Creep deformation behavior

In steam turbine power plants, steam pipes carry super heated vapor under high temperature (1050°F/565.5°C) and high pressure often at 3500 psiMPa or greater. In a jet engine temperatures may reach to 1000°C, which may initiate creep deformation in a weak zone. For these reasons, it is crucial for public and operational safety to understand creep deformation behavior of engineering materials. 

Fig. 6.20 Creep deformation behavior at different temperatures and stresses [57], With kind permission of John Wiley and Sons...

The creep deformation behavior of TPU under static load can be determined by dynamic hysteresis measurements in reduced testing times without the risk of changing morphoiogy. 

Before causing complete failure of a part, exceedingly high levels of deformation may also cause a reduction in the part s usability. The availability of a quick method to evaluate the creep deformation behavior of new material formulations proves to be crucial for material development operations. 

M. Kerr and N. Chawla, Creep Deformation Behavior of Sn-3.5Ag Solder/Cu Couple at Small Length Scales, Acta Mater., 2004, in press... 

Quantitative evaluation of global and locahzed creep deformation behavior of solder joints has been developed by mapping the distortion of a straight-hne ablation pattern imprinted by an excimer laser on the surface of shear lap solder joints [45]. Fig. 11 is an illustration of distortion due to creep deformation of a laser ablation pattern placed on a solder joint [46]. 

Lucas, J.P. Guo, F. McDougall, J. Bieler, T.R. Subramanian, K.N. Park, J.K. Creep deformation behavior in eutectic Sn-Ag solder joints using a novel mapping techniques. J. Electron Mater. 1999, 25(11), 1270-1275. 

In computing ordinary short-term characteristics of plastics, the standard stress analysis formulas may be used. For predicting creep and stress-rupture behavior, the method will vary according to circumstances. In viscoelastic materials, relaxation data can be used in Eqs. 2-16 to 2-20 to predict creep deformations. In other cases the rate theory may be used. 

Creep behavior, determining, 13 474-477 Creep curve, 21 742 analysis of, 13 472 Creep data analysis, 13 477-480 Creep deformation, 13 470, 471—480 effects of temperature and stress on, 13 474... 

More recently, Yoon and Chen68 developed a theory to predict the deformation behavior of particulate composites. Their theory treats the case of rigid particles embedded in a nonNewtonian matrix. The relative deformation rate, e/k0, is related to the volume fraction of particles, , the creep stress exponent of the matrix, n, and the stress concentration factor, k, of the inclusion in the matrix ... 

Background At elevated temperatures the rapid application of a sustained creep load to a fiber-reinforced ceramic typically produces an instantaneous elastic strain, followed by time-dependent creep deformation. Because the elastic constants, creep rates and stress-relaxation behavior of the fibers and matrix typically differ, a time-dependent redistribution in stress between the fibers and matrix will occur during creep. Even in the absence of an applied load, stress redistribution can occur if differences in the thermal expansion coefficients of the fibers and matrix generate residual stresses when a component is heated. For temperatures sufficient to cause the creep deformation of either constituent, this mismatch in creep resistance causes a progres-... 

To gain a better understanding of the creep behavior of fiber-reinforced ceramics, a simple 1-D analytical approach will be used to examine the effects of constituent behavior on composite creep deformation and changes in internal stress. Since the derivation of the model provides valuable insight into the parameters that influence composite creep behavior, the derivation of the 1-D concentric cylinder model will be outlined first. 

The Maxwell body is appropriate for the description of stress relaxation, while the Voigt element is more suitable for creep deformation. In a stress relaxation experiment, a strain yo is imposed atr = Oand held constant thereafter (dy/r// = 0) while r is monitored as a function of t. Under these conditions, Eq. (11-29) for a Maxwell body behavior becomes... 

The previous sections have been mostly concerned with the dislocations and microstructures observed in single crystals deformed to various strains under known experimental conditions. In some minerals, notably quartz and olivine, the macroscopic deformational behavior, as revealed by the creep and stress-strain curves, can be understood in terms of the micro-structural evolution during deformation and, furthermore, certain quantifiable characteristics of the microstructure correlate with the imposed... 

In a subsequent series of experiments, Landes and Wei [2] demonstrated that the phenomenon is real, and modeled the crack growth response in terms of creep deformation rate within the crack-tip process zone. The effort has been further substantiated by the work of Yin et al. [3]. The results and model development from these studies are briefly summarized, and extension to probabihstic considerations is reviewed. It is hoped that this effort will be extended to understand the behavior of other systems, and affirm a mechanistic basis for understanding and design against creep-dominated failures. The author relies principally on the earher works of Li et aL [1], Landes and Wei [2], Yin et al. [3], Krafft [4] and Krafft and Mulherin [5]. The findings rely principally on the laborious experimental measurements by Landes and Wei [2], and the conceptual modeling framework by Kraftt... 

A basic property is the melting temperature since it is known that materials parameters which characterize the deformation behavior are well correlated with the melting temperature (Frost and Ashby, 1982). Examples are the elastic moduli which not only control the elastic deformation, but are also important parameters for describing the plastic deformation, and the diffusion coefficients which control not only the kinetics of phase reactions, but also the kinetics of high-temperature deformation, i.e. creep. Furthermore, the melting temperature is intuitively regarded as a measure of the phase stability since it limits the application temperature range. 

Isochronous graphs are particularly valuable when obtained experimentally, because they are less time consuming and require less specimen preparation than creep curves. Such graphs at several time intervals can also be used to build up creep curves and indicate areas where the main experimental creep program could be most profitable. They are also popular as means of evaluating deformational behavior, because their method of data presentation is similar to the conventional tensile test data. 

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