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The high-temperature dynamic mechanical response of Alloy 718 produced via laser-powder bed fusion (LPBF) was investigated through compressive Split-Hopkinson Pressure Bar (SHPB) tests. Simulating the typical service conditions of Alloy 718, the tests were conducted at temperatures ranging from 298 K to 773 K and at strain rates of 1000 s−1 to 1500 s−1. Phenomenological material constitutive models, such as the modified versions of Johnson-Cook and Hensel-Spittel models, were developed based on the SHPB test results. Analysis of microstructural evolution under impact conditions highlighted that columnar grains with high Schmid factors tend to undergo preferential activation and dislocation pile-up. This process leads to the formation of adiabatic shear bands, grain disintegration, and intense lattice rotation, particularly at higher strain rates. Furthermore, increasing the dynamic deformation temperature facilitates the activation of discontinuous dynamic recrystallization (DRX), with strain accumulation promoting localized grain nucleation along heavily dislocated dendritic boundaries. Recognizing the limitations of phenomenological material constitutive models in accurately representing the underlying microstructural evolution, an artificial neural network (ANN)-based constitutive model employing a three-layer backpropagation learning algorithm was implemented, reducing the Average Absolute Relative Error (AARE) to 0.17%.

To investigate the dynamic mechanical response and damage mechanisms of I‐shaped steel‐concrete composite beams under explosive loads, experimental research and numerical simulations were conducted on steel‐concrete composite structures. The accuracy of the numerical analysis model was validated by comparing the damage characteristics of the structures obtained from explosive tests on the steel‐concrete composite components. Based on this, numerical simulations were performed on steel‐concrete composite beams using the explicit dynamic analysis software ANSYS/LS‐DYNA, and a study on their damage mechanisms was conducted. This study resulted in the acquisition of dynamic mechanical response patterns, including time‐dependent stress, strain, displacement, acceleration, and so on. Different structural damage characteristics under various explosive conditions were summarized, and key parameters affecting the blast resistance of the structure were analyzed. The research findings indicated that, in contrast to the failure characteristics of I‐shaped reinforced concrete (RC) beams, the failure characteristics of I‐shaped steel‐concrete composite beams mainly include punching and shearing failure of the steel‐RC slab and local buckling of the steel beam. Under the same explosive conditions, steel‐concrete composite structures exhibit superior blast resistance, with certain changes in structural parameters significantly improving blast resistance. The research results can provide theoretical support and a scientific basis for the proactive design of blast protection in steel‐concrete beams. [ABSTRACT FROM AUTHOR]

The influence of aging treatments on the dynamic mechanical response of the 7B52 laminated alloy, and the correlation between the SHPB impact performance of 7xxx laminated aluminum alloy and its base alloys were investigated. Through adjustments the aging temperature and duration, alloys were obtained under underaged, peak-aged, and overaged conditions. Subsequently, Split Hopkinson Pressure Bar (SHPB) impact tests were conducted. The results indicate that the SHPB impact strength of the base alloy is higher in the peak-aged state compared to the under-aged and over-aged states. Additionally, as the aging temperature decreases, the alloy's impact toughness increases. The impact strength of laminated plates can be assessed by computing a linear weighted sum of the impact strength of individual alloys. The impact toughness of laminated aluminum alloys is notably influenced by the disparity in impact strength between 7A52 and 7A62 alloys. When the difference in impact strength between base alloys is small, the deformation of laminated plates is uniform, which can enhance the additional impact toughness of laminated aluminum alloys. Finally, an impact performance prediction formula for laminated plates is provided through linear fitting. [ABSTRACT FROM AUTHOR]

