Dynamic Splitting Research Articles

Study on Dynamic Splitting Properties of S-PP Hybrid Fiber Concrete after High Temperatures

To study the dynamic tensile mechanical properties of steel polypropylene hybrid fiber reinforced concrete (SP-HFRC) after high temperature, split Hopkinson pressure bar (SHPB) dynamic splitting tests were carried out, and the optimal fiber content combination was obtained. With the plain concrete (PC) as the control, the effects of fiber addition on energy dissipation and failure forms of concrete specimens after high temperatures were analyzed. LS-DYNA software was used to simulate the dynamic splitting test. The results show that the splitting strength of specimens increases first and then deteriorates with the increase of temperature. After high temperatures, HFRC has a positive and negative fiber hybrid effect. Among the studied fiber mixture combinations, S1PP0.2 (1 vol% steel fiber + 0.2 vol% polypropylene fiber) concrete has the best splitting resistance. Compared with PC, the splitting strength increases by 106.8% at 25 °C and 128.2% at 800 °C. From the perspective of energy, we can conclude that adding hybrid fiber can significantly improve the dynamic splitting and tensile toughness of concrete after high temperatures, and defining damage variables can better characterize the damage degree of concrete. PC cracks seriously after high temperatures, while S1PP0.2 concrete cracks but does not disperse at 800 °C, showing ductile failure characteristics. By modifying some parameters of the HJC model, the state of high-temperature concrete mechanical properties can be better characterized after deterioration. The simulated failure process shows an excellent agreement with the experimental results.

Pressure-Induced Indirect-Direct Bandgap Transition of CsPbBr3 Single Crystal and Its Effect on Photoluminescence Quantum Yield.

Despite extensive study, the bandgap characteristics of lead halide perovskites are not well understood. Usually, these materials are considered as direct bandgap semiconductors, while their photoluminescence quantum yield (PLQY) is very low in the solid state or single crystal (SC) state. Some researchers have noted a weak indirect bandgap below the direct bandgap transition in these perovskites. Herein, application of pressure to a CsPbBr3 SC and first‐principles calculations reveal that the nature of the bandgap becomes more direct at a relatively low pressure due to decreased dynamic Rashba splitting. This effect results in a dramatic PLQY improvement, improved more than 90 times, which overturns the traditional concept that the PLQY of lead halide perovskite SC cannot exceed 10%. Application of higher pressure transformed the CsPbBr3 SC into a pure indirect bandgap phase, which can be maintained at near‐ambient pressure. It is thus proved that lead halide perovskites can induce a phase transition between direct and indirect bandgaps. In addition, distinct piezochromism is observed for a perovskite SC for the first time. This work provides a novel framework to understand the optoelectronic properties of these important materials.

Energy-Aware Scheduling of Two-Stage Flexible Flow Shop Based on Group Technology: Consideration of the Inconsistency of Process Differences

The diversity of consumer demand makes the manufacturing industry shift from the production mode of small variety and large batch to the production mode of multi-variety and small batch, which leads to the increase of production cost and the decrease of production efficiency, especially the increase of energy consumption. In this paper, the energy-aware scheduling problem of two-stage flexible flow shop based on group technology is studied, in which the process differences of jobs in the two stages are inconsistent. To solve the problem of unbalanced load of machines caused by group technology, this paper uses a dynamic splitting strategy to balance the load of machines on the basis of increasing the setup energy consumption as little as possible. Considering that the research problem is a multi-objective optimization problem, this study develops an improved multi-objective scatter search algorithm. According to the characteristics of the problem, the coding scheme, decoding scheme, diversity generation method and combination method are designed. The experimental results show that the group technology can effectively reduce energy consumption, and the dynamic split strategy can balance the load of machines effectively. Moreover, the results show the proposed method is better than the existing methods in terms of obtaining better solutions.

