High Dynamic Loads Research Articles

A 2D and 3D segmentation-based microstructure study on the role of brittle phases in diffusion brazed AISI 304L/NiCrSiFeMoB joints

Nickel-based filler metals are frequently used in high temperature vacuum diffusion brazing for austenitic stainless-steel joints when components are subjected to high static or dynamic loads, corrosive environments and elevated temperatures. Due to melting point depressing metalloids such as silicon and boron, hard and brittle intermetallic phases are formed during the brazing process depending on the diffusion mechanisms. These brittle phases significantly affect mechanical and corrosive properties of the compounds. To quantify the influences of their amount, morphology and distribution, deep learning image segmentation was applied to segment these phases of the athermal solidification zone and the diffusion zone. Subsequently, characteristic microstructure parameters were calculated from these. The parameters of six different brazed joint variations were compared with their experimental characterization of mechanical and corrosive properties so that several correlations could be identified. Finally, a layer-by-layer removal of a brazed joint was performed using a focused ion beam, and a 3D model was reconstructed from the generated images to gain a mechanism-based understanding beyond the previous 2D investigations.

On the PMU Placement Optimization for the Detection of False Data Injection Attacks

The graph signal processing (GSP) approaches could facilitate the design of detectors for false data injection attacks (FDIAs) on smart grids. However, enhancing the performance of FDIA detection by optimizing the placement of phasor measurement units (PMUs) on smart grids remains an open problem. We formulate herein the detection of FDIAs as a binary hypothesis testing problem within the Grid-GSP framework and develop a subspace-based projection detection (SPD) algorithm, incorporating a quasi-optimal PMU placement strategy and two double thresholds. The proposed quasi-optimal PMU placement strategy enhances the performance of the SPD in FDIA detection. We further propose to enhance the SPD with the dynamic double threshold for high dynamic load profiles beyond a simple yet efficient static double threshold. Illustrative simulations based on the IEEE 118 bus test grid and the ERCOT dataset validate the superior performance of the proposed quasi-optimal PMU placement strategy along with the two double thresholds.

Износостойкость и совместимость исследуемых материалов для шарнирного узла черпаковой цепи

The current unfavorable environmental and hydro-technical situation in some regions of the country has cre-ated a number of serious problems. The government of the Russian Federation has created projects and programs where dredging is an integral part. There are carried out dredging works, among other things, by multi-bucket dredgers, where a scoop chain is the main working body. The performance and reliability of the chain depends on the quality of materials that experience high dynamic loads, and the consequences of the abrasive environment, which leads to accelerated wear of the swivel. There are given the results of the study of wear characteristics, the range of compatibility of steels and alloys of the hinged connection of the dredger bucket chain and the technology for the restoration of these elements, with an increase in the resource of the chain connection unit. Experimental studies simulating the wear of the assembly on small-sized samples determined the wear re-sistance of the materials of the pair. The method of comparative analysis with reference pairs was used. The experimental material consisted of 13 pairs, including 2 pairs of standards made of steel 110Mn13, 38CrNi3M (sleeve-finger) and steel 110Mn13 (sleeve and finger), where the remaining pairs were made of materials: steels C35K, C45K, 110Mn13, 38CrNi3Mo, wear-resistant surfacing with E – 190Cr5Si7 – LEZ – T – 590 – NG electrodes, surfacing with wire SV08A, electrodes E50A – UONI 13/55 (E513B20H), E46 - ANO-4 (E433R24) after a complex of heat treatments, chemical-thermal treatments, surface plastic deformation, where the samples were subjected to a load of 6615 N (675 kgf) in water-abrasive medium, were tested on the friction machine. Fundamental dependences are revealed and graphs of the influence of the hardness of the samples and the carbon content of the friction surface on the wear-resistant characteristics of various structural classes are plotted. Promising pairs for full-scale tests were determined: 1. steel 110Mn13 (sleeve) - surfacing SV08A with chemical-thermal treatment (finger); 2. steel 38CrNi3Mo (sleeve) - steel C35K with chemical-thermal treatment (finger); 3. steel C35K with chemical-thermal treatment (sleeve) - cladding SV08A with chemical-thermal treatment (finger).

