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In order to prevent the body from overheating, a corresponding thermal protection device is usually designed on the inner wall of the combustion chamber. The working environment of this thermal protection device is very harsh, and it needs to withstand internal and external pressure loads and thermal radiation loads of the combustion chamber, especially at the connection between the cylinder and the support parts, the force is harsher. In order to avoid engine damage, causing unnecessary losses. In this article, the thermal–mechanical coupling analysis of the heat shield is carried out by finite element method to analyze the thermal stress and mechanical stress. According to the finite element simulation results, the initial cracks are inserted, respectively, at the stress concentration. Using linear elastic fracture mechanics and Forman–Newman–de Koning models, the crack growth lifetimes of cracks at different locations were calculated. The results of the study show that comparing the initial cracks at different locations, the cracks on the side near the edge of the heat shield have the largest reduction in crack growth life of 64.4% and the critical crack length of 52.0%. The linear superposition of thermal and mechanical stresses under different working conditions has different degrees of nonlinear effects on the crack growth life and critical crack length. The research work in this article can provide a basis for the evaluation of fatigue crack growth life of heat shield and can also provide a reference for engine maintenance. [ABSTRACT FROM AUTHOR]

Taking the compressor impeller as the research object, and based on the octagonal truss lattice structure, a novel lightweight lattice compressor impeller is designed, and its machinability is verified by using a SLM280 3D printer. In order to understand its 3D printing performance, the 3D printing process of the lattice impeller is simulated based on the finite element method (FEM). Based on the feasibility of using the numerical method to study the 3D printing process, the printing process of the lattice impeller at different power values is analyzed and compared with the solid compressor impeller under the same working condition. The results show that the layer deformation of the lattice impeller and the solid impeller is a process that increases layer by layer. Under the 7 working conditions studied in this paper, the maximum residual deformation and residual stress of the lattice impeller after printing are less than those of the solid impeller. The maximum residual deformation of the lattice impeller can be 20.19% smaller than that of the solid impeller, and the maximum residual stress can be 10.69% smaller than that of the solid impeller. This means that the lattice impeller is not only lighter, but also has a better printing performance than the solid impeller.

In order to improve the stress shielding effect caused by excessive elastic modulus of metal plates during fracture healing, a kind of 3D printing oriented lattice structure plate is designed based on topology optimization and the finite element modeling technology. A simplified finite element model of the titanium alloy tibial plate is established by using the finite element method. Combined with the finite element method and the data sampling method, the solid plate system and the lattice plate system are simulated, and the similarities and differences between their performances are compared. Based on the analysis of mechanical properties of lattice plate system, the lightweight design of the plate is realized and the stress shielding effect of the bone is improved. The results show that the weight of the lattice plate can be reduced by about 40% under the condition of guaranteed strength. The lattice plate is sensitive to the thickness. By reducing the thickness of the plate in a small range, the stiffness of the plate can be significantly reduced. The application of the lattice plate can effectively increase the average stress of the skeleton by about 4% and reduce the stress shielding effect of the skeleton. The simulated analysis results can provide references for the optimization design of low stress shielded plates.

Taking compressor impeller with pressure ratio less than 3 as research object, a prediction method of residual life of compressor impeller was proposed. Considering the action of "inertial" load centrifugal force, finite element method (FEM) technology and sub-model technology were used to comprehensively analyze the mechanical quantities, such as blade stress, and the hot spot stress location of compressor impeller was determined. Crack orientation was determined according to maximum principal stress criterion. The linear elastic fracture mechanics (LEFM) based on FEM and Forman-Newman-de Koning (FNK) model were used to investigate the whole process of crack growth, including stable growth and instability growth stages. The crack growth law and residual life of impeller at different rotate speeds were given. The results show that with the increase of rotate speed, the stress intensity factor (SIF) of initial crack front increases in a quadratic power law, the critical length decreases linearly, and the residual life decreases nonlinearly. The crack grows along the height of blade and then fractures after a deflection of about 90 degrees to the outer edge of blade. The obvious deflection of crack is the sign of crack transition from stable growth stage to instability growth stage. The life of crack in the instability growth stage can be neglected compared with that in the stable growth stage. The analysis method proposed in this article can provide a basis for the damage tolerance evaluation of compressor impeller, and can also provide a reference for maintenance work. [ABSTRACT FROM AUTHOR]

A new tubular lattice structure is designed based on the "pipe-like" microstructure. Different from the parameter optimization method for classical lattice and the design method of super structured lattice, this method reconstructs the classical lattice to avoid complex new geometric structure design. In addition, it can also ensure that the lattice has stronger mechanical properties while being lightweight. The results show that under the same volume fraction, the stress of the improved and strengthened new pipe lattice structure under the same load are 14% − 39% lower than column lattice respectively, and the deformation has a similar law. [ABSTRACT FROM AUTHOR]

Because the resonance of the structure is related to the fundamental frequency in most cases, in order to avoid the resonance of the structure, this paper takes the square plate structure as the research object, and uses the variable density method and draft technology to optimize the square plate, so that the optimized stiffened plate has a higher first-order natural frequency. The optimized stiffened plate is compared with the unreinforced plate and the conventional stiffened plate. The results show that under different mass constraints, the four optimized stiffened forms tend to be consistent in the distribution of main materials. Under the working condition of this paper, when the mass of the stiffened plate is 18.737 Kg, the first natural frequency of the optimized stiffened plate can be increased by 107.68%, 21.54% and 10.03% respectively compared with the first natural frequency of the unreinforced plate and the first natural frequencies of two conventional stiffened plates. When the first natural frequency of the stiffened plate is 537.39 Hz, the mass of the optimized stiffened plate can be reduced by 53.95%, 62.70% and 21.44% respectively compared with that of the unstiffened plate and the two conventional stiffened plates. The optimized stiffened plate is redesigned, and it is found that the designed stiffened plate still has advantages over the unstiffened plate and the conventional stiffened plate. This means that this paper provides a reference for the stiffener of square plates with low mass and high natural frequency. [ABSTRACT FROM AUTHOR]

