Evaluation of vibration stress of TA11 titanium alloy blade by quantitative fractography

Vibration fatigue is the main failure mode of compressor blade. Evaluating the vibration stress of blade that leads to cracking is very useful for analysis of vibration fatigue. In this paper, fatigue stress estimation methods by quantitative fractography were studied through experimental blade and in-service first-stage compressor blade in order to evaluate the initiation vibration stress of in-service blade. The analysis process of initiation vibration stress was established. The evaluating result of vibration stress of in-service blade subjected to centrifugal force and bending vibration stress agrees with aero engine test result. It is shown that the evaluation method can not only evaluate the equivalent fatigue stresses of different crack depths but also yield the initiation equivalent fatigue stress.

A Ply-By-Ply Discretized 2D FEA Approach with the Integrated XFEM-CE Strategy for Predicting Multiple Failures in Laminated Composite Structures

Delamination and matrix cracking are two common failure mechanisms in composite structures,and are usually coupled with each other,leading to multiple failures pattern.This paper proposed a fast damage prediction methodology for composite laminated structures based on the ply-by-ply 2D(two dimensional)FE model of composite laminates in the transverse plane.The layer-wise 2D FE model was firstly used in conjunction with the integrated XFEM/CE strategy,which simulated the interface delamination with cohesive elements and the intra-ply matrix crack with XFEM(extended finite element method).To realize ply-by-ply 2D FE(finite element)modeling of composite laminates,two 2D material models were developed based on the plane stress assumption and plane strain assumption,respectively.A general crack propagation scheme was developed in the framework of the integrated XFEM-CE method.Adopting the 2D material model based on the plane strain assumption,a ply-by-ply discretized 2D FEA procedure was conducted for an out-of-plane composite Pi joint under the static tensile load.The predicted load-displacement response and damage evolution process showed good agreement with the experimental results,which verified the proposed approach.

Characterization of creep behavior of TiAl alloy with high Nb content at elevated temperatures

Creep experiments of the TiAl alloy with high Nb content were conducted to consider both the temperature dependence and stress dependence of its creep behavior.The creep curves were characterized by Theta constitutive model,and Newton-Gauss method was applied to obtain the material parameters.Based on the rupture strain,the rupture life of the TiAl alloy was able to be predicted by Theta constitutive model.The results show that the creep curves of the TiAl alloy contain primary creep,secondary creep and tertiary creep stages,especially for the lower stress.The rupture life of the TiAl alloy decreases with the increase in either applied stress or temperature.Theta constitutive model is able to describe the creep deformation of the TiAl alloy accurately,and the predicted life agrees well with the experimental result.