Uniaxial Elongation Research Articles

Nanostructure and Photovoltaic Potential of Plasmonic Nanofibrous Active Layers.

Nanofibrous active layers offer hierarchical control over molecular structure, and the size and distribution of electron donor:acceptor domains, beyond conventional organic photovoltaic architectures. This structure is created by forming donor pathways via electrospinning nanofibers of semiconducting polymer, then infiltrating with an electron acceptor. Electrospinning induces chain and crystallite alignment, resulting in enhanced light-harvesting and charge transport. Here, the charge transport capabilities are predicted, and charge separation and dynamics are evaluated in these active layers, to assess their photovoltaic potential. Through X-ray and electron diffraction, the fiber nanostructure is elucidated, with uniaxial elongation of the electrospinning jet aligning the polymer backbones within crystallites orthogonal to the fiber axis, and amorphous chains parallel. It is revealed that this structure forms when anisotropic crystallites, pre-assembled in solution, become oriented along the fiber- a configuration with high charge transport potential. Competitive dissociation of excitons formed in the photoactive nanofibers is recorded, with 95%+ photoluminescence quenching upon electron acceptor introduction. Transient absorption studies reveal that silver nanoparticle addition to the fibers improves charge generation and/or lifetimes. 1ns post-excitation, the plasmonic architecture contains 45% more polarons, per exciton formed, than the bulk heterojunction. Therefore, enhanced exciton populations may be successfully translated into additional charge carriers.

Developable forming of high-strength corrugated sheet metal

The classical theory of folded developables suggests that curved crease folding can be applied to sheet metal of high strength to manufacture parts with complex geometries. However, its application has been limited to sheet metals with low strength and requires grooving or perforation of the material at the fold lines. Applying the geometrical concept otherwise remains unexplored despite its potential in sheet metal-intensive industries like automotive, transportation, and construction. The current study introduces a novel sheet metal forming technique called developable forming. The theory of folded developables is applied to design a die tool for flange drawing a developable-shaped steel sheet. A developable connection is produced from high-strength material without resorting to thickness accommodation techniques. Experimental findings establish that the novel process does not follow the premises of the theory of folded developables. New shape effects are observed and the terms curving and coning are introduced to describe these. Additionally, significant redundant strains are identified in the flange, highlighting the different deformation modes in the developable forming process. A higher formability is achieved for a material with limited uniaxial elongation highlighting the need for further investigation on the mechanisms involved in the novel process.

Pushing magnetic spirals beyond room temperature by reducing the uniaxial pyramidal elongation in layered Cu/Fe perovskites

The impact of a 3d divalent substitution for Cu using M2+ ions not presenting elongated MO5 pyramids has been explored in YBaCuFeO5 as a new strategy to upgrade the magnetic properties of this high-temperature spiral magnet and potential multiferroic. In this work we investigate the incidence of the Cu2+ with Co2+ substitution in YBa(Cu1−xCox)FeO5 compounds in which B-site disorder is kept invariant (disorder nd≈36%). The study validates the reduction of the uniaxial elongation distortion at Cu sites as an efficient alternative way to disorder that enables one to enhance the thermal stability of the spiral order. In addition, the rotation plane of the helix is reoriented by the Cu/Co substitution and nearby the triple point (when TS is maximal) the spiral order adopts an almost complete cycloidal magnetic configuration. These results lay the foundation of a new mechanism to tune the stability of the magnetic spirals in layered perovskites based on reducing the uniaxial elongation associated to the (4+1)-coordination of Cu2+ ions in square CuO5 pyramids. Published by the American Physical Society 2024

Visualization of crack generation of vulcanized butadiene rubber under uniaxial elongation by atomic force microscopy nanomechanics

