Energy Release Research Articles

Employing Williams’ series for the identification of fracture mechanics parameters from phase-field simulations

Fracture mechanics and damage mechanics are two theories that describe the degradation of the bearing capacity of structures. Fracture mechanics is based on a discontinuous description of cracking, while damage mechanics proposes a continuous description of material degradation. These two approaches are often opposed in the literature, from both theoretical and numerical points of view. This work suggests correlating the two approaches by applying Williams’ series, usually dedicated to experimental results, to phase-field computations. Williams’ series are employed to extract equivalent fracture mechanics parameters as a post-processing step. The proposed analysis based on a fracture mechanics description excludes the fracture process zone. Typical fracture mechanics parameters such as energy release rate, stress intensity factors, fracture process zone size, and crack tip position are determined from the phase-field computations. The approach is illustrated on a two-dimensional structure representing a beam whose notch opening displacement is controlled. The dependence on the choice of the internal length of the phase-field model is studied. Similarities and differences between both modeling routes are discussed.

An experimental and analytical study of mode I fracture and crack kinking in thick adhesive joints

This study investigates the fracture behavior of thick adhesive joints manufactured with composite adherends and bonded with an epoxy-based structural adhesive common to the wind turbine industry. For that purpose, double cantilever beam specimens with an adhesive thickness of approximately 10 mm and different pre-crack lengths are manufactured and tested under mode I loading. Analytical approaches are compared to assess the energy release rate, including the simple beam theory, modified beam theory, compliance calibration method, and beam on an elastic and elastic-plastic foundation. In order to evaluate the applicability of the analytical approaches, an in-situ measurement method based on Digital Image Correlation is also employed to determine the energy release rate of the thick adhesive joints. The crack propagation angle is determined theoretically using the second-order crack kinking theory. A good correlation is observed between the theoretical predictions and experimental results. Furthermore, it is demonstrated that due to the T-stress, the crack tends to deviate from the middle of the joint and propagate towards the interface. By comparing different data reduction methods to evaluate the energy release rate of thick adhesive joints, recommendations for their fracture analysis are made, pinpointing the beam on an elastic and elastic-plastic foundation as the most suitable model.

Disodium terephthalate as a multifunctional additive for simultaneous enhancing the energy release performance and weakening the water reactivity of aluminum

In this study, disodium terephthalate (Na2TP) has been successfully introduced as a novel multifunctional additive for simultaneous enhancing the energy release performance and weakening the water reactivity of micro-aluminum (μ-Al). Seven μ-Al/Na2TP composites with different contents of Na2TP (R-100 to R-700) and four comparison samples have been prepared to investigate the thermochemical behaviors, combustion performances and water reactivity. Importantly, structure characterizations as well as kinetic parameters (e.g., Ea, ΔS‡) have been performed to reveal the impacts of Na2TP on μ-Al oxidation. Moreover, incorporating Na2TP into μ-Al shows the enhancement of energy release, with R-400 exhibiting the highest heat release (4970 J/g) in the main oxidation stage, compared to μ-Al (1696 J/g). Interestingly, μ-Al shows an increased Ea while R-400 exhibits a decreased Ea as the oxidation proceeds. The decomposition of Na2TP generates both heat and CO2 gases, which are beneficial for destroying alumina shell and increasing oxidation kinetics, in consistent with higher positive ΔS‡ value, rougher surface, and higher surface O content for oxidation of R-400 compared to μ-Al. As a result, the enhanced combustion performances of higher peak pressure, pressurization rate and characteristic shock velocity as well as brighter/larger flame images have been achieved by μ-Al/Na2TP composites. On the other hand, water reactivity of μ-Al has been significantly suppressed by introducing Na2TP in terms of the 85.4 % decrease in heat release, elevated Ea, and alteration of reaction mechanism. Consequently, taking organic Na2TP as a multifunctional additive, two birds of enhancing the energy release and weakening the water reactivity is harvested, showing great potentials in improving the performances of metal-based energy systems.