Abstract The stability of coal and rock masses in water-rich mines is affected by both mine water erosion and dynamic disturbances. Thus, it is necessary to study the dynamic mechanical response and failure characteristics of coal and rock under the combination of saltwater and a high strain rate. To this end, a split Hopkinson pressure bar device was employed to investigate the effects of impact velocity, water content, and immersion liquid on the dynamic mechanical behaviours of coal and rock. The results revealed that the weakening effect of saltwater on the dynamic mechanical properties of coal and rock is much greater than that of distilled water. With increasing moisture content, the dynamic compressive strength of the coal specimens decreases monotonically, while that of the rock shows a trend of first increasing and then decreasing. The failure process and destruction of coal and rock are comprehensively affected by both the external impact load and the physical and mechanical properties of the material. The degree of damage of the coal and rock specimens increases with increasing impact velocity and water content. Moreover, the influence of various factors on the impact fracture mechanism of coal and rock under saltwater immersion conditions was revealed. These findings are highly important for the design and maintenance of underground coal and rock building structures.

The stability of coal and rock masses in water-rich mines is affected by both mine water erosion and dynamic disturbances. Thus, it is necessary to study the dynamic mechanical response and failure characteristics of coal and rock under the combination of saltwater and a high strain rate. To this end, a split Hopkinson pressure bar device was employed to investigate the effects of impact velocity, water content, and immersion liquid on the dynamic mechanical behaviours of coal and rock. The results revealed that the weakening effect of saltwater on the dynamic mechanical properties of coal and rock is much greater than that of distilled water. With increasing moisture content, the dynamic compressive strength of the coal specimens decreases monotonically, while that of the rock shows a trend of first increasing and then decreasing. The failure process and destruction of coal and rock are comprehensively affected by both the external impact load and the physical and mechanical properties of the material. The degree of damage of the coal and rock specimens increases with increasing impact velocity and water content. Moreover, the influence of various factors on the impact fracture mechanism of coal and rock under saltwater immersion conditions was revealed. These findings are highly important for the design and maintenance of underground coal and rock building structures. [ABSTRACT FROM AUTHOR]

Characterizing the dynamic mechanical properties of spinal cord tissue is deemed important for developing a comprehensive knowledge of the mechanisms underlying spinal cord injury. However, complex viscoelastic properties are vastly underexplored due to the spinal cord shows heterogeneous properties. To investigate regional differences in the biomechanical properties of spinal cord, we provide a mechanical characterization method (i.e., dynamic mechanical analysis) that facilitates robust measurement of spinal cord ex vivo, at small deformations, in the dynamic regimes. Load-unload cycles were applied to the tissue surface at sinusoidal frequencies of 0.05, 0.10, 0.50 and 1.00 Hz ex vivo within 2 h post mortem. We report the main response features (e.g., nonlinearities, rate dependencies, hysteresis and conditioning) of spinal cord tissue dependent on anatomical origin, and quantify the viscoelastic properties through the measurement of peak force, moduli, and hysteresis and energy loss. For all three anatomical areas (cervical, thoracic, and lumbar spinal cord tissues), the compound, storage, and loss moduli responded similarly to increasing strain rates. Notably, the complex modulus values of ex vivo spinal cord tissue rose nonlinearly with rising test frequency. Additionally, at every strain rate, it was shown that the tissue in the thoracic spinal cord was significantly more rigid than the tissue in the cervical or lumbar spinal cord, with compound modulus values roughly 1.5-times that of the lumbar region. At strain rates between 0.05 and 0.50 Hz, tan δ values for thoracic (that is, 0.26, 0.25, 0.06, respectively) and lumbar (that is, 0.27, 0.25, 0.07, respectively) spinal cord regions were similar, respectively, which were higher than cervical (that is, 0.21, 0.21, 0.04, respectively) region. The conditioning effects tend to be greater at relative higher deformation rates. Interestingly, no marked difference of conditioning ratios is observed among all three anatomical regions, regardless of loading rate. These findings lay a foundation for further comparison between healthy and diseased spinal cord to the future development of spinal cord scaffold and helps to advance our knowledge of neuroscience.

