Time-dependent Material Research Articles

Mechanical Response of Epoxy Resin-Flax Fiber Composites Subjected to Repeated Loading and Creep Recovery Tests.

Flax fiber-reinforced plastics have an innate eco-friendly nature due to the fiber reinforcement and reduced energy requirements in fabrication when compared to current fiber reinforced composite materials. They possess a complex time-dependent material behavior, which is investigated in the present paper. A composite material with flax fiber reinforcement on the load direction, embedded in an epoxy resin matrix, was studied. The procedures used were tensile tests, repeated loading-recovery, and creep-recovery tests, which were meant to expose the components of the response with respect to stress level and load duration. The results showed an elastic bi-linear behavior, a yield point at approximately 20% of the ultimate tensile stress, and tensile moduli of 35.9 GPa and 26.3 GPa, before and after yield. This is coupled with significant non-linear viscoelastic and, after yield, viscoplastic components, accounting for up to 14% of the strain response. The behavior is inherited from both the matrix and the fiber reinforcement and is attributed to the amorphous nature of the matrix combined with the microstructural re-organization of the fiber under load, which are partially reversible.

Effect of in-plane compression on the non-harmonic resonance of moderately thick time-dependent plates

This study investigates the nonlinear p-delta analysis and introduces a viscoelastic plate non-harmonic resonance in which the critical displacement will be several times more than the displacement at time zero. An innovative closed-form solution of Mindlin viscoelastic plate, under a dynamic out-of-plane exponential load decreasing over time and a constant in-plane compressive load is presented. The displacement vector of the Mindlin viscoelastic plate is explicitly formulated in space and time domains. Also, the critical time in which the non-harmonic resonance occurs is calculated. The stress–strain relationship of the viscoelastic material is defined according to the Boltzmann integral law. The displacement field is expressed by the product of a determinate geometrical function and a time function with two indeterminate coefficients. The time function coefficients are calculated with the help of the Laplace transform, satisfying the equilibrium equation at two asymptotic times. Abaqus software is used to confirm the results. The numerical results consider the effect of time-dependent material parameters, loads, boundary conditions, thickness-to-side ratios, and aspect ratios on the maximum displacements of moderately thick time-dependent plates.

Time-dependent photo-activated aminoborane room-temperature phosphorescence materials with unprecedented properties: simple, versatile, multicolor-tuneable, water resistance, optical information writing/erasing, and multilevel data encryption.

Triarylboranes-based pure organic room-temperature phosphorescence (RTP) materials are rarely investigated because of their large steric hindrance and the electron defect of the boron atom. As a result, creating functional triarylborane RTP materials is difficult. Herein, we report the first photo-activated RTP materials with lifetimes/quantum yields ≤0.18 s/6.83% based on donor (D)-π-acceptor (A) from methylene carbazole-functionalized aminoborane (BN)-doped polymethyl methacrylate (BN-o-Met-Cz@PMMA) under 365 nm UV irradiation (30 s). Incredibly, BN-o-Met-Cz@PMMA films exhibited unprecedented photo-activated RTP dual-response properties (e.g., air + 365 nm: τ P = 0.18 s, Φ P = 6.83%; N2 + 365 nm: τ P = 0.42 s, Φ P = 17.34%). Intriguingly, the BN (D-π-A) system demonstrated good versatility for photo-activated RTP whether the electron-donating group or electron-withdrawing group was placed in the ortho (meta)-position of the B atom. As a result, a series of photo-activated single-molecule organic RTP materials with multi-color emission, high quantum yields, and ultra-long lifetimes can be prepared rapidly. BN-X@PMMA films showed broad application prospects for information encryption, data erasure, anti-counterfeiting, and water resistance. Our method provides new strategies for the design, synthesis, and application of RTP materials, thereby enriching the types of organic RTP materials and facilitating further developments in this area.

