Spherical Indentation Creep Following Ramp Loading

2005 ◽  
Vol 20 (8) ◽  
pp. 2094-2100 ◽  
Author(s):  
Michelle L. Oyen
Keyword(s):  
Loading Rate ◽  
Peak Load ◽  
Polymeric Materials ◽  
Material Behavior ◽  
Spherical Indentation ◽  
Indentation Creep ◽  
Creep Function ◽  
Creep Tests ◽  
Single Experiment ◽  
Linear Viscoelastic Material

Elastic-viscoelastic correspondence, utilizing Boltzmann integral operators, was used to generate displacement–time solutions for spherical indentation testing of viscoelastic materials. Solutions were found for creep following loading at a constant loading rate and compared with step-loading solutions. Experimental creep tests were performed with different loading rate–peak load level combinations on glassy and rubbery polymeric materials. The experimental data were fit to the spherical indentation ramp–creep solutions to obtain values of shear modulus and time-constants; good agreement was found between the experimental results and known modulus values. A multiple ramp-and-hold protocol was examined for the measurement of creep responses at several loads (and depths) within the same test. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test a priori assumptions made in the correspondence solutions regarding linear viscoelastic material behavior and the creep function.

Spherical Indentation Creep Following Ramp Loading

2004 ◽  
Vol 841 ◽  
Author(s):  
Michelle L. Oyen
Keyword(s):  
Contact Stiffness ◽  
Peak Load ◽  
Polymeric Materials ◽  
Spherical Indenter ◽  
Material Behavior ◽  
Spherical Indentation ◽  
Indentation Creep ◽  
Indentation Testing ◽  
Depth Sensing ◽  
Linear Viscoelastic Material

ABSTRACTDepth-sensing indentation testing is a common way to characterize the mechanical behavior of stiff, time-independent materials but presents both experimental and analytical challenges for compliant, time-dependent materials. Many of these experimental challenges can be overcome by using a spherical indenter tip with a radius substantially larger than the indentation depth, thus restricting deformation to viscoelastic (and not plastic) modes in glassy polymers and permitting large loads and contact stiffness to be generated in compliant elastomers. Elastic-viscoelastic correspondence was used to generate spherical indenter solutions for a number of indentation testing protocols including creep following loading at a constant rate and a multiple ramp-and-hold protocol to measure creep response at several loads (and depths) within the same test. The ramp-creep solution was recast as a modification to a step-load creep solution with a finite loading rate correction factor that is a dimensionless function of the ratio of experimental ramp time to the material time constant. Creep tests were performed with different loading rates and different peak load levels on glassy and rubbery polymeric materials. Experimental data are fit to the spherical indentation solutions to obtain elastic modulus and time-constants, and good agreement is found between the results and known modulus values. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test the a priori assumption of linear viscoelastic material behavior used in the modeling.

Time Dependent Deformation During Indentation Testing

1996 ◽  
Vol 436 ◽  
Author(s):  
B. N. Lucas ◽  
W. C. Oliver ◽  
G. M. Pharr ◽  
J-L. Loubet
Keyword(s):  
Loading Rate ◽  
Time History ◽  
Tensile Tests ◽  
Constant Load ◽  
Indentation Creep ◽  
Creep Tests ◽  
Constant Rate ◽  
Indentation Tests ◽  
Constant Loading Rate ◽  
Indentation Strain

AbstractConstant loading rate/load indentation tests (1/P dP/dt) and constant rate of loading followed by constant load (CRL/Hold) indentation creep tests have been conducted on high purity electropolished indium. It is shown that for a material with a constant hardness as a function of depth, a constant (1/P dP/dt) load-time history results in a constant indentation strain rate (1/h dh/dt). The results of the two types of tests are discussed and compared to data in the literature for constant stress tensile tests. The results from the constant (1/P dP/dt) experiments appear to give the best correlation to steady-state uniaxial data.