In the pavement industry, there is a pressing need for the reuse of recycled asphalt pavement (RAP) materials. However, the rutting deformation in existing pavement structures is often overlooked in the design of recycled asphalt pavement, which hinders long-term performance prediction and durability assessment. This study examined the viscoelastic properties and fatigue performance of recycled asphalt mixtures. Different combinations of surface layers with varying RAP contents and binder layers with different rutting damage levels were designed. A 3D-Move Analysis model was used to analyze the dynamic mechanical response of these structures under moving loads. Results showed that the stiffness of recycled asphalt mixture increased with the RAP content, but the fatigue performance decreased by 39.4% when the RAP content reached 50%. Incorporating 50% RAP in the surface layer can reduce the compressive stress caused by vehicle loading, thus reducing the vertical compression strain and permanent deformation of the asphalt layers and the subgrade. However, the surface layer with higher RAP content is exposed to intense alternating tensile and compressive strains, leading to poor fatigue durability. The dynamic mechanical behavior of recycled asphalt pavement structures was found to be significantly impacted by the characteristics of the binder layer. The lower dynamic modulus of the binder layer (e.g., 18 mm rutting depth) can lead to more deformation and an increased risk of fatigue cracking. Moreover, the dynamic performance of mixtures with 0% and 50% RAP in the surface layer is even more affected by changes in the binder layer properties. It is recommended to consider the design of dynamic modulus combinations of existing binder layer materials and surface materials with higher RAP, in order to increase the utilization of RAP for high-grade highways and improve the stress distribution to enhance their durability. [ABSTRACT FROM AUTHOR]

In this paper, molecular dynamics simulations are performed to study the dynamic mechanical response and microstructural evolution of Ni-based single crystal superalloys under different shock velocities. The results show that when the shock velocity (Up ≤ 0.75 km/s), the interfacial dislocation network composed of the Stair-rod dislocation will prevent the Shockley dislocation from shearing the γ′ phase, the deformation of the microstructure is dominated by the slipping and dragging of dislocations. When the shock velocity (Up ≥ 1 km/s), the interfacial dislocation network is destroyed under the shock loading, the dislocations basically disappear, the atomic structure becomes disordered and undergoes structural phase transformation. In addition, the increase of the shock velocity leads to the regular increases of the shock pressure, internal energy and normal stress of the superalloys. However, the shear stress increases sharply once the shock velocity is greater than 1 km/s due to the change of the microstructural deformation mechanism. This work has an important guiding significance for in-depth understanding of the failure mechanism of Ni-based single crystal superalloys under shock loading.

• The HE-BMG exhibited a negative SRS under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. • Variation of spall strength with impact speed is dominated by strain rate. • The fracture behavior of the HE-BMG under different strain rates and stress states was compared. • The JH-2 model was established and its accuracy was verified by various experiments and simulations. In this work, the mechanical response and fracture characteristics of (Ti 37.31 Zr 22.75 Be 26.39 Al 4.55 Cu 9) 94 Co 6 high-entropy bulk metallic glass (HE-BMG) were investigated in detail over a wide range of strain rates (10−4–105 s−1). The HE-BMG exhibited a negative strain rate sensitivity under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. The shear band behavior translated from the dominance of multiple shear bands propagations under quasi-static compression to the rapid propagation of a single shear band to form cracks under dynamic compression. Under dynamic loading, the shearing velocity increased along an arc-shaped displacement path, and the local stress state on the shear fracture surface shifted from compressive-shear to tensile-shear, accompanied by changes in fracture morphologies. The spall strength of HE-BMG decreased as flyer impact speed increased, while the long-term dependence of spall strength on strain rate may be positive. With the increase of impact speed, the main microstructural features of the spalling surface translated from flat regions accompanied by dimples to cup-cone structures. Furthermore, the complete parameters of the Johnson–Holmquist II (JH-2) model for HE-BMG were obtained based on experimental data. Numerical simulations of planar impact, penetration, and hypervelocity impact are in good agreement with experimental results, demonstrating the validity of the JH-2 model parameters. The current work has important guiding value for the application of HE-BMG in space debris protection. [Display omitted] [ABSTRACT FROM AUTHOR]

