Elastic Energy Storage Research Articles

Autonomous, untethered gait-like synchronization of lobed loops made from liquid crystal elastomer fibers via spontaneous snap-through

The transition from one equilibrium state to another via rapid snap-through can store elastic energy and release it as kinetic energy for rapid motion as seen in Venus flytrap and hummingbird to catch insects mid-flight. They are explored in soft robotics for repeated and autonomous motions. In this study, we synthesize curved liquid crystal elastomer (LCE) fibers as the building blocks that can undergo buckling instability upon heated on a hot surface, leading to autonomous snap-through and rolling behaviors. When they are connected into lobed loops, where each fiber is geometrically constrained by the neighboring ones, they demonstrate autonomous, self-regulated, and repeated synchronization with a frequency of ~1.8 Hz. By adding a rigid bead on the fiber, we can fine-tune the actuation direction and speed (up to ~2.4 mm/s). Last, we demonstrate various gait-like locomotion patterns using the loops as the robot's legs.

Mechanical modeling of dowel action and the influence of small amounts of shear reinforcement on the shear‐transfer actions in RC beams

AbstractDowel action of the longitudinal reinforcement in RC beams without and with small amounts of shear reinforcement is typically considered a constant shear contribution determined from the splitting strength of the concrete cover. However, in a recent experimental investigation by the authors, it was shown that the shear force transferred by dowel action for beams without shear reinforcement should be determined from the dowel displacement and a linear elastic model and a rigid plastic dowel model. This article is aimed at extending this model to also cover members with small amounts of shear reinforcement. To that aim, a novel approach to calculate the shear force carried by dowel action of the longitudinal reinforcement in both beams with and without shear reinforcement is presented. The model is derived by establishing an equilibrium of work between the internal stored elastic or dissipated plastic energy and the external work performed by the shear force in the dowel. Additionally, a method to determine the displacement of the dowel from DIC measurements is presented. For the remaining shear‐transfer actions, reasonable constitutive models from the literature are adapted. On the basis of DIC measurements, the shear force carried by each of the shear‐transfer actions is calculated for 16 shear tests of beams without and with small amounts of shear reinforcement. The sum of shear force carried by each of the shear‐transfer actions is shown to predict the applied shear force fairly well, from the development of the critical shear crack until failure. Additionally, it is shown that for beams with shear reinforcement below the minimum requirements according to the current design standards, the shear capacity is governed by aggregate interlock, residual tensile stresses, and the inclination of the compression chord. While for beams with shear reinforcement above the minimum requirements, the shear capacity is governed by the shear reinforcement and dowel action.

Determination method of rock characteristic stresses based on the energy growth rate

Introduction: Precisely determining the characteristic stress value of a rock progressive failure process has important theoretical and practical significance for reasonably defining the rock deformation and failure stage, mechanical mechanism, and design parameters.Methods: Based on the energy characteristics in the process of rock deformation and failure, this paper proposes a new method of rock characteristic stress (EGR) around the index of elastic energy storage capacity, elastic energy growth rate, and dissipative energy growth rate. First, the rationality of the new method is verified by the indoor uniaxial and triaxial loading test data of coal and marble. Second, five different determination methods, namely, lateral strain method, lateral strain difference method, crack strain method, energy dissipation rate method, and volumetric strain method, are compared to further verify the scientific nature of the new method. Finally, the method is applied to the conventional triaxial unloading confining pressure test and true triaxial loading and unloading test of marble, and the new method is fully extended to verify its universality.Results: The results show that the theoretical basis of the EGR characteristic stress determination method is rigorous and sufficient, and the value process is objective and reasonable. Compared with different methods, the EGR method can accurately define the process of rock asymptotic failure, and its corresponding characteristic stress level is well-consistent and in a reasonable range.Discussion: The EGR method is applicable to the conventional triaxial unloading confining pressure test and true triaxial loading and unloading test and has good universality.