Non-reciprocal wave propagation in time-modulated elastic lattices with inerters

Non-reciprocal wave propagation in acoustic and elastic media has received much attention of researchers in recent years. This phenomenon can be achieved by breaking the reciprocity through space- and/or time-dependent constitutive material properties, which is an important step in overcoming the limitations of conventional acoustic- and phononic-like mechanical lattices. A special class of mechanical metamaterials with non-reciprocal wave transmission are latices with time-modulated mass and stiffness properties. Here, we investigate the non-reciprocity in elastic locally resonant and phononic-like one-dimensional lattices with inerter elements where mass and stiffness properties are simultaneously modulated through inerters and springs as harmonic functions of time. By considering the Bloch theorem and Fourier expansions, the frequency-band structures are determined for each configuration while asymmetric band gaps are found by using the weighting and threshold method. The reduction in frequency due to introduced inerters was observed in both phononic and locally resonant metamaterials. Dynamic analysis of finite-length lattices by the finite difference method revealed a uni-directional wave propagation. Special attention is given to phononic-like lattice based on a discrete-continuous system of multiple coupled beams. Moreover, the existence of edge modes in the discrete phononic lattice is confirmed through the bulk-edge correspondence and their time evolution quantified by the topologically invariant Chern number. The proposed methodology used to investigate non-reciprocal wave transmission in one-dimensional inerter-based lattices can be extended to study more complex two-dimensional lattices.

Time-dependent hyper-viscoelastic parameter identification of human articular cartilage and substitute materials

Numerical simulations are a valuable tool to understand which processes during mechanical stimulations of hydrogels for cartilage replacement influence the behavior of chondrocytes and contribute to the success or failure of these materials as implants. Such simulations critically rely on the correct prediction of the material response through appropriate material models and corresponding parameters. In this study, we identify hyper-viscoelastic material parameters for numerical simulations in COMSOL Multiphysics® v. 5.6 for human articular cartilage and two replacement materials, the commercially available ChondroFillerliquid and oxidized alginate gelatin (ADA-GEL) hydrogels. We incorporate the realistic experimental boundary conditions into an inverse parameter identification scheme based on data from multiple loading modes simultaneously, including cyclic compression-tension and stress relaxation experiments. We provide individual parameter sets for the unconditioned and conditioned responses and discuss how viscoelastic effects are related to the materials’ microstructure. ADA-GEL and ChondroFillerliquid exhibit faster stress relaxation than cartilage with lower relaxation time constants, while cartilage has the largest viscoelastic stress contribution. The elastic response predominates in ADA-GEL and ChondroFillerliquid, while the viscoelastic response predominates in cartilage. These results will help to simulate mechanical stimulations, support the development of suitable materials with distinct mechanical properties in the future and provide parameters and insight into the time-dependent material behavior of human articular cartilage.

Print parameter optimization and mechanical deformation analysis of alumina-nanoparticle doped photocurable nanocomposites fabricated using vat-photopolymerization based additive technology

As the recent trend of fabricating high-strength polymer has been gaining more attention in the market, researchers are exploring the possibility of using a 3D printing technique for the same. Vat-photopolymerization additive technology has good process capability and produces high-quality photopolymer parts with greater geometrical complexity. This paper proposes the vat-photopolymerization process to fabricate high-strength acrylate-based photopolymer composite with improved mechanical strength. The composite structures contain 1.0, 2.0, and 3.0 wt percentages of 13 nm average-sized alumina (Al2O3) nanoparticle (NP) as the reinforcement and acrylate photopolymer as matrix material. The viscosities of all the prepared suspensions were measured to determine the printing properties of the prepared nanocomposites, and these values are within the feasible printing limit. Furthermore, the depth of cure and time of exposure to UV light were optimized to achieve the desired level of printing performance. The thermogravimetric analysis (TGA) of the alumina nanocomposites reveals that the addition of alumina NP has minimal influence on the thermal stability of the photopolymer matrix. To ascertain the mechanical strength of the 3D printed products, tensile tests are performed, and it was witnessed that 1.0% weight fraction of alumina-NP loaded specimen experienced the highest tensile strength amongst all the weight fractions of alumina-NP considered, and its value increased by ∼48% when compared against the pure acrylate polymer sample. The increase in strength values for the alumina-NP loaded specimen was explained using dynamic mechanical analysis and optical and scanning electron micrographs. A constitutive elastic-viscoplastic isothermal non-linear time-dependent material model is also developed to predict the post-yield strain-softening behavior of these nanocomposites. The weight fraction and optimal weight fraction of alumina nanoparticles are correlated using semi-empirical equations of various model parameters.

