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In the future, the power of a commercial ocean current energy convertor will be able to reach the MW class, and its corresponding mooring rope tension will be very good. However, the power of convertors currently being researched is still at the KW class, which can bear less rope tension. The main mooring rope usually has a single cable and a single foundation. To investigate the dynamic response and rope tension of an MW-class ocean current generator mooring system, here, a similarity rule is proposed for (1) coefficients without any fluid–structure interaction (FSI) using the Buckingham theorem and (2) ones with FSI. The overall hydrodynamic drag and moment including the hydrodynamic coefficients in these two situations are represented in a Taylor series. Assuming similarity between the commercial MW-class and KW-class ocean current convertors, all hydrodynamic parameters of the MW-class system are estimated based on the known KW-class parameters and based on the similarity formula. In order to overcome the extreme tension of the MW-class system and to provide good stability, in this paper, we propose a pulley–rope design to replace the traditional single-traction-rope design. The static and dynamic mathematical models of this mooring system subjected to the impact of typhoon waves and currents are proposed, and analytical solutions are obtained. We find that the pulley–rope design can significantly reduce the dynamic rope tensions of the mooring system. The effect of the length ratio of the main traction rope, rope A, to the seabed depth on the dynamic tension of stabilizing converter rope D is significant. The length ratio is within a safe range, and the maximum rope dynamic tension is less than the fracture strength. In addition, if the rope length ratio is over the critical value, the larger the ratio, the higher the safety factor of the rope. In summary, the pulley–rope design can be safely used in an MW-level ocean current generator system. [ABSTRACT FROM AUTHOR]

Abstract The tensile properties of coal under dynamic loading are important mechanical characteristics of coal and are highly important for controlling coal rock stability under impact loading conditions, selecting blasting engineering parameters, and studying the mechanism of rockburst disasters. To investigate the dynamic tensile failure process of coal subjected to impact loading, this study used high-speed photography and digital image correlation technology to capture the dynamic tensile failure of coal under impact loading. The dynamic tensile evolution was quantitatively analyzed from the beginning of coal sample being loaded to failure. The captured images of the coal were processed, and the fractal dimension was used to quantitatively describe the evolution of the coal surface cracks under impact loading. The following conclusions were drawn from the experimental results: (1) An empirical formula was established to describe the dynamic tensile strength characteristics of coal under different loading rates. (2) Under impact loading, the maximum strain of a Brazilian disc coal sample first appeared at the contact end between the sample and the incident rod. (3) Under impact loading, a Brazilian disc coal sample cracked from the center of the sample outward, and the crack subsequently extended toward both ends. The fractal dimension of the crack exhibited a power function relationship with time, and the variation range of the fractal dimension of the crack was 1.05–1.39.

The CrCoNiSi0.3 MEA exhibits excellent cryogenic mechanical properties upon both quasi-static and dynamic tension. Under quasi-static tension at cryogenic temperature, the engineering yield and ultimate tensile strengths (UTS) reach 980 MPa and 1800 MPa, respectively, with notable ductility (62 %). The product of UTS and total elongation (TE) is 111.6 GPa %, surpassing most cryogenic high strength-ductility alloys. The significant mechanical strength enhancement is attributed to the denser deformation twins (DTs), multiple twinning, and extensive face-centered-cubic to hexagonal-close-packed (HCP) phase transitions, resulting in a high work hardening capacity. Upon dynamic tension at cryogenic temperature, the strength and strain hardening are further improved, which originates from the thickening DTs and HCP sequence and localized plastic deformation. The effects of temperature and strain rate on phase transition are studied. It is proposed that there is a competing relationship between high strain rate and increased stacking fault energy (SFE) due to temperature rise. The coupling effect of cryogenic temperature and high strain rate inhibits phase transition due to the deformation inhomogeneity in CrCoNiSi0.3 MEA. The findings make a valuable contribution to understand the influence of temperature and strain rate on the mechanism of FCC-to-HCP phase transition.

In the future, the power of a commercial ocean current energy convertor will be able to reach the MW class, and its corresponding mooring rope tension will be very good. However, the power of convertors currently being researched is still at the KW class, which can bear less rope tension. The main mooring rope usually has a single cable and a single foundation. To investigate the dynamic response and rope tension of an MW-class ocean current generator mooring system, here, a similarity rule is proposed for (1) coefficients without any fluid–structure interaction (FSI) using the Buckingham theorem and (2) ones with FSI. The overall hydrodynamic drag and moment including the hydrodynamic coefficients in these two situations are represented in a Taylor series. Assuming similarity between the commercial MW-class and KW-class ocean current convertors, all hydrodynamic parameters of the MW-class system are estimated based on the known KW-class parameters and based on the similarity formula. In order to overcome the extreme tension of the MW-class system and to provide good stability, in this paper, we propose a pulley–rope design to replace the traditional single-traction-rope design. The static and dynamic mathematical models of this mooring system subjected to the impact of typhoon waves and currents are proposed, and analytical solutions are obtained. We find that the pulley–rope design can significantly reduce the dynamic rope tensions of the mooring system. The effect of the length ratio of the main traction rope, rope A, to the seabed depth on the dynamic tension of stabilizing converter rope D is significant. The length ratio is within a safe range, and the maximum rope dynamic tension is less than the fracture strength. In addition, if the rope length ratio is over the critical value, the larger the ratio, the higher the safety factor of the rope. In summary, the pulley–rope design can be safely used in an MW-level ocean current generator system.

