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2023 Vol. 44, No. 4
Published: 2023-08-28
417
From Mechanical Description for Metal Fatigue Properties to Service Life Evaluation of Aircraft Structural Components: Status and Challenges
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.044
The safety and service life of aircraft metallic structures are dominated by fatigue failure, and corresponding academic research and engineering practice have been developing in mutual promotion. This paper concludes the features of fatigue problems in aircraft metallic structures; reviews the existing three fundamental methodologies of fatigue analysis, i.e. approach based on material fatigue properties, approach based on structural fatigue qualities, and approach based on fracture mechanics; dissects the respective intentions, procedures and potential developments for each methodology; discusses the revolutionary effects of progress in academic research and analysis methods on the anti-fatigue strategies for aircraft metallic structures. On the above basis, several concepts in fatigue research and some simplifications as well as assumptions in related methods are discussed; combined with new challenges and ideas raised by the development and application of advanced materials and innovate structures, as well as new requirements on fatigue and damage tolerance evaluations for future aircraft structures, this paper finally prospects the future research directions of fatigue analysis methods and methodologies.
2023 Vol. 44 (4): 417-457 [
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458
SH Guided Wave-based Inspection Method for Crack Localization in Orthotropic Steel Bridge Decks
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2023.012
The orthotropic steel bridge deck (OSBD) is widely used in long-span bridges. However, fatigue cracks easily occur in OSBDs, which seriously affects the safety of bridges. Conventional nondestructive testing methods usually only cover the local region below the transducer, so there is an urgent need to develop structural health monitoring (SHM) technologies to scan a large area from a single position on the bridge deck. Compared with the dispersive Lamb waves, the fundamental shear horizontal wave (SH0 wave) is an ideal wave mode in developing SHM systems for OSBDs due to its non-dispersive characteristics, but the related research is extremely scarce. This paper first studies the interaction between an SH0 wave and a U-shaped stiffener with a weld by finite element simulations. It is found that below the first cutoff frequency of SH guided wave, the U-shaped stiffener and weld have little influence on the propagation of the SH0 wave in the deck plate and can be neglected. Above the first cutoff frequency, a part of the SH0 wave will be converted into the SH1 wave (the first-order SH mode) when encountering the U-shaped stiffener, but the amplitude of the generated SH1 wave is quite small. Then, piezoelectric transducers are developed for excitation and reception of single mode SH0 wave in a 16 mm-thick deck plate. The developed transducer for generating the SH0 wave is a thickness-shear piezoelectric device, while the sensor for receiving the SH0 wave is a face-shear piezoelectric transducer. After that, experiments are conducted to verify the simulated results for the case of an SH0 wave encountering the U-shaped stiffener. The obtained experimental results accord well with the simulated ones. Finally, an SH0 wave-based inspection system is developed to detect cracks in OSBDs. Results show that the cracks in OSBDs can be accurately identified by SH0 wave. This work can lay a foundation for developing guided-wave-based intelligent monitoring technology for OSBDs.
2023 Vol. 44 (4): 458-469 [
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470
Application of Theory of Critical Distance in Multiaxial Notch Fatigue Life Prediction for Al-Li Alloy
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2022.042
The complex stress states at the notch roots on engineering components are usually caused by combinations of geometric discontinuities and multiaxial loading. As to the Theory of Critical Distance, the stress eigenvalue of a point, line or area near the notch root is used as the control parameter of fatigue failure, and a reasonable explanation for the notch effect is put forward. Therefore, the Theory of Critical Distance is considered to be a method of engineering application prospects for predicting the fatigue life of notched specimens. In this paper, the multiaxial fatigue life of notched specimens is predicted according to the Theory of critical distance. Firstly, fatigue tests carried out on 2297 Al-Li alloy under uniaxial and 90° non-proportional loading paths are introduced. Subsequently, the Nominal Stress Approach and the Theory of Critical Distance for multiaxial fatigue life prediction are elaborated. In particular, the value of the critical distance is determined by defining the function relationship between critical distance and fatigue life. The stress state in the vicinity of notch is then analyzed by the finite element method. With the obtained stress state, it is easy to determine the position of the critical plane by the shear stress-Maximum Variance Method. According to the stress parameters on the critical plane, the critical plane stress ratio is defined. Afterwards, the W?hler curve under multiaxial loading is modified by the critical plane stress ratio. Finally, the Theory of Critical Distance and Nominal Stress Approach are used to estimate the multiaxial fatigue life of 2297 Al-Li alloy, and the predicted results are compared. It is found that the Theory of Critical Distance combined with the Modified W?hler Curve Method has high calculation accuracy, for 92% of the predicted data points are in the triple error dispersion band. Compared with the Nominal Stress Approach, the calculation process of the Theory of Critical Distance is not complicated and the results are more reliable.