Experimental determination of cyclically stabilized material properties of the Mo-based alloy MHC in stress-relieved condition from room temperature to 1400 °C

The aim of the current study was the determination of the time-dependent visco-plastic material behavior of the molybdenum alloy MHC (Molybdenum-Hafnium-Carbon) in stress-relieved condition with cyclic strain-controlled low cycle fatigue experiments at room temperature, 800 °C and 1400 °C. To ensure high data quality, a servohydraulic testing machine modified with a vacuum chamber was utilized to avoid material oxidation. The long-time strain-controlled experiments were conducted with a laser extensometer with high accuracy up to the highest applied test temperature of 1400 °C. The determined data were appropriate to generate cyclic stress-strain curves, strain-Wöhler curves, and their descriptive parameters. Furthermore, the strain rate dependency of the cyclic stress response and the stress relaxation behavior of the cyclically stabilized material were also investigated at the mentioned temperatures. The current study indicates that MHC in stress-relieved condition has a softening ability during cyclic loading, especially at 800 °C and 1400 °C. The strain rate sensitivity of the stress amplitude for the case of cyclic stabilization shows similar behavior as described in the literature for the case of monotonously increasing loading conditions, with a minimum at 800 °C. An interesting effect was identified in relaxation tests with loading at different strain rates. A kind of rebound effect was observed at the highest utilized strain rate of 10−2 s−1, which disappears with decreasing strain rate. Elastic strain proportions can be converted into plastic strain proportions during the application of the slow strain rate.

A three-dimensional fractional visco-hyperelastic model for soft materials

Soft materials have attracted widespread attention and brought a wave of novel potential applications. Accurate mechanical characterization is crucial for improving the ration design of the desired soft elements and understanding the influence of deformation properties on themselves. However, the intrinsic complexity of mixed elasticity and viscosity in terms of their material property, posing new challenges for constitutive modeling. In this work, a fractional visco-hyperelastic constitutive model is developed by introducing the fractional viscoelasticity into finite strain: two branches are incorporated where a hyperelastic spring is used to describe the equilibrium response, and a non-linear fractional dashpot is introduced to characterize the time-dependent material response by employing the 3D fractional viscoelasticity. It provides a method from the perspective of fractional mechanics to avoid the increased number of governing equations and the associated complex calibration process caused by introducing the internal variables. The results show that the proposed model can successfully describe the rate dependent mechanical behavior of soft materials as well as predict the material behavior in different deformation modes with reasonable accuracy.

Comparison of in vivo visco-hyperelastic properties of uterine suspensory tissue in women with and without pelvic organ prolapse

The uterine suspensory tissue (UST) complex includes the cardinal (CL) and uterosacral “ligaments” (USL), which are mesentery-like structures that play a role in resisting pelvic organ prolapse (POP). Since there is no information on the time-dependent material properties of the whole structure in situ and in vivo, we developed and tested an intraoperative technique to quantify in vivo whether there is a significant difference in visco-hyperelastic behavior of the CL and USL between women with and without POP. Thirteen women with POP (cases) and four controls scheduled for surgery were selected from an ongoing POP study. Immediately prior to surgery, a computer-controlled linear servo-actuator with a series force transducer applied a continuous, caudally directed traction force while simultaneously recording the resulting cervical displacement in the same direction. After applying an initial 1.1 N preload, a ramp rate of 4 mm/s was used to apply a maximum force of 17.8 N in three “ramp-and-hold” test trials. A simplified bilateral four-cable biomechanical model was used to identify the material behavior of each ligament. For this, the initial cross-section areas of the CL and USL were measured on 3-T magnetic resonance image-based 3D models from each subject. The time-dependent strain energy function of CL/USL was defined with a three-parameter hyperelastic Mooney–Rivlin material model and a two-term Prony series in relaxation form. When cases were compared with controls, the estimated time-dependent material constants of CL and USL did not differ significantly. These are the first measurements that compare the in vivo and in situ visco-hyperelastic response of the tissues comprising the CL and USL to loading in women with and without prolapse. Larger sample sizes would help improve the precision of intergroup differences.

