Arbitrary Deformation Research Articles

Innovative approach for modelling gravity-induced signal path variations of VLBI radio telescopes

Gravitationally induced deformation of the receiving unit of radio telescopes used for Very Long Baseline Interferometry (VLBI) distorts the observations and biases the deduced products. As this deformation acts systematically and is individual for each radio telescope, the International VLBI Service for Geodesy and Astrometry (IVS) calls for gravitational deformation investigations to be able to correct VLBI data on the observation level. The most commonly used approach for modelling signal path variations was developed in 1988 during investigations at the 26-m VLBI radio telescope in Fairbanks (Alaska). This approach considers only homologous deformation of the receiving unit and takes into account three main deformation patterns affecting the signal path. For this reason, the measuring and modelling effort can be greatly simplified because the original spatial problem is reduced to a two-dimensional problem. However, more recent investigations refute the assumption of homogeneous deformation, because the receiver unit can be affected by arbitrary deformation patterns. Hence, identification and modelling as well as considering all deformation patterns that can be parameterised in a corresponding correction function require specific and more complex analysis approaches. In this contribution an innovative approach for modelling signal path variations is presented, based on Zernike polynomials. In contrast to the conventional approach, the proposed approach models the entire receiving unit spatially, and is not restricted to a homologous deformation pattern. This new approach has been successfully exercised on the 26-m radio telescope at the Mount Pleasant Radio Observatory Hobart (Tasmania, Australia). Despite the large dimensions of this radio telescope, the detected deformation is unexpectedly small, and leads to signal path variations of less than 2 mm.Graphical

Deformation of superintegrability in the Miwa-deformed Gaussian matrix model

We consider an arbitrary deformation of the Gaussian matrix model parametrized by Miwa variables za. One can look at it as a mixture of the Gaussian and logarithmic (Selberg) potentials, which are both superintegrable. The mixture is not, still one can find an explicit expression for an arbitrary Schur average as a linear transform of a polynomial made from the values of skew Schur functions at the Gaussian locus pk=δk,2. This linear operation includes multiplication with an exponential eza2/2 and a kind of Borel transform of the resulting product, which we call multiple and enhanced. The existence of such remarkable formulas appears intimately related to the theory of auxiliary K-polynomials, which appeared in superintegrable correlators at the Gaussian point (strict superintegrability). We also consider in great detail the generating function of correlators ⟨(TrX)k⟩ in this model, and discuss its integrable determinant representation. At last, we describe deformation of all results to the Gaussian β-ensemble. Published by the American Physical Society 2024

Hot deformation behavior and process optimization of TC4-DT alloy fabricated by wire and arc additive manufacturing with in-situ forging

The near net shape forging of a preform fabricated using additive manufacturing (AM) technique has attracted significant attention due to its exceptional material utilization rate. However, the complexity of the parts hinders its further development. This study investigated the hot deformation behavior of TC4-DT titanium alloy fabricated by wire and arc additive manufacturing (WAAM) with in-situ forging. The isothermal compression samples underwent homogenizing treatment to eliminate layer bright lines before being subjected to deformation at temperatures ranging from 800 to 950 °C and strain rates ranging from 0.01 to 1 s−1 with the height reduction of 60%. Subsequently, the hot deformation constitutive equations and hot processing map were established to analyze the characteristics of hot deformation and microstructure evolution. The results demonstrate that the hyperbolic sine constitutive equation considering strain can accurately predict flow stress under arbitrary deformation conditions, with an average relative error of 7.23%. Furthermore, microstructure analysis under different deformation conditions validated the applicability of the hot processing map, which identified preferable and easily achievable in-situ hot forging regions at temperatures between 900 and 950 °C and strain rates between 0.05 and 1 s−1 with the strain exceeded 0.4. Finally, WAAM combined with optimized in-situ hot deformation processing enables the production of macrostructures consisting of fully equiaxed prior-β grains while maintaining isotropy in mechanical properties, thereby providing a solid foundation for direct additive manufactured complex forgings featuring uniformly fine equiaxed grains and highly comprehensive properties.

