Determination Of Creep Parameters Research Articles

Pressure monitoring and deformation analysis of a brine-filled salt cavern - A case study of Jianghan, China

Deformation stability plays a crucial role in the construction and operation of hydrocarbon storage salt caverns. Monitoring and analyzing wellhead pressure data under closed well conditions provide valuable insights into the evaluation of cavern stability. In this study, an analysis of five factors influencing internal brine pressure was conducted, which revealed that salt creep and brine thermal expansion contribute to an increase in internal brine pressure, while brine penetration, salt dissolution and cavern compressibility lead to a decrease. The atmospheric pressure, surface temperature, and earth tides are the other factors influencing wellhead pressure fluctuations. Through the analysis of wellhead pressure data from brine-filled salt cavern under closed conditions, the creep parameters of salt formations were calculated using the Norton-Hoff creep model. To further understand the behavior of brine-filled salt cavern, numerical simulations were conducted to analyze the brine temperature distribution and deformation stability. The volumetric average temperature of the brine exhibits a nonlinear increase over time, characterized by a rapid rise in the initial stage followed by a slower rate of change. Finally, the brine temperature stabilizes and converges toward the formation temperature. From deformation analysis, it was observed that the closed condition is more favorable for the maintenance of cavern stability in comparison to the open condition. The subsidence of the cavern roof is particularly sensitive and requires careful attention, especially for flat-roof salt caverns. Under closed conditions, it is crucial to control the brine pressure decrease rate and prevent excessively high brine pressure to ensure the mechanical and penetration stability of the brine-filled salt cavern. These findings provide valuable insights into the factors influencing internal brine pressure, the determination of creep parameters, the distribution of brine temperature, and the deformation stability of brine-filled salt caverns.

Creep characterization of solder bumps using nanoindentation

Current nanoindentation techniques for the measurement of creep properties are applicable to viscoplastic materials with negligible elastic deformations. A new technique for characterization of creep behavior is needed for situations where the elastic deformation plays a significant role. In this paper, the effect of elastic deformation on the determination of creep parameters using nanoindentation with a self-similar nanoindenter tip is evaluated using finite element analysis (FEA). It is found that the creep exponent measured from nanoindentation without taking into account of the contribution of elastic deformation tends to be higher than the actual value. An effective correction method is developed to consider the elastic deformation in the calculation of creep parameters. FEA shows that this method provides accurate creep exponent. The creep parameters, namely the creep exponent and activation energy, were measured for three types of reflowed solder bumps using the nanoindentation method. The measured parameters were verified using FEA. The results show that the new correction approach allows extraction of creep parameters with precision from nanoindentation data.

Correct Interpretation of Creep Rates: A Case Study of Cu

Traditionally the deformation resistance in creep is characterized by the minimum creep rate ε˙min and its sensitivity to stress (stress exponent n) and temperature (activation energy Q). Various values of constant n have been reported in the literature and interpreted in terms of specific mechanisms. The present case study of coarse-grained Cu at 573 K yields a stress exponent n = 9 for ε˙min in tension and a relatively low activation energy. The evolution of the deformation resistance with strain at constant tensile creep load and comparison with creep in compression without fracture indicates that the tensile ε˙min result from transition from uniform deformation to strain localization during fracture. This is confirmed by the results of creep in compression where fracture is suppressed. Both the tensile ε˙min and the compressive creep rate at strains around 0.3 can be described using existing equations for quasi-stationary deformation containing the subgrain boundary misorientation θ as structure parameter. While in the latter case constant θ leads to monotonic increase of n with stress, the tensile nine-power-law results from variable θ, and has no simple meaning. The result of this case study means that uncritical interpretation of minimum tensile creep rates as stationary ones bears a high risk of systematic errors in the determination of creep parameters and identification of creep mechanisms.

Determination of creep parameters from three-point bending test with C-shape specimen

In this paper the creep parameters for a Norton law material are determined from the creep bending tests data by an elliptical arc shape specimen. According to the ideal time-dependent beam theory, the creep coefficient B and creep exponent are derived as a function of the applied load and displacement rate. Finite element simulations of the elliptical arc specimen bending creep are also carried out to validate the feasibility and accuracy of the proposed approach. Our work will contribute to a better understanding to derive creep parameters from creep bending test and extend its application for the milli/micro scale miniature specimen.

DETERMINATION OF CREEP PARAMETERS IN LAYERS OF BUILDING COMPOSITES

Summary Various composite building products consisting of layers of different physical-mechanical properties being tied rigidly together are manufactured and used in construction. In many cases such products curve, become flaky, crack and their thermo-insulating capability suffers. It occurs because deformation properties are not adjusted, different layers of such products deform differently under the load. And the deformation effects the behaviour of the whole structure. A correct adjustment of deformations can be achieved with allowance for creep of different layers and of the whole composite. Determination of creep parameters—creep coefficient and specific creep—depends on the orientation of layers in respect of the direction of force action. When layers are situated transverselly in respect of the direction of action of forces (stresses), creep parameters of composite depend on creep parameters of materials of separate layers and on relative volumes of these layers. Creep deformations of a composite c...