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2023 Vol. 44, No. 1
Published: 2023-02-28
1
RESEARCH PROGRESS ON CORROSION FATIGUE LIFE MODELS OF METAL STRUCTURAL MATERIALS
Corrosion fatigue is one of the key failure modes in modern industrial equipments. With the continuous development of new technology, equipments in aerospace, rail transit and offshore are becoming more and more high reliability, long life and intelligence. Therefore, an urgent need is required for predicting corrosion fatigue life accuratly and efficiently. In this paper, the corrosion fatigue damage mechanism and life prediction models for pre-corroded fatigue and corrosion fatigue are summarized and commented systematically. Meanwhile, the prospective research directions are proposed. Firstly, the corrosion fatigue failure mechanism and its characterization methods are briefly summarized involving the evolution of corrosion pit, crack initiation and crack propagation. Secondly, the single crack and multi cracks hypothesis based on traditional fracture mechanics models of pre-corroded fatigue are elaborated. The fatigue life prediction models of pre-corroded simple parts based on damage mechanics are also summarized. Those methods are similar to the conventional fatigue life prediction methods for defective components. Additionally, for corrosion fatigue, the different stages based on fracture mechanics models are reviewed. And several quantifying damage dynamically representive corrosion fatigue damage mechanics models are presented. Thirdly, the more efficient data-driven models of corrosion fatigue are thoroughly analyzed. And the advantages and disadvantages of existing models are generalized. At last, based on the current research status, the possible development directions in the future are prospected. It is necessary to realize the visualization research of pit to crack transition stage and short crack propagation process by means of 3D imaging technology and so as to further improve the existing fracture mechanics models of corrosion fatigue. It is suggested to establish a new multi-scale and multi-stage life prediction model with corresponding failure stage correlation. In addition it is important to point out that the new data-driven physical fusion method is a new development direction to predict corrosion fatigue life.
2023 Vol. 44 (1): 1-33 [
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34
Electromechanical coupling model and interlaminar stress analysis of piezoelectric smart composite laminated beams
Graphene nanosheets (GPL) are considered to be one of the most attractive reinforcement materials for composites due to their extraordinary physical properties. GPL reinforced materials can significantly improve the properties of piezoelectric and mechanical for polyvinylidene fluoride (PVDF). Under the action of electromechanical loading, it is crucial to predict the interlaminar stress of laminated beams containing uniform graphene sheets reinforced (GPRC) smart piezoelectric composites. If the prediction of interlaminar shear deformation of piezoelectric laminated beams subjected to electromechanical coupling and the material properties vary widely from layer to layer, the interlaminar stress may be too large which may lead to interlaminar failure. Therefore, an effective mechanoelectrical coupling model is proposed which satisfying the interlaminar continuity condition and suitable for analyzing such problems for the interlaminar stress analysis of composite laminated beams with GPRC actuators in this paper. Applying the Reissner mixed variation theorem (RMVT), the prediction of transverse shear stress considering the electromechanical coupling effect can be improved. The results obtained from three-dimensional (3D) elastic theory and selected model will be used to evaluate the performance of proposed beam model. In addition, the responses of displacements and stresses characteristics for composite laminated beams with GPRC actuators were systematically studied from the aspects of electromechanical load, the thickness of piezoelectric layer, graphene volume fraction and aspect ratio.
2023 Vol. 44 (1): 34-46 [
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47
Fully reaction-chemo-mechanical coupling analysis of a nanosphere electrode particles with surface effect
Surface effect plays a predominant role in nano-electrode particles. At first, a fully coupled reaction-diffusion-mechanics model with surface effect is developed during charge or discharge of LIBS. Then the comparisons of lithium ion concentration, radial stress and hoop stress are made between with and without surface effect. Finally, the influences of reaction coefficient and size effect on the concentration and diffusion-induced stress are discussed. The numerical results show that the surface effect has a vital influence on the stress distribution, and slower chemical reaction or smaller size of nano-electrode particles can decrease the stress of the electrode.
