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G M Pharr - One of the best experts on this subject based on the ideXlab platform.
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an improved relation for the effective Elastic Compliance of a film substrate system during indentation by a flat cylindrical punch
Scripta Materialia, 2006Co-Authors: G M PharrAbstract:Measurement of the mechanical properties of thin films on substrates by load and depth sensing indentation methods such as nanoindentation often requires accurate descriptions for the effective Elastic Compliance of the film/substrate system. Here, a simple modification of the commonly used solution derived by Gao et al. [H. Gao, C.H. Chiu, J. Lee, Int. J. Solids Struct. (1992) 2471] is presented, that significantly improves its accuracy and range of applicability, as demonstrated by comparison with finite element simulations.
B. Dkhil - One of the best experts on this subject based on the ideXlab platform.
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Single-domain (110) PbTiO3 thin films: Thermodynamic theory and experiments
Physical Review B: Condensed Matter and Materials Physics, 2016Co-Authors: P Mtebwa, P Tagantsev, T Yamada, N Setter, P. Gemeiner, B. DkhilAbstract:We report the thermodynamic potential for single-domain (110) thin films epitaxially grown on dissimilar cubic substrates. Using different sets of paraelectric phase Elastic Compliance coefficients of PbTiO 3 single crystal, calculated from the experimental room-temperature values, we predict rotational phases similar to those observed in (001) thin films under anisotropic biaxial misfit strain. The new sets of Elastic Compliance coefficients also predict a triclinic phase that could potentially lead to the enhancement of both dielectric and piezoelectric properties. We also conducted experimental studies on highly tetragonal monocrystalline PbZr 0.05 Ti 0.95 O 3 thin films of different thicknesses, epitaxially grown on (110) SrTiO 3 substrate by pulsed laser deposition technique. Piezoresponse force microscopy measurements showed that the as-grown films were single domain with the a 2 c phase, which corroborates with the prediction of the theory. Moreover, the T c values of both thin and thick films (17–90 nm) also fell within the predicted range (540–600 ± • C). The measured remanet polarization of 57 µC/cm 2 was in good agreement with the theoretical values of 55–58 µC/cm 2. Small-signal piezoelectric response measurements gave a piezoelectric coefficient of 40 pm/V, which is also in good agreement with the numerically calculated values of 38–42 pm/V.
P Mtebwa - One of the best experts on this subject based on the ideXlab platform.
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Single-domain (110) PbTiO3 thin films: Thermodynamic theory and experiments
Physical Review B: Condensed Matter and Materials Physics, 2016Co-Authors: P Mtebwa, P Tagantsev, T Yamada, N Setter, P. Gemeiner, B. DkhilAbstract:We report the thermodynamic potential for single-domain (110) thin films epitaxially grown on dissimilar cubic substrates. Using different sets of paraelectric phase Elastic Compliance coefficients of PbTiO 3 single crystal, calculated from the experimental room-temperature values, we predict rotational phases similar to those observed in (001) thin films under anisotropic biaxial misfit strain. The new sets of Elastic Compliance coefficients also predict a triclinic phase that could potentially lead to the enhancement of both dielectric and piezoelectric properties. We also conducted experimental studies on highly tetragonal monocrystalline PbZr 0.05 Ti 0.95 O 3 thin films of different thicknesses, epitaxially grown on (110) SrTiO 3 substrate by pulsed laser deposition technique. Piezoresponse force microscopy measurements showed that the as-grown films were single domain with the a 2 c phase, which corroborates with the prediction of the theory. Moreover, the T c values of both thin and thick films (17–90 nm) also fell within the predicted range (540–600 ± • C). The measured remanet polarization of 57 µC/cm 2 was in good agreement with the theoretical values of 55–58 µC/cm 2. Small-signal piezoelectric response measurements gave a piezoelectric coefficient of 40 pm/V, which is also in good agreement with the numerically calculated values of 38–42 pm/V.
Glen A Lichtwark - One of the best experts on this subject based on the ideXlab platform.
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effects of series Elastic Compliance on muscle force summation and the rate of force rise
The Journal of Experimental Biology, 2016Co-Authors: Dean L Mayfield, Andrew G Cresswell, Glen A LichtwarkAbstract:Compliant tendons permit mechanically unfavourable fascicle dynamics during fixed-end contractions. The purpose of this study was to reduce the effective Compliance of tendon and investigate how small reductions in active shortening affect twitch kinetics and contractile performance in response to a second stimulus. The series Elastic element (SEE) of the human triceps surae (N=15) was effectively stiffened by applying a 55 ms rotation to the ankle, through a range of 5°, at the onset of twitch and doublet [interstimulus interval (ISI) of 80 ms] stimulation. Ultrasonography was employed to quantify lateral gastrocnemius and soleus fascicle lengths. Rotation increased twitch torque (40-75%), rate of torque development (RTD, 124-154%) and torque-time integral (TTI, 70-110%) relative to constant-length contractions at the initial and final joint positions, yet caused only modest reductions in shortening amplitude and velocity. The torque contribution of the second pulse increased when stimulation was preceded by rotation, a finding unable to be explained on the basis of fascicle length or SEE stiffness during contraction post-rotation. A further increase in torque contribution was not demonstrated, nor an increase in doublet TTI, when the second pulse was delivered during rotation and shortly after the initial pulse (ISI of 10 ms). The depressant effect of active shortening on subsequent torque generation suggests that compliant tendons, by affording large length changes, may limit torque summation. Our findings indicate that changes in tendon Compliance shown to occur in response to resistance training or unloading are likely sufficient to considerably alter contractile performance, particularly maximal RTD.
George M. Pharr - One of the best experts on this subject based on the ideXlab platform.
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An improved relation for the effective Elastic Compliance of a film/substrate system during indentation by a flat cylindrical punch
Scripta Materialia, 2006Co-Authors: George M. PharrAbstract:Measurement of the mechanical properties of thin films on substrates by load and depth sensing indentation methods such as nanoindentation often requires accurate descriptions for the effective Elastic Compliance of the film/substrate system. Here, a simple modification of the commonly used solution derived by Gao et al. [H. Gao, C.H. Chiu, J. Lee, Int. J. Solids Struct. (1992) 2471] is presented, that significantly improves its accuracy and range of applicability, as demonstrated by comparison with finite element simulations.
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Assessment of New Relation for the Elastic Compliance of a Film-Substrate System
MRS Proceedings, 2001Co-Authors: Andrei Rar, H. Song, George M. PharrAbstract:A new closed-form relation for the Elastic Compliance of a film-substrate system indented by a flat cylindrical punch is presented. The relation is an extension of the work of Gao at al. [1] modified to increase the applicable range of modulus mismatch between the film and substrate. The accuracy of the relation is assessed by comparison to finite element simulations, other approximate numerical solutions, and nanoindentation experiments performed on a fluorinated silicate glass (FSG) film on a silicon substrate. The benefits and limitations of the relation are discussed.