Evolving non-aggregated ZIF-8 nanoparticles into hierarchically porous hollow carbon nanofibers for high-performance flexible zinc-ion hybrid supercapacitor

Zinc-ion hybrid supercapacitors are garnering widespread interest in wearable energy storage devices due to their high power density, intrinsic safety and cost-effectiveness. However, the primary obstacle to their progress lies in the scarcity of cathode materials that concurrently demonstrate excellent flexibility and high energy density. Herein, we deliberately design a coaxial electrospinning ZIF-8 derived hollow carbon nanofiber film electrode (C-PAN(ZIF-8)@PVP) to achieve high-performance flexible ZHSCs. The distinctive configuration of C-PAN(ZIF-8)@PVP electrode comprises a shell of homogeneously distributed ZIF-8 derived porous carbon nanoparticles, which are bound together by N-doped carbon fibers derived from polyacrylonitrile (PAN), and a channel through the fiber created by the decomposition of polyvinylpyrrolidone (PVP). This unique architecture coupled with N, O co-doping bestows ample electrolyte infiltration, complete exposure of active sites, and a rapid pathway for electron conduction, resulting in facilitated ion diffusion kinetics, abundant active sites and enhanced electronic conductivity of the C-PAN(ZIF-8)@PVP electrode. As a result, the assembled ZHSC delivers a high reversible capacity of 116 mAh g−1 at 0.1 A g−1 and remarkable capacity retention of 100% over 4000 cycles at 5 A g−1. Moreover, it exhibits exceptional mechanical flexibility, capable of delivering stable output under arbitrary deformation. The intricate structural design strategy offers valuable insights for the development of high-performance electrode materials.

Solvatochromic, solvent-assisted deformable, and self-reinforcing smart windows enabled by molecular reconfiguration

Smart materials in which transparency can be dynamically controlled have broad prospects in smart window applications. This study reports solvatochromic optical hybrid plastics designed using a carboxylated poly(methyl methacrylate) (PMAA)/poly(methyl methacrylate) (PMMA) molecular configuration for the development of self-reinforcing smart windows. The reversible transparency of this transparent plastic is 87.54 % (at 550 nm), which can be reduced to 1.69 % after water-assisted treatment and restored to 86.45 % after ethanol treatment, reversibly. Moreover, the toughness of PMMA/PMAA = 1:2 film is 0.59 ± 0.06 MJ m−3, 73.50 % higher than that of pure PMMA. The films also exhibit the capability of ethanol-assisted arbitrary deformation. This study offers a novel perspective on fabricating PMMA-based materials and their application in smart windows.

A Born Fourier Neural Operator for Solving Poisson’s Equation With Limited Data and Arbitrary Domain Deformation

A Born Fourier Neural Operator for Solving Poisson’s Equation With Limited Data and Arbitrary Domain Deformation

Analytical method for reconstructing the stress on a spherical particle from its surface deformation

The mechanical forces that cells experience from the tissue surrounding them are crucial for their behavior and development. Experimental studies of such mechanical forces require a method for measuring them. A widely used approach in this context is bead deformation analysis, where spherical particles are embedded into the tissue. The deformation of the particles then allows to reconstruct the mechanical stress acting on them. Existing approaches for this reconstruction are either very time-consuming or not sufficiently general. In this article, we present an analytical approach to this problem based on an expansion in solid spherical harmonics that allows us to find the complete stress tensor describing the stress acting on the tissue. Our approach is based on the linear theory of elasticity and uses an ansatz specifically designed for deformed spherical bodies. We clarify the conditions under which this ansatz can be used, making our results useful also for other contexts in which this ansatz is employed. Our method can be applied to arbitrary radial particle deformations and requires a very low computational effort. The usefulness of the method is demonstrated by an application to experimental data.

