Dianyin Hu

Reliability-Based Design Optimization Method of Turbine Disk with Transformed Deterministic Constraints

AbstractTo improve the computational efficiency of the reliability-based design optimization (RBDO) of a complex structure with nonlinear and implicit limit-state function, the single-loop-single-vector (SLSV)-limit-state factor (LSF) (SLSV-LSF) method was developed by fully considering the advantages of the SLSV approach and the LSF method to transform uncertain constraints into deterministic constraints. The mathematical models of SLSV and LSF were established and the basic RBDO process of the SLSV-LSF method is presented. The shape optimization of an aeroengine turbine disk was completed based on the proposed method. From the reliability sensitivity analysis of the turbine disk, it is revealed that an uncertain constraint of average circumferential stress can be transformed into a deterministic constraint and material density can be regarded as a deterministic variable. Through the min-mass shape design of the turbine disk based on different approaches, it is demonstrated that the developed method main...

Research on Surrogate Model Based on Local Radial Point Interpolation Method

In order to increase the accuracy of surrogate models in structural reliability analysis, we put forward a kind of surrogate model based on local radial point interpolation method (LRPIM). Three kinds of radial basis function (RBF) are employed for the shape function construction to form different kinds of LRPIM model.In order to illustrate the approximating ability of each surrogate model, we build up a nonlinear function model and carry out a numerical experiment on gas turbine disk’s estimated life-span. Compared with polynomial model, Chebyshev orthogonal polynomial model, Kriging model and RBF neural network model, LRPIM model has a demonstrable difference in terms of accuracy. For different polynomial basis order with constant sampling nodes amount, we conclude that fluctuant accuracy can be described by the balance between the describing improvement brought by polynomial basis order increase and the local impairment brought by support domain expansion. For sampling nodes amount with constant polynomial basis order, we conclude that accuracy of LRPIM model improves when sampling nodes amount increases.In order to illustrate the potential in reliability analysis, we apply the best performing LRPIM model to a set of widely used test problems, which certifies the accuracy and robustness of this kind of surrogate model.In a word, LRPIM model is one of the most promising surrogate models compared with other models on nonlinear approximating problems and reliability analysis.Copyright

Experimental and Numerical Analysis of Microstructures and Stress States of Shot-Peened GH4169 Superalloys

Combining experiments and finite element analysis (FEA), a systematic study was performed to analyze the microstructural evolution and stress states of shot-peened GH4169 superalloy over a variety of peening intensities and coverages. A dislocation density evolution model was integrated into the representative volume FEA model to quantitatively predict microstructural evolution in the surface layers and compared with experimental results. It was found that surface roughness and through-depth residual stress profile are more sensitive to shot-peening intensity compared to coverage due to the high kinetic energy involved. Moreover, a surface nanocrystallization layer was discovered in the top surface region of GH4169 for all shot-peening conditions. However, the grain refinement was more intensified under high shot-peening coverage, under which enough time was permitted for grain refinement. The grain size gradient predicted by the numerical framework showed good agreement with experimental observations.

Effects of Heat-Treatment Residual Stress on Low Cycle Fatigue Life of a Turbine Disk in PM Superalloy

Turbine disks in powder metallurgy (PM) superalloy have been widely used in advanced aeroengines. The production of PM superalloy turbine disks involves a series of heat treatment processes, which would inevitably create residual stresses. It has been proved that the low cycle fatigue (LCF) life of the turbine disk is affected by the residual stresses. The computational simulation of heat treatment is considered as an effective way to evaluate the residual stresses in a turbine disk. A finite element software was used to simulate the heat-treatment processes of a FGH95 turbine disk to obtain the residual stress field.To investigate the relaxation of residual stress in FGH95, smooth bar specimens were measured by X-ray diffraction before and after being loaded. Modified by the residual stresses, SWT model is used to predict the low cycle fatigue life of the turbine disk modified by the residual stress field obtained from the simulation of heat treatment.By the comparison between the prediction modified by the residual stress and the prediction without modification, a considerable decrease in low cycle fatigue life is indicated.Copyright

Dominant Damage Factors Determining for Single Crystal Nickel Superalloys Under Cyclic Loading Based on Principal Component Analysis

A critical plane approach in combination with principal component analysis (PCA) for determining dominant damage factors (DDFs) was developed for single crystal nickel superalloys at elevated temperature. Maximum resolved shear stress (RSS), maximum slip rate and other 2 mesoscopic parameters on the critical plane, defined as the preferential slip plane, were selected as damage parameters. Correlation analysis results indicated that there were strong correlations (i.e. multicollinearity) among the selected parameters. To address this issue, PCA was performed to eliminate the effect of multicollinearity and the DDFs were determined as well. Based on the DDFs a life model was proposed and then validated by the fatigue experimental results. Most of the experimental lives are within the factor three of the predicted ones. The life model has a relatively simple form with reliable constants which facilitates the application in industry design.Copyright