Load Splitting Research Articles

Experimental investigation on hydraulic fracturing in cement mortar with tensile stress

A novel device is proposed to test hydraulic fracturing in specimen with tensile stress. The device is composed of splitting apparatus and sealing apparatus. The tensile stress in specimen is realized via splitting load. It is confirmed that the sealing apparatus has a less effect on peak splitting load and the Young’s modulus of specimen. Some hydraulic fracturing experiments of cement mortar specimens with tensile stress are conducted. Critical water pressure of hydraulic fracturing will decrease with increase of the tensile stress. Hydraulic fracturing mechanism of cement mortar with tensile stress is revealed based on the Biot’s theory and fracture process zone. Applied high water pressure on initial crack surface, water pressure in water flow zone, and drag force along initial crack surface and water flow zone have a promotional effect on fracture propagation. The T stress in the test and pore water pressure caused by tensile strain near crack tip will restrain fracture propagation. A critical water pressure model (CWP) is proposed based on general maximum tangential stress criterion, and it is verified that the CWP model is rational and accurate. The T stress and pore water pressure gradient along polar angle direction have an effect on direction of crack initiation.

Collaborative multi-depot pickup and delivery vehicle routing problem with split loads and time windows

Optimization of collaborative multi-depot pickup and delivery logistics networks (CMDPDLN) with split loads and time windows involves a customer demand splitting strategy and a multi-depot pickup and delivery vehicle routing problem under time window constraints. In the collaborative network, the customer demand splitting scheme based on customer clustering aims to achieve the balance of demands’ spatial distribution and improve the efficiency of logistics transportation. The multi-depot pickup and delivery vehicle routing problem focuses on establishing a collaborative network optimization model to coordinate the pickup and delivery services among multiple depots and determine the optimal routes with reduced operating cost through logistics resource sharing. A 3D customer clustering algorithm with split load strategies is developed to reassign each customer to its favorable service provider considering multiple customer service characteristics. A hybrid genetic algorithm with tabu search is designed to optimize the pickup and delivery routes and maximize the logistics resource utilization. A realistic logistics network in Chongqing, China is used to test the performance of the proposed solution methods for the CMDPDLN optimization. Computational results show the effectiveness of customer clustering and demand splitting in simplifying and improving the large-scale collaborative network, and the adaptability of the hybrid algorithm in finding the minimal-cost vehicle routes. Therefore, the collaboration and demand split strategy adopted in network optimization can provide a reference for logistics operational management and facilitate sustainable pickup and delivery networks.

Study on the Effect of Precrack on Specimen Failure Characteristics under Static and Dynamic Loads by Brazilian Split Test

To analyse the dynamic failure characteristics of the rock with a crack in rock engineering, the Brazilian split tests were conducted on the split Hopkinson pressure bar (SHPB) using precrack specimens under dynamic loads. In the study, five groups of different precrack angles are selected; they are 0°, 30°, 45°, 60°, and 90°, respectively. The results show that the static failure load of the specimen as a whole decreases to increase with the growth of the loading angle, and the DIF linear increases with the increase of the loading rate; the failure load of the specimen with an angle of 45° precrack is the most sensitive to the loading rate, followed by 0°, 60°, 30°, and 90°. The crack initiation time of specimen with 30°, 45°, and 60°precrack decreases with the loading rate, while it has no obvious change with the loading rate with 0° and 90°precrack. The failure mode of the specimen was controlled by the stress concentration at the crack tip; the main cracks all point from the crack tip to the loading end. When the precrack and the loading direction are at a certain angle, the failure process will produce secondary cracks; it would be particularly obvious under dynamic load splitting. Once the precrack and the loading direction are at a certain inclination angle, type-II secondary cracks will develop under dynamic load splitting.

Study on the Acoustic Emission Characteristics of Different Rock Types and Its Fracture Mechanism in Brazilian Splitting Test

In order to investigate the relationship between rock microfracture mechanism and acoustic emission (AE) signal characteristic parameters under split loads, the MTS322 servo-controlled rock mechanical test system was employed to carry out the Brazilian split tests on granite, marble, sandstone, and limestone, while FEI Quanta-200 scanning electron microscope system was employed to carry out the analysis of fracture morphology. The results indicate that different scales of mineral particle, mineral composition, and discontinuity have influence on the fracture characteristics of rock, as well as the b-value. The peak frequency distribution of the AE signal has obvious zonal features, and these distinct peak frequencies of four types of rock fall mostly in ranges of 0–100 kHz, 100–300 kHz, and above 300 kHz. Due to the different rock properties and mineral compositions, the proportions of peak frequencies in these intervals are also different among the four rocks, which are also acting on the b-value. In addition, for granite, the peak frequencies of AE signals are mostly distributed above 300 kHz for granite, marble, and limestone, which mainly derive from the internal fracture of k-feldspar minerals; for marble, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of dolomite minerals and calcite minerals; AE signals for sandstone are mostly distributed in the range of 0–100 kHz, which mainly derive from the internal fracture of quartz minerals; for limestone, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of granular-calcite minerals. The relationship between acoustic emission signal frequency of rock fracture and the fracture scale is constructed through experiments, which is of great help for in-depth understanding of the scaling relationship of rock fracture.

