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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Themes: Fracture in Large Scale Metallic Infrastructure: Advances, Challenges, and Opportunities
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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