In this study, a numerical simulation was conducted to investigate the non-linear physical phenomena of a tension leg platform (TLP) of a 15-MW-class floating offshore wind turbine (FOWT). Computational fluid dynamics was employed as the numerical tool, and a deforming mesh technique was used to describe the moving body. To examine the non-linear physical phenomena, an irregular wave was generated with a focus on head sea conditions. The springing and ringing responses were calculated from the numerical simulation results, and the relations between the motions and dynamic tensions of the 15-MW-class FOWT TLP were investigated. From the irregular wave impact simulation, it was found that the springing response via the wave sum frequencies and the ringing response occurred at approximately three times the wave peak frequency. Additionally, whipping simulations were conducted under a focused wave. The results show that the response in pitch resonance frequency was caused by the wave impact. The numerical results of this study could be used as fundamental data for FOWT TLP design. [ABSTRACT FROM AUTHOR]

Icing is one of the key factors affecting the security and reliability of power system operation. Ice accumulation on the overhead line (OHL) conductors is often accompanied by strong winds, whose magnitude and direction are varied constantly, which imposes challenges to the on-line monitoring of OHL's ice load. This paper analyzed the dynamic characteristics of the tensional force for ice accumulated OHLs through both the on-site experiment and the finite element method (FEM). The correlation between the instantaneous wind speed, the thickness of the accumulated ice and the dynamic tensional force, the aerodynamic resistance coefficient of the conductor, is investigated. It is found that the axial dynamic tension at the end of the iced conductor is approximately proportional to the square of the instantaneous wind speed. The higher the wind speed, the larger the difference between the static tension and the maximum dynamic tension calculated using the 10-min average wind speed. Under the conditions of the example in this article (crescent-shaped icing), when the average wind speed is 20 m/s, the ratio of the difference to static tension is 11.19%. These conclusions are verified with the computational fluid dynamic (CFD) simulation, the same correlation is identified in comparison with the experiments. Due to the fact that the magnitudes of tensional force and vibration are determined by the instantaneous wind speed, significant error exists within traditional calculation methods where average wind speed is used instead. [ABSTRACT FROM AUTHOR]

Ice shedding on conductors of transmission lines can induce severe vertical vibrations and abrupt tension changes, potentially causing structural damage and power outages. Prior experiments and numerical simulations assumed that ice sheds instantaneously from transmission lines, neglecting the practical delays in the ice shedding process, which resulted in unrealistic conductor dynamic responses. This study introduces a reduced-scale modeling system designed to simulate delayed ice shedding on conductors. The jump height and dynamic tension of an isolated-span transmission line following delayed ice shedding are analyzed, and various factors such as the two-dimensional delay duration, shedding sequence, and weight of ice accretion are examined through reduced-scale model tests. Based on the experimental data, simplified formulas are proposed to calculate the conductor's jump height and maximum tension after ice shedding by taking the time delay of the shedding process into account. • A reduced-scale modeling system is designed to simulate delayed ice shedding on conductors. • Dynamic responses of a transmission conductor following delayed ice shedding are analyzed by reduced-scale model test. • Formulas for estimating the conductor's jump height and maximum tension following delayed ice shedding are newly proposed. [ABSTRACT FROM AUTHOR]

In this study, a numerical simulation was conducted to investigate the non-linear physical phenomena of a tension leg platform (TLP) of a 15-MW-class floating offshore wind turbine (FOWT). Computational fluid dynamics was employed as the numerical tool, and a deforming mesh technique was used to describe the moving body. To examine the non-linear physical phenomena, an irregular wave was generated with a focus on head sea conditions. The springing and ringing responses were calculated from the numerical simulation results, and the relations between the motions and dynamic tensions of the 15-MW-class FOWT TLP were investigated. From the irregular wave impact simulation, it was found that the springing response via the wave sum frequencies and the ringing response occurred at approximately three times the wave peak frequency. Additionally, whipping simulations were conducted under a focused wave. The results show that the response in pitch resonance frequency was caused by the wave impact. The numerical results of this study could be used as fundamental data for FOWT TLP design.

In this study, we formulate a mechanical model of spall fracture of copper, which describes both solid and molten states. The model is verified, and its parameters are found based on the data of molecular dynamics simulations of this process under ultrahigh strain rate of tension, leading to the formation of multiple pores within the considered volume element. A machine-learning-type Bayesian algorithm is used to identify the optimal parameters of the model. We also analyze the influence of the initial size distribution of pores or non-wettable inclusions in copper on the strain rate dependence of its spall strength and show that these initial heterogeneities explain the existing experimental data for moderate strain rates. This investigation promotes the development of atomistically-based machine learning approaches to description of the strength properties of metals and deepens the understanding of the spall fracture process. [ABSTRACT FROM AUTHOR]

Adverse climate events (ACE) have both direct and indirect effects on companies. The use of information about these events is important to guide decisions as well as to seek reflections that are transformed into improvement of the Management Control Systems (MCS). Emphasis is given to the use of MCS, using Simons's (1995) Levers of Control (LOC) framework and the contingency theory. Thus, the study aimed to verify how ACE influence the use of the MCS. The research, characterized as qualitative and a multiple cases study: three of which being affected by Tornadoes and three cases by Flood. Indicate that the history with repetitions of occurrences causes the processes to the preventions to be perfected and formalized, alteration of organizational priorities, communications, understanding of risks that should be avoided or minimized; identification of the relevance of the monitoring and stimulation to research. ACE influences management techniques, use of inventory reports and logistic, with emphasis on the interactive use of LOC's. Six dynamic tensions related to the event were observed. [ABSTRACT FROM AUTHOR]

