Uniaxial Elongation Research Articles

Coarse-Grained Molecular Dynamics Simulation of Epoxy-Based Chemically-Amplified Resist for MEMS Application

ABSTRACTA unique simulation method of epoxy-based chemically-amplified resist by coarse-grained molecular dynamics was proposed. The mechanical properties of an epoxy-based chemically-amplified resists with various cross-linking ratios were simulated using a newly developed coarse-grained molecular dynamics simulation that employs a bead-spring model. Models with the different cross-linking ratios were created in the molecular dynamics calculation step and uniaxial elongation simulations were performed. The results reveal that the simulated elastic modulus of the resist modeled by the bead-spring model with an extended angle bending potential depends on the cross-linking ratio; its dependency exhibits good agreement with that determined by nanoindentation tests.

In situ microwave characterization of microwire composites under mechanical stress

We present results of an experimental characterization of the dielectric properties and microwave absorption of rubber composite samples containing Fe4Co68.7Ni1B13Si11Mo2.3 amorphous microwires which are submitted to a low uniaxial tension. Measurements of the dielectric loss and microwave absorption as a function of strain over the frequency range of 300 MHz-6 GHz reveal that the uniaxial elongation randomly breaks wires at about 2.8% strain and this has for effect to decrease the loss factor for larger strain. Two possible mechanisms are identified to account for our observations, namely, the stress and shape effects. The ability to control this stretch breaking phenomenon will be instrumental to developing stress tunable microwire composites for sensing applications.

Linear and non-linear viscoelastic properties of ethylene vinyl acetate/nano-crystalline cellulose composites

This paper reports on the melt rheological properties of ethylene vinyl acetate containing between 0 and 10 wt.% of nano-crystalline cellulose (NCC). A complete set of rheological tests including frequency sweeps, shear transients, and uniaxial elongations was performed. Frequency sweeps showed that at low frequencies, a pseudo solid-like behavior was obtained for NCC concentrations higher than 5%. This behavior was related to hydrogen bonding between NCC particles and the creation of particle networks as the result of particle–particle interactions. For transient shear tests, all compositions presented a stress overshoot at high shear rates before reaching a steady state. It was found that the amplitude of this overshoot depends on both NCC content and shear rate. On the other hand, the time to reach the maximum was found to be highly shear rate dependent but concentration dependence was rather weak. For uniaxial extensional flow, higher extensional viscosity was observed with increasing NCC content. On the other hand, strain hardening was found to decrease with increasing NCC content.

Ageing of marine coating in natural and artificial seawater under mechanical stresses

In order to study the effect of a visco-elastic stress (tension and compression mode) onto the performances of a thick marine organic coating, free films and coated panels were immersed in natural seawater and in NaCl 3wt.% solution at room temperature (20°C), fixed temperature (45°C) or under cyclic temperatures. Free films were analysed using uniaxial elongation and Dynamic Mechanical Analysis (DMA) and the degradation of coated samples was investigated using Electrochemical Impedance Spectroscopy (EIS).In natural and artificial ageing, the glass transition temperature Tg and the Young modulus were found to increase with immersion time but different kinetics were observed depending on the ageing solution. For coated panels, the effect of tension was found to be harmful for the coating whereas the compression seemed to have a slight effect onto the coating degradation independently to the ageing environment.By comparing the degradation of coatings in natural and artificial sea water, it was shown that the kinetic of degradation was faster in artificial medium while the water absorption was larger in natural seawater. The results highlight the harmful impact of seasonal temperature variation in natural medium which could be explained by the development of internal stresses into the coating.

Perturbation solution for the viscoelastic flow around a rigid sphere under pure uniaxial elongation

We study the steady, three-dimensional creeping and viscoelastic flow around a rigid sphere subject to steady uniaxial extensional flow imposed at infinity. The viscoelastic response of the ambient fluid to the flow deformation is modeled using the second-order-fluid model, the Upper Convected Maxwell, the exponential affine Phan-Thien and Tanner and the Giesekus constitutive equations. A spherical coordinate system with origin at the center of the sphere is used to describe the flow field and the solution of the governing equations is expanded as a series in the Deborah number. The resulting sequence of differential equations is solved analytically up to second order and numerically up to fourth order in Deborah number by employing fully spectral representations for all the primary variables. In particular, Chebyshev polynomials are utilized in the radial coordinate and the Double Fourier Series in the longitudinal and latitudinal coordinates. The numerical results up to second-order agree within machine accuracy with the available analytical solutions clearly indicating the correctness and accuracy of the numerical method used here.