In order to improve the specific stiffness of negative Poisson's ratio metamaterial structures. In this paper, a novel circular NPR (negative Poisson's ratio) metamaterial structure was designed. The equivalent Poisson's ratio and the equivalent elastic modulus of the circular NPR were deduced, and the mechanical properties of the circular NPR structure and the cube NPR structure were compared. Meanwhile, the influence of geometrical size on the Poisson's ratio of the whole structure was studied. The results show that the circular structure has the properties of negative Poisson's ratio. Compared with the cube NPR structure, under the same external dimensions, the weight of the circular NPR structure was reduced by 16.7%. When the two structures were applied the same load, the Von Mises stress of the circular NPR structure decreased by 71.6% compared with that of the cube NPR structure in the elastic range. Due to its light weight and greater resistance to deformation, the specific stiffness of the circular NPR structure was larger. Meanwhile, by changing the geometric size, the negative Poisson's ratio of the circular NPR structure can be regulated. [ABSTRACT FROM AUTHOR]

A lattice compressor impeller whose stiffness and strength can be adjusted freely between unfilled impeller and solid impeller is designed. After ensuring the better calculation accuracy of Asymptotic Homogenization (AH) method, the static performance of lattice impeller with different cell filling rate is analyzed by AH method. The results show that the stiffness and strength of the lattice impeller are between unfilled impeller and solid impeller. The lattice impeller has better circumferential anti distortion ability and higher working efficiency. At the same time, the smaller axial stress provides strength guarantee for the design of a higher speed compressor impeller. [ABSTRACT FROM AUTHOR]

Based on the octagonal truss, a new lightweight lattice impeller (L-impeller) is designed. The 3D printing process of the design impeller is simulated by Finite Element Method (FEM). The machinability and simulation feasibility of the design impeller are verified by SLM280 Metal 3D printer. The printing process of L-impeller and solid impeller (S-impeller) under different power is analyzed and compared. The results show the maximum residual deformation of L-impeller is 20.19% smaller than that of S-impeller, and the maximum residual stress is 10.69% smaller than that of L-impeller, which means that the L-impeller will have better printing performance. [ABSTRACT FROM AUTHOR]

A lattice plate was designed based on topological optimization and finite element modeling. The simulation of solid plate system and lattice plate system was carried out. The lightweight design of plate was realized. The results show that the weight of the plate can be reduced by about 40%. The lattice plate is sensitive to the thickness. By reducing the thickness of the plate in a small range, the stiffness of the plate can be significantly reduced. The application of lattice plate improves the average stress of the skeleton by about 4% and reduces the stress shielding effect of skeleton. [ABSTRACT FROM AUTHOR]

AbstractFatigue crack fracture is a common failure mode in structures. For the propeller with initial crack, the hydrodynamic effect cannot be ignored when studying the fatigue crack propagation behavior. Taking the full-size KP505 propeller as the research object, its hydrodynamic performance is simulated and verified. By using the fluid-structure interaction (FSI), the pressure distribution and stress distribution of propeller under different working conditions are analyzed comprehensively, and the position of propeller hot spot stress is obtained. According to the principal stress and its direction of the hot spot stress, the location and orientation of possible macroscopic crack initiation are determined. By using the linear elastic fracture mechanics and finite element method (FEM), the propeller fatigue crack propagation law and life are calculated. The analysis results show that the Forman-Newman-de Koning (FNK) model predicts more complete fatigue crack propagation life than Paris model. The fatigue crack propagation of propeller has two stages, steady propagation stage, and accelerated propagation stage. The crack breaking blade thickness is the dividing point between the two stages. In addition, the effects of the advance coefficient, stress ratio, and initial crack size on the computed results are also analyzed, which provide reference for ship driving and propeller maintenance. [ABSTRACT FROM AUTHOR]

abstractHeat shield is one of the important parts in aero engine, its function is to effectively prevent engine overheating. Under normal operation, the heat shield is subjected to high temperature from the combustion chamber and pressure pulsations inside and outside, and the phase difference of this pulsation pressure results in a very harsh working environment. Based on the experimental results, the approximate equation of the pulsating pressure is established, and the finite element method (FEM) is used to simulate the pulsating pressure. Meanwhile, the mechanical quantities such as thermal stress and mechanical stress are considered comprehensively. Linear elastic fracture mechanics (LEFM), Paris and Forman-Newman-de Koning (FNK) models were employed during the study in order to calculate the fatigue crack propagation life (FCPL) of the heat shield. The results show that the heat shield has an infinite lifetime at a phase difference of zero. As the phase difference increases, the FCPL and critical crack length (CCL) tend to decrease nonlinearly. When the phase difference is π, the FCPL and CCL are the shortest, which are only 3% and 17.1% of those at π/6. This study can provide a reference for the improvement and overhaul of heat shields. [ABSTRACT FROM AUTHOR]