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Quasi-isentropic loading and unloading, employing graded density impactors (GDIs) as flyers in gas gun-driven plate impact experiments, can provide novel and valuable insights into the equation of state and strength properties of the loaded material. However, the internal ballistic process may lead to spalling or debonding of the GDI due to the intricate interactions between stress waves and interfaces. In this study, the wave propagation in the GDI was analyzed using the multimaterial Lagrangian elastic-plastic model and elastic wave propagation theory. The impact of gradient direction, power-law constant p, and thickness of the first and last layers on the tensile stress was investigated. The outcomes reveal that the mechanism of generating tensile stress varies for two gradient directions. Moreover, adjusting the constant p and the layer thickness may decrease the maximum tensile stress by 74.1% (forward graded) and 95.8% (reverse graded), respectively. The outcomes of this research provide a theoretical and simulation basis for designing and fabricating GDIs to be utilized in quasi-isentropic experiments. [ABSTRACT FROM AUTHOR]

The dynamic response characteristics of high and steep slopes under the action of earthquakes and blasting was focused on, especially the frequency distribution and propagation laws, which are crucial for slope stability assessment. Using stress wave theory as the theoretical basis and advanced FLAC3D numerical simulation technology, we systematically analyze the frequency response of slope under different joint conditions under seismic waves. The nonlinear characteristics of reflected P-wave coefficient and the significant sensitivity of joint to incident wave frequency are revealed when the Angle of incident P-wave changes. The results show that with the increase of the incidence Angle of the incident P-wave, the reflection coefficient of the reflected P-wave decreases slowly at first and then increases sharply to 1.0. The reflection coefficient of the wave at the joint is more sensitive to the frequency of the incident wave. In a biplanar rock mass, multiple reflections of waves between structural planes produce transmitted waves with different time differences. [ABSTRACT FROM AUTHOR]

The main cause of damage to maize during harvesting and processing is impact damage. This study aimed to investigate the evolution of impact damage to maize kernels under different impact velocities and orientations. Based on the damage characteristics observed in impact tests, an elastoplastic model has been established to accurately simulate the damage behaviour of maize kernels. The microscopic impact behaviour of maize kernels was presented by the finite element method. The results indicated that there were differences in the evolution of damage for different damage morphology in maize kernels. The nature of surface damage was the diffusion and reflection of stress waves, while the nature of local breakage was the concentration of tiny cracks and the release of elastic potential energy. The nature of fracture was the combined effect of compressive and tensile stresses. Meanwhile, under the surface damage, the maximum stresses in the contact area of maize kernels subjected to front orientation were 20.08 MPa, 10.71 MPa for side orientation, and 13.56 MPa for bottom orientation. Under the local breakage, the front orientation with the highest number of cracks occurred at a velocity of 27.3 m s−1, while for the side orientation, it occurred at 24.6 m s−1, and for the bottom orientation, it occurred at 26.2 m s−1. The results can be extended to the study of impact damage in irregularly shaped grains, which was beneficial for controlling product quality and optimising the design of relevant mechanical parameters in agricultural engineering and food engineering fields. [Display omitted] • Damage morphology of maize kernels was summarised. • Evolution rules of damage in multi-orientation maize kernels were explored. • Impact dynamic response of multi-orientation maize kernels was obtained. • Differences in impact damage of multi-orientation maize kernels were compared. [ABSTRACT FROM AUTHOR]

Underground mining disasters are generally caused by the deterioration in mechanical properties of coal and overlying rock exposed to mining loading–unloading, while their differential mechanical deterioration and catastrophe mechanisms are not well understood. Therefore, a series of uniaxial loading–unloading tests with ultrasonic monitoring are performed on coal and roof sandstone, while the mechanical responses are investigated using energy-based damage analysis and ultrasonic characterization method. The sandstone yields a greater strength and deformation modulus and experiences a brittle failure, while the coal possesses a larger Poisson's ratio and undergoes a ductile failure. A higher (lower) crack initiation (damage) ratio in coal reflects its faster crack propagation than sandstone. Energy evolution analysis shows that coal has a poorer elastic energy storage capacity, but its energy dissipation is severer. The energy-type catastrophe criteria for coal and sandstone are derived based on an elastic energy ratio. A new damage variable is defined by the cumulative dissipated energy and total input energy, and the damage energy release rate is introduced to develop a damage evolution model under uniaxial loading–unloading condition, from which it is indicated that the coal experiences a greater damage degree, but is less dependent on energy release rate. Furthermore, the differential energy controlling mechanisms of instability between coal and sandstone are revealed, i.e., the coal is controlled by pre-peak energy dissipation and post-peak energy release, while the sandstone is dominated by post-peak rapid energy release. Meanwhile, different wave velocity evolution patterns are generalized, where the denser sandstone yields a higher stress sensitivity of wave velocity. The structural degradation process is quantitatively characterized by using a combination of dynamic elastic parameters, intactness index, and disturbance damage factor. The structural deterioration occurs in the unloading and final loading failure stages, where coal shows a progressive pattern, while sandstone possesses a transient pattern. Finally, the quantitative relationships between wave velocity and stress, energy and damage are established. Highlights: Lithology significantly affects mechanical responses during uniaxial loading-unloading. Both stiffness enhancement and loss occur in a single uniaxial loading-unloading cycle. Failure mechanisms are governed by the interaction between energy dissipation and release. [ABSTRACT FROM AUTHOR]

Engineering rock masses typically feature natural discontinuities that span different scales, with filled joints as macroscopic discontinuities and microdefects as mesoscopic ones. However, the mechanism of wave propagation in the filled joints has been unclear. This study develops a novel dual-scale equivalent rock model to investigate the wave propagation in jointed rock masses. Firstly, two combination models at different scales were developed by using thin layers and contact interfaces to simulate filled joints and microdefects, respectively. Subsequently, a wave propagation equation was derived through a time-domain recursive method, and validated against the experimental data and the predictions of traditional models. Finally, a parametric analysis was conducted on the frequency response of wave propagation in jointed rock masses. The results show that this novel model can describe the wave dispersion and attenuation in dual-scale discontinuous rock masses, and its equation exhibits robustness. It is revealed that two independent mechanisms induce the wave dispersion in a single joint: multiple wave reflections inside the joint and the viscosity of the filling material. The effect of microdefects on wave attenuation mainly depends on propagation distance, while the influence of filled joints on wave propagation can be determined by the quality factor, thickness, effective wave velocity, and density of the filling. The wave velocity of the filling has a significantly higher influence on the transmission coefficient than the filling density. This challenges the conventional concept that the wave impedance of filling is a basic parameter for estimating the transmission coefficient. Highlights: A novel dual-scale equivalent model was proposed for wave propagation in jointed rock masses. The multiple reflection effects at rock joints were revealed to be the main cause of wave dispersion. Using wave impedance of joint filling to predict the transmission coefficient was found to be inaccurate. The frequency response difference in macroscopic and mesoscopic discontinuities of rock masses was revealed. [ABSTRACT FROM AUTHOR]

