scholarly journals Nanoscale Elastoplastic Wrinkling of Ultrathin Molecular Films

2021 ◽  
Vol 22 (21) ◽  
pp. 11732
Author(s):  
Gianfranco Cordella ◽  
Antonio Tripodo ◽  
Francesco Puosi ◽  
Dario Pisignano ◽  
Dino Leporini
Keyword(s):  
Cross Section ◽  
Critical Strain ◽  
Compressive Strain ◽  
Contour Length ◽  
Molecular Films ◽  
Extended Version ◽  
Dominant Wavelength ◽  
Wavy Structure ◽  
Manufacturing Methods ◽  
Dynamics Simulations

Ultrathin molecular films deposited on a substrate are ubiquitously used in electronics, photonics, and additive manufacturing methods. The nanoscale surface instability of these systems under uniaxial compression is investigated here by molecular dynamics simulations. We focus on deviations from the homogeneous macroscopic behavior due to the discrete, disordered nature of the deformed system, which might have critical importance for applications. The instability, which develops in the elastoplastic regime above a finite critical strain, leads to the growth of unidimensional wrinkling up to strains as large as 0.5. We highlight both the dominant wavelength and the amplitude of the wavy structure. The wavelength is found to scale geometrically with the film length, λ∝L, up to a compressive strain of ε≃0.4 at least, depending on the film length. The onset and growth of the wrinkling under small compression are quite well described by an extended version of the familiar square-root law in the strain ε observed in macroscopic systems. Under large compression (ε≳0.25), we find that the wrinkling amplitude increases while leaving the cross section nearly constant, offering a novel interpretation of the instability with a large amplitude. The contour length of the film topography is not constant under compression, which is in disagreement with the simple accordion model. These findings might be highly relevant for the design of novel and effective wrinkling and buckling patterns and architectures in flexible platforms for electronics and photonics.

scholarly journals Towards a quantitative understanding of period-doubling wrinkling patterns occurring in film/substrate bilayer systems

2015 ◽  
Vol 471 (2173) ◽  
pp. 20140695 ◽  
Author(s):  
Yan Zhao ◽  
Yanping Cao ◽  
Wei Hong ◽  
M. Khurram Wadee ◽  
Xi-Qiao Feng
Keyword(s):  
Potential Energy ◽  
Critical Strain ◽  
Deformation Behaviour ◽  
Compressive Strain ◽  
Period Doubling ◽  
Careful Examination ◽  
Deformation State ◽  
Quantitative Understanding ◽  
Surface Patterns ◽  
Film Substrate

Compression of a stiff film on a soft substrate may lead to surface wrinkling when the compressive strain reaches a critical value. Further compression may cause a wrinkling–folding transition, and the sinusoidal wrinkling mode can then give way to a period-doubling bifurcation. The onset of the primary bifurcation has been well understood, but a quantitative understanding of the secondary bifurcation remains elusive. Our theoretical analysis of the branching of surface patterns reveals that the wrinkling–folding transition depends on the wrinkling strain and the prestrain in the substrate. A characteristic strain in the substrate is adopted to determine the correlation among the critical strain of the period-doubling mode, the wrinkling strain and the prestrain in an explicit form. A careful examination of the total potential energy of the system reveals that beyond the critical strain of period-doubling, the sinusoidal wrinkling mode has a higher potential energy in comparison with the period-doubling mode. The critical strain of the period-doubling mode strongly depends on the deformation state of the hyperelastic solid, indicating that the nonlinear deformation behaviour of the substrate plays a key role here. The results reported here on the one hand provide a quantitative understanding of the wrinkling–folding transition observed in natural and synthetic material systems and on the other hand pave the way to control the wrinkling mode transition by regulating the strain state in the substrate.

scholarly journals Topological Disentanglement of Linear Polymers under Tension

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2580
Author(s):  
Michele Caraglio ◽  
Boris Marcone ◽  
Fulvio Baldovin ◽  
Enzo Orlandini ◽  
Attilio L. Stella
Keyword(s):  
Theoretical Description ◽  
Contour Length ◽  
Topological Invariants ◽  
Linear Polymers ◽  
Torus Knots ◽  
Semiflexible Polymer ◽  
Theoretical Predictions ◽  
Dynamics Simulations ◽  
Remarkable Agreement ◽  
Number Of Particles

