Mechanical Dynamic Characteristics Research Articles

Off-axis mechanical behavior and dynamic characteristics of UHMWPE composite laminates

An understanding of the off-axis mechanical behavior and failure mechanisms of ultra-high molecular weight polyethylene (UHMWPE) cross-ply laminates subjected to quasi-static and dynamic loadings is developed, with focus on the influence of off-axis angle and strain rate. For off-axis tension, UHMWPE laminates exhibit polymer shear response characteristics. An orientation-hardening phenomenon is captured, as fiber rotation leads to local increment of load capacity along the loading orientation. The failure strength presents an evidentially descending trend with off-axis angle from 0° to 45°. A non-monotonic variation of strength with strain rate is further observed: increasing with strain rate up to 500 s−1 but decreasing above, which is attributed to failure mode switching from plastic failure to brittle failure. The Tsai-Wu failure criterion, on homogenized cross-ply laminae, is experimentally modified with rate dependence. Further investigation on detailed information of the unidirectional properties should be conducted with the backing-out scheme to establish unidirectional failure criterion.

Rate-dependent constitutive model and dynamic response of composite laminates for laser-induced delamination

Laser Bond Inspection is a new technology to quantitatively evaluate the interfacial strength in composite materials. Constructing an effective constitutive model, especially considering strain rate effects, is a critical factor for this technology. In this work, a reliable rate-dependent constitutive model of composite laminates for laser-induced delamination is established. Based on an orthotropic constitutive relationship, we introduce dynamic increase factors in different directions to adjust constitutive parameters. The dynamic increase factors are obtained through an adaptive matching model based on deep transfer learning. Then we effectively determine material rate-dependent constitutive relationship and ultimately achieve numerical simulation of laser-shocked composite laminates. Combining empirical testing with numerical simulation results, we investigate the dynamic response law of composite laminates under different laser parameters. The findings indicate that the rate-dependent constitutive model, effectively describes the mechanical behavior and dynamic response characteristics of composite laminates under laser shock. The dynamic response characteristics are determined by laser energy, pulse width, and spot size. Both laser energy and spot size affect the range of delamination, and pulse width mainly affects the depth of delamination.

The 2022 Mw 6.6 Menyuan earthquake: An early-terminated runaway rupture by the complex fault geometry

The 2022 Mw 6.6 Menyuan earthquake, which caused unexpectedly large surface offsets (about 2.6–3.5 m) relative to the moment magnitude of this event, is one of the best-recorded strike-slip events in the northeastern Tibetan plateau. Although previous studies have revealed many kinematic features of this event, the mechanism and rupture dynamic characteristics underlying unexpectedly large surface dislocations need to be clarified. In this study, based on the grid search method, we conducted 61 dynamic rupture simulations considering terrain relief to screen out a preferred dynamic model that fits the geodetic, seismic, and geological observations well. The results show that the average stress drop of the nucleation part is relatively high (11 MPa), which could provide high initial rupture energy and give this event a chance to develop into a large earthquake. However, the rupture propagating eastward is slowed and terminated by two consecutive fault bends of about 10° each, and the westward propagating one might concentrate at a shallow depth (< 3 km) on the south secondary fault after it jumps over the stepover. These results imply that the complex fault geometry (the fault bend and stepover) might terminate the rupture early so that the observed magnitude of this event (Mw 6.6) is smaller than the estimated magnitude (Mw 7.1–7.2) based on the surface offsets. Our study again shows that, due to advances in computational power and observations (coverage and quality), physics-based dynamic rupture simulations have entered an era where it is possible to fit the observed data well, which is vital for further understanding the mechanisms of earthquakes.

Research of the Meshing Performance of New Concave-convex Ball Teeth

Aiming at the limitations of the existing hydraulic pumps, a new type of bidirectional water-hydraulic internal ball gear pump using concave-convex ball teeth meshing to transfer power is proposed. In this paper, the principle of internal gear pump is utilized to establish the model of internal ball gear pump, and its mechanical properties and dynamic meshing characteristics are numerically investigated by using the finite element method. The results show that (a) the concave-convex ball gears run smoothly without any interference, and (b) increasing the number of gear rows can effectively reduce the maximum stress and meshing impact under a given load and speed. This study provides a basis for the development of high-performance ball gear pumps.

