A Method for Estimating Creep Deformation of Structures Subjected to Cyclic Loading

1973 ◽  
Vol 40 (4) ◽  
pp. 928-934 ◽  
Author(s):  
J. J. Williams ◽  
F. A. Leckie
Keyword(s):  
Cyclic Loading ◽  
Creep Strain ◽  
Effective Stress ◽  
Creep Test ◽  
Creep Deformation ◽  
Cyclic Creep ◽  
Uniaxial Stress ◽  
Time Varying ◽  
Proportional Loading

A method is proposed for estimating structural creep deformation due to histories of cyclic proportional loading. The method applies to structures composed of materials whose creep strain due to constant uniaxial stress is given by an equation of the form ε(t)/ε0={σ/σ0}n{t/t0}m Knowledge of the form of the creep law for time-varying stress is not required, as use is made of an effective stress obtained from a single cyclic creep test.

On the Interrupted Creep Test Under Low Stress Levels for the Power Law Parameter Extraction

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Bin Yang ◽  
Fu-Zhen Xuan ◽  
Wen-Chun Jiang
Keyword(s):  
Creep Strain ◽  
Stress Level ◽  
Creep Test ◽  
Creep Deformation ◽  
Parameter Extraction ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Creep Stage ◽  
Strain Data

Abstract Low stress interrupted creep test, as an interim compromise, can provide essential data for creep deformation design. However, there are no clear guidelines on the characterization of the terminating time for interrupted low-stress creep test. To obtain a suitable terminating time in terms of economy and effectiveness, long-term creep strain data of 9%Cr steels are collected from literatures and their creep deformation characterization is analyzed. First, the variations of normalized time and strain of each creep stage with the stress level are discussed. Then, the effect of the terminating time on final fitted results of Norton–Bailey equation is estimated. Third, the relationship between demarcation points at different creep stages and minimum/steady-state creep rate is analyzed. The results indicate that when the creep rupture life is considered as an important factor for creep design, the tertiary creep stage is of greatest significance due to the largest life fraction and creep strain fraction at low stress level. However, the primary and secondary creep stages are of great significance for design due to their larger contribution to 1% limited creep strain. And the long-term secondary creep data could be extrapolated by combining the primary creep strain data obtained from interrupted creep tests with the time to onset of tertiary creep derived from a similar Monkman–Grant relationship.

scholarly journals Small Two-Bar Specimen Creep Testing of Grade P91 Steel at 650°C

2016 ◽  
Vol 35 (3) ◽  
pp. 243-252
Author(s):  
Balhassn S. M. Ali ◽  
Tom H. Hyde ◽  
Wei Sun
Keyword(s):  
Strain Rate ◽  
Creep Strain ◽  
Test Data ◽  
Creep Test ◽  
Uniaxial Stress ◽  
Creep Rupture ◽  
Creep Strain Rate ◽  
P91 Steel ◽  
Uniaxial Creep ◽  
Rupture Data

AbstractCommonly used small creep specimen types, such as ring and impression creep specimens, are capable of providing minimum creep strain rate data from small volumes of material. However, these test types are unable to provide the creep rupture data. In this paper the recently developed two-bar specimen type, which can be used to obtain minimum creep strain rate and creep rupture creep data from small volumes of material, is described. Conversion relationships are used to convert (i) the applied load to the equivalent uniaxial stress, and (ii) the load line deformation rate to the equivalent uniaxial creep strain rate. The effects of the specimen dimension ratios on the conversion factors are also discussed in this paper. This paper also shows comparisons between two-bar specimen creep test data and the corresponding uniaxial creep test data, for grade P91 steel at 650°C.

A Method for Quantifying Creep Strain Due to Cyclic Stress

1974 ◽  
Vol 41 (4) ◽  
pp. 953-958 ◽  
Author(s):  
J. J. Williams ◽  
F. A. Leckie
Keyword(s):  
Creep Strain ◽  
Creep Test ◽  
Cyclic Creep ◽  
Cyclic Stress ◽  
Constant Stress ◽  
Stress Tests ◽  
Creep Strains

A method is proposed for isolating the two constants required to quantify the creep strains caused by cyclic histories of stress. These constants can be determined from the results of a single cyclic creep test together with data from constant stress tests.

scholarly journals Evaluation of Deformation and Permeability Behavior of Amygdaloidal Basalt under a Triaxial Cyclic Loading Creep Test

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Long Yan ◽  
Weiya Xu ◽  
Biao Li ◽  
Hua Ji ◽  
Jinjian Gu
Keyword(s):  
Cyclic Loading ◽  
Creep Test ◽  
Creep Deformation ◽  
Axial Stress ◽  
Axial Direction ◽  
Axial Deformation ◽  
Reservoir Water ◽  
Lateral Direction ◽  
Reservoir Water Level ◽  
Dam Foundation

