Rate Equations for Elevated Temperature Creep

1979 ◽  
Vol 101 (4) ◽  
pp. 396-402 ◽  
Author(s):  
P. P. Pizzo
Keyword(s):  
Creep Behavior ◽  
Steady State Creep ◽  
Rate Equations ◽  
Steady State Creep Rate ◽  
Creep Properties ◽  
Rate Dependent ◽  
Predicting Performance ◽  
Major Transition ◽  
Definition Of

Creep deformation is characterized in terms of temperature, the applied load and the resultant steady-state creep rate. A correlation is often sought to describe accelerated test data and to provide a means of predicting performance in service. Since prediction often involves extrapolation outside the data range, there is concern for possible transitions in creep behavior. Rate dependent transitions in creep behavior are common for many commercial alloys, and research over the years has provided an understanding of some of the basic mechanisms involved. This understanding has led to definition of conditions under which different mechanisms are active and, thus, bounds at which transitions will occur. In this paper, the major transition mechanisms are briefly discussed and their significance to long-term extrapolation of creep properties is demonstrated.

Improved tensile creep properties of yttrium- and lanthanum-doped alumina: a solid solution effect

2001 ◽  
Vol 16 (2) ◽  
pp. 425-429 ◽  
Author(s):  
Junghyun Cho ◽  
Chong Min Wang ◽  
Helen M. Chan ◽  
J. M. Rickman ◽  
Martin P. Harmer
Keyword(s):  
Solid Solution ◽  
Steady State ◽  
Creep Behavior ◽  
Solubility Limit ◽  
Steady State Creep ◽  
Tensile Creep ◽  
Creep Properties ◽  
Uniform Microstructure ◽  
Equiaxed Grains ◽  
Rare Earth Doped

The tensile creep behavior of yttrium- and lanthanum-doped alumina (at dopant levels below the solubility limit) was examined. Both compositions (100 ppm yttrium, 100 ppm lanthanum) exhibited a uniform microstructure consisting of fine, equiaxed grains. The creep resistance of both doped aluminas was enhanced, compared with undoped alumina, by about two orders of magnitude, which was almost the same degree of improvement as for materials with higher dopant levels (in excess of the solubility limit). In addition, measured creep rupture curves exhibited predominantly steady-state creep behavior. Our results, therefore, verified that the creep improvement in these rare-earth doped aluminas was primarily a solid-solution effect.

Creep behavior of eutectic Sn–Ag lead-free solder alloy

2002 ◽  
Vol 17 (11) ◽  
pp. 2897-2903 ◽  
Author(s):  
M. L. Huang ◽  
L. Wang ◽  
C. M. L. Wu
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Behavior ◽  
Absolute Temperature ◽  
Steady State Creep ◽  
Steady State Creep Rate ◽  
Straight Line ◽  
The Matrix ◽  
Dislocation Pipe ◽  
Free Solder

Precipitation-strengthened tin-based eutectic Sn–3.5 Ag alloy was investigated for its creep behavior at three temperatures ranging from 303 to 393 K, under the tensile stress range of σ/E = 10−4 to 10−3. The steady-state creep rates cover seven orders of magnitude (10−3 to 10−9 s−1). The initial microstructure was found to have Ag3Sn intermetallic compound finely dispersed in the matrix of β–Sn. By incorporation of a threshold stress, σth, into the analysis, the creep data of eutectic Sn–Ag at all temperatures can be fitted by a single straight line with a slope of seven after normalizing the steady-state creep rate and the effective stress, indicating that the creep rates are controlled by the dislocation-pipe diffusion in the Sn matrix. The steady-state creep rate, , can then be expressed as , where QC is the creep activation energy, G is the temperature-dependent shear modulus, b is Burger's vector, R is the universal gas constant, T is the absolute temperature, σ is the applied stress, A is a material-dependent constant, and , in which σOB is the Orowan bowing stress and kR is the relaxation factor.

Effect of Off-Stoichiometry on the Creep Behavior of Binary and Ternary Ni3Al

1990 ◽  
Vol 213 ◽  
Author(s):  
Tohru Hayashi ◽  
Tetsumori Shinoda ◽  
Yoshinao Mishima ◽  
Tomoo Suzuki
Keyword(s):  
Activation Energy ◽  
Steady State ◽  
Power Law ◽  
Creep Behavior ◽  
Creep Resistance ◽  
Steady State Creep ◽  
Steady State Creep Rate ◽  
Creep Equation ◽  
Ternary Element ◽  
Ternary Additions

ABSTRACTCompressive creep behavior is investigated In polycrystalline Ni3Al intermetallic compounds in which the focus is put on the effect of offstoichiometry and ternary additions of Ti, Ta, V and Co on the creep resistance of the compounds. In all cases, the steady-state creep rate has the power-law type dependence on the applied stress. The stress exponent thereby obtained leads us to regard the creep behavior of the compound to be of the Class I type. It is shown that the creep resistance Increases with increasing Ni concentration on both sides of the stoichiometric Ni3Al composition and a discontinuity exists in the variation at stoichiometry. The gap at the discontinuity becomes clearer by the addition of ternary element in most cases as compared to the binary Ni3Al. Although the exact reason for the phenomenon is not clearly understood at present, it is shown that it could be interpreted by the concentration dependence of activation energy in the power-law type creep equation.

