Change In Elastic Energy Research Articles

Computational Morphogenesis of Lightweight Continous Concrete Shell Structures by Utilizing Metaheuristic Algorithms

While the hanging model and physical prototyping are reliable methods for form-finding continuous lightweight shell structures, they cannot explore various design possibilities and consider multiple criteria in the design. This research aims to employ metaheuristic algorithms as a search tool for simultaneous form-finding (form exploration) and optimization, known as computational morphogenesis. This workflow consists of a parametric model and metaheuristic algorithms, which were implemented through costume Python codes. To evaluate the workflow, a double-curvature footbridge was defined, and the forms that GA found were in line with the anticipation. The GA found a better solution (0.04022) than the SA (0.064) by considering elastic energy change. In case study II, the optimal form of a continuous lightweight shell was explored by utilizing GA, PSO, SA, and the hybrid algorithm of GAPSO. The GA improved the fitness solution by 35% in the second run, while PSO showed similar results, and the hybrid GAPSO algorithm did not yield better results. The results show that the optimum result based on different algorithms was not significantly different. Nevertheless, hyperparameters considerably affected finding the global minimum. Moreover, NSGA-II was utilized, which let the designer trade-off between alternatives while considering other criteria.

Mechanism of nucleation in ferroelastic domain switching

The mechanism of domain nucleation during ferroelastic domain switching is revealed by utilizing phase-field simulations. A complete compression-tension hysteresis loop is simulated, and the results show the nucleation of new domains at domain walls (DW). Due to relaxation of strain energy, the coherent DWs of the surviving domains often form features like steps, crevices and corners, and nucleation of new domains primarily takes place at these sites in a repeated fashion. The change in elastic strain energy around these sites is sufficient to provide the energy necessary for ferroelastic domain nucleation (FDN). The present simulations reveal that the apparent ellipsoidal shape of a nucleus might be an oblate spheroid when the nucleation takes place at a crevice. The present work also reveals that nucleation of triangular shaped domains is equally probable, and they take place at the steps or corners of DWs.

Tailoring the strength and impact toughness of 9Cr1.5Mo1Co steel by optimizing ultra-fine martensite and retained austensite

The urgent demands for more excellent mechanical properties to meet higher steam temperatures for 9Cr steels have been the driving force behind the increasing research efforts on heat treatment. This paper presents a systematic study of the effect of the ultra-fine martensite (ultra-fine M) and retained austensite (RA) obtained by austempering process on mechanical properties are studied by experimental observations and phase-field simulation. The results demonstrate that austempering leads to the split and incompletion of martensitic transition, producing a mixed microstructure consisting of lathy martensite(lathy-M), ultrafine martensite(ultra-M), and retained austensite (RA). Due to the change of local chemical free energy and elastic strain energy caused by the redistribution of C element, two types (isothermal and athermal) of ultra-M form by spontaneous nucleation and interfacial migration during austempering with appropriate temperatures. Further tempering produces dispersed finer M23C6 precipitated at the interfaces of high-dislocated ultra-M than lathy-M. Meanwhile, RA decomposes into fine globular M23C6 and ferrite. Consequently, a larger amount of ultra-M and RA in quenched state results in smaller effective grain sizes and smaller carbides' average size, leading to the enhancement of precipitation strengthening, grain boundary strengthening, and impact toughness. This work establishes the potential for tailoring the strength and impact toughness of 9Cr1.5Mo1Co steel by optimizing the ultra-fine martensite and retained austensite using austempering process.

Energy and Infrared Radiation Characteristics of the Sandstone Damage Evolution Process.

The mechanical characteristics and mechanisms of rock failure involve complex rock mass mechanics problems involving parameters such as energy concentration, storage, dissipation, and release. Therefore, it is important to select appropriate monitoring technologies to carry out relevant research. Fortunately, infrared thermal imaging monitoring technology has obvious advantages in the experimental study of rock failure processes and energy dissipation and release characteristics under load damage. Therefore, it is necessary to establish the theoretical relationship between the strain energy and infrared radiation information of sandstone and to reveal its fracture energy dissipation and disaster mechanism. In this study, an MTS electro-hydraulic servo press was used to carry out uniaxial loading experiments on sandstone. The characteristics of dissipated energy, elastic energy, and infrared radiation during the damage process of sandstone were studied using infrared thermal imaging technology. The results show that (1) the transition of sandstone loading from one stable state to another occurs in the form of an abrupt change. This sudden change is characterized by the simultaneous occurrence of elastic energy release, dissipative energy surging, and infrared radiation count (IRC) surging, and it has the characteristics of a short duration and large amplitude variation. (2) With the increase in the elastic energy variation, the surge in the IRC of sandstone samples presents three different development stages, namely fluctuation (stage Ⅰ), steady rise (stage Ⅱ), and rapid rise (stage Ⅲ). (3) The more obvious the surge in the IRC, the greater the degree of local damage of the sandstone and the greater the range of the corresponding elastic energy change (or dissipation energy change). (4) A method of sandstone microcrack location and propagation pattern recognition based on infrared thermal imaging technology is proposed. This method can dynamically generate the distribution nephograph of tension-shear microcracks of the bearing rock and accurately evaluate the real-time process of rock damage evolution. Finally, this study can provide a theoretical basis for rock stability, safety monitoring, and early warning.