Structural identification via the inference of the stochastic volatility model conditioned on the time-dependent bridge deflection

The time-dependent deflection data collected by a structural health monitoring (SHM) system contains information indicating the damage accumulation of prestressed concrete bridges (PSCBs). However, for this information to be used, the results must be fully translated into reliable metrics. Model-based structural identification (SI) targeting the time-dependent deflection of PSCBs is affected by time-dependent material behavior such as creep and shrinkage as well as the unknown path of structural deterioration, which should be considered in a stochastic volatility model (SVM). This paper presents an inference framework for an SVM conditioned on the time-dependent deflection of PSCBs. In this framework, the augmented state space includes the full ranges of the unobserved state variables affecting the time-dependent deflection of PSCBs, namely, structural rigidity, creep, shrinkage, prestress level and dead load level, along with the volatility parameters associated with the deterioration path of structural rigidity, which is modeled via the Wiener process. Exploiting the latent structure of the SVM, a cyclic Markov chain Monte Carlo (MCMC) sampler is proposed to draw samples from the joint posterior distribution of the unobserved state variables and volatility parameters. In an illustrative example, two-year continuous deflection monitoring data of an existing bridge are utilized as the target information for inference. The updated model can indicate the accumulated damage of the case bridge over the monitoring period. The proposed SI framework is able to support accurate probabilistic analysis of the time-dependent deflection of PSCB.

Impact of External Mechanical Loads on Coda Waves in Concrete.

During their life span, concrete structures interact with many kinds of external mechanical loads. Most of these loads are considered in advance and result in reversible deformations. Nevertheless, some of the loads cause irreversible, sometimes unnoticed changes below the macroscopic scale depending on the type and dimension of the impact. As the functionality of concrete structures is often relevant to safety and society, their condition must be known and, therefore, assessed on a regular basis. Out of the spectrum of non-destructive monitoring methods, Coda Wave Interferometry using embedded ultrasonic sensors is one particularly sensitive technique to evaluate changes to heterogeneous media. However, there are various influences on Coda waves in concrete, and the interpretation of their superimposed effect is ambiguous. In this study, we quantify the relations of uniaxial compression and uniaxial tension on Coda waves propagating in normal concrete. We found that both the signal correlation of ultrasonic signals as well as their velocity variation directly reflect the stress change in concrete structures in a laboratory environment. For the linear elastic range up to 30% of the strength, we calculated a velocity variation of −0.97‰/MPa for compression and 0.33%/MPa for tension using linear regression. In addition, these parameters revealed even weak irreversible changes after removal of the load. Furthermore, we show the time-dependent effects of shrinkage and creep on Coda waves by providing the development of the signal parameters over time during half a year together with creep recovery. Our observations showed that time-dependent material changes must be taken into account for any comparison of ultrasonic signals that are far apart in time. The study’s results demonstrate how Coda Wave Interferometry is capable of monitoring stress changes and detecting even small-size microstructural changes. By indicating the stated relations and their separation from further impacts, e.g., temperature and moisture, we anticipate our study to contribute to the qualification of Coda Wave Interferometry for its application as an early-warning system for concrete structures.

A dynamic assembly-induced emissive system for advanced information encryption with time-dependent security

The development of advanced materials for information encryption with time-dependent features is essential to meet the increasing demand on encryption security. Herein, smart materials with orthogonal and temporal encryption properties are successfully developed based on a dynamic assembly-induced multicolour supramolecular system. Multicolour fluorescence, including blue, orange and even white light emissions, is achieved by controlling the supramolecular assembly of pyrene derivatives by tailoring the solvent composition. By taking advantage of the tuneable fluorescence, dynamically controlled information encryption materials with orthogonal encryption functions, e.g., 3D codes, are successfully developed. Moreover, time-dependent information encryption materials, such as temporal multi-information displays and 4D codes, are also developed by enabling the fluorescence-controllable supramolecular system in the solid phase, showing multiple pieces of information on a time scale, and the correct information can be identified only at a specified time. This work provides an inspiring point for the design of information encryption materials with higher security requirements.