The rock–concrete interface serves as the weak point of concrete structures based on rocks; the initial failure of the interface under stress waves can easily cause instability and failure of rock concrete composite structures. This study conducted a range of numerical investigations using MAT-COHESIVE-MIXED-MODE cohesive element to describe the failure properties of rock–shotcrete's interface transition zone (ITZ). The research results can reveal ITZ's failure mechanism and mechanical property under different stress wave incidence orientations and confining pressures. It can be concluded that under multi-directional dynamic stress waves, the failure mode of the ITZ is represented as a complete failure with the angle from 0° to 45°, the local penetration failure of the ITZ with the angle from 60° to 90°, and the highest failure rate of only 4.89%. Under different confining pressure, the 40 MPa as a threshold can reduce the failure rate of the ITZ from 100% to 41.74%. The confining pressure delayed the stable stage initial angle of tensile and shear displacement from 60° to 75° under the coupling effect of the multi-directional stress wave and confining pressure. For interface displacement control, the incidence angle should be better than 75° under confining pressure, and the angle can be controlled above 60° without confining pressure. Therefore, for tunnel surrounding rock support, attention should be paid to displacement and deformation control at positions where the angle between the excavation blasting direction and the primary lining surrounding rock bonding surface is less than 75°. Highlights: The failure evolution law of rock–shotcrete ITZ subjected to multi-directional stress waves is investigated. The effect of confining pressure on the interface failure mechanism and the ITZ stress distribution of the rock–shotcrete was obtained. The interface stress and displacement of the rock–shotcrete acted upon by the coupling effect of stress waves and confining pressure were explored. [ABSTRACT FROM AUTHOR]

The major purpose of this study is to analyze the resistance of honeycomb ceramic matrix composites to penetration and to explore the effect of the performance characteristics of the filler materials on this capability. We used alumina ceramics, polyurea, quartz sand powder, and boron carbide powder to manufacture composite materials, and conducted impact tests and numerical simulations on them. The simulation results of Abaqus were found to be very consistent with the test results. The results demonstrate that the polyurea coating and filler materials may effectively improve the anti-penetration penetration performance of the composites, and different filler materials have varying energy absorption effects. Extended research on composites was carried out utilizing experimentally validated numerical models with filler materials comprising silicon carbide, aluminum nitride, and silicon nitride. After a comparative analysis of the simulation results of different composites, compared to quartz sand composites, the energy absorption efficiency of boron carbide composites increased by 12.03 %, silicon carbide composites increased by 14.63 %, aluminum nitride composites increased by 15.16 %, and silicon nitride composites increased by 18.29 %. Among the relevant materials in this study, there exists an optimal value of the stress wave impedance difference between the matrix material and the filler material. Honeycomb ceramic matrix composites with an ideal combination of stress wave impedance differences can considerably increase the anti-penetration efficiency of the composites. [ABSTRACT FROM AUTHOR]

Soil–steel composite structures are commonly considered competitive alternatives to conventional small road and railway bridges. The structure is made from corrugated steel plates and comes in various profiles and shapes, up to 32 m at most. These structures are also found in seismic areas. Despite this, knowledge of their seismic behavior is limited. The paper analyzes the seismic behavior of an existing soil–steel composite bridge in Poland, where full-scale tests have been conducted. The analyzed bridge has a total height of 6.05 m and a span length of 17.67 m and was built with 140×380 mm corrugation and 7-mm thick steel plates. Numerical analyses are performed on the bridge using the finite element (FE) program DIANA FEA with seismic records from the 1940 El Centro earthquake as a reference. Expanded polystyrene (EPS) geofoam is applied under the structure and studied in the numerical models to reduce the impact of seismic waves on the bridge. The first numerical model was created without geofoam for calibration purposes, and the latter five with EPS given different stiffness properties (densities and Young's modulus). The results suggest that EPS has advantageous features (especially with low stiffness) in reducing the maximum deformations and stresses on the steel shell by absorbing (damping) the energy of the seismic waves and rearranging the stresses away from the structure and to the soil. This trend was particularly evident when comparing the five models built with EPS to the model without EPS, where stresses in the structure were significantly higher, demonstrating the material's ability to rearrange the stresses away from the structure. Practical Applications: Soil–steel composite bridges are commonly considered competitive alternatives to conventional small road and railway bridges. The shell structure is made from corrugated steel plates backfilled by granular soil and comes in various profiles and shapes, up to a maximum of 32 m. These structures are also found in seismic areas. Despite this, knowledge of their seismic behavior is limited. This paper analyzes the seismic behavior of an existing soil–steel composite bridge. The EPS geofoams were applied under the structure and studied in the numerical models to reduce the impact of seismic waves on the bridge. The results suggest that EPS has advantageous features in reducing the maximum deformations and stresses on the steel shell by absorbing the energy of the seismic waves and rearranging the stresses away from the structure and the soil. The obtained results may contribute to the dissemination of these bridge structures in seismic areas. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of rock mass behavior necessitates the study of seismic waves generated by various sources of vibration within rocks. Joints and fractures are prevalent in rock masses and substantially impact their dynamic response to seismic waves. The present study has identified natural rubber latex (NRL) as an effective energy-absorbing medium in the rock masses for limiting wave propagation across the joint. Gypsum plaster has been used to replicate the natural rocks as a model material for conducting this study. The damping properties of rock mass have been determined using split shear plate (SSP) and resonant column (RC) tests. The mechanical response of intact gypsum plaster and NRL has been examined using resonant column testing. The influence of the thickness of the NRL layer on the damping characteristics of the jointed rock mass was studied by varying the thickness of the NRL layer within the joints from 2 to 5 mm. Using RC testing, the variations of shear moduli and damping ratios with different thicknesses of NRL have been studied. The variations of transmission coefficient (T), absorption coefficient (A), and reflection coefficient (R) with variable NRL thickness have been investigated utilizing SSP testing. The findings of the present study can be applied to developing numerical models that can anticipate the behavior of rock masses under dynamic loading conditions and for utilizing the NRL as an effective energy-absorbing material in the rock mass to reduce the vibrations that are transmitted to the structures. Practical Applications: The utilization of natural rubber latex (NRL) as an infill material in rock masses presents promising practical applications across various engineering domains. Its application extends to tunneling, mining, and stabilizing rock slopes. In tunneling and mining, NRL aids in increasing ground stability and controlling water intrusion during excavation, thereby enhancing safety and efficiency. In addition, it proves beneficial in stabilizing roofs and walls and preventing water and gas infiltration in mining operations. NRL reinforces joints within rock masses, reducing permeability and enhancing structural integrity. NRL stands out for its environmentally friendly and sustainable nature compared to synthetic polymers. Research indicates that NRL-stabilized soil has a lower carbon footprint than traditional cement-stabilized soil, thus offering an ecofriendly solution. Moreover, NRL presents opportunities for repurposing waste materials and reducing the environmental impact of concrete production. This study pioneers the application of NRL for vibration damping in jointed rocks, expanding the understanding of its dynamic properties under shear wave propagation. Through resonant column and split shear plate tests, this research explores the influence of NRL thickness on wave propagation, providing valuable insights for engineering practices in rock-dominated environments. [ABSTRACT FROM AUTHOR]

Under the influence of service life and the external environment, bolted connections are prone to loosening, which may lead to structural hazards. Thus, it is crucial to carry out real-time monitoring of bolted connections. Based on the active sensing method, previous researchers mainly focused on quantifying the single-bolt looseness, with little focus on locating and quantifying the multibolted connection. This study introduces an innovative approach to monitor multibolt looseness in steel structures. The proposed method utilizes multitask active sensing, incorporating a substructure cross-domain transfer learning technique. A finite-element model of a portal frame structure was first established by ABAQUS software, and the substructure was determined based on the stress wave propagation characteristics. Secondly, the location and degree of bolted connection in the substructure and portal frame structure were monitored using the piezoelectric active sensing method. Monitoring data of the substructure are tagged as the source domain, while data of the portal frame structure are tagged as the target domain. To efficiently decouple the characteristics of loosening, this study extracted multidomain energy and unthresholded multivariate recurrence plots from stress wave signals. These elements were employed to pinpoint the location and assess the degree of looseness. The multibolted connection was then monitored by the adversarial domain adaptation networks. Ultimately, using the target domain's input, the optimized model was able to precisely detect the location and degree of the multibolted connection step by step. The experimental results demonstrated that the suggested technique has a lot of promise for multibolt looseness monitoring. [ABSTRACT FROM AUTHOR]