Simulating Stress-Strain Behavior by Using Individual Chains: Uniaxial Deformation of Amorphous Cis- and Trans-1,4-Polybutadiene.

This work develops a probability-based numerical method for quantifying mechanical properties of non-Gaussian chains subject to uniaxial deformation, with the intention of being able to incorporate polymer-polymer and polymer-filler interactions. The numerical method arises from a probabilistic approach for evaluating the elastic free energy change of chain end-to-end vectors under deformation. The elastic free energy change, force, and stress computed by applying the numerical method to uniaxial deformation of an ensemble of Gaussian chains were in excellent agreement with analytical solutions that were obtained with a Gaussian chain model. Next, the method was applied to configurations of cis- and trans-1,4-polybutadiene chains of various molecular weights that were generated under unperturbed conditions over a range of temperatures with a Rotational Isomeric State (RIS) approach in previous work (Polymer2015, 62, 129-138). Forces and stresses increased with deformation, and further dependences on chain molecular weight and temperature were confirmed. Compression forces normal to the imposed deformation were much larger than tension forces on chains. Smaller molecular weight chains represent the equivalent of a much more tightly cross-linked network, resulting in greater moduli than larger chains. Young's moduli computed from the coarse-grained numerical model were in good agreement with experimental results.

Electrorheological effect and dielectric properties of Poly(ionic liquid) microspheres with different length of alkyl chain spacer between ion pair and backbone

Imidazolium-based poly(ionic liquid) analogues having different lengths of alkyl chain spacer between ion pair and backbone, named as P[ECnVim][PF6] (n = 2, 3, 6), were synthesized. Then, P[ECnVim][PF6] were transformed into microspheres by an evaporation-induced phase separation method. The influence of the length of alkyl chain spacer on the electro-responsive electrorheological effect and dielectric property of P[ECnVim][PF6] microsphere suspensions were studied. It showed that as the length of alkyl chain spacer increased, the electrorheological effect increased but the working temperature range of electrorheological effect became narrow. By combining dielectric spectra analysis and activation energy measurement, it was clarified that the influence of the length of alkyl chain spacer on electrorheological effect was mainly associated with the change of ionic conductivity and interfacial polarization, which was further related to the change of elastic potential energy of ion motion in P[ECnVim][PF6] with different lengths of alkyl chain spacer between ion pair and backbone. However, the working temperature range of electrorheological effect depended on the change of glass transition temperature with the length of alkyl chain spacer. The result provides the structure-property relationship insight for the design of poly(ionic liquid)-based electro-responsive electrorheological materials.

Strain‐Driven Thermal and Optical Instability in Silver/Amorphous‐Silicon Hyperbolic Metamaterials

AbstractHyperbolic metamaterials show exceptional optical properties, such as near‐perfect broadband absorption, due to their geometrically‐engineered optical anisotropy. Many of their proposed applications, such as thermophotovoltaics or radiative cooling, require high‐temperature stability. In this work, Ag/a‐Si multilayers are examined as a model system for the thermal stability of hyperbolic metamaterials. Using a combination of nanotomography, finite element simulations, and optical spectroscopy, the thermal and optical instability of the metamaterials is mapped. Although the thermal instability initiates at 300 °C, the hyperbolic dispersion persists up to 500 °C. Direct finite element simulations on tomographical data provide a route to decouple and evaluate interfacial and elastic strain energy contributions to the instability. Depending on stacking order the instability's driving force is either dominated by changes in anisotropic elastic strain energy due thermal expansion mismatch or by minimization of interfacial energy. These findings open new avenues to understand multilayer instability and pave the way to design hyperbolic metamaterials able to withstand high temperatures.

