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1.
Microdeformation patterns of lamellar TiAl specimens with various grain sizes under uniaxial tension are mapped using the
micro/nano experimental mechanics technique called SIEM (Speckle Interferometry w ith Electron Microscopy). The stress–strain
relationships were obtained from deformations within decreasing areas ranging from mm2 to μm2. We found that the stress–strain relationship of the material depends on the size of strain measuring area in relation to
the grain size. The stiffness at a grain boundary can be as large as 7–10 times more than that of the grain itself. From the
data obtained so far, it seems that the traditional way of using PST (polysynthetically twinned) single crystal to predict
polycrystalline behavior may not be appropriate. 相似文献
2.
Maria N. Charalambides Leonard Wanigasooriya J. Gordon Williams Suk M. Goh Sumana Chakrabarti 《Rheologica Acta》2006,46(2):239-248
The stress–strain curves of bread dough were derived under uniaxial compression, uniaxial tension and equi-biaxial tension loading conditions. In uniaxial compression, a lubricant was used to eliminate frictional effects between the loading platens and the sample. In uniaxial tension, cylindrical samples with thin flat discs at both ends (‘I’ samples) were tested. The discs at both ends were allowed to air-dry and were subsequently glued onto the loading platens. In equi-biaxial tension, a thin disc of dough was inflated into a bubble using pressurised air. The thickness at the top of the bubble was measured by shining a light through the walls of the bubble and recording the change in light intensity as the wall becomes thinner. All methods ensured that uniform deformation was obtained. Stress and strain were accurately evaluated using image analysis techniques. The tests were performed at various strain rates and speeds that defined the time dependence of the material. A non-linear viscoelastic model based on the Prony series and Van der Waals hyperelasticity was used to predict all test data. The model had a total of five material parameters and two time constants, which were set to represent the actual time scales of the experiments. A reasonable agreement between the experimental data and the chosen material model was observed. 相似文献
3.
V. L. Shkuratnik Yu. L. Filimonov S. V. Kuchurin 《Journal of Applied Mechanics and Technical Physics》2006,47(2):236-240
This paper gives results from experimental studies of the acoustic emission and strain memory effects in anthracite samples
under cyclic loading. Trends and regularities were found in the formation and manifestation of the acoustic emission memory
effect of coal in nonmonotonic uniaxial tests.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 2, pp. 103–109, March–April, 2006. 相似文献
4.
A. D. Drozdov 《Continuum Mechanics and Thermodynamics》2007,19(1-2):111-132
Observations are reported on low-density polyethylene in uniaxial tensile and compressive tests with various strain rates
and in tensile and compressive relaxation tests with various strains. A constitutive model is developed for the time-dependent
response of a semicrystalline polymer at arbitrary three-dimensional deformations with finite strains. A polymer is treated
as an equivalent network of chains bridged by junctions (entanglements between chains in the amorphous phase and physical
cross-links at the lamellar surfaces). Its viscoelastic behavior is associated with separation of active strands from temporary
junctions and merging of dangling strands with the inhomogeneous network. The viscoplastic response is attributed to sliding
of junctions between chains with respect to their reference positions. Constitutive equations are derived by using the laws
of thermodynamics. The stress–strain relations involve 6 material constants that are found by matching the observations.
相似文献
5.
We study global minimizers of a continuum Landau–De Gennes energy functional for nematic liquid crystals, in three-dimensional
domains, subject to uniaxial boundary conditions. We analyze the physically relevant limit of small elastic constant and show
that global minimizers converge strongly, in W
1,2, to a global minimizer predicted by the Oseen–Frank theory for uniaxial nematic liquid crystals with constant order parameter.
Moreover, the convergence is uniform in the interior of the domain, away from the singularities of the limiting Oseen–Frank
global minimizer. We obtain results on the rate of convergence of the eigenvalues and the regularity of the eigenvectors of
the Landau–De Gennes global minimizer. We also study the interplay between biaxiality and uniaxiality in Landau–De Gennes
global energy minimizers and obtain estimates for various related quantities such as the biaxiality parameter and the size
of admissible strongly biaxial regions. 相似文献
6.
We present two representations of the Doi–Edwards model without Independent Alignment explicitly expressed in terms of the
Finger strain tensor, its inverse and its invariants. The two representations provide explicit expressions for the stress
prior to and after Rouse relaxation of chain stretch, respectively. The maximum deviations from the exact representations
in simple shear, biaxial extension and uniaxial extension are of order 2%. Based on these two representations, we propose
a framework for Doi–Edwards models including chain stretch in the memory integral form. 相似文献
7.