The internal defects in rock masses can significantly impact the quality and safety of geotechnical projects. Mechanical waves, as a common nondestructive testing (NDT) method, can reflect the external and internal structures of rock or rock masses. Analyses on the reflected and transmitted waves enable nondestructive identification and assessment of potential defects within rocks. Previous studies mainly focused on the variation of single or limited wave features like main frequency, amplitude and energy between the intact and non‐intact samples. In fact, most information contained in the waveforms is neglected. Techniques of data mining can provide a powerful tool to reveal this information and therefore a more accurate determination of the internal structures. In this study, 995,412 NDT data from 14 types of granite and gypsum samples with different cross‐section shapes and different types of defects are recorded by an ultrasonic wave generation and collection system. This dataset can be used not only as the training data for defect classification in NDT but also as a good reference for conventional NDT analyses. Besides, time‐series data analysis is an opportunity and challenging issue, this dataset holds great potential for broader application in general time‐series classification analysis. [ABSTRACT FROM AUTHOR]

Summary The ability to accumulate nutrients is a hallmark for living creatures and plants evolved highly effective nutrient transport systems, especially for the uptake of potassium (K+). However, plants also developed mechanisms that enable the rapid extrusion of K+ in combination with anions. The combined release of K+ and anions is probably an ancient extrusion system, as it is found in the Characeae that are closely related to land plants. We postulate that the ion extrusion mechanisms have developed as an emergency valve, which enabled plant cells to rapidly reduce their turgor, and prevent them from bursting. Later in evolution, seed plants adapted this system for various responses, such as the closure of stomata, long‐distance stress waves, dropping of leaves by pulvini, and loading of xylem vessels. We discuss the molecular nature of the transport proteins that are involved in ion extrusion‐based functions of plants and describe the functions that they obtained during evolution. [ABSTRACT FROM AUTHOR]

Layered joints significantly affect the propagation and attenuation of engineering blasting stress waves and have a significant influence on rock breakage. In this study, the explosion crack propagation mechanism of a stratified rock mass with weak or no cementation is analyzed. Multilayer plexiglass plates are employed to simulate a layered rock mass, establishing an experimental model to investigate the vertical interaction between explosive charges and layered rock masses. The extent of ruptures and damage within the charging and sealing sections of the rock mass is analyzed. The explosion cracks at the bottom of the hole are relatively dense, whereas those at the hole opening are relatively sparse. The range of the crushing and fracture zones around the gun hole in the charging section is larger than that in the blocking section. Moreover, as the blocking section approaches the free plane, the crushing zone size decreases. A notable area of rapid damage escalation is identified between the blocking and charging sections, leading to a significant increase in damage intensity. The numerical analysis results indicate that the cumulative explosive energy within the charging section surpasses that of the blocking section, and the rate of energy accumulation is notably higher in the charging region. [ABSTRACT FROM AUTHOR]

AbstractDirectional fracturing blasting is effective for rock engineering, but it is inevitably disturbed by multiple reflected waves from different directions in natural rock mass due to discontinuous boundaries. Reflected waves affect both crack-tip stress and crack propagation, hence affect the results of directional fracturing blasting. In this paper, with the aid of high-speed photography, an optical caustics method is used to study effects of multiple reflected P waves on a directional blast-induced crack in a polymethyl methacrylate (PMMA) plate, specifically on crack path, crack fracturing mode, crack-tip stress and crack velocity. Crack-tip stress field is indicated by the shape of caustics pattern. Before the loading of reflected P waves, the mode I directional crack driven by blast-induced gases propagates in a straight path; crack-tip stress field is K-dominated, and crack-tip caustics pattern is consistent with classical caustics theory. On the contrary, under the loading of reflected P waves, the directional crack changes to be mixed-mode I + II and propagates in a curved path; Crack-tip stress field is non-K-dominated due to transient stress superposition of reflected P waves, and crack-tip caustics pattern is consistent with modified caustics theory. Transient stress superposition is not obvious for reflected P waves with a longer reflection distance. The tension loading of reflected P waves plays a more important role than the compression loading, which increases crack-tip stress intensity factors and crack velocity. This study provides a comprehensive understanding of effects of multiple reflected P waves from different directions on directional fracturing blasting. [ABSTRACT FROM AUTHOR]

The nearshore wind stress, u∗2 ${u}_{\ast }^{2}$, is examined using machine‐learning models for air‐ocean data collected via new flux buoys deployed across four experiments. Consistent with prior nearshore studies, existing open‐ocean models predict nearshore u∗2 ${u}_{\ast }^{2}$ with a large error of 0.0152 m2/s2. Gaussian Process Regression (GPR) for nearshore u∗BM2 ${u}_{\ast \text{BM}}^{2}$ is developed, reducing errors to 0.0108 m2/s2. Nearshore air‐sea parameterizations are examined with wind speed (61%) and the wind‐wave frequency of encounters (16%) being the most important. A simpler nearshore, GPR‐derived, wind‐dependent‐only model (u∗NSU2 ${u}_{\ast \text{NSU}}^{2}$) is developed, with errors of 0.0135 m2/s2. GPRs, evaluated using identical variables, were applied to nearshore observations, and these observations modeled with open‐ocean formulations for an initial comparison of parameterizations between these two regimes. The parameterizations are similar, though with subtle nonlinear differences. The new nearshore data set and machine‐learning models enhance the accuracy of predictions and understanding of differences from the open‐ocean. Plain Language Summary: Understanding and accurately parameterizing wind stress on the ocean surface is crucial for modeling oceanic and atmospheric phenomena. Despite its significance, nearshore wind stress and its influencing factors remain inadequately understood due to limited in situ observations and the complexity of the problem. To address this gap, ten shallow‐water air‐sea buoys were developed and deployed alongside directional wave buoys in four field experiments, yielding a substantial data set of nearshore wind stress and associated variables. Discrepancies between nearshore and open‐ocean models were observed, with open‐ocean models exhibiting large errors. Machine‐learning models enhance the accuracy of predictions and understanding of the input variables. A new data‐informed machine‐learning model for nearshore wind stress significantly reduced the error by 30%. Each variable parameterization is described, and a simple model for wind stress based solely on wind speed is provided. Furthermore, an examination of wind stress parameterizations revealed similarities and differences between nearshore and open‐ocean, primarily attributed to wind speeds. These findings significantly enhance the accuracy of weather and ocean forecasts, particularly for nearshore regions. Key Points: Ten air‐sea buoys for winds and fluxes, deployed with wave buoys in four experiments, improve nearshore wind stress observation gapsSupervised machine learning enhances nearshore wind stress predictions, yielding parameterized variable responses without preconceptionsNearshore wind stress parameterizations relative to the open‐ocean have similar variable responses though with small nonlinear differences [ABSTRACT FROM AUTHOR]

