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

This research investigates the creep phenomenon of a polymeric rotating disk using the generalized Maxwell’s visco-hyperelastic model. After extracting the Lagrangian partial differential equation of equilibrium governing the problem, the rotating disk was analyzed by scripting in FlexPDE. The disk modelling in ANSYS with coding in the APDL environment showed that the radial displacement and Von-Mises stress are in excellent agreement with the FlexPDE results. The advantages of FlexPDE over ANSYS include one-dimensional analysis of axisymmetric plane stress instead of two-dimensional analysis, reduction of computational cost, possibility of defining variable thickness (without additional coding) and need for fewer elements in the radial direction to achieve acceptable accuracy (necessity of using 20 elements in FlexPDE compared to 100 elements in ANSYS). It was shown that with the passage of time and the increase in angular velocity, the radial displacement and Von- Mises stress of the rotating disk due to the creep phenomenon increase. It was shown that by increasing the angular velocity and decreasing the power in the thickness profile n_h, the displacement and Von-Mises stress at a specific time increase, but the change in angular velocity (as the applied load) and the change in parameter n_h (as a geometric characteristic) do not have much effect on the relaxation time of the rotating disk.

Polymer-based adhesives undergo creep deformation under constant loading due to their viscoelastic nature. The aim of this study was Investigating the effect of 2-D defects on tensile and creep behavior of single-lap ceramic-metal joints (SLJs) manufactured with adhesive Aqua-Flex. Static tensile test was performed at three ambient temperatures, 40 and 60 ° C for flawless and defective adhesive joints in ceramics as well as defects in ceramics and aluminum, and then by applying final stress-to-strength ratios equal to 0.40 and 0.60, tensile creep test has been performed. By increasing the final stress-to-strength ratio from 0.40 to 0.60 at ambient temperature, the creep displacement for faultless connection is 36%, for defective connection in ceramic 33% and for connection defective in ceramic and aluminum 40%. Find. At 40 and 60 ° C, this increase is 35% and 18% for defective connection, 54% and 5% for defective connection in ceramic and 39% and 42% for connection with defective connection in ceramic and aluminum, respectively. Also, with increasing temperature from ambient temperature to 60 ° C, the breaking force for the three types of connections is reduced by 46%, 25% and 80%, respectively.

In this paper, by using the Chaboche kinematic hardening model with the isotropic hardening law, the effect of temperature and bending moments is investigated on the strain accumulation behavior of carbon steel piping branch. Carbon steel branch junctions under internal pressure and temperature with dynamic bending moment are tested at five temperatures of 20, 50, 100, 150 and 200 ° C. The results obtained by numerical analysis show that the highest amount of ratcheting occurred near the branch junctions in the circumferential direction. The strain ratcheting occurred mainly because of dynamic moments and high temperatures. The results show that in all three samples, the amount of strain ratcheting increases with increasing of dynamic moment level and temperature. With increasing of the ratio of diameter to thickness in branch junctions, the onset of strain accumulation occurs at low moment levels. It can be concluded that initially, the rate of strain ratcheting is high and with the increase of loading cycles, this rate decreased due to the strain hardening phenomenon. The increase of strain ratcheting at high temperatures is due creep strain because of high temperature and mainly accumulated plastic strain under dynamic bending moments because of cyclic plasticity.

In the present paper, gas turbine blade made of Inconel 939 superalloy creep behavior under rotation and thermal stress which is obtained from thermoelastic analysis is studied. Four models including Larson-Miller, Orr-Sherby-Dorn, Manson-Hoferd, and Minimum Commitment Method are used for creep analysis and their results are compared. At the first step, material constants of these four models are obtained by curve fitting of experimental results provided by COST-50. Then with use of these temperature dependent material constants, finite element model is created and stress due to temperature distribution and blade rotation is determined. Temperature range of blade is obtained from 1050 K to 1200 K. Because obtained von- Mises stress is below the yield stress of Inconel 939 at above temperature range, viscoelastic creep analysis is done by ABAQUS creep subroutine. Obtained results show that Larson-Miller and Minimum Commitment Method predict lower creep rate and creep strain relative to two other models. Also analysis results show that creep is more important at points with higher temperature.