Solving the thoracic inverse problem in the fruit fly

In many insect species, the thoracic exoskeletal structure plays a crucial role in enabling flight. In the dipteran indirect flight mechanism, thoracic cuticle acts as a transmission link between the flight muscles and the wings, and is thought to act as an elastic modulator: improving flight motor efficiency thorough linear or nonlinear resonance. But peering closely into the drivetrain of tiny insects is experimentally difficult, and the nature of this elastic modulation is unclear. Here, we present a new inverse-problem methodology to surmount this difficulty. In a data synthesis process, we integrate literature-reported rigid-wing aerodynamic and musculoskeletal data into a planar oscillator model for the fruit fly Drosophila melanogaster, and use this integrated data to identify several surprising properties of the fly’s thorax. We find that fruit flies likely have an energetic need for motor resonance: absolute power savings due to motor elasticity range from 0%–30% across literature-reported datasets, averaging 16%. However, in all cases, the intrinsic high effective stiffness of the active asynchronous flight muscles accounts for all elastic energy storage required by the wingbeat. The D. melanogaster flight motor should be considered as a system in which the wings are resonant with the elastic effects of the motor’s asynchronous musculature, and not with the elastic effects of the thoracic exoskeleton. We discover also that D. melanogaster wingbeat kinematics show subtle adaptions that ensure that wingbeat load requirements match muscular forcing. Together, these newly-identified properties suggest a novel conceptual model of the fruit fly’s flight motor: a structure that is resonant due to muscular elasticity, and is thereby intensely concerned with ensuring that the primary flight muscles are operating efficiently. Our inverse-problem methodology sheds new light on the complex behaviour of these tiny flight motors, and provides avenues for further studies in a range of other insect species.

Influence of water on rockburst of surrounding rock in deep circular tunnels under triaxial internal unloading conditions

Rockburst is one of the most serious engineering geological hazards encountered in deep rock mass. In this study, we investigate the influence of water on the rockburst mechanism in circular tunnels considering the whole stress path of high in situ stress + internal unloading + stress adjustment, based on external loading-internal unloading (ELIU) tests on intact air-dried and saturated sandstone cubic specimens (100 × 100 × 100 mm3). The proposed ELIU method uses true triaxial equipment to first load each intact cubic specimen with two-dimensional high stresses, followed by an internal drilling device for internal unloading to form circular holes. For comparison, cubic specimens with predrilled holes 25 mm in diameter were subjected to internal drilling – external loading (IDEL) tests, i.e., drilling first and then loading. The results show that water reduces the uniaxial compressive strength, Young's and initial moduli, and elastic energy storage capacity of sandstone materials, and increases the significance of shear failure. Furthermore, saturated tunnel structures induce static spalling failure, while dry tunnels lead to dynamic rockburst failure. The influence of water on the stability of the rock mass surrounding a tunnel is analyzed, including the induced weakening of surrounding rock strength and the amplification of the unloading effect. In summary, water prevents rockburst through the following mechanism: (i) water reduces the brittleness of the surrounding rock and enhances its plasticity; (ii) water reduces the elastic energy storage capacity and increases the energy dissipation capacity of the plastic zone; and (iii) water induces the redistribution of stress throughout the surrounding rock, which reduces the stress concentration near the free surface and transfers the maximum stress to the deeper surrounding rock.

Novel Electroformed Ni-Au Alloy for High Temperature Semiconductor Test Structures