Icing is one of the key factors affecting the security and reliability of power system operation. Ice accumulation on the overhead line (OHL) conductors is often accompanied by strong winds, whose magnitude and direction are varied constantly, which imposes challenges to the on-line monitoring of OHL’s ice load. This paper analyzed the dynamic characteristics of the tensional force for ice accumulated OHLs through both the on-site experiment and the finite element method (FEM). The correlation between the instantaneous wind speed, the thickness of the accumulated ice and the dynamic tensional force, the aerodynamic resistance coefficient of the conductor, is investigated. It is found that the axial dynamic tension at the end of the iced conductor is approximately proportional to the square of the instantaneous wind speed. The higher the wind speed, the larger the difference between the static tension and the maximum dynamic tension calculated using the 10-min average wind speed. Under the conditions of the example in this article (crescent-shaped icing), when the average wind speed is 20 m/s, the ratio of the difference to static tension is 11.19%. These conclusions are verified with the computational fluid dynamic (CFD) simulation, the same correlation is identified in comparison with the experiments. Due to the fact that the magnitudes of tensional force and vibration are determined by the instantaneous wind speed, significant error exists within traditional calculation methods where average wind speed is used instead.

[Display omitted] • CrCoNiSi 0.3 MEA exhibits excellent cryogenic mechanical properties upon both quasi-static and dynamic tension, exceeding most cryogenic high strength-ductility alloys. • The SFE is theoretically and experimentally proved to be decreased and promotes massive thicker HCP transition at cryogenic temperature. • The coupling effect of strain rate and temperature causes localized plastic deformation and inhibits HCP transition in current MEA. • It is proposed that high strain rate and improved SFE due to adiabatic heating is a competitive relationship. The CrCoNiSi 0.3 MEA exhibits excellent cryogenic mechanical properties upon both quasi-static and dynamic tension. Under quasi-static tension at cryogenic temperature, the engineering yield and ultimate tensile strengths (UTS) reach 980 MPa and 1800 MPa, respectively, with notable ductility (62 %). The product of UTS and total elongation (TE) is 111.6 GPa %, surpassing most cryogenic high strength-ductility alloys. The significant mechanical strength enhancement is attributed to the denser deformation twins (DTs), multiple twinning, and extensive face-centered-cubic to hexagonal-close-packed (HCP) phase transitions, resulting in a high work hardening capacity. Upon dynamic tension at cryogenic temperature, the strength and strain hardening are further improved, which originates from the thickening DTs and HCP sequence and localized plastic deformation. The effects of temperature and strain rate on phase transition are studied. It is proposed that there is a competing relationship between high strain rate and increased stacking fault energy (SFE) due to temperature rise. The coupling effect of cryogenic temperature and high strain rate inhibits phase transition due to the deformation inhomogeneity in CrCoNiSi 0.3 MEA. The findings make a valuable contribution to understand the influence of temperature and strain rate on the mechanism of FCC-to-HCP phase transition. [ABSTRACT FROM AUTHOR]

Some rock discontinuities, such as bedding planes, incipient and healed joints, can sustain significant tension. Rock masses are often subjected to dynamic loadings. However, the ways in which dynamic tension affects the properties of rock discontinuities remain poorly understood. To investigate the tensile response of rock discontinuities under high strain rates, direct tension tests using the split Hopkinson tension bar were conducted on natural limestones with discontinuities including stylolitic joints and mineral healed joints. The results demonstrate that the dynamic tensile strengths of these joints increase with increasing strain rate, and a nonlinear empirical relationship is proposed to capture these effects. In addition, the dynamic tensile stress sustained by the discontinuity shows a nonlinear relationship with its opening (i.e., displacement of the discontinuity under tension). The critical joint opening increases almost linearly with increasing strain rates. The findings of this study can enhance the understanding of the behavior of rock discontinuities under dynamic tension, and facilitate dynamic and seismic analyses for various rock engineering problems. Highlights: The split Hopkinson tension tests were conducted on rock discontinuity. Rock discontinuity deforms nonlinearly under dynamic direct tension. The dynamic direct tensile strength of rock discontinuity exhibits an obvious strain rate effect. [ABSTRACT FROM AUTHOR]

This research proposes a mooring system for an ocean current generator that is working under the impact of typhoon waves. The turbine and the platform are kept stable at a designed water depth to ensure that the generator remains undamaged and continuously generates electricity under excessive water pressure. In this design, the turbine generator is mounted in front of the floating platform by ropes and withstands the force of ocean currents, while the platform is anchored to the deep seabed with lightweight, high-strength PE ropes. In addition, two pontoons are used to connect the generator and the platform with ropes. When the balance is reached, the depth of the generator and the depth of the platform's dive can be determined by the length of the ropes. In this study, typhoon irregular wave is represented by the Jonswap wave spectrum. The irregular wave is simulated by six regular waves. The equation of motion of the mooring system is derived. The theoretical solution of the dynamic system is presented to determine the dynamic displacements of the platform, pontoon, turbine and the dynamic tensions of the ropes. The dynamic tensions of the ropes increase with the cross-sectional area of pontoon. The natural frequency of the mooring system depends on the parameters, including the mases of elements, the lengths of ropes and the cross-sectional area of pontoons. In the proposed mooring configuration, the dynamic tension of the rope is far less than the breaking strength of the rope; thus, the ocean turbine is stable, and no water that flows through will be disturbed by the floating platform. [ABSTRACT FROM AUTHOR]

