Energy Release Research Articles

Facile Energy Release from Substituted Dewar Isomers of 1,2‑Dihydro‐1,2‑azaborinines Catalyzed by Coinage Metal Lewis Acids

Molecular solar thermal systems (MOST) represent an auspicious solution for the storage of solar energy. We report silver salts as a unique class of catalysts, capable of releasing the stored energy from the promising 1,2‐dihydro‐1,2‐azaborinine based MOST system. Mechanistic investigations provided insights into the silver catalyzed thermal backreaction, concurrently unveiling the first crystal structure of a 2‐aza‐3‐borabicyclo[2.2.0]hex‐5‐ene, the Dewar isomer of 1,2‐dihydro‐1,2‐azaborinine. Quantification of activation energies by kinetic experiments has elucidated the advantageous energy outcomes associated with Lewis acid catalysts, a phenomenon corroborated through computational analysis. By means of low temperature NMR spectroscopy, mechanistic insights into the coordination of Ag+ to the 1,2‐dihydro‐1,2‐azaborinine were gained.

Effect of laser treatment on strength of moisture-degraded epoxy adhesive joints and microscopic observation of treated surface

ABSTRACT We examined the effect of laser processing surface treatment on the mechanical strength of adhesion. In addition to laser processing, double cantilever beam (DCB) and lap joint (LJ) specimens were prepared using an epoxy adhesive on aluminum plates that underwent acid etching, sandblasting, and acetone wiping. The open face method was employed to accelerate moisture degradation, and the tensile-shear strength and energy release rate of the specimens were measured. Laser processing resulted in remarkably high values of the measured energy release rate, even when the adhesive deteriorated. To examine the reason for the high strength, we performed a detailed fracture surface analysis and electron microscopic observation of the adhesive interface. When the interface of the fractured surface was observed, the laser treated surface was densely formed with fine filamentous protrusions that held the adhesive well. These filaments exhibited high oxidation resistance and achieved strong adhesion even when the adhesive and adherend deteriorated because of moisture. The laser treated adherend surface exhibited two strong anchoring effects owing to a significant increase in the surface area and the microfilamentous structure on the surface. However, the type of surface treatment did not have a significant effect on the LJ adhesion strength.

Fracture mechanics modeling of aortic dissection.

Aortic dissection, a critical cardiovascular condition with life-threatening implications, is distinguished by the development of a tear and its propagation within the aortic wall. A thorough understanding of the initiation and progression of these tears, or cracks, is essential for accurate diagnosis and effective treatment. This paper undertakes a fracture mechanics approach to delve into the mechanics of tear propagation in aortic dissection. Our objective is to elucidate the impact of geometric and material parameters, providing valuable insights into the determinants of this pivotal cardiovascular event. Through our investigation, we have gained an understanding of how various parameters influence the energy release rate for tear propagation in both longitudinal and circumferential directions, aligning our findings with clinical data.

Solar Eruptions in Nested Magnetic Flux Systems

The magnetic topology of erupting regions on the Sun is a key factor in the energy buildup and release, and the subsequent evolution of flares and coronal mass ejections (CMEs). The presence/absence of null points and separatrices dictates whether and where current sheets form and magnetic reconnection occurs. Numerical simulations show that energy buildup and release via reconnection in the simplest configuration with a null, the embedded bipole, is a universal mechanism for solar eruptions. Here we demonstrate that a magnetic topology with nested bipoles and two nulls can account for more complex dynamics, such as failed eruptions and CME–jet interactions. We investigate the stalled eruption of a nested configuration on 2013 July 13 in NOAA Active Region 11791, in which a small bipole is embedded within a large transequatorial pseudo-streamer containing a null. In the studied event, the inner active region erupted, ejecting a small flux rope behind a shock accompanied by a flare; the flux rope then reconnected with pseudo-streamer flux and, rather than escaping intact, mainly distorted the pseudo-streamer null into a current sheet. EUV and coronagraph images revealed a weak shock and a faint collimated outflow from the pseudo-streamer. We analyzed Solar Dynamics Observatory and Solar TErrestrial RElations Observatory observations and compared the inferred magnetic evolution and dynamics with three-dimensional magnetohydrodynamics simulations of a simplified representation of this nested fan-spine system. The results suggest that the difference between breakout reconnection at the inner null and at the outer null naturally accounts for the observed weak jet and stalled ejection. We discuss the general implications of our results for failed eruptions.