(Invited) Aemion+® AEM Water Electrolysis with Excellent Iridium-Free Performance and Industrially Relevant Stability in Hot, Caustic Electrolyte

Hydrogen has a unique ability to maximize the utility of and enable new business models for intermittent renewable deployment. It can be stored cost-effectively in geological storage, transported between regions to suit geographic needs and bridge Dunkelflautes. Global electrolysis capacity must increase from the current <2 GW to 850 GW in 2030 (IEA Net Zero 2050) and in excess of 3500 GW in 2050 to enable this transition.Both traditional Alkaline (AWE) and proton-exchange membrane electrolyzers (PEMWE) are mature technologies that are anticipated to split the overall market share. However, each of these technologies face fundamental challenges:AWE operate at low current density, requiring large and difficult to transport systems, require high concentration electrolytes (e.g. 30 wt% KOH) to conduct hydroxides and ensure low gas solubilities for safety, which necessitates the use of expensive and difficult to machine high-nickel steels, especially in advanced, pressurized designs. Additionally, the porous nature of the electrode separator (e.g. Zirfon) compromises the desired dynamic load for pairing with intermittent renewables.PEMWE use a proton-conductive membrane to enable high current densities, dynamic loads, and differential hydrogen pressures, however, the most efficient operation requires iridium catalyst, which presents a near-term challenges with scalability, together with Ti and PGM structural elements that further impede cost-effectiveness.Alkaline anion-exchange water electrolyzers (AEMWE) address both of these challenges by operating with a cohesive, hydroxide-transporting membrane together with alkaline electrolyte to enable high efficiency, high current density operation, without iridium electrocatalysts or other scarce or expensive components. The realization of capital cost-effectiveness, dynamic load, and compact systems in one technology enables the most cost-effective green hydrogen and represents a step-change in the trajectory towards the DOE Hydrogen Shot target of $1/kg.The instability of alkaline anion exchange membrane chemistries based on quaternary amines or pendant imidazolium groups in relevant temperatures and alkalinities to industrial operations have historically resulted in untenable compromises and too-short lifetimes for industrial-scale deployment. Ionomr's Aemion+® AF2-AWP8-75-X and AF3-HWK9-75-X membranes are based on a sterically-protected imidazolium chemistries that are chemically robust (e.g. 6 months, 1 M, 80 °C without alteration to chemical or mechanical properties), and additionally exhibit low swelling to provide mechanical integrity to electrodes and enable operation in low concentration electrolytes. These membranes are an enabling technology for long-duration AEM water electrolysis.This talk highlights how Ionomr's Aemion+® membranes demonstrate target performances (e.g. >2 A/cm² at 2 V) with non-PGM OER catalysts with no apparent losses to 1000 hours operation across several configurations at ≥70 °C and 1 M KOH operation, and several longer lifetime demonstrations including 1 year durability using AWE electrodes and >6 months including hydrogen crossover measurement. This talk further highlights the potential for the three-dimensionality of electrodes in alkaline AEMWE and the necessary processing and operational requirements to create reproducible and stable GDEs with catalyst ink-based deposition techniques. Figure 1

Investigating the T-stub connection with different web-to-flange joint configurations

This article evaluates the impact of different web-to-flange joints in the T-stub connection. Mechanical properties of T-stub components were evaluated by experimental tests and by finite element simulations. Three different web-to-flange junctions are evaluated: laminated components, fillet welding and full penetration welding. Generally, laminated and fillet welded T-stub profiles have been considered in the past to study the behavior of the tension zone in the end plate connections. However, in structures predominately subjected to low and high cycle dynamic loads, and susceptible to a fatigue crack, is mandatory full penetration welds execution. This article evaluates the influence of full penetrated welding in the behavior of the full component, and not only in the mechanical capacity of the weld and the weld area. This article analyses how the increment of the free span between the bolt position and the web modifies the position of plastic hinges in the vicinity of the web, with the consequent reduction of strength and stiffness. A total of 72 experimental samples with 8 different geometries were tested to evaluate the different behavior of the web-to-flange joint configuration. A detailed finite element model of the T-stub component has been developed for each joint configuration. The model has been calibrated with experimental results, and it is able to accurately capture the full range behavior of the T-stub featuring any failure model. From the results of the experimental tests and their validation by finite element analysis, it can be concluded that the welded T-stub connection has a lower mechanical resistance, with no significant differences between fillet welding and full penetration welding. And the effect of the type of welding is only seen in ductility, and not in resistance or stiffness. On average, the typologies with full penetration welding have a maximum displacement 1.43 times higher than the fillet welded one.

