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2022 Vol. 43, No. 4
Published: 2022-08-28
369
Characterization, evaluation and expectation of fatigue damage behavior for series PM nickel-based superalloys (FGHxx)
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.008
Series powder metallurgy (P/M) nickel-based superalloys (FGHxx) are one of main high temperature structures materials as Chinese damage tolerance P/M superalloys which consisted of FGH95, FGH96 and FGH97 etc.. It is the primary purpose that the service temperature strength, fracture toughness and resistances of fatigue cracking behaviors of P/M superalloys can be effectively enhanced in lower cost through the optimization of the processing parameters including the powder size or other parameters. In this article, the microstructure characteristics, fatigue data scatter peculiarity in S-N curves, fatigue crack initiation and propagation behavior, SEM in-situ testing technology, predication models of fatigue life, fatigue limit, notch factor Kt of 3D K-T diagram were established. And the relative influence factors of series FGHxx superalloys were analyzed and discussed in detail based on the research status including our latest findings.
2022 Vol. 43 (4): 369-385 [
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386
Research on knockdown factor determination method of thin-walled cylinder considering geometric tolerances
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2021.064
Imperfection sensitivity is one of the main problems faced in the design of thin-walled cylindrical shell structures. A knockdown factor is usually used to quantify the degree of sensitivity to imperfections in the cylindrical shell structure. However, most of the existing imperfection sensitivity analysis methods aimed at predicting the lower limit of the shell knockdown factor, and did not consider the influence of different geometric tolerance levels on the shell knockdown factor. Aiming at this problem, this paper proposes a method to determine the knockdown factor of thin-walled cylindrical shells considering the geometric tolerances. The method is based on the worst perturbation load method of multiple points to search for the worst imperfection modes, and obtains the lower limit of the knockdown factor under different geometric tolerances of the cylindrical shell, thereby determining the knockdown factor of the thin-walled cylindrical shell considering the geometric tolerance, and the incomplete reduced stiffness method is used to accelerate the calculation process. The results of the calculation examples show that the knockdown factor determination method proposed in this paper can effectively improve the prediction accuracy of the knockdown factor and eliminating unnecessary safety margins under the premise of ensuring safety and reliability, which has positive effect on structural weight savings. Based on this method, the research on the new knockdown factor design criteria of aerospace structure thin-walled cylindrical shells can be carried out, and can further improve the design of aerospace shell structure and the level of refinement and light-weight.
2022 Vol. 43 (4): 386-396 [
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107
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406
Tunning characteristic of bandgaps of a mechanical-piezoelectric hybrid elastic metamaterial beam
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.002
A hybrid elastic metamaterial beam is designed to achieve broadband low-frequency vibration attenuation, in which the mechanical resonator and the piezoelectric shunt resonator with negative capacitance in series are respectively placed on the upper and lower sides of the substrate. Based on the transfer matrix method, a theoretical model is established to calculate the dispersion relation and dynamic effective parameters of the hybrid metamaterial beam, which is verified by the finite element method. The tunning mechanism of the circuit parameters on bandgaps of the hybrid metamaterial beam was studied by theoretical model. The vibration attenuation of the hybrid meta-structure was studied by the finite element method. Furthermore, the interaction between the two resonators was analyzed through comparing with the bandgaps of metamterials only with a single resonator. The results show that the circuit parameters mainly affect the position, width and vibration attenuation coefficient of the bandgap produced by the piezoelectric shunt resonator. In addition, the overlapping region of the two bandgaps produced by two resonators is not always the passband. Moreover, the two resonators will influence each other due to the adjacent negative dynamic effective stiffness ranges. This investigation will provide reference for the design of such hybrid metamaterial.
2022 Vol. 43 (4): 406-418 [
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108
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419
Design and Performance Analysis of Sandwich Flexible Structure with Large Deformation Based on Ω-shaped Honeycomb
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.003
Morphing aircraft change the wing shape according to different flight conditions to obtain the best aerodynamic performance, thus improving the ability to execute multi-objective missions under multiple working conditions. The flexible skin of surface structure is one of the key technologies to realize morphing structure, so flexible skin structure is not only designed to have enough sufficient synergistic deformation ability but also can withstand aerodynamic loads on the surface and maintain smooth aerodynamic shape. To meet the needs, this paper proposes a sandwich flexible skin structure with large deformation based on Ω-shaped honeycomb (Ω-shaped flexible skin). The topological structure of Ω configuration is determined by using parameter optimization techniques to minimize the stiffness of configuration deformation direction; the in-plane equivalent elastic performance prediction formula of Ω-shaped flexible skin honeycomb structure is derived, while the in-plane deformation performance and out-of-plane bearing capacity of the structure are analyzed by numerical simulation. By comparing with in-plane deformation capacity of two sandwich flexible skin structure, namely serpentine-shaped honeycomb and sine-cosine-shaped honeycomb verifies this flexible skin good performance. The results show that the proposed Ω-shaped flexible skin honeycomb structure has good in-plane recoverable large deformation ability and out-of-plane bearing ability.