Crack resistance performance by oxidation must be considered in rubber product development because cracks are the starting point for fracture. When rubber is stretched extensively, mechanical stresses can break apart its molecular chains, generating radicals and promoting mechanochemical oxidation. This reaction is one of the causes of cracking. However, it is not fully understood how cracks are formed in vulcanized rubber with an inhomogeneous crosslinking structure. Atomic force microscopy (AFM) nanomechanics has been utilized to observe vulcanized butadiene rubber in an elongated state. It was shown that crack generation is related to mechanochemical oxidation, and that the cracks could be clearly visualized as stress-concentrated regions at the nanoscale. Additionally, crack formation is accelerated with increasing elongation of the rubber. This demonstrates that AFM nanomechanics is an effective tool for observation of the generation of cracks associated with mechanochemical oxidation in rubber materials.

Microstructure, compressive performance and wear resistance of pure molybdenum additively manufactured via laser powder bed fusion

Pure molybdenum (Mo) additively manufactured via laser powder bed fusion is challenging due to its high laser reflectivity and sensitivity to cracking. To achieve crack-free pure Mo alloy and enhance production efficiency, this study employs a high-power (350 W) printing process with a layer thickness of 30 μm, resulting in the successful fabrication of pure Mo with a relative density of 99.2%. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) revealed that the pure Mo specimens prepared by LPBF process exhibited different preferential grain orientations and lattice distortions in various building directions, with higher texture strength on the XOZ plane and greater lattice distortion on the XOY plane. The hardness of the pure Mo specimens reached 208 HV, with uniaxial compressive strength and elongation at 535 MPa and 20.9%, respectively, surpassing existing literature values by 37.2% and 8.0%. Furthermore, the dry friction behavior and mechanism of LPBF-manufactured pure molybdenum were investigated for the first time and compared to traditional powder metallurgy. Consequently, this research offers valuable insights for manufacturing crack-free LPBF pure molybdenum components with 30 μm layer thickness, boasting superior mechanical and wear resistance.

Deformation induced evolution of plasmonic responses in polymer grafted nanoparticle thin films.

Multi-functional nanoparticle thin films are being used in various applications ranging from biosensing to photo-voltaics. In this study, we integrate two different numerical approaches to understand the interplay between the mechanical deformation and optical response of polymer grafted plasmonic nanoparticle (PGPN) arrays. Using numerical simulations we examine the deformation of thin films formed by end-functionalised polymer grafted nanoparticles subject to uniaxial elongation. The induced deformation causes the particles in the thin film network to rearrange their positions by two different mechanisms viz. sliding and packing. In sliding, the particles move in the direction of induced deformation. On the other hand, in packing, the particles move in a direction normal to that of the induced deformation. By employing a Green's tensor formulation in polarizable backgrounds for evaluating the optical response of the nanoparticle network, we calculate the evolution of the plasmonic response of the structure as a function of strain. The results indicate that the evolution of plasmonic response closely follows the deformation. In particular, we show that the onset of relative electric field enhancement of the optical response occurs when there is significant rearrangement of the constituent PGPNs in the array. Furthermore, we show that depending on the local packing/sliding and the polarization of the incident light there can be both enhancement and suppression of the SERS response.

Thixo-elastoviscoplastic modeling of human blood

We propose an enhanced model for the rheological characterization of human blood that accounts for thixotropy, viscoelasticity, and yield-stress. Blood plasma is assumed to act as a Newtonian solvent. We introduce a scalar variable, λ, to macroscopically describe the structure of blood. The temporal evolution of λ is governed by an equation that accounts for aggregation of red blood cells and breakdown of rouleaux structures. We introduce a Gaussian function that qualitatively describes experimental findings on rouleaux restructuring and the expression that was proposed by Stephanou and Georgiou for the breakdown term. The constitutive equation for stresses is based on the elastoviscoplastic formalism by Saramito. However, the max term of the viscoplastic deformation rate has been replaced by a continuous function of λ to account for smooth solid-fluid transition, following the experimental evidence. The continuous yielding description provides improved rheological predictions, especially in small amplitude oscillatory shear. The model predicts finite viscous dissipation at small amplitude oscillation, as we would expect from a gel material-like human blood. Overall, it has nine adjustable parameters that are fitted simultaneously to experimental data by nonlinear regression. The model can accurately predict numerous flow conditions: steady shear, step shear, hysteresis loops, and oscillatory shear. We compare this model (TEVP 9) to our previous formulation for human blood (TEVP 11), and we show that the predictions of the new model are more accurate, despite using fewer parameters. We provide additional predictions for uniaxial elongation, which include finite normal stress difference, extensional hardening at large values of the extensional rate, and extensional thinning at extremely large extensional rates.