A numerical model considering the seabed friction is developed to investigate the dynamic behavior of anchor cable in this paper. In the model, the anchor cable was divided into hanging and lying parts. The governing equations of hanging and lying anchor cables were established respectively based on finite difference method and coupled according to the boundary conditions. The coupled equations of anchor cable were solved by Newton iteration and the static anchor cable parameters used for the initial values were confirmed by double bisection method. To illustrate the reasonability and validity of the model, several simulations of vessel sway in wind with different time and space step sizes and different seabed friction coefficients were presented. The simulation results show that anchor cable snap load is 3–5 times of average tension, the variation of anchor cable bearing is 2 times of ship heading, and the sway amplitude of the ship's center of gravity is about one times of ship length. Compared with the experimental data, the model and algorithm in this paper can successfully provide the realistic prediction of the dynamic tension and configuration of anchor cable, and can be used as a reference for anchoring operation. Farther, this paper found out that the normal seabed friction coefficient has considerable impact on the cable tension. [ABSTRACT FROM AUTHOR]

In this study, we formulate a mechanical model of spall fracture of copper, which describes both solid and molten states. The model is verified, and its parameters are found based on the data of molecular dynamics simulations of this process under ultrahigh strain rate of tension, leading to the formation of multiple pores within the considered volume element. A machine-learning-type Bayesian algorithm is used to identify the optimal parameters of the model. We also analyze the influence of the initial size distribution of pores or non-wettable inclusions in copper on the strain rate dependence of its spall strength and show that these initial heterogeneities explain the existing experimental data for moderate strain rates. This investigation promotes the development of atomistically-based machine learning approaches to description of the strength properties of metals and deepens the understanding of the spall fracture process.

In this study, the Fe 40 Mn 20 Cr 20 Ni 20 HEA is successfully prepared, and the deformation mechanism and microstructure evolution upon dynamic tension are investigated. The alloy achieves excellent strength-ductility synergies and extraordinary work-hardening capabilities under conditions of decreasing the temperature or increasing the strain rate. After cold rolling and annealing, the Fe 40 Mn 20 Cr 20 Ni 20 HEA exhibited apparent secondary work hardening during dynamic tension (the temperature is 298 K and the strain rate is ∼1400 s−1). The yield strength and ultimate tensile strength increased from ∼416 to ∼555 MPa and from ∼742 to higher than 950 MPa, respectively. At the same time, the plasticity is increased. This improvement is similar to that at cryogenic temperature and quasi-static tension (the temperature is 77 K and the strain rate is ∼10−3 s−1). The above two cases have a different deformation mechanism. The activation and evolution of the deformation mechanism under dynamic loading at room temperature with increasing strain are determined through dynamic interruption experiments. Deformation mechanisms such as dislocations, nano-twins, stacking faults & deformation twin networks, precipitated phases, and possibly 9R phases undergo evolutions with increasing plastic deformation. Their extensive interactions are the dominant reasons for the improved mechanical performance, which is rarely identified under quasi-static deformation. The σ phase plays a crucial role during the plastic deformation of the alloy at high strain rates, delaying the onset of necking together with deformation twins. [ABSTRACT FROM AUTHOR]

In this work, we systematically investigated mechanical behaviors and deformation mechanisms of MP159 superalloy over wide strain rate range (10−4/s – 103/s). The results show that when the strain rate increases from 10−4/s to 1500/s, the yield strength of the current alloy is increased from ∼850 MPa to ∼1155 MPa, and the elongation remains around 30 %, exhibiting an extraordinary strength-ductility synergy and remarkable strain-hardening capacity. Furthermore, the plastic deformation mechanism performs a transition from stacking faults (SFs) at low strain rates to a large number of twinning at high strain rates. The MP159 alloy exhibited excellent mechanical properties at high strain rates, which stem from the nanotwins and twin-SF interactions. This study reveals the plastic deformation mechanisms of MP159 superalloy under dynamic loading, providing feasible suggestions for the selection and design of structural materials in extreme environments. • The MP159 superalloy possesses superior synergistic behaviors over wide strain rate range (10−4/s – 103/s). • Multiple strengthening mechanisms facilitate extraordinary strain-hardening capacity. • The contribution of the separation strengthening is 449 MPa caused by the fine and dispersed L1 2 particles in the matrix. • Stacking fault energy is approximately calculated as 21.63 mJ/m2 from thermodynamic. [ABSTRACT FROM AUTHOR]

The use of industrial by-products, e.g., fly ash, slag, as complete replacement of Portland cement to make alkali-activated concrete (AAC) has become a hot topic due to the contribution to sustainability in construction industry. AAC has comparable compressive strength compared to the ordinary Portland cement concrete (OPC) and has many advantages, such as excellent durability and corrosion resistance. However, similar to OPC, AACmaterial still has certain shortcomings such as brittleness, low tensile strength, and poor impact resistance, which can be improved by incorporating fibers in the matrix. This paper considers the basalt fiber-reinforced alkali-activated concrete (BFRAAC), and explores the dynamic compressive and tensile strengths through a series of impact tests. The test results show that the dynamic strength of BFRAAC exhibits significant strain rate effect, that is, the material strength increases with the strain rate. Compared to the compressive strength of the material, the strain rate sensitivity of its tensile strength is more marked. Based on the test results, empirical formulas describing the relation between dynamic strength and strain rate of BFRAAC are proposed.