Numerical simulation of elastic buckling in 3D concrete printing using the lattice model with geometric nonlinearity

This paper explores buildability quantification of randomly meshed 3D printed concrete objects by considering structural failure by elastic buckling. The newly proposed model considers the most relevant printing parameters, including time-dependent material behaviors, printing velocity, localized damage and influence of sequential printing process. The computational uniaxial compression tests were first conducted to calibrate age-dependent elastic modulus and yield stress. Subsequently, analyses of the 3D printing process of a free wall structure and a square layout were performed. The model can reproduce the asymmetry of buckling failure accurately and the predicted critical printing height is in excellent agreement with experimental data from the literature. It can be concluded the combined effect of material variability and non-uniform gravitational loading due to sequential printing process resulted in structural failure during 3D concrete printing. Using this model, printing parameters can be optimized and a suitable printing scheme can be devised to improve structure buildability.

Novel Modeling of Heat and Moisture Diffusion in Adhesive Joints

Abstract A novel two-dimensional shear stress-heat and moisture diffusion model is proposed for adhesive single-lap joints. Spatial and time-dependent material properties are derived from coupled partial differential equations governing moisture diffusion and heat transfer through the exposed adhesive edges. Constituting differential equations are numerically solved for the shear stress distribution in the bonded area. Several diffusion scenarios and boundary conditions are analyzed. Significant improvements are achieved in the prediction of the shear stress distribution in the adhesive layer when compared to the one-dimensional models in the literature. Scenarios of moisture diffusion generate stress gradients through the bondline, while the relatively fast internal thermal conductivity reduces temperature differentials within the joint. Moisture diffusion in the adhesive layer is significantly accelerated at high temperatures. The results of the proposed model show reasonable agreement with a three-dimensional finite element analysis.

Kinetic Model of Acid Gas Induced Defect Propagation in Zeolitic Imidazolate Frameworks

Understanding the degradation of nanoporous materials under exposure to common acid gas contaminants (e.g., SO2, CO2, NO2, and H2S) is essential to elongate their lifetime and thus enable their practical applications in separations and catalysis. Previous theoretical investigations have focused on the formation of isolated point defects, which are insufficient to provide direct insights into the long-term evolution of the bulk properties of materials such as zeolitic imidazolate frameworks (ZIFs) under sustained acid gas exposure. To bridge this divide in both length and time scales, we developed a first-principles lattice-based kinetic model to simulate the defect propagation and bulk material breakdown in ZIFs. This model closely reproduces the experimentally measured macroscopic evolution of the time-dependent bulk materials proprieties and also yields important new insights regarding the autocatalytic nature of ZIF degradation and the spatial distribution of defects. Our results suggest new experimental directions to identify nascent defect clusters in degraded ZIFs and avenues to mitigate degradation under challenging conditions of acid gas exposure.

Branching during axial compression histories of solid cylinders of time-dependent materials

This work considers the uniaxial compression of a solid circular cylinder of time-dependent material. Initially, the cylinder undergoes a homogeneous compression history. The purpose is to determine a time when this deformation history can form a new inhomogenous branch. Material time dependence is described by a nonlinear single-integral constitutive equation that relates the stress in the material to its deformation history. A criterion is developed for determining branching times using a Pipkin–Rogers constitutive equation for nonlinear incompressible isotropic viscoelastic solids. For the purpose of numerical examples, material parameters are chosen so that the material acts as a neo-Hookean material in its short-time response and a softer one in its long-time equilibrium response. Examples show that characteristic relaxation times and deformation histories influence the time to branch and the corresponding compressive stretch and compressive force.