Metamaterial design and continuously adjustable mechanical properties based on novel planetary gear trains

Mechanical metamaterials have been pursuing as valuable properties attribute to the unique internal architecture, but are generally limited to the predetermined properties after manufacturing, resulting in the inability to continuously change the properties during application. Aiming for the continuously adjustable property under environments with high reliability requirements, this research developed two types of mechanical metamaterials based on planetary gear train. The principle of continuously adjustable mechanical property and dynamic characteristics of metamaterial based on planetary gear train is researched though a theoretical model of curved beam under varying radial load. Further, mechanical metamaterials based on double-layers planetary gear (DLPG) train and Ravigneaux planetary gear (RPG) train are designed. The compressive elastic modulus, shear modulus, and amplitude-frequency response are calculated and investigated with finite element simulation. The results, with an adjustable range respectively within 9–15 times and 2–3 times in compressive elastic modulus of and shear modulus, show a good agreement between the theoretical and simulated results, and illustrate the adjustability and reliability of the mechanical metamaterials based on planetary gear train. Finally, the potential configurations and applications of metamaterial based on planetary gear train are presented.

Analysis of mesoscopic mechanical dynamic characteristics of ballast bed with under sleeper pads

The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads (USPs) was studied. The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scanning techniques, and the 3D dynamic model of the rail–sleeper–ballast bed was constructed using the coupled discrete element method–multi-flexible-body dynamics (DEM–MFBD) approach. We analyse the meso-mechanical dynamics of the ballast bed with USPs under dynamic load on a train and verify the correctness of the model in laboratory tests. It is shown that the deformation of the USPs increases the contact area between the sleeper and the ballast particles, and subsequently the number of contacts between them. As the depth of the granular ballast bed increases, the contact area becomes larger, and the contact force between the ballast particles gradually decreases. Under the action of the elastic USPs, the contact forces between ballast particles are reduced and the overall vibration level of the ballast bed can be reduced. The settlement of the granular ballast bed occurs mainly at the shallow position of the sleeper bottom, and the installation of the elastic USPs can be effective in reducing the stress on the ballast particles and the settlement of the ballast bed.

Investigation of mechanical properties and dynamic characteristics of OPEFB Fiber Composite

Composite materials is increasingly experiencing an increa- sing trend, the manufacture of composites currently uses a lot of natural fiber reinforcement, Oil Palm Empty Fruit Bunches (OPEFB) fiber is a fiber that comes from oil palm empty fruit bunches waste that grows a lot in Indonesia and has the potential to be used as reinforcement in the manufacture of composites. With natural fiber reinforcement. The manufacture of composites in this study varied the fiber volume fraction by 5%, 15%, and 25%. Many previous studies on composite materials have focused on studying the physical and mechanical properties of composites. Even though damage to a structure or material is not only caused by static loads but also by dynamic loads. Vibration is a dynamic load experienced by material or structure, so it is necessary to determine the dynamic character of composite materials, one of the dynamic characteristics of materials is their natural frequency, the determination of the natural frequency in this study was carried out by using the finite element method in the ANSYS software. The results of the analysis in the form of tensile strength values and modulus of elasticity were obtained from tensile testing and dynamic characters in the form of natural frequencies and vibration modes were obtained from the analysis modal simulation process. From the results of the tensile test, it was found that the composite with a variation of 15% OPEFB fiber volume had the highest tensile strength and modulus of elasticity, as well as the results of the analysis modal simulation, a composite with 15% OPPEFB fiber, had the highest natural frequency value among the other two variations.

Mesoscopic study on mechanical properties and dynamic damage characteristics of self-healing microcapsule

Mesoscopic study on mechanical properties and dynamic damage characteristics of self-healing microcapsule

Mechanical properties and dynamic multifractal characteristics of shale under anisotropic stress using AE technology

The mechanical properties and failure mechanism of shale under anisotropic stress is the key to evaluate the stability of wellbore. Meanwhile, the fracture instability process of shale needs to be characterized by the reasonable monitoring technology. This paper performs a series of uniaxial, biaxial and true triaxial loading tests on shale specimens. A monitoring technology, Acoustic emission (AE), is adopted to record the fracture process of shale. The effects of anisotropic stress on the mechanical behaviors of shale are analyzed. The evolution characteristics of AE event rate are applied to describe the fracture process of shale. The transition from AE quite period to AE active period effectively characterizes the macro-cracking process within shale specimens. The multifractal theory is adopted to analyze the dynamic multifractal characteristics and to quantitatively characterize the fracture instability process of shale. The distribution difference of multifractal parameters can be served as an early warning information for the stable and unstable macro-cracking within shale. The anisotropic stress evidently affects the failure mechanism of shale. The results of this study will be important to ensure the production efficiency of shale gas and the stability of drilling operation.