Research on end-route planning for community group purchasing for vehicles with different energy sources

To address the issue of final delivery route planning in the community group purchase model, this study takes into full consideration logistics vehicles of different energy types. With the goal of minimizing the sum of vehicle operating costs, delivery timeliness costs, goods loss costs, and carbon emissions costs, a multi-objective optimization model for community group purchase final delivery route planning is constructed. An improved genetic algorithm with a hill-climbing algorithm is utilized to enhance adaptive genetic operators, preventing the algorithm from getting stuck in local optima and improving the solution efficiency. Finally, a case study simulation is conducted to validate the feasibility of the model and algorithm. Experimental results indicate that currently, among the three types of vehicles, fuel logistics vehicles still have an advantage in terms of vehicle usage cost. Electric logistics vehicles exhibit the poorest performance with the highest cost per hundred kilometers, but their sole advantage lies in their high energy release efficiency, enabling optimal low-carbon vehicle performance. Battery-swapping logistics vehicles perform the best in terms of carbon emissions, combining the advantages of both fuel-based and electric logistics vehicles. Therefore, battery-swapping logistics vehicles are a favorable choice for replacing fuel-based logistics vehicles in the future, offering promising prospects for future development.

Unraveling the Rich Fragmentation Dynamics Associated with S-H Bond Fission Following Photoexcitation of H2S at Wavelengths ∼129.1 nm.

H2S is being detected in the atmospheres of ever more interstellar bodies, and photolysis is an important mechanism by which it is processed. Here, we report H Rydberg atom time-of-flight measurements following the excitation of H2S molecules to selected rotational (JKaKc') levels of the 1B1 Rydberg state associated with the strong absorption feature at wavelengths of λ ∼ 129.1 nm. Analysis of the total kinetic energy release spectra derived from these data reveals that all levels predissociate to yield H atoms in conjunction with both SH(A) and SH(X) partners and that the primary SH(A)/SH(X) product branching ratio increases steeply with ⟨Jb2⟩, the square of the rotational angular momentum about the b-inertial axis in the excited state. These products arise via competing homogeneous (vibronic) and heterogeneous (Coriolis-induced) predissociation pathways that involve coupling to dissociative potential energy surfaces (PES(s)) of, respectively, 1A″ and 1A' symmetries. The present data also show H + SH(A) product formation when exciting the JKaKc' = 000 and 111 levels, for which ⟨Jb2⟩ = 0 and Coriolis coupling to the 1A' PES(s) is symmetry forbidden, implying the operation of another, hitherto unrecognized, route to forming H + SH(A) products following excitation of H2S at energies above ∼9 eV. These data can be expected to stimulate future ab initio molecular dynamic studies that test, refine, and define the currently inferred predissociation pathways available to photoexcited H2S molecules.

Reactive Ti/Ni multilayer composites produced via accumulative roll-bonding (ARB): post-annealing treatment

ABSTRACT Ti/Ni multilayers, produced through the accumulative-roll bonding (ARB) process, serve as reactive multilayer, capturing energy to optimize manufacturing processes and contribute to TiNi (shape memory alloy) production. This research specifically examines the impact of the number of layers on microstructural and thermal properties after activation through heating. Energy-dispersive spectroscopy (EDS), field emission scanning electronmicroscopy (FESEM), and differential scanning calorimeter (DSC) were employed to analyse samples subjected to various ARB cycles. The findings indicate that in low-cycle ARB processing, the interdiffusion of Ni and Ti under normal conditions initiates the production of a very thin layer of TiNi at 800 °C, requiring extended holding times for increased thickness. Conversely, the formation of intermetallic compounds, particularly TiNi, and diffusion in high-cycle ARB-processed composites are accelerated. According to the DSC results, complete activation and phase transformation, accompanied by the release of energy (43–50 kJ/mol), occur at approximately 500–525°C without the need for any holding time. Consequently, for achieving a uniform TiNi phase, heat treatment of high-cycle ARB-processed composites up to 800°C – a temperature surpassing the activation temperature – without any holding time can be effectively employed.