Structural assessment of underground utility services pit using Bayesian inference

ABSTRACT Ageing infrastructure is becoming an increasing challenge as a result of deterioration and greater loading demands. Modern cities were built on top of complex underground infrastructure networks many of which are still in-service beyond their design life. The safety assessment of underground structures is of utmost importance to avoid catastrophic failures and develop cost-effective renewal and rehabilitation strategies. However, the lack of design documentation and absence of data on the level of structural deterioration make determination of current structural capacity a challenge. This paper presents a probabilistic based assessment framework for underground utility service pits using Bayesian updating technique, which is used to refine the probabilistic distribution of material properties from the prior distribution constructed using published data. A case study of an underground pit located in Central Melbourne is provided. Extensive experimental testing was conducted to characterise the material properties and a full-scale masonry wall was tested to understand the failure mode due to earth pressure and traffic load. The test data was used in strength prediction models to achieve a more accurate estimate for wall capacity. Further, the strength degradation models were integrated to develop the time-dependent material models, which were eventually used to compute reliability index.

A comprehensive risk assessment view on interval type-2 fuzzy controller for a time-dependent HazMat routing problem

Hazardous material transportation is an integral part of industries that pose significant risks. Hazardous material transportation risk of is proportional to the volume of materials transferred, the length of the link, and the population density, which varies over time. By modeling the effects of time on population density, this paper presents a multi-objective time-dependent hazardous materials routing problem for efficiently managing hazardous material transportation. The proposed model's objectives include the reduction of transportation risks and travel costs. Given the uncertainty associated with hazardous materials routing, an interval type-2 fuzzy logic controller is used to estimate risk; its inputs include population density, vehicle load, link length, and time of day. A type-2 fuzzy multi-objective evolutionary algorithm based on decomposition is used to optimize the proposed model and an adaptive large neighborhood search to enhance the local neighbor search mechanism. Additionally, by utilizing the nadir reference point, the distribution of Pareto front approximation is improved. Furthermore, a new metric is introduced to evaluate the dispersion of Pareto front approximation. The proposed method is compared to three other state-of-the-art evolutionary algorithms using eleven different performance metrics for validation. Then, using the multiple-criteria decision-making approach, the meta-heuristics algorithms are evaluated. The obtained results demonstrate the proposed solution method algorithm's competitiveness and superiority over the other three evolutionary algorithms.

Numerical simulation of axially impacted elastic bar

This numerical analysis considers a model of an elastic cylindrical bar impacted by rigid mass, where the accuracy of the model is benchmarked by a closed-form solution developed for this impact process. The analytical solution provides theoretical background and understanding, however, practical problem is not always restricted to a simple one-dimensional geometry and boundary conditions of a purely elastic material behaviour. Hence, the current work numerically simulates the impacted elastic bar, then explores parameters which are not considered in its theoretical model. A two-dimensional (2D) solid axisymmetric system is considered, in which rigid impactor is assigned with initial velocity corresponding to certain drop height and a 2D contact type is defined between interacting bodies. Both elastic and time-dependent viscoelastic material models are considered in this study. The simulation results reveal time intervals gradually increase in every sequential intervals, while relatively small discrepancies are recorded for peak load and pulse width outputs. The parameters of impactor’s mass, drop height and structural stiffness are varied; showing how these parameters individually affect the resulting force response at end struck. The models then evaluate time-dependent viscoelastic material model; showing stiffer response of the resulting force in comparison to models assigned with long-term elastic moduli. Derived elastic modulus-output variable relations show comparable mathematical forms to corresponding equations formulated analytically.

Nonreciprocal acoustic scattering from an elastic plate with spatiotemporally modulated material properties

Acoustic and elastic metamaterials with space- and time-dependent material properties have received great attention recently as a means to realize nonreciprocal wave propagation. The nonreciprocal behavior of propagating waves in a spatiotemporally modulated infinite medium is usually characterized by directional bandgaps present in the frequency-wavenumber spectrum. However, less attention has been given to acoustic scattering from spatiotemporally modulated media. In this work, we consider nonreciprocal reflection and transmission from a spatiotemporally modulated, infinite elastic plate excited by a plane wave at oblique incidence. A semi-analytical approach is developed that considers the coupling between the acoustic waves and the displacement of the plate. The reflection and transmission response of the plate for each generated frequency harmonic as a function of the incident angle are reported. Finally, we find conditions on the modulation parameters that yield a large degree of nonreciprocity. The present analysis leads to potential applications in acoustic communications, such as directional wave sensing.