2023 Vol. 44 (1): 47-54 [
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55
Study on meso geometric modeling of 3D woven composite
In this paper, a simplified method of yarn deformation is proposed to establish the meso geometric model of 3D woven composites. Considering the model parameters, such as yarn cross sectional shape, yarn section torsion and yarn bending coefficient, a modeling method is established with adjustable model parameters. Using this method, the effects of yarn layers, model size and yarn bending coefficient on material properties are analyzed. The results show that the boundary effect has a great influence on the material properties of a model with few yarn layers, and the periodic boundary condition is not suggested to apply in the thickness direction; Under the free boundary condition, when the length of the model is about 2 times the cell size, as well as the width is about 1.5 times the cell size, the error range of stiffness test can be controlled within 2%. Furthermore, the yarn bending coefficient has a great influence on the composite stiffness. Appropriate yarn bending coefficients lead to the prediction error of stiffness within 7%. Hence, the real yarn bending coefficient should be considered in the modeling.
2023 Vol. 44 (1): 55-69 [
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70
Design of lightweight and fail-safe structures using bi-directional evolutionary structural optimization method
Fail-safe designed structures with redundant load paths exhibit high tolerance to damage (residual load-bearing capacity), which is of essential significance to the safety of flight vehicles. Meanwhile, the redundant structural configuration resulted from safety consideration inevitably increases the weight and reduces consequently the efficiency of flight vehicle structures. This paper proposes to design lightweight and fail-safe structures using Bi-directional Evolutionary Structural Optimization (BESO) method. Specifically, the design method with "0/1" discrete topology variables minimizes structural weight (material volume), meanwhile constrains the residual load-bearing deformation of locally damaged structures below a safety threshold. To address the bottleneck of the BESO method in dealing with multiple constraints, the deformation constraints are aggregated by the p norm global measure. The aggregated p norm constraint is augmented to the design objective with the introduction of a Lagrange multiplier, achieving simultaneous design for lightweight and fail-safe. Furthermore, the significance of local region to the damage tolerance is calibrated according to the maximum residual load-bearing deformation. The design efficiency can be largely improved by saving the residual load-bearing deformation analyses and constraints of the low-significant local regions. The effectiveness and efficiency of the proposed method is demonstrated through a series of benchmark design examples.
2023 Vol. 44 (1): 70-83 [
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Influence of particles periodic distribution on free vibration of eccentrically rotating ring-shaped structures
In engineering practice, some rotationally symmetric design structures often show eccentric rotation due to manufacturing and installation errors, which affect the stability of the structures. Considering the eccentric motion of this kind of ring-shaped periodic structures, the effects of periodic distribution parameters of added particles and eccentricity on the natural frequency and dynamic stability of the system are studied. Firstly, the following coordinate system is established on the ring structure, and the dynamic model is established with using Hamilton principle. Then the eigenvalues are calculated with classical vibration theory, and the modal characteristic and instability are studied through various parameters combinations. Finally, the dynamic responses are obtained with numerical method, which verify the main results. The results show that natural frequency splitting can occur due to the certain relation between the number of added particles and wavenumbers. For different eccentricities and periodic distribution characteristics, the dynamic performance of the system varies greatly at different speeds. Properly increasing the eccentricity and selecting the appropriate number and size of added particles can effectively suppress the instability. The research contributes to the optimization of dynamic stability analysis for similar structures, which can guide the vibration control in engineering practice.
2023 Vol. 44 (1): 84-95 [
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96
SIMPLE REFINED PLATE THEORY FOR FUNCTIONALLY GRADED PLATE BENDING AND FREE VIBRATION ANALYSIS
In this paper, a simple refined plate theory that can be used to analyze the bending and free vibration behavior of functionally graded plates is proposed. This theory requires only three unknowns for analyzing the bending of a functionally graded plate and only one for analyzing the free vibration of a functionally graded plate. Compared with the classical plate theory which contains three unknown quantities, the simple refined plate theory proposed in this paper takes into account the transversely shear effect and improves the accuracy of the calculation. Unlike the first-order shear deformation plate theory, this simple refined plate theory introduces a polynomial-type shear strain function that satisfies the boundary condition of zero shear stress on the upper and lower surfaces of the plate, so no shear correction is required. The accuracy and convenience of this simple refined plate theory were verified by comparing with existing literature, and the bending and free vibration mechanical behaviors of functionally graded plates were investigated based on this simple refined plate theory.