The ongoing reduction in semiconductor and package pitch leads to challenges for engineering suitable miniaturized test and measurement contact vehicles. Traditional probe card approaches for miniaturization may reach fundamental limits for reduction in scale and pitch. Direct electroforming of conductive electrical contacts at pitch using LIGA technology can allow for direct registration to the test points, the simultaneous formation of all contacts and an opportunity to extend the roadmap for miniaturization. We report here on a new and novel nickel-gold alloy (one to three percent gold by weight) that can be produced by electroforming. This new material was computationally designed to optimize the thermodynamics of the two alloy components such that the alloy has a temperature stable nanocrystalline grain structure which produces highly desirable mechanical and physical properties. Specifically, the alloy is highly electrically and thermally conductive with a resistivity of 10 micro-ohm-cm, while also having a yield strength in excess of 1.5 GPa and an elastic modulus of 130 GPa. This combination of high strength and moderate elastic modulus creates and optimum for mechanical elastic stored energy in a formed contact beam. That is to say, contacts engineered from this material are flexible and strong enough to remain in the elastic regime and have sufficient normal force to maintain low and stable contact resistance, which boosts their long term service life. Further, the alloy shows a fixed cantilever beam bending fatigue limit of more than 1 GPa, further enhancing its viability for long term service. For applications requiring even more strength a 2 GPa yield strength version has also been produced, however this version leads to minor trade-offs in terms of ductility and electrical resistivity and cost. Since these contacts will be used at elevated temperature, the alloy has been designed to be nearly as electrically conductive as plated unalloyed nickel and thermodynamically stable under long term high temperature storage conditions of 400 C. Characterization of the microstructure shows that it is a supersaturated solid solution of Au in a Ni host matrix with evidence of preferential Au segregation to the Ni grain boundaries. Xray diffraction analysis confirms a nanocrystalline grain structure whose size varies as a function of the alloying content. By segregating the Au to the grain boundaries, we extend the electron mean free path and boost electrical conductivity. We also reduce the grain size of the metal leading to improvements in mechanical properties such as yield and fatigue. The electroplating solution is environmentally friendly with no significantly hazardous materials and is REACH compliant. We have shown chemical compatibility with a limited test set of standard photo-resists and masks used for the LIGA process. The plating process is reasonably fast and has shown the ability to plate layers as thick as 400 um without cracks, defects or voids. For some applications it may be desirable to add more plated layers to engineer the contact surface. Gold and other precious metals can be plated on top of the Ni-Au layer with good adhesion and lead to improvements in long term low level contact resistance.

Mechanism of elastic energy storage of honey bee abdominal muscles under stress relaxation

Energy storage of passive muscles plays an important part in frequent activities of honey bee abdomens due to the muscle distribution and open circulatory system. However, the elastic energy and mechanical properties of structure in passive muscles remain unclear. In this article, stress relaxation tests on passive muscles from the terga of the honey bee abdomens were performed under different concentrations of blebbistatin and motion parameters. In stress relaxation, the load drop with the rapid and slow stages depending on stretching velocity and stretching length reflects the features of myosin-titin series structure and cross-bridge-actin cyclic connections in muscles. Then a model with 2 parallel modules based on the 2 feature structures in muscles was thus developed. The model described the stress relaxation and stretching of passive muscles from honey bee abdomen well for a good fitting in stress relaxation and verification in loading process. In addition, the stiffness change of cross-bridge under different concentrations of blebbistatin is obtained from the model. We derived the elastic deformation of cross-bridge and the partial derivatives of energy expressions on motion parameters from this model, which accorded the experimental results. This model reveals the mechanism of passive muscles from honey bee abdomens suggesting that the temporary energy storage of cross-bridge in terga muscles under abdomen bending provides potential energy for springback during the periodic abdomen bending of honey bee or other arthropod insects. The finding also provides an experimental and theoretical basis for the novel microstructure and material design of bionic muscle.

Acoustic emission and DSC investigations of anomalous stress-stain curves and burst like shape recovery of Ni49Fe18Ga27Co6 shape memory single crystals

Simultaneous acoustic emission, AE, and DSC measurements under compression along [110]A direction were carried out on Ni49Fe18Ga27Co6 shape memory single crystals. The compression resulted in anomalous stress-strain loops with stress drops/jumps on it, reflecting a sudden formation/dissolution of a more stable (detwinned) martensite structural modification than the thermally induced (twinned) one. The final detwinned martensite, obtained below a certain temperature, was stable even after downloading: during heating it showed a burst-like recovery at about 35K higher transformation temperature than that of the thermally induced one, with an audible click. It was obtained that the number of acoustic events showed strong asymmetry: e.g. for stress induced transformations the number of hits for uploading was larger. Simultaneous measurements of stress-time curves and AE versus time revealed that in the nucleation/dissolution processes in both (up and down) directions, as an intermediate step, the twinned martensite was first formed and resulted in additional AE events. This was interpreted by the easy as well as difficult nucleation of the twinned and detwinned martensites, respectively. The stress drops on the uploading stress-strain curve were attributed to subsequent nucleation of the detwinned martensite from the twinned modification and were followed by a sharp decrease of the AE activity. This indicated that the formation of detwinned martensite is a sudden, fast process and can take place without significant elastic energy storage. This was also in agreement with the fact that during burst like thermal recovery the width of the transition was very small (Af≅ As). Similarly, during downloading the stress jumps were interpreted as sudden dissolutions of the detwinned phase by retwinning and at all stress jumps there were local maxima on the AE activity curve.