Linear viscoelastic model for elongational viscosity by control theory

Flows involving different types of chain branches have been modelled as functions of the uniaxial elongation using the recently generated constitutive model and molecular dynamics for linear viscoelasticity of polymers. Previously control theory was applied to model the relationship between the relaxation modulus, dynamic and shear viscosity, transient flow effects, power law and Cox–Merz rule related to the molecular weight distribution (MWD) by melt calibration. Temperature dependences and dimensions of statistical chain tubes were also modelled. The present study investigated the elongational viscosity. We introduced earlier the rheologically effective distribution (RED), which relates very accurately and linearly to the viscoelastic properties. The newly introduced effective strain-hardening distribution (REDH) is related to long-chain branching. This REDH is converted to real long-chain branching distribution by melt calibration and a simple relation formula. The presented procedure is very effective at characterizing long-chain branches, and also provides information on their structure and distribution. Accurate simulations of the elongational viscosities of low-density polyethylene, linear low-density polyethylene and polypropylene, and new types of MWDs are presented. Models are presented for strain-hardening that includes the monotonic increase and overshoot effects. Since the correct behaviour at large Hencky strains is still unclear, these theoretical models may aid further research and measurements.

Constitutive structure in coupled non-linear electro-elasticity: Invariant descriptions and constitutive restrictions

A constitutive framework for electro-sensitive materials in the context of non-linear elasticity is analyzed. Constitutive equations are given in terms of energy functions that depend on several invariants. The study includes both the analysis of the invariants, which are present in the energy functions, and the analysis of constitutive restrictions that have to be obeyed by the constitutive functions. Isotropic as well as non-isotropic electro-sensitive elastomers are studied. The set of invariants that describe each material model is analyzed under two homogeneous deformations: (i) an uniaxial elongation and (ii) a simple shear deformation. These deformations are chosen since they are relevant to specific experiments, from which one may try to fit constitutive equations. The constitutive restrictions developed are based on classical ones used for isotropic non-linear elastic materials, in particular, are based on the Baker–Ericksen inequality and the ellipticity condition.

The Behaviour of Three-Dimensional Polymers of Oligoester Acrylates under Conditions of Uniaxial Elongation

The influence on the stress–strain diagram of three-dimensional polymers of oligoester acrylates of the chemical nature of the groups (ester, carbonate, amide, urethane, and urea) in the oligomer block and the length of the latter was established.

Impacts of uniaxial elongation on the bandstructures of two-dimensional sonic crystals and associated applications

Influences of uniaxial elongation along the [11] direction of triangular and [10] direction of square sonic crystals under the constraint of conserved unit cell area are investigated by examining band structures and equi-frequency contours. Lowest-lying band gap of the triangular lattice observed at high filling fractions diminishes for negative elongation (compression), whereas another band gap develops at lower frequencies whose width reaches appreciable values for moderate elongation. The band gap of the square lattice, which appears at high filling fractions, is modified slightly with elongation. Frequency ranges of the bands, and thus the group velocities along the high-symmetry directions, vary with elongation which may be useful in applications like slow sound propagation. Elongation is observed to modify the equi-frequency contours significantly through reducing the lattice symmetry. The most prominent impact is the transformation of closed contours into open ones, whereas the rest are stretched either along or normal to the elongation axis of the 1st Brillouin Zone. This observation is utilized to implement wide-band all-angle self-collimation and superprism effect, which are demonstrated through Finite-Element computations.