Tensile Stress Reduction and Strain Concentration of Epoxy Resin Caused by Heterogeneity: A Multiscale Approach Combining Molecular Dynamics Simulation and Finite Element Method.

In this study, we investigated the effect of heterogeneity on the mechanical properties of epoxy resin by combining coarse-grained molecular dynamics (CG-MD) and finite element method (FEM) simulations. To evaluate the heterogeneity effect in the uniaxial elongation, heterogeneous and homogeneous FEM models of micrometer-scale cubic epoxy resin were constructed. For the heterogeneous FEM model, parameters of nanometer-scale elements were determined by CG-MD simulations, where nanometer-scale blocks have different cross-linked structures. For the homogeneous FEM model, the averaged parameters were used for all elements. The calculated stress-strain (S-S) curves of the heterogeneous model exhibit similar tensile stress values when compared to the experimental data, whereas the homogeneous model yields notably higher values. Moreover, a clear strain concentration associated with the formation of the shear band-like structure was observed in the heterogeneous model and not in the homogeneous model.

Structural and morphological changes at initial state under uniaxial elongation of rolled polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) membranes, which are prepared by a biaxial stretching process of rolled sheets, have a porosity structure consisting of nodes and fibrils, and exhibits a unique mechanical behavior. We investigated the differences in deformation behavior of rolled PTFE sheets between the rolling and the cross directions using synchrotron radiation in situ WAXD and in situ SAXS measurements. The mechanical anisotropy for rolled PTFE sheets results from a planar or strip-biaxial deformation mode. The rolled PTFE sheets showed an extended chain crystal (ECC) structure. According to in situ WAXD profiles and 2D-SAXS patterns during deformation, the stretching in the rolling direction (RD) causes the fibrillation accompanied with the mechanical yielding, at which the stretching in the RD resulted in pore expansion and lattice distortion rather than obvious chain orientation. The direction of the pore expansion changed to the cross direction (CD) when stretching perpendicular to the RD. We found a positive dependence between the pore size in CD and the average molecular weight of PTFE sheets.

Predicting High-Density Polyethylene Melt Rheology Using a Multimode Tube Model Derived Using Non-Equilibrium Thermodynamics.

Based on the Generalized bracket, or Beris-Edwards, formalism of non-equilibrium thermodynamics, we recently proposed a new differential constitutive model for the rheological study of entangled polymer melts and solutions. It amended the shortcomings of a previous model that was too strict regarding the values of the convective constraint release parameter for the model not to violate the second law of thermodynamics, and it has been shown capable of predicting a transient stress undershoot (following the overshoot) at high shear rates. In this study, we wish to further examine this model's capability to predict the rheological response of industrial polymer systems by extending it to its multiple-mode version. The comparison with industrial rheological data (High-Density Polyethylene resins), which was based on comparison with experimental data available in (a) Small Amplitude Oscillatory shear, (b) start-up shear, and (c) start-up uniaxial elongation, was noted to be good.