Calcareous sand is widely used as shallow foundations, where the mechanical behavior of calcareous sand under impact loading would be affected by the particle sizes and moisture contents in the foundation. Herein, a series of impact loading tests were carried out with a modified Split-Hopkinson Pressure Bar (SHPB) system to investigate the mechanical characteristics of calcareous sands subjected to varying particle sizes and moisture contents. In particular, a new specimen chamber in the SHPB system was proposed to hold the sand specimen. Subsequently, several impact tests were conducted on calcareous sands with different particle sizes, where the uniform sizes of 0.074–0.5, 0.5–1.0, 1.0–2.0, and 2.0–3.0 mm and moisture contents from 0 to 16 % were adopted. Afterwards, the effects of the strain rates such as 165 s−1, 214 s−1, and 256 s−1 were studied on mechanical and particle breakage behaviors of the calcareous sands. The impact response, particle-size distribution curves and relative breakage curves were then analyzed. Results indicated that the peak stress decreased with the increase of moisture contents in medium- and coarse-sized calcareous sands. The effect of moisture content on the particle breakage of unsaturated calcareous sand decreased with increasing particle sizes. The relative breakage has an exponential relationship with the particle sizes of calcareous sand, which was expressed by an effective diameter. The outcome of this study indicated that the energy dissipation effect of calcareous sand protective cushion was effectively improved by appropriate moisture content of calcareous sand. • A series of impact tests were conducted for mechanical characteristics of calcareous sands. • A new specimen chamber in the SHPB system was proposed to hold the sand specimen. • The impact response, particle-size distribution curves and relative breakage were analyzed. • Relative breakage has an exponential relationship with the particle sizes of calcareous sand. [ABSTRACT FROM AUTHOR]

In underground engineering constructions, fractured rock masses are likely to be subjected to three-dimensional static stress and dynamic loading simultaneously. In this study, via a modified split Hopkinson pressure bar (SHPB) system, a series of triaxial dynamic tests are carried on sandstone containing a pre-existing flaw under different radial confining pressures ranging from 5.7 to 22.7 MPa and different strain rates varying by 85–252 s−1. The results indicate that both the dynamic strength and energy dissipation density of single-flawed sandstone feature a positive correlation with the rising radial confining pressure and strain rate; while the dynamic elastic modulus, failure strain and energy utilization efficiency all exhibit an evident radial confining pressure enhancement effect, these are insensitive to the strain rate. Moreover, the fragment distributions of single-flawed sandstone are adequately characterized by combining sieving tests and generalized extreme value function. Under a higher strain rate, the single-flawed specimen is featured by smaller average fragment size and wider fragment distribution range, while the higher confining pressure has the opposite effect. By post-mortem examination, three main failure types are classified, and the fracturing mechanism of new cracks is revealed by microscopic observation using a scanning electron microscope (SEM). The macro oblique shear crack and through shear crack are mainly induced by the shear slip mechanism, while the quasi-coplanar crack is tensile dominated. Highlights: Conducted a series of triaxial SHPB tests on the three-dimensional confined sandstone containing a pre-existing flaw. Investigated the radial confining pressure and strain rate effect on the dynamic mechanical response and failure characteristics of flawed rocks. Revealed the fracturing mechanism of new cracks from a microscopic perspective by the scanning electron microscope. [ABSTRACT FROM AUTHOR]