V. Tarigopula O. S. Hopperstad M. Langseth A. H. Clausen F. Hild O.-G. Lademo M. Eriksson 《Experimental Mechanics》2008,48(2):181-196
Large plastic deformation in sheets made of dual phase steel DP800 is studied experimentally and numerically. Shear testing
is applied to obtain large plastic strains in sheet metals without strain localisation. In the experiments, full-field displacement
measurements are carried out by means of digital image correlation, and based on these measurements the strain field of the
deformed specimen is calculated. In the numerical analyses, an elastoplastic constitutive model with isotropic hardening and
the Cockcroft–Latham fracture criterion is adopted to predict the observed behaviour. The strain hardening parameters are
obtained from a standard uniaxial tensile test for small and moderate strains, while the shear test is used to determine the
strain hardening for large strains and to calibrate the fracture criterion. Finite Element (FE) calculations with shell and
brick elements are performed using the non-linear FE code LS–DYNA. The local strains in the shear zone and the nominal shear
stress-elongation characteristics obtained by experiments and FE simulations are compared, and, in general, good agreement
is obtained. It is demonstrated how the strain hardening at large strains and the Cockcroft–Latham fracture criterion can
be calibrated from the in-plane shear test with the aid of non-linear FE analyses.
An erratum to this article can be found at 相似文献
8.
K. N. Jonnalagadda I. Chasiotis S. Yagnamurthy J. Lambros J. Pulskamp R. Polcawich M. Dubey 《Experimental Mechanics》2010,50(1):25-35
A new microscale uniaxial tension experimental method was developed to investigate the strain rate dependent mechanical behavior
of freestanding metallic thin films for MEMS. The method allows for highly repeatable mechanical testing of thin films for
over eight orders of magnitude of strain rate. Its repeatability stems from the direct and full-field displacement measurements
obtained from optical images with at least 25 nm displacement resolution. The method is demonstrated with micron-scale, 400-nm
thick, freestanding nanocrystalline Pt specimens, with 25 nm grain size. The experiments were conducted in situ under an optical
microscope, equipped with a digital high-speed camera, in the nominal strain rate range 10−6–101 s−1. Full field displacements were computed by digital image correlation using a random speckle pattern generated onto the freestanding
specimens. The elastic modulus of Pt, E = 182 ± 8 GPa, derived from uniaxial stress vs. strain curves, was independent of
strain rate, while its Poisson’s ratio was v = 0.41 ± 0.01. Although the nanocrystalline Pt films had the elastic properties
of bulk Pt, their inelastic property values were much higher than bulk and were rate-sensitive over the range of loading rates.
For example, the elastic limit increased by more than 110% with increasing strain rate, and was 2–5 times higher than bulk
Pt reaching 1.37 GPa at 101 s−1. 相似文献
9.
We present a model in this paper for predicting the inverse Hall–Petch phenomenon in nanocrystalline (NC) materials which
are assumed to consist of two phases: grain phase of spherical or spheroidal shapes and grain boundary phase. The deformation
of the grain phase has an elasto-viscoplastic behavior, which includes dislocation glide mechanism, Coble creep and Nabarro–Herring
creep. However the deformation of grain boundary phase is assumed to be the mechanism of grain boundary diffusion. A Hill
self-consistent method is used to describe the behavior of nanocrystalline pure copper subjected to uniaxial tension. Finally,
the effects of grain size and its distribution, grain shape and strain rate on the yield strength and stress–strain curve
of the pure copper are investigated. The obtained results are compared with relevant experimental data in the literature. 相似文献
10.
The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of high-density
polyethylene (a metallocene and a ZN-HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed
at temperatures below and well above the peak melting point of the polyethylenes in order to characterize their flow-induced
crystallization behavior at rates relevant to processing (elongational rates up to 30 s − 1 and shear rates 1 to 1,000 s − 1 depending on the application). Generally, strain and strain rate found to enhance crystallization in both shear and elongation.
