An Empirical Creep Law From a Single Test

A method is described by which an empirical creep law, relating stress, strain, and strain rate, may be obtained from a single constant-load creep test. An example to illustrate the method is given, and the empirical creep law is compared with the results of several constant stress creep tests.

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Some New Approaches in the Analysis of High-Temperature Deformation

Journal of Engineering Materials and Technology ◽

10.1115/1.3443331 ◽

1976 ◽

Vol 98 (1) ◽

pp. 2-8 ◽

Cited By ~ 3

Author(s):

D. A. Woodford

Keyword(s):

Strain Rate ◽

Constant Strain Rate ◽

Constant Load ◽

High Temperature Deformation ◽

Temperature Deformation ◽

Stress Range ◽

Creep Tests ◽

Stress Strain ◽

Creep Analysis ◽

Good Agreement

Creep tests on two heats of a CrMoV steel at 811K (1000°F) are analyzed using a new graphical procedure to solve the equation σ = C(t) H(ε). This enables prediction of both constant load and constant stress creep behavior at different stresses within the range examined which included tests lasting in excess of 10,000 hr. An analytical solution of the equation is also described and used to generate isochronous stress-strain curves. Attempts to predict the response in relaxation and constant strain rate tests where the load is continuously changing are described. Reasonable agreement was obtained in the former type of test using a total strain rule, which assumes a unique relationship between stress, strain and time, when the stress range covered was within the range used in the creep analysis. For constant strain rate testing, where a much broader stress range was involved, it was necessary to use incremental analysis to achieve good agreement between predicted and experimental curves up to about 2 percent strain.

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Impression creep of lead

Journal of Materials Research ◽

10.1557/jmr.1994.0903 ◽

1994 ◽

Vol 9 (4) ◽

pp. 903-908 ◽

Cited By ~ 34

Author(s):

Donyau Chiang ◽

J. C. M. Li

Keyword(s):

Creep Test ◽

Elevated Temperatures ◽

Constant Load ◽

Constant Stress ◽

Tensile Creep ◽

Indentation Creep ◽

Impression Creep ◽

Creep Tests ◽

Creep Measurements ◽

Cylindrical Punch

The impression creep behavior of lead was investigated using a 100 μm diameter punch at ambient and elevated temperatures (433 K-563 K) under punching stresses of 6–70 MPa. The results were compared with the data obtained from conventional creep tests reported in the literature. Unlike the indentation creep test, the impression creep test showed a steady-state velocity after a short transient period when the flat-end cylindrical punch was pushed against the lead surface by a constant load. Both the temperature and stress dependences were comparable to those of the constant stress tensile creep tests under similar conditions. A master curve for lead was established by collecting data from the impression creep tests and the constant stress tensile creep tests. The indentation creep measurements for lead were included also. However, the indentation data depend on the load applied.

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Evolution of specimen strain rate in split Hopkinson bar test

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406218813386 ◽

2019 ◽

Vol 233 (13) ◽

pp. 4667-4687 ◽

Cited By ~ 5

Author(s):

Hyunho Shin ◽

Jong-Bong Kim

Keyword(s):

Strain Rate ◽

Rate Equation ◽

Constant Strain Rate ◽

Strain Curve ◽

Hopkinson Bar ◽

Stress Strain ◽

Split Hopkinson Bar ◽

Specimen Diameter ◽

Strain And Strain Rate ◽

Split Hopkinson

The specimen strain rate in the split Hopkinson bar (SHB) test has been formulated based on a one-dimensional assumption. The strain rate is found to be controlled by the stress and strain of the deforming specimen, geometry (the length and diameter) of specimen, impedance of bar, and impact velocity. The specimen strain rate evolves as a result of the competition between the rate-increasing and rate-decreasing factors. Unless the two factors are balanced, the specimen strain rate generally varies (decreases or increases) with strain (specimen deformation), which is the physical origin of the varying nature of the specimen strain rate in the SHB test. According to the formulated strain rate equation, the curves of stress–strain and strain rate–strain are mutually correlated. Based on the correlation of these curves, the strain rate equation is verified through a numerical simulation and experiment. The formulated equation can be used as a tool for verifying the measured strain rate–strain curve simultaneously with the measured stress–strain curve. A practical method for predicting the specimen strain rate before carrying out the SHB test has also been presented. The method simultaneously solves the formulated strain rate equation and a reasonably estimated constitutive equation of specimen to generate the anticipated curves of strain rate–strain and stress–strain in the SHB test. An Excel® program to solve the two equations is provided. The strain rate equation also indicates that the increase in specimen stress during deformation (e.g., work hardening) plays a role in decreasing the slope of the strain rate–strain curve in the plastic regime. However, according to the strain rate equation, the slope of the strain rate–strain curve in the plastic deformation regime can be tailored by controlling the specimen diameter. Two practical methods for determining the specimen diameter to achieve a nearly constant strain rate are presented.

