Deformation mechanisms in nacre

2001 ◽  
Vol 16 (9) ◽  
pp. 2485-2493 ◽  
Author(s):  
R. Z. Wang ◽  
Z. Suo ◽  
A. G. Evans ◽  
N. Yao ◽  
I. A. Aksay
Keyword(s):  
Steady State ◽  
Inelastic Deformation ◽  
Inelastic Strain ◽  
Shear Resistance ◽  
Deformation Mechanisms ◽  
Interfacial Sliding ◽  
Underlying Mechanisms ◽  
Loading Axis ◽  
State Stress ◽  
Mollusc Shells

Nacre (mother-of-pearl) from mollusc shells is a biologically formed lamellar ceramic. The inelastic deformation of this material has been experimentally examined, with a focus on understanding the underlying mechanisms. Slip along the lamellae tablet interface has been ascertained by testing in compression with the boundaries oriented at 45° to the loading axis. The steady-state shear resistance τss has been determined and inelastic strain shown to be as high as 8%. The inelastic deformation was realized by massive interlamellae shearing. Testing in tension parallel to the tablets indicates inelastic strain of about 1%, occurring at a steady-state stress, σsss ≈ 110 MPa. The strain was associated with the formation of multiple dilatation bands at the intertablet boundaries accompanied by interlamellae sliding. Nano-asperities on the aragonite tablets and their interposing topology provide the resistance to interfacial sliding and establish the level of the stress needed to attain the inelastic strain. Detailed mechanisms and their significance for the design of robust ceramics are discussed.

Material Selection Issues for a Nozzle Guide Vane Against Service-Induced Failure

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Xijia Wu ◽  
Zhong Zhang ◽  
Leiyong Jiang ◽  
Prakash Patnaik
Keyword(s):  
Gas Turbine ◽  
Material Selection ◽  
Guide Vane ◽  
Failure Process ◽  
Inelastic Strain ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Strain Component ◽  
Combustion Gas ◽  
Nozzle Guide

Nozzle guide vanes (NGV) of gas turbine engines are the first components to withstand the impingement of hot combustion gas and therefore often suffer thermal fatigue failures in service. A lifting analysis is performed for the NGV of a gas turbine engine using the integrated creep–fatigue theory (ICFT). With the constitutive formulation of inelastic strain in terms of mechanism-strain components such as rate-independent plasticity, dislocation glide-plus-climb, and grain boundary sliding (GBS), the dominant deformation mechanisms at the critical locations are thus identified quantitatively with the corresponding mechanism-strain component. The material selection scenarios are discussed with regards to damage accumulated during take-off and cruise. The interplay of those deformation mechanisms in the failure process is elucidated such that an “optimum” material selection solution may be achieved.

A constitutive model for anisotropic, kinematic hardening materials

1997 ◽  
Vol 32 (3) ◽  
pp. 175-181
Author(s):  
W Deng ◽  
A Asundi ◽  
C W Woo
Keyword(s):  
Inelastic Deformation ◽  
Internal State ◽  
Kinematic Hardening ◽  
Small Deformation ◽  
Inelastic Strain ◽  
State Variables ◽  
Internal State Variables ◽  
Deformation Plasticity ◽  
Independent Variable ◽  
Evolution Laws

Based on previous work by the authors, a model for anisotropic, kinematic hardening materials is constructed to describe constitutive equations and evolution laws in rate-independent, small deformation plasticity on the basis of thermodynamics. Unlike other theories developed earlier wherein only internal state variables are chosen to describe inelastic deformation, the present paper also considers inelastic strain as an independent variable. This can be shown to reduce to the well-known plastic strain in the case of rate-independent plasticity.