Characterizing the dynamic mechanical properties of spinal cord tissue is deemed important for developing a comprehensive knowledge of the mechanisms underlying spinal cord injury. However, complex viscoelastic properties are vastly underexplored due to the spinal cord shows heterogeneous properties. To investigate regional differences in the biomechanical properties of spinal cord, we provide a mechanical characterization method (i.e., dynamic mechanical analysis) that facilitates robust measurement of spinal cord ex vivo , at small deformations, in the dynamic regimes. Load-unload cycles were applied to the tissue surface at sinusoidal frequencies of 0.05, 0.10, 0.50 and 1.00 Hz ex vivo within 2 h post mortem . We report the main response features (e.g., nonlinearities, rate dependencies, hysteresis and conditioning) of spinal cord tissue dependent on anatomical origin, and quantify the viscoelastic properties through the measurement of peak force, moduli, and hysteresis and energy loss. For all three anatomical areas (cervical, thoracic, and lumbar spinal cord tissues), the compound, storage, and loss moduli responded similarly to increasing strain rates. Notably, the complex modulus values of ex vivo spinal cord tissue rose nonlinearly with rising test frequency. Additionally, at every strain rate, it was shown that the tissue in the thoracic spinal cord was significantly more rigid than the tissue in the cervical or lumbar spinal cord, with compound modulus values roughly 1.5-times that of the lumbar region. At strain rates between 0.05 and 0.50 Hz, tan δ values for thoracic (that is, 0.26, 0.25, 0.06, respectively) and lumbar (that is, 0.27, 0.25, 0.07, respectively) spinal cord regions were similar, respectively, which were higher than cervical (that is, 0.21, 0.21, 0.04, respectively) region. The conditioning effects tend to be greater at relative higher deformation rates. Interestingly, no marked difference of conditioning ratios is observed among all three anatomical regions, regardless of loading rate. These findings lay a foundation for further comparison between healthy and diseased spinal cord to the future development of spinal cord scaffold and helps to advance our knowledge of neuroscience., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Jin, Yu, Li and Ye.)

Pearlitic rail steels with excellent mechanical and wear properties are widely employed for high-speed railways. During the service period, the presence of track irregularities, switches, as well as crossings can cause intense dynamic loadings, which accumulate the severe deformation of rails, and sometimes even facilitate crack initiation and failure. Knowledge of the dynamic mechanical response and damage behaviors of the rail steels is therefore important for the service performance estimation of railways. In this study, the pearlite U71MnG rail steel was deformed using a split Hopkinson pressure bar (SHPB) apparatus to reach a wide range of strain rates and temperatures. Microstructures including the grain morphology, deformation characteristic of cementite lamellae, dislocation substructures in ferrite lamellae, and phase transformation at pearlite colony boundaries were characterized. Based on the microstructural observations, the rate-controlling strengthening mechanism and temperature-dependent softening mechanism of the steel were revealed when the process for the dynamic loading-induced cementite decomposition at boundaries was discussed. In consideration of the athermal deformation mechanism, thermally activated mechanism, and viscous-drag effect, a physically based constitutive model was proposed to describe the dynamic mechanical response of the pearlite rail steel. The predicted flow stresses were found to be consistent with the experimental one for all strain rates and temperatures. • Analyzed rate-controlling deformation mechanism of high-strength rail steel over a wide strain rate and temperature range. • Reveled the mechanism of dynamic loading induced cementite transformation along pearlite colony boundaries. • Proposed a physically-based constitutive model to predict dynamic mechanical response of pearlite rail steel. [ABSTRACT FROM AUTHOR]

• The dynamic mechanical response of CSP specimens with different filling thicknesses were investigated. • The final failure modes and crack propagation behaviors of CSP specimens with different filling thicknesses were obtained. • A crack propagation model was proposed, and the fracture mechanism of CSP specimens under impact loads was discussed. Structural planes are the primary variables determining the stability of rock masses. Numerous non-penetrating structural planes exist in nature and are concealed inside the slopes or underground rock formations. The concealed structural planes (CSP) pose a possible hazard to the construction safety of rock mass engineering, particularly for the rock mass subjected to dynamic load. Using rock-like materials, intact specimens and specimens with CSP of varying filling thicknesses are constructed in order to examine the dynamic mechanical response and fracture mechanism of rock masses with CSP. Single impact experiments and cyclic impact experiments are carried out at various speeds using the Split Hopkinson Pressure Bar experimental system (SHPB). The results demonstrate that the specimens' peak stress is negatively correlated with the filling thickness, and that as the reflection coefficient increases and the transmission coefficient decreases, the filling thickness increases. Also, the energy dissipation rate of the specimens is positively correlated with the increase in thickness of filling at impact velocities of 3.7 m/s and 4.5 m/s, with the rate showing an increasing trend followed by a decreasing trend at impact velocities of 5.5 m/s and 6.5 m/s. The main surface and internal cracks of specimens can be categorized into seven types, which are combined into three failure modes. As the filling thickness increases, the failure mode changes from transverse tensile failure to combined tensile and shear failure to bi-directional tensile failure under combined transverse and axial tensile action. The crack propagation behavior and the fracture mechanism from the interior to the exterior of the CSP specimens are investigated using the impact test results, finite element model, and mechanical theory analysis, which can be used as a reference to reveal the destabilization process of the rock mass with CSP. [ABSTRACT FROM AUTHOR]