Difunctional POM-based artificial leaf with directed charge transfer to promote photosynthetic overall reaction

The photosynthetic overall reaction represents a highly attractive and challenging research direction. Polyoxometalate-cellulose hybrid artificial leaves can improve photosynthetic activity by directed charge transport. At present, the overall reaction is confined to the interaction of gases with liquids, involving micro-substrate conversion in the same reaction system. In this paper, we report on a membranous polyoxometalate-based artificial leaf (3 %Ru3SiW12@cellulose) that efficiently performs 5-hydroxymethylfurfural oxidation coupled with furfural and CO2 reduction, exhibiting high selectivity across two spatially separate reaction systems. Notably, the photocatalysis and charge separation efficiency, facilitated by the regulation of cellulose, have significantly increased, positioning this approach at the forefront of photocatalyst research. Crucially, the artificial leaf is capable of light absorption, charge separation, charge storage, and energy release, allowing for the spatial and temporal decoupling of light and dark reactions. Overall, this study proposes a novel strategy for the development of a promising polyoxometalate-based reaction system with enhanced solar energy utilization.

Experimental studies of confined detonations of plasticized high explosives in inert and reactive atmospheres

When explosives detonate in a confined space, repeated boundary reflections result in complex shock interactions and the formation of a uniform quasi-static pressure (QSP). For fuel-rich explosives, mixing of partially oxidized detonation products with an oxygen-rich atmosphere results in a further energy release through rapid secondary combustion or ‘afterburn’. While empirical formulae and thermochemical modelling approaches have been developed to predict QSP, a lack of high-fidelity experimental data means questions remain around the deterministic quality of confined explosions, and the magnitude and mechanisms of afterburn reactions. This article presents experimental data for RDX- and PETN-based plastic explosives, demonstrating the high repeatability of the QSP generated in a sealed chamber using pressure transducers and high-speed infrared thermometry. Detonations in air, nitrogen and argon atmospheres are used to identify the contribution of afterburn to total QSP, to estimate the duration of afterburn reactions and to speculate on the flame temperature associated with this mechanism. Computational fluid dynamic modelling of the experiments was also able to accurately predict these effects. Understanding and quantifying explosions in complex environments are critical for the design of effective protective structures: the mechanisms described here provide a significant step towards the development of fast-running engineering models for internal blast events.

High-efficiency synthesis of B@Mg@KNO3 by solvent extraction enhances the ignition and energy release performance of B

Boron (B) is widely acknowledged as the preferred fuel for rocket ramjets. Nevertheless, the presence of boron oxide (B2O3) on the surface of boron impedes the interaction between the oxidized component and the internal active component B, leading to challenges in ignition and constraints on reactivity and combustion efficiency. To mitigate these issues, high-energy materials featuring a B@Mg@KNO3 coating structure were efficiently and expeditiously prepared using a solvent extraction method. The B@Mg@KNO3 material distributes magnesium inside and outside the B shell, while KNO3 serves as the load layer. The addition of the load layer facilitates closer contact between Mg and the oxidizer, reducing the diffusion distance between oxygen and fuel. As a result, the ignition energy of B is reduced, and the energy release characteristic of B is improved through multi-effect coordination. In comparison with the B/KNO3 sample, the heat release of B@Mg@KNO3 increased by 113.1%, the ignition temperature decreased by 50°C, and the ignition energy decreased by 62.5% as indicated by the ignition test. The flame temperature increased by 51.8%, the combustion efficiency of B@Mg@KNO3 increased by 23.92%, and the apparent activation energy decreased by 109.6kJ/mol. Consequently, B@Mg@KNO3 is anticipated to expedite the application and advancement of boron-based rocket ramjet engines.

Thermodynamic and economic analysis of multi-generation system based on LNG-LAES integrating with air separation unit

LNG consumption is rising globally, releasing significant cold energy during regasification. Coupling LNG vaporization with liquid air energy storage (LAES) maximizes this cold energy recovery, enhancing LAES efficiency. However, current LNG-LAES systems face issues like insufficient high-grade cold energy use and high liquid air temperatures. LAES's inability to recover LNG cold energy during energy release necessitates cold storage fluid, increasing costs. Safety concerns also arise from LNG and air coexisting in the same heat exchanger, and LNG vaporization fluctuations can destabilize LAES operations. This study proposes a multi-generation system (LNG-LAES-ASU) incorporating an air separation unit (ASU) to address these challenges. The ASU recovers LNG cold energy during energy release, adapts to LNG vaporization fluctuations, and reduces ASU energy consumption. Energy, economic, and peak-shaving performance analyses show the system achieves a 91.07 % round-trip efficiency (RTE). The ASU's average energy consumption is 0.1356–0.1506 kWh/Nm³ O₂, much lower than a standalone ASU's 0.4 kWh/Nm³ O₂. Over 30 years, the system yields a net present value (NPV) of $56,111,291 and a dynamic payback period of 3.23 years. Its peak-shaving capacity is 2.47–2.57 times greater than LNG-LAES alone. This research offers valuable insights into efficient LNG cold energy utilization.

