جستجوی مقالات مرتبط با کلیدواژه « Impact Loading » در نشریات گروه « فنی و مهندسی »

In this research, the plastic deformation and failure mechanism of sandwich structures with aluminum face-sheets and waste rubber particles core under low-velocity impact loading have been investigated. The drop hammer testing machine was used to apply the impact load to the sample at seven different energy levels 34.3, 68.6, 102.9, 137.2, 154.3, 171.5, and 205.8 J. To achieve the mentioned energy levels, the weight of the hammer was considered constant and equal to 3.5 kg and the standoff distance of the hammer was changed from 1 to 6.5 m. 10 test samples were considered in two types of layering with and without the core of rubber particles. In this series of experiments, the thickness of aluminum face-sheets was constant at 1 mm and two different thicknesses of 16 and 32 mm were considered for the core. Experimental results showed that, the sandwich panel with 16 mm had a 37 and 18 % smaller deformed area for fall heights of 2 and 3 meters, respectively, due to the less porous space between two aluminum face-sheets. Also, compared to the coreless sandwich structure, the use of a low-mass waste rubber particle cores at low energy levels increased the front sheet perforation diameter by 19 %.

This study aims to analytically investigate the impact response of FRP-retrofitted RC slabs. In this regard, based on the orthotropic plate theories, an applicable formulation is derived to assess the displacement of simply supported RC slabs due to the applied impact loading induced by dropping an impactor. The results have then been compared with the experimental data available in the literature. The proposed analytical formulation is proved to be reliable and efficacious to an extent that the displacement can be attained up to seven percent error. The effect of number of FRP layers and compressive reinforcement ratio have also been examined on the impact response of FRP-retrofitted RC slabs. The results indicate that adding 7 layers of GFRP strips to the bottom face of the RC slabs can attenuate the displacement values up to 33 percent. Moreover, the effect of compressive reinforcements on improving the impact response of RC slabs was estimated to be 30 and 23 percent, respectively, for RC slabs being examined.

Today, the importance of using Underground structures to protect vital and sensitive national infrastructure such as urban train tunnels, strategic item storage centers, urban underground facilities, shelters, as well as military uses is not hidden from anyone. One of these important loads in terms of intensity and time is impact and seismic loading. Due to the fact that the environment around the underground structures is rock and soil environment, so it is necessary to achieve a good result in reducing the effect of mechanical waves on these spaces, to ensure sufficient reduction of the environment. One of these important loads in terms of intensity and time is impact and seismic loading. On the other hand, natural phenomena such as gas explosion or fire can also be easily incorporated into the structure. These are enough reasons to pay more attention to the science of rebuilding structures against different loads on them. The importance of protecting these spaces increases when they have strategic applications. Therefore, in locating and designing them, it should be noted that they must have sufficient resistance to impact loading In order to achieve a plan that by using the properties of the environment including such spaces, the effect of the impact transmitted in the environment on the underground space can be reduced. Therefore, in the past few years, this software has attracted the attention of many researchers. Finite element modeling and analysis was performed with the commercial software package ABAQUS. The package was selected due to its diverse library of material behavior models and ease of Explicit/Implicit solution procedures. In this paper, impact loading on Underground structures is numerically modeled using the Coupled-Eulerian-Lagrangian (CEL) method in the ABAQUS software. In this regard, modeling of single-layer, two-layer and three-layer soil arrangement, as well as a combination of soil and stone layers, has been done in ABAQUS finite element software. The maximum pressure due to impact load has been compared in different models and finally, by comparing the results of the models used in this study, it shows that the arrangement of the layer in the soils is effective in reducing the maximum pressure due to impact load, So that the maximum amount of shock wave damping is achieved when the rock layer with the highest degree of weathering, or sandy soil (similar to type 2 soil in Regulation TM5-855) is in the closest position to the desired underground space.

According to increasing the use of PET products, the present study aimed to the use of PET fibers in the concrete industries. Moreover, the behavior of normal concrete contained recycled fibers is not studied and the guidelines aren’t published yet. The aim of this study was to determine the effect of polyethylene terephthalate fibers on the mechanical properties of hardened concrete. Fibers were used in three volumetric percentages of 0.15%, 0.30%, and 0.45% with the lengths of 1, 2, and 3 centimeters, separately. So, 10 combinations of specimens including the control specimen and 9 combinations of PET fiber reinforced concrete were made. All mixtures were examined for compressive strength, tensile strength, flexural strength, shrinkage, durability, and impact loading.The results showed that by adding the PET fibers, the compressive strength, the bending strength, and energy absorption increase 5 to 18 percent, 6 to 30 percent, and 30 to 156 percent, respectively. However, no noticeable change was observed in tensile strength , while even a reduction in tensile strength is monitored. The impact strength of the fiber concrete was increased two to seven times in comparison with the control concrete. By comparing the experimental results it was determined that the combinations that contained 2 cm fibers with 0.45% volume had the best performance compared with the other mixtures.

In the current research study, the large plastic deformation and failure mechanism of sandwich structures with aluminum facesheets and pumice core under low-velocity impact loading have been investigated. The drop hammer testing machine was used to apply the impact load on the specimen at seven different energy levels 34.3, 68.6, 102.9, 137.2, 171.5, 205.8, and 223 J. To achieve the mentioned energy levels, the weight of the impactor was considered constant and equal to 3.5 kg and the standoff distance of the hammer was changed from 1 to 6.5 m. 16 experimental samples were considered in two types of layering with and without pumice core. Also, in this series of experiments, the thickness of facesheets was fixed and two different thicknesses of 16 and 32 mm were considered for the core. Experimental results showed that at all energy levels, the sandwich panel with 16 mm pumice core shows a smaller deformed area due to the shorter porous space between two facesheets. Also, at low energy levels, the thickness of the pumice core does not play a key role in improving the impact resistance of the structure. Compared to the coreless sandwich structure, the use of a very low-mass pumice core can prevent the plastic deformation of the rear facesheet, and the 16 mm thickness of the pumice core can even prevent the front surface from petalling.

The present paper deals with experimental and numerical investigation of the mechanical properties of a piece produced by a dynamic powder compaction process under high-rate impact loading. Experimental tests are performed on metal powders made of aluminum by a gas launcher system. To validate the results obtained from the presented mathematical functions, we compare the results of the neural network model and the experimental data. In examining the error of experimental data and prediction based on the squared mean of the errors and the coefficient of determination show that the results obtained from the mathematical functions provide mathematical models for the final properties of the segment under optimal impact loading.