Mechanical reliable, NIR light-induced rapid self-healing hydrogel electrolyte towards flexible zinc-ion hybrid supercapacitors with low-temperature adaptability and long service life

Hydrogel electrolytes hold great potential in flexible zinc ion supercapacitors (ZICs) due to their high conductivity, good safety, and flexibility. However, freezing of electrolytes at low temperature (subzero) leads to drastic reduction in ionic conductivity and mechanical properties that deteriorates the performance of flexible ZICs. Besides, the mechanical fracture during arbitrary deformations significantly prunes out the lifespan of the flexible device. Herein, a Zn2+ and Li+ co-doped, polypyrrole-dopamine decorated Sb2S3 incorporated, and polyvinyl alcohol/ poly(N-(2-hydroxyethyl) acrylamide) double-network hydrogel electrolyte is constructed with favorable mechanical reliability, anti-freezing, and self-healing ability. In addition, it delivers ultra-high ionic conductivity of 8.6 and 3.7 S m−1 at 20 and −30 °C, respectively, and displays excellent mechanical properties to withstand tensile stress of 1.85 MPa with tensile elongation of 760%, together with fracture energy of 5.14 MJ m−3. Notably, the fractured hydrogel electrolyte can recover itself after only 90 s of infrared illumination, while regaining 83% of its tensile strain and almost 100% of its ionic conductivity during −30–60 °C. Moreover, ZICs coupled with this hydrogel electrolyte not only show a wide voltage window (up to 2 V), but also provide high energy density of 230 Wh kg−1 at power density of 500 W kg−1 with a capacity retention of 86.7% after 20,000 cycles under 20 °C. Furthermore, the ZICs are able to retain excellent capacity even under various mechanical deformation at −30 °C. This contribution will open up new insights into design of advanced wearable flexible electronics with environmental adaptability and long-life span.

Large-scale combined torsional and axial loading system (TorAx) – A new perspective on multiaxial testing of fracture and stress transfer in plain and reinforced concrete

Civil engineering structures are exposed to complex loading scenarios leading to multiaxial fracture and activation of stress transfer mechanisms along cracks controlled by combined deformations in two independent spatial directions (crack opening and crack sliding). Such multi-degree of freedom conditions cannot be properly investigated by state-of-the-art testing procedures. That is why – based on a thorough review of existing experimental procedures – this paper presents a novel testing methodology that applies shear via torsional loading and can simultaneously load specimens in axial direction (TorAx) to explore the material behavior before, during, and after macro-cracking. Independent control of both degrees of freedom allows the generation of arbitrary biaxial load or deformation paths. To prove the technical feasibility of the proposed testing method, several tests on thin-walled concrete tubes have been conducted. The obtained results proved uniformity of strain distribution along the tested ligament which guarantees several advantages (e.g., elimination of size/boundary effects and reduced scatter) over existing testing methods. With low costs (material/time) TorAx will serve as a benchmark for future studies under monotonic, cyclic, and fatigue loading. By experimentally quantifying all stress transfer mechanisms in one unifying test setup, an unbiased comparison of the individual mechanisms is possible, which is the first necessary step towards accelerated yet economical and reliable mechanical and numerical models.

Ultrahigh-Ionic-Conductivity, Antifreezing Poly(amidoxime)-Grafted Polyzwitterion Hydrogel for Facile Integrated into High-Performance Stretchable Flexible Supercapacitor.

Developing wearable supercapacitors (SCs) with high stretchability, arbitrary deformability, and antifreezing ability is still a challenge. In the present work, an ultrahigh-ionic-conductivity, antifreezing poly(amidoxime)-graft-polyzwitterion (PAO-g-PSBMA) hydrogel electrolyte is fabricated by grafting PSBMA in PAO. Owing to the abundant hydrophilic and high ionic adsorption capacity of amidoxime groups in PAO and zwitterion groups in PSBMA, the as-prepared PAO-g-PSBMA hydrogel can facilitate the dissociation of lithium salt and exhibit an ultrahigh ionic conductivity of 29.8 S m-1 at 25 °C and 3.4 S m-1 even at -30 °C. Employing mATi3C2Tx and mSTi3C2Tx, which contain small amounts of PAO-AGE and PAO-g-PSBMA dispersions, respectively, coated onto both sides of the PAO-g-PSBMA hydrogel, we followed a thermal treatment to facilely form integrated stretchable flexible SCs. The as-prepared SCs show an outstanding recoverable tensile stain of 80% and an excellent electrochemical stability under many types and times of arbitrary deformation. More importantly, as-prepared mATi3C2Tx- and mSTi3C2Tx-based SCs present fantastic antifreezing ability and excellent stability with 74.6 and 78.3% retention of the initial capacitance, respectively, even after 1000 times of stretching to 60% at -30 °C. This work offers a new strategy of using PAO-grafted polyzwitterion for obtaining an antifreezing stretchable SC, which shows a high potential for application in next-generation integrated stretchable devices in various fields.