• Crushable aggregates with the real shape are generated by using "ball-clump-cluster" method. • A SHPB simulation test system is proposed by the coupled DEM-FDM method. • The effect of end friction constraint on dynamic compressive behavior of concrete is studied. • The effect of end friction constraint on the distribution of microcracks is quantitatively analyzed. This paper presents a quantitative evaluation of the effect of end friction on the dynamic mechanical response and damage evolution of concrete based on the coupled Discrete Element Method (DEM) - Finite Difference Method (FDM) method. Considering the heterogeneity of concrete, a three-phase meso -scale model of concrete (mortar, aggregate and interfacial transition zone) is constructed by DEM, and the crushability, real geometry and random distribution of aggregates are considered by combining 3D scanning techniques and the "ball-clump-cluster" method. Meanwhile, the split Hopkinson pressure bar (SHPB) device is constructed by FDM, and the interface deformation coordination between the concrete sample and metal rods is realized by coupling algorithm. On this basis, the quantitative effects of end friction on the stress–strain response, dynamic increase factor (DIF), damage distribution and failure mode of concrete are investigated. The results indicate that the dynamic compressive strength increases significantly when the interfacial friction coefficient μ i increases from 0 to 0.1, and the interfacial friction enhancement effect weakens significantly when >0 μ i.1. With the increase of strain rate, the friction contribution coefficient tends to decrease. The end friction has a significant effect on the distribution of microcracks in the axial direction. The end friction confinement changes the local stress state and damage distribution of concrete, which is beneficial to improve the compressive strength of concrete. [ABSTRACT FROM AUTHOR]

As an important magnetic functional material, sintered NdFeB has gradually applied from mild places to environments that need to withstand impact. The reliability of materials to work in this environment has received extensive attention, but current research cannot provide corresponding support of experimental data and theoretical model for this problem yet. To tackle this, we carried out research on the magnetomechanical behavior of sintered NdFeB under dynamic impact environment. Specifically, dynamic mechanics and impact demagnetization experiments were conducted separately. Then, according to the characteristics of brittleness and strain rate dependence shown in dynamic mechanical experiments, a dynamic damage constitutive model was established. Additionally, a new magnetic degradation model was proposed in which the stress knee position existed and the relationship between impact load and irreversibility was established. The co-simulation model of impact demagnetization based on dynamic mechanical constitutive model and magnetic degradation model was designed to better display the demagnetization process of materials. Meanwhile, the parameter identification process was carried out to determine the unknown parameters in the model. Finally, the effectiveness of identified parameters were verified by comparing the simulation values with the experimental values. • The dynamic magnetomechanical experiments of sintered NdFeB are carried out. • A new dynamic damage constitutive model and impact-induced magnetic degradation model are proposed. • The co-simulation calculation method of impact demagnetization process is developed, and the key parameters are identified. [ABSTRACT FROM AUTHOR]

The effects of strain rate and temperature on the dynamic behavior of Fe-based high temperature alloy was studied. The strain rates were 0.001-12,000 s, at temperatures ranging from room temperature to 800 °C. A phenomenological constitutive model (Power-Law constitutive model) was proposed considering adiabatic temperature rise and accurate material thermal physical properties. During which, the effects of the specific heat capacity on the adiabatic temperature rise was studied. The constitutive model was verified to be accurate by comparison between predicted and experimental results. [ABSTRACT FROM AUTHOR]

