forming process. The three-layer aluminum/polymer/aluminum sheets are prepared under laboratory conditions using the aluminum 5754 and in 0.5/0.6/0.5 thickness arrangement. The effect of the pin penetration depth and pin conical angle on the joint properties is investigated. The joint cross-section is considered to compare the neck thickness and interlock in different joining conditions. Also, the joints’ strength is investigated using shear and peel tests. The results indicate that increasing the pin penetration depth to an optimum value, improves the interlock and joint strength. Additionally, the strength of the joint created by the straight pin is higher than that of the 3deg conical pin, in the same pin penetration depth. In all test conditions, the best joining conditions happened when the failure mode was a combination of the bottom separation and neck fracture.

In electric arc welding, the heat generated by the arc causes non-uniform expansion and contraction in the weld and surrounding areas. Uneven expansion and contraction and the resulting plastic deformation are the main sources of residual distortion and stress in welded structures. The distribution of residual stresses in a welded joint depends on factors such as heat input, arc welding speed, material properties, preheating, part thickness, groove geometry and welding execution schedule. In this research, a head to head joint is investigated by penetration welding with experimental methods and finite element simulation. Residual stresses are measured by the central hole drilling method and by converting the obtained data into residual stresses, the obtained results are used to verify the developed finite element model. In the finite element model, the non-coupled thermal-mechanical mode is used and the method of birth and death of the elements is used in the simulation of filler materials. In the simulation, the phase transformation process is considered and with the help of LTT filler introduced, the residual stresses in the single-pass welding show a 15% reduction in the tensile residual stresses. By examining the effect of misaligned welding on the specimens, the amount of residual stresses generated increases significantly.

In this research, a composite pressure vessel with a liner under internal pressure is investigated. Stress analysis is performed using a computer code written in MATLAB. Therefore, the stress components in the composite part of the studied vessel are extracted using the classical lamination theory (CLT) and then the occurrence of failure in the most critical layer is examined using the Hashin failure criteria. thus, the failure pressure associated with the first-ply-failure is obtained. Then, based on the ply-discount method in the context of continuum damage mechanics, the mechanical properties of the damaged layer are reduced and the stress analysis is performed again and the vessel failure is evaluated. This process repeats until all the layers experience failure and final pressure is reported as burst pressure. In the next step, by considering manufacturing-induced uncertainties and applying Monte Carlo method, the failure pressure of the vessel is obtained and the influence of uncertainties on the results is also studied. In this study, the parameters of fiber volume fraction and fiber orientations are assumed as the uncertainties. Comparison of the results with the experimental data indicates the accuracy of this method. Then, the reliability of each layer of the composite pressure vessel is studied using the first-order reliability method and finally, the Monte Carlo simulation is used to validate the results.