Soil tensile strength is important in different geotechnical structures such as earth dams, roads, airports, landfills, and retaining walls. There are several experiments to study the tensile behavior of soils with different advantages and disadvantages. One of the methods used to investigate soil tensile behavior is tensile hollow cylinder apparatus, which has seldom been used. In this research, a hollow cylindrical device to measure the tensile properties of soil was built and operated. This device can apply tensile stress evenly to the entire soil sample so that stress concentration does not occur at any point in the sample.  After designing, manufacturing, and assembling the apparatus, validation tests were performed to ensure the device was operating well. The results of the repeatability tests show the accurate performance of the device. Also, in this study, the effect of plasticity index (PI) on the tensile behavior of kaolinite clay was investigated. Clayey soils with plasticity indices of 10 and 24% were selected. The results show that for clays with a similar mineral, the tensile strength increases and the tensile failure strain decreases with increasing the plasticity index.

Tensile failures including tensile cracks on the upper part of instable slopes, earth fissures, tensile cracks in earth dams, and any kind of tensile failures resulted from tensile stresses within soil body are considered as important engineering geological features. Studying tensile strength and deformation characteristics of soils can have a great role in the prevention of adverse phenomena resulted from tensile failures in soils. The Varamin collapsible soils are subjected to tensile fractures and earth fissuring because of the tensile stresses raised from the land subsidence of the Varamin plain. Therefore, in this study, the strength and deformation characteristics of these soils were investigated at undisturbed, reconstituted and treated states. Results indicate that, when undisturbed collapsible soils are subjected to tensile stresses, they show a low tensile strength and behave brittle in tension. Reconstituted soils have a lower tensile strength in comparison with undisturbed soils and behave very soft and fail easily in tension. Treated soils have a higher tensile strength in comparison with undisturbed soils and behave more ductile in tension and tolerate more deformation before tensile failure. Results indicate that the treatment of the collapsible soils with stabilizer materials together with compaction is an efficient method for strengthening these soils against tensile stresses and for improving their performance in tension.

There are many reports indicating that the maximum measured stress in the composite laminated beams under flexural loading appears different from that under tensile loading. The current study compares the results of Hashin failure criteria in the form of stress and strain components for prediction of failure strength in GFRP laminated beams. In the experimental program the composite laminates were tested under tensile and three-point-bending (3PB) loads. Then, it was trying to predict the flexural failure in laminates based on the measured ultimate stresses and strains in the tensile tests. The strain-based failure criteria employed in the FE models could achieve more admissible predictions for maximum load carrying capacity in the laminates compared to the stress-based criteria. Progressive failure analyses showed that due to higher elastic modulus of laminates under bending load, the maximum experienced stress under bending load becomes larger.