Research on size effect of fracture toughness of sandstone using the center-cracked circular disc samples

In order to investigate the size effect and reason of rock fracture toughness, the split loading test was carried out in the GCTS rock mechanics testing machine using the center-cracked circular disc (CCCD) samples with diameters of 50 mm, 100 mm, 150 mm and 205 mm, respectively. The lengths of fracture process zone (lFPZ) were determined by the maximum normal stress criterion. The size effect of the lFPZ , fracture toughness test value (KIc), and fracture energy (Gf) were analyzed. The influence of the lFPZ on the size effect of the KIc was revealed. The crack growth paths and failure characteristics of the samples were discussed. The results show that the lFPZ and the KIc increase linearly with the sample size, and there is obvious size effect within the range of the test. The KIc and the lFPZ do not always increase linearly with the size in a larger size range, but gradually stabilize by extrapolation analysis. The lFPZ increases with the size, which means the release of stored energy increases with the size corresponding to the size effect of the Gf, and in turn leads to the size effect of the KIc. It is helpful to deeply understand the cause of the size effect reason of rock fracture toughness.

Study of the effect of loading modes on the acoustic emission fractal and damage characteristics of cemented paste backfill

To investigate the relationship between damage variables and fractal dimensions during the deformation and destruction of tantalum–niobium tailing cemented paste backfill (CPB), uniaxial compression and Brazilian split tests were conducted on tantalum–niobium tailing CPB. The changes in the damage variables and fractal dimensions of the CPB during the damage process were investigated using a damage model based on the acoustic emission (AE) ringing count rate and the calculation of the AE energy rate fractal dimension. During the deformation and destruction of the CPB, the fractal dimensions of the CPB gradually decreased, and the damage variables gradually increased; moreover, the stages of reduction in the fractal dimensions corresponded to the stages of increase in the damage variables. The fractal dimensions of the CPB before deformation and failure did not decrease significantly and gradually tended to converge to a certain value. Under different loading modes, the fractal dimensions of the CPB before deformation and failure were different. The damage variability and energy emitted during the initial loading phase of deformation damage were lower than those during the later phase. Before the damage of the CPB, both the damage variables and energy emitted increased rapidly. For both uniaxial compression and Brazilian split loading, the fractal dimensions of the AE of the CPB gradually approaching a certain value is an important precursor of the overall macroscopic destruction of the CPB. Based on this feature, it can be used to predict and analyze the stability of the tantalum-niobium mine tailing CPB in the underground support roof.

An Investigation of High-Performance Self Compacting Concrete under Flexural Loading

To shorten construction period, to assure compaction in the structure especially in confined zones where vibrating compaction is difficult and to eliminate noise due to vibration effective especially at concrete products plants SCC is developed in practice. Also, SCC is applied to tunnel lining for preventing the cold joint Self-compacting concrete has been used. Currently, the main reasons for the employment of self-compacting concrete can be summarized as follows: developing alternate binders that are environment-friendly and contribute to sustainable management. The properties of SCC in fresh concrete stage cost reduced time and substantial effective construction expertise in Special concrete of High-Performance Self Compacting Concrete (HPSCC) properties, the present work as major aspects like Effect of fibers with Fly ash on Fresh concrete properties and Behavior of polypropylene fibers Specimens under split tensile & Flexural loading. The first parts of the work have been focused on the effect of polypropylene fibers on Fresh and harden concrete of Ultimate Strength with replacement of varying Polypropylene fibers by 0% to 1.5% at the interval of 0.5 and next part of the work focusing the behavior of fiber under Flexural loading. The results obtained from this work are expected to be useful in determining behavior of SCC with polypropylene fiber Specimens. This will help the designing SCC specimens to resist Flexural loading.