Sustained Elongation of Sperm Tail Promoted by Local Remodeling of Giant Mitochondria in Drosophila

Sperm length in Drosophilidae varies from a few hundred microns to 6 cm as a result of evolutionary selection. In postcopulatory competition, longer sperm have an advantage in positioning their head closer to the egg. Sperm cell elongation can proceed in the absence of an axoneme, suggesting that a mechanism besides intraflagellar transport emerged to sustain it. Here we report that sperm elongation in Drosophila melanogaster is driven by the interdependent extension of giant mitochondria and microtubule array that is formed around the mitochondrial surface. In primary cultures of elongating spermatids, we demonstrated that the mitochondrial integrity and local dynamics of microtubules at the tail tip region are essential for uniaxial elongation of the sperm tail. Mitochondria-microtubule linker protein Milton accumulated on mitochondria near the tail tip and is required for the sliding movement of microtubules. Disruption of Milton and its associated protein dMiro, and of potential microtubule crosslinkers Nebbish and Fascetto, caused strong elongation defects, indicating that mitochondria-microtubule association and microtubule crosslinking are required for spermatid tail elongation. Mitochondria play unexpected roles in sperm tail elongation in Drosophila by providing a structural platform for microtubule reorganization to support the robust elongation taking place at the tip of the very long sperm tail. The identification of mitochondria as an organizer of cytoskeletal dynamics extends our understanding of mechanisms of cell morphogenesis.

Quasi-linear viscoelastic modeling of arterial wall for surgical simulation

Realistic soft tissue deformation modeling and haptic rendering for surgical simulation require accurate knowledge of tissue material characteristics. Biomechanical experiments on porcine tissue were performed, and a reduced quasi-linear viscoelastic model was developed to describe the strain-dependent relaxation behavior of the arterial wall. This information is used in surgical simulation to provide a realistic sensation of reduction in strength when the user holds a virtual blood vessel strained at different levels. Twelve pieces of porcine abdominal artery were tested with uniaxial elongation and relaxation test in both circumferential and longitudinal directions. The mechanical property testing system consists of automated environment control, testing, and data collection mechanism. A combined logarithm and polynomial strain energy equation was applied to model the elastic response of the specimens. The reduced relaxation function was modified by integrating a rational equation as a corrective factor to precisely describe the strain-dependent relaxation effects. The experiments revealed that (1) stress is insensitive to strain rate in arterial tissue when the loading rate is low, and (2) the rate of stress relaxation of arterial wall is highly strain dependent. The proposed model can accurately represent the experimental data. Stress-strain function derived from the combined strain energy function is able to fit the tensile experimental data with R(2) equals to 0.9995 in circumferential direction and 0.999 in longitudinal direction. Modified reduced relaxation function is able to model the strain-dependent relaxation with R(2) equals to 0.9686 in circumferential direction and 0.988 in longitudinal direction. The proposed model, based on extensive biomechanical experiments, can be used for accurate simulation of arterial deformation and haptic rendering in surgical simulation. The resultant model enables stress relaxation status to be determined when subjected to different strain levels.

Dough microstructure: Novel analysis by quantification using confocal laser scanning microscopy

The effect and the correlation of water addition to flour on the microstructure and viscoelastic properties of wheat flour dough were investigated using confocal laser scanning microscopy and a spectrum of rheological methods. Dough with water addition in the range of 52.5–70.0 g water 100 g −1 flour was investigated using a stickiness test, uniaxial elongation test, and fundamental rheology like small amplitude oscillatory shear measurement and a creep recovery test. A method for quantifying the microstructure of dough protein gained by CLSM was established with image processing and analysis. The complex shear modulus decreased rapidly with water addition due to the plasticization effect of water molecules and increased mobility in the continuous phases. Elastic behavior, determined as loss factor tan δ and relative elastic part J el decreased. Rheological tests showed high linear correlations with each other (r of |0.66|–|0.98|). Image analysis measurements (average size, area fraction, perimeter, circularity, and fractal dimension) showed high linear correlations (r of |0.66|–|0.85|) with water addition and rheological attributes like the complex shear modulus (r = 0.85) and J el (r = 0.86). CLSM in combination with image processing and analyzing has proven to be an applicable and powerful tool for examining and quantifying dough protein microstructure. Hence, it was possible to prove the dependency of rheology on the microstructure of dough.

