Mechanical Energy Release Research Articles

Mechanical testing of particle streaming and intact extracellular mucilage nanofibers reveal a role of elastic force in diatom motility

Diatoms are unicellular microalgae with a rigid cell wall, able to glide on surfaces by releasing nanopolymeric fibers through central slits known as raphes. Here we consider the model Nitszchia communis to perform quantitative studies on two complementary aspects involved in diatom gliding. Using video microscopy and automated image analysis, we measure the motion of test beads as they are pulled by extracellular polymeric substances (EPS) fibers at the diatom raphe (particle streaming). A multimodal distribution of particle speed is found, evidencing the appearance of short-time events of high speed and acceleration (known as jerky motion) and suggesting that different mechanisms contribute to set diatom velocity during gliding. Furthermore, we use optical tweezers to obtain force-extension records for extracellular diatom nanofibers; records are well described by the worm-like chain model of polymer elasticity. In contrast to previous studies based on application of denaturing force (in the nN regime), application of low force (up to 6 pN) and using enable us to obtain the persistence length of intact fibers. From these measurements, mechanical parameters of EPS fibers such as radius and elastic constant are estimated. Furthermore, by modeling particle streaming as a spring in parallel with a dashpot, we show that the time involved in the release of mechanical energy after fiber detachment from beads (elastic snapping) agrees with our observations of jerky motion. We conclude that the smooth and jerky motions displayed by gliding diatoms correspond to molecular motors and elastic snapping, respectively, thus providing quantitative elements that incorporate to current models of the mechanics behind diatom locomotion.

Double peak quasi-periodic pulsations in a circular-ribbon flare

We study quasi-periodic pulsations (QPPs) during the impulsive phase of the C8.3 flare SOL2002-08-06T01:43. The shape of an extended 5.7 GHz source is similar to a tadpole with the head located above the region of a negative magnetic polarity, surrounded by positive polarity patches and with a remote tail source. The flare configuration includes bright extreme ultraviolet (EUV) ropes with footpoints near the boundary of the negative magnetic field region and it can be identified as a circular ribbon flare. We use simultaneous observations carried out by the Siberian Solar Radio Telescope at 5.7 GHz, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)/HXR, and the Transition Region and Coronal Explorer (TRACE) imaging in the extreme ultraviolet. The flare HXR emission is produced by a compact source located at the south periphery of the Negative Magnetic field Region (NMR). The QPPs are observed during a one-minute interval after the start of the impulsive phase, when this HXR source appeared. The remote source is detected on the variation maps of the of the brightness temperature at 17 GHz and is located at the end of tadpole tail about 60 arcsec eastward. More than a dozen cotemporal HXR and microwave pulses with timescales from 1.5 s up to about 8 s were observed in the flare kernel. At 5.7 GHz, the pulses are more prominent near the remote source where they are highly polarized and generated by the electron beams propagating from the flare kernel. The main tone of the QPP periodicity corresponds to the oscillations with a period of 8 s and is accompanied by the variations in the hardness of nonthermal electrons, that is, in the efficiency of the acceleration mechanism. The second intensity harmonic (about a 3-s period) appears due to a double peak structure of the QPP event. Such pulse shapes suggest oscillations of the current sheet during the loop coalescence as a modulation mechanism of the flare energy release.

Novel Multi-Segment Foot Model Incorporating Plantar Aponeurosis for Detailed Kinematic and Kinetic Analyses of the Foot With Application to Gait Studies.