MPM vs. CEL: Numerical modelling of penetration processes

MPM vs. CEL: Numerical modelling of penetration processes

Hot Deformation Behavior and Dynamic Recrystallization of a Medium Carbon Cr–Mo Steel for Class 16.8 Bolts

AbstractThis study investigates the hot workability of medium carbon Cr–Mo steels for manufacturing ultra-high strength bolts. The main purpose of this research is to establish a constitutive equation and a kinetic model of dynamic recrystallization of the material for industrial applications. Hot torsion tests were conducted at temperatures of 1173, 1273, and 1373 K and strain rates of 0.1, 0.5, 1.0, and 2.0/s. Strain rate sensitivities and work-hardening coefficients of the material were calculated at various strain rates and temperatures using the Fields–Backofen equation. Results indicated that the material’s strain rate sensitivities and work-hardening coefficients generally increased with temperature. Stress–strain curves showed a general variation depending on the strain rates and the deformation temperatures, with higher strain rates and lower temperatures resulting in increased flow stresses. However, peak stresses were not clearly observed due to the presence of Nb in the material. A constitutive equation for flow stresses was derived, with a thermal activation energy for deformation of 238.57 kJ/mol. Zener–Hollomon parameter was used to analyze the relationship between peak strains and critical strains, finding that the critical strains being about 0.17 times the peak strains. The volume fractions of dynamic recrystallization were estimated using an Avrami form of the kinetic equation, and the Avrami constants $$k$$ k and $$m$$ m were 0.84 and 6.89, respectively. The kinetic model of dynamic recrystallization that we developed can be applied to arbitrary deformation conditions, enabling the optimization of the hot rolling process for this material. Graphic Abstract

A unified determinant-preserving formulation for compressible/incompressible finite viscoelasticity

This paper presents a formulation alongside a numerical solution algorithm to describe the mechanical response of bodies made of a large class of viscoelastic materials undergoing arbitrary quasistatic finite deformations. With the objective of having a unified formulation that applies to a wide range of highly compressible, nearly incompressible, and fully incompressible soft organic materials in a numerically tractable manner, the viscoelasticity is described within a Lagrangian setting by a two-potential mixed formulation. In this formulation, the deformation field, a pressure field that ensues from a Legendre transform, and an internal variable of state Fv that describes the viscous part of the deformation are the independent fields. Consistent with the experimental evidence that viscous deformation is a volume-preserving process, the internal variable Fv is required to satisfy the constraint detFv=1. To solve the resulting initial–boundary-value problem, a numerical solution algorithm is proposed that is based on a finite-element (FE) discretization of space and a finite-difference discretization of time. Specifically, a Variational Multiscale FE method is employed that allows for an arbitrary combination of shape functions for the deformation and pressure fields. To deal with the challenging non-convex constraint detFv=1, a new time integration scheme is introduced that allows to convert any explicit or implicit scheme of choice into a stable scheme that preserves the constraint detFv=1 identically. A series of test cases is presented that showcase the capabilities of the proposed formulation.