Spring efficiency assessment and efficient use of spring methods of statically balanced planar serial manipulators with revolute joints only

Abstract. This paper proposes a spring efficiency assessment of a statically spring-balanced planar serial manipulator. The admissible spring configurations for the static balancing of planar serial manipulators without auxiliary links have been determined in the past. Gravity is balanced by the spring configuration systematically; however, the spring configuration also contains counter-effects between springs. Conceptually, with fewer counter-effects between springs, there is less burden on the spring system, which means that the springs are used more efficiently, and accordingly, the system would be safer, and its service life would be longer. In this study, the spring energy is represented in a quadratic form. The coefficients in a quadratic form represent the change in elastic energy with the relative position between links, which is named “elastic pseudo-stiffness”. Compared to the quadratic form of gravity energy, those elastic pseudo-stiffnesses for static balancing are regarded as positive contributions of a spring, while those that contain counter-effects are seen as negative ones. Spring efficiency is defined as the ratio of the elastic pseudo-stiffnesses, which has positive contributions for balancing to total elastic pseudo-stiffnesses. To use springs efficiently, the counter-effects, which are functions of spring parameters, need to be decreased, including spring stiffness and the attachment location of springs on links. A method to use spring efficiently by adjusting spring parameters is developed. Furthermore, it is found that, for a spring attached between adjacent links, the spring efficiency is 100 %, and the spring efficiency decreases while the number of joints over which the spring spans increases. In a spring manipulator system, the efficiency is negatively correlated to the payload. As an example, an efficiency assessment on a 3 degrees of freedom (DOF) manipulator is shown at the end.

PZT and PVDF piezoelectric transducers’ design implications on their efficiency and energy harvesting potential

Abstract Despite the intensive research carried out in the last two decades, the actual performance of piezoelectric energy harvesters needs significant improvement for widespread applicability. Custom designed experimental set-ups and methods can be applied for the evaluation of new piezoelectric energy harvesters or modified design versions of existing transducers, in terms of efficiency and specific power. In this context, two representative types of commercial cantilever piezoelectric transducers, made of PZT and PVDF material respectively, were tested in various combinations of aerodynamic and harmonic base excitation. A line type laser was used along with long exposure photography for the visualisation of the piezofilm’s mode shapes, tip deflection and the digitization of the elastic line at the oscillation extrema. The harvested power was measured at on-resonance conditions and studied relative to the excitation combinations and the mode shapes. Energy conversion efficiency, defined as the ratio of the electric-field energy accumulated by the supercapacitors, over the total elastic strain energy change of the material during the oscillations is measured and compared. Design improvements are proposed for both transducer types to extract and absorb higher amounts of energy and improve their bandwidth to match the available excitation source characteristics.

Extracellular DNA plays a key role in the structural stability of sulfide-based denitrifying biofilms.

Sulfide-based biofilm processes are increasingly used for wastewater denitrification, yet little is known about the extracellular polymeric substance (EPS) composition of sulfide-oxidizing biofilms. This can have an important impact on biofilm mechanical strength and stability. In this research, the properties and roles of EPS components in biofilm stability were investigated. Weak biofilm stability characterized by high roughness and numerous "needle" structures was visualized by optical coherence tomography (OCT) and microscopy. A high abundance of extracellular DNA (eDNA) and a low protein to polysaccharide ratio were found in the biofilm. The roles of eDNA, protein and polysaccharide in biofilm cohesion and adhesion were identified through enzyme treatment and atomic force microscopy (AFM). The enzymatic hydrolysis of eDNA increased the elastic modulus of biofilms by 57 times and reduced the adhesion energy by 96%. The hydrolysis of proteins led to an increase of elastic modulus by 27 times and a loss of adhesion energy by 95.5%. The enzymatic hydrolysis of polysaccharides caused minimal changes in elastic modulus and adhesion energy. These results suggest that eDNA was the key EPS component for biofilm cohesion and adhesion, possibly because it provided special binding sites and can form strong cross-linking with magnesium or other multivalent cations. This study provided new insights into the role of eDNA in biofilm stability and shed light on the development of sulfide-based denitrifying biofilms.

Nanocracks in nature and industry.

Nanocracks in nature and industry.

Isotropy of precipitate distribution in pre-stretched Al-Cu-(Sc)-(Zr) alloys

Pre-stretching prior to ageing in Al-Cu alloys leads to preferential formation of precipitates in certain habit planes and produces anisotropic mechanical properties. In this work, we attempt to eliminate this problematic anisotropy by adding Sc and Zr to an Al-Cu alloy. When pre-stretching the binary Al-Cu alloy along the [001]Al zone axis, transmission electron microscopy (TEM) reveals that precipitation of θ″ occurs mostly on the (001)Al plane (and not on the (100)Al and (010)Al planes). This “stress orienting effect” is caused by the local change in elastic strain energy induced by the pre-stretching. In the pre-stretched Al-Cu-Sc-Zr alloy, the presence of coherent Al3(Sc, Zr) dispersoids is found to promote equivalent nucleation of θ′ precipitates in all three habit planes (at the expense of θ″), resulting an isotropic precipitate distribution. The strengthening potential of these different precipitate distributions is analytically modelled and discussed.

