On the numerical modelling of quasi-static crack growth in linear elastic fracture mechanics

2005 ◽  
Vol 65 (2) ◽  
pp. 174-189 ◽  
Author(s):  
P. Heintz
Keyword(s):  
Fracture Mechanics ◽  
Numerical Modelling ◽  
Crack Growth ◽  
Linear Elastic Fracture Mechanics ◽  
Linear Elastic ◽  
Static Crack ◽  
Elastic Fracture

Evaluation of Crack Growth in Oxygenated High Temperature Water Using Full Size Pipe Tests

1986 ◽  
Vol 108 (1) ◽  
pp. 50-56
Author(s):  
R. M. Horn
Keyword(s):  
High Temperature ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Crack Depth ◽  
Ultrasonic Inspection ◽  
Linear Elastic Fracture Mechanics ◽  
Growth Data ◽  
Full Size ◽  
Linear Elastic ◽  
Elastic Fracture

Full Size pipe tests have been conducted as part of EPRI research programs at the General Electric Company to verify IGSCC crack growth predictions made using a linear elastic fracture mechanics model. The tests on 10.16 cm (4″ pipes) were performed in oxygenated, high temperature, high purity water. The pipes were produced through standard manufacturing procedures which in turn led to characteristic field piping sensitization levels in the heat affected zones (HAZ) and characteristic through wall weld residual stresses. The tests were conducted at stresses equal to or below the yield strength under constant load with limited cycling. Ultrasonic inspection and metallography were used to characterize crack depth after several test phases and used to verify model predictions. Significant cracks were detected and radial and circumferential growth were documented. These test results support the predictions made using linear elastic fracture mechanics modeling, and are discussed in terms of crack growth data developed in CT specimens in the laboratory. The stress level and oxygen level are shown to influence the crack growth rates. Rates of circumferential crack growth are also evaluated. The paper discusses the results in the context of other stress corrosion evaluations as well.

A Practical Approach to Implementing Linear Elastic Fracture Mechanics in Gas Turbine Rotor Disk Analyses

2015 ◽  
Author(s):  
Scott Keller
Keyword(s):  
Finite Element ◽  
Fracture Mechanics ◽  
Gas Turbine ◽  
Crack Growth ◽  
Turbine Rotor ◽  
Linear Elastic Fracture Mechanics ◽  
Linear Elastic ◽  
Rotor Disk ◽  
Elastic Fracture ◽  
Growth Analyses

The failure of vital components is not uncommon in the gas turbine industry. In the event excessive degradation occurs within a component, e.g. extensive cracking in a turbine blade or vane, solutions exist to either repair or replace defective parts. Such parts are readily accessible and mostly exchangeable in the field, limiting the amount of outage time and assessment required for defective parts. When more critical components exhibit extreme wear or cracking, e.g. a crack in a rotor disk, repairs typically necessitate a complete rotor destack and refurbishment or have the potential to require the replacement of individual disks. In extreme cases, defects found in rotor disks can be known to retire an entire compressor or turbine rotor. The OEM solution of replacing disks puts a substantial cost on the customer, thus providing an incentive for characterization and advanced analyses to determine the residual life in critical rotating components. Considered an advanced analysis, linear elastic fracture mechanics (LEFM) provides the theory and fundamental structure to conduct crack growth analyses in components that exhibit nominally elastic behavior. Successful implementation of LEFM requires extensive characterization of the material, engine operating boundary conditions, and high fidelity finite element models. Upon the detection of a flaw, whether an internal or external indication, the results from finite element analyses can be used to derive the crack tip stress field and subsequent crack tip driving parameters. These parameters are then utilized in a comprehensive crack propagation model, calibrated to temperature- and load-dependent material data, to determine the number of cycles to unstable propagation. As a result, the remaining life of a component with a given indication is readily obtained, enabling our engineering team to provide a thorough life assessment of critical rotating components. An overview of the linear elastic fracture mechanics crack growth analyses conducted is presented, with a special emphasis on compressor and turbine disks.

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