Effect of AP distribution on energy release characteristics and functional force of HMX/AP/Al explosives

AbstractIn order to understand the reaction kinetics of HMX/AP/Al ternary system, the different distribution of AP in HMX/AP/Al explosives was realized by two different preparation techniques. Detonation test results show that the detonation velocity, explosion heat and detonation pressure of HAP samples are higher than those of HAl samples, but the extent of improvement is not high, not more than 5 %. The results of scanning electron microscopy showed that AP in HAP samples was distributed on the surface of HMX crystal. AP were dispersed around HMX crystals in HAl samples. The experimental results of explosive fireball performance show that the fireball expansion speed of HAP samples is better than that of HAl samples, demonstrating a good fireball effect. Underwater test results show that the shock wave peak pressure and bubble pulsation period of HAP samples increase by 3.06 % and 7.95 % respectively, and shock wave energy and bubble energy increase by 9.8 % and 25.42 % compared with bubble energy. The experimental results show that HAP samples are superior to HAl samples in accelerating ability of Al flies. The dispersion of AP on the HMX crystal surface promotes the energy release of HMX/AP/Al explosives more.

Design, fabrication and experimental verification of a drag sail based on thermal-driven controllable bi-stable shape memory polymer composite booms

Deployable drag sails are used for passively deorbiting defunct satellites and other spacecraft. Designing the deployable boom is the main challenge in this technology. We present a bi-stable shape memory polymer composite (Bi-SMPC) boom with high stiffness, a high unfolding/folding ratio, and consistent roll-out deployment. It was designed and fabricated by a strategy of controlling the gradual release of elastic energy stored in a bi-stable composite structure through thermal-driven SMP matrix. Two heating layer strategies were investigated experimentally to determine the optimal driving layer and driving parameters. Based on these parameters, verification tests of a four-stage deployment Bi-SMPC boom were conducted. Meanwhile, a proof-of-concept prototype of a four-stage deployment drag sail based on the Bi-SMPC booms was designed and fabricated. Tests were conducted to verify the effectiveness of the drag sail deployed by the booms. It was found that SMPs can effectively control the deployment of bistable composite structures. The nickel-chromium alloy heating layer offers a more uniform driving temperature field compared to carbon fiber. The drag sail can be deployed successfully under the driving of four Bi-SMPC booms.

Study on combustion characteristics and pyrotechnic cutting effects of bimetal thermite Ni/Al/Fe2O3 system

AbstractNano‐thermite has become a subject of significant interest in the composite energetic materials field due to its high energy release rate. To cater to diverse engineering needs, thermite formulations are often customized to fulfill specific criteria. This study investigates the potential of metal nickel (Ni) as an additive to modify nano‐thermite formulations, selected for its optimal calorific values and chemical reactivity. The base materials, nano‐aluminum (Al) and iron oxide (Fe2O3), are blended with varying mass ratios of Ni (1 %, 3 %, 5 %, 7 %, 9 %) using the wet ball milling method. Pre‐reaction and post‐reaction morphological and compositional alterations in the resultant thermite samples are scrutinized through SEM and XRD characterization tests. Moreover, DSC analysis and combustion experiments were conducted to examine the pyrolysis and combustion behaviors of the evaluated samples. The results reveal a reduced exothermic peak on the DSC curves with the introduction of Ni, making the liquid‐solid (L‐S) phase reaction more challenging compared to the Al/Fe2O3 thermite. Intriguingly, Ni addition progressively decreases the combustion temperature of thermites as the Ni's mass ratio increases, with a peak efficiency at 7 % in the perforation tests on stainless‐steel plates. This research further reveals that the thermite reaction mechanism is a combined consequence of the “pre‐ignition‐fusion” and “fusion‐diffusion” mechanisms. These insights can provide valuable guidance for designing thermite formulations for potential applications in storage, management, and pyrotechnic cutting areas.

Characterization of the damage mechanism in CFRP composites under mode I based on comprehensive analysis of AE signals

This study utilises several methods centred on acoustic emission (AE) waveform characteristics to conduct in-depth analysis of the damage mechanism of composite materials under mode I. Combined with the peak frequency statistics and continuous wavelet transform (CWT) of AE signals, three damage modes of laminated composites during loading are identified. The cumulative energy of three damage modes separated by variational modal decomposition (VMD) is used to characterize their damage evolution process. Based on the findings, delamination and fiber–matrix debonding are proven to be the dominant damage mechanisms for mode I. The comprehensive analysis results from AE's accumulated energy, peak frequency distribution, CWT, VMD, and sentry function can accurately detect the onset time of delamination in laminates. The equivalent crack length is calculated by the load value determined at the initial time of delamination, and the strain energy release rate calculated by the load value and crack length at this time is used as the interlaminar fracture toughness value of mode I. This research method will provide a new idea for the damage tolerance analysis of mode I delamination in laminated structures.