Summary Failure mechanism is different due to stress conditions and rock types, and it is very important to stability of structures. One of the investigations of failure mechanism’s techniques is using triaxial compression test. The aim of the research is determination of failure plane and failure mechanism of Rhyolite Tuff experimentally in different confining pressures and then investigating failure mechanism numerically using three-dimensional finite difference method in details. From the experimental results it was found that with increasing confining pressure, failure angle changes from vertical to oblique. Then numerical model was calibrated with laboratory data and analyzed the details of failure process, which could not be investigated experimentally. Investigations showed that failure process, started with plastic strains at the center of the sample and continued to achieve shear failure plane. Moreover, the results showed that the numerical model is in good agreement with the laboratory tests.
Introduction Given the increasing production of minerals, the need to expand and deepen mines is inevitable. With deeper mining, sustainability issues have become more important. All of underground structures have been constructed in rock and the recognition of the rock mechanics issues in relation to the stability of these structures is very important. One of the main topics of rock mechanics, which plays a significant role in the stability of structures, is the rock failure mechanism. Since these structures are located deep in the ground and the behavior of rock failure in different conditions of stress is different, recognizing the rock deformation process under stress conditions can provide a better picture of rock behavior in real conditions .When the distribution and turbulence of the stress creates an imbalance in the rock mass, rock failure occurs by the distribution and interconnection of the micro cracks. Still, there are ambiguities about how rocks are really broken and how the cracks begin to spread. Therefore, prediction of models for fracturing of rocks is very complicated, and it is impossible to predict the failure of rocks with simple models. Therefore, fundamental studies are needed to evaluate the failure process and damage of rocks in different stages of stress.
Methodology and Approaches By using uniaxial and triaxial tests, a stress-strain graph was drawn for a rhyolite rock sample. Analyzing the experimental results, it was observed that, with increasing lateral stress, rock resistance increased, and the direction of the fracture plane was maximally illuminated and more angular than the direction of the main stress. It was also found that the behavior of rock with the Mohr Columb's failure criterion is good. For numerical modeling of laboratory experiments, cohesion parameters, internal friction angle, shear modulus, volume modulus and specific gravity were used. To calibrate the model, the meshes and the rate of application applied to the top of the specimen were changed to see the fracture and ultimate strength similar to the laboratory sample in the numerical model. After calibrating the model, the details of the failure stages were carefully examined.
Results and Conclusions In numerical models with increasing lateral stress, the angle of deflection compared to the original stress was increased. Tensile plastic strains were formed at the beginning of the loading at the center of the sample. As the loading steps progressed, shear plastic strains started from the corners of the sample and proceeded to the center of the sample. This condition continued until the complete failure of the model and the creation of the plane shear failure. Also, with increasing lateral stress, the initiation of plastic strain occurred in higher stresses and later formed in the sample. Plastic tensile strains appeared at the center of the sample at the beginning of the loading. In the following, the strain began from the two corners of the sample and extended towards the center of the sample. It then extended its path until a plane was formed. Shear and tensile strains were formed in the form of shear-n and (tensile-n) in the sample. These strains may create a shear failure sheet. In fact, joining these strains continuously created a failure plane in the model. The final shear plane was the result of shear-n joining of the shear strains.

Incremental tube forming process is capable of manufacturing tubes with different cross sections and dimensions using simple and inexpensive forming tools. In the current study, seven different ductile failure criteria are used in finite element simulations in order to obtain the forming limit diagram (FLD) of Al6063 aluminium tubes at high temperatures. The predicted FLD using these criteria are compared with experimental data to select the optimum criterion. Standard universal tensile tests in different temperatures and strain rates along with Zener-holloman parameter are performed to calibrate the failure criteria. The effects of process parameters including temperature, forming depth and forming feed are considered. The results showed that failure criteria can predict the time and location of rupture in incremental tube forming process with a good accuracy. In high temperatures, Cockroft-Latham and normalized Cockroft-Latham criteria which consider the effect of the largest tensile stress had the best prediction. Investigation of temperature and strain rate showed that by increasing temperature, the forming limit goes higher but increasing strain rate causes to decrease it.

In this paper, 50CrV4 steel wire with a diameter of 4 mm were subjected to pure Zn electroplating. The effect of shot peening before and baking after electroplating on tensile performance of steel was investigated. Bombardment was done before plating for 20 minutes with shots 0.5 mm and 58 RC. Baking was performeIn this paper, 50CrV4 steel wire with a diameter of 4 mm were subjected to pure Zn electroplating. The effect of shot peening before and baking after electroplating on tensile performance of steel was investigated. Bombardment was done before plating for 20 minutes with shots 0.5 mm and 58 RC. Baking was performed after plating for 24 hours at 200°C. Finally, the samples were subjected to slow strain rate test, microhardness test and SEM imaging. The results showed that the effect of baking on improving the mechanical life of the sample under tension alone is greater than the shot peening. The mean time to failure of plated and baked samples was 2.5 hours, but for shot and plated samples was 2.1 hours. The simultaneous effect of pre-plating shot peening and post-plating baking led to further improvement of the tensile performance of the wire and the mean failure time reached 3.55 hours in the slow strain rate test. The embrittlement susceptibility index is now reduced from 0.76 for only plated samples to 0.13 for shot peened and baked samples, which shows a very good improvement. The effect of shot peening on the tensile properties of steel can be attributed to the formation of a residual compressive stress layer on the substrate surface, which leads to a reduction in the growth rate of microcracks due to tensile stresses under working conditions. The results also showed that due to the baking, continuous microcracks are created in the coating / substrate interface, which provide suitable paths for hydrogen to leave the substrate. after plating for 24 hours at 200°C. Finally, the samples were subjected to slow strain rate test, microhardness test and SEM imaging. The results showed that the effect of baking on improving the mechanical life of the sample under tension alone is greater than the shot peening. The mean time to failure of plated and baked samples was 2.5 hours, but for shot and plated samples was 2.1 hours. The simultaneous effect of pre-plating shot peening and post-plating baking led to further improvement of the tensile performance of the wire and the mean failure time reached 3.55 hours in the slow strain rate test. The embrittlement susceptibility index is now reduced from 0.76 for only plated samples to 0.13 for shot peened and baked samples, which shows a very good improvement. The effect of shot peening on the tensile properties of steel can be attributed to the formation of a residual compressive stress layer on the substrate surface, which leads to a reduction in the growth rate of microcracks due to tensile stresses under working conditions.