This research proposes a mooring system for an ocean current generator that is working under the impact of typhoon waves. The turbine and the platform are kept stable at a designed water depth to ensure that the generator remains undamaged and continuously generates electricity under excessive water pressure. In this design, the turbine generator is mounted in front of the floating platform by ropes and withstands the force of ocean currents, while the platform is anchored to the deep seabed with lightweight, high-strength PE ropes. In addition, two pontoons are used to connect the generator and the platform with ropes. When the balance is reached, the depth of the generator and the depth of the platform’s dive can be determined by the length of the ropes. In this study, typhoon irregular wave is represented by the Jonswap wave spectrum. The irregular wave is simulated by six regular waves. The equation of motion of the mooring system is derived. The theoretical solution of the dynamic system is presented to determine the dynamic displacements of the platform, pontoon, turbine and the dynamic tensions of the ropes. The dynamic tensions of the ropes increase with the cross-sectional area of pontoon. The natural frequency of the mooring system depends on the parameters, including the mases of elements, the lengths of ropes and the cross-sectional area of pontoons. In the proposed mooring configuration, the dynamic tension of the rope is far less than the breaking strength of the rope; thus, the ocean turbine is stable, and no water that flows through will be disturbed by the floating platform.

An overhead transmission line system is a typical wind-sensitive structure with high flexibility, light weight, and low structural damping. Wind-induced dynamic reaction of the transmission line system is a determining factor in structural design of the supporting tower. In this study, we employ a closed-form solution and a series of wind tunnel tests to investigate three-dimensional dynamic reaction of transmission lines bundled with an insulator in three types, including I-type, V-type, and strain-type. The response comprises the background and resonant component. It is found that the background component constitutes a major part of the response, and the resonant component is closely related to the first symmetric out-of-plane mode. Furthermore, the closed-form solution is discussed and validated by the aeroelastic wind tunnel testing in the frequency domain. Based on the experimental data, this study provides a theoretical method for predicting wind-induced loads on transmission tower structures. [ABSTRACT FROM AUTHOR]

For the galloping of iced transmission lines, the influences of two simplified methods of dynamic tension on the galloping characteristics of transmission lines are investigated. Based on the variational principle for Hamiltonian, the partial differential equation of galloping of iced transmission lines is derived, then it is transformed into ordinary differential equation by Galerkin method. Two different simplified methods are used to convert the partial differential equation into ordinary differential equation. One is to average the dynamic tension over the span length, then Galerkin method is used. The other is that Galerkin method is used to convert the partial differential equation into ordinary differential equation directly. Firstly, the influences of two simplified methods on coefficients of ordinary differential galloping equation are studied. Second, the influences of the bending stiffness on the first-order frequency have been researched. In addition, the average method of two degrees of freedom (DOFs) is proposed and the galloping characteristics of iced transmission lines are studied by using multiscale method and average method, then the results are compared with that obtained by using numerical method. The parameters analysis shows that the two simplified methods of dynamic tension have significant influences on the coefficients of the two DOFs ordinary differential equation. By comparing the coefficients of galloping equation obtained by the two simplified methods of dynamic tension, it can find that with the increasing of tension and span length, the influences of bending stiffness on in-plane and out-of-plane natural frequency becomes smaller and smaller. The results of multiscale method and average method both show that the two simplified methods of dynamic tension have certain influences on the frequency, phase and amplitude of galloping of iced transmission lines. The conclusions obtained by this paper would promote the perfection of theoretical modeling about iced transmission lines, and could also give some references to practical engineering. [ABSTRACT FROM AUTHOR]

In this paper, the use of the virtual fields method for the identification of a strongly asymmetric compression–tension response of rock‐like materials under dynamic tensile loading is investigated. The photomechanical spalling set‐up is used, which induces an indirect tensile load in a non‐balanced sample, and the inertial component of the test is directly related to the measured dynamic stress with no previous assumption on the material behaviour. This experimental method provides a direct route to identifying the material asymmetric constitutive response in compression and tension under a uniaxial stress state as well as the material non‐linear response after tensile strength is reached. To validate this approach, the entire measurement chain for the case of a post‐peak response is investigated through simulated experiments that incorporate a damage model and synthetic grid images. Finally, the method is applied to the case of granite rock, namely, a Bohus granite, as to directly measure the material asymmetric compression–tension and the softening response after peak tensile stress. [ABSTRACT FROM AUTHOR]