A 12-mm caliber gas gun was used to launch a high-strength steel cylindrical projectile to impact a polyurea-coated B4C ceramic target plate to investigate the effects of the polyurea coating position and the thickness of the polyurea coating on the protective ability of the ceramic composite target plate, reveal the penetration resistance mechanism of the polyurea-coated B4C ceramic plate and protection mechanism of polyurea coating. The result showed that the ceramic cone top diameter of the composite target plate coated with polyurea on the front side was 52.4–60.5% lower than that of the uncoated ceramic target plate, and the ceramic cone bottom diameter was 0.2–4% lower than that of the uncoated ceramic target plate. For the same area density, the ceramic target plate coated with polyurea on both sides had the largest percentage of mass remaining and the smallest mass of dislodged ceramic fragments. In addition, composite target plates coated with polyurea on the back side and both sides significantly reduced the head velocity of the post-target debris cloud. The polyurea coating on the front of the target plate utilizes the strain rate effect to dissipate the kinetic energy of the projectile and inhibit the spallation of ceramic fragments toward the front of the target plate. The polyurea coating on the back of the target plate utilizes bulge deformation to dissipate the kinetic energy of the projectile and intercepts the scattering of the post-target debris cloud. The polyurea coating effectively reduces ceramic target plate damage and improves composite target plate integrity level and resistance penetration. [ABSTRACT FROM AUTHOR]

The damage ability of hypervelocity kinetic energy projectile penetrating ground has become a hotspot in modern military research. In this study, a hypervelocity impact test on a granite target subjected to projectiles using a two-stage light gas gun is conducted to study the stress wave evolution in granite under hypervelocity penetrations. The parameters of the *MAT_JOHNSON_HOLMQUIST_CERAMICS(JH-2) constitutive equation are calibrated using the results of the splinter impact test and the static test, and numerical simulations are performed using the smoothed particle hydrodynamics method coupled with finite element method (SPH-FEM coupled method) to extend the resulting data. A formula for calculating the stress wave peak attenuation is established, indicating that the maximum impact pressure produced by the hypervelocity impact decreases exponentially with scaling distance, and the attenuation coefficient is related to the degree of rock damage. Additionally, the attenuation of the speed of sound is used to characterize rock damage, and the damage deterioration law of granite under hypervelocity impact is analyzed based on the damage factor. [ABSTRACT FROM AUTHOR]

Recent observations show that certain rupture phase can propagate backward relative to the earlier one during a single earthquake event. Such back‐propagating rupture (BPR) was not well considered by the conventional earthquake source studies and remains a mystery to the seismological community. Here we present a comprehensive analysis of BPR, by combining theoretical considerations, numerical simulations, and observational evidences. First, we argue that BPR in terms of back‐propagating stress wave is an intrinsic feature during dynamic ruptures; however, its signature can be easily masked by the destructive interference behind the primary rupture front. Then, we propose an idea that perturbation to an otherwise smooth rupture process may make some phases of BPR observable. We test and verify this idea by numerically simulating rupture propagation under a variety of perturbations, including a sudden change of stress, bulk or interfacial property and fault geometry along rupture propagation path. We further cross‐validate the numerical results by available observations from laboratory and natural earthquakes, and confirm that rupture "reflection" at free surface, rupture coalescence and breakage of prominent asperity are very efficient for exciting observable BPR. Based on the simulated and observed results, we classify BPR into two general types: interface wave and high‐order re‐rupture, depending on the stress recovery and drop before and after the arrival of BPR, respectively. Our work clarifies the nature and excitation of BPR, and can help improve the understanding of earthquake physics, the inference of fault property distribution and evolution, and the assessment of earthquake hazard. Plain Language Summary: Under the traditional view on earthquakes, rupture is typically considered to propagate away from where it starts, a process called forward propagation. However, recent studies show that sometimes rupture can reverse its propagation direction relative to the earlier one, which is referred to as back‐propagating rupture (BPR). The lack of a comprehensive understanding of BPR motivates us to explore why and how BPR could occur, by combining theoretical analyses, computer simulations, and experimental or natural observations. Our theoretical analyses suggest that BPR in terms of back‐propagating stress wave should almost always exist during dynamic ruptures, but can also be masked by the canceling effect of interfering waves. Nonetheless, introducing perturbations during a relatively smooth rupture process may highlight certain phases of BPR. We verify the above idea by computer simulations and available observations, showing that perturbed rupture propagation, for example, by the encountering of free surface, another rupture, and fault asperity, indeed can excite observable BPR. We further classify BPR into interface wave and high‐order re‐rupture, when there is a negligible and finite offset to the baseline of shear stress, respectively. Our work provides new insights into earthquake source process and can help improve earthquake hazard assessment. Key Points: Back‐propagating rupture (BPR) (as stress wave) is an intrinsic feature during dynamic ruptures but can be masked by destructive interferenceObservable BPR can be excited by introducing a variety of perturbations to an otherwise smooth rupture processBPR represents interface wave or high‐order re‐rupture, and can help infer the evolution behind the primary rupture [ABSTRACT FROM AUTHOR]

Fragmentation by blasting is a critical process in hard rock mining. The interaction between the rock mass and blast energy influences the outcomes, specifically on the rock mass response to higher stresses and loading rates, and the properties of structures. In this study, LS-DYNA is used to model the nonlinear dynamic fracturing of the rock to understand the effects of rock mass properties on the blast outcomes. The results are verified and compared with the case study, and they show that the formation of damage zones around the charge is highly influenced by rock mass strength and discontinuity properties. [ABSTRACT FROM AUTHOR]

There are controversial findings on how projectile penetration into the human tissue can induce tissue damage. The evidence from recent experimental investigations has explained the related underlying mechanisms. To understand and simulate the exact biomechanical mechanisms of projectile penetration-induced tissue damage, we evaluated effects of two-dimensional (2D) transient stress wave propagation of 2D-functionally graded material (FGM, radial and circumferential inhomogeneity) in an infinite hollow cylinder. A periodic radial and circumferential material gradation fluctuating a constant value has been considered as the effective material properties, across the cylinder wall and the problem has been solved by implementing the graded finite element method with nonlinear Lagrangian shape functions. In contrast with other researches, the stress wave propagation for $ r $ r and $ \theta $ θ -inhomogeneity is different compared to the case in which the $ r $ r or $ \theta $ θ -inhomogeneity has been considered, separately. Moreover, this example resembles the bullet penetration in human tissue that produces stress wave propagation, resulting in unintentional trauma in human organs. For the case of 1D-FGM ( $ r $ r – inhomogeneity), the responses are pulse-like and symmetric. Finally, due to shear waves, the $ \theta $ θ -inhomogeneity has more visible effect on the stress wave propagation than $ r $ r – inhomogeneity due to shear waves, especially when the pulse collapses. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the wave attenuation coefficient and wave number of the heated granite after water cooling (W-C) and air cooling (A-C) treatments. The granite specimens heated to five temperatures (25 °C, 100 °C, 200 °C, 300 °C and 400 °C) were subjected to the W-C and A-C treatments, respectively. The pendulum impact test was performed on the cooled granite at room temperature to obtain the separated stress pulse. The wave attenuation ratio in the cooled granite was investigated. Propagation coefficients (attenuation coefficient and wave number) were introduced to describe the harmonic wave attenuation in the cooled granite. The effects of W-C and A-C treatments on the attenuation coefficient and wave number were discussed. The results show that the P-wave velocity decreases as temperature increases, while the wave attenuation ratio increases as temperature increases. The P-wave velocity of the granite after the W-C treatment is smaller than that of the granite after the A-C treatment. The wave attenuation ratio, attenuation coefficient and wave number of the stress pulse in the granite after the W-C treatment are larger than those of the stress pulse in the granite after the A-C treatment. The differences of P-wave velocity, wave attenuation ratio, attenuation coefficient and wave number after two cooling treatments increase as temperature increases. [ABSTRACT FROM AUTHOR]