Kinetic multi-segment foot models have been proposed to evaluate the forces and moments generated in the foot during walking based on inverse dynamics calculations. However, these models did not consider the plantar aponeurosis (PA) despite its potential importance in generation of the ground reaction forces and storage and release of mechanical energy. This study aimed to develop a novel multi-segment foot model incorporating the PA to better elucidate foot kinetics. The foot model comprised three segments: the phalanx, forefoot, and hindfoot. The PA was modeled using five linear springs connecting the origins and the insertions via intermediate points. To demonstrate the efficacy of the foot model, an inverse dynamic analysis of human gait was performed and how the inclusion of the PA model altered the estimated joint moments was examined. Ten healthy men walked along a walkway with two force plates placed in series close together. The attempts in which the participant placed his fore- and hindfoot on the front and rear force plates, respectively, were selected for inverse dynamic analysis. The stiffness and the natural length of each PA spring remain largely uncertain. Therefore, a sensitivity analysis was conducted to evaluate how the estimated joint moments were altered by the changes in the two parameters within a range reported by previous studies. The present model incorporating the PA predicted that 13%–45% of plantarflexion in the metatarsophalangeal (MTP) joint and 8%–29% of plantarflexion in the midtarsal joints were generated by the PA at the time of push-off during walking. The midtarsal joint generated positive work, whereas the MTP joint generated negative work in the late stance phase. The positive and negative work done by the two joints decreased, indicating that the PA contributed towards transfer of the energy absorbed at the MTP joint to generate positive work at the midtarsal joint during walking. Although validation is limited due to the difficulty associated with direct measurement of the PA force in vivo, the proposed novel foot model may serve as a useful tool to clarify the function and mechanical effects of the PA and the foot during dynamic movements.

Quantitative characterization of Q235B steel electrochemical corrosion by acoustic emission

The mechanism of dissolving acoustic source of Q235B corrosion anode metal is the basis of acoustic emission (AE) source identification and corrosion site evaluation and analysis. In this paper, the local mechanical energy release and the characteristics of radiated elastic wave pulse in the process of metal dissolution are analyzed by using the principles of corrosion dynamics, damage thermodynamic energy conversion, local mechanical energy release and radiation elastic wave pulse characteristics of metal dissolving process, and the theoretical analysis is verified by atomic first numerical method. Combined with AE and electrochemical testing technology, the mechanism of Q235B steel corrosion acoustic source is studied experimentally. The characteristics of the metal dissolved acoustic source are obtained, and the energy conversion value of anode metal in the process of dissolution is extracted. The quantitative characterization formula of the corrosion behavior of the AE is established, which provides a basis for the assessment of the severity of the corrosion state of Q235B steel.

Application of Modern Acoustic Technology and Acoustic Emission Equipment in Rock Mechanics

The development of modern physics has promoted the progress of traditional rock physics and mechanics, especially Sheng emission technology based on acoustics. In order to study the acoustic characteristics of rock specimens under compression, the test is carried out with the help of Sheng emission technology, the mechanical characteristic parameters of rock physics and mechanics are measured, and the sound source position and radiation energy parameters of rock fracture are obtained. Combined with the numerical simulation software MATLAB and fractal theory, the energy release mechanism of rock samples is analyzed. The acoustic characteristics of rock samples are remarkable, and the three-dimensional spatial coordinates of rock fracture source can be measured scientifically and accurately, with an accuracy of 99.98%, making it possible to reproduce the three-dimensional fracture source. It is found that the distribution of main fracture sources and high-energy fracture sources can be one-to-one corresponding and consistent with the external fracture failure mode of rock; Through interpolation inversion and energy parameter simulation analysis, slice processing is carried out to obtain the inversion results of energy distribution and test pieces. The process of microcrack propagation and propagation is completely consistent. Based on the analysis of physical mechanics and acoustic characteristics: the numerical simulation analysis of rock specimen failure process can not only reflect the dynamic failure process of rock, but also provide guidance for the prediction and analysis of mine disaster evolution.

Programming Soft Shape-Morphing Systems by Harnessing Strain Mismatch and Snap-Through Bistability: A Review.

Multi-modal and controllable shape-morphing constitutes the cornerstone of the functionalization of soft actuators/robots. Involving heterogeneity through material layout is a widely used strategy to generate internal mismatches in active morphing structures. Once triggered by external stimuli, the entire structure undergoes cooperative deformation by minimizing the potential energy. However, the intrinsic limitation of soft materials emerges when it comes to applications such as soft actuators or load-bearing structures that require fast response and large output force. Many researchers have explored the use of the structural principle of snap-through bistability as the morphing mechanisms. Bistable or multi-stable mechanical systems possess more than one local energy minimum and are capable of resting in any of these equilibrium states without external forces. The snap-through motion could overcome energy barriers to switch among these stable or metastable states with dramatically distinct geometries. Attributed to the energy storage and release mechanism, such snap-through transition is quite highly efficient, accompanied by fast response speed, large displacement magnitude, high manipulation strength, and moderate driving force. For example, the shape-morphing timescale of conventional hydrogel systems is usually tens of minutes, while the activation time of hydrogel actuators using the elastic snapping instability strategy can be reduced to below 1 s. By rationally embedding stimuli-responsive inclusions to offer the required trigger energy, various controllable snap-through actuations could be achieved. This review summarizes the current shape-morphing programming strategies based on mismatch strain induced by material heterogeneity, with emphasis on how to leverage snap-through bistability to broaden the applications of the shape-morphing structures in soft robotics and mechanical metamaterials.