We develop a theoretical description of the topological disentanglement occurring when torus knots reach the ends of a semiflexible polymer under tension. These include decays into simpler knots and total unknotting. The minimal number of crossings and the minimal knot contour length are the topological invariants playing a key role in the model. The crossings behave as particles diffusing along the chain and the application of appropriate boundary conditions at the ends of the chain accounts for the knot disentanglement. Starting from the number of particles and their positions, suitable rules allow reconstructing the type and location of the knot moving on the chain Our theory is extensively benchmarked with corresponding molecular dynamics simulations and the results show a remarkable agreement between the simulations and the theoretical predictions of the model.

Experimentally Benchmarked Computational Fluid Dynamics Simulations of a 7×7 Array of Heated Rods Within a Square-Cross-Section Enclosure Filled With Rarefied Helium

2017 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Cross Section ◽  
Heat Generation ◽  
Maximum Temperature ◽  
Helium Pressure ◽  
Nuclear Fuel Assembly ◽  
Jump Model ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

Computational fluid dynamics simulations of a 7×7 array of heated rods within a square-cross-section enclosure filled with rarefied helium are performed for heat generation rates of 50 W and 100 W and various helium pressures ranging from 105 to 50 Pa. The model represents a section of nuclear fuel assembly between two consecutive spacer plates inside a nuclear canister subjected to during vacuum drying process. A temperature jump model is applied at the solid-gas interface to incorporate the effects of gas rarefaction at low pressures. The temperature predictions from simulations are compared to measured temperatures. The results showed that when helium pressure decreased from 105 to 50 Pa, the maximum temperature of the heater rod array increased by about 14 °C. The temperatures of the hottest rod predicted by simulations are within 4°C of the measured values for all pressures. The random difference of simulated rod temperatures from the measured rod temperatures are 3.33 °C and 2.62 °C for 100 W and 50 W heat generation rate.

Effect of Soil Restraint on the Buckling Response of Buried Pipelines

2010 ◽  
Author(s):  
Hiva Mahdavi ◽  
Shawn Kenny ◽  
Ryan Phillips ◽  
Radu Popescu
Keyword(s):  
Critical Strain ◽  
Mechanical Response ◽  
Ground Deformation ◽  
Compressive Strain ◽  
Local Buckling ◽  
Engineering Practice ◽  
Buried Pipelines ◽  
Limit States ◽  
Axial Thrust ◽  
New Criterion

Long-term large deformation geohazards can impose excessive deformation on a buried pipeline. The ground displacement field may initiate pipeline deformation mechanisms that exceed design acceptance criteria with respect to serviceability requirements or ultimate limit states. Conventional engineering practice to define the peak moment or compressive strain limits for buried pipelines has been based on the pipeline mechanical response for in-air conditions. This methodology may be conservative as it ignores the soil effect that imposes geotechnical loads and restraint on buried pipelines. The importance of pipeline/soil interaction and load transfer mechanisms that may affect local buckling of buried pipelines is not well understood. The authors previously developed a new criterion for local buckling strain of buried pipelines in stiff clay through response surface methodology (RSM) [1, 2]. In this paper the new criterion was compared with a number of available in-air based criteria to study the effect of soil restraint on local buckling response of buried pipelines. This criterion predicted larger critical strain than selected in-air based criteria which shows the significant influence of soil presence. The supportive soil effect is discussed. The soil restraining effect increases the pipeline bending resistance, when the pipeline is subjected to large displacement-controlled ground deformation. A correlation between Palmer’s et al. (1990) conclusion [3] and current study’s results has been made. The critical strain increases as the ratio between axial thrust and pipeline bending stiffness decreases.

