Layer Structures. 4. Role of Long Alkane Spacers in Poly(ester imide)s Derived fromN-(4‘-Hydroxyphenyl)-4-hydroxyphthalimide

1996 ◽  
Vol 29 (12) ◽  
pp. 4234-4240 ◽  
Author(s):  
Hans R. Kricheldorf ◽  
Nicolas Probst ◽  
Gert Schwarz ◽  
Christoph Wutz
Keyword(s):  
Layer Structures

On velocity gradient dynamics and turbulent structure

2015 ◽  
Vol 780 ◽  
pp. 60-98 ◽  
Author(s):  
J. M. Lawson ◽  
J. R. Dawson
Keyword(s):  
Velocity Gradient ◽  
Local Strain ◽  
Turbulent Structure ◽  
Stochastic Estimation ◽  
Spatially Resolved ◽  
Gradient Dynamics ◽  
Layer Structures ◽  
Non Local ◽  
Conditional Averaging

The statistics of the velocity gradient tensor $\unicode[STIX]{x1D63C}=\boldsymbol{{\rm\nabla}}\boldsymbol{u}$, which embody the fine scales of turbulence, are influenced by turbulent ‘structure’. Whilst velocity gradient statistics and dynamics have been well characterised, the connection between structure and dynamics has largely focused on rotation-dominated flow and relied upon data from numerical simulation alone. Using numerical and spatially resolved experimental datasets of homogeneous turbulence, the role of structure is examined for all local (incompressible) flow topologies characterisable by $\unicode[STIX]{x1D63C}$. Structures are studied through the footprints they leave in conditional averages of the $Q=-\text{Tr}(\unicode[STIX]{x1D63C}^{2})/2$ field, pertinent to non-local strain production, obtained using two complementary conditional averaging techniques. The first, stochastic estimation, approximates the $Q$ field conditioned upon $\unicode[STIX]{x1D63C}$ and educes quantitatively similar structure in both datasets, dissimilar to that of random Gaussian velocity fields. Moreover, it strongly resembles a promising model for velocity gradient dynamics recently proposed by Wilczek & Meneveau (J. Fluid Mech., vol. 756, 2014, pp. 191–225), but is derived under a less restrictive premise, with explicitly determined closure coefficients. The second technique examines true conditional averages of the $Q$ field, which is used to validate the stochastic estimation and provide insights towards the model’s refinement. Jointly, these approaches confirm that vortex tubes are the predominant feature of rotation-dominated regions and additionally show that shear layer structures are active in strain-dominated regions. In both cases, kinematic features of these structures explain alignment statistics of the pressure Hessian eigenvectors and why local and non-local strain production act in opposition to each other.

Role of Adhesive Interlayer in Transverse Fracture of Brittle Layer Structures

2000 ◽  
Vol 15 (4) ◽  
pp. 1017-1024 ◽  
Author(s):  
Herzl Chai ◽  
Brian Lawn
Keyword(s):  
Crack Initiation ◽  
Glass Surface ◽  
Hard Spheres ◽  
Glass Plate ◽  
Critical Conditions ◽  
Transverse Fracture ◽  
Adhesive Interlayer ◽  
Layer Structures ◽  
Brittle Layer

The role of a soft adhesive interlayer in determining critical conditions for fracture in brittle layer structures from indentation with hard spheres is investigated. A model transparent trilayer system consisting of a glass plate overlayer (thickness range 80 μm to 2 mm) joined to a glass plate underlayer (thickness 5.6 mm) by an epoxy adhesive (thickness range 5 μm to 8 mm), loaded at its top surface with a hard tungsten carbide sphere (radius 3.96 mm), facilitatesin situobservations of the crack initiation and propagation. Whereas in bulk glass fracture occurs by inner Hertzian cone cracking immediately outside the contact circle, the soft adhesive allows the overlayer glass plate to flex, initiating additional transverse fracture modes within the overlayer: downward-extending outer ring cracks at the top glass surface well outside the contact, and upward-extending radial cracks at the bottom glass surface (i.e., at the glass/adhesive interface) on median planes containing the contact axis. The top and bottom surfaces of the glass overlayers are given selective prebonding abrasion treatments to ensure uniform flaw states, so as to enable accurate comparisons between crack initiation conditions. The adhesive bonding is strong enough to preclude delamination in our layer system. Of the three transverse crack systems, the subsurface radials generates most easily in systems with large adhesive thicknesses (and smaller overlayer thicknesses). Semi-empirical relations are specified for the dependence of the critical loads for radial and ring cracking on adhesive as well as overlayer thickness, based on the assumption that crack initiation occurs when the maximum tensile stresses in the flexing glass plate exceed the bulk strength of the (abraded) glass. Coupled with the traditional “Auerbach's law” for cone crack initiation, these relations afford a basis for the construction of simple design diagrams for brittle layer systems joined by adhesives.