Giant mechanical energy storage capacity and long-term mechanical cyclability in a fine-grained Heusler-type Co51V33Ga16 shape memory alloy

Shape memory alloys can be exploited for the storage of mechanical energy by utilizing the stress-driven superelasticity. However, the intrinsic hysteresis and non-linear stress-strain response endowed by the first-order martensitic transformation cripple the efficient utilization and controllable release of stored energy. Here, we demonstrate an effective strategy to realize stable linear superelasticity with low hysteresis and giant mechanical energy storage capacity. By utilizing rapid solidification to engineering grain size and crystallographic orientation, a fine-grained Co51V33Ga16 alloy with weakly preferred orientation was synthesized through suction casting. Such microstructure enables large amounts of residual martensite to be trapped by mechanical training, yielding a rate-independent linear superelasticity in a wide temperature range from 290 K to 400 K. Moreover, under a maximum strain of 4.5 %, giant stored energy higher than 20.5 MJ m−3 and small dissipated energy lower than 0.5 MJ m−3 can be retained for more than 200000 cycles of superelastic deformation, being superior to those in most shape memory alloys reported so far.

Fracture toughness resistance curves for a delamination in CFRP MD laminate composites, Part II: Mixed-mode deformation

The use of composite laminates continues to increase, especially in the aerospace industry, due to their high strength-to-weight ratio, resistance to corrosion, and surface degradation. However, in such materials, separation of plies, referred to as delamination, is common. Characterization of the driving forces causing delamination initiation and propagation is different in the case of mode I, mode II, or mixed-mode I/II deformations. This paper is Part II of a two-paper series. Results from calibrated end-loaded split specimens, producing nearly mode II deformation, were presented in Part I. Here, mixed-mode end-loaded split, quasi-static tests were performed. Two multi-directional carbon fiber reinforced polymer material systems are considered and are referred to as the ’wet-layup’ and ’prepreg’, which is attributed to their manufacturing process. Based upon results from three-dimensional finite element analyses in conjunction with the displacement extrapolation method, as well as with the conservative interaction energy or M-integral, stress intensity factors were determined. Based upon the obtained stress intensity factors, the in-plane and out-of-plane mode mixities were evaluated by means of phase angles as a function of the delamination extension through the specimen width. In addition, fracture toughness resistance curves, or R-curves, were generated as a function of delamination extension. The critical interface initiation and fracture resistance interface energy release rate values were determined based on the obtained stress intensity factors and compared with values obtained from the J-integral. Both methods are considered local. Additionally, the global experimental compliance method was employed.Differences of less than 4% for the prepreg and 12% for the wet-layup were observed between the results obtained using the global and local methods. Moreover, it was found that although the materials and interfaces tested are different, the average in-plane mode mixity, as measured by the in-plane phase angle, was found to range between 0.645 rad and 0.668 rad. This implies that the opening mode is dominant for these specimens. In addition, the critical values of the interface energy release rate for initiation Gic and the steady state propagation Giss of the two materials were found to be relatively close although the failure mechanisms are not the same.