Experimental study on dynamic compressive and splitting tensile properties of high strength expansive concrete

Concrete shrinkage usually results in the decrease in bearing capacity, durability and impact resistance of Concrete-Filled steel tube (CFST) structures during its service life. High strength expansive concrete (HSEC) is recently developed to deal with the shrinkage cracking in CFST structures. In this study, dynamic compressive tests and dynamic splitting tensile tests on the developed grade C60, C70 and C80 HSEC were performed using a split Hopkinson pressure bar device. Test results show that the expansive concrete is a typical rate-sensitive material, and its dynamic compressive strength and dynamic splitting tensile strength both increase with the strain rate. The compressive strength dynamic increase factor (DIFc) of HSEC is smaller than that of the ordinary concrete under the same strain rate, whereas the splitting tensile dynamic increase factor (DIFt) is larger than that of the ordinary concrete. All the test data were classified to establish calculation models of DIFc, peak toughness ( Rp), specific energy absorption (SEA), and DIFt, which provide a theoretical basis for the design and application of HSEC and CFST in engineering.

Investigation of the Deformation and Failure Characteristics of High-Strength Concrete in Dynamic Splitting Tests

The dynamic response properties of concrete have been of interest during the use of buildings due to seismic, impact, and explosion events. The splitting Hopkinson lever is a classical device for testing the dynamic mechanical properties of materials. In this paper, dynamic splitting tests on concrete were conducted using it, and a time series predictive computational model for the incident, reflected and transmitted pulses of high-strength concrete specimens at high strain rates was developed, and the extension mechanism of splitting tensile cracks in high-strength concrete was detected and analyzed based on the DIC technique. The results show that: the peak strength of C60 specimens and C80 specimens increased by about 60% and 90%, respectively, from 0.05 MPa to 0.09 MPa in impact strength; the triangular damaged area at the end of the contact surface of the specimen and the rod subjected to high impact pressure increased significantly, the dynamic energy dissipation increased, and the damage degree of the specimens increased; under the action of high strain rate, the brittleness of the concrete specimens with higher strength increased, the damage rate The higher strength concrete specimens have increased brittleness, faster damage rate and higher crack extension under high strain rate. The results of the paper can provide important references for the design of buildings under impact loading.

Hybridization of battery and ultracapacitor for electric vehicle application with dynamic energy management and non-linear state feedback controller

• Proposed a dynamic energy management system for hybrid sources in an electric vehicle. • Buck-boost H-bridge converters are introduced for bidirectional power flow control. • System non-linearities are addressed using a nonlinear state feedback controller. • The proposed system accurately delivers instantaneous vehicle speed and torque. This paper describes a methodology to control a multi-source battery-capacitor hybrid EV incorporating a dynamic power splitting strategy. Considering the requirement for precise speed control characteristics of the EV and the non-linear behavior of traction motor with system disturbances, a non-linear state feedback controller (NLSFC) with a disturbance observer is suggested as the speed control technique for the EV traction motor. To interface a parallel configured multi-source system, a non-inverted buck-boost H-bridge is proposed as the source side converter for effective recovery of the braking energy. Detailed control design for traction motor and converter is also presented for efficient control of EV. Besides, an adaptive energy management strategy considering power profile and dynamic source characteristics is incorporated into the overall control system. The simulation results from various case studies indicate that the proposed system can follow the required vehicle speed and torque despite the sudden change in EV load torque. Furthermore, the comparative analysis between NLSFC and PI controller shows improvement with steady-state error reduction from 0.43 to 0.0014 and peak overshoot drop from 12.07% to 3.51% during acceleration of the system when proposed NLSFC is adopted. The proposed solutions will be implemented in a prototype EV system in the future.

Experimental and mesoscopic investigation of self-compacting rubberized concrete under dynamic splitting tension

Self-compacting rubberized concrete (SCRC) has gained extensive investigations due to its good impact resistance and environmental friendliness, while the dynamic splitting tensile properties of SCRC are seldom studied. In this study, river sand in SCRC was replaced by three rubber volume fractions (5%, 10%, 15%). The experiments indicated that the static compressive strength, static tensile strength, elastic modulus and dynamic splitting tensile strength declined with the increase of rubber content. The dynamic splitting tensile strength, dynamic increase factor (DIF) and failure mode of SCRC were sensitive to strain rate. SCRC with a higher rubber volume had a greater DIF. The critical strain rate of different SCRC was obtained by piecewise fitting, which decreased with the enhancement of rubber content. Meanwhile, a three-dimensional mesoscopic model of SCRC was established. The rubber particles were generated by a random polyhedron algorithm and randomly thrown into the sample by the take and place algorithm. The numerical calculation suggested that the mesoscopic model could exhibit the fracture process of SCRC under high strain rates. The propagation of cracks bypassed the rubber particles and produced a mass of branch cracks under high strain rates, dissipating a large amount of energy and elevating the DIF, which is consistent with the macroscopic failure pattern. In addition, the effect of strain rate and rubber volume on DIF was discussed combined with the mesoscopic model.