Solutions for unloading stress waves in the continuous medium are widely applied to analyze the transient effect of excavation unloading in deep-buried tunnel engineering. This paper explores a semianalytic model for studying dynamic stress adjustments during transient excavation unloading in deep underground tunnels. The model employs finite time steps and toroidal elements on temporal and spatial scales, utilizing an iterative algorithm for dynamic response calculation. Griffith and Mohr–Coulomb strength criteria are introduced to calculate the difference in the critical generalized additional stress. This difference classifies stress adjustment paths into crack–shear (crack first and then shear) and shear models (shear only). Updated discontinuous boundaries are considered in the cracked element. Investigating the effects of unloading duration and initial in situ stress on dynamic response, a stress release index is realized to quantify the dynamic stress adjustment. Shorter unloading durations lead to more pronounced stress fluctuations, and higher stress release aggregation results in smaller plastic zones. Positive correlations between initial in situ stress and response characteristics are observed, resembling triaxial unloading test results. The model proposed in this paper enhances the understanding of the failure mechanism in the unloading process for deep hard rocks in underground engineering. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rock mass consists of many discontinuities, such as faults, joints, etc., and layered joints are a common kind of rock mass structure. The joints affect the stress wave propagation, and blasting is an economical and efficient rock fragmentation method for rock mass engineering. So, the rock mass fragmentation effect and construction progress are affected by these layered joints. Numerical studies were carried out to analyze the damage evolution process of intact rock and rock mass with layered joints subjected to blasting loads based on the Riedel–Hiermaier–Thoma (RHT) model in LS-DYNA software (smp s R11.0.), and the effects of the location of initiation points and the fracture distribution on dynamic damage evolution of the rock mass were discussed. Bottom initiation tends to direct the blasting energy toward the blasthole mouth, resulting in effective rock fragmentation and ejection. Gradually adjusting the initiation point upward can improve the stress and damage distribution, allowing some of the blasting stress waves to propagate toward the bottom and enhance the fragmentation of the rock at the bottom. The distribution of layered joints exacerbates the damage to the rock mass on the upstream surface, but also acts as a certain shield to the propagation of stress waves, increasing the asymmetry of the damage distribution. It is useful to know the damage mechanism of the rock mass with layered joints to improve the effect of rock mass fragmentation by blasting. These results have very important theoretical significance and application value for the optimization of blasting construction technology. [ABSTRACT FROM AUTHOR]

This study focuses on existing pruning equipment; cutting blades show cutting resistance and lead to high energy consumption. Using finite element (FEA) numerical simulation technology, the branch stress wave propagation mechanism during pruning was studied. The cutting performance of the bionic blade was evaluated with cutting energy consumption as the test index and the branch diameter and branch angle as the test factors, respectively. The test results showed that the blades imitating the mouthparts of the three-pecten bull and the beak of the woodpecker performed well in pruning, and the energy consumption during cutting was reduced by 18.2% and 16.3% compared to traditional blades, making these blades significantly better. These two blades also effectively reduced the cutting resistance and branch splitting by optimizing the edge angle design and increasing the slip-cutting action. In contrast, the imitation shark's tooth blade increased cutting energy consumption by 14.4% due to the large amount of cutting resistance in the cutting process when cutting larger-diameter branches, making it unsuitable for application in the pruning field. Therefore, the blades imitating the mouthparts of the three pectins and the beak of the woodpecker have significant advantages in reducing the cutting resistance and improving the pruning quality. These findings provide an important theoretical reference for the development of energy-efficient pruning equipment. [ABSTRACT FROM AUTHOR]

The elastic properties and wave propagation of porous rocks are sensitive to the stress variation. The existing theories mainly focus on the impacts of effective stress, confining and pore pressures. The physics of uniaxial stress effect on rock elasticity and wave propagation is seldom well studied, although the uniaxial stress case is frequently encountered in several scenarios, such as the laboratory loading and the subsurface tectonic deformation. Therefore, we propose a new dual‐porosity model to describe the effect of uniaxial effective stress on elastic properties of dry porous rocks, based on the Palmer equation and Shapiro dual‐porosity model. The Gurevich squirt‐flow model is then incorporated to model the dispersion and attenuation of wave velocities of fluid‐saturated porous rocks. Modelling results show that the increase of uniaxial effective stress inflates the P‐ and S‐wave velocities along the stress direction until the velocities asymptotically reach their maximum values within the elastic limit. However, the relevant wave dispersion and attenuation gradually decline with the elevating stress possibly due to the gradual closure of cracks. The effect of viscosity, fluid modulus and crack aspect ratio on wave dispersion is investigated in detail as well. By comparing our model to the published laboratory ultrasonic measurements, we confirm the validity of our model. Furthermore, our dual‐porosity model is used to establish a rock‐physics approach to estimate the wave velocities with the well‐logging data. The well‐logging examples show the reasonable agreement between the predicted results and real data, illustrating the feasibility of our approach. [ABSTRACT FROM AUTHOR]

With the increase of mining scope, rockburst occurs frequently, but its generation mechanism has not been understood comprehensively. Based on a rockburst in the coal pillar area of high tectonic stress zones (HTSZs), this study analyzed the distribution characteristics of large-energy microseismic (MS) events by using data statistics. The mechanical cause of the MS event that induced the rockburst was revealed by means of seismic moment tensor inversion. On this basis, by using numerical simulation, this study explored the distribution characteristics of static load in rockburst area and the effect of dynamic load in the floor, and then proposed the rockburst mechanism. The results show that under the squeezing action, the floor strata in HTSZs implode and transmit energy outward in the form of stress waves. This causes the cumulative damage and stress of the coal body in the fast track of coal pillar area increase in a short time. Since the coal in this area has already been in the critical stress state, small stress changes may lead to coal failure and rockburst. In this case of rockburst, the high static load of coal is the main force source, and the dynamic load plays a role in increasing coal body damage and inducing rockburst. Combined with seismic moment tensor inversion and numerical simulation, this paper proposes a rockburst research scheme, which makes the simulation of dynamic load more reasonable. The results provide the theoretical basis for rockburst control under similar conditions. [ABSTRACT FROM AUTHOR]

Passive non-destructive evaluation tools such as acoustic emission (AE) testing and acousto-ultrasonics (AU) approach present a complex problem in damage localisation in complex and nonhomogeneous geometries. A novel AU-guided AE frequency interpretation approach is proposed in this research work which aims at overcoming this limitation. For the experimental evaluation, the damage sources from a geometrically complex clear dental aligners are tested under cyclic compression load and their origins are evaluated. Despite the rapid worldwide diffusion of the clear aligners, their mechanical behaviour is poorly investigated. In this work, the frequency characteristics of the artificially simulated stress wave, generated from different dental positions of the clear aligners, are studied using the AU approach. These frequency characteristics are then used to analyse the AE signals generated by these aligners when subjected to cyclic compressive loading. In addition, the time domain characteristics of the AE signals are studied using their Time of Arrival (ToA). The Akaike Information Criterion (AIC) is used to estimate the ToA. These frequency and time domain characteristics of the AE signals are used to estimate the local damage origin in the clear dental aligners. This will help in identifying localised damage sources during the usage period of the aligners. Experimental results revealed significant damages in the left maxillary premolar and right maxillary third molar of the aligners. [ABSTRACT FROM AUTHOR]

