Non-destructive estimation of three-dimensional inelastic strain via nonlinear inverse analysis using displacement

Abstract

The service life of mechanical structures is influenced by the inelastic strain generated during manufacturing and operation. Therefore, non-destructive estimation of three-dimensional inelastic strain is essential to ensure structure safety even during operation. Accordingly, an inverse problem method was proposed to estimate the inelastic strain over the entire component based on the eigenstrain theory using non-destructively measured surface displacement. However, this method assumes micro-deformation, in which the causal inelastic strain and resulting displacement are linearly related. In practice, the value of inelastic strain is large, which results in large deformation and a nonlinear effect on displacement determined by the magnitude of the inelastic strain. This study considers the inverse problem of estimating the creep strain in a turbine blade for power generation from the displacement caused by the creep strain and proposes a method to derive the exact solution even for large deformation problems. Numerical simulations using a simplified turbine model show that the estimates converge to the correct solution value with relatively high accuracy in the absence of measurement errors. Moreover, the result of the iterative calculations used in the proposed method converge around the correct value, even in the presence of measurement errors in the displacement by the laser displacement meter.

Keywords

• inverse problem
• nonlinear
• turbine blade
• creep strain
• displacement
• finite element method
• non-destructive
• creep-fatigue