A physics-based defect tolerant design approach to predict the tensile performance of aluminium alloys with a defect

Inherent manufacturing defects are observed in additively manufactured and casted metallic alloys. During loading, the stress concentration due to defect results in poor tensile ductility and fatigue performance. A physics-based defect tolerant design approach is used in the present work to calculate the uniaxial tensile performance of cast ADC12 Aluminum alloys. The proposed model elucidates the correlation between tensile ductility and the dimensions of material defects. It derives a material constant referred to as the critical defect size, which is determined through a combination of uniaxial tensile testing on specimens with defects and employing finite element simulations. The proposed approach calculates well the tensile properties such as complete tensile stress–strain curve, ultimate tensile strength, and uniaxial tensile elongation.

Intermediate Encoding Layers for the Generative Design of 2D Soft Robot Actuators: A Comparison of CPPN’s, L-Systems and Random Generation

This paper introduced a comparison method for three explicitly defined intermediate encoding methods in generative design for two-dimensional soft robotic units. This study evaluates a conventional genetic algorithm with full access to removing elements from the design domain using an implicit random encoding layer, a Lindenmayer system encoding mimicking biological growth patterns and a compositional pattern producing network encoding for 2D pattern generation. The objective of the optimisation problem is to match the deformation of a single actuator unit with a desired target shape, specifically uni-axial elongation, under internal pressure. The study results suggest that the Lindenmayer system encoding generates candidate units with fewer function evaluations than the traditional implicitly encoded genetic algorithm. However, the distribution of constraint and internal energy is similar to that of the random encoding, and the Lindenmayer system encoding produces a less diverse population of candidate units. In contrast, despite requiring more function evaluations than the Lindenmayer System encoding, the Compositional Pattern Producing Network encoding produces a similar diversity of candidate units. Overall, the Compositional Pattern Producing Network encoding results in a proportionally higher number of high-performing units than the random or Lindenmayer system encoding, making it a viable alternative to a conventional monolithic approach. The results suggest that the compositional pattern producing network encoding may be a promising approach for designing soft robotic actuators with desirable performance characteristics.

Calculation of Strain Energy Density Function Using Ogden Model and Mooney-Rivlin Model Based on Biaxial Elongation Experiments of Silicone Rubber.

Strain energy density functions are used in CAE analysis of hyperelastic materials such as rubber and elastomers. This function can originally be obtained only by experiments using biaxial deformation, but the difficulty of such experiments has made it almost impossible to put the function to practical use. Furthermore, it has been unclear how to introduce the strain energy density function necessary for CAE analysis from the results of biaxial deformation experiments on rubber. In this study, parameters of the Ogden and Mooney-Rivlin approximations of the strain energy density function were derived from the results of biaxial deformation experiments on silicone rubber, and their validity was verified. These results showed that it is best to determine the coefficients of the approximate equations for the strain energy density function after 10 cycles of repeated elongation of rubber in an equal biaxial deformation state, followed by equal biaxial elongation, uniaxial constrained biaxial elongation, and uniaxial elongation to obtain these three stress-strain curves.

Stretch-orientation-induced reduction of friction in well-entangled bidisperse blends: a dual slip-link simulation study

We investigated the rheological properties of bidisperse entangled-polymer blends under high-deformation-rate flows by slip-link simulations with a friction reduction mechanism. The friction reduction mechanism induced by the stretch and orientation (SORF) is important to predict the viscoelasticity under uniaxial elongational flows. To test the applicability of this mechanism for bidisperse systems, we incorporated an expression of friction reduction (Yaoita et al. Macromolecules 45:2773–2782 2012) into the Doi-Takimoto slip-link model (DT model) (Doi and Takimoto Philos Trans R Soc Lond A 361:641–652 2003). For six experimental bidisperse systems, i.e., four polystyrene blends and two polyisoprene blends, the extended DT model where the order parameter of the friction reduction mechanism is evaluated through the component averages succeeds in reproducing the data under uniaxial elongation and shear. This success is due to the suppression of the stretch of the longer chains using the statistical average over each component. Through this study, the SORF expression improves the rheological prediction for bidisperse entangled polymer melts under uniaxial elongational flows with strain rates comparable to or larger than the inverse of the Rouse relaxation time of the longer chains. Additionally, the predictions with the SORF using the component average for the stretches reproduce the steady viscosities because under elongational flows, the states of the components with different molecular weights clearly differ from each other depending on their Rouse relaxation time. The finding means that for chain dynamics, the friction coefficient is determined by the state of the surrounding polymer chains and the state of the chain.