Flat, wrinkled, or ridged: Relaxation of an elastic film on a viscous substrate undergoing continuous compression

We conduct a finite element computational study of the dynamics of a thin elastic film bonded to a much thicker viscous substrate undergoing compression at a fixed rate. The applied compression tends to continuously increase the strain, and hence the elastic energy, of the film. In contrast to the well-studied case of a soft elastic substrate, a viscous substrate cannot store elastic energy; instead it regulates the kinetics of the various mechanisms that dissipate elastic energy of the film. Sufficiently short films remain flat because shear flow in the liquid near the ends allows rapid relaxation of the strain over the entire film length. In longer films, end-relaxation cannot relax film strain in the mid-section, which therefore buckles. Buckles initially appear as packets of approximately-sinusoidal wrinkles. With increasing strain, these packets transform into tall localized ridges separated by nearly flat regions. In all cases, the buckles cause end-relaxation to become dynamically confined to a narrow region near the ends We construct a state map identifying regions of the parameter space of strain vs film length in which the film remains flat, develops wrinkle packets, or develops localized ridges. The evolution of the film energy during continuous compression shows that ridge localization appears due to a competition between two effects: a well-spaced ridges offer a lower energy state than uniform wrinkles, but wrinkles can develop faster because they require the viscous fluid to move over shorter distances.

Experimental study on dynamic mechanical properties of mortar-sandstone composite under impact load

Mortar-rock composite structures are very common in underground engineering. Their mechanical behaviour and failure modes are much more complicated than those of pure mortar or rock structures. Understanding the energy and damage evolution of composite structures under impact loads is important for the stability of engineering structures. In this paper, dynamic compression tests of different grades of mortar-sandstone composite specimens were carried out by using the Hopkinson pressure bar system and a high-speed photography system to investigate the effects of impact velocities and mortar strength on the mechanical properties, energy dissipation and failure modes of the composite specimens. The results showed that the dynamic peak stress, energy consumption characteristics, impact toughness index and fragmentation blocks of the mortar-sandstone composite were obviously affected by strain rate. The mortar-sandstone composites had a progressive failure mechanism, and the strengths of the end and the junction of the mortar specimens were less than those of other regions. Cracks formed in the composite specimens mainly from both ends of the mortar, and the specimens were dominated by splitting failure. Increasing the mortar strength grade improved the dynamic compressive strength and the elastic energy storage of the samples, resulting in larger bearing capacity and less damage. With increasing impact velocity, the degree of fragmentation of the composite specimens increased, the average fragmentation blocks decreased, and the mortar specimens were damaged more severely than the sandstone. The mortar specimens finally broke into powder debris, while the sandstone finally broke into fragments.

Mechanical Properties and Functions of Elastin: An Overview

Human tissues must be elastic, much like other materials that work under continuous loads without losing functionality. The elasticity of tissues is provided by elastin, a unique protein of the extracellular matrix (ECM) of mammals. Its function is to endow soft tissues with low stiffness, high and fully reversible extensibility, and efficient elastic-energy storage. Depending on the mechanical functions, the amount and distribution of elastin-rich elastic fibers vary between and within tissues and organs. The article presents a concise overview of the mechanical properties of elastin and its role in the elasticity of soft tissues. Both the occurrence of elastin and the relationship between its spatial arrangement and mechanical functions in a given tissue or organ are overviewed. As elastin in tissues occurs only in the form of elastic fibers, the current state of knowledge about their mechanical characteristics, as well as certain aspects of degradation of these fibers and their mechanical performance, is presented. The overview also outlines the latest understanding of the molecular basis of unique physical characteristics of elastin and, in particular, the origin of the driving force of elastic recoil after stretching.