Indentation Creep and Relaxation Measurements of Polymers

2004 ◽  
Vol 841 ◽  
Author(s):  
Mark R. VanLandingham ◽  
Peter L. Drzal ◽  
Christopher C. White
Keyword(s):  
Stress Relaxation ◽  
Mechanical Response ◽  
Creep Compliance ◽  
Relaxation Modulus ◽  
Polymeric Materials ◽  
Indentation Creep ◽  
Dimethyl Siloxane ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
Creep And Stress Relaxation

ABSTRACTInstrumented indentation was used to characterize the mechanical response of polymeric materials. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for creep compliance and stress relaxation modulus for epoxy, poly(methyl methacrylate) (PMMA), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison to the indentation creep and stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than rheometry values. Additional study of the deformation remaining in epoxy after creep testing revealed that a large portion of the creep displacement measured was due to post-yield flow. Indentation creep measurements of the epoxy using a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the PDMS were mainly linear elastic, but the filled PDMS exhibited some time-dependence and nonlinearity in both rheometry and indentation measurements.

Depth sensing indentation of magnesium/boron nitride nanocomposites

2018 ◽  
Vol 53 (13) ◽  
pp. 1751-1763 ◽  
Author(s):  
M Haghshenas ◽  
R Islam ◽  
Y Wang ◽  
YT Cheng ◽  
M Gupta
Keyword(s):  
Boron Nitride ◽  
Loading Rate ◽  
Volume Fraction ◽  
Microwave Sintering ◽  
Peak Load ◽  
Pure Magnesium ◽  
Indentation Creep ◽  
Time Data ◽  
Depth Sensing ◽  
Indentation Tests

Magnesium nanocomposites, considered as energy-saving lightweight materials of future, are a fairly new family of composite materials with enhanced specific strength and ductility compared to pure magnesium and/or magnesium alloys. In the present study, time-dependent plastic deformation of novel light-weight magnesium/boron nitride nanocomposites containing 0.5, 1.5 and 2.5 vol% of nano-boron nitride particulates is studied through a depth-sensing indentation approach against monolithic pure magnesium. The synthesis of magnesium–boron nitride nanocomposites was accomplished using powder metallurgy technique coupled with microwave sintering, followed by hot extrusion (end products are 8-mm diameter rods). The depth sensing indentation creep tests were conducted at room temperature (∼0.32Tm of magnesium) using an instrumented indentation platform via a self-similar pyramidal (Berkovich) indenter. To assess the influence of loading rate on the indentation-induced deformation behavior of the materials, a dual stage indentation creep including a constant loading rate followed by a constant load-holding scheme was used; indentation tests were performed on the specimens. The specimens were loaded at rates of 0.05, 0.5, 5, and 50 mN/s to a peak load of 50 mN then force was held constant for 400 s while load/displacement/time data were recorded continuously. The results of the depth sensing indentation tests were correlated and explained using the microstructural characteristics placing special emphasis on the volume fraction of reinforcement and the indentation loading rate. Finally, the controlling creep mechanisms of the magnesium–boron nitride nanocomposites and the base metal (pure magnesium) were discussed in the present paper. The results of this paper can be used as a baseline for high-temperature creep analysis of magnesium–boron nitride nanocomposites which is of engineering significance.

scholarly journals Creep Behavior of Passive Bovine Extraocular Muscle

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Lawrence Yoo ◽  
Hansang Kim ◽  
Andrew Shin ◽  
Vijay Gupta ◽  
Joseph L. Demer
Keyword(s):  
Relaxation Function ◽  
Loading Rate ◽  
Creep Function ◽  
Testing Conditions ◽  
Loading Rates ◽  
Creep Coefficient ◽  
Wide Range ◽  
The Mean