Today, due to the importance of reducing the time between design and production, the use of methods such as fused deposition modeling (FDM), is considered as a good alternative compared to reduction production methods. Poly lactic acid (PLA) is used as a biocompatible polymer in many engineering and medical fields. Improving the long-term load bearing capacity of such products is one of the essential criteria to ensure the proper performance of these components. In this study, in order to improve the fatigue life and creep resistance of samples made of poly lactic acid polymer during the fused deposition modeling, to evaluate the effect of layer height, layer thickness, infill percentage and infill pattern on fatigue behavior. And creep resistance of the samples was investigated. Also, in order to benefit from statistical analysis, the response surface methodology has been used. Analysis of variance (ANOVA) showed that the percentage of filling and layer thickness had the greatest effect on increasing the fatigue life and reducing the creep rate of the samples. The results showed that layering based on layer height of 0.1 mm, layer thickness of 0.3 mm, infill percentage of 75% using honeycomb pattern had the highest fatigue life and creep resistance of the samples.

In this paper, the creep strength of Rene 80 superalloy in both uncoated and coated states is studied experimentally. The operation temperature range of this superalloy is 760–982 °C, in order to increase its resistance to surface degradation factors such as oxidation, hot corrosion and erosion at high temperatures, a coating is applied on it and its use without coating is not recommended. In this paper, diffiosion aluminide coatings were applied to this superalloy by two separate methods of pack cemantation and slurry under the brand names of Codep B and IP1041, respectively, and the effect of these coatings on the creep life of this superalloy at 982 °C and metallography is examined by SEM was investigated. For this purpose, samples according to ASTM-E8 standard were produced and after coating along with uncoated samples were subjected to creep test according to ASTM-E139 standard. Control parameters including temperature, stress and service life of uncoated samples are evaluated according to C50TF28 standard. Uncoated creep samples lost their strength after an average of 33 hours and rupture occured. Codep-B coated samples lost their strength after on average of 45 hours and slurry-coated samples lost their strength after on average of 51 hours. The results showed that the coatings increased the creep life of the coated samples compared to the uncoated samples by at least 12 hours.

In the present study, the finite element method based on the shear-lag model was used for stress analysis as well as deformation of the creep stable state of short fiber composites under axial loading. A perfect fiber/matrix interface is assumed and the steady-state creep behavior of the matrix is described by Norton numerical model. Special boundary conditions applied to the unit cell model and imaginary fiber technique has been used. Then ANSYS software is used for the calculation of all stresses and strains at the fiber/matrix interface and the outer surface of the unit cell. Then the results were verified and the values of axial and shear stresses at different points of the composite were investigated. The results show that the composite unit cell can be used as a composite representative for stress analysis. Also, the use of an imaginary fiber technique is a useful and reliable way to achieve a stress transfer model. This Model has sufficient accuracy and contrary to previous studies can predict all stresses and strains in all points.

In this research, effects of introducing 0.5wt% reduced graphene oxide (RGO) reinforcement on the creep behavior of the adhesivelybonded joints are investigated at 25oC,55oC. To this aim, uni-axial creep tests are conducted,creep deformations of the bulkspecimens produced via the neat adhesive,adhesive-RGO composite are recorded. Also, creep tests are performed to obtaincreep behavior of the single lap joints. Furthermore, results of the bulk specimen tests are used in a finite element based numericalanalysis to simulate the creep behavior of the joints. Results show that, a significant decrease in the creep deformations along with aremarkable increase of 30% in the creep life time occurs in the reinforced joints. Finally, comparing the numerical results andexperimental data shows that the numerical analysis accurately simulates the creep behavior of the joints.

Rotating discs have been used in numerous industrial machineries. In most of these applications discs are worked at high temperatures and high rotational speeds. Such a working conditions lead to the more sever thermo-mechanical stresses in rotating discs. In this situation of high temperature and stress the creep phenomenon is the most important and it can impose the irreversible damages to structure. Therefore it is important to investigate the creep behavior in rotating discs. Studies have shown that the creep is entirely dependent on the material structure. In recent years using of a new type of material called functionally graded materials (FGM) has been expanded continuously. Nowadays the functionally graded materials are used in construction of various component of machinery including rotating discs because of their spatial benefits. As a result the creep analysis in FGM rotating discs is a valuable problem. In this paper the rotating discs steady state creep equations are extracted and the effect of particle distribution and threshold volume fraction as well as prevailing temperature on the creep rates and stress fields of FGM rotating disc are investigated.

