The crack tip opening angle (CTOA) has been used as a reliable fracture toughness to characterize stable crack growth for thin-wall structures in low-constraint conditions. Recently, it has been found that CTOA can be also utilized as a robust fracture parameter to describe arrest fracture toughness for gas transmission pipelines in modern ductile steels. This is a great improvement of the traditional fracture control technology for gas pipelines, where a Charpy-vee notch (CVN) impact energy based two curve model developed at Battelle (BTCM) was used to determine the arrest toughness. While the CVN-based BCTM is not applicable to modern pipeline steels with grades X70 and above, the CTOA-based BTCM works well for these high grades, but requires constant CTOA. This work develops four methods to determine constant CTOA using the single edge notched bend (SENB) specimens, including a load-displacement linear fit method, a logarithmic load-displacement linear fit method, a stable tearing energy method, and a J-differentiation method. The test results for A285 carbon steel show that these CTOA methods can determine nearly identical critical CTOA values over stable ductile crack growth using the SENB specimens.
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Themes: Fracture in Large Scale Metallic Infrastructure: Advances, Challenges, and Opportunities
FAILURE ANALYSIS AND RESIDUAL LIFE ESTIMATION USING A MIXED METHOD OF X-RAY FRACTOGRAPHY AND SIMULATION
In order to guarantee passengers safety while improving rolling stock maintenance, the French railroad company, SNCF, studies the evolution of cracks that can propagate in fatigue loading situations, particularly for locomotive axles. This research aims to determine the crack propagation history, which is a determining factor in maintenance, studying fracture surfaces while combining X-ray fractography analysis and numerical methods for variable amplitude loads
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WARP3D: OPEN SOURCE SOFTWARE FOR 3D NONLINEAR FRACTURE MECHANICS [Keynote]
The WARP3D project (warp3d.net) provides all source code, extensive documentation and ready-to-run executables on Windows, Linux and macOS for researchers and practitioners worldwide. Developed by a group at the University of Illinois starting in the late 1990s to support academic research, WARP3D capabilities focus on modeling nonlinear fracture processes primarily in metals from the microscale to structural components. This presentation describes the origin and several key capabilities of the code.
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ASSESSING UNCERTAINTY IN CREEP LIFE OF GRADE 91 STEEL USING CRYSTAL PLASTICITY AND GRAIN BOUNDARY MICROSTRUCTURAL MODELS
This paper examines time to minimum creep rate and its uncertainty with respect to a set of fourteen material parameters. The microstructural model of Grade 91 steel includes both dislocation creep and grain boundary opening/sliding within a finite element model, and hence the simulations are relatively expensive and have several sources of nonlinearity. We will propagate uncertainty in the input material parameters of these two mechanisms and determine the aggregate uncertainty in the predicted time to minimum creep rate as well as the sensitivities of the parameters. The cost, stability, accuracy of the polynomial chaos expansion as a means for stochastic dimensional reduction is assessed against the classical Monte Carlo method.
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TOWARDS PRACTICAL SIMULATION OF STEEL FRACTURE IN STRUCTURAL AND EARTHQUAKE ENGINEERING APPLICAITONS [Keynote]
Over twenty-five years ago, unexpected fractures occurred in dozens of welded steel frame buildings during the 1994 Northridge earthquake. This prompted major research programs to (1) develop more reliable connection details for new buildings, (2) develop strategies to repair and retrofit damaged buildings, and (3) to assess the seismic safety of buildings. Efforts to develop alternative designs for new and retrofitted steel connections primarily relied on large-scale laboratory testing of connection subassemblies. Since then, significant advancements have been made in nonlinear finite element techniques to simulate the inelastic behavior of structural components and systems, although challenges remain to reliably simulate fracture, particularly for seismic design, where structural components are designed to undergo large-scale yielding. This presentation will summarize research on continuum-based fracture mechanics, where cyclic void growth models are used to assess ductile fracture initiation and propagation under large scale cyclic yielding. The models are implemented through finite element analyses and validated through a series of tests on notched axial bars, compact tension specimens, and large scale steel subassembly tests of braces and column base connections. Applications to use detailed finite element models to calibrate macro-scale models for incorporating fracture limit states in overall structural system response are also described.
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