PIPE RUPTURE SIMULATIONS FOR TWO-PHASE CO2-MIXTURE

Control of ductile fracture propagation to ensure arrest is an essential element of design of pipelines transporting natural gas and other fluids such as dense-phase CO2. Full-scale pipe rupture simulations have been carried out using Finite Element Analysis (FEA). The simulations captured an accurate pressure loading profile behind the crack tip resultant from the escaping fluid. Results for loading profiles representative of both natural gas and a CO2 mixture are compared, the difference being that the CO2 mixture can exist as a two-phase fluid (liquid and gas) compared to the single-phase natural gas.
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FATIGUE LIFE ASSESSMENT OF A TRUSS GIRDER BRIDGE USING LINEAR FRACTURE MECHANICS APPROACH

In transportation system, bridges are continuously subjected to vehiclular loads that causes accumulation of stresses in different components. The weakest region are some times prone to the development of fatigue crack, that grows leading to collapse if proper maintenance and reparing are not carried out. In this paper, a method of estimation of fatigue life of a truss girder bridge has been outlined using linear fracture mechanics approach after synthesizing the vehicle induced stress history. Von-Mises stresses which accounts for all the principal stresses at a gusset plate of a critical joint was utilized to obtain stress-cycle histogram. Number of cycles required to grow an initially detected crack of very small dimension to a threshold value has been obtained to predict the fatigue failure. The effect of the length of the bridge, vehicle speed and compound traffic growth on remaining life of the bridge has been studied
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ENHANCED REAL TIME FATIGUE CRACK MONITORING AND UPDATING IN WELDED STRUCTURAL COMPONENTS

Cracks emerging from geometrically discontinuous locations under cyclic environmental loadings are critical concerns for the safety of the existing structural components. The crack-based fatigue assessment is essential for the evolving digital twin of sustainable infrastructures, including bridges, ships, and offshore platforms, to optimize the lifetime cost of these structures. This study presents an enhanced neural network-bootstrap particle filtering algorithm to construct the complex relationship between the normalized strain relaxation indicators and the crack profiles based on the numerical simulation and experimental validation. The high-cycle fatigue bending test of the welded plate connections confirms the robustness of the proposed approach in estimating the fatigue crack initiation and propagation through both strain measurement and nondestructive testing data. To overcome the uncertainties caused by the limited strain measurement, crack measurement, and different non-destructive techniques, this study combines a bootstrap particle filtering approach with an interpolation method to update the crack prediction algorithm. As validated by the experimental results, the intelligent crack sizing approach demonstrates a potential solution for crack size forecasting through affordable strain gauges in the broad framework of digitally twinning the next-generation infrastructure.
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EFFECT OF NON-METALLIC INCLUSIONS ON THE FRACTURE TOUGHNESS OF 42CRMO4 STEEL IN THE DUCTILE-BRITTLE TRANSITION RANGE

In this article, the effect of the volume content and distribution of non-metallic inclusions on the fracture toughness of a quenched and tempered 42CrMo4 steel is investigated. The investigations focused on the material behavior in the ductile-brittle transition range. To this end, fracture toughness tests were performed on 42CrMo4 with different inclusion characteristics. These were achieved by metal melt treatment with functional filter materials. The results showed a significant effect of both volume content and distribution of the non-metallic inclusions. The transition to brittle material behavior was accompanied by a decreasing fracture toughness as well as low scatter of the test data.
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LOW-CYCLE FATIGUE ANALYSIS OF ALUMINUM ALLOY GUSSET JOINTS AND LATTICED SHELL BASED ON CONTINUUM DAMAGE MECHANICS

Aluminum alloys have been widely used for structures in environments subject to corrosion. However, aluminum alloys have lower elastic modulus as compared to steels, and are more sensitive to low-cycle fatigue failure. This study performed low-cycle fatigue experiments of aluminum alloy gusset joints. A damage-coupled cyclic plastic constitutive model of 6061-T6 aluminum alloy was established based on continuum damage mechanics. Numerical simulations of the joints and a latticed shell were carried out incorporating the constitutive model. Low-cycle fatigue life of the joints and the latticed shell structure were estimated based on damage distribution calculated by the simulations.
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MODELLING OF PLASTICITY AND DUCTILE FRACTURE FOR LOW TO MEDIUM INDIAN STRUCTURAL STEEL GRADES

The data points available for developing a Fracture Locus (FL) database for structural steel used in the Indian construction industry are extremely limited. The current study is conducted to determine the FL data points for three different grades of Indian structural steel, namely E250, E350, and E450. Uniaxial tests on notched dog bone specimens of three different specimen configurations are performed. The selected configuration is used to determine points for plotting FL corresponding to high-stress triaxiality (0.7 < T >1) and Lode angle (L) almost equal to 1. With the help of numerical simulation, the FL points are obtained and reported. The accuracy of numerical simulation is checked by precisely matching the load versus displacement obtained from the experiment. Six fracture prediction models are chosen for the present study. These six models are chosen using the following criteria, (1) only depends on stress triaxiality (b) depends on both stress triaxiality and Lode angle and (c) the number of coefficients used. The effectiveness of all the selected models in predicting fracture initiation across all three steel grades is compared, and the findings are reported.
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THE TIP FIELDS OF SHARP V-NOTCH UNDER CREEPING CONDITION CONSIDERING OUT-OF-PLANE EFFECT

Notches in creeping solids at high temperatures have drawn considerable attention due to their importance in structural integrity assessment. Understanding the three-dimensional (3D) effect on the notch tip field is important for the fracture mechanics analysis of engineering materials and structures. This paper presents an asymptotic solution for 3D sharp V-notched structures subjected to mode Ⅰ creep loading condition.
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CONSTANT CTOA DETERMINATION FOR STABLE DUCTILE CRACK GROWTH AND ITS APPLICATION TO RUNNING FRACTURE CONTROL FOR GAS TRANSMISSION PIPELINE

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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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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