The Assessment of strain accumulation due to nonlinear events like creep, plasticity or ratcheting phenomenon has gained importance, since it causes an increase in creep and fatigue damage of materials. Some factors like the magnitude of loading, constitutive equations or the elastic regions around the nonlinear events have effect on the rate of strain accumulation. The elastic follow-up can explain the mechanism of strain accumulation. This phenomenon may occur when a mechanical structure with elastic manner is connected to non-linear events and they are subjected to a displacement load. In these cases, the high rigidity portion of elastic region of mechanical structure may enhance the force to the regions with low rigidity. So in the local non-linear portion, the strain is accumulated. This phenomenon is proposed as an important instruction in mechanical assessment codes. In this study, the effects of Elastic Follow-up phenomenon on strain accumulation due to elastic-plastic and local creep are investigated. So the Elastic Follow-up parameter is defined by the methods which are described in high temperature assessment procedures (R5). The results revealed that the strain accumulation depends on the elastic region in structures which is described by the Elastic Follow-up phenomenon.

In this paper the creep behavior of a functionally graded (FG) rotating disc made of Aluminum 6061 and Silicon Carbide is investigated and the optimum volume fraction of FG disc and its profile has been obtained. For this purpose, the temperature gradiant along the disc radius is obtained by solving the govering heat transfer differential equation. All the thermal properties of the material are assumed to be the function of temperature and volume fraction. To obtain material properties, two models of Mori-Tanaka and Hashin-Schtrickman are used. To validate the results, they are compared with those given in the literature. Two solution semi-analytical and closed form are employed and the results are compared. The optimum design is carried out with one, and multi-objective methods which are based on genetic algorithm. The objectives are increasing the factor of safety, reducing the weight of the disc and reducing the range between minimum and maximum safety factors. The design variables are percentage of volume fraction, the power of material distribution formula, and the thickness of the disc. The results show that two solution methods compare well. Also, it has been shown that high fraction of Silicon Carbide in the outer side the disc provide optimum results. Also, contradiction of the objectives is reviled, hence the results are presented as Pareto front.

Gas Turbines have wide applications in power plants and aerospace industries. Nowadays, based on welding of two different materials, some economic methods for repairing turbine blades have been developed. In this paper, a method, for determining creep life of a RTB (Repaired Turbine Blade) of two substances, based on transient FEM method had been developed. To find the effect of the difference between creep properties of materials of two substances RTBs, a simple 2D model under centrifugal forces was modeled. The base and filler metals were GH 4049 and Inconel 718, respectively. Creep is time dependent deformation of metals at elevated temperatures, therefore stresses are also time dependent. Hence, the life of RTB was estimated using damage fraction rule. These were performed using APDL ANSYS commercial software codes. To verification of the method, an experiment test has been established which defined the way critical elements behaved. In this experiment, pure lead was used as softer and Tin70%-lead30% was used as harder metal in creep. Experimental and numerical models were compared and good agreements between them were found. Rupture point was truly predicted and relative error was only 6% (traditional methods had 20% error). Results showed that the difference between creep properties of base and filler metals for supposed geometry and repaired location, leads to 90% decrement of designed life.

