جستجوی مقالات مرتبط با کلیدواژه « بارگذاری مکرر » در نشریات گروه « مکانیک »

One of the objectives of the present study is to optimize the effective parameters in the free sheet forming process under underwater explosive loading. In the experimental part, in order to investigate the effect of loading type on the maximum permanent deflection and thickness distribution of the plate, blasted-loaded plates due to 12 g and 4 g of explosive charge were used for single loading and repeated loading, respectively. Also, in order to investigate the effect of effective parameters on the process and optimize them, the Coupled Eulerian-Lagrangian method was firstly used for numerical simulation in ABAQUS finite element software. Then, in the optimization section, in order to investigate the simultaneous effect of explosive charge mass at each stage and the standoff distance on the maximum deformation and thickness of the sheet, Design-Expert software and Response Surface Methodology were used. The p-value obtained for the proposed model was less than 0.05, which indicates the significance of the model with a reliability of over 95%. The obtained results showed that the model provided by the software is suitable for this experiment and the values obtained from predicting the model are consistent with the experimental and numerical results. Also, the optimal conditions for the least change in plate thickness and the highest amount of permanent deflection were presented.

In the present study, the dynamic response of rectangular steel plates under repeated impulsive loading was investigated. In this regard, experiments were performed on three different structures: unstiffened, stiffened with one and two welding lines. To investigate the deformation modes and the failure mechanism of the experimental specimens, dynamic loads in a wide range were applied up to 3 loads by 25, 35, 45, and 50 g charge masses. Experimental observations demonstrate that with increasing charge mass, the Mode Ia and Mode Ib are observed in a higher charge mass and loading repetitions in a higher number. For the unstiffened plate, at the 3rd load with a mass of 25g, a change Mode Ia is observed, however, the same deformation mode occurs for the stiffened plate with a single and two weld lines at the 3rd blast load by 35g and 45 g charge mass, respectively. These observations indicate the effect of the weld line and its numbers on the variation of failure modes. Furthermore, in the numerical modeling section, the Group Method of Data Handling (GMDH) neural network was used to present a mathematical model based on dimensionless numbers to predict the maximum permanent deflection of tested specimens. Good agreement between the proposed model and the corresponding experimental results is obtained and all data points are within the ±10% error range for every two patterns.

In the current research study, the large plastic deformations of similar and dissimilar single- and multi-layered metallic plates with the same areal density under repeated uniform impulsive loading have been investigated. The ballistic pendulum along a 200 mm length standoff blast tube was used to apply the blast load on the specimen. Forty testing specimen in three different layering configurations including single-, double, and triple-layered, and eight different arrangements were considered. For the same loading and experimental condition, 10 g plastic explosive was utilized and the dynamic response of structures was studied up to five consecutive loads. The experimental results indicated large plastic global deformation with thinning happening at the clamped boundary and also tearing for some experiments. The results also represented that the maximum permanent deflections of plates were increased by the number of blast loads and the progressive deflection of the plates at the center was decreased exponentially with increasing the number of blasts. Placing a thick front layer a thin back layer gives better blast performance to the tested specimen against repeated impulsive loading. The obtained result for multi-layered configurations with the same material is completely consistent with those structures made of dissimilar layers.