This paper characterized bovine extraocular muscles (EOMs) using creep, which represents long-term stretching induced by a constant force. After preliminary optimization of testing conditions, 20 fresh EOM samples were subjected to four different loading rates of 1.67, 3.33, 8.33, and 16.67%/s, after which creep was observed for 1,500 s. A published quasilinear viscoelastic (QLV) relaxation function was transformed to a creep function that was compared with data. Repeatable creep was observed for each loading rate and was similar among all six anatomical EOMs. The mean creep coefficient after 1,500 seconds for a wide range of initial loading rates was at1.37±0.03(standard deviation, SD). The creep function derived from the relaxation-based QLV model agreed with observed creep to within 2.7% following 16.67%/s ramp loading. Measured creep agrees closely with a derived QLV model of EOM relaxation, validating a previous QLV model for characterization of EOM biomechanics.

Effect of multi-pass friction stir processing on thermal distribution and mechanical properties of AZ91

2020 ◽  
Vol 21 (4) ◽  
pp. 411
Author(s):  
Hoda Agha Amini Fashami ◽  
Nasrollah Bani Mostafa Arab ◽  
Mohammad Hoseinpour Gollo ◽  
Bahram Nami
Keyword(s):  
Mechanical Properties ◽  
Creep Strength ◽  
Friction Stir Processing ◽  
Material Behavior ◽  
Az91 Alloy ◽  
Residual Stress Field ◽  
Three Dimensional Model ◽  
Creep Tests ◽  
Friction Stir ◽  
Thermal Distribution

In this paper, the effect of multi-pass friction stir processing on mechanical properties of AZ91 alloy has been studied. For this purpose, the microhardness, tensile, and creep tests were conducted at several temperatures. Optical microscopy and scanning electron micrograph were used to study the microstructure of the processed samples. The experimental results indicated that at room temperature, the microhardness, tensile, and creep strength of the processed samples as compared to the unprocessed ones increased by 23%, 29%, and 38%, respectively. Also, after friction stir processing, the tensile and creep strength of the samples at 210 °C increased by 31% and 47%. In addition, a three-dimensional model was developed to simulate two-pass friction stir processing using ABAQUS/Explicit software. This model involved the Johnson-Cook models for defining material behavior during the process and identifying the fracture criterion. To control the mesh distortion during consecutive passes, the Arbitrary Lagrangian-Eulerian technique was used. Using the developed model, the peak temperature, thermal distribution, and residual stress field during multi-pass friction stir processing on AZ91 have been studied. The empirical results indicated the beneficial influence of the multi-pass friction stir processing on the microstructure and high-temperature mechanical properties of AZ91 alloy.

An investigation of the creep processes in tin and aluminum using a depth-sensing indentation technique

1992 ◽  
Vol 7 (3) ◽  
pp. 627-638 ◽  
Author(s):  
V. Raman ◽  
R. Berriche
Keyword(s):  
Stress Exponent ◽  
Constant Load ◽  
Indentation Creep ◽  
Depth Sensing ◽  
Creep Tests ◽  
Si Substrates ◽  
Uniaxial Creep ◽  
Rate Versus ◽  
Deformation Properties ◽  
Film Substrate

Constant load creep experiments were conducted using a depth-sensing indentation instrument with indentation depths in the submicron range. Experiments were conducted on polycrystalline Sn and sputtered Al films on Si substrates. The results show that the plastic depth versus time curves and the strain rate versus stress plots from these experiments are analogous to those obtained from conventional creep experiments using bulk specimens. The value of the stress exponent for Sn is close to the reported values from uniaxial creep tests. Tests on Al films showed that the stress exponent is dependent on the indentation depth and is governed by the proximity to the film/substrate interface. Load change experiments were also performed and the data from these tests were analyzed. It is concluded that indentation creep experiments may be useful in elucidating the deformation properties of materials and in identifying deformation mechanisms.