While foot immersion and neck cooling have been recommended for protecting heat-vulnerable groups, recent evidence does not support their efficacy for mitigating increases in physiological heat strain in older adults. However, their influence on self-reported environmental symptoms and mood-state remains unclear. Seventeen older adults (nine females, median [interquartile range] age: 72 [69–74]) completed three randomized heat exposures (6-h; 38°C, 35% relative humidity) with no cooling (control), foot immersion to mid-calf in 20°C water for the final 40-min of each hour (foot immersion), or foot immersion with a wet towel (20°C) around the neck (foot immersion with neck cooling). Core temperature, skin temperature, and heart rate areas under the curve (AUC) were assessed as indicators of cumulative physiological strain. Environmental symptom scores (68-item environmental symptoms questionnaire) and mood disturbance (40-item profile of mood states questionnaire) were evaluated at end-heating (adjusted for pre-exposure). Core temperature AUC was not different between conditions (p = 0.418). However, the skin temperature and heart rate AUCs were 11.8°C · h [95% confidence interval: 8.1, 15.5] and 12.5 bpm · h [0.1, 24.8] lower for foot immersion and 16.6°C · h [12.9, 20.3] and 19.6 bpm · h [7.2, 32.0] lower for foot immersion with neck cooling compared to control (p ≤ 0.032). Environmental symptom scores were 0.8-fold [0.6, 1.0] lower for both foot immersion with and without neck cooling, compared to control (both p = 0.036). Mood disturbance was not different between conditions (both p ≥ 0.275). Foot immersion with and without neck cooling reduces self-reported environmental symptoms in older adults despite having little effect on physiological heat strain. [ABSTRACT FROM AUTHOR]

In practical engineering, noise and impact hazards are pervasive, indicating the pressing demand for materials that can absorb both sound and stress wave energy simultaneously. However, the rational design of such multifunctional materials remains a challenge. Herein, inspired by cuttlebone, we present bioinspired architected metamaterials with unprecedented sound-absorbing and mechanical properties engineered via a weakly-coupled design. The acoustic elements feature heterogeneous multilayered resonators, whereas the mechanical responses are based on asymmetric cambered cell walls. These metamaterials experimentally demonstrated an average absorption coefficient of 0.80 from 1.0 to 6.0 kHz, with 77% of the data points exceeding the desired 0.75 threshold, all with a compact 21 mm thickness. An absorptance-thickness map is devised for assessing the sound-absorption efficiency. The high-fidelity microstructure-based model reveals the air friction damping mechanism, with broadband behavior attributed to multimodal hybrid resonance. Empowered by the cambered design of cell walls, metamaterials shift catastrophic failure toward a progressive deformation mode characterized by stable stress plateaus and ultrahigh specific energy absorption of 50.7 J/g—a 558.4% increase over the straight-wall design. After the deformation mechanisms are elucidated, a comprehensive research framework for burgeoning acousto-mechanical metamaterials is proposed. Overall, our study broadens the horizon for multifunctional material design. Noise and impact hazards are pervasive in engineering, necessitating materials capable of absorbing both sound and stress wave energy. Here, we present bioinspired metamaterials with exceptional sound-absorbing and mechanical properties using a weakly-coupled design strategy. These materials incorporate multi-layered resonators for superior acoustic performance and cambered cell walls for enhanced structural strength. They achieve an average absorption coefficient of 0.80 across the 1.0 to 6.0 kHz range, all within a sleek 21 mm thickness. Furthermore, the design transitions failure modes from catastrophic to progressive, resulting in a remarkable 558.4% increase in energy absorption compared to conventional designs. [ABSTRACT FROM AUTHOR]

To address the conflict between pressure relief and support effectiveness caused by large-diameter boreholes in roadway surrounding rock, this paper proposes a method involving variable-diameter boreholes for pressure relief and energy dissipation. With a typical rock burst coal mine as the engineering context, the study establishes a mechanical model for variable-diameter boreholes through theoretical analysis to examine the elastic stress distribution around boreholes within the coal body. Physical similarity simulation tests are conducted to investigate the influence of conventional borehole and variable diameter borehole on the transmission pattern of dynamic load stress waves. Furthermore, numerical simulations are employed to explore the effects of reaming diameter, depth, and spacing on pressure relief, energy dissipation, and attenuation of dynamic stress wave transmission in roadway surrounding rock. The results demonstrate that stress within the coal surrounding the variable-diameter borehole correlates with the borehole radius, lateral pressure coefficient, and distance from the point to the borehole center, the extent of the plastic zone is influenced by borehole diameter, spacing, and depth. Increased diameter, reduced spacing, and greater depth of deep reaming holes exacerbate the transfer of stress concentration from the surrounding rock of the roadway to the deeper regions, facilitating the formation of stress double peak areas. Moreover, the variable diameter position should be within the original stress peak position of the surrounding rock in the roadway, with deep reaming passing through the stress concentration area for optimal results. This study offers guidance on the prevention and control technology for rock bursts in deep coal mining operations. [ABSTRACT FROM AUTHOR]

Aims: China is one of the countries in the world most seriously affected by typhoons, which pose a great threat to the eucalyptus plantation industry. However, few studies have comprehensively accounted for the impact of key traits on the wind damage/resistance of eucalyptus. Methods: To identify the key factors affecting the wind resistance of eucalyptus, 20 eucalyptus genotypes were selected; a total of 18 traits, including the wind damage index, growth traits, and wood traits, were measured, and the wind resistance was determined via the tree-pulling test. Results: Correlation, principal component, canonical correlation, and path analyses were performed to evaluate these traits. Correlation analysis revealed that the wind resistance of eucalyptus plants was related to the tree height, volume, and duration of stress wave propagation. Principal components and tree-pulling variables were further used for correlation and path analyses. Canonical correlation analysis and the PA-OV model showed that holocellulose and lignin contents and fiber width, as well as growth traits, were important factors affecting the stability of standing trees under typhoon conditions. The key traits influencing the wind resistance of Eucalyptus camaldulensis, which may provide a reference for evaluating the wind resistance of Eucalyptus varieties for forest management, were identified. Conclusion: This study provides a knowledge base for forest management and planning in typhoon-prone coastal areas, and provides a theoretical basis for the breeding and genetically improving eucalyptus stocks based on wind resistance characteristics. [ABSTRACT FROM AUTHOR]

Wood quality has been an ongoing concern for science, having become increasingly important in the current context, in which the demand for wood is increasing and forest fires are more frequent and violent. This study aims to evaluate the quality of wood in trees affected by fires and the negative impact of these phenomena on the speed of wood degradation, as a result of weakening the trees due to the action of stress factors. The study was carried out using modern techniques on beech trees (Fagus sylvatica L.) remaining in an area affected by a litter fire in 2017. Measurements were taken with the Arbotom Rinntech sound tomograph, the IML Resi F-500S resist graph, and the Pressler core sampler to observe the quality of the wood inside the trees. It was found that all the trees were in various stages of decay, the tomograms being able to characterize the severity of decay only in the case of fully decayed wood as a result of the action of xylophages fungi, whose harmful influence is more pronounced when the injuries sustained by the trees are higher. Although the trees attempted to close the fire wounds through their own defense mechanisms, the destructive action of the fungi intensified with time. After the forest fires, for an effective assessment of the wood's internal quality, the resist graph can be used. For valuable trees, one could use the tomograph, but the measurements have to be taken only by qualified operators. [ABSTRACT FROM AUTHOR]

Open-pit coal mining offers high resource recovery, excellent safety conditions, and large-scale production. However, the process generates significant dust, leading to occupational diseases such as pneumoconiosis among miners and adversely affecting nearby vegetation through dust deposition, which hinders photosynthesis and causes ecological damage. This limits the transition of open-pit mining to a green, low-carbon model. Among these processes, blasting generates the most dust and has the widest impact range, but the specific amount of dust generated has not yet been thoroughly studied. This study integrates indoor experiments, theoretical analyses, and field tests, employing the Split Hopkinson Pressure Bar (SHPB) system to conduct impact loading tests on coal–rock samples under pressures ranging from 0.13 MPa to 2.0 MPa. The results indicate that as the impact load increases, the proportion of large-sized blocks decreases while smaller fragments and powdered samples increase, signifying intensified sample fragmentation. Using stress wave attenuation theory, this study translates indoor impact loadings to field blast shock waves, revealing the relationship between blasting dust mass fraction and impact pressure. Field tests at the Haerwusu open-pit coal mine validated the formula. Using image recognition technology to analyze post-blast muck-pile fragmentation, the estimated dust production closely matched the calculated values, with an error margin of less than 10%. This formula provides valuable insights for estimating dust production and improving dust control measures during open-pit mine blasting operations. [ABSTRACT FROM AUTHOR]

