The static modulus of elasticity from the load-settlement line of a second load cycle in a plate load test (PLT), Ev2, is a key parameter to control embankment bearing capacity, settlement and track quality in general. Because of the greater sensitivity in bearing capacity and settlement of high speed understructure, more strict limitations in this issue should be concerned in high speed rail codes so as each individual layer of fill should satisfy a special amount of Ev2. The PLT, as a test to determine Ev2, is expensive and time consuming. But, tests like Light Weight Deflecto meter (LWD) that determines the dynamic modulus of elasticity could be economically more efficient. In this study, field data from several PLT and LWD tests, which have been performed over different layers of embankment in the Qom-Isfahan high speed railway, were analyzed. Then, linear and non-linear regression methods were used to extract the best-fit equations among the results. Similary, the relationship between these field data and laboratory tests of California bearing ratio was extracted. Furthermore, back-calculation was used to determine the static and dynamic elastic moduli of each layer individually.

During the last few decades, application of geotextile in asphalt concrete before laying it for the purpose of reducing the overlay thickness has drawn the attention of many researchers, therefore determination of its structural value is considered as an important issue.Falling Wight Deflectometer (FWD) is the most popular non - destructive test for thedetermination of asphalt overlay structural value. In this paper, to determine this value, twelve sections, 150 meters each, were studied on Tehran–Qom old road. Each section was tested twice (once before and once after the overlay implementation) and each time, at least 12 FWD tests were carried out. Overlay thickness was determined using the tests results. For the first time, a model has been developed to evaluate the asphalt overlay structural value using FWD test data of 5 sections with pure asphalt overlay (4 sections to develop the model and one to verify the output). The seven remaining sections were implemented using various popular, Iranian or foreign geotextiles as interlayers, and their structural values were determined by help of a developed model. Based on the outcome of the present research, the average structural value of overall geote´tiles is equivalent to a 2.67 cm thick Hot Mix Asphalt (HMA) overlay while that of the Iranian ones equals 2.29 cm.

Evaluation of pavement structure is an important part of the pavement management system at the network and project levels, which is usually performed by using falling weight deflectometer (FWD) device. In using the FWD device, strength of the pavement layers is determined by back-calculations method. Using this method is not financially and temporally affordable for management at network level because of complexity and need for accurate initial information, and therefore it is usually used at the project level. Dynamic cone penetrometer (DCP) is another equipment, which is fast and cheap, and is used in evaluation of pavement structure at network level. In this research, 50 km of arterial road of Kermanshah province was tested by using the FWD and DCP devices. Results showed acceptable correlation between penetration index, as DCP output, and the obtained data of FWD device for pavement layers. The PI variation range for different pavement structure situations at network level was presented by analyzing the FWD and DCP outputs. Output results of network analysis using both methods showed acceptable PI criterion validity as simple and cheap criterion for pavement structure evaluation in pavement management at network level.

In this paper based on the plastic stress wave propagation theory, a new analytical model is presented for impact of the cylindrical projectiles on the rigid surface. In this analytical model, Johnson-Cook material behavior equation, Mie–Grueneisen equation of state, Johnson-Cook strain at fracture equation and kinematics equations of motion, are used. Also, the conservation equations of mass, momentum and energy in front of plastic stress wave are determined.For solving the governing equations, a computer program is developed. The values of stress, strain, strain rate, velocity and length and radius of rigid and deformed region of projectile were determined. Using new model proposed in this paper, the compressive stress at different plastic strain and strain rates were determined. The results of the new model have been compared with ABAQUS finite element simulations and available experimental results.It shows that the length and radius of deformed region of projectile predicted by the new model have good agreements with experimental results and ABAQUS FE simulations. Furthermore, the compressive dynamic stress is determined as a function of the final projectile dimensions and material behavior coefficients.

The purpose of this research is to investigate low velocity impact effect on fracture energy of DWTT specimen made of API X65 steel. As in some cases due to sudden impact (pre Loading) and permanent deformation, fracture energy of steel may be changed, the investigation of this study is important. Test specimen is API X65 steel of single edge notch type with Chevron notch with a depth of 5.1 mm which is cut from a spiral seam welded steel pipe with an outside diameter of 1219mm and wall thickness of 14.3mm. This steel is widely used in oil and gas industery in the world. The experiments were performed on 21 specimens. In the first stage, the drop height of the hammer was low so that the specimens did not fail and only the area adjacent to the crack tip entered the plastic zone. Subsequently, the samples were fractured by applying a second impact from a standard height of 2 meters. By analyzing experimental data, the fracture energy for each sample was calculated and compared with each other. By plotting the fracture energy in terms of the initial impact energy, it was observed that by increasing the initial impact energy in the sample, its fracture energy decreased. Finally, a linear relationship with acceptable accuracy for this energy drop was proposed, which showed a direct relationship between the fracture energy and the initial impact energy.

In this study, effect of chromium addition on the fracture toughness of Hadfield steel was investigated by using charpy impact test. For this purpose, 3 casting blocks were prepared from Hadfield steel (without Cr addition, and containing 1. 5% Cr and 3% Cr) by using coreless induction furnace. After casting, all blocks austenitized in 1100° C for 2 hours and immediately quenched in the pure water. In the next step, uniaxial tensile test, hardness test and charpy impact test were applied on specimens. Evaluation of the microstructures was conducted by optical microscope and the fractured surfaces were observed by scanning electron microscope. The results of charpy impact test and fracture toughness empirical relationships were used for determination of fracture toughness values of specimens. As a result, it was found that sample without Cr had lowest hardness – highest fracture toughness value – highest critical crack length and the sample containing 3% Cr had the highest hardness – lowest fracture toughness value – lowest critical crack length. Also, scanning electron microscope images indicated increasing crack growth in the charpy impact test specimens by addition of Cr to chemical composition of Hadfield manganese steel.

Nowadays, railway has been identified as the safest and most proper transportation system. Failure of rails, as one of the most importance elements of railway systems, can cause accidents and affect its safety. In this study, 55 steel samples extracted from UIC60 rail have been tested by Charpy impact test equipment in different temperatures ranged between -40 and 60 C. Then, fracture toughness of rail in different temperatures has been calculated by using known experimental relation between fracture toughness and measured fracture energy. Finally, the rail critical crack length has been determined by replacing calculated fracture toughness in formula of stress intensity factor. In order to restrict rail fracture and increase service life of the rail, critical crack length, in addition to none destructive tests for maintenance process of rails.