Direct Observations of Twinning Dislocations in Iron Single Crystals

1971 ◽  
Vol 29 ◽  
pp. 104-105
Author(s):  
Keiichi Ogawa ◽  
Tomoyuki Takeuchi
Keyword(s):  
Single Crystals ◽  
Cross Section ◽  
Strain Field ◽  
Compressive Strain ◽  
Surface Layers ◽  
Fringe Contrast ◽  
Impact Compression ◽  
Direct Observations ◽  
Deformation Twins ◽  
Emery Paper

Experimental confirmations so far obtained of twinning dislocations in bcc metals have been limited to the observation of the phase change in the stacking fault fringe contrast. In the present experiments, twinning dislocations in iron crystals have been directly observed by their strain field contrast.Deformation twins were introduced into iron single crystals (1.8x6 mm2 in cross section) by an impact compression along <110> at 78°K. The compressive strain given was about 4%. The twinned specimens were mechanically sliced nearly parallel to the twin boundary {112} by a slitting saw. After mechanical polishing by emery paper, these slices were chemically polished to remove the damaged surface layers. The final thinning was performed by both jet and electrolytic polishing.

scholarly journals A novel framework for molecular characterization of atmospherically relevant organic compounds based on collision cross section and mass-to-charge ratio

2016 ◽  
Vol 16 (20) ◽  
pp. 12945-12959 ◽  
Author(s):  
Xuan Zhang ◽  
Jordan E. Krechmer ◽  
Michael Groessl ◽  
Wen Xu ◽  
Stephan Graf ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Cross Section ◽  
Cross Sections ◽  
Collision Cross Section ◽  
Molecular Structures ◽  
Molecular Signature ◽  
Charge Ratio ◽  
Dynamics Simulations ◽  
Chemical Class ◽  
Atmospherically Relevant

Abstract. A new metric is introduced for representing the molecular signature of atmospherically relevant organic compounds, the collision cross section (Ω), a quantity that is related to the structure and geometry of molecules and is derived from ion mobility measurements. By combination with the mass-to-charge ratio (m∕z), a two-dimensional Ω − m∕z space is developed to facilitate the comprehensive investigation of the complex organic mixtures. A unique distribution pattern of chemical classes, characterized by functional groups including amine, alcohol, carbonyl, carboxylic acid, ester, and organic sulfate, is developed on the 2-D Ω − m∕z space. Species of the same chemical class, despite variations in the molecular structures, tend to situate as a narrow band on the space and follow a trend line. Reactions involving changes in functionalization and fragmentation can be represented by the directionalities along or across these trend lines, thus allowing for the interpretation of atmospheric transformation mechanisms of organic species. The characteristics of trend lines for a variety of functionalities that are commonly present in the atmosphere can be predicted by the core model simulations, which provide a useful tool to identify the chemical class to which an unknown species belongs on the Ω − m∕z space. Within the band produced by each chemical class on the space, molecular structural assignment can be achieved by utilizing collision-induced dissociation as well as by comparing the measured collision cross sections in the context of those obtained via molecular dynamics simulations.

Analyzing the influence of median cross-section design on highway safety using vehicle dynamics simulations

2010 ◽  
Vol 42 (6) ◽  
pp. 1769-1777 ◽  
Author(s):  
Jason S. Stine ◽  
Bridget C. Hamblin ◽  
Sean N. Brennan ◽  
Eric T. Donnell
Keyword(s):  
Cross Section ◽  
Vehicle Dynamics ◽  
Highway Safety ◽  
Section Design ◽  
Dynamics Simulations

Tensile Behavior of Single-Crystal Nanosized Copper Beams with Voids

2016 ◽  
Vol 258 ◽  
pp. 53-56
Author(s):  
Solveig Melin ◽  
Aylin Ahadi ◽  
Per Hansson
Keyword(s):  
Single Crystal ◽  
Cross Section ◽  
Crystal Orientation ◽  
Tensile Behavior ◽  
Beam Size ◽  
Beam Length ◽  
Tensile Response ◽  
Final Failure ◽  
Dynamics Simulations ◽  
Crystallographic Orientations

The tensile response under displacement controlled loading of nanosized single crystal Cu beams, solid or holding square shaped through-the thickness voids, have been investigated through 3D molecular dynamics simulations using free-ware LAMMPS [1]. For the same beam size and void height, the void width along the beam length axis was varied. Two different crystallographic orientations were considered. It was found that, under some circumstances, voids were able to close and heal the beam cross section, causing final failure through necking in the region of the initial void. For other cases instead the void split in two, smaller voids that both eventually healed. A third scenario was that the void widened, splitting the beam in two ligaments that each necked individually. As expected, both defect geometry and crystal orientation influences the mechanical behavior.

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