High-temperature Deformation Kinetics of Gold at 473K to 773K

2008 ◽  
Vol 1137 ◽  
Author(s):  
Vineet Bhakhri ◽  
Robert J. Klassen
Keyword(s):  
High Temperature ◽  
Cell Structure ◽  
Dislocation Cell ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Indentation Creep ◽  
Creep Tests ◽  
Dislocation Glide ◽  
Deformation Kinetics ◽  
Temperature Constant

AbstractHigh-temperature constant-force indentation creep tests of 200 seconds duration were performed on an annealed gold specimen at 473K to 773K, to investigate the dependence of the micro-/nano-indentation deformation kinetics upon indentation stress, temperature and time. The indent stress displayed a clear indentation size effect at 473 K. An analysis of the measured indentation creep rate, and its dependence upon temperature and stress, indicate that the strength of the deformation rate limiting obstacles increases with temperature. This is consistent with the expected temperature dependent evolution of the dislocation cell structure whose boundaries become the primary obstacles to dislocation glide.

Improved Nanoindentation Phase Transformation in Functional Structure of NiTi SMA and Graphene

2015 ◽  
Vol 1119 ◽  
pp. 160-164
Author(s):  
Abbas Amini ◽  
Chun Hui Yang ◽  
Yang Xiang
Keyword(s):  
Indentation Depth ◽  
Loading Rate ◽  
Spherical Indentation ◽  
Niti Shape Memory Alloy ◽  
Cooling Process ◽  
Graphene Layers ◽  
Loading Rates ◽  
Rate Dependent ◽  
Niti Sma ◽  
Superelastic Deformation

Graphene layers were deposited on the surface of NiTi shape memory alloy (SMA) to enhance the spherical indentation depth and the phase transformed volume through an extra nanoscale cooling. The graphene-deposited NiTi SMA showed deeper nanoindentation depths during the solid-state phase transition, especially at the rate dependent loading zone. Larger superelastic deformation confirmed that the nanoscale latent heat transfer through the deposited graphene layers allowed larger phase transformed volume in the bulk and, therefore, more stress relaxation and depth can be achieved. During the indentation loading, the temperature of the phase transformed zone in the stressed bulk increased by ~12-43°C as the loading rate increased from 4,500 μN/s to 30,000 μN/s. The layers of graphene enhanced the cooling process at different loading rates by decreasing the temperature up to ~3-10°C depending on the loading rate.

Poroelastic Indentation Analysis for Hydrated Biological Tissues

2006 ◽  
Vol 975 ◽  
Author(s):  
Michelle L. Oyen ◽  
Amanpreet K. Bembey ◽  
Andrew J. Bushby
Keyword(s):  
Indentation Test ◽  
Biological Tissues ◽  
Time Dependent ◽  
Spherical Indentation ◽  
Indentation Creep ◽  
Polar Solvents ◽  
Viscoelastic Analysis ◽  
Wide Range ◽  
Indentation Problem

ABSTRACTIndentation techniques are employed for the measurement of mechanical properties of a wide range of materials. In particular, techniques focused at small length-scales, such as nanoindentation and AFM indentation, allow for local characterization of material properties in heterogeneous materials including natural tissues and biomimetic materials. Typical elastic analysis for spherical indentation is applicable in the absence of time-dependent deformation, but is inappropriate for materials with time-dependent responses. Recent analyses for the viscoelastic indentation problem, based on elastic-viscoelastic correspondence, have begun to address the issue of time-dependent deformation during an indentation test. The viscoelastic analysis has been shown to fit experimental indentation data well, and has been demonstrated as useful for characterization of viscoelasticity in polymeric materials and in hydrated mineralized tissues. However, a viscoelastic analysis is not necessarily sufficient for multi-phase materials with fluid flow. In the current work, a poroelastic analysis—based on fluid motion through a porous elastic network—is used to examine spherical indentation creep responses of hydrated biological materials. Both analytical and finite element approaches are considered for the poroelastic Hertzian indentation problem. Modeling results are compared with experimental data from nanoindentation of hydrated bone immersed in water and polar solvents (ethanol, methanol, acetone). Baseline (water-immersed) bone responses are characterized using the poroelastic model and numerical results are compared with altered hydration states due to polar solvents.

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