2023 Vol. 44 (1): 96-108 [
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109
Exact Solution of Free Vibration and Buckling of One-Dimensional Hexagonal Simple-Supported and Layered Quasicrystal Beams
The pseudo-Stroh formula can transform the governing equations of multi-field coupling materials such as quasicrystals into a linear eigen-system and obtain the exact solution of multilayered structures with simple supported boundary conditions, which provides an important reference for various numerical and experimental methods of quasicrystal beams in engineering practice. This paper focuses on the exact analysis of free vibration and buckling problem of one-dimensional hexagonal simply-supported and layered quasicrystal beams. The relation of the extended displacement (phonon displacement and phason displacement) and the extended stress (phonon stress and phason stress) is established firstly, and the governing equations of one-dimensional hexagonal quasicrystal beams are then deduced by using the pseudo-Stroh formula. By solving the linear eigensystem, the general solution of one-dimensional hexagonal quasicrystal homogeneous beam is obtained. Furthermore, the exact solutions of the natural frequencies of free vibration and the critical buckling load of layered quasicrystal beams are derived by propagating matrix method. The correctness and effectiveness of the pseudo-Stroh formula presented in this paper are verified by comparing with the previous results of the shear deformation theory of beams. The numerical examples are illustrated to show the effect of stacking sequence, high-span ratio, layer-thickness ratio and the number of layers on the natural frequency, critical buckling load and mode shape of two kinds of sandwich quasicrystal beams. The results indicated that the stacking sequence, the high-span ratio and the layer-thickness of beam had a great effect on the natural frequency of free vibration and the critical buckling load of quasicrystal beams. When the quasicrystals with high stiffness were used as the surface layers of the layered beam, the natural frequency and critical buckling load of the quasicrystal beams could be enhanced by increasing the high-span ratio and the layer-thickness. Thus, the optimal natural frequency and the critical buckling load of quasicrystal beams could be obtained by adjusting the geometrical size and the stacking sequence of the beams. Besides, the presented results would be a foundation on the further study of layered quasicrystal beams at micro-/nano-scale.
2023 Vol. 44 (1): 109-119 [
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Wave propagation in multiferroic cylinders of sectorial annular cross-section
The multiferroic materials, which combine two or more ferroic properties together, have attracted extensive researchers’ attention since the millennium, and have significant application prospects in sensors, transducer, memory devices, energy harvesters and smart structures. Working performance of these devices is closely relevant to the material property, the characteristics of wave propagation and attenuation in the structures. Hence, wave propagating in multiferroic materials has drawn an ever-increasing interest from the academic community. Based on the linear theory of electro-magneto-elasticity, the propagation of elastic waves in multiferroic cylindrical waveguides of sectorial annular cross-section is analyzed. The longitudinal cuts are covered by non-extensible, and electrically/magnetically shorted membranes and the cylindrical surface may have arbitrary boundary conditions. A wave potential method is exploited to solve the three-dimensional coupled equations, and the characteristic equation is established in analytical form, from which the dispersion relations are readily obtained. Representative examples are performed to investigate the crucial characteristics of the waves by looking into the full dispersion spectra, phase velocity curves and cutoff frequencies. Numerical results demonstrate that phase velocities and cutoff frequencies depend considerably on the waveguide’s angular measure, radius ratio and weak interface parameter, which should be significant factors to control the dispersion characteristics of the multiferroic waveguide of specific materials. It’s noteworthy to point out that a peculiar frequency bandgap is found in phase velocity curves for special boundary condition, which is normally emerged in periodic structure. Due to the analytical feature of the present method and formulations, the present study can be used to verify other numerical methods, and to serve as a benchmark for monitoring in cylindrical structures or devices.
2023 Vol. 44 (1): 120-132 [
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