Cluster‐Size‐Dependent Linear Magnetoelectric Coupling Effect in Na0.5Bi0.5TiO3/FeCo Composites

A size effect of magnetic FeCo clusters in Na0.5Bi0.5TiO3/FeCo composites is presented, which is embodied by a strong size‐dependent magnetostrictive effect and magnetoelectric (ME) coupling effect. The size evolution of magnetic clusters induces the change of elastic energy in the magnetic phase, which is the key reason for the tunable magnetostrictive and mangetoelectric effects. An interface stress transferring mode is used to describe the coupling effect of the composites. This work explores a route to modulate ME materials by amorphous alloy clusters, which is of great significance to the development of magnetoelectronics.

Energizing ASTM lap joint fracture standards.

Several ASTM standards on the fracture of glued and welded joints need attention because they do not consider the Griffith energy criterion of cracking which was proposed a century ago. It is almost as if Griffith never existed because the ASTM definition of failure is the stress criterion postulated by Galileo in 1638 in which stress at failure (i.e. strength = force/area) is defined as the determinant of fracture. Irene Martinez Villegas (Villegas, Rans 2021 Phil. Trans. R. Soc. A 376, 20200296. (doi:10.1098/rsta.2020.0296)) shows in this volume that attempts to use ASTM D5868 to standardize welded composite (carbon fibre reinforced polymer, CFRP) lap joints reveal major problems. First, the test is a low angle bend-peel test; not shear. Second, the energy required to break the joint is not emphasized so that joints may have high strength properties but also low toughness; third, the fracture force is not proportional to the lap joint area so the concept of strength independent of sample size is false; fourth, as the CFRP panels are made thicker, the strength rises at constant overlap area so the strength can be any value you want; fifth, the strength of larger joints goes down; this is the size effect noted in many bend-cracking tests, much as Galileo suggested for bent beam fracture in his famous book 'the larger the machine, the greater its weakness'. The purpose of this paper is to demonstrate that poor ASTM 'shear strength' standards should be replaced by a definition of welded lap joint performance based on Griffith's energy conservation argument in which fracture surface energy is the main parameter resisting failure. The foundation of this Griffith-style lap joint analysis for long cracks goes back to 1975 but has been largely ignored until now because it does not fit the Griffith equation for cracked sheets, has no 'stress intensity factor', and travels at constant speed, not accelerating like the standard Griffith tension crack. This study of tensile delamination shows that a long lap crack is not driven by stress near the crack but by changes in stored elastic energy in the stretched strips remote from the crack tip, while strain energy release rate is negative. It would be more appropriate to call this lap failure a tensile delamination crack. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Criterion for Imminent Failure During Loading—Discrete Element Method Analysis

It has recently been reported that the equal load sharing fiber bundle model predicts the rate of change of the elastic energy stored in the bundle reaches its maximum before catastrophic failure occurs, making it a possible predictor for imminent collapse. The equal load sharing fiber bundle model does not contain central mechanisms that often play an important role in failure processes, such as localization. Thus, there is an obvious question whether a similar phenomenon is observed in more realistic systems. We address this question using the discrete element method to simulate breaking of a thin tissue subjected to a stretching load. Our simulations confirm that for a class of virtual materials which respond to stretching with a well-pronounced peak in force, its derivative and elastic energy we always observe an existence of the maximum of the elastic energy change rate prior to maximum loading force. Moreover, we find that the amount of energy released at failure is related to the maximum of the elastic energy absorption rate.

Isotropy of Precipitate Distribution in Pre-Stretched Al-Cu-(Sc)-(Zr) Alloys

Pre-stretching prior to ageing in Al-Cu alloys leads to preferential formation of precipitates in certain habit planes and produces anisotropic mechanical properties. In this work, we attempt to eliminate this problematic anisotropy by adding Sc and Zr to an Al-Cu alloy. When pre-stretching the binary Al-Cu alloy along the [001]Al zone axis, Transmission electron microscopy (TEM) reveals that precipitation of θ″ occurs mostly on the (001)Al plane (and not on the (100)Al and (010)Al planes). This “stress orienting effect” is caused by the local change in elastic strain energy induced by the pre-stretching. In the pre-stretched Al-Cu-Sc-Zr alloy, the presence of coherent Al3(Sc, Zr) dispersoids is found to promote equivalent nucleation of θ′ precipitates in all three habit planes (at the expense of θ″), resulting in isotropic precipitate distribution. The strengthening potential of these different precipitate distributions is analytically modelled and discussed.