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Nanoindentation Studies of Plasticity and Dislocation Creep in Halite

Geosciences ◽

10.3390/geosciences9020079 ◽

2019 ◽

Vol 9 (2) ◽

pp. 79 ◽

Cited By ~ 2

Author(s):

Christopher Thom ◽

David Goldsby

Keyword(s):

Strain Rate ◽

Stress Exponent ◽

Creep Behavior ◽

Constant Load ◽

Dislocation Creep ◽

Indentation Creep ◽

Creep Tests ◽

Creep Flow ◽

A Value ◽

Flow Laws

Previous deformation experiments on halite have collectively explored different creep mechanisms, including dislocation creep and pressure solution. Here, we use an alternative to conventional uniaxial or triaxial deformation experiments—nanoindentation tests—to measure the hardness and creep behavior of single crystals of halite at room temperature. The hardness tests reveal two key phenomena: (1) strain rate-dependent hardness characterized by a value of the stress exponent of ~25, and (2) an indentation size effect, whereby hardness decreases with increasing size of the indents. Indentation creep tests were performed for hold times ranging from 3600 to 106 s, with a constant load of 100 mN. For hold times longer than 3 × 104 s, a transition from plasticity to power-law creep is observed as the stress decreases during the hold, with the latter characterized by a value of the stress exponent of 4.87 ± 0.91. An existing theoretical analysis allows us to directly compare our indentation creep data with dislocation creep flow laws for halite derived from triaxial experiments on polycrystalline samples. Using this analysis, we show an excellent agreement between our data and the flow laws, with the strain rate at a given stress varying by less than 5% for a commonly used flow law. Our results underscore the utility of using nanoindentation as an alternative to more conventional methods to measure the creep behavior of geological materials.

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High-Temperature Creep Tests of Two Creep-Resistant Materials at Constant Stress and Constant Load

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.827.246 ◽

2019 ◽

Vol 827 ◽

pp. 246-251

Author(s):

Vàclav Sklenička ◽

Květa Kuchařová ◽

Marie Kvapilová ◽

Luboš Kloc ◽

Jiří Dvořák ◽

...

Keyword(s):

Creep Behaviour ◽

Constant Load ◽

Complex Stress ◽

Constant Stress ◽

Fracture Mechanisms ◽

Stress Tests ◽

Creep Tests ◽

Deformation And Fracture ◽

Dependent Component ◽

The Difference

Creep is defined as a time dependent component of plastic deformation. Creep tests can be performed either at constant load or at constant applied stress. Engineering creep tests carried out at constant load are aimed at determination of the creep strength or creep fracture strength, i.e. the data needed for design. The constant stress tests are important as a data source for fundamental investigations of creep deformation and fracture mechanisms and for finite element modelling of more complex stress situations. For some materials, the difference between the two type of testing can be very small, while for other materials is large, depending on the creep plasticity of the material under testing. The paper aims to compare the creep results of two different creep-resistant materials: the advanced 9%Cr martensitic steel (ASME Grade P91) and a Zr1%Nb alloy obtained by both testing methods and to clarify the decisive factors causing observed differences in their creep behaviour.

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A Study of Creep Behavior of TSV-Cu Based on Nanoindentaion Creep Test

Journal of Mechanics ◽

10.1017/jmech.2016.55 ◽

2016 ◽

Vol 32 (6) ◽

pp. 717-724 ◽

Cited By ~ 4

Author(s):

W. Wu ◽

F. Qin ◽

T. An ◽

P. Chen

Keyword(s):

Strain Rate ◽

Creep Behavior ◽

Rate Sensitivity ◽

Constant Load ◽

Mean Value ◽

Creep Tests ◽

Rate Method ◽

The Mean ◽

Previous Loading ◽

Indentation Strain

AbstractThrough-Silicon-Via (TSV) is considered to be the most potential solution for 3D electronic packaging, and the mechanical properties of TSV-Cu are critical for TSV reliability improving. In this paper, to make deeply understand the creep behavior of TSV-Cu, nanoindentation creep tests were conducted to obtain its creep parameters. At first, the TSV specimens were fabricated by means of a typical TSV manufacturing process. Then a combination programmable procedure of the constant indentation strain rate method and the constant load method was employed to study the creep behavior of TSV-Cu. To understand the influence of the previous loading schemes, including the different values of the indentation strain and the maximum depths, the nanoindentation creep tests under different loading conditions were conducted. The values of creep strain rate sensitivity m were derived from the corresponding displacement-holding time curves, and the mean value of m finally determined was 0.0149. The value of m is considered no obvious correlation with the different indentation strain rates and the maximum depths by this method. Furthermore, the mechanism for the room temperature creep was also discussed, and the grain boundaries might play an significant role in this creep behavior.