In particular, extensional flow was found to be a much stronger stimulus for polymer crystallization compared to shear. At
temperatures well above the melting peak point (up to 25°C), polymer crystallized under elongational flow, while there was
no sign of crystallization under simple shear. A modified Kolmogorov crystallization model (Kolmogorov, Bull Akad Sci USSR,
Class Sci, Math Nat 1:355–359, 1937) proposed by Tanner and Qi (Chem Eng Sci 64:4576–4579, 2009) was used to describe the crystallization kinetics under both shear and elongational flow at different temperatures. 相似文献
11.
T. M. Poletika A. P. Pshenichnikov 《Journal of Applied Mechanics and Technical Physics》2009,50(3):525-531
The macrolocalization of plastic strain in samples of zirconium alloys with hexagonal close-packed structure under uniaxial
tension was studied by laser speckle interferometry and surface profiling. The occurrence of oscillatory instability in the
parabolic stage of plastic flow of zirconium alloys was found to be due to a local nonuniform change of the sample shape.
The kinetics of process was shown to be determined by oscillatory changes in the contraction and elongation strains at the
macrolocalization site in the hardening-softening regime.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 197–204, May–June, 2009. 相似文献
12.
A. I. Khromov A. A. Bukhan'ko O. V. Kozlova S. L. Stepanov 《Journal of Applied Mechanics and Technical Physics》2006,47(2):274-281
Based on the theory of an ideal rigid-plastic body, an approach is formulated for determining fracture constants on the basis
of standard mechanical tests on uniaxial extension of plane and cylindrical samples. Instead of the experimentally determined
characteristics of fracture of materials (dimensionless elongation and constriction of the sample during its fracture), two
invariant tensor characteristics of the degree of sample deformation are introduced, which correspond to the moment of origination
of a macrocrack and critical strain at the crack tip determining the process of crack propagation.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 2, pp. 147–155, March–April, 2006. 相似文献
13.
A. D. Drozdov J. de C. Christiansen 《Archive of Applied Mechanics (Ingenieur Archiv)》2003,72(10):779-803
Summary A series of uniaxial tensile tests is performed on isotactic polypropylene at room temperature with cross-head speeds ranging
from 5 to 100 mm/min. Prior to mechanical testing, injection-molded samples are annealed for 24 h at the temperature 160 °C that ensures that the specimens can be drawn up to the Hencky strain of 0.6 without necking. A constitutive model is derived
for the viscoplastic behavior of a semicrystalline polymer at finite strains. The stress–strain relations are determined by
five adjustable parameters that are found by matching the observations. Fair agreement is demonstrated between the experimental
data and the results of numerical simulation. It is shown that the material parameters in the constitutive equations are strongly
affected by the strain rate.
Received 9 July 2002; accepted for publication 12 November 2002 相似文献
14.
E. V. Karpov 《Journal of Applied Mechanics and Technical Physics》2009,50(1):163-169
This paper gives the results of an experimental study of the deformation and fracture of a spheroplast under uniaxial low-cycle
loading (compression and unloading) at a temperature T = 25 and 100°C. Various mechanisms of damage accumulation at various temperatures and degrees of damage to the material are studied. The
experimental results are compared with the well-known dependences taking into account damage accumulation for metals. It is
established that the basic propositions of these theories are suitable for the low-cycle fracture of spheroplast — a ductile
material of complex structure.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 197–204, January–February, 2009. 相似文献
15.
Jeremiah G. Murphy 《Journal of Elasticity》2000,60(2):151-164
The most general strain energy function that yields a power law relationship between the principal stretches in the simple
tension of nonlinear, elastic, homogeneous, compressible, isotropic materials is obtained. The approach taken generalises
that used by Blatz and Ko. The strain energy function obtained depends on the choice of two stretch invariants. The forms
of the strain energy function for a number of such choices are obtained. Finally, some consequences of the choice of strain
energy function on the stress–strain relationship for uniaxial tension are investigated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Local strain data obtained throughout the entire weld region encompassing both the weld nugget and heat affected zones (HAZs)
are processed using two methodologies, uniform stress and virtual fields, to estimate specific heterogeneous material properties
throughout the weld zone. Results indicate that (a) the heterogeneous stress–strain behavior obtained by using a relatively
simple virtual fields model offers a theoretically sound approach for modeling stress–strain behavior in heterogeneous materials,
(b) the local stress–strain results obtained using both a uniform stress assumption and a simplified uniaxial virtual fields
model are in good agreement for strains ɛ
xx < 0.025, (c) the weld nugget region has a higher hardening coefficient, higher initial yield stress and a higher hardening
exponent, consistent with the fact that the steel weld is overmatched and (d) for ɛ
xx > 0.025, strain localization occurs in the HAZ region of the specimen, resulting in necking and structural effects that complicate
the extraction of local stress strain behavior using either of the relatively simple models.