AE energy evolution during CJB fracture affected by rock heterogeneity and column irregularity under lateral pressure

Considering that the mechanical mechanism and energy release law of gradual failure of columnar jointed basalt (CJB) are affected by lateral pressure, rock heterogeneity and column irregularity, etc., the numerical CJB models with various column dip angles, irregularity degrees of column and lateral pressures were established through the digital image correlation. The progressive failure process and released energy of CJBs were simulated under the loading rate of 0.05 mm/step based the continuum mechanics and statistical damage theory. The influences of rock inhomogeneity, column irregularity degree, and model boundary on the nonlinear deformation and failure of CJB were comprehensively investigated. The results demonstrate that the effect of the inhomogeneity index depends on column dip angle, and the equivalent deformation modulus of CJBs is more sensitive to the inhomogeneity index than the lateral pressure. Moreover, the compressive strength along the direction perpendicular to the column axis basically decreases with column irregularity degree increasing when the meso strength of rock is 120 MPa. Besides, the mechanical properties and elastic energy of irregular CJBs are greatly affected by the model boundaries. These achievements will contribute to understanding the inner failure mechanism and energy evolution of CJBs.

Quantitative determination of impact release energy for TiZrHfX0.3 multicomponent materials in vacuum environment

Multicomponent materials have been widely used in the field of national defense due to their excellent mechanical properties and impact energy release characteristics. In order to obtain the effect of trace element and impact velocity on energy release, TiZrHfCu0.3, TiZrHfAl0.3 and TiZrHfNi0.3 multicomponent materials are used as the research object. The response parameters such as perforation diameter and penetration depth, flash radiant temperature, gas overpressure, flame propagation velocity and vessel wall temperature rise induced by multicomponent materials projectile impacting on the target in vacuum environment are measured in a quasi-closed vessel. The deformation energy of target, mixed gas enthalpy in the vessel, flash radiant energy, absorbed energy of quasi-closed vessel wall and injected gas enthalpy are calculated theoretically, respectively. Then the impact energy release is determined quantitatively and compared with the calculating results of the Ames impact energy release model. The results show that the impact release energy of per unit mass projectile increases with the increasing of impact velocity, but the increase amplitude is small. However, the impact energy release capacity from the strongest to the weakest is TiZrHfCu0.3, TiZrHfAl0.3 and TiZrHfNi0.3, respectively. Because the energy loss is not considered in the Ames model, the calculating result of the Ames model is lower than that of this method.

Energy release characteristics and mechanism of rock beam fracture: a case study from laboratory tests to field application

Energy release characteristics and mechanism of rock beam fracture: a case study from laboratory tests to field application

Triggering the energy release in molecular solar thermal systems: Norbornadiene-functionalized trioxatriangulen on Au(111)

Molecular solar thermal systems (MOST) based on molecular photoswitches are a promising technology for the smart management of solar energy at small scale. In this work, we study the catalytically triggered energy release mechanism in the norbornadiene/quadricyclane (NBD/QC) couple. We scrutinize a tailor-made NBD-functionalized trioxatriangulen (TOTA-NBD) derivative, which is assembled in form of atomically defined films on an ultraclean Au(111) surface. By in-situ infrared reflection absorption spectroscopy (IRAS) we show that TOTA-QC in direct contact with Au is rapidly back-converted to TOTA-NBD, while there is no back-conversion of TOTA-QC molecules in the second layer or in the multilayer. Our results suggest that Au catalyzes the energy release from QC with very high efficiency through direct electronic coupling to the metal states. This mechanism provides a pathway for the energy release from NBD/QC photoswitches without activation of CH bonds and may enable the design of catalytically triggered MOST devices with very high cyclability