Start-up process optimization of pumped-storage unit with Tilt–Integral–Derivative controller

Focused on the hydraulic–mechanical coupled transient behaviors of the pumped-storage unit (PSU), this paper discusses the theoretical implementation and the parameter optimization of tilt–integral–derivative (TID) controller in turbine start-up processes. A novel learning backtracking search algorithm (LBSA) is adapted to optimize the control parameters, and a comprehensive index combining the relative deviation of the rotational speed and the relative deviation of the volute’s water pressure is designed as the objective function. A nonlinear mathematical model which can reflect hydraulic and mechanical dynamic characteristics of the pumped-storage governing system (PSGS) is established for the simulation of the transient period. Simulation experiments of two typical operating conditions are carried out under no-load condition. The simulation results show that the TID controller attaches significance to suppressing the amplitude of water hammer pressure and damping the hydraulic fluctuations. It will also restrain the trend of state trajectories oscillating back and forth in the unstable “S” shaped regions.

First-principles study on the effect of Ni addition on the stability of B2 Ti50Ru50 – a supercell approach

Shape memory alloys (SMA's) are a special kind of metal alloys with unique structural properties, such as shape memory effect (SME) and pseudo-elasticity (SE) that were well-observed in TiNi alloy, which commercially trades as Nitinol. This polymorphic crystal behaviour arose from the reversible phase transition between an ordered high-temperature B2 and low-temperature martensite phase (L10/B19/B19′). Due to the high ductility of Ru, this work employed a supercell approach to track the effect of nickel addition on highly stable B2-Ti50Ru50 with the intent to stimulate SME. Thermodynamic, mechanical, electronic structure and lattice dynamic characteristics were estimated using first-principles calculations. The phonons spectra of B2 Ti50Ru50 consisted of only positive frequencies, but the addition of Ni above 18.75 at. % resulted in positive and negative frequencies, indicative of a possible martensitic transformation, which is a strong character for SME.

Design of a New TBM Integrated Cutter System Based on Analysis of Mechanical Properties and Dynamic Characteristics

During the rock-breaking process, severe vibration frequently leads to cutter system failures. The traditional cutter system is complicated in structure, and the cutter-changing operation is highly dependent on the manual operation, resulting in a low construction efficiency and a high risk. Thus, this paper designed an integrated cutter system with a simple structure, which lays a theoretical foundation for popularizing the cutter-changing robot. In the statics performance experiment, we built an integrated cutter system finite element model, calculated the stress value under a nominal load; manufactured the scaled cutter system based on the similarity principle, obtained the measured stress value through the load experiment; and verified the accuracy of this cutter system’s finite element model. In the dynamics experiment, we calculated the cutter system and each components dynamic response based on the concentrated mass method and the Newmark method, obtained the measured vertical vibration displacement through a scaled loading experiment and verified the correctness of the vertical dynamics model, and set the real disc cutter linear cutting load as the external excitation to verify the feasibility of the new cutter system design scheme.

Mechanical Mechanism and Dynamic Characteristics of Barge–Whole Bridge Collision Behaviours

Collision between a moving ship and a bridge in inner rivers is a frequent occurrence that seriously endanger the safety of the bridge. Existing studies mostly address the action of a ship colliding with a bridge pier that is used as a substitution of the associated whole bridge. Such a simplification necessarily induces errors in reflecting the mechanical mechanism and dynamic characteristics of ship–whole bridge collisions. To circumvent this problem, the mechanical behavior of collision between a barge and a whole bridge was studied via elaborating a delicate barge–whole bridge collision simulation underpinned by impact mechanics and materials theories. The main contributions of this study are fourfold: (i) the entire process of the collision between the barge and a whole bridge was fully inspected; (ii) the progressive evolution of collision-induced damage in the bridge pier as well as in the barge was investigated; (iii) the effect of impact velocity, impact angle and barge mass on the collision behavior were elucidated, and (iv) the influences of the superstructure of the whole bridge on the peak value and temporal feature of the impact force, evolution of damage, and top displacement of the bridge pier were clarified. This study yielded more accurate, comprehensive, and reliable results on dynamics and damage evolution of collision in comparison with the outcome of a barge colliding a pier. These findings collectively reveal the mechanical mechanism and dynamic characteristics of collision, providing a scientific basis for developing post-collision damage assessment methods and anti-collision facilities.