Effect of Aging on Impression Creep Behavior of Pb-Free Solders

2013 ◽  
Author(s):  
B. Talebanpour ◽  
U. Sahaym ◽  
I. Dutta ◽  
P. Kumar
Keyword(s):  
Creep Behavior ◽  
Impression Creep ◽  
Creep Properties ◽  
Particle Spacing ◽  
Ag3sn Particle ◽  
Creep Stress ◽  
Microstructural Coarsening ◽  
Creep Stress Exponent ◽  
Sac Solder

During service and/or storage, Sn-Ag-Cu (SAC) solder alloys are subjected to temperatures ranging from 0.4 to 0.8 Tm (where Tm is the melting temperature of SAC alloys), making them highly prone to significant microstructural coarsening. The microstructures of these low melting point alloys continuously evolve during service. This results in evolution of creep properties of the joint over time, thereby influencing the long-term reliability of microelectronic packages. Here, we study microstructure evolution and creep behavior of two Sn-Ag-Cu (SAC) alloys, namely Sn-3.0Ag-0.5Cu and Sn-1.0Cu-0.5Cu, isothermally aged at 150°C for various lengths of time. Creep behavior of the two SAC solders after different aging durations was systematically studied using impression creep technique. The key microstructural features that evolve during aging are Ag3Sn particle size and inter-particle spacing. Creep results indicate that the creep rate increases considerably with increasing inter-particle spacing although the creep stress exponent and creep activation energy are independent of the aging history.

High-temperature deformation of mullite and analysis of creep curves

2003 ◽  
Vol 18 (8) ◽  
pp. 1771-1776 ◽  
Author(s):  
H. Rhanim ◽  
C. Olagnon ◽  
G. Fantozzi ◽  
A. Azim
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Behavior ◽  
Slow Crack Growth ◽  
Steady State Creep ◽  
The Other ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Steady State Creep Rate ◽  
Creep Curves

The creep behavior of mullite was studied under different stresses and in the temperature range 1200–1450 °C, and an analysis of creep curves was proposed. The study of creep behavior of mullite at high temperatures clearly indicates that this material exhibits concurrent creep and slow crack growth. An effective transition stress exists at each temperature. The analysis takes account of the total creep curve; in particular, the primary and stationary stages. It is now possible to determine by extrapolation the steady-state creep rate for specimens that break in the transient domain during tests. Thus, one can verify the influence of the stress on the steady-state creep rate over a wide stress range. On the other hand, this analysis clearly indicates the existence of two values of the activation energy around 1300 °C; this suggests a change of creep mechanism at this temperature.

Deformation Mechanism Maps: Their Use in Predicting Creep Behavior

1976 ◽  
Vol 98 (2) ◽  
pp. 125-130 ◽  
Author(s):  
F. A. Mohamed ◽  
T. G. Langdon
Keyword(s):  
Steady State ◽  
Creep Behavior ◽  
Deformation Mechanism ◽  
Simple Form ◽  
Steady State Creep ◽  
Deformation Mechanisms ◽  
Total Strain ◽  
Improved Method

A simple form of deformation mechanism map is presented which graphically illustrates the behavior of materials under steady-state creep conditions. Examples are given of maps for deformation mechanisms occurring both independently and sequentially. The use of deformation mechanism maps in the prediction of creep behavior is reviewed in detail, and an improved method is presented for estimating the total strain experienced after long-term exposure to stress and temperature.

Effects of a layered structure on the physicomechanical properties and extended creep behavior of bamboo-polypropylene composites (BPCs) determined by the stepped isostress method

Holzforschung ◽  
2018 ◽  
Vol 72 (7) ◽  
pp. 589-597 ◽  
Author(s):  
Chin-Yin Hsu ◽  
Teng-Chun Yang ◽  
Tung-Lin Wu ◽  
Ke-Chang Hung ◽  
Jyh-Horng Wu
Keyword(s):  
Creep Behavior ◽  
Bottom Layer ◽  
Short Term ◽  
Creep Properties ◽  
Polypropylene Composites ◽  
Plastic Composite ◽  
Accelerated Creep ◽  
Term Creep ◽  
Better Than