Development of shock absorber with quasi-zero stiffness effect to reduce dynamic effects on pump unit

The article is devoted to the improvement of the vibration isolation and shockproof properties of the shock absorber used in the vibration isolation compensator system of the pumping unit (PU). The set task is to create an elastic damping system with the desired low (quasi-zero) stiffness, which makes it possible to reduce the detrimental effect of pumping unit vibrations both on human health and on the equipment itself. High internal dynamic (vibration) loads are the main causes of early failure of pumping units, which are transmitted to the equipment through pipelines and foundations, mainly due to various operational factors. A promising trend in increasing the operating reliability and efficiency of pumping and power equipment is the use of a vibration-isolating compensator system (VICS). To obtain greater efficiency of vibration isolation, it is proposed to apply a modern method of vibration damping – the use of elastic mechanical systems with quasi-zero stiffness. The damping devices with a quasi-zero stiffness effect were studied. An assessment of the operability and effectiveness of these dampers at oil and gas facilities was given. Based on the information studied, a new concept of a quasi-zero stiffness damping device is proposed. The method of mathematical analysis determined its power curve. A 3D model of the damper device was built using a simulation software. The functional check of the damper was performed with mathematical modeling carried out on the computing device with the help of a specialized Ansys software that allows performing a system analysis of an object using the finite element method. The following results were obtained: the design of the damper with the effect of quasi-zero stiffness allows to widen the range of basement load transmission coefficient reduction towards low frequencies. The low rigidity of the system at the operating point ensures low values of the frequency of natural oscillations, and, consequently, high vibration isolation qualities.

Stress analysis of aluminium die-cast parts including the STL-data of pores

PurposePores and shrink holes are unavoidable defects in the die-casting mass production process which may significantly influence the strength, fatigue and fracture behaviour as well as the life span of structures, especially if they are subjected to high static and dynamic loads. Such defects should be considered during the design process or after production, where the defects could be detected with the help of computed tomography (CT) measurements. However, this is usually not done in today's mass production environments. This paper deals with the stress analysis of die-cast structural parts with pores found from CT measurements or that are artificially placed within a structure.Design/methodology/approachIn this paper the authors illustrate two general methodologies to take into account the porosity of die-cast components in the stress analysis. The detailed geometry of a die-cast part including all discontinuities such as pores and shrink holes can be included via STL data provided by CT measurements. The first approach is a combination of the finite element method (FEM) and the finite cell method (FCM), which extends the FEM if the real geometry cuts finite elements. The FCM is only applied in regions with pores. This procedure has the advantage that all simulations with different pore distributions, real or artificial, can be calculated without changing the base finite element mesh. The second approach includes the pore information as STL data into the original CAD model and creates a new adapted finite element mesh for the simulation. Both methods are compared and evaluated for an industrial problem.FindingsThe STL data of defects which the authors received from CT measurements could not be directly applied without repairing them. Therefore, for FEM applications an appropriate repair procedure is proposed. The first approach, which combines the FEM with the FCM, the authors have realized within the commercial software tool Abaqus. This combination performs well, which is demonstrated for test examples, and is also applied for a complex industrial project. The developed in-house code still has some limitations which restrict broader application in industry. The second pure FEM-based approach works well without limitations but requires increasing computational effort if many different pore distributions are to be investigated.Originality/valueA new simulation approach which combines the FEM with the FCM has been developed and implemented into the commercial Abaqus FEM software. This approach the authors have applied to simulate a real engineering die-cast structure with pores. This approach could become a preferred way to consider pores in practical applications, where the porosity can be derived either from CT measurements or are artificially adopted for design purposes. The authors have also shown how pores can be considered in the standard FEM analysis as well.