Study on dynamic splitting tensile damage characteristics of basalt fiber reinforced concrete based on AE and DSCM

This paper aims to study the action mechanism of basalt fiber on concrete and the internal damage evolution of basalt fiber reinforced concrete (BFRC) in Brazilian disc splitting tensile tests using acoustic emission (AE) technology and digital speckle correlation method (DSCM). The effects of loading rate and basalt fiber content on splitting tensile failure mode and deformation capacity of BFRC, as well as AE frequency domain characteristics were investigated herein. Then the strain field and local damage factor of BFRC under dynamic splitting tensile load were analyzed based on DSCM. The results indicate that the increase of loading rate and basalt fiber content can change the failure into a complex tensile-shear mixed failure. And the deformation capacity of BFRC can be considerably enhanced by adding a proper amount of basalt fibers. It is also found that the damage degree and damage mechanism of BFRC can be identified by analyzing the wavelet peak frequency of specific frequency range. Furthermore, the crack evolution of BFRC under dynamic splitting tensile load can be reflected well on the change of strain field nephogram of BFRC obtained by DSCM.

Influence of interface morphology on dynamic behavior and energy dissipation of bi-material discs

To investigate the dynamic behavior and energy dissipation of the rock−concrete interface, dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar. The test results reveal that with the change of the interface inclination angles (θ), the influence of interface groove width on the bearing capacity of specimens also varies. When θ increases from 0° to 30°, the bearing capacity of the specimen increases first and then decreases with the rise of the interface groove width; the optimal groove width on the rock surface in this range of interface inclination angles is 5 mm. When θ increases from 45° to 90°, the bearing capacity of the specimen has no obvious change. Moreover, when θ increases from 0° to 45°, the dissipated energy of the specimens rises obviously at first and then tends to be stable as the width of the interface groove increases.

A Microscopic Platoon Stability Model Using Vehicle-to-Vehicle Communication

With Vehicle-to-Vehicle (V2V) communication capability, vehicle platoon on the highway helps to reduce traffic congestion. However, the dynamic nature of vehicles imposes challenges on the V2V-based platoon management. In this paper, by considering the characteristics of a Vehicular Ad-hoc Network (VANET), a microscopic platoon management scheme is proposed to deal with three basic dynamic platoon maneuvers, namely merging, splitting, and speed-change. The congestion detection feature of VANET is used as a scale for platoon merging, splitting, and speed selection. Real-time congestion is detected if the number of vehicles in a given road segment exceeds the occupancy rate or the time headway is less than the thresholds. In the proposed platoon management scheme, platoon maintenance is triggered in congestion detection. Finally, a VANET-based platoon platform is built by using Network Simulator Version 2 (NS2) network simulation to assess the performance over some real road traces generated by Simulation of Urban MObility (SUMO). It is shown that V2V-based dynamic vehicle platoon management provides an inexpensive technique to cope with the dynamic platoon management requirement.

