Papers by Keyword: Creep Rate

Abstract: Copper alloys have high thermal conductivity, relatively high mechanical strength, and toughness over a wide range of temperature; hence they are highly sorted for complex structural applications that required extreme heat flux under load. Creep of materials is classically associated with time-dependent plasticity under a constant stress/load at an elevated temperature, often greater than the absolute melting temperature. This research is aimed to study the evaluation of stress and creep rate in copper, identifying the mechanisms at which copper can easily be exposed to stress and creep deformations in structures. A 12 mm diameter copper rod with the composition of 52.05 % CuO and 30.26 % SnO₂ was procured locally. Samples from the procured rod were heat treated to 650^°C for 30 minutes and cooled in the still air as well as inside the furnace. Creep test was carried out at 760uC with a constant load corresponding to an initial stress (between 1.5 MPa and 350 MPa) and stress relation was carried out on a 98 kN capacity stress relaxation frame (from 350 MPa to 300 MPa). Rockwell hardness test and metallographic analysis (at 200 mm) were also conducted on the heat treated and unheated control samples. It was established that heat treatment reduced the hardness property of stress relaxed copper, accelerated the stress relaxation process up to 60 %, speed up both primary creep rate and the tertiary creep rate as well altered the linear creep pattern and behaviour.

Abstract: In this work, the creep analysis of thick-walled rotating cylinder made of Aluminum Silicon Carbide under internal pressure has been investigated taking some assumptions, viz. no change in the volume of the cylinder, cylinder material is anisotropic, principal axes coincides with the axes of anisotropy, effective stress is dependent upon effective strain rate, and there is zero strain in the axial direction (Z direction in polar coordinate). Sherby’s law has been used to calculate the creep rate. After finding the formulas for radial, tangential and axial stresses for anisotropic cylinder, the findings have been validated by checking the values and comparing the graphs for an isotropic cylinder case with one of the already published research for isotropic cylinders with similar conditions. The graphs plotted in cases of anisotropic cylinder, enables us to conclude that despite large stress values in the radial and tangential directions, the creep rates in such cylinders were found to be approximately zero. This led to deduce that anisotropy is very helpful in designing long-lasting cylinders. In corollary, anisotropy helps in minimizing creep behaviour in radial and tangential directions.

Abstract: P92 heat-resistant steel was used to demonstrate that creep rupture life evaluation period could be shorted by the assistant of the creep data from short-period stress relaxation test without reducing the prediction precision. Research showed that the minimum creep rate and the relaxation creep rate were exchangeable, and the stress exponent and the apparent activation energy analysis of the constant strain creep and the constant stress creep showed a similar deformation mechanism at the condition of T and . The creep rupture life predicted through the combination of these two kinds of creep data was closer to the real creep data than that evaluated by the traditional method based on the time to rupture only, and the precision of the evaluated creep strength increased at last 14.5 %.

Abstract: Magnesium alloys with enhanced thermal stability are being developed for automobile engine applications. The available commercial Mg-alloys are usually alloyed with aluminum that are thermally stable only for T < 150^o C. Development of new Mg-alloys is underway and Mg-Sn alloys are a promising option. In Mg-Sn alloy, the Mg₂Sn phase has high thermal stability and is expected to enhance the high temperature properties. In this study, Mg-5Sn alloy is incorporated with Ag as a minor alloying element (0.175 wt. %). The creep behavior of the Mg-Sn-Ag alloy is investigated using the impression creep technique. The impression creep tests were carried out under punching stress in the range of 80-320 MPa and temperature of 373-573 K, for dwell times up to 5 hours. The results highlight that creep of the alloy was load and temperature dependent, i.e. increasing the load and temperature resulted in higher creep rates.

Abstract: Through experimental study on creep characteristics of conductors with large aluminum-steel section ratio, the creep characteristic curve of conductors with aluminum-steel section ratio between 11.34 and 14.47 are obtained. It is recommended that the conductor should have a temperature-reduction value of 25°C according to the conductor temperature-reduction value analyzed by amount of creep, which can be used for reference during line design and construction.

Abstract: Unconsolidated sandstone is a kind of formation with low strength and large deformation property. Deeper unconsolidated sand formations have larger geostress and perform the plastic and rheological characteristics. After the borehole has been drilled into, this kind of sandstone will creep, which will cause some problems such as pipe stuck and casing deformation failure etc. Therefore, creep parameters of unconsolidated sandstone are critical for designing drilling fluid density and choosing casing material. Through indoor experiments, creep data of unconsolidated sandstone from Zhujiang group of X oil field in the west of South China Sea was get. The experiments results indicate that creep law of this sandstone conforms to Nishihara’s model, and the creep parameters were calculated based on experiments data. According to Nishihara’s model, using numerical simulation method, this paper analyzes the relationship of sandstone creep shrinkage rate with time of Zhujiang group reservoir sandstone and determines the drilling fluid density that ensures the safety of horizontal wells drilling, which has guiding significance for well design and drilling.

Abstract: Based on the BP neural network theory, the creep rate prediction model of T92 steel was established under multiple stress levels. Obtained the experimental results and using the model, the experimental results were trained. The results show that the simulation results match the measured results well with a high forecast precision. The BP neural network method can serve as research on T92 steel creep behavior.

Abstract: In order to investigate self-excited vibration mechanism of wheel-rail lateral contact system, a two DOF elasticity position wheelset lateral vibration model is established which considers the dry friction; the mechanism of the wheelset lateral self-excited vibration is investigated from the energy point of view. It shows that: the bifurcation diagram of this wheel-rail lateral contact system has a supercritical Hopf bifurcation. The energy of self-excited vibration derives from a part of traction energy; the creep rate in the wheel-rail system act as a feedback mechanism in the wheelset lateral self-excited vibration system. The stability of the wheelset self-excited vibration system depends mainly on the total energy removed from and imported into the system.

Abstract: The applicability of the Monkman-Grant relationship was analyzed and validated for ultrafine-grained metallic materials under investigation. A special attention has been given to the creep damage tolerance factor which is defined as the ratio of the strain to fracture to the Monkman-Grant ductility and which describes the coupling between creep deformation and damage based on continuum creep damage approach. It was found, that ultrafine-grained materials generally obey the Monkman-Grant relationship, however, the relationship is especially suitable for materials exhibiting short secondary creep and long tertiary creep stages when dislocation-controlled creep is dominant.

Abstract: This paper studied the mechanical behavior of the filament/staple fiber composite yarn and the pure cotton yarn under the isostress and isostrain of cycling tensile strength with the conditions of small deformation. And it also analyzed the elastic recovery rate, creep rate and stress relaxation rate under the different deformation rate and load. The results show that the mechanical properties of elastic recovery rate, stress relaxation and creep all keep in good range in the experiment of cycling tensile strength with low certain elongation and constant load; as the increase of certain elongation and constant load, the mechanical properties of elastic recovery rate, stress relaxation and creep have much difference, just in terms of the conformality under the cyclic tensile strength, PET/PU/cotton composite yarn shows the best, next is the PU/cotton composite yarn, and then next is the PET /cotton composite yarn, and the pure cotton yarn shows the worst.