Wing kinematics measurement and aerodynamics of hovering droneflies with wing damage

In this study, we performed successive unilateral and bilateral wing shearing to simulate wing damage in droneflies (Eristalis tenax) and measured the wing kinematics using high-speed photography technology. Two different shearing types were considered in the artificial wing damage. The aerodynamic force and power consumption were obtained by numerical method. Our major findings are the following. Different shearing methods have little influence on the kinematics, forces and energy consumption of insects. Following wing damage, among the potential strategies to adjust the three Euler angles of the wing, adjusting stroke angle (φ) in isolation, or combing the adjustment of stroke angle (φ) with pitch angle (ψ), contributed most to the change in vertical force. The balance of horizontal thrust can be restored by the adjustment of deviation angle (θ) under the condition of unilateral wing damage. Considering zero elastic energy storage, the mass-specific power (P 1) increases significantly following wing damage. However, the increase in mass-specific power with 100% elastic energy storage (P 2) is very small. The extra cost of the unilateral wing damage is that the energy consumption of the damaged wing and intact wing is highly asymmetrical when zero elastic energy storage is considered. The insects may alleviate the problems of increasing power consumption and asymmetric power distribution by storage and reuse of the negative inertial work of the wing.

Self-organization and mechanism of friction during cutting

The regularities of friction during cutting are considered on the basis of the approaches of thermodynamics and the theory of self-organization. It is shown that the average coefficient of friction during cutting is significantly determined by the intensity of phase and structural transformations in the zone of secondary chip deformation, which affect the contact length, chip shrinkage, and its load-bearing capacity. From the standpoint of the theory of self-organization, friction during cutting should be considered as the storage of elastic deformation energy in the boundary layer and its dissipation through various mechanisms that cause wear of the cutting tool and self-oscillations during cutting. Keywords: metal cutting, secondary deformation, structural changes, plastic structures. uru.40@mail.ru

Designing Custom Mechanics in Running-Specific Prosthetic Feet via Shape Optimization.

Running-specific prosthetic feet are curved cantilever springs, distinguished from ordinary prosthetic feet by their size, shape, and greater ability to store and return elastic potential energy. Finite element analyses show how modifications to prosthesis shape alter the multidimensional and nonlinear mechanics, but designers seeking to prescribe custom mechanics are limited by the complex constraints and high dimensionality of possible geometries. We introduce two simple formulations for describing foot mechanics, and use them with a custom spline-based shape optimization to generate new prosthetic foot shapes given desired endpoint mechanics. We then tackle a relevant example problem using this approach, designing and characterizing three running-specific prosthetic feet with similar vertical and angular deflections but varied horizontal deflections, with the expectation that knee extension moments would increase with anterior deflection of the toe. Finally, we compare the prostheses' endpoint mechanics and resulting biomechanics in an athlete with unilateral transfemoral amputation. The shape optimization was able to derive shapes that substantially alter prosthesis mechanics along all dimensions of endpoint behavior, and benchtop testing validated the behavior of two new feet constructed from the optimization. The subject's knee moments increased with horizontal endpoint deflection as expected. We developed and validated a shape optimization tool using a simplified formulation of foot behavior to achieve desired running prosthesis mechanics. With this framework, researchers can begin to elucidate the link between prosthesis mechanics and athlete biomechanics and performance.