The absolute nodal coordinate formulation in the analysis of offshore floating operations Part I: Theory and modeling

The analysis of flexible structures is essential to the design and safety in various offshore floating operations. It is challenging to take full considerations of the flexibility and large motion generated by the coupled floating systems under dynamic loads. In this paper series, the absolute nodal coordinate formulation (ANCF) is introduced to model and study the flexible cable in various types of floating operations. ANCF employs coordinate slope instead of angle to enable arbitrary large deformation in flexible cable without considering centrifugal and Coriolis effects. Linear expression of inertial force is derived and the hydrodynamic-structure and soil–structure interactions are also fully considered in dynamic analysis. The theory and modeling of dynamic flexible cable, multibody hydrodynamics and dynamics of floating systems, as well as the numerical calculation process in time domain are derived. The in-house code MiNos dedicated for flexible cable dynamics and program KraKen for multibody floating operation analysis were developed. Dynamic analysis of flexible cable in several floating operation scenarios by ANCF is performed and the in-house code MiNos is validated. The results show the advantage of ANCF for solving flexible structures with fewer elements and good accuracy as well as the robustness, which makes this method feasible and suitable for dynamic cable problems in most situations of floating offshore operations. Part I of this paper series contains the detailed theory and modeling of ANCF and a short review on methodology of hydrodynamics and dynamics of floating systems. Part II focus on the in-house code validation and analysis of flexible cable and mooring line in actual floating operation scenarios.

The absolute nodal coordinate formulation in the analysis of offshore floating operations, Part II: Code validation and case study

The absolute nodal coordinate formulation (ANCF) proposed in Part I of this paper series is applied to simulate flexible structures in the offshore operation analysis. The Part II of this paper series aims to validate the in-house code MiNos developed based on ANCF, a module of software KraKen, and employ the code to the static and dynamic analysis in time domain for flexible cables and mooring lines in actual operation scenarios. Three validation cases are conducted to demonstrate the accuracy and robustness of the in-house program for time domain analysis of arbitrary large deformation flexible structures. Furthermore, various floating operations, including crude export, production riser operation, and emergency disconnection of a turret are simulated by MiNos for both static and dynamic analysis, the results of the flexible cables and lines in these cases are compared with commercial software OrcaFlex. The high continuity of ANCF elements ensures high accuracy in the analysis of floating operation which comprises sophisticated vessel motions, wave loads, and soil contact. Besides, the inherent numerical problems of nonlinear dynamic analysis such as non-physics oscillations and peaks can be mitigated by ANCF. Therefore, ANCF could be considered as a promising theory for the dynamic analysis of flexible structure of cables and lines in marine operations.

Spatio-Temporal FFT Based Approach for Arbitrarily Moving Object Classification in Videos of Protected and Sensitive Scenes

Arbitrary moving object detection including vehicles and human beings in the real environment, such as protected and sensitive areas, is challenging due to the arbitrary deformation and directions caused by shaky camera and wind. This work aims at adopting a spatio-temporal approach for classifying arbitrarily moving objects. The proposed method segments foreground objects from the background using the frame difference between the median frame and individual frames. This step outputs several different foreground information. The mean of foreground images is computed, which is referred to as the mean activation map. For the mean activation map, the method employs the fast Fourier transform, which outputs amplitude and frequencies. The mean of frequencies is computed for moving objects in using activation maps of temporal frames, which is considered as a frequency feature vector. The features are normalized to avoid the problems of imbalanced features and class sizes. For classification, the work uses 10-fold cross-validation to choose the number of training and testing samples and the random forest classifier is used for the final classification of arbitrary moving and static videos. For evaluating the proposed method, we construct our dataset, which contains videos of static and arbitrarily moving objects caused by shaky cameras and wind. The results of the video dataset show that the proposed method achieves the state-of-the-art performance.