High-strain-rate deformation: Stress-induced phase transformation and nanostructures in a titanium alloy

Microstructural evolution in adiabatic shear bands of a Ti-10V-2Fe-3Al (wt.%) alloy subjected to high strain-rate dynamic loading was investigated in detail via high-resolution transmission electron microscopy (HRTEM), focusing on the underlying plastic deformation mechanisms. The alloy after solution treatment consisted of a coarse body-centered cubic β single-phase microstructure, which exhibited double-yield and stress-collapse characteristics. The former was a result of stress-induced martensite transformation accompanied by the formation of nanotwins in the martensite, and the latter was caused by thermal softening stemming from dynamic recovery. Substantial grain refinement with three orders of magnitude grain size reduction occurred in the center of adiabatic shear bands due to severe plastic deformation along with dynamic recovery. Multiple deformation mechanisms in the adiabatic shear bands were identified, including the formation of face-centered orthorhombic α″ martensite, {111}α″ type I nanotwins, and hexagonal close-packed α phase, where distinctive nano-twinned structures and phase transformation from α″ to α with an orientation relationship of {1¯11}α″//{1¯101}α were observed. The transition area of the adiabatic shear bands contained mainly high-density dislocation regions and plate-like structures with relatively fewer nanoscale grains, where the transition from nanokinks to nanotwins along with phase transformation was also revealed, corroborating that kink bands served as nanotwin nucleation sites. The mechanisms of the microstructural evolution in relation to the mechanical response during the high strain-rate dynamic loading were discussed.

Twinning transfer in a near β-Ti alloy under high strain rate dynamic loading

The microstructure evolution of near β-Ti alloys with initially lamellar and equiaxed microstructures subjected to dynamic loading was investigated. Results showed that during high strain rate compression, shear failure is more likely to occur in equiaxed microstructure. Owing to temperature rise and stress concentration, the lamellar α phase in adiabatic shear band (ASB) zone was recrystallized and re-melted, while the equiaxed α phase transformed in strip-shaped following the propagating direction of adiabatic shear band. During high strain rate loading, the twinning transfer was observed between β matrix and α phase, which demonstrates that twinning is the dominant deformation mode to accommodate plastic deformation.

Results of modelling the effect of temperature on the thickness of the surfactants layer

Problem. Earthmoving machines operate under high loads, so their tribo-joints periodically operate under unsteady load conditions, which leads to their increased wear and, as a result, a rapid decrease in the residual service life of the units and the reliability of the machines in general. Under unsteady load conditions, friction in the joints of hydraulic drive elements occurs under the boundary lubrication regime. This lubrication mode occurs at high contact loads, high temperatures in the contact zone, and relatively low sliding speeds of the mating surfaces. The combination of boundary lubrication and high dynamic loads often leads to partial destruction of the boundary layer. This leads to direct contact of individual micro-irregularities of the friction surfaces, which is accompanied by a wear process. Hence the importance of the quality of both the parameters of the surface layer of friction surfaces and the parameters of the applied lubricant (oils, working fluids) on the strength and wear resistance of hydraulic drive elements. Goal. The aim of this work is to determine the effect of temperature and radius of curvature of a microroughness on the thickness of the layer of surface-active substances adsorbed on it. Methodology. The solution of the tasks involved the formation of a model of adsorption-desorption equilibrium in the system "working fluid - micron-surface", taking into account the ambient temperature, and its application to determine the dependence of the thickness of the adsorbed surfactant layer under conditions of temperature change. Results. The thickness of the adsorption layer depends mainly on the size of the adsorbing surface field and the energy of thermal vibrations of molecules. It decreases with increasing PP and increases with increasing radius of curvature of the micron roughness. The change in the thickness of the adsorption layer of surfactant molecules on the surface of the micron roughness with a change in the temperature of the RS is not uniform. With an increase in the PP temperature within 300...400 K, the thickness of the adsorption layer of surfactant molecules on the surface of the micron roughness decreases by ~24 %. With an increase in the temperature of the PP in the range of 400...450 K, the thickness of the adsorption layer of surfactant molecules on the surface of the microroughness decreases by ~76 %. The formation of a surfactant adsorption layer on the surface of the microroughness at a temperature above 443 K stops. Originality. A model of the formation of a surfactant adsorption layer on the surface of a separate microroughness on the basis of adsorption-desorption equilibrium in the system "working fluid - microroughness surface" was proposed, taking into account the ambient temperature, which allows us to analyse the nature of the temperature effect on the thickness of the adsorbed surfactant layer. Practical value. The use of the proposed mathematical model makes it possible to estimate the parameter of the surfactant adsorption layer on the surfaces of microroughnesses and rough friction surfaces based on the ambient temperature and the geometry of individual microroughnesses.