In this research, the hybridization effect of Semic arbon fibers (SCFs) with glass fibers on tensile pr operties and burning rate of composites as compared to glass fibers reinforced e poxy matrix composite was investigated. In this reg ard, four plies composites with different arranging of SCFs and glass fibers w ere fabricated by hand lay-up method. The hybridiza tion of SCFs with glass fibers was caused reducing tensile strength and ela stic modulus of these composites as compared to gla ss fibers reinforced composite. But the failure strain of these composit es was improved. Also, the obtained results showed that both failure strain and tensile strength have important role on energy abso rption in composites that the effectiveness of thes e factors proportionate SCFs and glass fibers ratio. The results of rate and the cross section of burning showed that with increasi ng SCFs to glass fibers ratio, the flame retardancy of composite increases.

In the current study tensile properties of a self-healing metal matrix composite with a matrix made of Sn-13%Bi alloy and Ni-Ti SMA wires as reinforcement have been studied experimentaly utilizing taguchi method in order to determine the effect of wires volume fraction, pre-strain and healing temperature on results. Matrix alloy was molten in furnace at 300℃ and was casted in a preheated metallic mold. SMA wires was installed inside the mold in different quantities (1, 2, 3 wires) and different pre-strains (0, 2, 4 percent). By considering 3 healing temperature and using L-9 taguchi array, specimens in 9 main state was fabricated and tensile tested until failure. After the first test and fracture, specimens was placed in a furnace at healing temperature for 24 hours and then another tensile test was conducted in order to calculate the amount of recovered mechanical properties and introduce the efficiency level of each parameter on healing effectiveness. Results show that the presence of 2 wires with 4 percent of pre-strain and consecutively 190℃ and 180℃ healing temperatures create the best circumstances to achive highest amont of self healing efficiency for ultimate tensile strength and toughness.

Oxidized Polyacrylonitrile fibers (OPF) are made by thermal stabilization of polyacrylonitrile (PAN) fibers and are used as precursors materials for production of carbon fibers. In this paper, effect of adding these fibers on tensile properties of polymer matrix composites was studied. So thirteen kind weights of epoxy matrix composite reinforced with one of the carbon, Kevlar and glass fabrics including OPF by hand lay up method as four layers with different layering were made. For making of composites epoxy Bisphenol F resin and polyamine hardener were used and the resin to fiber fraction was selected as 60 percent. Then tensile properties and failure cross section of them were studied. Results showed that by increasing OPF to carbon, Kevlar and glass fabric ratio; the tensile and modulus strength decreased but in more than 50 weight percent ratios failure strain increased. Study of the fail cross section showed that composites made with one of the carbon, Kevlar, glass fabrics including OPF have lateral, explosive and edge delamination failure modes respectively and with increasing the OPF to carbon, Kevlar and glass fabric transverse failure mode happens.

Determining the caving height in the block caving method requires considering a suitable caving criterion discussed in this study. The comparison between different caving criteria and choosing appropriate caving criteria for use in rock mass cavability study is the main idea of this study, which has not been investigated in previous studies. In this paper,  through FEM (Finite Element Method) software, the height of the caving area in different undercutting stages was calculated using the criteria of displacement and shear and tensile failure. The results revealed that when using shear and tensile failure, the height of the caving was almost four times higher than the displacement criterion. The height of the caving reaches 249.15 m in this case. However, it is 59 and 107 m considering the allowable displacement and strain criteria, respectively. According to empirical methods, the caving propagated to the highest block height. Thus, the shear and tensile failure criteria predict the caving height better than the displacement criteria.