Effect of strain rate on the behavior of three-dimensional polymers of oligoesteracrylates under the conditions of the uniaxial elongation

For three-dimensional polymers based on the dimethacryloil derivatives adipic and sebasinoil acids and dicarbonyloxyethylene we have established the influence of the deformation velocity (Ve) on their behaviour under the conditions of the uniaxial elongation. With the increase of Ve up to a distinct value of Vel, the ultimate stress σm for of the polymers grows, but at Ve > Vel the value of σm decreases. This phenomenon is explained. With the rise of Ve, the module of elasticity E1 increases and the curves σ(e) are shifted to the left along the e axis. The change of the character of the structural organization of three-dimensional polymers in the deformation process of their samples was established.

Constitutive modeling of complex interfaces based on a differential interfacial energy function

An important theory on the dynamics of complex interfaces is the Doi and Ohta theory where the interfacial contribution to the Cauchy stress tensor is determined from an interfacial conformation tensor. For a uniform deformation field in the Eulerian framework, Doi and Ohta adopted a decoupling approximation to reduce a fourth-order tensor into two second-order tensors and derived a differential equation governing the evolution of the interfacial conformation tensor. In this paper, a different formulation is presented for establishing the Cauchy stress tensor based on a path-independent interfacial energy function. By differentiating this interfacial energy function against a Lagrangian strain tensor, a nearly closed-form solution for the stress tensor was determined, involving only elementary algebraic and matrix operations. From this process, the stress-conformation relation proposed by Doi and Ohta is also confirmed from a thermodynamic perspective. The testing cases with uniaxial elongation and simple shear further showed improved fitting to the analytical or exact solutions.

A nonequilibrium Green’s function study of thermoelectric properties in single-walled carbon nanotubes

The phonon and electron transport in single-walled carbon nanotubes (SWCNT) are investigated using the nonequilibrium Green’s function approach. In zigzag SWCNT (n,0) with mod(n,3)≠0, the thermal conductance is mainly attributed to the phonon transport, while the electron only has few percentage contribution. The maximum value of the figure of merit (ZT) is about 0.2 in this type of SWCNT. The ZT is considerably larger in narrower SWCNT because of enhanced Seebeck coefficient. ZT is smaller in the armchair SWCNT, where Seebeck coefficient is small due to zero band gap. It is found that the cluster isotopic doping can reduce the phonon thermal conductance obviously and enhance the value of ZT. The uniaxial elongation and compress strain depresses phonons in whole frequency region, leading to the reduction in the phonon thermal conductance in whole temperature range. Interestingly, the elongation strain can affect the phonon transport more seriously than the compress strain, because the high frequency G mode is completely filtered out under elongation strain ϵ>0.05. The strain also has important effect on the subband edges of the electron band structure by smoothing the steps in the electron transmission function. The ZT is decreased by strain as the reduction in the electronic conductance overcomes the reduction in the thermal conductance.

Shape Recovery Versus Breakup of Deformed Droplets in a Polymer Blend after Uniaxial Extension

The morphology development in a PS/LLDPE 95/5 blend after uniaxial elongation at constant stress is investigated with a special attention on the influence of the temperature on the competition between shape recovery and droplet breakup. The lower the recovery temperature, the finer the morphology obtained, i.e. fibril breakup was preferred against shape recovery. This is due to a stronger retraction of matrix molecules at higher temperatures in early stages of recovery which forces the fibrils to shrink back to less deformed states and thus suppresses the droplet breakup. The elasticity of the blend was found to increase with temperature although the elasticity of pure PS is temperature independent. This is explained as a consequence of the temperature dependence of the morphology development.