AbstractA layered bamboo-plastic composite (BPC) consisting of bamboo (Phyllostachys makinoi) particles and polypropylene was investigated. The influence of the layering conditions, including the thickness and bamboo content in various layers, was the focus in terms of the physicomechanical and creep properties of the BPCs. The results showed that a three-layered BPC (BPC3L) with a 1:3:1 thickness ratio and with top/bottom layer containing 40% bamboo exhibited the best specific flexural properties. An accelerated creep test approach was applied, known as the short-term stepped isostress method (SSM), to predict the long-term creep behavior of BPC3L. The results indicated that the creep master curves, which are constructed from different SSM testing parameters, agree well with the long-term experimental creep data and that the creep resistance of homogeneous single-layered BPC was better than that of BPC3L.

scholarly journals Study on the Creep Characteristics of Sandstone under Coupled Stress-water Pressure

2019 ◽  
Author(s):  
Zuosen Luo ◽  
Jianlin Li ◽  
Lehua Wang ◽  
Eleyas Assefa ◽  
Huafeng Deng
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Strain ◽  
Water Pressure ◽  
Steady State Creep ◽  
Three Gorges Reservoir Area ◽  
Steady State Creep Rate ◽  
Axial Pressure ◽  
Coupled Stress

Long-term interaction between stress and water pressure leads to creep damage of reservoir bank slope. As a result there will be instability of the bank slopes in many water conservancy projects. The rock mass creeping effect of coupled stress-water pressure was studied by using a typical sandstone rock from the Three Gorges reservoir area. The experiment was conducted by using the rock immersion-air-drying cyclic load rheometer device (designed and manufactured by our research team). Based on the experimental results, the following key points were observed: 1) the creep strain and the steady-state creep rate was increasing when the water pressure increased (at the same stress level). Under the same water pressure, the increase in the axial pressure resulted in the increase in the creep strain and steady creep rate of the sandstone specimens. 2) the increase in the axial pressure increased the creep strain and steady-state creep rate of the sandstone specimens while the water pressure increased. The mechanical properties of the sandstone specimens were affected by the water pressure. 3) the water infiltrates through the pore surfaces. As a result, the rate of deformation will increase while the bearing capacity and long-term strength of the rock decrease. This paper provides a solid theoretical foundation for the evaluation and prediction of reservoir geological hazards.

Central Otago - Built on gold, growing on grass.

2014 ◽  
Vol 76 ◽  
pp. 15-23
Author(s):  
Barrie J. Wills
Keyword(s):  
Economic Growth ◽  
Land Use ◽  
National Economy ◽  
Local Community ◽  
Central Government ◽  
Future Generations ◽  
Economic Potential ◽  
District Council ◽  
Definition Of

A warm welcome to our "World of Difference" to all delegates attending this conference - we hope your stay is enjoyable and that you will leave Central Otago with an enhanced appreciation of the diversity of land use and the resilient and growing economic potential that this region has to offer. Without regional wellbeing the national economy will struggle to grow, something Central Government finally seems to be realising, and the Central Otago District Council Long Term Plan 2012-2022 (LTP) signals the importance of establishing a productive economy for the local community which will aid in the economic growth of the district and seeks to create a thriving economy that will be attractive to business and residents alike. Two key principles that underpin the LTP are sustainability and affordability, with the definition of sustainability being "… development that meets the needs of the present without compromising the ability of future generations to meet their own needs."

Populism and Liberal Democracy

2019 ◽  
Author(s):  
Takis S. Pappas
Keyword(s):  
United States ◽  
Liberal Democracy ◽  
The United States ◽  
Comprehensive Theory ◽  
The People ◽  
Original Definition ◽  
Key Issues ◽  
Great Relevance ◽  
Definition Of

Based on an original definition of modern populism as “democratic illiberalism” and many years of meticulous research, Takis Pappas marshals extraordinary empirical evidence from Argentina, Greece, Peru, Italy, Venezuela, Ecuador, Hungary, the United States, Spain, and Brazil to develop a comprehensive theory about populism. He addresses all key issues in the debate about populism and answers significant questions of great relevance for today’s liberal democracy, including: • What is modern populism and how can it be differentiated from comparable phenomena like nativism and autocracy? • Where in Latin America has populism become most successful? Where in Europe did it emerge first? Why did its rise to power in the United States come so late? • Is Trump a populist and, if so, could he be compared best with Venezuela’s Chávez, France’s Le Pens, or Turkey’s Erdoğan? • Why has populism thrived in post-authoritarian Greece but not in Spain? And why in Argentina and not in Brazil? • Can populism ever succeed without a charismatic leader? If not, what does leadership tell us about how to challenge populism? • Who are “the people” who vote for populist parties, how are these “made” into a group, and what is in their minds? • Is there a “populist blueprint” that all populists use when in power? And what are the long-term consequences of populist rule? • What does the expansion, and possibly solidification, of populism mean for the very nature and future of contemporary democracy? Populism and Liberal Democracy will change the ways the reader understands populism and imagines the prospects of liberal democracy.

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