Insect-scale jumping robots enabled by a dynamic buckling cascade

Millions of years of evolution have allowed animals to develop unusual locomotion capabilities. A striking example is the legless-jumping of click beetles and trap-jaw ants, which jump more than 10 times their body length. Their delicate musculoskeletal system amplifies their muscles' power. It is challenging to engineer insect-scale jumpers that use onboard actuators for both elastic energy storage and power amplification. Typical jumpers require a combination of at least two actuator mechanisms for elastic energy storage and jump triggering, leading to complex designs having many parts. Here, we report the new concept of dynamic buckling cascading, in which a single unidirectional actuation stroke drives an elastic beam through a sequence of energy-storing buckling modes automatically followed by spontaneous impulsive snapping at a critical triggering threshold. Integrating this cascade in a robot enables jumping with unidirectional muscles and power amplification (JUMPA). These JUMPA systems use a single lightweight mechanism for energy storage and release with a mass of 1.6 g and 2 cm length and jump up to 0.9 m, 40 times their body length. They jump repeatedly by reengaging the latch and using coiled artificial muscles to restore elastic energy. The robots reach their performance limits guided by theoretical analysis of snap-through and momentum exchange during ground collision. These jumpers reach the energy densities typical of the best macroscale jumping robots, while also matching the rapid escape times of jumping insects, thus demonstrating the path toward future applications including proximity sensing, inspection, and search and rescue.

Musculoskeletal simulations to examine the effects of accentuated eccentric loading (AEL) on jump height.

During counter movement jumps, adding weight in the eccentric phase and then suddenly releasing this weight during the concentric phase, known as accentuated eccentric loading (AEL), has been suggested to immediately improve jumping performance. The level of evidence for the positive effects of AEL remains weak, with conflicting evidence over the effectiveness in enhancing performance. Therefore, we proposed to theoretically explore the influence of implementing AEL during constrained vertical jumping using computer modelling and simulation and examined whether the proposed mechanism of enhanced power, increased elastic energy storage and return, could enhance work and power. We used a simplified model, consisting of a ball-shaped body (head, arm, and trunk), two lower limb segments (thigh and shank), and four muscles, to simulate the mechanisms of AEL. We adjusted the key activation parameters of the muscles to influence the performance outcome of the model. Numerical optimization was applied to search the optimal solution for the model. We implemented AEL and non-AEL conditions in the model to compare the simulated data between conditions. Our model predicted that the optimal jumping performance was achieved when the model utilized the whole joint range. However, there was no difference in jumping performance in AEL and non-AEL conditions because the model began its push-off at the similar state (posture, fiber length, fiber velocity, fiber force, tendon length, and the same activation level). Therefore, the optimal solution predicted by the model was primarily driven by intrinsic muscle dynamics (force-length-velocity relationship), and this coupled with the similar model state at the start of the push-off, resulting in similar push-off performance across all conditions. There was also no evidence of additional tendon-loading effect in AEL conditions compared to non-AEL condition. Our simplified simulations did not show improved jump performance with AEL, contrasting with experimental studies. The reduced model demonstrates that increased energy storage from the additional mass alone is not sufficient to induce increased performance and that other factors like differences in activation strategies or movement paths are more likely to contribute to enhanced performance.

Geometric latches enable tuning of ultrafast, spring-propelled movements.

The smallest, fastest, repeated-use movements are propelled by power-dense elastic mechanisms, yet the key to their energetic control may be found in the latch-like mechanisms that mediate transformation from elastic potential energy to kinetic energy. Here, we tested how geometric latches enable consistent or variable outputs in ultrafast, spring-propelled systems. We constructed a reduced-order mathematical model of a spring-propelled system that uses a torque reversal (over-center) geometric latch. The model was parameterized to match the scales and mechanisms of ultrafast systems, specifically snapping shrimp. We simulated geometric and energetic configurations that enabled or reduced variation of strike durations and dactyl rotations given variation of stored elastic energy and latch mediation. Then, we collected an experimental dataset of the energy storage mechanism and ultrafast snaps of live snapping shrimp (Alpheus heterochaelis) and compared our simulations with their configuration. We discovered that snapping shrimp deform the propodus exoskeleton prior to the strike, which may contribute to elastic energy storage. Regardless of the amount of variation in spring loading duration, strike durations were far less variable than spring loading durations. When we simulated this species' morphological configuration in our mathematical model, we found that the low variability of strike duration is consistent with their torque reversal geometry. Even so, our simulations indicate that torque reversal systems can achieve either variable or invariant outputs through small adjustments to geometry. Our combined experiments and mathematical simulations reveal the capacity of geometric latches to enable, reduce or enhance variation of ultrafast movements in biological and synthetic systems.