A Large Neighborhood Search for the Pickup and Delivery Problem with Time Windows, Split Loads and Transshipments

In the pickup and delivery problem (PDP) a fleet of capacitated vehicles must be routed in order to satisfy a set of customer requests. In this article, we address a variant of the one-to-one PDP where each customer location can be visited several times and load may be transshipped from one vehicle to another at specific locations. The goal is to minimize the sum of travel costs and transshipment costs. The corresponding problem is called the PDP with time windows, split loads and transshipments. We present an arc-based mixed-integer formulation for the problem and propose a large neighbourhood search metaheuristic for solving it. Extensive computational experiments using both benchmark instances from the literature and instances based on real-world data illustrate the performance of the solution method and give insights regarding the benefits of combining split loads and transshipments.

Electromagnetic simulation of an external rotor PM hub motor power device for distributed driving electric vehicle

In order to increase efficiency and reliability of hub motor power device for distributed driving electric vehicle, a novel hub motor with an external rotor PM (permanent magnet) is designed and optimized. The performance parameters of hub motor are computed and selected based on vehicle dynamics indicators and the driving equations. This paper determines the optimum primary size of hub motor by choosing appropriate magnetic circuit structure and integrating three key parameters, including as stator split ratio, electromagnetic load and viscous damping coefficient. This paper has built the analysis model of external rotor PM hub motor, and simulated and analyzed the transient magnetic field of hub motor under no-load and load transient or steady state. Simulation results indicate that the external rotor PM hub motor designed by combining stator split ratio, electromagnetic load and viscous damping coefficient has satisfactory electromagnetic performance, which can satisfy the performance requirements and indicators of hub motor power device for distributed driving electric vehicles.

Phase Inverter with Split Load on Basis of Bragg Diffraction

There is represented an information about phase inverters with split load. It is noted the problem of provision of identity of different polar signals at split loads. There are mentioned the specificities of Bragg’s diffraction in context of shaping of two different polar signals. It is shown that in case of modification of the frequency of electric signal at the input of acousto-optic modulator the diffraction order shifts in the plane which is perpendicular to the optical axis. It is represented the structural circuit of acousto-optic phase inverter with split load. For generation of two different polar signals the deflected beam is divided into two beams biased in the same direction. Slits in the screens are placed correspondingly at the left and at the right halves of the shaped beams. It is researched the theoretic aspects of generation of different polar signals which are used for numerical analysis of the proposed circuit functionality. The results of the theoretic researches are proved experimentally. It is represented the circuit of the experimental set. Experimental sample of the phase inverter is made using acousto-optical modulator fabricated from glassy photo elastic material of TF-7 type. Laboratory sample of photo receiving device is used for experimental researches. There are represented the results of experimental researches and it is shown their identical match the theoretic researches results.

The Pickup and Delivery Problem with Split Loads and Transshipments: A Branch-and-Cut Solution Approach

This paper addresses the design of routes for a fleet of vehicles serving customer requests. It is a pickup and delivery problem where each customer location can be visited several times, and load may be transshipped from one vehicle to another at specific locations. The aim is to minimize the sum of travel costs and transshipment costs. We present an arc-based mixed-integer formulation for the problem and propose a branch-and-cut algorithm for solving it. Extensive computational results illustrate the performance of the algorithm.

A multicommodity unpaired pickup and delivery vehicle routing problem with split loads and unloads

PurposeThis paper aims to explore the commodity transshipment planning among customers, which is commonly observed in production/sales enterprises to save the operational costs.Design/methodology/approachA mixed integer programming (MIP) model is built and five types of valid inequalities for tightening the solution space are derived. An improved variable neighborhood search (IVNS) algorithm is presented combining the developed multistart initial solution strategy and modified neighborhood local search procedure.FindingsExperimental results demonstrate that: with less decision variables considered, the proposed model can solve more instances compared to the existing model in previous literature. The valid inequalities utilized to tighten the searching space can efficiently help the model to obtain optimal solutions or high-quality lower bounds. The improved algorithm is efficient to obtain optimal or near-optimal solutions and superior to the compared algorithm in terms of solution quality, computational time and robustness.ractical implicationsThis research not only can help reduce operational costs and improve logistics efficiency for relevant enterprises, but also can provide guidance for constructing the decision support system of logistics intelligent scheduling platform to cater for centralized management and control.Originality/valueThis paper develops a more compact model and some stronger valid inequalities. Moreover, the proposed algorithm is easy to implement and performs well.