The technique of multi-long-hole blasting with large empty holes has been used in practice to break rock mass. However, the damage mechanism of rock mass surrounded by empty holes and boreholes under this type of blasting has not yet been well-understood and identified, which may lead to inappropriate design of the configurations of empty holes for multi-long-hole blasting. The present study investigates the damage modes and mechanism of rock mass under multi-long-hole blasting with large empty holes by conducting a field test and numerical simulations. The results show that multi-long-hole blasting with empty holes mainly causes compressive damage of rock mass around boreholes, reflected tensile damage near empty holes and ground surface, bending-induced tensile damage between empty holes and boreholes, shear damage along the side tangents and bottom of empty holes and boreholes, and tensile damage along the connection of boreholes caused by the superposition of stress waves. In addition, parametric studies are conducted to examine the effects of depths and diameters of empty holes and the spacing between boreholes and empty holes on the damage and fragmentation of rock mass under blast loads. It is found that the flexural stiffness and confined levels of rock mass can be greatly influenced by the variation of configurations of empty holes, which thus induces different damage and fragmentation under multi-long-hole blasting. Analytical formulas for the evaluation of shear and bending-induced damage of rock mass under multi-long-hole blasting are finally proposed to provide references for the design of empty holes in multi-long-hole blasting. Highlights: Damage modes and mechanisms of multi-long-hole blasting with large empty holes are identified. Rock fragmentation characteristics under this blasting are examined. Effects of configurations of empty holes on the performance of multi-long-hole blasting are revealed. Analytical formulas are developed to evaluate rock damage under this blasting. [ABSTRACT FROM AUTHOR]

The evolution characteristics of rock fracturing in presplit blasts are generally affected by in situ stress resulting from tectonic forces in the Earth's crust and from gravity. In this study, rock fracturing under coupled static stress and presplit blasting conditions is comprehensively investigated by combining experimental, theoretical and numerical methods. Model tests of two-borehole presplitting on 200 × 200 × 50 mm granite samples are carried out using a biaxial hydrostatic loading system, and blast-induced rock fracture is identified using high-speed digital image correlation. The postblast granite samples are further image processed using ImageJ to show the detailed rock fragmentation and fracture networks. The rock fracturing behaviours and fractal characteristics in presplitting under various biaxial and uniaxial stresses, and under constant uniaxial stress with different β values (angle between the orientation of uniaxial stress and the line connecting blastholes), are examined. Blast tests show that the number and length of blast-created fractures in presplitting decrease with increasing static stress, and thus, presplit crack formation gradually fails, producing a rock crack pattern with relatively low fractal dimension and fractal damage levels. Moreover, the formation of crack coalescence fails between presplit holes, and the damage to the remaining rock significantly increases when β is larger than 15°. Then, the variations in crack patterns in recent presplitting tests are analysed based on elastic mechanics by calculating the transmission and superimposition of detonation stress waves and the static stress distribution near presplit holes. Later, after performing numerical verification, the rock fracturing processes in presplitting are numerically modelled in LS-DYNA. The influences of boundary conditions on presplitting test results and the implications of the recent findings for practical presplitting are discussed accordingly. Highlights: Rock cracking in presplitting under static stress is experimentally tested. Rock cracking in presplitting under initial stress is numerically 3D modelled. The fractal characteristic of rock fractures in presplitting is investigated. The effects of uniaxial and biaxial stresses on presplit blasting are analysed. [ABSTRACT FROM AUTHOR]

The East African Coastal Current (EACC) is an important western boundary current of the tropical south Indian Ocean and plays an important role in the ocean circulation and biogeochemical cycles in the Indian Ocean. This study investigates the interannual variability of the EACC and its dynamical mechanisms. The result shows that the EACC has interannual variability associated with El Niño–Southern Oscillation (ENSO) during 1993–2017. The EACC shows a significantly positive correlation with the Niño-3.4 index with a correlation coefficient of 0.65, lagging the Niño-3.4 index by 18 months. During the decaying phases of El Niño (La Niña) events, the negative (positive) sea level anomaly (SLA) propagates westward as upwelling (downwelling) Rossby waves from the southeast Indian Ocean to the southwest Indian Ocean and then strengthens (weakens) the EACC due to zonal SLA gradient off the East African coast under geostrophic equilibrium. The SLA gradually weakens in the southeast Indian Ocean during its westward propagation but strengthens in the southwest Indian Ocean promoted by local wind stress curl anomaly. This study can improve our understanding of the relationship between the western boundary current of the tropical south Indian Ocean and large-scale ENSO air–sea processes and is important for managing marine fisheries and ecosystems on the East African coast. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Water hammer (WH) is a critical phenomenon in fluid-filled piping systems that can lead to severe pressure surges and structural damage. The characteristics of the pipe material, geometry, and support conditions play a crucial role in the fluid–structure interaction (FSI) during WH events. This study investigates the impact of various pipe parameters, including material, length, thickness, and diameter, on the WH behavior using an FSI-based numerical approach. A comprehensive computational model was developed based on the algorithm presented in Delft Hydraulics Benchmark Problem (A) to simulate the WH phenomenon in pipes made of different materials, such as steel, copper, ductile iron, PPR (polypropylene random copolymer), and GRP (glass-reinforced plastic). This study examines the influence of pipe parameters on WH performance in pipelines, utilizing FSI to analyze the phenomenon. The results show that the pipe material has a significant influence on the pressure wave speed, stress wave propagation, and the overall system response during WH. Pipes with lower modulus of elasticity, such as PPR and GRP, exhibit lower pressure wave speeds but higher stress wave speeds compared with steel pipes. Increasing the elastic modulus, pipe wall thickness, length, and diameter enhances the pipe's stiffness and impacts the timing, magnitude of pressure surges, and the likelihood of cavitation. The findings of this study provide valuable insights into the design and mitigation of WH in piping systems. [ABSTRACT FROM AUTHOR]