2023 Vol. 44 (4): 470-482 [
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483
Research on the Inverse Problem of Thin Plate Based on Physics-informed Neural Networks
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2023.005
In order to adapt to the intelligent development trend of solving the inverse problem of thin plate, this paper established a novel framework for solving the inverse problem of thin plate using physics-informed neural networks based on the hybrid driving idea of data and model. Inspired by the fine-tuning learning in few-shot learning method, a step-by-step training method for freezing parameters is proposed to solve the problem of long time for neural network to calculate higher order terms. To optimize the sampling area in view of the large error at the edge for supervised learning of the deflection of thin plate, an edge cutting method is proposed. The measured data of thin plate deflections are obtained by calculating the deflection partial differential equation based on the Kirchhoff thin plate theory combined with the analytical solution formula and superimposing random noise, thus a physics-informed neural networks model for solving the inverse problem of thin plate is constructed. In addition, ablation experiments are carried out to analyze and verify the effectiveness of the proposed improvement measures. The numerical results show that under the acceleration of NVIDIA RTX 3060 video card, the inversion time of the ratio of uniformly distributed load to flexural rigidity, uniformly distributed load and modulus of elasticity of simply supported and clamped rectangular thin plates is less than 30 seconds and the relative error is less than 3% in low noise environment. For rectangular thin plates with four edges clamped, the relative error of linear load inversion clamped under hydrostatic pressure is less than 11%. The results show that the inversion method of thin plate problem based on physics-informed neural networks is correct and effective, and can accurately invert the parameters of various mechanical models. The corresponding step-by-step training inversion algorithm of cutting edge-freezing parameters has the advantages of fast speed, high precision, strong robustness and small parameter redundancy. This research creates conditions for adaptive, efficient and accurate solution of thin plate inverse problem, and provides a useful reference for intelligent health monitoring of thin plate structures.
2023 Vol. 44 (4): 483-496 [
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497
Experiment and Analysis on the Multi-mode Deformations of the Origami Spring Structure
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2023.009
Origami spring structure is a simple origami structure，which is obtained by folding two long paper strips of the same size and gluing them to each other. It has received a lot of attention because of its multi-mode large deformation ability.In this paper，the multi-mode deformation capability and mechanical properties of the origami spring structure are studied experimentally，including the axial stretch-twist-coupling deformation and the bending deformation in all directions.Two bending modes，namely vertex-to-vertex bending and side midpoint-to-midpoint bending of the side，are found.The results show that the force-displacement curves of the bending process are approximately linear，but there are obvious jumps in the force-displacement curves of some of the bending experiments，which corresponds to the snap-through transition of the bending facet.To explain the above phenomena，we introduce virtual creases on the facet. Based on the different combinations of mountain and valley folds of virtual creases，a single origami spring cell exhibits four geometrically different configurations.The kinematic model of the rigid folding of the origami spring structure is obtained by deriving the displacement transformation matrix of the vertex coordinates based on the stacking of rotation and translation between cell.This model can describe all deformation modes of the origami spring structure.The potential energy constitutive landscape and the constitutive profile of the force-displacement relation for different deformation modes are clarified by specifying the torsional stiffness at the crease and based on the principle of minimum potential energy.The nonlinear axial stretch-twist-coupling deformation characteristics and linear bending deformation characteristics in all directions of origami spring structure are also qualitatively verified.The findings of this paper contribute to the design and development of origami robots with three-dimensional deformation and locomotion capability.