Steady-State stress distributions in circumferentially notched bars subjected to creep

1982 ◽  
Vol 17 (3) ◽  
pp. 123-132 ◽  
Author(s):  
K D Al-Faddagh ◽  
R T Fenner ◽  
G A Webster
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Stress Index ◽  
Stress Distributions ◽  
Computer Solution ◽  
Time Intervals ◽  
Throat Region ◽  
Intermediate Time ◽  
State Stress ◽  
Good Agreement

The paper describes a procedure, based on a finite element method, for calculating directly the steady-state stress distribution in circumferentially notched bars subjected to creep without the need for obtaining solutions at intermediate time intervals. Good agreement is obtained with relevant approximate plasticity solutions and with numerical calculations which approach the steady-state over a period of time from the initial elastic stress distribution. Also, the procedure is equally applicable to primary, secondary, and tertiary creep, provided the variables of stress and time are separable in the creep law. Results obtained for a range of notch geometries and values of the stress index, n, are reported. It is found for each profile that a region of approximately constant effective stress, σ, independent of n, is obtained which can be used to characterise the overall behaviour of the notch throat region when a steady-state is reached sufficiently early in life. An approximate method for estimating the maximum equivalent steady-state stress across the notch throat is also presented which does not require a computer solution.

Dependence of stress on cross-bridge phosphorylation in vascular smooth muscle

1989 ◽  
Vol 256 (1) ◽  
pp. C96-C100 ◽  
Author(s):  
P. H. Ratz ◽  
C. M. Hai ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Vascular Smooth Muscle ◽  
Light Chain ◽  
Phorbol Esters ◽  
Receptor Activation ◽  
Bay K 8644 ◽  
Cross Bridge ◽  
Cross Bridges ◽  
State Stress

Cross-bridge phosphorylation associated with agonist-stimulated contraction of vascular smooth muscle is often transiently elevated. Such observations led to the concept that phosphorylation of the 20-kDa myosin regulatory light chain (Mp) was required for initial activation and cross-bridge cycling but might not be necessary for steady-state maintenance of stress in the latch state. The possibility that stress maintenance is not regulated by phosphorylation has received some experimental support in contractions induced by phorbol esters and the calcium channel activator BAY K 8644 in which significant increases in Mp were not detected. Our aim was to test the hypothesis that phosphorylation is both necessary and sufficient for activation and for maintenance of steady-state stress. Activation of swine carotid media using agents that bypass receptor activation and elevate Ca2+ influx without mobilizing intracellular Ca2+ stores (BAY K 8644 and ionomycin) produced monotonic increases in both stress and Mp. Transient initial peaks in Mp were absent. Steady-state stress induced by both receptor- and nonreceptor-mediated activation was dependent on small increases in Mp. Increases in Mp greater than 0.3 mol Pi/mol myosin light chain had small effects on stress but produced large increases in the maximum rate of cross-bridge cycling at zero load (Vo). The experimentally determined dependence of stress on Mp was quantitatively predicted by our working hypothesis. This model proposes that Ca2+-stimulated cross-bridge phosphorylation is obligatory for cross-bridge attachment. However, dephosphorylation of attached cross bridges to form noncycling "latch bridges" allows stress maintenance with reduced Mp and cycling.

Investigation of Flow Stress Behavior and Microstructural Evolution of 7050 Al Alloy

2007 ◽  
Vol 546-549 ◽  
pp. 1065-1068 ◽  
Author(s):  
You Ping Yi ◽  
Hua Chen ◽  
Yong Cheng Lin
Keyword(s):  
Steady State ◽  
Strain Softening ◽  
Type Equation ◽  
Al Alloy ◽  
Compression Tests ◽  
Hollomon Parameter ◽  
Deformation Behaviors ◽  
Three Stages ◽  
Increasing Temperature ◽  
State Stress

The plastic deformation behaviors of 7050 Al alloy were investigated by compression tests at temperatures ranging of 250°C450°C under constant strain rates of 0.01s−1, 1s−1 and 10s−1. The results showed that all the flow curves consisted of three stages, i.e. strain-hardening, strain-softening and steady state-strain. Initially, the stress rises steeply at microstrain deformation, and then increases at a decreased rate, followed by a strain-softening until a steady state stress. The stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in an exponent-type equation, 1 19 7.202 σ p 80.71 sinh (1.64 10 Z) = ⋅ −  × − ⋅ −  . Elongated grains with serrations developed in the grain boundaries were observed; the dynamic recrystallization (DRX) occurs with increasing temperature and dislocation density, and the shape of grain at steady state is nearly equiaxial. It can be concluded that the DRX phenomenon is sensitive to the temperature and the dynamic flow softening is mainly as the result of dynamic recovery and DRX.