A three-dimensional coupled thermo-elastic-plastic phase field model for the brittle-ductile failure mode transition of metals

Dynamic brittle fracture and shear banding are two typical failure modes of metals, and the transformation of the brittle-ductile failure mode has been observed in the Kalthoff test. This paper establishes a thermo-elastic-plastic coupled three-dimensional phase field model to simulate brittle-ductile failure mode transition of metals. The expression for the variation of the Taylor-Quinney coefficient with stress triaxiality is adopted, and the critical energy release rate is automatically adjusted using the Taylor-Quinney coefficient. Then, the Kalthoff test is simulated using the proposed model. The brittle-ductile failure mode transformation phenomenon is reproduced, which agrees well with the experimental results. It can be well proved that impact velocity is crucial in determining the transition to failure mode. At low-velocity impact, the energy is insufficient to drive the plastic accumulation of the shear band, resulting in brittle tensile fracture. At high-velocity impact, the energy is sufficient to drive the formation of adiabatic shear bands, resulting in tensile shear failure. In addition, three-dimensional simulations show that the tip of the shear band exhibits a crescent-shaped non-two-dimensional extension state under finite thickness. This numerical framework provides a predictive tool to understand the evolution of the dynamic failure of metals under impact loading.

Study of synergistic and competitive mechanisms on toughening CFRP composites with intrinsic and extrinsic multiscale interleaves

Delamination damage is a common failure mode of carbon fiber reinforced polymer (CFRP) laminates, which severely limits their application. This paper proposes a novel interlaminar toughening structure based on intrinsic and extrinsic multiscale toughening mechanisms using nanoscale multi-walled carbon nanotubes (MWCNTs) and microscale core-shell rubber (CSR). The resin sample M-0.5/C-8, containing 0.5 wt% MWCNTs and 8 wt% CSR, exhibited significant improvements in fracture toughness, with increases of 183.3 % in KIC, Resin and 412.1 % in GIC, Resin. However, its flexural strength and modulus decreased by 3.1 % and 3.3 %, respectively. Introducing MWCNTs and CSR into the interlayers of the CFRP, the interleaved toughened CFRP laminate exhibited a 123.3 % improvement in the mode-I critical energy release rate (GIC, Comp) and a 79.6 % increase in the mode-II critical energy release rate (GIIC, Comp) during the crack propagation stage, without sacrificing flexural performance. This remarkable enhancement in interlaminar fracture toughness results from the simultaneous triggering of nanoscale extrinsic toughening and microscale intrinsic toughening during crack growth. The flexural properties and fracture toughness of Epoxy/MWCNTs/CSR composites were also investigated to understand the properties transformation from resin matrix to CFRP. Morphological characterization and numerical analysis were used to analyze the synergies and constraints between two energy dissipation behaviors.

Quantitative evaluation of PI-RDL interfacial delamination in fan-out wafer-level packaging during unbiased highly accelerated stress test

Fan-Out Wafer-Level Packaging (FOWLP) is increasingly utilized for its superior performance, facilitated by flexible heterogeneous integration. Despite its advantages, the interface between Polyimide (PI) and Redistribution Layers (RDL) is susceptible to significant vulnerabilities, notably delamination. This study introduces a quantitative method to assess PI-RDL interface delamination in FOWLP under unbiased Highly Accelerated Stress Tests (uHAST), a standard approach in accelerated reliability testing characterized by high humidity and temperature. Central to our methodology is the development of a time–temperature-moisture equivalence-based creep constitutive model, which significantly enhances our understanding of the impact of temperature and moisture on creep behavior. Furthermore, we have developed an innovative “open moisture absorption” method for preparing samples for four-point bending tests, enabling precise quantification of the time-induced degradation of PI-RDL interfacial fracture toughness under saturated conditions. Our comprehensive finite element model integrates moisture diffusion, the newly developed creep constitutive model, and solid mechanics to accurately simulate the accumulation of strain energy release rate during uHAST, facilitating precise predictions of delamination initiation times in FOWLP. Experimental validation under two uHAST conditions—130 °C/85 %RH for 96 h and 110 °C/85 %RH for 264 h—demonstrates the effectiveness of our approach, predicting the delamination initiation time at the PI-RDL interface with over 80 % accuracy. This predictive methodology is pivotal in enhancing the structural optimization and extending the service life of FOWLP in varied environmental conditions.