2023 Vol. 44 (4): 497-511 [
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512
Molecular Dynamics Simulation of Nanoindentation Cyclic Deformation of Single Crystal NiTi Shape Memory Alloy Films
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2023.006
The nanoindentation cyclic deformation behavior of single crystal NiTi shape memory alloy films are simulated using the second nearest neighbor modified embedded atomic potential molecular dynamics method, and the effect of temperature on the microstructure evolution is mainly discussed. To further reveal the plastic deformation mechanism of single crystal NiTi shape memory alloy films, the effects of martensitic phase transformation, dislocations, disordered structure and elastic recovery coefficient involved in indentation are analyzed. The simulation results show that a critical load of steep drop in load-displacement curves at different temperatures (350K, 450K, 550K) is different, which is mainly related to the nucleation of dislocations. Increasing temperature can promote the nucleation and slip of dislocations, resulting in a decrease in resistance to plastic deformation. In addition, the superelastic cyclic deformation can reach stability after a certain number of cycles, and there is a correlation between plastic deformation and crystal structure evolution. The accumulation of nanoindentation residual deformation originates from dislocation slip, twinning deformation, residual martensite phase accumulation and disordered structural plasticity.
2023 Vol. 44 (4): 512-525 [
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526
Piping Vibration Analysis and Verification of Aero-engine Bearing Chambers Based on the Absolute Nodal Coordinate Formulation
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2023.008
A vibration analysis method based on absolute node coordinate method is proposed and verified for the bearing cavity pipeline structure of an aircraft engine. First, based on the extended Lagrange equation, a theoretical model, considering the fluid-structure interaction comprehensively, is established. And the nonlinear equations of motion are discretized by the absolute node-coordinate method aiming to translate the formula into a solvable form. The static deformation of pipeline is then solved by equation decoupling. The specific process is deriving static equation including generalized force vector and stiffness matrix by omitting the time related terms, and the response of pipeline is obtained by solving the static equation by numerical iteration of node coordinates. The convergence analysis of the theoretical algorithm is then carried out to determine the optimal number of elements. Finally, compare the theoretical results with the fluid-structure interaction simulation results from two aspects: the accuracy of static deformation results and the effectiveness of natural frequency results. On the one hand, it is qualitatively shown that the static deformation of the theoretical results is consistent with the simulation results, and the displacement of a node on the pipeline is quantitatively analyzed. On the other hand, the nonlinear equation of motion is reduced to a linear equation, and the stability of the pipeline is analyzed to obtain the natural frequency of fluid-structure interaction simulation results and the theoretical results. The comparison results show that the theoretical results are more reliable. Further, the mechanism of static deformation is obtained from the flow field distribution at the bend of the pipeline. And the difference between the theoretical and simulated natural frequency results is explained from the perspective of flow field. The results of this study provide theoretical and technical support for the optimization design and vibration control of aero-engine bearing cavity pipeline.
2023 Vol. 44 (4): 526-536 [
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537
Subharmonic Resonance and Stability of the Ferromagnetic Rectangular Thin Plate in an Air-gap Magnetic Field
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2023.007
The subharmonic resonance and stability of a ferromagnetic rectangular thin plate with four edges clamped in the air-gap magnetic field are studied. Based on the theory of large deflection of thin plate and the basic theory of electromagnetic field, the boundary conditions satisfying the scalar magnetic potential are given, the distribution of magnetic induction intensity of air-gap magnetic field and the equations for the magnetization force on the surface of the ferromagnetic plate and the electromagnetic torque in the body are solved. Considering the electromagnetic force on the thin plate, the nonlinear magnetoelastic coupled vibration equation of the thin plate with magnetostatic load is established by applying the Hamiltonian variational principle, and the partial differential equation is discretized by using Galerkin integral method. Then, the analytical solution and the amplitude-frequency response equation of the subharmonic resonance of the fixed thin plate are further obtained by the averaging method, and the stability conditions of the system are determined according to Lyapunov stability criterion. By means of examples, the curves of the static deflection and electromagnetic force of the thin plate under the variation of parameters are investigated. Based on the amplitude-frequency response equation and the critical conditions of stability solution, the influence laws of the excitation force, the parameters of air-gap magnetic field and the thickness of plate on the amplitudes and stability regions of the thin plate are obtained. The correctness of the analytical solution of this paper is verified by comparing with the numerical calculation result.
2023 Vol. 44 (4): 537-554 [
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