Amygdaloidal basalt is a typical rock mass in the dam foundation of the Baihetan hydropower project in southwest China. With rising and drawdown of the reservoir water level, the permeability and creep deformation characteristics of the amygdaloidal basalt are much complicated in the long-term cyclic loading processes. A cyclic loading-unloading creep test on the amygdaloidal basalt was performed to evaluate its deformation and permeability behavior. The results showed that Poisson’s ratio and elastic modulus of the rock specimen varied significantly under different loading processes with a relatively large irreversible deformation. The permeability and strain rates of rock changed in two phases under lower deviatoric stresses, while there are three typical stages of strain growth with the final stress level of 121.8 MPa. For axial stress of 128 MPa, the creep deformation and creep rate in the axial direction are smaller than these in the lateral direction. Before the sample failure, the lateral deformation accelerates earlier than the axial deformation. The results also suggested that the permeability of the rock specimens decreases considerably during each loading process and then tends to be constant with time. No apparent change in steady permeability is observed with variation of stress. For 128 MPa axial stress, the permeability first decreases, then tends to be in a stable value, and at last increases during the sample failure.

Origin and Effect of Back Stress on Cyclic Creep Deformation of 316H Stainless Steel

2015 ◽  
Author(s):  
Abdullah Al Mamun ◽  
Richard James Moat ◽  
P. John Bouchard
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Creep Deformation ◽  
Deformation Rate ◽  
Cyclic Creep ◽  
Back Stress ◽  
Secondary Creep ◽  
Creep Equation ◽  
Simplified Approach ◽  
Power Law Creep

Components in power generation plants operate at high temperature and often go through complex cyclic loading sequence during its operations. ‘Back stress’ is generated during such cyclic loading due to inhomogeneity in deformation at micro scale and significantly affects the overall creep lifetime of the materials of these components. Using a time of flight neutron diffraction facility, we studied the origin of back stress and its effects on creep deformation rate of AISI type 316H austenitic steel during cyclic creep at 650 °C. The result shows, during high temperature cyclic loading of this material for any given level of stress, the magnitude of back stress vary significantly depending on the point in the cycle being observed. The effective back stress levels associated with dwells introduced at different points in the cycle shows good co-relation with the measured macroscopic secondary creep deformation rate. Moreover, a simplified approach using modified power law creep equation is proposed to quantify back stress from a known creep deformation rate.

Analysis of creep deformation under cyclic loading conditions

1975 ◽  
Vol 20 ◽  
pp. 261-266 ◽  
Author(s):  
D.K. Shetty ◽  
T. Mura ◽  
M. Meshii
Keyword(s):  
Cyclic Loading ◽  
Creep Deformation ◽  
Loading Conditions

An approach to the determination of cyclic creep strain

1979 ◽  
Vol 11 (11) ◽  
pp. 1225-1229 ◽  
Author(s):  
V. P. Golub
Keyword(s):  
Creep Strain ◽  
Cyclic Creep

Creep Deformation of Particle-Strengthened Metal-Matrix Composites

1989 ◽  
Vol 111 (1) ◽  
pp. 99-105 ◽  
Author(s):  
Z. G. Zhu ◽  
G. J. Weng
Keyword(s):  
Constitutive Equation ◽  
Metal Matrix Composites ◽  
Creep Strain ◽  
Creep Deformation ◽  
Creep Resistance ◽  
Metal Matrix ◽  
Order Approximation ◽  
Stress Redistribution ◽  
Matrix Composites ◽  
The Matrix

A multiaxial theory of creep deformation for particle-strengthened metal-matrix composites is derived. This derivation is based on the observation that there are two major sources of creep resistance in such a system. The first, or metallurgical effect, arises from the increased difficulty of dislocation motion in the presence of particles and is accounted for by a size- and concentration dependent constitutive equation for the matrix. The second, or mechanics effect, is due to the continuous transfer of stress from the ductile matrix to the hard particles and the corresponding stress redistribution is also incorporated in the derivation. Both power-law creep and exponential creep in the matrix, each involving the transient as well as the steady state, are considered. The constitutive equations thus derived can provide the development of creep strain of the composite under a combined stress. The multiaxial theory is also simplified to a uniaxial one, whose explicit stress-creep strain-time relations at a given concentration of particles are also given by a first- and second-order approximation. The uniaxial theory is used to predict the creep deformation of an oxide-strengthened cobalt, and the results are in reasonably good agreement with the experiment. Finally, it is demonstrated that a simple metallurgical approach without considering the stress redistribution between the two constituent phases, or a simple mechanics approach without using a modified constitutive equation for the metal matrix, may each underestimate the creep resistance of the composite, and, therefore, it is important that both factors be considered in the formulation of such a theory.

scholarly journals Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk

2018 ◽  
Vol 55 (11) ◽  
pp. 1577-1591 ◽  
Author(s):  
R.M. Buckley ◽  
R.J. Jardine ◽  
S. Kontoe ◽  
B.M. Lehane
Keyword(s):  
Cyclic Loading ◽  
Effective Stress ◽  
Test Site ◽  
Static Tension ◽  
Load Testing ◽  
Stress Regime ◽  
Effective Stresses ◽  
Axial Cyclic Loading ◽  
Tension Testing ◽  
Static And Cyclic Loading

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method.

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