The uniaxial tensile mechanical properties of D1 wheel steel and U71MnG rail steel were investigated experimentally at a wide range of strain rates from 0.0001 to 100 s−1. Influence of the strain rate on stress–strain response, ductility, fracture morphology and energy absorption was analyzed and discussed, respectively. Both D1 wheel steel and U71MnG rail steel are demonstrated to be strain rate sensitive, and D1 wheel steel specimens generally exhibit a larger elongation and a better ductility than U71MnG rail steel specimens at each strain rate. The fracture mechanism of D1 wheel steel is a ductile fracture at lower strain rates and quasi-ductile fracture at higher strain rates, while U71MnG rail steel tends to a quasi-ductile fracture at lower strain rates and a brittle fracture at higher strain rates. The specific energy absorption values of D1 wheel steel and U71MnG rail steel increase with the increase in true strain and elevated strain rate. Finally, the Johnson–Cook model is adopted to predict the stress–strain response of wheel/rail steels studied, and a better agreement is found. [ABSTRACT FROM AUTHOR]

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Engineered cementitious composites (ECC) showed promising potentials in structural protection against quasi-static and dynamic tension due to their superior tensile ductility. To facilitate its application as reinforcement layer of existing reinforced concrete structures, the thickness effect of ECC in terms of ultimate tensile strength and tensile strain capacity was experimentally investigated. The influence of the strain rate effect, the specimen thickness, and their coupling were examined and discussed in detail. It was found that ECC exhibited significant strain rate effect when subjected to uni-axial tension of strain rate ranging from 10−5 /s to 100 /s. Compared to those obtained from standard specimens under quasi-static loading, the ultimate tensile strength increased by 338%, and the tensile strain capacity decreased by 62%, respectively, under strain rate 100 /s. Particularly, the strain rate effect was observed more remarkable under relatively higher strain rates, i.e. from 10 /s to 100 /s. Moreover, subjected to a certain tensile loading rate, both the ultimate tensile strength and tensile strain capacity decreased with increasing specimen thickness. The degradation of strength was relatively slower under a higher strain rate, i.e. 50 /s and 100 /s, than under a lower strain rate. To facilitate the design of the ECC reinforcement layer, a formula was proposed capable of predicting the ECC ultimate tensile strength simultaneously considering both the strain rate effect and specimen thickness effect. • ECC exhibits significant strain rate effect under uni-axial dynamic tension. • Ultimate tensile strength and tensile strain capacity decrease with thickness. • The increased constraint in thickness direction degrades ECC tensile property. • Proposes a formula for ECC tensile strength considering strain rate and thickness. [ABSTRACT FROM AUTHOR]

For the automobile engine timing belt system,by using the AVL-Excite Timing Drive to carry out a periodic dynamic simulation analysis. The variation law of the load when the loose and tight of belt contact with pulley is studied. The results show that dynamic tension and its fluctuation of the belt between the idler and the exhaust camshaft pulley are the largest. And the peak mechanism of the belt toot load is studied. Based on the analysis of the vibration performance of the main vibration source,the system parameters are optimized. The results show that the vibration of the main vibration source is reduced and the transmission error of is reduced.

The nonlinear dynamics of a horizontal, initially taut, elastic string, subjected to a traveling point-mass driven by an assigned time-dependent force, is studied. A kinematically exact nonlinear model for the free boundary problem, previously derived by the authors through a variational procedure, is resumed. The model is developed in the framework of a mixed formulations, ruling the time-evolution of the configuration variables and the reactive contact forces. The model is then consistently simplified, via a static condensation of the horizontal displacements of the string. Differently from most of papers in literature, here the dynamic tension is accounted in the equations of motion, as a nonlinear effect. The simplified equations are discretized by the Galerkin method, which leads to a set of ordinary differential equations in the amplitudes of the trial functions and in the unknown abscissa of the point-mass. As a further simplified model, the mass of the string is neglected, and a set of two ordinary differential equations in the coordinates of the point-mass is derived. Numerical results are obtained, aimed at exploring the influence of the mass of the string and of the dynamic tension. The focus is on analyzing peculiar 'back and forth' motions of the point-mass, when this is driven by small or even zero forces. [ABSTRACT FROM AUTHOR]

The development of wind energy alleviates the issue of energy shortage at present, but the development technology of offshore wind energy is not mature, so the research on the performance of offshore wind turbine system is the key to develop clean wind energy. Based on the theory of time-domain coupling analysis, this paper studies the hydrodynamic performance of offshore wind turbine under environmental load, and probes into the hydrodynamic performance of offshore wind turbine system. It is found that the offshore wind turbine will stop operation when the wind speed is greater than 28m/s, and the calculation results show that the offshore wind turbine in this study meets the requirements of the specification for the stability of large inclination angle. The environmental load determines the initial offset of the offshore wind turbine system, in which the mean wave drift force is much smaller than the offshore wind force. With the increase of wind speed, the wind turbine system can automatically adjust the pitch of the blades. When the wind speed exceeds the limit wind speed, the wind turbine stops working. When operating at rated power, wind turbine occurs under the action of wind force will have an offset, which is large. The offset of wind force and wind turbine decreases with the increase of wind speed. This study provides a theoretical basis for the application of offshore wind energy development system. [ABSTRACT FROM AUTHOR]