R‌e‌s‌i‌d‌u‌a‌l s‌t‌r‌e‌s‌s‌e‌s c‌a‌n c‌h‌a‌n‌g‌e p‌a‌r‌t‌s p‌e‌r‌f‌o‌r‌m‌a‌n‌c‌e, m‌e‌c‌h‌a‌n‌i‌c‌a‌l p‌r‌o‌p‌e‌r‌t‌i‌e‌s a‌n‌d a‌l‌s‌o h‌a‌v‌e n‌o d‌e‌s‌i‌r‌e‌d i‌n‌f‌l‌u‌e‌n‌c‌e o‌n l‌i‌f‌e t‌i‌m‌e. S‌o‌m‌e m‌e‌c‌h‌a‌n‌i‌c‌a‌l a‌n‌d t‌h‌e‌r‌m‌a‌l e‌f‌f‌e‌c‌t‌s c‌a‌n b‌e t‌h‌e r‌e‌a‌s‌o‌n f‌o‌r t‌h‌e‌s‌e s‌t‌r‌e‌s‌s. A h‌e‌a‌t t‌r‌e‌a‌t‌m‌e‌n‌t p‌r‌o‌c‌e‌s‌s, i‌n o‌r‌d‌e‌r t‌o d‌e‌c‌r‌e‌a‌s‌e t‌h‌e s‌u‌r‌f‌a‌c‌e h‌a‌r‌d‌n‌e‌s‌s o‌f l‌o‌c‌a‌l‌l‌y h‌a‌r‌d‌e‌n‌e‌d r‌o‌t‌o‌r s‌t‌e‌e‌l b‌y s‌t‌r‌e‌s‌s r‌e‌l‌i‌e‌v‌i‌n‌g, h‌a‌s b‌e‌e‌n s‌p‌e‌c‌i‌f‌i‌e‌d. I‌n o‌r‌d‌e‌r t‌o s‌e‌t t‌h‌e m‌a‌i‌n h‌e‌a‌t t‌r‌e‌a‌t‌m‌e‌n‌t p‌a‌r‌a‌m‌e‌t‌e‌r‌s, s‌u‌c‌h a‌s t‌i‌m‌e a‌n‌d t‌e‌m‌p‌e‌r‌a‌t‌u‌r‌e, t‌w‌o m‌e‌t‌h‌o‌d‌s w‌e‌r‌e e‌m‌p‌l‌o‌y‌e‌d u‌s‌i‌n‌g c‌r‌e‌e‌p p‌r‌i‌n‌c‌i‌p‌l‌e‌s. I‌n t‌h‌e f‌i‌r‌s‌t m‌e‌t‌h‌o‌d, a‌f‌t‌e‌r e‌q‌u‌a‌l‌i‌z‌i‌n‌g l‌o‌c‌a‌l h‌a‌r‌d‌n‌e‌s‌s b‌y i‌n‌t‌e‌r‌n‌a‌l s‌t‌r‌e‌s‌s, a c‌o‌u‌p‌l‌e‌d e‌x‌p‌l‌i‌c‌i‌t t‌h‌e‌r‌m‌a‌l-s‌t‌r‌u‌c‌t‌u‌r‌a‌l f‌i‌n‌i‌t‌e e‌l‌e‌m‌e‌n‌t a‌n‌a‌l‌y‌s‌i‌s i‌m‌p‌l‌e‌m‌e‌n‌t‌i‌n‌g c‌r‌e‌e‌p s‌t‌r‌e‌s‌s r‌e‌l‌i‌e‌v‌i‌n‌g w‌a‌s c‌a‌r‌r‌i‌e‌d o‌u‌t. T‌h‌i‌s m‌e‌t‌h‌o‌d c‌r‌e‌a‌t‌e‌d a g‌o‌o‌d o‌p‌p‌o‌r‌t‌u‌n‌i‌t‌y t‌o d‌e‌t‌e‌r‌m‌i‌n‌e t‌h‌e i‌n‌f‌l‌u‌e‌n‌c‌e o‌f h‌e‌a‌t‌i‌n‌g r‌a‌t‌e a‌n‌d c‌o‌n‌s‌t‌a‌n‌t t‌e‌m‌p‌e‌r‌a‌t‌u‌r‌e t‌i‌m‌e o‌n s‌t‌r‌e‌s‌s r‌e‌l‌a‌x‌a‌t‌i‌o‌n. T‌h‌e s‌e‌c‌o‌n‌d m‌e‌t‌h‌o‌d e‌m‌p‌l‌o‌y‌e‌d c‌r‌e‌e‌p e‌q‌u‌a‌t‌i‌o‌n‌s r‌e‌l‌a‌t‌e‌d d‌i‌r‌e‌c‌t‌l‌y t‌o h‌a‌r‌d‌n‌e‌s‌s.I‌n t‌h‌e f‌i‌n‌i‌t‌e e‌l‌e‌m‌e‌n‌t m‌o‌d‌e‌l‌i‌n‌g (F‌E‌M), r‌e‌s‌i‌d‌u‌a‌l s‌t‌r‌e‌s‌s‌e‌s o‌n r‌o‌t‌o‌r s‌t‌e‌e‌l a‌r‌e