جستجوی مقالات مرتبط با کلیدواژه "مدول الاستیک" در نشریات گروه "مواد و متالورژی"

Vinyl ester resins are widely used in structural composites because of their excellent mechanical properties. One of the main goals of adding nanofillers to polymer matrix is to enhance the Young’s modulus and strength of the original base polymers. Due to the rigid structure of carbon nanotube as well as their aspect ratios, they can effectively increase the elastic modulus and stiffness of the polymer matrix. The main practical target of the present study is to obtain the best distribution of the multi-walled carbon nanotubes (MWCNTs) with carboxylic group in order to simultaneously improve the elastic modulus, tensile strength and toughness of the resulted nanocomposite. In this regard, nanocomposites with six different weight fractions (wt%) of MWCNTs are made and the specimens are subjected to the tensile test. The results exhibit that addition of MWCNTs with low concentration leads to improvement in the mechanical properties of the vinyl ester polymer such that the optimum mechanical properties are obtained with 0.25wt% of MWCNTs. In this case, the fracture toughness, tensile strength and Young’s modulus are respectively enhanced by amount of 52%, 23%, and 14%. In order to validate the experimental results and investigation the role of MWCNTs on tensile behavior of vinyl ester resin, the scanning electron microscope (SEM) is used and the most important failure mechanisms are discussed and studied in details. Also, the experimental results are compared with existing theoretical models and a new correction factor based on Hirsch’s theory and experimental results is introduced for future industrial applications.

Changes in strength and hardness of alloys are the main factor affecting the strain rate during creep. Thus measuring these properties and studying their correlations to creep resistance is an important issue. In the current study, the relationship between hardness and creep resistance for H13 steel was investigated during short-term creep. Creep fracture and 1% creep ductility tests were carried out at 500-600 C and stress of 872-926.5 MPa. Hardness test was carried out on all specimens and tensile test was performed on 1% creep ductility specimens at room temperature. The stress power of 4.5 indicated that dislocation creep was the dominant mechanism. The creep activation energy was lower than the activation energy of the self diffusion of alpha iron (109 kJ/mol), which indicated the role of stress in the apparent activation energy of this alloy. A linear relationship has been observed between hardness variation ratio and creep life ratio, although the slopes for the head and gage were slightly different. This linear relationship makes it possible to more accurately predict the life of H13 steel in creep condition.

In this study, mechanical properties, including elastic modulus and impact strength of nanocomposites based on polypropylene and polyethylene, linear low-density blends, in the presence of titanium oxide nanoparticles have been studied. 0, 2 and 4 wt% titanium dioxide nanoparticles were added to the basic ingredients polypropylene / polyethylene linear low density with a fixed ratio of 60/40 wt. % to reach the final composition that was prepared using an extruder. Tensile and impact tests were carried out in order to determine the elastic modulus and impact strength of compounds. It was observed that the presence of titanium dioxide nanoparticles at 2 wt. %, elastic modulus and impact strength compared to the basic polypropylene/polyethylene linear low-density increase and the presence of higher level of titanium dioxide nanoparticles up to 4 wt. % decrease mechanical properties of compounds. It was also seen that usilng low weight percent of nano particles, increase impact strength of the samples up to 7 percenrt.

In the present study, an investigation of coefficient of thermal expansion, elastic modulus, yield strength of compression, wear resistance and hardness of 3 layers called inner, intermediate and outer are investigated for functionally graded Al based cylindrical shell containing 26 wt.% Cu and 8 wt.% Si. The microstructure is studied by using TESCAN MIRA3 field emission scanning electron microscopy (FESEM) and TITAN scanning transmission electron microscope (STEM) is revealed that intermetallic compound content reaches its maximum volume fraction at the inner layer with 33.3 Vol.% and then reduces gradually to 26.4 Vol.% at outer layer. In addition, wear rate was 5.4gr/m2 and hardness was 153 HV at inner layer and then gradual increase by 7.07 gr/m2 and decrease by 149 HV, respectively at outer layer. Moreover, the value of yield strength of compression is determined 275, 460 and 415 MPa at outer, intermediate and inner layers, respectively.

Titanium and its alloys are known as one of the most significant metallic materials used in the orthopedic and dental implants due to their excellent mechanical properties, corrosion resistance and biocompatibility. One of the main issues in dental implant is the fabrication of the biomaterials that have early and sufficiently strong bonding with the surrounding bone. In the present study, porous Ti6Al4V scaffolds were produced using magnesium as a space holder by powder metallurgy. The specimens were sintered in 950°C, below the β transition temperature, close to magnesium vaporization point. To evaluate the porosity and effect of magnesium on it, the micro structure was investigated by optical microscopy and SEM and then mechanical properties and electrochemical corrosion behavior of the specimens were studied. Biocompatibility was investigated by MTT test, and it was deduced that the cell proliferation and biocompatibility was increased with increasing the porosity. This investigation showed that the compressive strength and elastic modulus of the porous scaffold with 10% magnesium and 31% porosity are 155MPa and 9GPa, respectively and close to dental bone. Also, the corrosion results and cell proliferation showed the appropriate corrosion behavior and osseointegration of this scaffold. Due to the importance of strength in the dental implant and according to these results, the Ti6Al4V scaffold with 10%Mg could be an advanced alternative for clinical applications which two factors of strength and osseointegration are required.

In this research, stiffness of polymer-clay nanocomposites was simulated by Mori-Tanaka and two and three dimensional finite element models. Nanoclays were dispersed into polymer matrix in two ways, namely parallel and random orientations toward loading direction. Effects of microstructural parameters including volume fraction of nanoclays, elastic modulus of nanoclays and interphase, thickness of interphase, aspect ratio of nanoclays and random orientation of nanoclays on elastic modulus of the nanocomposite were investigated by finite element model. Comparing the simulation with experimental results showed that the Mori-Tanak simulation results were closer to the experimental results. Analysis of results showed that the volume fraction of nanoclay, elastic modulus of nanoclay, deviation of nanoclay layers with respect to loading direction, nanoclays aspect ratio, thickness of interphase and the elastic modulus of interphase had respectively the most to the least effect on elastic modulus of nanocomposite.

For improving the mechanical and thermal properties of polyurethanes based on glycidyl azide polymer (GAP), a series of polyurethane elastomers with two soft segments were prepared from hexamethylene diisocyanate (HDI) / (GAP) / (PPG) /TMP and isophorone diisocyanate (IPDI) / GAP/ PPG/ TMP formulation. The weight ratio of soft segments GAP/PPG in polyurethane samples is changed as following order: 0:100, 30:70 and 50:50. For the study the structure – property relationships of polyurethane samples, the average molecular weight between cross-link junctions and effective cross-link density (νe) of samples were calculated from swelling and dynamic mechanical analysis tests. Both tests have shown that, as the GAP contents of copolyurethane samples are increased, molecular weight between cross-links (Mc) is increased. Also, dynamic mechanical analysis results of polyurethane samples have shown that by increasing of GAP ratio in the soft segment of polyurethane, the storage modulus at elastic region decreased and the glass transition temperature (Tg) have increased. As well as, hardness of samples is measured and indicated that by increasing the GAP extent of polyurethane samples, the migration of soft segment to the surface of polyurethane is improved and causes the dropping of the sample hardness.