Evolution Laws of Stress–Energy and Progressive Damage Mechanisms of Surrounding Rock Induced by Mining Disturbance

The rock burst induced by the mutual disturbance of mining and excavation is significantly influenced by high static load stress and external dynamic load disturbance. In this paper, the evolution characteristics and progressive damage mechanism of surrounding rock in the process of mutual disturbance of mining and excavation are systematically studied. The results show that the evolution of surrounding rock stress can be roughly divided into three stages: rapid rise in the early stage, continuous rise and step-like decline in the middle stage, and slow rise in the late stage. In the process of parallel mining, the overlying rock movement above the goaf shows the sequence of horizontal penetration of tiny fissures—fracture intensification transition to stratification—non-coordinated caving of middle–low overlying rock—obvious horizontal cracks in the upper key layer. Only under the quasi-static loading mining action does the upper key layer not reach the breaking condition. The wave side of the heading face which is close to the focal point is affected by the dynamic load disturbance, the acceleration duration is short, and the attenuation is relatively fast, so it is the area prone to the earliest impact failure in the face of mining disturbance. The conclusion is helpful to deepen the understanding of the coal burst mechanism of mutual disturbance of mining and excavation.

Controlling wheel loader motion along a desired trajectory

Problem. Rigid-frame skid steer front loaders are popular material-handling machines widely used in various industries. However, such loaders experience frequent breakdowns due to high dynamic loads; they are often subjected to intensive tyre wear and excessive fuel consumption. Frequently, these issues arise from the improper actions of an operator. Given the labour intensity of the workflow, an operator, regardless of qualification, cannot ensure optimal loader control at an acceptable speed for a long time. In addition, an operator usually works in harsh environments with a high risk of injury, e.g. due to loss of stability. Manual control of loaders also limits the use of these machines in places that are dangerous for humans, for example, during the response to disasters. The solution to these issues is to automate the loader and exclude the operator from the machine work. One of the tasks of loaders automation is to ensure their movement along a given trajectory from the face to the place of unloading the material and back in the opposite direction. Goal. This work aims to increase the productivity and energy efficiency of a rigid-frame skid steer loader by ensuring its following along a given trajectory. Methodology. Based on the kinematics model of the loader, a two-loop control system for motion along a desired trajectory is designed. The control system combines feedforward and feedback loops. The feed-forward control is based on the desired speeds and accelerations. The closed loop is a state controller that uses the loader distance from the desired trajectory at a given time and the course angle as the state variables. Results. According to the simulation results, the proposed two-loop control system ensures the movement of the loader along a desired trajectory with an accuracy of up to 0.3 m. Originality. Further development of the up-to-date control theory was achieved by applying it to a new object, namely a skid steer front loader with a rigid frame. Practical value. The implementation of the proposed control system will increase the productivity of the loader, as well as reduce the number of accidents at construction sites.

Dynamic tensile mechanical properties of thermally damaged sandstone under impact loads and the influence mechanism of composition

The stability of surrounding rock in the combustion void is the key to continuous, safe, and efficient gas production in an underground coal gasification project. The key factors influencing the stability of surrounding rock in the combustion void are high temperature and impact dynamic load. At the same time, rock structure failure mainly depends on the rock materials’ tensile strength. Therefore, it is fundamental to study the dynamic tensile mechanical properties of thermally damaged rocks to control the surrounding rock stability of the combustion void in UCG projects. This paper used the coal measures as the research object. The dynamic direct tensile test of thermally damaged sandstone was carried out using a high-temperature load system and split Hopkinson tension bar (SHTB) test system. The test results showed that the dynamic tensile strength of sandstone increased linearly with the increase in strain rate. In contrast, it increased first and then decreased with temperature. In addition, the nonlinear regression method was applied to establish the prediction model of dynamic tensile properties of thermally damaged sandstone. XRD analyzed the composition and mass fractions of sandstone. From the standpoint of composition change, the change mechanism of the mechanical properties of thermally damaged coal measured in sandstone was illustrated.