s‌i‌m‌u‌l‌a‌t‌e‌d b‌y p‌r‌e‌a‌p‌p‌l‌y‌i‌n‌g s‌t‌r‌e‌s‌s‌e‌s. T‌h‌e a‌d‌v‌a‌n‌t‌a‌g‌e o‌f t‌h‌i‌s m‌e‌t‌h‌o‌d (F‌E‌M) i‌s i‌n a‌p‌p‌l‌y‌i‌n‌g t‌h‌e i‌n‌f‌l‌u‌e‌n‌c‌e o‌f t‌h‌e p‌r‌e‌s‌e‌n‌t‌a‌t‌i‌o‌n o‌f b‌u‌l‌k m‌a‌t‌e‌r‌i‌a‌l a‌r‌o‌u‌n‌d t‌h‌e h‌e‌a‌t‌i‌n‌g s‌e‌c‌t‌i‌o‌n o‌f t‌h‌e m‌o‌d‌e‌l.R‌e‌s‌u‌l‌t‌s o‌b‌t‌a‌i‌n‌e‌d f‌r‌o‌m b‌o‌t‌h m‌e‌t‌h‌o‌d‌s w‌e‌r‌e c‌o‌m‌p‌a‌r‌e‌d w‌i‌t‌h e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌a‌l d‌a‌t‌a. O‌u‌r m‌e‌t‌h‌o‌d‌s s‌h‌o‌w‌e‌d s‌t‌r‌e‌s‌s r‌e‌l‌i‌e‌v‌i‌n‌g a‌t 684 t‌o 690$^c‌i‌r‌c$Ci‌n 5-6 h‌o‌u‌r‌s, w‌a‌s e‌f‌f‌i‌c‌i‌e‌n‌t w‌h‌i‌c‌h i‌s i‌n g‌o‌o‌d a‌g‌r‌e‌e‌m‌e‌n‌t w‌i‌t‌h e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌a‌l r‌e‌s‌u‌l‌t‌s. P‌e‌r‌f‌o‌r‌m‌i‌n‌g t‌h‌i‌s e‌x‌p‌e‌r‌i‌m‌e‌n‌t h‌a‌s s‌o‌m‌e s‌p‌e‌c‌i‌a‌l c‌o‌n‌s‌i‌d‌e‌r‌a‌t‌i‌o‌n‌s; t‌h‌e t‌e‌m‌p‌e‌r‌a‌t‌u‌r‌e s‌h‌o‌u‌l‌d b‌e i‌n‌c‌r‌e‌a‌s‌e‌d, a‌n‌d t‌h‌e m‌o‌d‌e‌l m‌u‌s‌tb‌e k‌e‌p‌t i‌n b‌a‌l‌a‌n‌c‌e‌d f‌o‌r‌m a‌n‌d p‌r‌e‌v‌e‌n‌t‌e‌d f‌r‌o‌m a‌n‌y c‌o‌r‌r‌o‌s‌i‌o‌n a‌n‌d o‌x‌i‌d‌i‌n‌g, w‌h‌i‌c‌h a‌r‌e s‌h‌o‌w‌n i‌n t‌h‌e p‌i‌c‌t‌u‌r‌e‌s a‌n‌d d‌e‌s‌c‌r‌i‌p‌t‌i‌o‌n‌s i‌n t‌h‌i‌s p‌a‌p‌e‌r.O‌u‌r r‌e‌s‌u‌l‌t‌s s‌h‌o‌w‌e‌d t‌h‌a‌t t‌h‌e a‌n‌a‌l‌y‌t‌i‌c‌a‌l m‌e‌t‌h‌o‌d i‌s v‌e‌r‌y q‌u‌i‌c‌k a‌n‌d e‌f‌f‌e‌c‌t‌i‌v‌e, a‌n‌d c‌a‌n b‌e e‌m‌p‌l‌o‌y‌e‌d i‌n p‌r‌a‌c‌t‌i‌c‌e. T‌h‌e p‌r‌e‌s‌e‌n‌t‌e‌d m‌e‌t‌h‌o‌d c‌a‌n b‌e a‌p‌p‌l‌i‌e‌d t‌o o‌t‌h‌e‌r i‌n‌d‌u‌s‌t‌r‌i‌a‌l m‌o‌d‌e‌l‌s t‌o d‌e‌t‌e‌r‌m‌i‌n‌e f‌i‌n‌a‌l r‌e‌s‌i‌d‌u‌a‌l s‌t‌r‌e‌s‌s‌e‌s a‌n‌d s‌u‌r‌f‌a‌c‌e h‌a‌r‌d‌n‌e‌s‌s a‌f‌t‌e‌r a t‌e‌m‌p‌e‌r‌i‌n‌g h‌e‌a‌t t‌r‌e‌a‌t‌m‌e‌n‌t.