Fracture characteristics and energy evolution analysis of pre-cracked granite under uniaxial compression based on a 3D-Clump model

To develop a numerical model that can truly reflect the internal structure and mechanical properties of pre-cracked granite realistically, an efficient method for constructing a three-dimensional Clump (3D-Clump) numerical model of pre-cracked granite was proposed based on three-dimensional Particle Flow Code (PFC3D) in this paper. Laboratory uniaxial compression experiments and numerical simulations were conducted on six different pre-cracked granite cylinder specimens with the dimension of ϕ50 mm × 100 mm to obtain the stress–strain response and damage modes. The axial loading rate on the specimens and numerical models was 0.10 mm/min. The relative errors of peak strength σp and elastic modulus E were also compared and analyzed. The relationship between each energy and the variation of stress–strain and cracking during the loading process of numerical simulation was also explored. Results indicate that the relative errors of peak strength and elastic modulus between numerical simulation and laboratory experiments are below 5.00 %. The consistency between the experimental and numerical results indicates that the proposed 3D-Clump numerical model of pre-cracked granite is reliable. A wider damage zone forms in the numerical model at the interconnected crack between the pre-cracked endpoints or at the secondary crack, which is in good agreement with the damage mode of the laboratory experiment. Before the peak point under uniaxial compression in the numerical simulation is mainly the storage of elastic strain energy and the slow dissipation of energy. After the peak point, the elastic strain energy releases sharply, the dissipation energy increases rapidly, the microcrack extension rate increases sharply, the slip dislocation appears obviously, and the crack penetration leads to the destruction of the specimen eventually.

Fracture Energy and Breakdown Work During Earthquakes

Large seismogenic faults consist of approximately meter-thick fault cores surrounded by hundreds-of-meters-thick damage zones. Earthquakes are generated by rupture propagation and slip within fault cores and dissipate the stored elastic strain energy in fracture and frictional processes in the fault zone and in radiated seismic waves. Understanding this energy partitioning is fundamental in earthquake mechanics to explain fault dynamic weakening and causative rupture processes operating over different spatial and temporal scales. The energy dissipated in the earthquake rupture propagation along a fault is called fracture energy or breakdown work. Here we review fracture energy estimates from seismological, modeling, geological, and experimental studies and show that fracture energy scales with fault slip. We conclude that although material-dependent constant fracture energies are important at the microscale for fracturing grains of the fault zone, they are negligible with respect to the macroscale processes governing rupture propagation on natural faults. ▪ Earthquake ruptures propagate on geological faults and dissipate energy in fracture and frictional processes from micro- (less than a millimeter) to macroscale (centimeters to kilometers). ▪ The energy dissipated in earthquake rupture propagation is called fracture energy ( G) or breakdown work ( Wb) and scales with coseismic slip. ▪ For earthquake ruptures in natural faults, the estimates of G and Wbare consistent with a macroscale description of causative processes. ▪ The energy budget of an earthquake remains controversial, and contributions from different disciplines are required to unravel this issue.

Magnetically controlled bio-inspired elastomeric actuators with high mechanical energy storage.

Many biological systems are made to operate more quickly, efficiently, and with more power by storing elastic energy. This work introduces a straightforward bioinspired design for the quick manufacture of pre-stressed soft magnetic actuators. The actuator requires a lower magnetic field strength to be activated and can regain its original shape without the need for external stimuli. These characteristics are demonstrated in this work through the creation of actuators with round and helical shape structures inspired by the tendril plant and chameleon's tongue. Both the final form of the actuator and its actuation sequence may be programmed by controlling the direction and strength of the force utilised to pre-stress the elastomeric layer. Analytical models are presented to trace the actuators' energy storage, radius, and pitch. High-speed shape recovery after releasing the magnetic force and a strong grasping force are achieved due to the stored mechanical elastic energy. Experiments are conducted to analyse the shape changes, grasping action, and determine the actuation force. The manufacture of the grippers with zero-magnetic field strength holding capacities of up to 20 times their weight is made possible by the elastic energy that actuators store in their pre-stressed elastomeric layer. The outcomes of our research show that a unique magnetic field-controlled soft actuator can be created in different shapes and designs based on requirements.