Investigation on interface fracture properties and nonlinear fracture model between ECC and concrete subjected to salt freeze-thaw cycles

The work aims at investigating on interface fracture properties and nonlinear fracture model between ECC and concrete under salt freeze-thaw cycles. Based on the interface nonlinear fracture mechanism, a three-parameter nonlinear fracture model was proposed to comprehensive and accurately reflect the degradation law of interface fracture properties under salt freeze-thaw cycles. The experimental results showed that the salt freeze-thaw erosion had a very negative effect on interface fracture properties. Moreover, the occurrence of interface fracture under salt freeze-thaw cycles was affected remarkably by ECC strength grade, and the higher ECC strength always leads to later occurrences of interface fracture. Regardless of cycles, the fracture propagation process of all specimens included three phases: initial crack, stable crack propagation, and instability failure. Moreover, the three phases all occurred at the interface, and the crack did not extend to ECC or concrete substrate. Meanwhile, the fibers bridging effect was very significant at the phases of crack stable propagation and instability failure. Only one kind of wedge-splitting load-crack mouth opening displacement (CMOD) curve was observed. As number of cycles increased, slope of rising section curve and ultimate wedge-splitting loads all gradually decreased, while the CMOD corresponding to ultimate splitting load had little change. The salt freeze-thaw erosion had a very negative effect on three fracture parameters. Moreover, the three fracture parameters all decreased continuously with the increasing number of cycles.

The Vehicle Scheduling Problem of Third-Party Passenger Finished Vehicle Logistics Transportation: Formulation, Algorithms, and Instances

In this article, a vehicle scheduling problem of third-party passenger finished vehicle logistics transportation networks is studied. An integer programming model of open heterogeneous fleet pickup and delivery problem with time windows and split load (OHFPDPTWSL) is established to maximize the total profit, and a hybrid parallel heuristic algorithm combining with path buffer clustering operator (PBC), multi-mark split operator (MMS) and four variable neighborhood search operators (PBCMMSVNSHPA) is proposed to solve this problem with high quality in a relatively short time. The PBC operator with three different clustering types can effectively cluster the orders and the transport vehicles before the route planning, and the MMS operator can greatly reduce the complexity and computation of the path planning at the expense of little algorithm precision. Then a set of instances which represents the realistic characters of OHFPDPTWSL modified from benchmark instances is introduced. The experimental results on these instances show that PBCMMSVNSHPA is suitable for real-time requirement or large-scale dataset, and the experimental results on the actual instance of an enterprise show that this algorithm can solve the instance with 200 orders and 500 vehicles within 3 minutes.

A Load Balancing Routing Strategy for LEO Satellite Network

The LEO network composed of massive satellite nodes is a hot research field at present. In such a network, the problem of load balancing should be reconsidered due to the large number of satellite nodes, the frequently changing topology, and the uneven distribution of global ground users. To solve such problem, a selective iterative Dijkstra algorithm (SIDA) is proposed to optimize the path finding process by reducing the reuse frequency of nodes. On the basis of SIDA, a selective split load balancing strategy (SSLB) is proposed to solve the link congestion problem in low latitude LEO network. SSLB is a distributed strategy, which diverts the traffic flow of congestion nodes to neighboring nodes. SSLB reduces the burden of neighbor nodes, which need the less demand of computing resources and signaling interaction. Simulation results show that SIDA reduces the number of congestion links and balances the load distribution, while SSLB can effectively suppress the number of new congestion links after traffic diversion. These algorithms provide a load balancing solution for LEO satellite network.

Laser-assisted cyclic chipless splitting for hard-to-cut thick wall tubes and fatigue fracture mechanism analysis

High-quality precision cropping of hard-to-cut thick wall tubes is urgently needed as the first process for precision forming of tubular parts. Due to the deficiencies of large cutting load and waste of chips and coolants in the present cutting methods, a laser-assisted cyclic chipless splitting (LACCS) method is developed, which prefabricates circumferential crack with large stress concentration by laser, and exerts cyclic rotary load at a low amplitude simultaneously to split the tube. The theoretical laser crack depth and critical loads are derivated for fatigue crack propagation and instant rupture, respectively, and an XFEM model based on cohesive damage criterion is established to reveal the fracture mode based on stress intensity factors. Finally, section quality and microfracture mechanism are investigated by experimental tests with different initial crack depths and load control curves. The results show that critical fatigue splitting load and instant rupture load gradually drop with crack depth at a decreasing rate; for crack depth of 0.7 mm, the critical loads are 0.67% and 34.36%, respectively, of that in the traditional cutting method. The type I crack is the primary fracture mode in this LACCS process, and the stress intensity factor KI varies as a cosine curve with peak amplitude of 436.09 MPa(m)1/2. Step-reduction frequency load can smoothly transite the crack propagation to final rupture, and obtains high-quality sections in 16–32 s, with outer roundness error of 0.6%, flatness error of 0.2–0.3 mm and final rupture area of 0.25–1.19 mm2. The fractographies typically show laser affected zone, cracks propagation zone and final rupture zone. Micro-cracks initiate from the tangency points on the laser notch curve with maximal stress change rate, and the ductile striations propagate with growth rate of 3.3–5.1 μm/cycle. Final rupture zone forms under shear stress, featured by quasi-parabolic dimples involving microvoid coalescence.