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High Temperature Plastic Behaviour of Icosahedral AlCuFe Quasicrystals.

MRS Proceedings ◽

10.1557/proc-643-k7.3 ◽

2000 ◽

Vol 643 ◽

Author(s):

Jan Fikar ◽

Joël Bonneville ◽

Nadine Baluc ◽

Pierre Guyot

Keyword(s):

Strain Rate ◽

Constant Strain Rate ◽

Friction Stress ◽

Dislocation Model ◽

Compression Tests ◽

Creep Tests ◽

Flow Strength ◽

Stress Strain ◽

Softening Effect ◽

Dislocation Interaction

AbstractIcosahedral AlCuFe poly-quasicrystalline specimens were deformed in constant strain rate compression tests at temperatures ranging between 300K - 1020K. Below nearly 0.7 Tm (Tm is the melting temperature) the specimens were brittle. Above the brittle-to-ductile transition temperature, after the elastic stage the stress-strain curves exhibit a marked yield-point followed by a stage of strain softening only. Transient creep tests were performed at different given stress/strain levels after interrupting the constant strain-rate deformation tests. After the transient tests, the flow strength of the specimens was investigated anew at constant strain rate. The results are interpreted in the framework of a dislocation model, where two effects opposing dislocation movement are considered: firstly, the usual elastic dislocation interaction, yielding a work-hardening contribution, and, secondly, a friction stress specific to the quasiperiodic lattice, leading to a softening effect.

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Experimental investigation on the creep behavior of an unsaturated clay

Canadian Geotechnical Journal ◽

10.1139/cgj-2013-0064 ◽

2014 ◽

Vol 51 (6) ◽

pp. 621-628 ◽

Cited By ~ 27

Author(s):

X.L. Lai ◽

S.M. Wang ◽

W.M. Ye ◽

Y.J. Cui

Keyword(s):

Strain Rate ◽

Large Scale ◽

Axial Strain ◽

Creep Model ◽

Three Gorges Reservoir Area ◽

Hyperbolic Function ◽

Creep Tests ◽

Suction Control ◽

Strain And Strain Rate ◽

Influence Of Water

To better understand the long-term deformation of landslides with consideration of the influence of water content variation, a series of triaxial creep tests with suction control was conducted on clay specimens taken from one large-scale landslide in the Three Gorges Reservoir area in China. Results indicate that, in the double-logarithmic coordinates, the axial strain increases linearly and the axial strain-rate decreases linearly with the elapsed time; the axial strain and strain rate increase with increasing deviator stress levels and decreasing matric suction. For theoretical analysis, based on the simulation of the test results by an empirical creep model developed for saturated soils, a linear relationship was established between suction and one of the parameters of the model. Then, a revised model with consideration of suction effects was developed. In the revised model, a power function was adopted for the description of the strain–time relationship and a hyperbolic function was employed for the stress–strain relationship. Verification indicated that the calculated results were in good agreement with the experimental ones.

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Estimation of Stress-Strain behavior of polyethylene terephthalate (PET) at different strain rates by Artificial Neural Network under simultaneous stretch scenario

10.25518/esaform21.1995 ◽

2021 ◽

Author(s):

Fei Teng ◽

Gary Menary ◽

Savko Malinov ◽

Shiyong Yan

Keyword(s):

Neural Network ◽

Artificial Neural Network ◽

Strain Rate ◽

Strain Rates ◽

Stress Strain ◽

Strain Behavior ◽

Strain And Strain Rate ◽

Artificial Neural ◽

Artificial Neural Network Ann ◽

High Degree

In this paper, an Artificial Neural Network (ANN) is used to predict the stress-strain behavior of PET at conditions relevant to Stretch Blow Moulding i.e. Large equibiaxial deformation at elevated temperature and high strain rate. The input vectors considered are temperature, strain, and strain rate with a corresponding output parameter of stress. In the present work, a feed-forward back backpropagation algorithm was used to train the ANN. The ANN is able to approximate the relationship between stress and strain at various strain rates & temperatures to a high degree of accuracy for all conditions tested.

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