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A Fe–0.20C–1.49Mn1.52Si–0.58Cr–0.05Nb low-carbon steel was treated by a novel quenching-partitioning-tempering (Q-P-T) process and the traditional quenching and tempering (Q&T) process for comparison, respectively. X-ray diffraction results indicate that there is 10.8% volume fraction of retained austenite (VRA) in the Q-P-T martensitic steel, while no diffraction peak of retained austenite was detected in Q&T martensitic steel. The Q-P-T steel and the Q&T steel were subjected to a dynamic tensile test at a strain rate of 500 s−1 and a quasi-static tensile test at a strain rate of 5.6 × 10−4 s−1, respectively. The results indicate that the high strain rate in the dynamic tension raises the strength of the Q-P-T and Q&T steels compared with their quasi-static tensions owing to strain rate hardening effect, however, the elongation of Q-P-T steel decreases slightly, while the elongation of Q&T steel evidently increases. This difference is attributed that the existence of the dislocation absorption by the retained austenite (DARA) effect in quasi-static tension is suppressed under dynamic tensile loading so that the enhancement influence of DARA effect on ductility cannot be effectively compensated by the adiabatic softening of the martensitic matrix, which leads to a slight decrease in the elongation of the Q-P-T steel in dynamic tension compared with that in the quasi-static tension. While Q&T steel has no DARA effect in quasi-static tension due to no retained austenite, and thus the adiabatic softening of the martensitic matrix increases the ductility of Q&T steel in dynamic tension. [ABSTRACT FROM AUTHOR]

In this paper we investigate flow localization in viscoplastic slender bars subjected to dynamic tension. We explore loading rates above the critical impact velocity: the wave initiated in the impacted end by the applied velocity is the trigger for the localization of plastic deformation. The problem has been addressed using two kinds of numerical simulations: (1) one-dimensional finite difference calculations and (2) axisymmetric finite element computations. The latter calculations have been used to validate the capacity of the finite difference model to describe plastic flow localization at high impact velocities. The finite difference model, which highlights due to its simplicity, allows to obtain insights into the role played by the strain rate and temperature sensitivities of the material in the process of dynamic flow localization. Specifically, we have shown that viscosity can stabilize the material behavior to the point of preventing the appearance of the critical impact velocity. This is a key outcome of our investigation, which, to the best of the authors' knowledge, has not been previously reported in the literature. [ABSTRACT FROM AUTHOR]

This study presents a nonlinear analysis framework of three-dimensional galloping of multi-span ice-accreted transmission line conductors suspended by insulators. The vertical, lateral and torsional conductor displacements are described by modal displacements with mode shapes of single span conductors, and the insulators are modeled as pendulums. The aerodynamic forces on the conductor are modeled using quasi-steady theory. The linear equations of motion with respect to the static equilibrium are also derived. The analysis framework is applied to two- and three-span four-bundled ice-accreted transmission conductors with complex eigenvalue analysis and response history analysis. A harmonic balance approach is also proposed for a direct calculation of steady-state galloping response. The accuracy and efficiency of the proposed frameworks are verified using the results estimated from a finite element model. The similarities and differences of galloping characteristics, i.e., initiation condition, steady-state amplitude, dynamic tension, between single- and multi-span conductors are investigated. The role of suspension insulators on multi-span galloping is clarified. The longitudinal motions of insulators result in reduced vertical modal frequencies of conductor, thus lead to different galloping characters. The galloping of multi-span conductors with closely spaced modal frequencies can be initiated from multiple modal branches with a beating phenomenon. • A nonlinear analysis framework of wind-induced three-dimensional galloping of multi-span ice-accreted transmission line conductors suspended by insulators is presented. • The vertical, lateral and torsional conductor displacements are described by modal displacements, and the insulators are modeled as pendulums. • The proposed analysis framework is applied to predict the galloping responses of two- and three-span four-bundled ice-accreted transmission conductors through complex eigenvalue analysis and response history analysis. • A harmonic balance approach is also proposed for direct calculation of steady-state galloping amplitudes and phase differences. • The galloping response is also calculated using finite element model to verify the accuracy and efficiency of the proposed frameworks. • The similarities and differences of galloping characteristics, i.e., initiation condition, steady-state amplitude, dynamic tension, between single- and multi-span conductors are investigated. [ABSTRACT FROM AUTHOR]

To bolster the safety and efficacy of blasting and impact drilling for underground works in composite rock strata, the dynamic tension of composite rocks requires thorough examination. Given the challenges of composite rock sampling, cement mortars with varying mix ratios are utilized to create composite rock-like test blocks. These blocks are composed of two different strength materials, further processed into differently sized experimental samples as required. Using a split Hopkinson pressure bar (SHPB) test device, we conducted dynamic Brazilian splitting tests at varying incident angles α (the angle between the incident wave direction and the bedding plane) and strain rates on these composite rock-like samples. The modes of crack propagation in some samples were recorded with a high-speed camera. Laboratory tests and PFC2D simulation were used to analyze the dynamic tensile mechanical properties and failure mechanisms of composite rock samples. Findings indicate the dynamic tensile strength of a composite rock sample is governed by the bedding plane inclination angle. As the incident angle rises from 0° to 90°, the dynamic tensile strength of the composite rock sample first decreases, then increases, consistently reaching a minimum value at α = 30°. The damage model of composite rock samples is also influenced by the dip angle of the bedding planes. At α = 0°, the composite rock sample exhibits through-cracks along the incident wave direction and splitting tensile damage is observed. As α increases, the failure mode gradually transitions from splitting tensile damage to a combination of tensile and shear slip damage along the bedding. Tensile damage always manifests in materials of lower strength. When α surpasses 45°, the failure mode reverts from combined damage to splitting tensile damage. Cross-sectional tensile stress clouds generated by PFC software demonstrate that the tensile stress contours at the specimen's center are elliptically distributed, with the ellipse's long axis nearly parallel to the bedding plane. [ABSTRACT FROM AUTHOR]