Influence of 3D-printed polymer structures on dynamic splitting and crack propagation behavior of cementitious tailings backfill

Originally developed for polymer materials, 3D printing is an encouraging technique to create versatile geometric shapes and high-precision construction elements from various materials. 3D-printed polymer structures are now employed effectively in various industries, including construction and mining since they significantly improve the ductility properties of cementitious materials like cemented tailings backfill (CTB). Considering the lower tensile strength of CTB (compared to its compressive strength), the study of fill's tensile properties is significant for improving the safety and ensuring the stability of the underground CTB structures. Indeed, this aspect is fairly crucial for the development of green mining which allows sustainable and affordable mining operations. To supremely enhance the tensile strength of CTB, three kinds (OR: ordinary resin) and forms (cross, quarter, and 8 equal parts) of 3D printing polymers (3D-PPL) were employed for this study. A number of experiments including Brazilian splitting tests, digital image correlation (DIC) measurements, and SEM failure/micro-structure analyses were fulfilled for exploring both dynamic splitting and crack propagation behavior of 3D-PPL reinforced CTBs. Results designated that dynamic splitting characteristics of 3D-PPL reinforced CTB samples unveiled a robust strain rate dependence. Besides, the tensile strengths of 3D-PPL reinforced CTB samples are increased under the same conditions and the best results are obtained for cross-shaped reinforced CTB increased by 31.6%. 3D-PPL reinforced CTB samples are characterized with higher strains, and the addition of 3D-PPL effectively inhibits the overall damage process of ordinary CTB and improves the backfill’s strength property. As a result, the results of this study are vital and prominent for realizing the tensile/crack behavior of the backfills placed in underground mined-out openings.

Dynamic Brazilian splitting experiment of bedding shale based on continuum-discrete coupled method

Exploring the dynamic mechanical properties of shale helps to understand the damage of shale reservoirs under dynamic loading. In this paper, static Brazilian splitting experiments were conducted to obtain the static Brazilian strength of shales with loading angles ranging from 0° – 90° (at 15° intervals), and corresponding bedding shale models were developed based on the discrete element method. Then, the split Hopkinson pressure bar system was simulated according to the coupling of the continuous-discrete method, and dynamic Brazilian splitting simulations with loading rates of 100 – 170 GPa/s were carried out. The experimental results show that the Brazilian strengths of the shale at a loading rate of 0.05 mm/s are 4.73 MPa – 7.63 MPa, and the shale matrix and bedding can be simulated using the Flatjoint and Linearpbond models, respectively. The model parameters calibrated by static Brazilian splitting experiments were not applicable under dynamic loading; the microscopic tensile strength of the matrix and bedding increased by 2.7 and 3.1, and the microscopic cohesion increased by 1.8 and 1.7, respectively, for dynamic simulation tests. At a loading rate of 115 GPa/s, the dynamic tensile strength of the shale was 14.5 MPa – 18.2 MPa and increased with the increase of loading angle. There is a linear correlation between the dynamic tensile strength and the loading rate. The loading rate affects the damage pattern of the shale, with cracks tending to expand along the bedding. As the loading rate increases, the primary energy dissipated changes gradually from fracturing the rock to an increase in kinetic energy of the broken fragments.

Effect of steel fiber type and content on the dynamic tensile properties of ultra-high performance cementitious composites (UHPCC)

As one of the most promising construction and building materials in the past 30 years, ultra-high performance concrete (UHPC) has attracted a great deal of attention and the studies on its improvement and dynamic tensile behaviors become more important for its wider use in the related fields. In this contribution, a novel ultra-high performance cementitious composites (UHPCC) was developed with lower cement content, 20% of cement is replaced with fly ash and blast furnace slag, to reduce the raw material cost and carbon emission in production. Uniaxial compression, quasi-static and dynamic splitting tests were carried out to investigate the influences of steel fiber type (straight fiber and waved fiber) and content (volume fraction (0%, 1%, 2%)) on the uniaxial compressive strength, static tensile strength and dynamic tensile behaviors for current UHPCC material. The dynamic splitting tests were conducted on 100 disc specimens (75 mm in diameter and 37.5 mm in thickness) under five different impact pressure at a strain-rate range of 20–110 s−1 to study the strain rate effect by using a Split Hopkinson pressure bar (SHPB) system and the samples’ failure processes were captured by a high-speed camera. Based on the test results, the variations of energy absorption with the fiber type and content under static and dynamic tensile conditions are also analyzed, and combined with the experimental data from previous studies, an improved empirical tensile strength rate sensitivity (DIFft) model is proposed, which agrees well with the experiment results and can be used in the numerical simulation. At last, the failure process and pattern of different types of UHPCCs in the dynamic splitting test are also studied.

