جستجوی مقالات مرتبط با کلیدواژه « Strength » در نشریات گروه « مکانیک »

Ceramic materials are desirable in structural applications because of their strength at high temperatures, low thermal expansion, and excellent wear resistance. However, ceramic structures are generally brittle and will fail due to inherent flaws that can be introduced into the material through processing, handling, or while in service. In the strength test samples of ceramic materials, the observed strength depends on the sample volume and the test method, and the results have significant scattering. On the other hand, it is important to recognize the variability of the strength of ceramic materials for structural design, and in the design process, this variability usually requires a probability-based failure criterion, which, due to the brittle fracture of ceramics, usually uses the Weibull distribution to represent their strength. With the help of Weibull distribution, the concept of effective volume is defined and by using it, the strength of a test sample with a specific geometry and loading is predicted from another sample that has a different geometry and loading. In this research, the effective volume for a truncated cone under internal pressure has been derived analytically. With the effective volume for this configuration and a sufficient number of flexural strength tests with the help of small and low-cost flexural specimens, it is possible to predict the tensile strength of the ceramic truncated cone without conducting expensive tests. for a problem with a specific material property and dimensions, the effective volume was calculated numerically and it had a 3% error compared to the analytical value.

Nowadays, extrusion-based additive manufacturing is an emerging manufacturing method that is receiving much attention and is the basis of FFF 3D printers. In this method, molten polymer is deposited layer by layer through a nozzle to create a three-dimensional object. Due to the rapid freezing of the layers, small gap and cavities may be created between the layers and lead to a decrease in the mechanical properties, including the strength of the parts. Since predicting and improving the mechanical properties is one of the challenges of this production method, the purpose of this study is to investigate the factors affecting the strength of parts produced by FFF. Investigation of the previous studies shows that the influencing factors are the nozzle temperature, filling percentage, sample alignment, filament deposition angle, layer thickness and nozzle diameter. Furthermore, it is concluded that increasing the nozzle temperature, filling percentage, and nozzle diameter and decreasing the layer thickness improve the strength of the produced parts. This is due to an increase in the contact surface of the deposited filaments as well as a decrease in the empty gaps between them. Also, considering the deposition angle in the tension axis of the part can greatly increase its strength.

This research is mainly focused on to study microstructure and mechanical properties of AA5051 aluminum alloy deformed by equal-channel angular pressing (ECAP) process at 200˚C and in BC routes and 4 four passes. The ECAP processing was carried out using die with an intersecting channel angle ‘ϕ’= 120° and corner angle ‘Ψ’= 20°. The results of uniaxial tensile test showed that tensile strength was found to be increased from 115MPa for annealed sample to 239MPa after four passes ECAP in route BC that shows that the strength in ECAP samples has increased. In addition, the percentage of elongation also decreased in initially passes and then increased slowly. Microstructure and grain refinement of specimens were investigated by optical microscopy and scanning electron microscopy and fractography were investigated by scanning electron microscopy. The grain size of annealed sample was 123μm and decreased to 18μm after four passes ECAP in route BC. The hardness also increased from 51HV in annealed sample to 90HV the fourth passes.

In this research, the effect of strain rate on the tensile behavior of the graphene/epoxy nanocomposites was investigated. The specimens were prepared for 0.05, 0.1, 0.3 and 0.5 wt.% graphene oxide and were subjected to tensile tests at different strain rates. The experimental results showed that the maximum improvements in the tensile strength, the modulus, and nanocomposite were 9%, 16%, and 0.1 wt.%, respectively. Also, the results indicated that the epoxy and its nanocomposites were sensitive to the strain rate. The rate sensitivity decreased with the increase of the graphene weight percentages. Moreover, it was shown that by increasing the strain rate, the tensile strength and modulus for pure epoxy were improved by 15.8% and 16.8%, respectively. In this study, the appropriateness and applicability of the Johnson-Cook material model for describing the stress-strain relation of the nanocomposites were examined by a combined experimental-numerical-optimization technique. The numerical simulations were carried out using Abaqus commercial program and the optimizations were performed using the Surrogate modeling. The results showed that the Johnson-cook model is not accurate at very low strain rates. However, the accuracy of the model was remarkably improved by increasing the graphene weight percentage or increasing strain rate.

Welding plays an important role in manufacturing and it is a reliable and efficient joining process in which the coalescence of metals is achieved by fusion. Nowdays welding is as the main and most common process for joint of metals. Among the welding methods, Laser Beam Welding) has the potential of welding very small and precise components. Localized heating with solidification of the melt, makes the connection between parts. In this thesis, laser spot welding process, which is one of the varieties of LBW process, is studied. In fact the laser spot welding is a simple type of laser welding that is widely used in various industries. The low strength of joints can damage structures. Therefore it is important that the strength of the joint be estimated and optimized. In this research, investigation and optimization of the laser spot welding process using design of experiments and response surface method is considered. Three parameters (peak power, pulse duration and thickness) of the process at three levels were the input factors. Material of sheets that was used in this research is AISI 304 stainless steel. The response or output factor was tensile - shear strength. Minitab16 software was used for design of experiments and analysis of the results. Finally, results showed that increase the peak power until 4250 watt and pulse duration until 3/5 millisecond provide the most tensile - shear strength (2200 Kg), and Square of thickness has the most negative effect on tensile shear strength of the joint.

In this paper, the Accumulative Channel-die Compression Bounding (ACCB) method is investigated as a new method of severe plastic deformation to produce Nano-crystalline bulk metals on the basis of pressing in a channel mold. Aluminum as One of the most usable metal in industry is processed using this method. Analyzing the processed samples show that after four passes of ACCB method, the ultimate strength of samples reaches to 120 from 60 Mpa. The grain sizes of samples reaches to 627 nm from 8-6µm in annealed phase after four passes of ACCB method. Also, the vicker's hardness of samples reaches to 51.8 from 20 HV after four passes. These changes consist of the increasing the hardness and strength of aluminum sample and achieving to the high ratio of strength to weight of sample can help us to better use this materials to fabricate less weight structures for using in automotive and airplane industry.