Nonlinear dynamic characteristics analysis and adaptive avoid vortex-coordinated optimal control of hydropower units under grid connection

Hydropower units operate as the first option for renewable energy supply. The coupling characteristics of hydro-turbine governing system (HTGS), misaligned shafting (MSH), and power grid (PG) (HTGS-MSH-PG) have always been omitted. Meanwhile, the safety hazard from the draft tube vortex zone (DTVZ) and the difficulty of coordinating the ultra-low frequency oscillation (ULFO) and primary frequency regulation (PFR) performance of hydropower unit grid-connected operation have not been resolved. In this study, we aim to investigate the interaction mechanism and nonlinear dynamic characteristics of the HTGS-MSH-PG coupling system and determine the optimal control strategy for considering the DTVZ, ULFO, and PFR of hydropower units. First, a novel coupling model of HTGS-MSH-PG is established. Thereafter, the stability of the HTGS-PG coupling system is examined by employing the Hopf bifurcation theory, and the damping characteristics are obtained using the hydraulic damping model. The nonlinear dynamic behavior of misaligned distance, nonlinear vibration characteristics of MSH, and influence of MSH vibrations on HTGS and PG are revealed based on this model. Finally, an adaptive avoid vortex-coordinated optimize control strategy which considers the means to prevent a strong DTVZ and coordinate the ULFO and PFR performance of HTGS, MSH, and PG is proposed. NSGA-II is introduced to obtain the Pareto optimal solution set, and the optimal scheme is determined by the fuzzy satisfaction method. Moreover, the nonlinear dynamic characteristics of hydropower units under optimal control are revealed. The results demonstrate that the nonlinear dynamic characteristics of the HTGS-MSH-PG coupling system mainly include the quasi-periodic multi-frequency vibration of MSH and multi-frequency dynamic performance of HTGS and PG. The adaptive avoid vortex-coordinated optimal control strategy can effectively prevent a strong DTVZ, coordinate the ULFO and PFR performance of HTGS, MSH, and PG, and increase the satisfaction rate by 72.2%. These results lay a theoretical and technical foundation for the safe, stable, and optimal operation of hydropower units.

Study on dynamic characteristics of flexible feed system by mechanical parameters

The dynamic characteristics of CNC feed system are determined by the dynamic characteristics of mechanical drive and control parameters. The dynamic characteristics of transmission link are closely related to the mechanical characteristic parameters. The designer must find the matching control parameters by analyzing the law of mechanical characteristic parameters and dynamic characteristics. In this paper, the relationship between inertia ratio, resonant frequency and velocity loop control gain is analyzed by using the established three-inertia system model, and the parameters are input into the system model for simulation. It provides a method for the designers of CNC machine tools to adjust the internal control parameters, which has important theoretical and practical value.

Effect of manufacturing processes and multi‐walled carbon nanotube loading on mechanical and dynamic properties of glass fiber reinforced composites

AbstractAn effective manufacturing process and high‐performance composite structures are indispensable in the aerospace, automobile, and shipbuilding industries. The current study focuses on the combined effect of carbon nanotube (CNT) reinforcement and manufacturing methods such as co‐curing, co‐bonding, and secondary bonding (SB) on mechanical and free vibrational behavior of glass fiber reinforced plastic composite. Results affirmed that composite fabricated using co‐cure manufacturing method with 1 wt% CNT loading improved the tensile strength by 22.8%, 12.7% compared to co‐bonded and secondary bonded composites due to rougher surface formation over the fiber improved the adhesion between fiber and matrix. On the other hand, 0.25 wt% CNT added secondary bonded composite had the highest (398.19 MPa) flexural strength. The modal analysis asserted that 1 wt% CNT added co‐cured composite beam had the higher fundamental natural frequencies while higher wt% CNT loading enhanced the damping properties owing to higher interaction among fiber and matrix. The current study exposes that mechanical properties and free vibrational characteristics can be improved by selecting the right manufacturing technique and appropriate weight fractions of CNTs. The co‐cure manufacturing with 1 wt% of CNTs and SB with 0.25 wt% of CNTs provided the greatest enhancement to adhesively bonded composites' mechanical properties and dynamics characteristics.

Modeling and dynamics simulation of spur gear system incorporating the effect of lubrication condition and input shaft crack

PurposeThe paper is devoted to presenting a systematic investigation on the mechanical model and nonlinear dynamic characteristics of spur gear system with and without input shaft crack.Design/methodology/approachConsidering the backlash, load-distribution, time-varying meshing stiffness and sliding friction, the modelling of a 5DOF gear system is proposed. Likewise, stiffness and damping models under elastohydrodynamic lubrication are developed, and sliding friction between gear pair is also outlined. In particular, a cracked input shaft which affects the support stiffness is presented, and breathing crack in keyway is adopted. On this basis, the dynamic responses of a gear system with and without input shaft crack are examined using numerical method, and some classical response diagrams are given, illustrating the effect of the important parameters on the gear system.FindingsDynamic simulation demonstrates that there exist periodic, quasi-periodic and chaotic motions in the gear system, and rational speed of the gear pair has noteworthy effects on vibration characteristic. Besides, comparison between healthy and cracked condition of input shaft indicates that occurring of crack convert periodic motion to quasi-periodic or chaotic motion.Originality/valueThe results give an understanding of the operating conditions under which undesirable dynamic behavior occurs, and provide some useful information to design and diagnose such gear system with crack fault.