This work investigates the mechanism of nanoscale helium (He) bubbles influencing the dynamic tensile response of quasi two-dimensional (2D) polycrystalline copper (Cu), based on molecular dynamics simulations. The dynamic fracture behaviors are explored under two different loading conditions (uniaxial tensile loading and shock loading). For uniaxial tensile loading, it's found the effect of He bubble on the tensile strength gets weaker with the increasing strain rate. A strain rate-dependent fracture mechanism that transforms from the growth and coalescence of He bubbles to the cleavage fracture of grain boundaries (GBs) as the strain rate increases is investigated. Under shock loading, the effect of He bubble on reducing the spall strength of polycrystalline Cu is more significant at lower impact velocities and will disappear as the impact velocity increases higher. The mechanism of spall damage is investigated by comparing the effect of He bubbles, voids and GBs under different impact velocities. Additionally, the dynamic response under the above two loading conditions is compared. The results indicate that the effect of He bubble distribution on the strength is more significant under shock loading than uniaxial tensile loading. [Display omitted] • The dynamic tensile fracture behavior of polycrystalline copper with He bubble distributed in grain boundaries and grain interiors is studied under uniaxial tensile loading and shock loading. • The effect of He bubble on reducing the tensile strength gets weaker as the strain rate increases. • A strain rate-dependent fracture mechanism that transforms from the growth and coalescence of He bubbles to the cleavage fracture of GBs as the strain rate increases is investigated. • The effect of He bubble distribution on the strength is more significant under shock loading than uniaxial tensile loading. [ABSTRACT FROM AUTHOR]

Abstract The grain size dependence of the strain rate sensitivity (SRS) of copper were systematically investigated via tensile deformation at strain rates of ~10−4 s−1 and ~103 s−1. In contrast to the general perception that SRS increases with decreasing grain size at low strain rates in FCC metals, the SRS increases monotonously with grain size under deformation at high strain-rates of ~103 s−1. Analytical formulation based on the Nemat-Nasser-Li (NNL) and Modified-Rusinek-Klepaczko (MRK) models was established to reveal the essential dependence of SRS on grain size, at the change of strain rate: that the opposite dependence of SRS on grain size at low vs high strain rates can be attributed to the transformation of the dominant rate-controlling deformation mechanism from thermal activation at low strain rates to viscous drag at high strain rates. It is demonstrated that the thermal activation component of SRS, m * , which is nearly strain rate independent, increases with reducing grain size; while the viscous drag component of SRS, m v s , which is enhanced significantly at high strain rates, decreases with reducing grain size. Microstructural observation based on local misorientation characterization and statistics confirms that the viscous-drag dominates at high strain-rate deformation, and becomes progressively influential as grain size increases. This unveils the essence of viscous drag in the opposite grain size dependence of SRS at low vs high strain rates. [ABSTRACT FROM AUTHOR]

Abstract In-situ La 74 Al 14 Cu 6 Ni 6 metallic glass matrix composites exhibit distinct work-hardening capability under quasi-static tension, attributed to the profuse deformation twins. Under dynamic tension, 2% tensile ductility and significant negative strain rate sensitivity (SRS) of the yielding strength was revealed. A modified Cooperative-Shear model was employed to explain the negative SRS behavior. [ABSTRACT FROM AUTHOR]

Reliable dynamic mechanical properties of high nitrogen steels are necessary for the design and assessment of armor structures subject to impact and blast. A series of experiments, based on Hopkinson bar techniques, were conducted and described in this study. The dynamic compression, tensile and shear properties of high nitrogen steel had been tested, and the stress-strain curves under high strain rates were obtained. The results have been showed as follows: High nitrogen steel has a remarkable strain rate strengthening effect. Compared to the static curves, the constitutive curves of dynamic tension and compression move upper. The dynamic compressive yield strength of high nitrogen steel increases first and then decreases with the increase of strain rate, and the yield strength varies in the range of 1465-1549MPa within the range of 1147e2042 s-1 strain rate; The tensile strength of high nitrogen steel increases with the increase of strain rate. When the strain rate is greater than 1341 s-1, the tensile strength will not increase and the curve tends to be gentle. The pure shear yield strength of the high nitrogen steel is above 800 MPa. [ABSTRACT FROM AUTHOR]

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In this paper we assess, using finite element calculations performed with ABAQUS/Explicit, the influence of porosity in the development of necking instabilities in flat metallic samples subjected to dynamic tension. The mechanical behaviour of the material is described with the Gurson–Tvergaard–Needleman [6, 22, 23] constitutive model pre-implemented in the finite element code. The novelty of our methodology is that we have included in the gauge of the specimen various non-uniform distributions of initial porosity which, in all cases, keep constant the average porosity in the whole sample. This has been carried out assigning random values of initial porosity (within specified bounds) to some nodes and zero to the others. Therefore, the larger the percentage of nodes with non-zero initial porosity, the smaller their initial value of porosity. The goal is to provide an idealized modelling of the distributions of void nucleating particles which in many structural metals nucleate early in the deformation process and lead to material porosity. The key point of this paper is that, following this methodology, we reproduce the experimentally-observed asymmetric-growth of the pair of necking bands which define the localization process in flat tensile samples subjected to dynamic loading [25]. [ABSTRACT FROM AUTHOR]