A General Approach to the Practical Solution of Creep Problems

1959 ◽  
Vol 81 (4) ◽  
pp. 585-594 ◽  
Author(s):  
A. Mendelson ◽  
M. H. Hirschberg ◽  
S. S. Manson
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Temperature Gradient ◽  
Successive Approximations ◽  
Appreciable Effect ◽  
Rotating Disks ◽  
Transient Conditions ◽  
Practical Solution ◽  
State Stress ◽  
General Method

A general method is presented for the solution of creep problems by the use of successive approximations. The method is equally applicable to different creep laws and loading paths. Examples are presented for the creep in a flat plate with a temperature gradient and for several cases of rotating disks. In these disk problems the transient conditions prior to the establishment of steady-state stress distribution are included and shown to have an appreciable effect on the total creep strains. The use of different cumulative creep laws such as the time-hardening and strain-hardening laws are illustrated.

Length-dependent activation in intact ferret hearts: study of steady-state Ca(2+)-stress-strain interrelations

1996 ◽  
Vol 270 (6) ◽  
pp. H1940-H1950 ◽  
Author(s):  
R. Stennett ◽  
K. Ogino ◽  
J. P. Morgan ◽  
D. Burkhoff
Keyword(s):  
Steady State ◽  
Heart Function ◽  
Hill Coefficient ◽  
Physical Factors ◽  
Stress Strain ◽  
Ventricular Structure ◽  
Intact Muscle ◽  
Rapid Stimulation ◽  
Whole Heart ◽  
State Stress

We examined the steady-state stress-strain relationships and the steady-state stress-intracellular calcium concentration ([Ca2+]i) relationship in intact ferret hearts and compared these to previously published analogous relationships in skinned and intact muscle. Langendorff-perfused ferret hearts were treated with ryanodine and tetanized by rapid stimulation to create steady-state conditions. [Ca2+]i was measured concurrently by macroinjected aequorin. Over a range of volumes corresponding to strains between 1.0 and 0.75, steady-state stress decreased by 33% when saturating levels of perfusate calcium were used, indicating the degree to which physical factors contribute to the Frank-Starling relationship. The steady-state stress-[Ca2+]i relationship was sigmoidal with a mean Hill coefficient (nH) of 4.91 +/- 0.29 at a strain of 1.0, and the [Ca2+]i required for half-maximal activation (K1/2) was 0.41 +/- 0.03 microM. K1/2 increased and nH decreased with decreasing strains. These results are similar to those observed in intact muscle but differ quantitatively from results obtained in isolated, skinned preparations. Based on these results, we suggest that whole heart function can be related to average sarcomere function without the need for complex models of ventricular structure.

Scanning Electron Microscopic Analysis on the Deformation Mechanisms in NACRE

2001 ◽  
Vol 7 (S2) ◽  
pp. 1118-1119
Author(s):  
R.Z. Wang ◽  
Z. Suo ◽  
A.G. Evans ◽  
N. Yao ◽  
I.A. Aksay
Keyword(s):  
Inelastic Deformation ◽  
Microscopic Analysis ◽  
Deformation Mechanisms ◽  
Biological Macromolecules ◽  
Electron Microscopic ◽  
Princeton University ◽  
Structural Details ◽  
Tension And Compression ◽  
Stereo Microscope ◽  
Scanning Electron

Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544 Some biological materials exhibit structural robustness, despite the brittle nature of their constituents.Nacre (mother-of-pearl), the pearly internal layer of many mollusc shells, is addressed in this study. This material comprises about 95% aragonite tablets (a mineral form of CaC03), The polygonal tablets were glued with only a few percent of biological macromolecules into layered structure. The goal of the present study is to elucidate the basic inelastic deformation mechanisms.Typical stress /strain curves in tension and compression are plotted in Fig. 1. All tensile curves exhibited extensive inelastic deformation. After testing, the samples were initially examined using a stereo microscope (Leica MZ8) and a metallurgical microscope (Leica MEF4M) followed by analysis of the structural details using scanning electron microscopy (Philip XL-30). Optical imaging provided a visualization of the inelastic zone, manifest as white tension lines.

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