Contraction model of skeletal muscle driven by external electrical stimulation-Proposal and Identification.

Biohybrid actuators consisting of skeletal muscle and artificial lattice have unique characteristics such as self-growth and self-repair functions. As a first step for developing model-based design and model-based control methods for the biohybrid actuators, we have developed a muscle contraction model. When the stimulation voltage is applied to the muscle, the electrical charges are stored in the dihydropyridine receptor, and the calcium ions are released. According to the concentration of the ions, the contractile elements generate contraction force. We have modeled this phenomenon with three characteristics in the proposed model-electrical dynamic, physiological, and mechanical dynamic characteristics. Unlike the previous models, the proposed model was verified under the condition of tetanus and incomplete tetanus with the muscle length changed. The simulated contraction force showed good agreement with the experimentally measured contraction force generated by the gastrocnemius muscle of a toad.Clinical Relevance- Biohybrid actuators are expected as a new material for medical and assistive devices having a soft and flexible characteristic. This study provides a basic contraction model for such biohybrid actuators.

Research on mechanism configuration and dynamic characteristics for multi-split transmission line mobile robot

PurposeThe purpose of this paper is to achieve the optimal system design of a four-wheel mobile robot on transmission line maintenance, as the authors know transmission line mobile robot is a kind of special robot which runs on high-voltage cable to replace or assist manual power maintenance operation. In the process of live working, the manipulator, working end effector and the working environment are located in the narrow space and with heterogeneous shapes, the robot collision-free obstacle avoidance movement is the premise to complete the operation task. In the simultaneous operation, the mechanical properties between the manipulator effector and the operation object are the key to improve the operation reliability. These put forward higher requirements for the mechanical configuration and dynamic characteristics of the robot, and this is the purpose of the manuscript.Design/methodology/approachBased on the above, aiming at the task of tightening the tension clamp for the four-split transmission lines, the paper proposed a four-wheel mobile robot mechanism configuration and its terminal tool which can adapt to the walking and operation on multi-split transmission lines. In the study, the dynamic models of the rigid robot and flexible transmission line are established, respectively, and the dynamic model of rigid-flexible coupling system is established on this basis, the working space and dynamic characteristics of the robot have been simulated in ADAMS and MATLAB.FindingsThe research results show that the mechanical configuration of this robot can complete the tightening operation of the four-split tension clamp bolts and the motion of robot each joint meets the requirements of driving torque in the operation process, which avoids the operation failure of the robot system caused by the insufficient or excessive driving force of the robot joint torque.Originality/valueFinally, the engineering practicability of the mechanical configuration and dynamic model proposed in the paper has been verified by the physical prototype. The originality value of the research is that it has double important theoretical significance and practical application value for the optimization of mechanical structure parameters and electrical control parameters of transmission line mobile robots.

Actuation and dynamic mechanical characteristics of a core free flat dielectric electro-active polymer soft actuator

Various complex shapes of dielectric electro-active polymer (DEAP) actuator have been promoted for several types of applications. In this study, the actuation and mechanical dynamics characteristics of a new core free flat DEAP soft actuator were investigated. This actuator was developed by Danfoss PolyPower. DC voltage of up to 2000 V was supplied for identifying the actuation characteristics of the actuator and compare with the existing formula. The operational frequency of the actuator was determined by dynamic testing. Then, the soft actuator has been modelled as a uniform bar rigidly fixed at one end and attached to mass at another end. Results from the theoretical model were compared with the experimental results. It was found that the deformation of the current actuator was quadratic proportional to the voltage supplied. It was found that experimental results and theory were not in good agreement for low and high voltage with average percentage error are 104% and 20.7%, respectively. The resonance frequency of the actuator was near 14 Hz. Mass of load added, inhomogeneity and initial tension significantly affected the resonance frequency of the soft actuator. The experimental results were consistent with the theoretical model at zero load. However, due to inhomogeneity, the frequency response function’s plot underlines a poor prediction where the theoretical calculation was far from experimental results as values of load increasing with the average percentage error 15.7%. Hence, it shows the proposed analytical procedure not suitable to provide accurate natural frequency for the DEAP soft actuator.