Showing 6 results for Loading Rate
Volume 8, Issue 2 (10-2017)
Abstract
The aim of this study was to evaluate the performance of Horizontal Sub-Surface Flow Constructed Wetland (HSSFCW) for the removal of Cr by Phragmitis australis and to assess the effect of the plant, bed material, hydraulic loading rate and hydraulic retention time on system performance. In this study, 12 cells of pilot system were built in parallel way and in dimensions of 50 × 75 × 200cm at the end of water treatment plant in Birjand University. Temperature and pH were same in all the cells. The results showed that the removal of Cr in cells containing plants was higher than cells without Phragmitis australis. Change of the bed material from coarse texture to fine-grained texture will make significant increase in the average percentage of Cr removal(the removal percent insamedischarge 100(l/d), in fine and coarse-textured plant cells was%31.87 and %24.61respectively and inlack ofplant'scells,with fine and coarse textures was%31.25 and %14.92, respectively). By increasing the retention time of 1 to 5 days, Cr concentration and consequently the removal rate were increased. These results are indicative of the positive effect of HSSFCW system in the presence of Phragmitis australis in removal of heavy metals such as Cr, therefore to remove heavy metals from wastewater, cultivation ofPhragmitis australis and fine-grained texture is recommended.
Volume 14, Issue 2 (3-2012)
Abstract
Mechanical properties of non-split pistachio nuts are among the lada required for the design of equipment needed for processing of the nut. Unsplit pistachio nut samples were uniaxially loaded to determine the nut’s needed splitting force and energy, as well as Poisson’s ratio and Young’s modulus of elasticity. The tests were carried out at four moisture contents (5, 10, 15 and 20% wb), under four loading rates (10, 20, 30 and 40 mm min-1), and on two varieties (O’hadi and Badami) of the nut. The highest splitting forces for the varieties (281.9 N for Badami and 102.4 N for O’hadi) were obtained at a moisture content of 5% wb and loading rate of 40 mm min-1, while the lowest forces, 97.0 N for Badami and 16.8 for the case of O’hadi, occured at moisture contents of 20% wb along with loading rate of 10 mm min-1. Different trends were observed between O'hadi and Badami varieties for the required energy to split nuts with increasing moisture content and loading rates. By increasing moisture content, Poisson’s ratio for unsplit pistachio nuts increased from 0.374 to 0.388 and from 0.326 to 0.337 for O’hadi and Badami varieties, respectively. Young’s modulus exhibited an indirect relationship with moisture content while a direct relationship with loading rate, in either of the varieties. Increase in moisture content from 5 to 20% wb led to a decrease in Young's modulus, from 322.59 to 223.23 MPa and from 816.25 to 719.28 MPa, for O’hadi and Badami variety nuts, respectively.
Hamed Ahmadi, , Mahmoud Mehrdad Shokrieh,
Volume 14, Issue 4 (7-2014)
Abstract
Epoxy / ceramic micro balloon syntactic foams are used in marine and automobile industries because of their high specific strength and capability of absorbing energy. In this paper, the neat epoxy and 9 series of syntactic foams with 3 kinds of ceramic micro balloon with different diameters and crush strength in different volume fractions (20%, 40% & 60%) were fabricated. Effect of varying these parameters on the mechanical properties of syntactic foams is investigated. Besides of all, the effect of different loading rate is investigated, too. All of the samples were tested in 10-1, 10-2 and 10-3 strain rates. The results indicate that with increasing the strain rate from quasi-static to moderate rates, the strength of foams became more. Also the results show that the syntactic foam with bigger micro balloon was weak in compression. In syntactic foams of low volume fraction the size effects is more. On the other hand, with increasing the volume fraction, the crush strength of micro balloon is become effective. Plateau stress and absorbed energy results show these facts obviously. With increasing the strain rate, the strength is increased considerably.