Impact-initiated chemical reaction behavior of PTFE/Al reactive materials—A theory-based numerical method

Reactive materials (RMs) are special type of impact-initiated energetic materials that have been widely studied with broad military application prospects. However, simulating the ignition and reaction of RMs using current numerical methods is difficult due to their complex mechanism related to high dynamic loads. In this work, based on a theoretical model consisting of impact ignition criteria and chemical reaction rate of polymer-based RMs, a numerical method with a unified equation of state was proposed and compiled as an executable program. Experiments consisting of typical polytetrafluoroethylene /Al RM projectiles impacting double-spaced plates were conducted and simulated using the user-compiled program, and the results verified the effectiveness of the numerical method. The simulation also qualitatively analyzed the second-collision induced reaction enhancement mechanism. In addition, the results revealed that the kinetic-chemical combined effect is a crucial factor that determined the damage enhancement effect on the rear plates.

A high-entropy alloy syntactic foam with exceptional cryogenic and dynamic properties

Metal foams are in great demand in extreme service environments with cryogenic temperatures and high strain rates due to their unique properties. However, the reduced ductility and impact toughness under such conditions limit their applications. In this work, we tested the quasi-static and dynamic compression properties of CoCrFeMnNi high entropy alloy syntactic foam at liquid nitrogen temperature (−196 °C). We found that it exhibits ultra-high strengths and energy absorption capacity, especially a superior resistance to embrittlement at cryogenic temperature. Microstructural characterizations reveal that the foam matrix has a high twinning activity and shear localization propensity in cryogenic environments. Dense deformation twins and multiple shear bands intersected, forming a weave-like microstructure that can disperse the deformation and benefits energy absorption. Deformation twins can also strengthen the matrix and delay the crack nucleation and growth. While under dynamic loading, an FCC to HCP phase transformation was activated, forming a nano-laminated dual-phase (NLDP) FCC/HCP structure in the matrix, leading to further strengthening and toughening. Deformation twinning and HCP phase transformation act as additional plastic deformation mechanisms along with stacking faults and shear bands to offset the shortcomings caused by limited dislocation movements at low temperatures and high strain rate dynamic loading, enabling the high strength and energy absorption of the syntactic foam.

Data Acquisition System Based on the Bluesky Suite in the Shanghai Synchrotron Radiation Facility

The Shanghai Synchrotron Radiation Facility Phase-II Project is now under construction and it consists of 16 newly built advanced beamlines. The experiments carried out at these new beamlines tend to be characterized by high flux, multi-mode, ultra-fast frequency, in situ and dynamic loading. To meet these emerging experimental demands of SSRF Phase-II beamlines, the authors have developed a unified and extensible data acquisition system based on Bluesky suite. It has been applied at the BL07U Spatial-resolved and Spin-resolved ARPES and magnetism beamline. The experiment results show that with up to 5 channel signals, the system is capable of collecting total electron yield signals of experimental sample and standard sample, and incident photon flux signals simultaneously. It improves the user experimental efficiency and quality. In addition, thanks to Bluesky suite, all devices can be abstracted as motors or detectors and then represented by a Python object. Therefore, with the architecture, modules and interface developed for BL07U, the system can be extended to more beamlines efficiently and easily.

Free vibration analysis of sandwich plates

Laminated sandwich plates consisting of a soft core bounded by two relatively thin and stiff faces exhibit excellent strength to weight and stiffness to weight ratios. This makes them very suitable for applications where weight saving is a major concern, such as in aerospace and automotive structures. Piezoelectric layers or patches, due to their simple electro-mechanical properties, can easily be integrated with sandwich composites. The objective of integrating piezoelectric patches is to use them as sensors and actuators in order to control the excessive deformations and vibrations of the structure. Such a structure will have self-correcting capabilities against external loads and is called a smart structure. This further reduces the weight of the structure without compromising on strength or stiffness and becomes a very suitable choice for aerospace applications. Since these structures are often subjected to high dynamic loadings, it becomes important to have an insight of their free vibration characteristics. The work presented includes a study of the free vibration response of laminated sandwich plates using different core materials. From the study it was found that the material of the core significantly influences the free vibration behaviour of the plate, the natural frequency increases with the increase in density of the core material and also with an increase in mode number. The investigation will help in acquiring a better insight of the dynamic behaviour of sandwich plates with surface bonded piezoelectric patches. The efficiency and accuracy of the used elements is established by validation of the results with the published literature.