Dynamic splitting tensile behavior of rock–concrete bimaterial disc with multiple material types under different interface inclination angle

AbstractThe experimental investigation on the dynamic mechanical properties and failure behavior of rock–concrete composite is of great significance for understanding the mechanical response of rock–shotcrete supporting structures. In the paper, impact splitting tests were performed on Brazilian disc specimens of the rock–concrete bimaterial with different interface inclination angles. Effects of interface inclination angle and material type on dynamic response and failure behavior under dynamic impact were analyzed experimentally. The results show that the dynamic splitting strength and energy dissipation ratio increase with the increase of interface inclination angle. However, the incorporation of fibers will reduce the splitting tensile strength. The crack‐resisting effect of sandstone–fiber concrete is more obvious, and the hysteresis plateau phenomenon appears in the post‐peak section of the stress‐time curve. The interface failure behavior is related to the stress state of the interface and can be divided into three patterns: tensile fracture, shear fracture, and interface non‐ fracture.

Throughput Maximization for Backscatter- and Cache-Assisted Wireless Powered UAV Technology

This paper investigates a wireless powered unmanned aerial vehicle (UAV) communication network with backscatter and caching technologies. Specifically, we assume a self-energized UAV with a cache memory is deployed as a flying backscatter device (BD), term the UAV-enabled BD (UB), to relay the source’s signals to the destination. Whereas the source S can act as a wireless charging station or a base station to supply power or transmit information to the UB using the dynamic time splitting (DTS) method. The UAV utilizes its harvested energy for backscattering (i.e., passive communication) and transmit information (i.e., active communication) to the destination. In this context, we aim to maximize the total throughput by jointly optimizing the DTS ratio and the UB’s trajectory with caching capability at the UB. The formulation is troublesome to solve since it is a non-convex problem. To find solutions, we decompose the original problem into two sub-problems, whereas we first optimize the DTS ratio for a given UB’s trajectory and the UB’s trajectory optimization for a given DTS ratio. By using the KKT conditions, a closed-form expression for the optimal value of the DTS ratio is obtained, greatly reducing the computation time. Moreover, the solution of the second sub-problem can be acquired by adopting the successive convex approximation (SCA) technique. Consequently, an efficient alternating algorithm is proposed by leveraging the block coordinate descent (BCD) method. To show the advantages of the proposed BCD-based algorithm, we also provide the solution of the original problem applying the inner approximation (IA) method. Finally, the intensive numerical results demonstrate that our proposed schemes achieve significant throughput gain in comparison to the benchmark schemes.

Research on energy dissipation and damage evolution of dynamic splitting failure of basalt fiber reinforced concrete

Based on split Hopkinson bar (SHPB) loading system and digital image correlation (DIC) technology, a series of dynamic splitting experiments of basalt fiber reinforced concrete (BFRC) were carried out to reveal the effects of basalt fiber content and loading level on the dynamic tensile properties, energy dissipation and damage evolution. The results show that the dynamic tensile strength and dynamic increase factor (DIF) have obvious strain rate effect, and the appropriate basalt fiber content (0.39%) can remarkably improve the dynamic tensile strength of concrete. According to the changing trend of dissipated energy curve, the dynamic splitting process can be divided into compaction stage, elastic stage, plastic yield stage and softening stage. Appropriate basalt fiber content (0.39%) can effectively improve the dissipated energy and dissipated energy rate of BFRC. The loading level only promotes the dissipated energy of BFRC, but has no obvious effect on the dissipated energy rate. Adding an appropriate basalt fiber content (0.39%) can reduce the shear strain, thereby reducing the damage degree of the shear failure zone, and delaying the cracking time in the center of the specimen to a certain extent.