Effect of Aluminum Powder Content on Air Blast Performance of RDX-Based Explosive Grenade Charge

For aluminized explosive, the charge performance of explosive grenade is very significant for promoting their application. Firstly, the detonation performance of cyclotrimethylenetrinitramine (RDX) based explosives with different aluminum powder (0%, 20%, 25%, 30%, 35%, and 40%, respectively) content was investigated. Next, the air blast tests of RDX-based aluminized explosives were carried out. Then, RDX-based explosive grenade charges of L-1 and L-2 where the aluminum powder content was 20% and 25% were selected for air blast and static blasting fragments velocity tests. Finally, the energy release mechanism of the air blast was deduced via calculation. The results show that RDX-based aluminized explosives have higher detonation heat, detonation velocity, and detonation volume when the aluminum powder content is 20%, and the shock wave over pressure as well as impulse keep a high level at the same time within 4.5 m. The air blast performance of L-1 is better than L-2 within 2.2 m. As the distance increases, the air blast energy of L-1 is mainly used for shell rupture and fragment acceleration, while the contribution of L-2 is less than that of L-1. This study demonstrated that the explosion power of RDX-based explosive grenade charge is the most powerful where the content of aluminum powder is about 20%.

Mechanisms of stored energy release in silicon carbide materials neutron-irradiated at elevated temperatures

Understanding the stored energy release behavior of SiC is crucial for the design of SiC-based fuel cladding for light water reactors because stored energy release affects response during accident conditions. Differential scanning calorimetry was used to evaluate the stored energy of monolithic SiC and SiC fiber–reinforced SiC matrix composite variants following neutron irradiation under light water reactor–relevant dose and temperature conditions. The tests were performed at heating rates of 0.5, 3, and 20 K/min up to 1,273 K. The onset temperature of the energy release roughly corresponded to the irradiation temperature, and energy release was delayed as the heating rate increased. The monolithic and composite specimens exhibited similar stored energy release behavior up to ∼ 1,000 K, and above that temperature, the energy release depended more on material type. The energy release measured in this study is below the material-specific heat capacity at temperatures below ∼1,000 K but exceeds it under certain material and annealing conditions at temperatures above ∼1,000 K. The amount of irradiation-induced volumetric swelling of the specimens was an indication of the total stored energy. Based on this observation, the energy release behavior was described by a swelling recovery model.

In-situ thermal analysis of intermetallic and thermite projectiles in high velocity impact experiments

Particle fragmentation influences thermochemical energy conversion processes in different ways and is of significance in energy generation technologies. Different reactive material formulations trigger varied thermal response in extreme environments such as high velocity impact. This study investigated optical thermal response of powder gun launched intermetallic (Al:Zr) and thermite (Al:MoO3) projectiles using pyrometry and thermography. Projectiles were launched at 1250 m/s into an air-filled chamber and impacted a steel witness plate to create a dust explosion. The pyrometer was configured to measure temperatures directly at the point of impact, while the thermographic system measured temperatures throughout the explosion chamber. Results show that impact temperatures ranged between 3500 and 4000 K, but that the dynamics of energy conversion were different for the intermetallic and thermite projectiles. The intermetallic exhibited secondary reactions due to fragmented debris impacting the walls of the chamber. The thermite exhibited greater gas generation, propelling the debris field, and producing a more stochastic response with faster spreading and dissipation of thermal energy. Unique features such as microexplosions within fragmented particles were also analyzed. While both reactive materials produce similar temperatures, their mechanisms of energy conversion and release are different, indicating the potential of these materials for different ballistic applications.

Hysteresis‐Free Nanoparticle‐Reinforced Hydrogels

AbstractThe elastic storage and release of mechanical energy has been key to many developments throughout the history of mankind. Resilience, absent hysteresis, has been an elusive goal to achieve, particularly at large deformations. Using a low‐crosslink‐density polyacrylamide hydrogel at 96% water content having hyperbranched silica nanoparticles (HBSPs) as the major junction points, a hysteresis‐free material is realized. The fatigue‐free characteristic of these composite hydrogels is evidenced by the invariance of the stress–strain curves at strain ratios of 4, even after 5000 cycles. At a strain ratio of 7, only a 1.3% hysteresis is observed. A markedly increased strain‐ratio‐at‐break of 11.5 is observed. The unique attributes of these resilient hydrogels are manifested in the high‐fidelity detection of dynamic deformations under cyclic loading over a broad range of frequencies, difficult to achieve with other materials.