2022 Vol. 43 (4): 419-433 [
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138
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434
Elastic-plastic Theory Analysis of Three-dimensional Wheel-rail Normal Contact Mechanical Behavior
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.004
The wheel-rail interaction has always been one of the most important research topics in the field of high-speed railway. And with the development of higher speed and larger axle-load for trains, the wheel-rail system will undergo plastic deformation during long-term service, resulting in the aggravation of wheel-rail rolling contact fatigue and damage, which seriously threatens the safety, stability and comfort of train operation. In the present work, a combined theoretical analysis and numerical simulation are conducted to study the elastic-plastic mechanical behavior of wheel-rail normal contact. Firstly, based on the Hertz contact theory and the bilinear hardening model, the elastic-plastic theoretical analysis model of wheel-rail normal contact was established, the wheel-rail elastic-plastic mechanical response characteristics were obtained, and the influence of axle load on contact pressure and contact deformation was discussed. Secondly, based on the three-dimensional wheel-rail contact finite element model, the wheel-rail contact mechanical behavior was simulated, and the theoretical error coefficient in terms of contact pressure and contact deformation was introduced to investigate the difference between the elastic and bilinear hardening models on the prediction results of the wheel-rail contact mechanics response, which verifies the reliability of the elastic-plastic theoretical analysis model of wheel-rail normal contact. It is found that the wheel-rail contact pressure and contact deformation increase with the increase of axle load. The theoretical error coefficient of the bilinear hardening model with regard to wheel-rail contact pressure and contact deformation is small, and the bilinear hardening model is accurate enough to predict the elastic-plastic mechanical behavior of wheel-rail normal contact, which can be used for further in-depth insight into the wheel-rail rolling contact elastic-plastic mechanical response characteristic. The obtained results can provide theoretical basis and technical support for the safe service and damage assessment of wheel/rail system.
2022 Vol. 43 (4): 434-445 [
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134
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446
Vibration Isolation Performance Analysis of Quasi-zero-stiffness Vibration Isolation System with Mechanical Frequency Modulated Dynamic Vibration Absorber
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.005
Based on the working principle of dynamic vibration absorption, a two degree of freedom vibration isolation system is proposed by coupling the frequency adjustable dynamic vibration absorber with the single degree of freedom quasi-zero-stiffness vibration isolator. First, the working principle of dynamic vibration absorber is introduced, and its mechanical model is established. Second, through the analysis of static characteristics, a set of relations between the parameters of the system is derived when the system meets the condition of zero stiffness, and the influences of mechanical and structural parameters on stiffness characteristics of the system are studied. Then, the nonlinear dynamic equation of two degree of freedom vibration isolation system is established. By using the harmonic balance method, the expression of force transmissibility of the system is obtained. Last, using the numerical analysis method, the effects of different damping, stiffness, mass, excitation force amplitude and the effective length of spring on force transmissibility are numerically discussed. In addition, by comparing with the single degree of freedom quasi-zero-stiffness vibration isolation system and the two degree of freedom linear vibration isolation system, the vibration isolation performance of the system is studied. The results show that the designed two degree of freedom quasi-zero-stiffness vibration isolation system can effectively reduce the initial vibration isolation frequency of the system, and the low-frequency vibration isolation performance of the system in different excitation frequencies can be improved by adjusting the parameters of the dynamic vibration absorber. Furthermore, by selecting appropriate values of the damping, stiffness and mass of the dynamic vibration absorber, the effective vibration reduction frequency band width can be further expanded, the attenuation rate of the system force transmissibility in a specific frequency band can be obviously accelerated, and the low-frequency vibration isolation performance of the system can be dramatically improved.
2022 Vol. 43 (4): 446-455 [
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130
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456
Research on Non-uniform Corrosion Expansion Stress of Reinforcing Bars in Concrete Members
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.007
The study of the mechanism of the cracking of the concrete protective layer caused by the corrosion of steel bars is of great significance for evaluating the remaining life of the concrete structure affected by the corrosion. This paper presents an analytical method for solving the stress field of non-uniform corrosion of steel bars. Based on Muskhelishvili's complex variable function method and Verruijt conformal mapping formula, using the von Mises distribution-based reinforcement non-uniform corrosion model as the displacement boundary condition, the analytical solution of the non-uniform corrosion expansion stress of the reinforcement is obtained. By comparing with the simulation results based on ANSYS finite element, the validity of the analytical solution is verified. Comparing the stress caused by different rust modes, it is found that the maximum stress caused by non-uniform rust is much larger than the maximum stress caused by uniform rust. Through examples, various factors affecting the corrosion expansion force of steel bars are discussed. The research shows that the larger the diameter of the steel bar, the smaller the corrosion expansion force, and the easier the concrete protective layer is to crack; the greater the thickness of the concrete protective layer, the greater the corrosion expansion force; The higher the rust expansion force of the steel bar is, the greater. It provides a scientific basis for the design of reinforced concrete components that are susceptible to corrosion.