OAM-SWIPT for IoE-Driven 6G

Simultaneous wireless information and power transfer (SWIPT), which achieves both wireless energy transfer (WET) and information transfer, is an attractive technique for future Internet of Everything (IoE) in 6G mobile communications. With SWIPT, battery-less IoE devices can be powered while communicating with other devices. Line-of-sight (LoS) RF transmission and near-field inductive-coupling-based transmission are typical SWIPT scenarios, which are both LoS channels and without enough degree of freedom for high spectrum efficiency as well as high energy efficiency. Due to the orthogonal wavefronts, orbital angular momentum (OAM) can facilitate SWIPT in LoS channels. In this article, we introduce OAM-based SWIPT and discuss some of its basic advantages and challenges. After introducing OAM-based SWIPT for IoE, we first propose an OAM-based SWIPT system model with the OAM mode-assisted dynamic power splitting. Then four basic advantages of OAM-based SWIPT are reviewed with some numerical analyses to further demonstrate the advantages. Next, four challenges regarding integrating OAM into SWIPT and possible solutions are discussed. OAM technology provides multiple orthogonal streams to increase both spectrum and energy efficiencies for SWIPT, thus creating many opportunities for future WET and SWIPT researches.

Dynamic Mechanics and Crystal Structure Fracture Characteristics of Rock-like Materials in Coal Mines

Deep rock bears dynamic loads such as machinery, blasting and disturbance in the mining process. The dynamic fracture mechanism of deep rock is a necessary prerequisite for engineering design and analysis. To study the dynamic fracture mechanism of rock under high in situ stress, deep mudstone and sandstone were selected as research objects. The dynamic mechanical properties and energy dissipation of mudstone sandstone were assessed by using a 50 mm diameter separated Hopkinson test device. According to the similarity criterion, the similarity of strength was assumed as primary factor to prepare similar model materials. Then, dynamic mechanical tests of these similar materials were carried out under dynamic compression splitting and active confining pressure. The results show that materials similar to mudstone and sandstone mainly show axial fracture tensile failure and crushing failure. Both the average strain rate dynamic strength and peak strain of these similar materials increase with increasing impact pressure, and the dynamic strength of similar materials increases exponentially with increasing strain rate. This result is consistent with the regularity of original rock. The dynamic splitting of mudstone-like materials is dominated by the failure of intermediate cracks, and sandstone-like materials also show secondary cracks in addition to intermediate splitting cracks. The dynamic peak strength of mudstone-like materials increases with increasing active confining pressure, and the dynamic peak strength of sandstone-like materials increases nearly twofold under the action of active confining pressure.

Investigation on the Deformation and Failure Characteristics of Concrete in Dynamic Splitting Tests.

The dynamic response behavior of concrete is constantly concerned because of seismic, impact and explosion events in the service of constructions. As a classic device for testing the dynamic mechanical properties of materials, the splitting Hopkinson pressure bar was used to carry out dynamic splitting tests on concrete in this paper. The variation of the dynamic tensile strength against the stress rate was fitted by the incubation time criterion. The full-field strain distribution on the observed surface of the specimen at the crack initiation stage was obtained by the digital image correlation (DIC) method. Morphological characteristics of the fragmentized process of concrete specimens in splitting processes were obtained by combining the image processing techniques and the FracPaQ. The size distribution of fragments of concrete specimens was obtained by sieving. The results show that the strain concentration zone and crack initiation appear along the loading direction through the center of the specimen. The secondary cracks initiated occurred at the contact end of the specimen, which expanded along the strain concentration zone and then interacted with the main crack. At the early stage of crack extension, the main crack dominates the normalized length of fracture traces in the horizontal direction. The normalized length of the vertical fracture trace increases with the main cracks opening width and the expansion of the secondary crack. The relationship between the length and angle of fracture traces in the dynamic splitting process of concrete conforms to the Gaussian function. Finally, the fragment sizes decrease with the stress rates of impact loads.

Size effect on dynamic splitting tensile strength of concrete: Mesoscale modeling

The size effect on the dynamic strength of concrete has been recognized, but the main causes of this phenomenon are not well understood. In this study, a mesoscale particle model was established to simulate the dynamic splitting tensile behavior of concrete and calibrated with experimental data. An equivalent momentum scheme based on mesoscale modeling was proposed for the quantitative division of the dynamic increase factors. The results showed that the inertia effect and multiple cracks improved the tensile strength, owing to the rate effects. However, the inertia factor played a dominant role, whereas the multiple crack factor minimally influenced the dynamic size effect of concrete.