Fractal-based hydraulic model of unsaturated flow in deformable soils considering the evolution of pore size distribution

This paper presents a fractal-based hydraulic model for unsaturated flow, which includes the soil water retention curve (SWRC) and relative hydraulic conductivity curve (RHCC), and considers the evolution of pore size distribution (PSD) during soil deformation. In this model, soil PSD is assumed to follow the fractal scaling law, and soil deformation is characterized by a change in the fractal dimension and air entry value. By combining the intrinsic constraint between void ratio and fractal dimension, the fractal description of PSD evolution during volumetric deformation of soils is clearly defined, and the void ratio-dependent SWRC and RHCC are derived. All model parameters can be calibrated from the SWRC data of soils under two initial void ratios, and can then be used to predict the SWRC and RHCC of the soil under arbitrary deformation states. Eight experimental data sets, including SWRC and RHCC data under different initial void ratios, are used to evaluate the proposed model. Results show that: (1) the fractal-based hydraulic model can well describe the influence of volumetric deformation on the hydraulic properties of unsaturated soils, and (2) ignoring the evolution of PSD during soil compression will significantly overestimate the water retention ability and hydraulic conductivity of soils.

Laser-patterned PEDOT:PSS-aramid nanofiber composite electrodes for in-plane supercapacitors with high performance, shape-diversity and ultrahigh deformation resistance

The rapid development of portable and wearable modern electronics is in urgent need of the compatible energy storage devices, among which the flexible in-plane micro-supercapacitor (MSC) has emerged as a promising candidate. In this work, a facile and efficient laser-ablation technique was used to fabricate high performance metal-free all-solid-state in-plane MSCs with dimethyl sulfoxide-treated composite electrode (D-PA) composed of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS, PH1000) and aramid nanofibers. The effect of D-PA mass loading on the electrical and electrochemical properties of electrodes and devices was studied. The optimal MSC delivers high areal capacitance (15.4 mF/cm2 at 2 mV/s), superior charge/discharge cycling stability (capacitance hardly changes after 10,000 cycles), excellent rate performance (11.1 mF/cm2 at 3 mA/cm2) and ultrahigh resistance to arbitrary and extreme mechanical deformation (including circle-bending, free-twisting and multi-folding), which are superior to many state-of-the-art PH1000-based MSCs. Furthermore, performance of the shape-diverse device is easily tailored by series and/or parallel integration without usage of the metallic component. Such high performance MSC presents a great potential application in portable and wearable electronics even under severe deformed states.

Precisely Controllable Artificial Muscle with Continuous Morphing based on "Breathing" of Supramolecular Columns.

Skeletal muscles are natural motors executing sophisticated work through precise control of linear contraction. Although various liquid crystal polymersbased artificial muscles havebeen designed, the mechanism based on mainly the order-disorder transition usually leads to discrete shape morphing, leaving arbitrary and precise deformation a huge challenge. Here, one novel photoresponsive hemiphasmidic side-chain liquid crystal polymer with a unique "breathing" columnar phase that enables continuous morphing is presented. Due to confinement inside the supramolecular columnar assembly, the cooperative movements of side-chains and backbones generate a significant negative thermal expansion and lead to temperature-controllable muscle-like elongation/contraction in the oriented polymer strip. The irreversible isomerization of the photoresponsive mesogens results in the synergistic phototunable bending and high-contrast fluorescence change. Based on the orthogonal responses to heat and light, controllable arm-like bending motions of this material, which is applicable in constructing advanced artificial muscles or intelligent soft robotics, are further demonstrated.

Continuum effective Hamiltonian for graphene bilayers for an arbitrary smooth lattice deformation from microscopic theories

We provide a systematic real space derivation of the continuum Hamiltonian for a graphene bilayer starting from a microscopic lattice theory, allowing for an arbitrary inhomogeneous smooth lattice deformation, including a twist. Two different microscopic models are analyzed: first, a Slater-Koster like model and second, ab-initio derived model. We envision that our effective Hamiltonian can be used in conjunction with an experimentally determined atomic lattice deformation in twisted bilayer graphene in a specific device to predict and compare the electronic spectra with scanning tunneling spectroscopy measurements. As a byproduct, our approach provides electron-phonon couplings in the continuum Hamiltonian from microscopic models for any bilayer stacking. In the companion paper we analyze in detail the continuum models for relaxed atomic configurations of magic angle twisted bilayer graphene.