Investigating the Performance and Safety of Li-Ion Cylindrical Cells Using Acoustic Emission and Machine Learning Analysis

Acoustic emission (AE) is a low-cost, non-invasive, and accessible diagnostic technique that uses a piezoelectric sensor to detect ultrasonic elastic waves generated by the rapid release of energy from a localised source. Despite the ubiquity of the cylindrical cell format, AE techniques applied to this cell type are rare in literature due to the complexity of acoustic wave propagation in cylindrical architectures alongside the challenges associated with sensor coupling. Here, we correlate the electrochemical performance of cells with their AE response, examining the differences during pristine and aged cell cycling. AE data was obtained and used to train various supervised binary classifiers in a supervised setting, differentiating pristine from aged cells. The highest accuracy was achieved by a deep neural network model. Unsupervised machine learning (ML) models, combining dimensionality reduction techniques with clustering, were also developed to group AE signals according to their form. The groups were then related to battery degradation phenomena such as electrode cracking, gas formation, and electrode expansion. There is the potential to integrate this novel ML-driven approach for widespread cylindrical cell testing in both academic and commercial settings to help improve the safety and performance of lithium-ion batteries.

Uncovering the freezing energy release of salted grass carp (Ctenopharyngodon idella) flesh: Effects of water state and protein structure on the thermal properties

The effect of NaCl content on the protein structures, water status and thermal properties of grass carp flesh, along with its relationship with energy required for freezing was investigated to improve the quality of frozen flesh and to reduce energy consumption for freezing. Adding salt prompted the shifting of the secondary structure of α-helix to β-sheet, β-turn and random coil. The interaction between water molecules and hydrophilic groups in the unfolded protein structure increased nonfreezing water content, which decreased specific heat capacity, thermal conductivity of sample during freezing. The lowest energy required (235.69 kJ/kg) for freezing was found in 7% NaCl salted sample, indicating a 38.39% reduction compared to the unsalted sample. Few pores between muscle fibers were observed in the 3% and 5% NaCl salted sample. Therefore, an optimal salt concentration improved quality of frozen flesh and reduced the energy required for freezing, promoting energy-efficient freezing of aquatic products.

Self-activated energy release cascade from anthracene-based solid-state molecular solar thermal energy storage systems

Self-activated energy release cascade from anthracene-based solid-state molecular solar thermal energy storage systems

Energy characteristics and damage constitutive model of pre‐cracked granite with or without filling materials

AbstractIn order to study the effects of pre‐crack inclination angle and filling material on granite, uniaxial compression tests were performed on pre‐cracked granite specimens without filling material and specimens filled with epoxy resin, gypsum, and organosilicon. Results indicate that the peak strength and apparent stiffness of pre‐cracked granite without filling materials increase with increasing pre‐crack inclination angle. The strain energy absorbed by the filling material improves the energy storage limit, inhibits the energy release effect when microcracks are connected to each other, and ultimately improves the compressive resistance and energy storage capacity. The strengthening effect of gypsum and epoxy resin is relatively better, which is more significant when the pre‐crack inclination angle equals 0°–60°. Finally, a damage constitutive model is established, which is in good agreement with the test and numerical simulation data. The results can provide reference for the research of grouting reinforcement of rock masses.

“Fireworks” ignition and combustion of metal nanoparticles: Based on the rapid conversion and transmission of microwave energy by energetic ionic liquids

The metal nanoparticles (MNPs) are widely used to improve the output performance of various explosives and propellants, which ignition is an important link for the energy release of fuel. The microwaves have been recognized as a safer and smart ignition method. However, it is difficult to achieve rapid ignition of MNPs under microwave radiation due to the low heating rate. The ADN energetic ionic liquids could efficiently absorb microwaves owing to excellent polarity. This work proposes a method of fast “fireworks” ignition and combustion of MNPs under microwave radiation, by employing ADN as the “central hub” for microwave energy conversion. The dispersion of Al and Ti NPs in ADN endowed the solution with nanofluid properties and significantly improved the thermal conductivity. The solution boiled violently under microwave radiation, causing the temperature of MNPs to rise continuously. Meanwhile, the acidic components produced by ADN pyrolysis destroyed the oxide shell of MNPs, further accelerating the ignition process. The ignition phenomenon of Al and Ti NPs were different due to distinct microwave absorption properties and ignition temperature. When the expanding liquid film broken, the shock wave blew the Al NPs into the air to realize the “fireworks” ignition and combustion. The Ti NPs was ignited in the solution, which further ignited the ADN solution, allowing the system for controllable ignition and combustion. The “fireworks” ignition and combustion performance of MNPs could be modulated by the input microwave power. In summary, the new ignition and combustion methods of MNPs will have a profound impact on the design of ignition sequence, the improvement of microwave energy utilization and the expansion of the application of ADN-based liquid propellants.