M. Habibi, J. Yousefi, M. Ahmadi,
Volume 19, Issue 12 (12-2019)
Abstract
Delamination or interlayer cracking is one of the most important imperfections in composite materials. The existence of this defect in a structure reduces the strength and, as a result, disables the structure. To analyze the effective factors in interlayer separation, it is necessary to analyze the effective loading parameters. In this paper, the effect of the change in loading rate on the failure mechanism in I failure mode was analyzed using an acoustic emission for unidirectional samples made of glass fiber/epoxy resin. At first composite, samples were made according to standard and placed at different rates of displacement under loading. Force data, displacement and crack growth rate for different loading rates were used to calculate the exact strain energy release rate. In addition to the extensometer, the Dino camera was used. In this paper, a high-reliability method was proposed to evaluate the separation between the layered composites using acoustic emission method. By comparing mechanical data and acoustic emission signals, the mechanical behavior obtained for each loading rate was determined so that the mechanical behavior of the composite material varied with the change in loading rate. The results show that, with increasing loading rates, the resin lost its elastic properties, and the specimen exhibited a more rigid behavior and is quite rigorous so that the fracture failure process is changed. The failure processes and crack growth rate was validated by use of acoustic emission signals. There was good agreement between the fracture toughness of accretion of acoustic emission signals with the experimental values.
Volume 23, Issue 4 (10-2023)
Abstract
In mechanics of rock fracture and comminution, researchers have always been looking for a relationship between the consumed energy and the particle size distribution of the disintegrated rock specimen. This relationship has important industrial applications considering the fact that comminution of rock is a very energy demanding process and its efficiency is very low. Furthermore, investigating the damage evolution of rock under different loading rates, helps to better understand and more accurately design rock structures such as tunnels, rock slopes and foundations subjected to dynamic loading. In this work, a hybrid finite-discrete element numerical model was used to simulate rock disintegration under different loading rates in the Split Hopkinson Pressure Bar (SHPB) system. The rock and the steel bars in the SHPB apparatus were simulated by the Bonded Particle Model (BPM) and finite element model, respectively. BPM is a simplified version of the discrete element method in which the discrete particles are spherical in shape. Spherical particles or balls in the BPM are very useful in reducing the computational time; the contact detection of the spherical particles is computationally very fast. The computer program CA3, which is a 3D code for static, dynamic and nonlinear simulation of geomaterials was used for the numerical analysis. To capture the rate dependent behavior of rock, a micromechanical model was utilized in which the bond strength at a contact point increases as a function of relative velocity of involved particles. The numerical model was calibrated to mimic the mechanical behavior of Masjed Soleyman sandstone. To facilitate and expedite the calibration process of the BPM system, the curves and dimensionless parameters introduced in the literature were used. Input pulses with different intensities were applied to the specimen in the numerical modeling of the SHPB system. The input energy and the energy consumed to disintegrate the numerical rock specimen were evaluated by the numerical integration. Different particle sizes in the BPM system were used to investigate the impact of combined particle size and input energy on the rock disintegration. The results suggest that the energy consumption density for rock crushing changes linearly with the stress rate. Furthermore, it is shown that the dynamic strength of the rock increases with the increase in the consumed energy density. The disintegrated numerical specimen was carefully inspected and its particle size distribution was obtained. This was achieved by using a searching algorithm to identify the clusters in the damaged specimen; each cluster was made of one or several spherical particles. The volume of each cluster was calculated by finding the volume of its constituent particles and the porosity of the specimen. This volume was used to obtain the equivalent radius of the cluster; the cluster shape was imagined as a sphere to identify the equivalent particle or cluster size. The mean particle size (D50) of the damaged numerical specimen shows a linear relationship with the stress rate in a logarithmic coordinate system, which is consistent with the physical test results reported in the literature.
Mohammad Albonasser, Hojjat Badnava, Sayed Hassan Nourbakhsh,
Volume 24, Issue 12 (11-2024)
Abstract
The accurate prediction of crack initiation and growth in manufacturing processes is crucial for minimizing production costs and enhancing the reliability of components. This study focuses on integrated experimental investigation and fracture modeling approach for ductile metals, particularly addressing the mechanisms of ductile fracture and shear localization. The importance of establishing robust damage criteria for accurate reliable numerical simulations cannot be denied. Current literature reveals a significant lack of data on shear and ductile fracture criteria for materials like stainless steel alloy 304. To address this gap, a series of experimental tests was conducted to extract the necessary coefficients for these criteria. Various sample geometries were analyzed to investigate the effects of different triaxiality stress states and loading rates on fracture initiation. The triaxiality stress states were chosen within a range of 0.2 to 2 and strain rates were applied at values of 0.02 s-1, 4.5 s-1, and 30 s-1. A set of coefficients for modeling ductile and shear fracture was derived, taking into account the effects of loading rate and orientation. This research not only provides critical coefficients for fracture modeling but also supports the optimization of manufacturing processes in the automotive industry and other sectors, ultimately contributing to improved material performance and component reliability