Micromechanics of slow granular flows

It has been contemplated for a long time that dense granular materials flow in a stick-slip manner, and large fluctuations in the stresses are associated with it. However, the particle scale mechanics for this type of macroscopic motion has not been understood so far. We have analyzed the time evolution of contact networks from particle dynamics simulations and found that the rate of change of elastic energy of the packing can distinguish the stick regimes and the slip events. The isostatic criterion (number of contacts for a minimally stable particle) has been used to construct a cascade failure mechanism which reveals that the effect of the random breaking of contacts due to applied shear can be system-spanning for some cases. The size of the cascade failures follows a power law that explains experimentally observed large fluctuations is stresses. We expect that this power law distribution can connect the microstructure of a granular packing to its mechanical response.

Isogeometric analysis of the new integral formula for elastic energy change of heterogeneous materials

In recent years, more and more attention has been paid to isogeometric methods, in which shape functions are used to accurately describe CAD models and approximate unknown fields. The isogeometric boundary element method (IGABEM) realizes the integration on the exact boundary of the region, which means there is no geometric discretization error. In this paper, a more general interface integral formula for elastic energy increment of heterogeneous materials is extended from previous work (Dong, 2018), in which the only unknown variable is the displacement located on the interface between matrix and inclusion. This feature makes it more compatible with boundary element method (BEM) because of none of volume parametrization. However, the geometry discontinuity on the boundary called ‘corner point problem’ increases the difficulty and decreases the accuracy when solving complex numerical examples when heterogeneous structures are considered. The discontinuous element method combined with IGABEM is presented and applied to deal with ‘corner point problem’. In the numerical examples, the interface between matrix and inclusion is discretized by quadratic isogeometric elements. Compared with the analytical solution, the numerical results show that the method has higher accuracy and efficiency.

Interactions between 〈a〉 dislocations and three-dimensional [formula omitted] twin in Ti

〈a〉dislocations on basal or prismatic planes and {112¯2} compression twins are commonly activated in deformed Titanium (Ti). In the present work, their interactions are investigated by both crystallographic analysis and atomistic simulations. For a three-dimensional {112¯2} twin, we firstly analyze seven possible twin boundaries (TBs) bonding two low index planes in matrix and twin. Next, we focus on the two lower energy boundaries, {112¯2}M/T∥{112¯2}T/M coherent twin boundary (CTB) and {1¯21¯1}M/T∥{12¯11¯}T/M. Depending on dislocation character and boundary type, we define four types of interactions between 〈a〉 dislocations and these TBs. Further, we predict possible dislocation reactions on/across TBs using crystallographic analysis according to the deformation compatibility and the change in elastic energy, such as twinning/detwinning of the primary twin, slip transmission and secondary twinning, for each type of interaction. Molecular dynamics (MD) simulations are then conducted for all interactions under pre-selected loadings in order to explore the dynamic process associated with each of these interactions and examine the predicted reactions. MD simulations predict that the interaction between 〈a〉 dislocations and some facets can lead to the formation of secondary twins and 〈a〉 dislocations on basal or prismatic planes in twins, and reveal the possibility of forming 〈c〉 and 〈c+a〉 dislocations in twins. Moreover, some of the possible reactions take place on lateral TBs other than CTBs.

Analysis of dynamic mechanical properties of sprayed fiber-reinforced concrete based on the energy conversion principle

In order to study the dynamic mechanical properties of sprayed fiber-reinforced concrete under impact loads, a φ50mm split Hopkinson (SHPB) device was employed to perform dynamic compression experiments on sprayed plain concrete, polypropylene fiber-reinforced concrete, and plastic steel fiber-reinforced concrete. Variations in the fracture state and waveform of different sample were obtained through experimentation. The toughness, energy consumption, and strength increased with increasing of strain rate. These fibers improved the dynamic mechanical properties of shotcrete. Plastic steel fibers significantly increased the dynamic compressive strength of shotcrete, while polypropylene fibers significantly improved the toughness and energy consumption ratio. The strain rate effect and the fiber reinforcement principle were analyzed from an energy conversion perspective. A correlation analysis of the elastic strain energy change rate and the dynamic compressive strength was used to obtain a fitting curve, and showed a positive linear correlation between the two. This provides a theoretical basis for further studies on how to improve the dynamic mechanical properties of fiber-reinforced concrete from an energy conversion perspective.