Novel resveratrol-based hyperbranched epoxy resin suitable for comprehensive modification of epoxy resins

Hyperbranched epoxy resins are efficient modifiers for epoxy resins but still require simultaneous improvements in terms of thermomechanical/mechanical properties and thermal stability. Herein, a novel resveratrol-based hyperbranched polyether epoxy resin (HBPEER) was designed for all-purpose epoxy resin modification. To this end, hyperbranched polyether with terminal phenolic hydroxyl groups was first synthesized from commercially available 1,6-dibromohexane (A2-type monomer) and resveratrol (B'B2-type monomer). Surface modification with epichlorohydrin was afterward implemented to produce hyperbranched polyether with terminal epoxy groups (HBPEER). Next, various HBPEER-modified epoxy thermosets were prepared and characterized. The results suggested that compared to the neat diglycidyl ether of bisphenol A (DGEBA) thermoset, the 6 wt% HBPEER-modified epoxy thermoset showed an increase in impact strength, elongation at break, critical stress intensity factor (KIC), critical crack propagation energy release rate (GIC), flexural strength, tensile strength, storage modulus, glass transition temperature (Tg), and initial thermal decomposition temperature (Td5%) by 69.6 %, 87.0 %, 32.0 %, 68.2 %, 29.3 %, 37.0 %, 8.1 %, 3.5 %, and 1.6 % respectively. Moreover, the dielectric constant and loss of 6 wt% HBPEER-modified epoxy thermoset decreased by 16.2 % and 16.5 %, respectively. Such comprehensive performance modifications were caused by the combined effects of crosslink density improvement, efficient intramolecular cavity, rigid stilbene units, and flexible aliphatic backbone of HBPEER.

Numerical simulation on the bomb case effects of non‐ideal aluminized explosive

AbstractThe detonation process of non‐ideal explosives is influenced by the casing of the bomb. Non‐ideal charges in the process of the explosion of live ammunition energy output mechanism and distribution ratio, the impact of the case on the explosion flow field, and other issues cannot be obtained through the existing theoretical analysis and testing techniques to obtain specific values. This paper establishes a “detonation+afterburning” energy output model to characterize the energy release characteristics of non‐ideal charges, using step‐by‐step numerical simulation of the near and middle, and far fields of the explosion, and verify simulation results through experiments, quantitative analysis the case of a type of earth penetrator on the normal particle size (4 μm) and two times the normal particle size (8 μm) of non‐ideal charges of aluminum powder explosion process. The results indicate that the presence of the casing enhances the energy output of aluminum powder with 4 μm by ≈5 %. When the particle size of aluminum powder is doubled, the maximum reaction rate and the peak of the shock wave are merely around 35 % and 75 %, respectively, compared to those of normal particle size. The detonation products, case fragments, and air constitute 49 %, 48 %, and 3 % of the overall explosion energy, respectively. The proportional equation of the conversion between the chemical energy of the explosion and the kinetic energy of the case fragments is obtained. These conclusions can provide data support for the design of non‐ideal charge warheads, lethality assessment, and establishment of engineering protection standards.

Natural radioactivity of the crust as an important factor of the chemical evolution of the early Earth

The long-lived (billions of years) 40K, 235U, 238U, and 232Th isotopes have a high energy capacity and represent a potent internal source of energy. Together with the external action of the Sun, the natural radioactivity was apparently an important component of evolution of the early Earth and development of Earth's life. The decay of isotopes initiated radiation chemical reactions involving water, which were accompanied by the formation of hydrogen and oxygen and the transformation of Earth's inorganic matter into organic compounds, including prebiotic molecules. Water radiolysis in the Earth's crust continuously produces H2, which is now considered as the main electron donor (food) for microorganisms several kilometers below the Earth's surface. Here we calculate the initial radioactivity of the early Earth's crust from the relative abundances of elements and dynamics of variation of the radioactivity and energy release upon the decay of particular radioactive isotopes. The energy released upon the decay of heavy 235U, 238U, and 232Th throughout the existence of the Earth (4.6 billion years) was 4.5 × 1030 J, while the energy released upon the decay of 40K was approximately 1.0 × 1030 J. The energy release per year during the first billion years decreased from 3.0 × 1021 J to 1.5 × 1021 J for heavy isotopes and from 0.70 × 1021 J to 0.45 × 1021 J for 40K. Over the last billion years, the energy decreased approximately threefold. Analysis of the data on the radiation chemical formation of hydrogen in the wet components of the Earth's crust (cements, zeolites, geopolymers, and other) and bottom sediments indicates that hydrogen is formed upon direct action of radiation on water in yields characteristic of pure water. According to calculations, over the past 4 billion years, approximately 1.7 × 1022 M of hydrogen was formed. Furthermore, ∼93 % of H2 was due to the decay of uranium and thorium, while the contribution of 40K did not exceed 7 %. The global rate of hydrogen formation in the Earth's crust is ∼ 1.5 × 1012 mol per year. A mechanism involving ionic and radical products of water radiolysis was proposed to describe the formation of prebiotic molecules (amino acids, sugars, etc.) from carbon-, nitrogen-, and sulfur-containing inorganic compounds.