Shear localization is an important deformation and failure mechanism for the high strength near beta fine-grain-sized titanium alloy used in aircraft's gear at high rate deformation. Hat-shaped specimens are used to induce the formation of an adiabatic shear band under controlled shock-loading tests. Unstable shear deformation of the alloy emerges after the true flow stress reaches 1147 MPa, the first vibration peak during the split Hopkinson pressure bar testing, and the whole process lasts about 68 μs. The microstructures within the shear band in the alloy are investigated by means of light microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that the grains in the boundary of the shear band are highly elongated along the shear direction, and the core of the shear band consists of ultrafine-equiaxed grains with diameters 0.1-0.3 μm, low dislocation density, and no observed phase transformation. The rotational dynamic recrystallization is used to explain the microstructural evolution mechanism in the shear band. Kinetic calculations indicate that the recrystallized ultrafine grains are formed during the deformation and do not undergo significant growth by grain boundary migration after deformation. [ABSTRACT FROM AUTHOR]

• The dynamic mechanical response of CTB under cyclic impact loading were studied. • The dynamic compressive strength of CTB was improved by alkaline rice straw (ARS). • The mechanism of ARS improving the dynamic mechanical behavior of CTB was revealed. • The cumulative damage degree of CTB under cyclic impact load was reduced by ARS. Dynamic disturbances such as blasting excavations cause damage to backfills. To ascertain and improve the dynamic mechanical response of backfill under frequent disturbance, single and cyclic impact load tests were conducted on cemented tailings backfill mixed (CTB)with different contents of alkalized rice straw (ARS) using a split Hopkinson pressure bar. The evolution laws of the dynamic mechanical properties and damage characteristics of CTB with the impact times and the ARS content were analyzed. The results showed that (1) The dynamic compressive strength (DCS) of CTB was improved by the ARS under single impact load with different strain rates. (2) Under the cyclic impact loads, the DCS, dynamic elastic modulus, and peak strain of CTB decreased with the increase in the cyclic impact times. Under the same impact times, the DCS of the backfill first increased and subsequently decreased with the increase in the ARS content, and 0.3% was the best content. (3) The unit volume absorbed energy of CTB was increased by the ARS and the longitudinal wave velocity (LWV) decay rate of CTB was decelerated under the cyclic impact loads. (4) The established damage evolution equation of CTB based on the LWV showed that its cumulative damage degree was increased by the cyclic impacts. Moreover, the incorporation of ARS was beneficial for decelerating and reducing the damage evolution rate and degree. The ARS was wrapped by hydration products in the CTB matrix, and its adhesion with the matrix promoted the ARS to play a bridging role, and inhibited and slowed down the development, propagation degree and propagation rate of cracks in CTB under cyclic impact. When the content of ARS was further increased, the probability of overlapping was significantly improved, which was not conducive to the adhesion between ARS and CTB matrix, resulting in the decline of the mechanical properties of CTB. The research results provide a reference for the understanding of the dynamic mechanical response of CTB with ARS under frequent blasting disturbances. [ABSTRACT FROM AUTHOR]

The effect of three kinds of graphitic fillers with distinct morphologies, natural graphite sheets (NGs), chemically reduced graphite oxide sheets (CRGs) and thermally reduced graphite oxide sheets (TRGs), on the crystallization, rheological behavior and mechanical properties of poly(vinylidene fluoride) (PVDF)-based composites has been investigated comparatively. NGs exhibit smooth surface and multilayer-stacked structure; most CRGs are in the form of aggregates that are restacked during reduction; while TRGs show a wrinkled topography of relatively thin graphene sheets. The introduction of these graphitic fillers into the PVDF matrix contributes differently to the crystallization, rheological behavior and mechanical properties of the composites. Among them, TRGs show the greatest strengthening effect, as revealed by rheological and dynamic mechanical responses. Compared with chemical reduction technology, thermal reduction is a more economical, environmentally friendly and scalable approach to prepare functionalized graphene sheets. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]