Integrated optimization model of a biomass feedstock delivery problem with carbon emissions constraints and split loads

The biomass feedstock supply logistics of biomass power plants in China suffers from low levels of efficiency and high levels of carbon emissions that affect the development of the biomass energy industry. This paper investigates the integrated optimization problem of biomass feedstock delivery in a two-echelon feedstock delivery system. An integrated two-echelon location and routing model is proposed for determining the optimal locations and sizes of biomass satellites collecting stations and delivery routes, considering the expected carbon reduction level and split load. A hybrid genetic algorithm embedded with tabu search and local search is developed to solve the proposed model. Computational experiments are provided to validate the effectiveness of the hybrid genetic algorithm in solving the proposed model. A realistic case study from China is carried out, together with sensitivity analysis of some key model parameters. Some practical insights and managerial implications of biomass feedstock delivery are obtained.

Compact high Q bandpass filter by using substrate integrated waveguide and split rings capacitive load post

A substrate integrated waveguide cavity filter is designed by loading with two split rings capacitive posts. Using these split rings posts results in high quality factor, low insertion loss (2.1 dB), very narrow bandwidth (2%) at 4.6 GHz centre frequency and compact (0.97×0.5 λ g 2 ) bandpass filter structure. The filter measured results are in good agreement with the simulation ones which prove the idea.

Mechanical property and damage evolution of concrete interface of ballastless track in high-speed railway: Experiment and simulation

The interface damage of ballastless tracks in high-speed railway is considered as one of the most critical damage problems, however, the mechanical property and damage evolution of the concrete interface of ballastless tracks are rarely ascertained, and maintenance of the interface damage has been a heavy burden on the modern railway networks. This work aims to reveal the damage constitutive relationship and fatigue performance of the concrete interface of double-clock ballastless track based on experimental tests and simulation analysis. Firstly, by making the composite specimen composed of half track-slab concrete and half supporting-layer concrete and by designing experiment programs for the interface cracking test, the full-field evolution of strain distribution of the specimen under monotonic splitting loading is obtained based on the digital image correlation (DIC) technique, and the key parameters of a cohesive zone model for describing the interface stress-displacement relationship is determined. Subsequently, the interface damage evolution is investigated by applying cyclic splitting loads, and the interface fatigue S-N curve is acquired and validated by comparing with relevant references. It is found that the fatigue life of the concrete interface can be easily predicted with only knowing its secondary growth rate of the opening displacement amplitude. Furthermore, to elucidate the practical application of the experiment data and proposed models, the interface damage evolution of the double-block ballastless track under monotonic and cyclic temperature gradient loads are investigated, respectively. Simulation results show that much attentions should be paid to the negative temperature gradient load (below −60 °C/m) that could cause initiation of interface cracks. The proposed fatigue S-N curve enable a convenient and effective prediction for the interface fatigue damage of ballastless track with different service state under random loading cycles.

Influence of splitting load on transport properties of ultra-high performance concrete

This paper presents an experimental investigation on the influence of splitting load on transport properties (air permeability and sorptivity) of UHPC incorporating different dosages of steel fibers (0%, 1%, 2% and 3%). ϕ100 mm × 50 mm specimens were subjected to splitting loads with stress levels varying from 50% to 80% of the ultimate splitting tensile strength. The splitting load induced damage was characterized by the crack pattern, crack opening displacement (COD) and penetrable porosity. Gas permeability and water sorptivity tests were carried out to evaluate the transport property of UHPC specimens after exposure to different levels of splitting load. The correlation among splitting tensile stress level, COD and transport property degradation of UHPC was analyzed. The results indicate that gas permeability and sorptivity of UHPC before loading are much better than that of normal concrete. The splitting tensile strength of UHPC is almost doubled by the addition of 1 ∼ 3% steel fibers in volume and the peak lateral deformation is increased by more than 10 times. Both the maximum value of COD (CODmax) under loading and the residual COD (CODres) after unloading of UHPC specimen increase with the more addition of steel fibers when exposed to the same stress level of splitting load. Both gas permeability and sorptivity of UHPC increase with the splitting load induced CODres. The higher dosage of steel fibers plays a positive effect on improving the transport properties of UHPC with the same CODres value. The sorptivity is more sensitive under a low deformation damage and the gas permeability is a better indicator to describe the durability degradation of UHPC under a high level of deformation.