Ptfe-modified Al through bridging approach to enhance combustion reaction and energetic performance

Aluminum/Polytetrafluoroethylene (Al/PTFE) composites have attracted a great deal of attention due to their remarkable energy density and wide range of applications. Unfortunately, the inert oxide layer (Al2O3) on the surface of Al and the interfacial contact area between PTFE and Al seriously impact the combustion reaction kinetics and energy output efficiency. Here, an approach is utilized to significantly enhance the interfacial contact area between Al and PTFE through F2601 serving as the bridging agent. The ignition, combustion reaction, and energetic performance (pressure and combustion heat) can be adjusted by varying the particle size of Al and PTFE content. The energy release efficiency of bridging Al/PTFE has been improved significantly as PTFE content increases and the particle size of Al decreases. The bridging Al/PTFE with 10 μm Al and nano Al exhibit a bright and wide flame, and a fierce flame propagation process, as well as much high pressure output (167.73 kPa and 199.92 kPa) and heat release (11879 J/g and 12322 J/g). Furthermore, the critical mass ratio (approximately 88/12) of bridging Al/PTFE for self-sustained combustion has been obtained for the first time. The improvement of energy output performance is attributed to the interfacial contact between PTFE and Al and the reaction of fluorine and Al2O3 resulted from bridging Al/PTFE through F2601. The prepared bridging Al/PTFE with high energy output characteristics holds great potential in solid propellants, reactive materials, and other high-energy fuels.

Design, construction, and testing of an exploding wire pulsed plasma system for generating shock waves in industrial applications

Exploding Wire Pulsed Plasma System (EWPPS) used in oil recovery operations has been construct and developed with an initial energy release of 1.5 kJ in a fusion laboratory. Recently, the final experiments have been carried out on the purpose device operating in microsecond time scale in air and fluid medium successfully. In this setup, a single wire feeder is used for tests. Also, to study and develop the shock waves caused by wire explosions in the industry, the diagnostic tools of voltage probe, current coil, pressure probe and photodiode have been used. Choosing the optimal material of wire is one of the basic factors in creating a suitable shock wave. In addition, the impact of wire inductance on discharge current, voltage, pressure and shock wave strength has been investigated by applying two sets of wires, refractory (Cu, Cu-Ni, and Steel) and non-refractory (W, W-Al, Mo). The results show that the strongest shock wave is produced while the transition from warm wire to dense plasma happens. The soft X-ray intensity of both wire series has been measured using a photodiode BPX-65 (<10 keV). The comparison shows higher X-ray intensity for non-refractory wires than that for refractory wires. In good agreement, the maximum value of the shock wave was 8.7 and 6.6 MPa for non-refractory metals with high inductance and refractory metals with low inductance, respectively.

Experimental and statistical physics illumination of Pb(II) adsorption on magnetic chitosan-graphene oxide surface

Adsorption stands for a promising technique for heavy metal remediation. Herein, a high efficiency adsorbent based on magnetic chitosan-graphene oxide (MCGO) was prepared via a simple co-precipitation procedure. Afterwards, adsorption behaviour of Pb(Ⅱ) on MCGO surface was illuminated via batch adsorption experiment and statistical physics calculation. Result presents, MCGO reaches adsorption percent and adsorption quantity 93.06 % and 372.24 mg·g−1 for Pb(Ⅱ) in 44 min, showcasing favorable remediation efficiency. Statistical physics calculation proposes multi-ionic adsorption mechanism. With the increase of temperature, adsorption site density is increased to yield ameliorated adsorption capacity. Moreover, calculation result of the thermodynamic functions designates exothermic, randomness increasing, spontaneous and energy releasing feature. Kinetic fitting based on various models assigns chemical interaction as the rate controlling step. Finally, adsorption mechanism was clarified in atomic level via spectroscopic inspection. Specifically, C=O, C–O, O–H, N+ and –C(=O)NH– contribute to Pb(Ⅱ) adsorption via donating lone pair electrons. This work provides both experimental and statistical physics insights for understanding the adsorption behaviour of typical heavy metal pollutants onto the surface of bio adsorbent like magnetic chitosan-graphene oxide.