Microballoons: Osmotically-inflated elastomer shells for ultrafast release of encapsulants and mechanical energy

HypothesisMicrocapsules with osmotically-inflated elastic shells exhibit an ultrafast release of encapsulants while mechanically stimulating the microenvironments, akin to popping balloons. ExperimentsTo prepare elastic shells with uniform thickness and size, monodisperse water-in-oil-in-water (W/O/W) double-emulsion drops are produced in a capillary microfluidic device. The polydimethylsiloxane (PDMS)-containing oil phase is thermally cured to create the elastic shell. The elastic shells are inflated by pumping water into the lumen in hypotonic conditions. The inflated microcapsules produced undergo mechanical compression, and their release properties are studied. FindingsBy controlling the osmotic pressure difference, Microballoons are inflated into a diameter of 200 μm – 316 μm and shell thickness of 7.8 μm – 0.7 µm, respectively. The inflated shell pops due to mechanical failure when subjected to mechanical stress above a certain threshold, resembling a balloon. During popping, the stretched shell rapidly retracts to the original uninflated state, resulting in an ultrafast release of encapsulants from the lumen within a millisecond. This process converts elastic potential energy stored in the shell into mechanical energy with substantial power. The microballoons mechanically stimulate the local environment, leading to the direct and rapid release of encapsulants. This has the potential to improve absorption efficiency.

From kink instability to magnetic reconnection to oscillations in solar flares

We show how some different fundamental plasma processes - the ideal kink instability, magnetic reconnection and magnetohydrodynamic oscillations - can be causally linked. This is shown through reviewing a series of models of energy release in twisted magnetic flux ropes in the solar corona, representing confined solar flares. 3D magnetohydrodynamic simulations demonstrate that fragmented current sheets develop during the nonlinear phase of the ideal kink instability, leading to multiple magnetic reconnections and the release of stored magnetic energy. By coupling these simulations with a test particle code, we can predict the development of populations of non-thermal electrons and ions, as observed in solar flares, and produce synthetic observables for comparison with observations. We also show that magnetic oscillations arise in the reconnecting loop, although there is no oscillatory external driver, and these lead to pulsations in the microwave emission similar to observed flare quasi-periodic pulsations. Oscillations and propagating waves also arise from reconnection when two twisted flux ropes merge, which is modelled utilising 2D magnetohydrodynamic simulations.

Strain energy dependent numerical simulation of rock fracture initiation and propagation using soundless cracking demolition agents (SCDA): Effects of SCDA-filled rock joints

Soundless Cracking Demolition Agents (SCDA) are gaining traction as an innovative technique for controlled rock fracturing in applications such as underground energy, mineral extraction, and excavation. This paper presents a novel numerical approach to simulate SCDA-charged rock fracture initiation using the strain energy density of SCDA. This approach eliminates the need for prior knowledge of the peak expansive pressure developed in a rock, a common requirement in conventional SCDA modelling. An empirically derived model is presented which captures the rate of energy release in SCDA as a function of applied strain to the surrounding material. The model was implemented in the 3-dimensional Distinct Element Code by applying an exponential strain-rate decay function. The proposed fracture stimulation method accurately mimics the expansion behaviour and finite strain energy release from SCDA expansion. The method was extended to simulate SCDA expansion in rock joints. The SCDA expansion method was assessed by creating a numerical model in which a central injection well was intersected by a horizontal joint and SCDA expansion was simulated in the injection well and the joint. The simulations were verified against laboratory fracture experiments. The model was extended to evaluate the fracturing performance of SCDA under varying joint roughness and confining pressures. SCDA expansion in rock joints introduces an additional compressive stress field that inhibits fracture initiation and propagation near the joint. Increasing fracture roughness suppressed fracture growth, but led to more fracture nucleation points around the injection well and shear damage at the joint interface. The simulation method employed shows sensitivity to confining pressures and simulates the fracturing potential of SCDA in different rocks subjected to confining pressures without requiring further calibration of the SCDA expansion parameters. The proposed numerical simulation method improves the accuracy in investigating the fracturing potential of expansive agents over existing simulation methods for SCDA.