Improved convergence based on two-point Padé approximants: Simple shear, uniaxial elongation, and flow past a sphere

We investigate the performance of two-point Padé approximants on the truncated series solutions for the shear and elongational viscosities (obtained directly from the exact solutions or by asymptotic methods) for viscoelastic flows modeled with the Giesekus constitutive equation. Τhe major dimensionless groups are the Weissenberg number ( Wi), the Giesekus mobility parameter ( α), and the ratio of the polymer viscosity to the total viscosity of the fluid ( ηp) in terms of which the exact analytical solutions for the shear and elongational viscosities are found. The exact solutions are used to derive truncated series expansions in terms of the Weissenberg number at the Newtonian limit (zero Wi) and in terms of the inverse of the Weissenberg number at the purely elastic limit (infinite Wi). These series are then used to construct low- and high-order two-point diagonal Padé approximants. It is found that both the low- and high-order formulas predict the right trends over the entire range of Wi, from the Newtonian limit to the pure elastic limit. As expected, the high-order formula is much more accurate than the low-order formula. The results show that viscoelastic phenomena, such as shear thinning and extensional thickening, at any value of the Weissenberg number can be predicted analytically with acceptable accuracy using the proposed two-point Padé non-linear analysis. Finally, a fourth-order formula in terms of the Weissenberg number (or in terms of the Deborah number) for the drag force on a rigid sphere that translates with constant speed in a Giesekus fluid is also provided along with a discussion regarding the missing information from the literature, that is, required to perform the proposed non-linear analysis.

Threading Polystyrene Stars: Impact of Star to POM‐POM and Barbwire Topology on Melt Rheological and Foaming Properties

AbstractPolymer topology highly impacts rheological melt and foaming properties. Grafting sidechains onto a linear polymer typically results in shear thinning and strain hardening in elongation flow. To study the influence of an increasing number of covalently connected polystyrene (PS) starsswith a linear PS chain (Mw,PS= 90 kg mol−1), low‐disperse branched polymers withsranging from one to four are synthesized. Each star contains approximately 12 sidechains with a length ofMw,a≈ 25 kg mol−1. Oscillatory shear measurements indicated that the zero‐shear viscosityη0scales withη0 ≈ atTref= 180 °C. Moreover, uniaxial elongation rheology allows determining the strain hardening factorSHF, which varies betweenSHF= 2–135, with increasings. Foaming experiments revealed that combining viscosity reduction with the improvement of stretchability promotes higher volume expansion ratios (VER= 3.21–10.41) and the formation of larger cells (D= 4.8–14.8 µm).

Comb and Branch‐on‐Branch Model Polystyrenes with Exceptionally High Strain Hardening Factor SHF > 1000 and Their Impact on Physical Foaming

AbstractThe influence of topology on the strain hardening in uniaxial elongation is investigated using monodisperse comb and dendrigraft model polystyrenes (PS) synthesized via living anionic polymerization. A backbone with a molecular weight of Mw,bb = 310 kg mol−1 is used for all materials, while a number of 100 short (SCB, Mw,scb = 15 kg mol−1) or long chain branches (LCB, Mw,lcb = 40 kg mol−1) are grafted onto the backbone. The synthesized LCB comb serves as precursor for the dendrigraft‐type branch‐on‐branch (bob) structures to add a second generation of branches (SCB, Mw,scb ≈ 14 kg mol−1) that is varied in number from 120 to 460. The SCB and LCB combs achieve remarkable strain hardening factors (SHF) of around 200 at strain rates greater than 0.1 s−1. In contrast, the bob PS reach exceptionally high SHF of 1750 at very low strain rates of 0.005 s−1 using a tilted sample placement to extend the maximum Hencky strain from 4 to 6. To the best of the authors’ knowledge, SHF this high have never been reported for polymer melts. Furthermore, the batch foaming with CO2 is investigated and the volume expansions of the resulting polymer foams are correlated to the uniaxial elongational properties.

