Papers by Keyword: Stress Relaxation

Abstract: Coefficients of dynamic viscosity for AL7050-T7451 at room temperature is extracted by creep and stress relaxation simulations in Ansys. An analogy has been established for both creep and stress relaxation, with simple Maxwell Model. The stress relaxation curve thus obtained is then used to generate the Prony series coefficients which are then used to run some dynamic analysis in Ansys to see the effect of loading at different frequencies on the value of η (i.e dynamic viscosity). This will be verified with the simple analytical dynamic formulation based on the Maxwell Model. A good agreement has been found for both quasi-static and dynamic tests with Maxwell model.

Abstract: Micro-particles and nano-wires, small outgrowths were found to appear on upper film surface when metal thin film is confined between two Si3N4 layers deposited by magnetron sputtering and is annealed at an appropriate temperature. The stress evolution during this process is monitored by multi-beam optic stress sensor, and is qualitatively interpreted in terms of elastic and plastic deformation, as well as bulk diffusion. Additionally, the interface constraint effect among different layers is explored. Stress relaxation of nano-sandwiched thin films behaves in different stress modes. As a comparative study, Si3N4/Zn/Si3N4 sandwiches were prepared and studied by the same method. Experimental results show that the pertinent geometry is strongly dependent on material types and stress states of the substrates. Finally, an appropriate mode was suggested to interpret this phenomenon.

Abstract: Because of stress and sleeping obstacle for 21th century people, the purpose of this study is to design a home decorative fabric which has the function of releasing from stress and enhancing sleeping quality. The optical fiber were sewn on the surface of optical fabric in form of three kinds of curvature patterns. Guiding the LED light into the optical fiber, the light will emit out of the optical fiber and stimulate our visual system in order to change the form of brain wave. Afterwards, the EEG instrument was used to evaluate the function of stress relaxation of such fabrics. The results were shown that human’s brain wave can be changed from relaxed and sober status to shallow-sleeping status after the stimulation of light emitting from the optical fiber fabrics. For the effect of causing shallow-sleeping status, female is more significant than male. Therefore, the light stimulating visual system by using the optical fiber fabrics can change the form of brain wave and achieve the effect of stress relaxation.

Abstract: In this paper, a series of relevant theoretical analyses and experimental researches have been carried out for precision forming of a typical aerospace revolver. By use of the material stress relaxation principle, the finite element numerical simulation and the preforming sizing process technology of stress relaxation, it have been revealed that the new process can be used for precision forming of titanium alloy sheet and its forming precision can meet the manufacturing requirements of aerospace sheet-metal parts. The precision forming technology of titanium alloy can also be used to improve the digital manufacturing technologies of aerocraft sheet-metal parts, and thus has potential application prospects.

Abstract: The stress relaxation behavior of as-deposited and rolling nanocrystalline NiFe alloy was studied by nanoindentation tests. The results indicated that both the hardness and activation volume of rolling NiFe are larger than that of as-deposited samples. Furthermore, the hardness decreases with increasing indentation depth. The reduction of indentation stress during holding becomes much faster with decreasing the indentation depth. Dislocation density is remarkably enhanced by rolling deformation, leading to the hardening behavior. Dislocation multiplication and accumulation mediated process is believed to the dominant plastic deformation mechanism.

Abstract: Glass molding press is an efficient and promising process for glass lens manufacturing. Molding temperature and velocity are crucial factors for pressing, and the annealing rate directly influences the residual stress and volume change of the final lens. The research contributes to studying the key factors that influence the quality of the molded lens. In the paper, by incorporating stress relaxation and structural relaxation of the viscoelastic material, numerical simulation is undertaken to determine the proper process parameters. Furthermore, the whole process of a spherical lens molding is simulated to predict the final residual stress and volume change, also the influence of different annealing rates is estimated.

Abstract: The effect of the annealing temperature (390°C, 410 °Cand 430°C) on the stress relaxation of air side and tin side of ion exchanged glasses was investigated. The annealing time dependence of stress at different temperature can be well fitted by a second order exponential function. The stress relaxation rate on tin side is larger than air side at the ion exchange temperature (410°C) or below (390°C) but smaller above the ion exchange temperature (430°C). The depths of stress layer (DOL) of all ion exchanged glasses increase with the increasing of annealing time and the DOL on air side is always larger than tin side. These provide useful information for subsequent treatment of ion exchanged glasses.

Abstract: Generally, as for the material of catheter, a soft characteristic is necessary so as not to damage vascular wall etc. On the other hand, responsivity and enough rigidity are required for the surgical operations such as myocardial infarction or cerebral infarction. Therefore, the catheter, which is made of soft nylon resin and is reinforced with thin stainless wires so called “braid”, is chosen as the subject of this study. The purpose of this study is to reveal the effect of braid on the mechanical property of the catheter by investigating the relationship of the stress relaxation and the relative angle between the braid and the principal axis of stress. Especially, in order to investigate the stress relaxation under combined loading, the experiments of two-stage step strain for tension and torsion are carried out with different deformation paths. Consequentially, the phenomenon of the stress relaxation reduces with the relative angle becomes smaller. Moreover, the numerical model under two-stage step strain is proposed in this paper, and the validity of this model is confirmed by comparing the calculated results with the experimental results.

Abstract: We propose a mathematical model of large elastoplastic deformations with rheological features. As an example of applying the model relations, we present a solution of the boundary-value problem on collapsing process of microdefect continuity in elastic-creep-plastic materials under uniform pressure. In the case of a single micropore we obtained quantitative estimates of this process. The fields of stress and the residual deformation are computed.

Abstract: Due to the lack of historical data, sealing performance of O-rings in the fuel system of aircraft engines is particularly difficult to study. As great efforts are being made to develop alternative fuels in aviation industry, their compatibility issue with elastomeric O-ring materials has become a major concern. So far, no data has been published on how O-rings would behave in alternative fuel scenario while taking the temperature factor into consideration. The purpose of this paper is to investigate into O-ring’s sealing performance under various temperature conditions, with comparison between Gas-to-Liquid (GtL) synthetic fuel and Jet A-1. Technique used to stimulate the real service scenario for O-rings is the stress relaxation test. Distinguishing from regular relaxation techniques, an advanced stress relaxation rig (Elastocon EB17) with the capability of temperature cycling was employed for this study. Nitrile and fluorosilicone O-ring materials which are commonly found in the fuel system were tested respectively. Three sets of tests were designed to look at how each O-ring material will behave under different temperature conditions. Results obtained so far indicated under extremely low temperature conditions, the relaxation processes of both O-ring materials seem to be ‘frozen’ as the sealing force stops decreasing and maintains a relatively stable level. No fuel preference has shown during the process as O-rings in both GtL and Jet A-1 behaved similarly. Nitrile O-ring showed better relaxation characteristic in Jet A-1 than that in GtL under the 24-hour temperature cycling test; while fluorosilicone presented little differences in these two fuels.