A finite crack growth energy release rate for interlaminar fracture analysis of composite material at different temperatures

The interlaminar fracture toughness of unidirectional fiber reinforced polymer composite material is temperature and crack growth history dependence. The non-constant interlaminar fracture toughness challenges the wide application of the linear elastic fracture mechanics-based approach for analyzing the interlaminar crack growth in composite material and structures. In addition, a quantitative relationship between the ductility of the matrix and interlaminar fracture toughness of the fiber reinforced composite is still highly desirable. In this paper, both pure resin and composite double cantilever beam (DCB) are tested at different temperatures. A finite crack growth energy release rate is used to analyze the interlaminar crack growth behavior of composite material at different temperatures. The plasticity of the composite DCB is modeled by Hill’s anisotropic plasticity, with the properties determined from multiscale analyses. It is found that a single constant finite growth energy release rate can well predict the interlaminar mode I crack growth of composite material at different temperatures. The roles of the ductility of matrix, thickness of the DCB, and crack growth history on the interlaminar mode I fracture toughness of composite material are quantitatively determined by using the present method.

Compression after impact (CAI) failure mechanisms and damage evolution in large composite laminates: High-fidelity simulation and experimental study

This study focuses on developing and validating a high-fidelity finite element model for predicting damage evolution and residual strength in fiber-reinforced composite panels. Impact and compression after impact (CAI) tests were conducted at both barely visible impact damage (BVID) and clearly visible impact damage (CVID) levels. The ASTM D7137 standard 100 mm × 150 mm CAI coupons were inadequate to cover the range of experimental studies required for model validation. Therefore, larger 254 mm × 304.8 mm laminates were investigated under two CAI testing conditions: one a scaled-up version of ASTM standard coupon, and the other with additional anti-buckling support plates to reduce unsupported areas to 127 mm × 177.8 mm. The model captured inter- and intra-laminar failure modes, including fiber breakage, splitting, kinking, pull-out, and crushing as well as matrix cracking, delamination, and their interactions. This was achieved by cohesive zone modeling technique and enhancement of the LaRC05 failure criteria through modeling the fiber damage evolution and utilizing an efficient search algorithm to determine the matrix fracture plane and fiber kink band angle. This study underscores the efficacy of the high-fidelity modeling approach in accurately predicting both impact damage and CAI strength in typical aircraft impact damage scenarios. Additionally, it provides insights into complex CAI failure mechanisms and energy release associated with various damage modes and highlights the effect of global buckling on the failure behavior and compressive strength of composite laminates. Furthermore, it shows that the proposed fixture with support plates is suitable for testing a broader range of impact scenarios without experiencing global buckling.

Universal slope-based J-integral methods for characterization of the mode I, mode II and mixed mode I/II fracture behaviour of adhesively bonded interfaces

Universal slope-based J-integral methods have been developed for the determination of the energy release rate for adhesively bonded joints under mode I, mode II and mixed-mode (I/II) loading conditions. The individual J components corresponding to the mode I and mode II loading were separated based on the J-integral decomposition theory. The proposed methods use the slopes of the substrates at various locations to characterize the energy release rate and thus avoid the measurement of crack lengths, which are especially suitable for characterizing the tough interfaces associated with large fracture process zones ahead of crack tips. Under linear elastic deformation, the slope-based J equations were found to be equivalent to classical G equations based on linear elastic fracture mechanics (LEFM). Both experimental and numerical testing of adhesively bonded joints were undertaken to validate the slope-based J equations. The universal slope-based J-integral methods provide a reliable alternative to the measurement of G for adhesive joints or laminated composites undergoing nonlinear or inelastic deformations where conventional LEFM is not valid. It is shown that LEFM, even when coupled with an effective crack length approach, can be inaccurate when damage occurs in a test specimen away from the fracture process zone, as was seen here in mode II. Slope-based J equations can avoid these inaccuracies with a careful selection of contour paths. Slope based methods are therefore strong candidates for selection in future test standards for mode II fracture characterisation of structural adhesive joints.