Role of indenter material and size in veneer failure of brittle layer structures

2007 ◽  
Vol 82B (1) ◽  
pp. 253-259 ◽  
Author(s):  
Sanjit Bhowmick ◽  
Juan José Meléndez-Martínez ◽  
Ilja Hermann ◽  
Yu Zhang ◽  
Brian R. Lawn
Keyword(s):  
Layer Structures ◽  
Brittle Layer

Metastability in SiGe/Si Strained-Layer Structures

1988 ◽  
Vol 116 ◽  
Author(s):  
Brian W. Dodson
Keyword(s):  
Experimental Data ◽  
Plastic Deformation ◽  
Crystal Growth ◽  
Strain Relaxation ◽  
Dislocation Dynamics ◽  
Strained Layer ◽  
Layer Structures ◽  
Standard Models ◽  
Stability Limits

AbstractThe physics governing growth and stability properties in SiGe/Si strainedlayer structures is reviewed. The role of metastability in crystal growth is outlined. Experimental data on stability limits and rates of strain relaxation are examined. We conclude that essentially all observations on relaxation of semiconductor strained-layer structures can be explained by standard models of plastic deformation adapted to the special conditions controlling dislocation dynamics in these structures.

Dislocation Nucleation in Heteroepitaxial Semiconducting Films

2009 ◽  
Vol 156-158 ◽  
pp. 251-259
Author(s):  
Bernard Pichaud ◽  
N. Burle ◽  
Michael Texier ◽  
C. Fontaine ◽  
V.I. Vdovin
Keyword(s):  
Dislocation Nucleation ◽  
Support Surface ◽  
Atomic Simulation ◽  
Gaas Substrates ◽  
Surface Steps ◽  
Layer Structures ◽  
Classical Models ◽  
Nucleation Centre ◽  
Original Dislocation

The nucleation of dislocation in semiconductors is still a matter of debate and especially in heteroepitaxial films. To understand this nucleation process the classical models of dislocation nucleation are presented and discussed. Two main points are then developed: emission of dislocations from surface steps and the role of point defects agglomeration on dislocation nucleation. Recent atomic simulation of half loops emission from surface steps and experimental evidences of anisotropic relaxation of GaInAs films deposited on vicinal (111) GaAs substrates strongly support surface steps as preferential sites for nucleation. In low temperature buffer layer structures (SiGe/Si) an original dislocation structure is observed which corresponds to the dislocation emission in different glide systems by a unique nucleation centre.

scholarly journals Permeability of multi-layer structures

e-Polymers ◽  
2004 ◽  
Vol 4 (1) ◽  
Author(s):  
Stanislav E. Solovyov ◽  
Anatoliy Ya. Goldman
Keyword(s):  
Polymer Matrix ◽  
Transmission Rate ◽  
Rate Equations ◽  
Heterogeneous Structure ◽  
Design Decisions ◽  
Practical Applications ◽  
Structural Identity ◽  
Layer Structures ◽  
Structural Transmission

Abstract In this paper we show that ‘permeability’ of a heterogeneous structure with mass transport and thermodynamic properties varying across its thickness is a misleading concept leading to incorrect results and design decisions while two structural transmission rate equations are recommended for practical applications. The notion of structural identity of multi-layer films is introduced to explain the apparent failure of the ‘permeability’ concept. Structural identity of two or more films means the same material sequence in the structure relative to separated environments with constant relative thickness of each corresponding layer. Structurally identical films indeed have the same ‘permeability’, however the notion of identity is shown to contradict the practical goals of multi-layer film design. Engineering examples are provided to demonstrate potential misuses of the ‘permeability’ concept in practical multi-layer design decisions. Correct problem statements and calculation procedures are included. Some general limitations of transmission rate equations are also discussed. These include the role of boundary conditions, temperature and concentration dependence of permeant diffusivity and solubility in a polymer matrix, the presence of co-permeants, surface sorption effects, film thickness, homogeneity of polymer matrix for permeation purposes and correct utilization of available data for predicting gas transport properties of multilayer films.

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