2022 Vol. 43 (4): 456-466 [
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106
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467
SH Wave Propagation in Piezoelectric Semiconductor Plate with Initial Stress
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.009
Piezoelectric semiconductors (PSs) have the physical properties of both piezoelectric and semiconductor materials. Devices and structures based on PSs have recently drawn particular attention due to their potential applications in multi-functional electronic devices. The core property of PSs is the interaction between the internal electric field and the charge carrier when under a mechanical force or a bias voltage. In the processing and application of PSs, the existence of initial stress is inevitable. At the same time, the initial stress is usually applied in the manufacturing process in order to prevent brittle fracture of materials. In this paper, the propagation behavior of shear-horizontal (SH) waves in an infinite n-type PS plate with initial stress is studied. The linear macroscopic theory of PSs is used. Based on the three-dimensional equations, the elastic surface wave problem is converted into a homogeneous linear eigenvalue system. Finally, making use of the boundary conditions on the top and bottom surfaces of the PS plate, a transcendental equation that determines the dispersion relation is obtained analytically. Numerical examples are presented to systematically study the effect of boundary condition, steady-state carrier density, plate thickness, and initial stress on the wave speed and attenuation of SH wave. In addition, SH wave propagation in two different PS materials under initial stress is discussed. It is found that the real and imaginary parts of wave velocity under short-circuit are correspondingly smaller than open-circuit boundary. The SH wave characteristics in the PS plate are the same as that in the corresponding piezoelectric plate when the steady-state carrier density is small (the semiconductor properties can be ignored). The results also show that the effect of small initial stress on phase velocity is negligible, and the wave speed decreases sharply when the initial stress reaches a certain value. Similarly, attenuation increases gradually as the initial stress becomes large enough. The calculation results in this paper could be helpful as theoretical guidance when designing PS surface acoustic wave devices.
2022 Vol. 43 (4): 467-476 [
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142
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477
Interpretation of the flexoelectric effect in solids based on multi-scale model
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.014
The flexoelectric effect in solids is explained in this paper based on Chen's multi-scale model. The flexoelectric effect is a multi-field coupling phenomenon across scales. The current macroscopic flexoelectric theories are based on continuum mechanics and describe the phenomenon phenomenally according to the micro mechanism that the local crystal inversion symmetry is destroyed by the strain gradient. However, due to the great difference between the macroscopic theory and the microscopic flexoelectric theory based on lattice dynamics and density functional theory, it is difficult to combine these two theories to study the flexoelectric effect in materials across scales. In view of this point, according to the atomic field theory proposed by Chen, the relationship between atomic displacement and polarization is obtained from the perspective of material microstructure evolution, and a new multi-scale flexoelectric model is established to explain the micro mechanism of flexoelectric effect. By deriving the polarization expression, it is found that the distance between atoms and the center of the unit cell is an important micro quantity affecting flexoelectric polarization. The flexoelectric effect establishes the relationship with temperature and time through this micro quantity at the atomic scale. In addition, the order of magnitude of the distance between atoms and the center of the unit cell is Angstrom. Expressions of the piezoelectric polarization contain the linear term while the flexoelectric polarization contain the quadratic term of this position, this result in the fact that the flexoelectric effect is much smaller than the piezoelectric effect at the macro scale. The multi-scale flexoelectric model established in this paper can be suitable for complex situations such as internal defects of materials, and provides some ideas for the follow-up study of multi-scale flexoelectric effect.
2022 Vol. 43 (4): 477-484 [
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158
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485
Acoustics of porous media: from microscopic geometrical structures to macroscopic sound absorption performances
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.018
Conventional porous media such as fibers and foams have good sound absorption characteristics at mid and high frequencies. They are commonly used in fields of construction, automotive, aviation, industry and environmental noise control. The complex microstructures and various macroscopic sound absorption properties of porous media have been highly concerned and studied by researchers. These studies are often based on the first principles in acoustics, start from the sound absorbing mechanism, and explore scientific laws in microscopic and macroscopic levels in order to discover or create novel structures with better sound absorption performances. This paper combs the studies from microscopic geometrical structure analyses to macroscopic sound absorption characteristics, and exhibits related achievements and orientations in the past one or two decades. First, the microstructure characteristics, visualization pathway, and geometric parameters are introduced. Secondly, the history from establishment to improvement of acoustic models is reviewed. Thirdly, physical quantities that determine the acoustic performance are summarized, and their physical meanings are discussed. Then, the theoretical calculations, numerical simulations, and experimental measurements for the macroscopic properties are described and compared. Finally, relevant empirical fitting formulas that associate micro-macro relations between two scales are listed aiming to analyze factors that affect the acoustic performance. The prospects are discussed at last.
2022 Vol. 43 (4): 485-518 [
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247
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