STUDY OF RIB KNITS COURSEWISE TENSILE PROCESS

Stretchability of knitwear is one of the most important factors of wearing comfort. Elasticity of knitted structures in course wise direction is usually higher than along wales and often characterized by crosswise shrinkage. Existing methods of knitting program development do not consider the real rate of wale wise shrinkage of rib knitted structure under the course wise extension. During the study experimental research has been carried out to fulfill empirical data on the relationship between samples’ length and width under uniaxial course wise elongation. A range of samples of rib 1×1, 2×2, 3×3, 4×4 and 5×5 knits, made of cotton, bamboo, polyacrylonitrile (PAN), wool/acrylic blend and wool yarn, were stretched with a tensile machine WDW-05M. In the process of stretching the width of each specimen was defined in the moments of extension by 50, 100, 150, 200, 250 and 300 per cent. It has been found that linear approximation can be applied to describe the dependence of specimen’s width on its relative course wise elongation. It was found that the stitch height/width ratio changes unevenly. In the beginning of the process of course wise stretching of a rib knitted structure, it does exist, such an interval, where an increase of the knit’s linear size along the courses occurs without a significant shrinkage in the wale wise direction. It is suggested to name the upper limit of this interval as “unidimensional extension limit” and define it as an extension of a standard (100×50mm) specimen, at which its width decreases by 10%. It was found as well that the value of this index significantly depends on the ribbing variation and much less on the type of raw materials

Forming a composite model for non-Brownian suspensions

We propose a two-part composite model to describe the rheology of non-Brownian suspensions. The stress response is composed of the sum of a matrix part (Tm) described by a multi-mode Oldroyd-B model and a second component (To) which is assumed to be a Thompson–Souza Mendes model. We show how to determine the parameters to satisfy agreement with experiments in steady viscometric flows, uniaxial elongation flows, small to medium size sinusoidal strains, and reversing shear strain rates. Where possible, comparison is made with computations. Agreement with experiments and computations is reasonable, but more accurate computations and experiments would be welcome.

Sustainable Synthesis of Non‐Isocyanate Polyurethanes Based on Renewable 2,3‐Butanediol

AbstractIn this work, three different cyclic carbonates are obtained from renewable diols and transformed into carbamates by reacting them with renewable 11‐amino undecanoic acid methyl ester to synthesize non‐isocyanate poly(ester urethane)s in a sustainable manner. A procedure using 2,3‐butanediol (2,3‐BDO) as a renewable starting material to synthesize a cyclic carbonate with dimethyl carbonate (DMC) is introduced, catalyzed by 1,5,7‐triazabicylco[4.4.0]dec‐5‐ene (TBD). Three purification strategies, i.e., column chromatography, extraction, and distillation, are compared regarding their E‐Factors. Propylene glycol (PG) and ethylene glycol (EG) are used as alternative starting materials to broaden the substrate scope and compare material properties, their cyclic carbonates likewise react to carbamates with 11‐amino undecanoic acid methyl ester. All carbamates are then polymerized in a bulk polycondensation reaction, yielding non‐isocyanate polyurethanes (NIPUs), specifically poly (ester urethane)s, with molecular weights (Mn) up to 10 kDa. Complete characterization is reported using differential scanning calorimetric (DSC), size exclusion chromatographic measurements (SEC), 1H‐NMR as well as IR spectroscopy. The rheological properties of the poly(ester urethane)s are investigated in the framework of small amplitude oscillatory shear (SAOS) and uniaxial elongation.