Numerical Investigation on Fracture Mechanisms and Energy Evolution Characteristics of Columnar Jointed Basalts With Different Model Boundaries and Confining Pressures

To reveal the mechanical mechanisms and energy release characteristics underlying progressive failure of columnar jointed basalts (CJBs) with various model boundaries and confining pressures, by combining the meso-damage mechanics, statistical strength theory, and continuum mechanics, inhomogeneous CJB models with different dip angles to the column axis are constructed. In the cases of plane stress, plane strain, and between plane stress and plane strain, the gradual fracture processes of CJBs are simulated under different confining pressures and the acoustic emission (AE) rules are obtained. The results show that: 1) in the case of plane stress, the fracture process of CJBs along direction I orthogonal to the column axis: at the initial stage of loading, the vertical joints and the transverse joints in the CJB specimen are damaged. Then, more columns in the upper middle part are cracked; 2) in the case between plane stress and plane strain, the fracture process of CJBs along the direction parallel to the column axis: at the initial stage of loading, the columnar joints are damaged. Then, the area of the damaged and broken columns at the top of the specimen increases and the crushing degree intensifies; 3) for the case between plane stress and plane strain, the AE energy accumulation before the peak stress is higher than the plane strain state along the direction orthogonal to the column axis. Meanwhile, along the direction parallel to the column axis, this value becomes larger when changing from the state between plane stress and plane strain to the plane strain state. These achievements will certainly improve our understanding of the fracture mechanism and energy evolution of CJBs and provide valuable insights into the instability precursor of CJBs.

White-light Continuum Observation of the Off-limb Loops of the SOL2017-09-10 X8.2 Flare: Temporal and Spatial Variations

Abstract Observations of the Sun’s off-limb white-light (WL) flares offer rare opportunities to study the energy release and transport mechanisms in flare loops. One of the best such events was SOL2017-09-10, an X8.2 flare that occurred near the Sun’s west limb on 2017 September 10 and produced a WL loop system lasting more than 60 minutes and reaching an altitude higher than 30 Mm. The event was well observed by a suite of ground- and space-based instruments, including the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) that captured its off-limb loops in WL continuum near Fe i 6173 Å, and the Atmospheric Imager Assembly (SDO/AIA) that observed its ultraviolet (UV) and extreme-ultraviolet (EUV) counterparts. We found quasi-periodic pulsations in the WL and UV emissions at the flare loop-top with a period around 8.0 minutes. Each pulsation appears to have an EUV counterpart that occurs earlier in time and higher in altitude. Despite many similarities in the WL and UV images and light curves, the WL flux at the loop-top continues to grow for about 16 minutes while the UV fluxes gradually decay. We discuss the implication of these unprecedented observations on the understanding of the enigmatic off-limb WL flare emission mechanisms.

Size Effect on Inclined Cracking in Unidirectional Composites

The fracture and size effect properties of the unidirectional (UD) laminae were investigated based on the fracture energy analysis. The crack propagations on inclined fiber orientation may result in different energy release mechanisms. Therefore, the size effect behavior of these types of failures may vary according to the fracture parameters of the UD composites. This study aims to develop a fracture analysis of UD plies with inclined fibers relative to the loading axis. A numerical work with a developed material model was conducted to predict the size effect trends. The size effect law was used to fit the strength reduction with increasing size. The fundamentals of the quasibrittle fracture mechanics are shown to be applicable to analyze these types of structures. It is shown that the composite structures as quasibrittle materials, can exhibit a significant size effect.