相似文献
S. M. AdeebEmail: |
17.
An experimental study is undertaken to examine the dynamic stress–strain characteristics of ligaments from the human cervical
spine (neck). Tests were conducted using a tensile split Hopkinson bar device and the engineering strain rates imposed were
of the order of 102∼103/s. As ligaments are extremely soft and pliable, specialized test protocols applicable to Hopkinson bar testing were developed
to facilitate acquisition of reliable and accurate data. Seven primary ligaments types from the cervical spines of three male
cadavers were subjected to mechanical tests. These yielded dynamic stress–strain curves which could be approximated by empirical
equations. The dynamic failure stress/load, failure stain/deformation, modulus/stiffness, as well as energy absorption capacity,
were obtained for the various ligaments and classified according to their location, the strain rate imposed and the cadaveric
source. Compared with static responses, the overall average dynamic stress–strain behavior foreach type of ligament exhibited
an elevation in strength but reduced elongation. 相似文献
18.
Julien Férec Marie-Claude Heuzey José Pérez-González Lourdes de Vargas Gilles Ausias Pierre J. Carreau 《Rheologica Acta》2009,48(1):59-72
The behavior of short glass fiber–polypropylene suspensions in extensional flow was investigated using three different commercial
instruments: the SER wind-up drums geometry (Extensional Rheology System) with a strain-controlled rotational rheometer, a
Meissner-type rheometer (RME), and the Rheotens. Results from uniaxial tensile testing have been compared with data previously
obtained using a planar slit die with a hyperbolic entrance. The effect of three initial fiber orientations was investigated:
planar random, fully aligned in the stretching flow direction and perpendicular to it. The elongational viscosity increased
with fiber content and was larger for fibers initially oriented in the stretching direction. The behavior at low elongational
rates showed differences among the various experimental setups, which are partly explained by preshearing history and nonhomogenous
strain rates. However, at moderate and high rates, the results are comparable, and the behavior is strain thinning. Finally,
a new constitutive equation for fibers suspended into a fluid obeying the Carreau model is used to predict the elongational
viscosity, and the predictions are in good agreement with the experimental data. 相似文献
19.
Manish K. Tiwari Alexander V. Bazilevsky Alexander L. Yarin Constantine M. Megaridis 《Rheologica Acta》2009,48(6):597-609
Rheological behavior of concentrated suspensions of chemical vapor deposition carbon nanotubes in uniaxial elongation and
simple shear is studied experimentally and theoretically. Nanotubes are suspended in viscous host liquids—castor oil or its
blends with n-decane. The elongational measurements are performed by analyzing self-thinning (due to surface tension effect) liquid threads
of nanotube suspensions. A quasi-one-dimensional model is used to describe the self-thinning process, whereas corrections
accounting for thread nonuniformity and necking are introduced a posteriori. The effects of nanotube concentration and aspect
ratio, viscosity of the suspending liquid, and initial diameter of the self-thinning thread in uniaxial elongation are elucidated.
The results for uniaxial elongation are compared with those for simple shear. The correspondence in the results of the shear
and elongational measurements is addressed and interpreted. The results conform to the Herschel–Bulkley rheological constitutive
equation (i.e., power law fluids with yield stress). However, the yield stress in elongation is about 40% higher than in simple
shear flow, which suggests that the original Herschel–Bulkley model need modification with the yield stress being a function
of the second invariant of the deviatoric stress tensor. The present effort is the first to study capillary self-thinning
of Herschel–Bulkley liquids, which are exemplified here by suspensions of carbon nanotubes. 相似文献
20.
We investigate the structure of nematic liquid crystal thin films described by the Landau–de Gennes tensor-valued order parameter model with Dirichlet boundary conditions on the sides of nonzero degree. We prove that as the elasticity constant goes to zero in the energy, a limiting uniaxial nematic texture forms with a finite number of defects, all of degree or all of degree , corresponding to vertical disclination lines at those locations. We also state a result on the limiting behavior of minimizers of the Chern–Simons–Higgs model without magnetic field that follows from a similar proof. 相似文献