Reinforcing effects of carbon nanotubes on cement-based grouting materials under dynamic impact loading

Carbon nanotubes (CNTs) are reasonable materials to modify the property of cement-based grouting materials to improve their strength and durability, optimize their pore structure, and reduce their carbon emissions. However, dynamic impact loading frequently occurs in underground engineering, while there is very limited research concerning the reinforcing effects of CNTs on cement-based materials under dynamic impact loading. Hence, in this work, we applied the split Hopkinson pressure bar to investigate the dynamic mechanical behaviors of CNTs cement-based grouting materials. The results exhibited that CNTs cement-based grouting materials presented superior impact resistance, with a maximum peak stress of 59.33 MPa. Compared with plain cement grouting materials, mixing CNTs and fly ash into cementitious composites could reinforce the dynamic compressive properties by 10.25%–31.86%. The impact resistance of CNTs cement-based grouting materials was more significant under high dynamic loading, enhancing the dynamic properties by up to 31.86%, which indicates that CNTs reinforcement is more efficient in impacting engineering. The strain nephogram and fractal dimension further suggested that the excellent capacity of the CNTs in cement-based grouting materials could be achieved after ultrasonic treatment. A mathematical physical model was then established for CNTs reinforcing cement-based materials, revealing the whole process of CNTs extraction from the cement-based and giving a factor that can measure reinforcement performance. The findings of this study not only promote that the CNTs cement-based grouting materials can enhance the dynamic loading properties and reduce cement usage, but also provide a theoretical basis for the subsequent research on the mechanism of the microscopic reinforcement of CNTs.

Study of effect of provision of cut-outs on axial collapse behaviour of circular aluminium tubes

Geometrical modification of thin-walled tubular structure is one of the innovative ways in the development for vehicle safety design. This research is developed in accordance with the need of investigation on behaviour of tubular structures with geometrical modifications like cut-outs under dynamic loading technique. Diamond and elliptical cut-out shapes are provided in multiple number arranged circumferentially in a single row on a tube surface. Tubes with cut-outs are loaded axially at three different velocities, corresponding to three different strain rates. Energy absorption characteristics like energy efficiency, specific energy absorption, peak collapse force, mean collapse force and efficiency of peak force reduction at the initiation of tube deformation are calculated and compared using finite element (FE) based ABAQUS/Explicit® software. Split-Hopkinson Pressure Bar (SHPB) is modelled in the FE software to understand the material behaviour under high strain dynamic loading. Johnson-Cook material model parameters are incorporated in the study to understand the strain rate sensitive behaviour of aluminium alloy material. Results revealed that providing diamond and elliptical cut-outs on tube is much efficient than providing circular cut-outs on tube, in terms of percentage peak load reduction as well as energy efficiency of structure. It was observed that number of cut-outs influences the polygonal deformation pattern of tube with cut-outs. Overall study significantly helps to achieve the aim of improving vehicle crashworthiness characteristics by implementing cut-outs in a crash frame.

THE SIGNIFICANCE OF DYNAMIC FORCES ACTING ON A GONDOLA CAR WHEN UNLOADING BY A ROTARY CAR DUMPER

The article considers the factors influencing the strength of gondola cars during unloading on rotary car dumpers, before which a preliminary careful analysis of their characteristic damage and malfunctions was carried out. The calculated schemes of the system design are constructed and the analytical determination of the inertial components of the dynamic overturning process is performed. Initial recommendations for the design of the body structure, which is exposed to high dynamic loads during the mandatory unloading of the freight vehicle. The issue of fleet conservation is important for owners and operators of rolling stock, based on the balance of working and non-working fleet. The main cause of damage to the load-bearing structure of the gondola is non-compliance with the content of regulatory documents when performing loading and unloading operations. Unloading of gondola cars in the method of overturning was introduced at industrial enterprises in the last century during the intensive industrialization of the German experience and supply of equipment and is now successfully carried out using special technical devices - stationary rotor tippers. According to the results: acceleration of the PV body occurs at an angle of rotation of about 60°; the maximum values of accelerations are observed at an angle of rotation of 125°. This is done at the final stage of the flow of the load, because the final component of the full angle of rotation no longer affects the dynamics, because the load in the body is not a large part. The results of theoretical research at the design stage of the PV allow to take into account possible dynamic factors due to the overturning of the PV body, and prevent probable damage, assess the margin of safety and reliability of the body structure, which will ultimately reduce maintenance costs and increase life cycle load.