Microseismic Response Characteristics Induced by Mining Activities: A Case Study

For deep coal mines, geological disturbances or mining activities can cause damage to coal and rock masses, easily inducing dynamic disasters such as rock bursts or coal and gas outbursts, which seriously threaten the safety production of coal mine. In this paper, first, the Liyazhuang Coal Mine introduced the SOS MS (Sensor Observation Service Microseismic) monitoring system from the Polish Research Institute and verified the accuracy of its positioning. Then, to study the characteristics of MS signals induced by different mining activities, based on the field monitoring results, the waveform and frequency spectrum characteristics of MS signals at different energy levels induced by different mining activities are analyzed, and the energy levels of MS signals caused by different mining activities are classified. Studies have shown that there are large differences in the waveform and spectral characteristics of MS signals at different energy levels. High-level energy seismic signals are characterized by large amplitudes, low frequencies, relatively concentrated distribution, long vibration duration, and slow attenuation. In addition, the relationship between mining activities and MS events is also statistically analyzed based on the spatial and temporal distribution of MS events with the advancement of working face, and the results show that the increase of vibration frequency and energy can be precursor information for roof pressure. With the advance of the working face, the MS energy has the characteristic of periodic distribution, which is consistent with the periodic weighting revealed by the working resistance of the support. This study provides a reference for further revealing the energy release mechanism of rock burst.

Phase-field modeling of electromechanical fracture in piezoelectric solids: Analytical results and numerical simulations

The optimal design, reliable manufacture and durable utilization of electromechanical systems demand objective modeling of failure under coupled electric field and mechanical actions. This is still a challenging and largely an open issue despite the large volumes of contributions from the discontinuous approach and the phase-field community for brittle fracture. In this work we propose a length scale insensitive phase-field cohesive zone model (PF-CZM) for electromechanical fracture in linear piezoelectric solids, overcoming all the issues of mesh dependence, crack tracking complexity, length scale sensitivity and crack nucleation inconsistency. More specifically, in the electromechanically coupled phase-field constitutive relations, the evolution law for the crack phase-field is established from the geometric regularization of sharp cracks and the energetic criterion in global form. In order to capture the unsymmetric mechanical and electrical fracture behavior, the mechanical energy release rate contributed from the positive cone of the effective stress in energy norm is employed as the crack driving force, resulting in a hybrid formulation. With a set of phase-field characteristic functions optimal for cohesive fracture, the critical stress upon crack nucleation and the post-peak softening regime are derived in close-form for the first time, and the experimentally observed effects of the electric field on the fracture load are predicted qualitatively. The proposed electromechanical PF-CZM is numerically implemented in the multi-field finite element method and applied to several representative examples. In all cases, as those for purely mechanical problems, the predicted crack patterns and fracture loads are insensitive to the phase-field length scale and the experimental results are well reproduced. In particular, the effect of electric field on the deflection of crack paths can be captured. These merits make the proposed PF-CZM promising in the modeling of electromechanical fracture in piezoelectric solids.

Mechanical Characteristics and Energy Dissipation Trends of Coal-Rock Combination System Samples with Different Inclination Angles under Uniaxial Compression

Coal mines are composed of multiple complex rock strata with different mechanical characteristics and energy accumulation and release performances. This implies uneven energy distribution in the coal-rock combination system (CRCS). To explore the effect of the included angle between the loading direction and the coal-rock contact surface on the mechanical properties, crack propagation mode, and energy evolution characteristics of the CRCS, the uniaxial compression tests were carried out on the CRCS samples with zero and 30° inclination angles. The obtained mechanical properties and energy dissipation trends of the tested samples were similar to those of the pure (raw) coal and rock ones but strongly depended on the inclination angles. The impact energy index of the CRCS samples was smaller than those of the pure coal and pure rock samples, and its impact tendency was less pronounced. The deformation and failure of the CRCS samples occurred in the coal part, the rock part inhibiting the development and deformation of the coal. According to the deformation and failure characteristics of the CRCS, the coal support far away from the contact surface should be strengthened in engineering practice to avoid the rock mass failure caused by the expansion and evolution of cracks in the coal part. At a 30° inclination angle, the CRCS sample was tensioned at the coal-rock contact surface, and the original cracks and pores were gradually compacted under the stress component perpendicular to the contact surface. With an increase in the inclination angle, the difference between the total energy accumulated before the peak and the released energy after the peak was reduced, and the difference between the total energy accumulated before the peak and the dissipated energy increased gradually. CRCS samples with different inclinations exhibited three damage stages: initial damage, stable damage growth, and rapid damage growth. The results obtained are considered instrumental in rockburst preventing, monitoring, and early warning under different stress environments.