An investigation of the relative effects of thickness and strength on the formability of steel sheet

The relative effects of thickness and material strength level on the in-plane forming limits of thin sheets of a low carbon Deep Drawing Steel has been experimentally investigated. To investigate the effects of sheet thickness at constant strength, the sheet material was chemically thinned from a starting thickness of either 0.318 mm or 0.310 mm to various levels down to 0.152 mm. In order to establish the effect of material strength level at a given thickness, the starting material was cold rolled to different thicknesses. Strength effects were deduced by comparing results of tests from cold rolled material with chemically thinned material at different thickness levels. Uniaxial tensile elongations and plane strain limit strains appear to be relatively unaffected by changing thickness at a given strength level, while the balanced biaxial stretching limit strain decreases gradually with decreasing thickness at constant strength. Increasing strength, however, dramatically reduces the tensile elongation and plane strain limit strain, while the balanced biaxial stretching limit decreases more gradually with increasing strength, but more rapidly than the balanced biaxial stretching limit strain decreases with decreasing sheet thickness at constant strength. As far as the authors are aware this is the first paper to investigate the effect of sheet thickness on formability when the strength of the sheet has been held constant as the thickness of the sheet is varied.

Coupled effects of size and uniaxial force on phase transitions in copper nanowires

By means of molecular dynamics simulations, we investigate solid–solid phase transitionsbetween the regular crystalline structure and the unbuckled atomic-sized one in ultrathincopper nanowires under uniaxial elongation and compression. The interatomic potentialemployed has been verified to be capable of describing the structural and mechanicalproperties of ultrathin copper nanowires. The coupled effects of size, uniaxialforce and relaxing temperature on the transitions have been revealed. Both thereported phase transition from the crystalline structure to the helical one andthe unexpected inverse behavior are found. At a relaxing temperature of 900 K,helical structures are dominant for effective diameters less than 0.8 nm, whilethe uniaxial force may lead to helical–crystalline phase transitions for thickerones. We also observe that the transition from a helical 12–7–1 nanowire to acrystalline [110] nanowire is much easier than the inverse transition. Our resultsdemonstrate the structural phase transitions between the crystalline structuresand the unbuckled atomic-sized ones of the force-suspended metal nanowires.

Behavior of Deformed Droplets in an Immiscible Polymer Blend: A Comparative Study of Electron Microscopy and Small‐Angle X‐Ray Scattering

AbstractThe deformation of dispersed droplets in a PS/LLDPE 95:5 blend during uniaxial elongation and after cessation of the flow was studied. The behavior of the dispersed droplets during elongation is in a good agreement with a prediction of the modified capillary number model using transient elongational viscosities. The phase structure changes after the elongation was studied in relaxation and recovery modes. The morphology was investigated using scanning electron microscopy and small‐angle X‐ray scattering. Thus the dimensions of the dispersed particles and their degree of orientation were estimated. It was shown that the SAXS as an integral method gives new additional information which is hardly accessible by SEM as a method providing local information about discrete locations in the sample. The results of both methods proved that the stress in the sample is a decisive parameter determining the morphology development after cessation of the flow.magnified image

In Situ Orientation Studies of a Poly(3-hydroxybutyrate)/Poly(ε-caprolactone) Blend by Rheo-Optical Fourier Transform Infrared Spectroscopy and Two-Dimensional Correlation Spectroscopic Analysis

In the present study, the orientation of a poly(3-hydroxybutyrate) (PHB)/poly(epsilon-caprolactone) (PCL) blend was monitored during uniaxial elongation by rheo-optical Fourier transform infrared (FT-IR) spectroscopy and analyzed by generalized two-dimensional correlation spectroscopy (2D-COS). The dichroism of the delta(CH(2)) absorption bands of PHB and PCL was employed to determine the polymer chain orientation in the PHB/PCL blend during the elongation up to 267% strain. From the PHB and PCL specific orientation functions it was derived that the PCL chains orient into the drawing direction while the PHB chains orient predominantly perpendicular to the applied strain. To extract more detailed information about the polymer orientation during uniaxial elongation, 2D-COS analysis was employed for the dichroic difference of the polarization spectra recorded during the drawing process. In the corresponding synchronous and asynchronous 2D correlation plots, absorption bands characteristic of the crystalline and amorphous regions of PHB and PCL were separated. Furthermore, the 2D-COS analysis revealed that during the mechanical treatment the PCL domains orient before the PHB domains.