Hai-Kun Wang

Probabilistic Physics of Failure-based framework for fatigue life prediction of aircraft gas turbine discs under uncertainty

A probabilistic Physics of Failure-based framework for fatigue life prediction of aircraft gas turbine discs operating under uncertainty is developed. The framework incorporates the overall uncertainties appearing in a structural integrity assessment. A comprehensive uncertainty quantification (UQ) procedure is presented to quantify multiple types of uncertainty using multiplicative and additive UQ methods. In addition, the factors that contribute the most to the resulting output uncertainty are investigated and identified for uncertainty reduction in decision-making. A high prediction accuracy of the proposed framework is validated through a comparison of model predictions to the experimental results of GH4133 superalloy and full-scale tests of aero engine high-pressure turbine discs.

A unified criterion for fatigue–creep life prediction of high temperature components:

A unified ductility criterion for fatigue–creep life prediction is presented based on the static fracture toughness exhaustion and dissipated cyclic strain energy density of high temperature components. It provides a general failure criterion for both low and high cycle fatigue regimes. The effects of mean stress, creep and loading waveform on fatigue life are incorporated into this criterion. Applicability and prediction accuracy of the newly proposed criterion was validated through comparing model predictions to experimental results taken from the literature. The results show that the proposed criterion is robust for different loading conditions and more accurate than other existing strain energy/ductility-based methods.

A new approach to the investigation of load interaction effects and its application in residual fatigue life prediction

Fatigue damage under variable amplitude loading is related to load histories, such as load sequences and load interactions. Many nonlinear damage models have been developed to present load sequences, but load interactions are often ignored. This paper provides a new approach to present load interaction effects for nonlinear damage accumulation. It is assumed that the ratio of two consecutive stress levels is used to describe the phenomenon on damage evolution. By introducing the approach to a nonlinear fatigue model without load interactions, a modified model is developed to predict the residual fatigue life under variable amplitude loading. Experimental data from three metallic materials and welded joints in the literature are employed to verify the effectiveness of the proposed method under two-level loading. The result shows that the modified model predicts more satisfactory estimations than the primary model and Miner rule. Furthermore, the proposed method is calibrated and validated by the case of multilevel loading. It is found that the modified model shows a good estimation and its damage curve presents a typical nonlinear behavior of damage growth. It is also convenient to calculate the residual fatigue life by the Wöhler curve.

Condition-Based Maintenance With Scheduling Threshold and Maintenance Threshold

In order to arrange maintenance resources according to system condition, the lead time needs to be considered within the context of condition-based maintenance (CBM). Therefore, a scheduling threshold is introduced to replace the time to schedule, which is used as a decision variable in combination with a maintenance threshold and a failure threshold. The long-run expected cost rate for maintenance considers the maintenance cost, the cost of the waiting time of suppliers and customers. In this way, suppliers can schedule maintenance services in advance when the system condition reaches the scheduling threshold, and perform maintenance when the system condition exceeds the maintenance threshold. Furthermore, the optimal maintenance plan is updated dynamically in the framework of Prognostics and Health Management (PHM). Finally, a numerical example is provided to demonstrate the effectiveness and the dynamic nature of the proposed method.

Remaining useful life estimation under degradation and shock damage

This article presents a prognostic approach to estimate remaining useful life for systems subjected to dependent competing failure processes. In the literature, shock damage is the damage to a soft failure process caused by a shock process. However, how the degradation process causes damage to a hard failure process has not been well studied. In this article, the degradation damage is modeled as the damage to a hard failure process from a degradation process. Degradation and shock processes, as “elemental processes,” result in failures via either a soft failure or a hard failure process, namely, “compound processes.” Instead of leading to a direct failure, elemental processes construct compound processes: the soft failure process consists of a degradation process and shock damage, and the hard failure process consists of a shock process and degradation damage. In this way, the damage in this article especially represents the effect of an elemental process on other compound processes. Furthermore, a particle filter is applied based on the established model for system statement estimation and on-line prediction of remaining useful life distribution with and without measurement noise in prognostics. Finally, a numerical example is presented with sensitivity analysis.

Finite element analysis for turbine blades with contact problems

Abstract Turbine blades are one of the key components in a typical turbofan engine, which plays an important role in flight safety. In this paper, we establish a establishes a three-dimensional finite element model of the turbine blades, then analyses the strength of the blade in complicated conditions under the joint function of temperature load, centrifugal load, and aerodynamic load. Furthermore, contact analysis of blade tenon and dovetail slot is also carried out to study the stress based on the contact elements. Finally, the Von Mises stress-strain distributions are obtained to acquire the several dangerous points and maximum Von Mises stress, which provide the basis for life prediction of turbine blade.

Fatigue lifetime assessment of aircraft engine disc based on multi-source information fusion

Fatigue lifetime assessment for an aircraft engine disc is important for the assessment of the engine reliability. This paper provides a new opinion to the fatigue lifetime assessment for aircraft engine disc based on the multi-source information fusion method using Bayesian inference. Subjective information quantifying method is used to transform the expert knowledge into prior distribution. Different expert prior distributions are characterized by consistent degree. The fusion factor is determined through a Bayesian version of Pearsons goodness-of-fit. This opinion effectively extends sample size and makes up the defects where the traditional methods in small sample fatigue lifetime assessment cannot.

Near-extreme system condition and near-extreme remaining useful time for a group of products

When a group of identical products is operating in field, the aggregation of failures is a catastrophe to engineers and customers who strive to develop reliable and safe products. In order to avoid a swarm of failures in a short time, it is essential to measure the degree of dispersion from different failure times in a group of products to the first failure time. This phenomenon is relevant to the crowding of system conditions near the worst one among a group of products. The group size in this paper represents a finite number of products, instead of infinite number or a single product. We evaluate the reliability of the product fleet from two aspects. First, we define near-extreme system condition and near-extreme failure time for offline solutions, which means no online observations. Second, we apply them to a continuous degradation system that breaks down when it reaches a soft failure threshold. By using particle filtering in the framework of prognostics and health management for a group of products, we aim to estimate near-extreme system condition and further predict the remaining useful life (RUL) using online solutions. Numerical examples are provided to demonstrate the effectiveness of the proposed method.

Probabilistic PoF based Framework for Fatigue Life Prediction of Aircraft Gas Turbine Discs

A probabilistic Physics of Failure-based framework for fatigue life prediction of aircraft gas turbine discs under uncertainty is developed. It incorporates the overall uncertainties appearing in structural integrity assessment. Thereby, a comprehensive uncertainty quantification (UQ) procedure is presented to quantify multiple types of uncertainty using multiplicative and additive UQ methods. Furthermore, the factors that contribute most to the resulting output uncertainty are investigated and identified for uncertainty reduction. High prediction accuracy of the proposed framework is validated through a comparison of model predictions to experimental results of GH4133 superalloy.