Background and purpose: Dynamic methods (non-destructive) tests is based on creating stress without failure in the samples and save time and costs for evaluating mechanical properties. Knots or the encapsulated branches are the most important factor in the grading of wood. Therefore, the objectives of this research are: detection of knots by non-destructive methods, measuring the dynamic modulus of elasticity of beech log using stress waves, and the effect of knot size on the speed of stress waves subsequently, and the value of dynamic modulus of elasticity. Materials and methods: The studied area was Shafarood series 11, which is located in the southern part of the Shafarood watershed, starts at an altitude of 500 meters and continues up to an altitude of 1650 meters. From this area, five beech trees were cut and divided into three equal parts of three meters by cross cutting, and according to the size of the knots, the properties of density, stress waves velocity and subsequently, the dynamic modulus of elasticity were measured. From the tangential image of the external indicator and the radial image of the internal indicator and using the Digimizer image4 software, the characteristics of each knot such as the diameter and angle of the knot were measured. For non-destructive detection of beech tree knot, ultrasonic tomography, stress wave velocity and CT scan methods were used. In the stress waves velocity method, a Fakopp microsecond timer device was used to measure the time of stress waves. In the radiographic method and to prepare CT scan images, a digital ground column device with two detectors made in France belonging to a medical clinic was used. To measure the density, 30 cylindrical stems with knots of small, medium and large classes were used, and according to the relationship between density and stress wave velocity, the value of dynamic elasticity modulus was calculated and evaluated. The diameter of the knot along the length of the stem, the density and the dynamic modulus of elasticity of the beech tree stem were measured. To analyze the data at the 95% confidence level, the one-way anova test was used, and to determine the normality of the data and the homogeneity of the variance, the Kalmograph Smirnov and Leven tests were used. To compare the means, Tukey's test was used by using SPSS software. Results: In the detection of beech tree knot with the three mentioned non-destructive methods, the results show the existence of limitations in each method. The ultrasonic tomography is not able to detect knots inside the beech tree trunk and the stress wave method also does not detect very small knots. The accuracy of the CT scan method in detecting the knot is high, but the cost of its detection is high. According to the growth stages of the beech tree, factors such as growth speed, branch encapsulation speed and natural pruning are different. The origin of the branch is pith of the stem. As a result, the number and size of the created knots are different along the tree. Therefore, most of the small knots are created in the main trunk of the tree. The diameter of the knot has also increased with the increase in the height of the stem. The knot has increased the density. The density results have shown that the samples with large, medium and small knots have significant differences. Considering that the ultrasonic tomography method is based on the reduction of density, it is not able to detect the knot. But in the radiography method, the parts with higher density are seen in light color and the parts with lower density are seen in darker color. The size of the knot is effective on reducing the speed of stress waves and thus reducing the dynamic modulus of elasticity of wood. In comparison with the samples without knots, the samples with small, medium and large knots reduce the modulus of elasticity by 20%, 50% and 70% respectively. Conclusion: In general, among the non-destructive methods, only the CT scan method is able to detect small knots and evaluate the clear wood and defects. In comparison with the control sample (without knots), increasing the size of the knot, the value of the density increases and the stress wave velocity decreases Subsequently, the dynamic elasticity modulus of the samples decreases. [ABSTRACT FROM AUTHOR]

Grey cast iron releases energy in the form of stress waves when damaged. To analyse the evolution of the physical and mechanical properties and acoustic emission characteristics of grey cast iron under uniaxial compression, acoustic emission signals were collected at different rates (0.5, 1, and 2 mm/s). Combined with load-time curves, damage modes were identified and classified using the parametric RA-AF correlation analysis method. The results indicate the loading rate effects on the strength, deformation, acoustic emission (AE), and energy evolution of grey cast iron specimens. The acoustic emission counts align with the engineering stress–strain response. To better illustrate the entire failure process of grey cast iron, from its internal microstructure to its macroscopic appearance, X-ray diffraction (XRD) and optical microscopy (OM) were employed for qualitative and quantitative analyses of the material's internal microstructural characteristics. The equivalent crystal model of grey cast iron was constructed using a Particle Flow Software PFC2D 6.00.30 grain-based model (GBM) to simulate uniaxial compression acoustic emission tests. The calibration of fine parameters with indoor test results ensured good agreement with numerical simulation results. Acoustic emission dynamically monitors the compression process, while discrete element particle flow software further analyses the entire damage process from the inside to the outside. It provides a new research method and idea for the study of crack extension in some metal materials such as grey cast iron. [ABSTRACT FROM AUTHOR]

In underground construction projects, traversing hard rock layers demands concentrated CO2 fracturing energy and precise directional crack expansion. Due to the discontinuity of the rock mass at the tip of prefabricated directional fractures in CO2 fracturing, traditional simulations assuming continuous media are limited. It is challenging to set boundary conditions for high strain rate and large deformation processes. The dynamic expansion mechanism of the 3D fracture network in CO2 directional fracturing is not yet fully understood. By treating CO2 fracturing stress waves as hemispherical resonance waves and using a particle expansion loading method along with dynamic boundary condition processing, a 3D numerical model of CO2 fracturing is constructed. This model analyzes the dynamic propagation mechanism of 3D spatial fractures network in CO2 directional fracturing rock materials. The results show that in undirected fracturing, the fracture network relies on the weak structures near the rock borehole, whereas in directional fracturing, the crack propagation is guided, extending the fracture's range. Additionally, the tip of the directional crack is vital for the re-expansion of the rock mass by high-pressure CO2 gas, leading to the formation of a symmetrical, umbrella-shaped structure with evenly developed fractures. The findings also demonstrate that the discrete element method (DEM) effectively reproduces the dynamic fracture network expansion at each stage of fracturing, providing a basis for studying the CO2 directional rock cracking mechanism. [ABSTRACT FROM AUTHOR]

The study of blast loads on structures is important due to the potential of significant consequences in various scenarios. From terrorist attacks to industrial accidents, comprehending how structures respond to blast waves is critical for ensuring public safety and designing resilient structures. Studying these effects typically involves two main methods: free-field tests with live explosives and shock tube tests. Although shock tube testing offers certain advantages, both approaches are costly and demand significant space. This research aims to develop a cost-effective and straightforward technique for generating stress waves that closely replicate the progressive and spatial characteristics of free-field or shock tube blast waves. This method was designed to evaluate the dynamic response of laminated glass panels. The stress wave was generated by impacting a piston on the fluid inside a tube, which was connected to a fluid chamber. This setup produced impulsive loads that were distributed across a laminated glass test panel. Moreover, it was used to simulate the shock near filed explosions for a certain part of a structure. High-speed cameras were utilized to analyze the initial velocity of flying glass fragments. The apparatus successfully produced various blast waves and impulsive profiles for different drop weight heights. The initial velocities of randomly selected flying shards ranged from 3 m/s to 4 m/s. [ABSTRACT FROM AUTHOR]

Dynamic compaction is a method of ground reinforcement that uses the huge impact energy of a free-falling hammer to compact the soil. This study presents a DC method for strengthening coral reef foundations in the reclamation area of remote sea islands. Pilot tests were performed to obtain the design parameters before official DC operation. The standard penetration test (SPT), shallow plate-load test (PLT), and deformation investigation were conducted in two improvement regions (A1 and A2) with varying tamping energies. During the deformation test, the depth of the tamping crater for the first two points' tamping and the third full tamping was observed at two distinct sites. The allowable ground bearing capacity at two disparate field sites was at least 360 kPa. The reinforcement depths were 3.5 and 3.2 m in the A1 and A2 zones, respectively. The DC process was numerically analyzed by the two-dimensional particle flow code, PFC2D. It indicated that the reinforcement effect and effective reinforcement depth were consistent with the field data. The coral sand particles at the bottom of the crater were primarily broken down in the initial stage, and the particle-crushing zone gradually developed toward both sides of the crater. The force chain developed similarly at the three tamping energies (800, 1500, and 2000 kJ), and the impact stress wave propagated along the sand particles primarily in the vertical direction. [ABSTRACT FROM AUTHOR]

Honeycomb is a splendid kind of structure for aerospace engineering with the advantages of light weight, good shock absorption, and good structural stability. This article aims to provide methods to isolate Pyroshocks based on a honeycomb structure and guarantee the safety of such equipment against a high-frequency shock response. According to stress wave theory, an equation for stress wave transmittance of the honeycomb structure is derived considering the effect of cell wall length and thickness, where desirable honeycomb parameters are obtained. The complexity of the transfer path of the honeycomb structure is exploited to build the spacecraft–rocket interface, which could increase the impedance of the stress wave dramatically. Both finite element analysis and experiments are carried out to validate the shock isolation strategies. The influence of parameters, such as cell wall length and the thickness of the stainless-steel honeycomb, on the isolation performance is analyzed. It is revealed that the honeycomb structure has a significant effect on Pyroshock isolation performance when the wall length of the honeycomb cell is 8 mm and the thickness of the cell is 0.1 mm. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)