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Carbon fiber reinforced polymer (CFRP) reinforcement is emerging as an efficient means of elongating the service life of cracked metallic structures. An experimental program was conducted to investigate the fatigue behavior of compact-tension (CT) specimens repaired by different CFRP configurations. In parallel, numerical simulations of the fatigue crack growth in the CFRP-repaired specimens were also conducted. The eXtended finite element method (XFEM) was employed and shown to provide accurate and efficient calculations of the stress intensity factor (SIF), without remeshing the models during crack propagation. The mechanical properties of the adhesive were simulated using a cohesive traction-separation relationship. Good agreement was observed between the numerical and experimental results of the SIF and fatigue life, with the latter numerically predicted based on the experimentally derived Paris law constants. Insight into the debonding behavior between the CFRP and steel specimens has also been provided. Due allowance for the weakening effect of damage initiation and evolution between the FRP-steel interfaces is required in the reinforcement calculations.

Hydrogen assisted cracking (HAC) is a common type of failure mechanism that can affect a wide range of metals and alloys. Experimental studies of HAC are cumbersome due to various intrinsic and extrinsic parameters and factors (associated with stress, hydrogen and the materials microstructure) contributing to the hydrogen crack kinetics. The microstructure of many materials consists of diverse constituents with characteristic features and mechanical properties which only occur in very small material volumes. The only way to differentiate the effect of these individual constituents on the hydrogen crack kinetics is to miniaturise the testing procedures. In this paper we present a new experimental approach to investigate hydrogen assisted crack growth in a microstructural constituent, i.e. acicular ferrite. For this purpose, sharply notched micro-cantilevers were fabricated with a Focus Ion Beam within this selected microscopic region. Acicular ferrite can be found in many ferrous alloys including ferritic weld metal and has specific features that control its intrinsic susceptibility to HAC. These features were characterised via Electron Backscatter Diffraction and the specimens were subsequently loaded under uncharged and hydrogen charged conditions with a nano-indenter. The outcomes of the testing, demonstrated that the threshold stress intensity factor, Kth, to initiate crack propagation in acicular ferrite ranges between 1.56 MPa m1/2 and 4.36 MPa m1/2. This range is significantly below the values of Kth reported for various ferrous alloys in standard macro-tests. This finding indicates that the mechanisms and resistance to HAC at micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

In the present study, the Welding Institute of Canada (WIC) restraint test was used to simulate the restraint conditions of full-scale girth welds on energy pipelines to ascertain the influence of welding process parameters on welding stresses. Finite element models are developed, and validated with neutron diffraction measurements, to evaluate the welding stresses for under-matched, matched and over-matched welds. The effects of heat input, wall thickness and variable restraint lengths of WIC sample are systematically investigated. As a practical outcome, this work can help in selection of the appropriate restraint length for WIC tests to simulate the specified stress conditions in the pipeline, and, ultimately, reduce the risk of Hydrogen Assisted Cold Cracking (HACC) in high strength low alloy.

Hydrogen assisted cracking (HAC) is a common type of failure mechanism that can affect a wide range of metals and alloys. Experimental studies of HAC are cumbersome due to various intrinsic and extrinsic parameters and factors (associated with stress, hydrogen and the materials microstructure) contributing to the hydrogen crack kinetics. The microstructure of many materials consists of diverse constituents with characteristic features and mechanical properties which only occur in very small material volumes. The only way to differentiate the effect of these individual constituents on the hydrogen crack kinetics is to miniaturise the testing procedures. In this paper we present a new experimental approach to investigate hydrogen assisted crack growth in a microstructural constituent, i.e. acicular ferrite. For this purpose, sharply notched micro-cantilevers were fabricated with a Focus Ion Beam within this selected microscopic region. Acicular ferrite can be found in many ferrous alloys including ferritic weld metal and has specific features that control its intrinsic susceptibility to HAC. These features were characterised via Electron Backscatter Diffraction and the specimens were subsequently loaded under uncharged and hydrogen charged conditions with a nano-indenter. The outcomes of the testing, demonstrated that the threshold stress intensity factor, Kth, to initiate crack propagation in acicular ferrite ranges between 1.56 MPa m1/2 and 4.36 MPa m1/2. This range is significantly below the values of Kth reported for various ferrous alloys in standard macro-tests. This finding indicates that the mechanisms and resistance to HAC at micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

In the present study, the Welding Institute of Canada (WIC) restraint test was used to simulate the restraint conditions of full-scale girth welds on energy pipelines to ascertain the influence of welding process parameters on welding stresses. Finite element models are developed, and validated with neutron diffraction measurements, to evaluate the welding stresses for under-matched, matched and over-matched welds. The effects of heat input, wall thickness and variable restraint lengths of WIC sample are systematically investigated. As a practical outcome, this work can help in selection of the appropriate restraint length for WIC tests to simulate the specified stress conditions in the pipeline, and, ultimately, reduce the risk of Hydrogen Assisted Cold Cracking (HACC) in high strength low alloy.

Hydrogen assisted cracking (HAC) is a common type of failure mechanism that can affect a wide range of metals and alloys. Experimental studies of HAC are cumbersome due to various intrinsic and extrinsic parameters and factors (associated with stress, hydrogen and the materials microstructure) contributing to the hydrogen crack kinetics. The microstructure of many materials consists of diverse constituents with characteristic features and mechanical properties which only occur in very small material volumes. The only way to differentiate the effect of these individual constituents on the hydrogen crack kinetics is to miniaturise the testing procedures. In this paper we present a new experimental approach to investigate hydrogen assisted crack growth in a microstructural constituent, i.e. acicular ferrite. For this purpose, sharply notched micro-cantilevers were fabricated with a Focus Ion Beam within this selected microscopic region. Acicular ferrite can be found in many ferrous alloys including ferritic weld metal and has specific features that control its intrinsic susceptibility to HAC. These features were characterised via Electron Backscatter Diffraction and the specimens were subsequently loaded under uncharged and hydrogen charged conditions with a nano-indenter. The outcomes of the testing, demonstrated that the threshold stress intensity factor, Kth, to initiate crack propagation in acicular ferrite ranges between 1.56 MPa m1/2 and 4.36 MPa m1/2. This range is significantly below the values of Kth reported for various ferrous alloys in standard macro-tests. This finding indicates that the mechanisms and resistance to HAC at micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

In the present study, the Welding Institute of Canada (WIC) restraint test was used to simulate the restraint conditions of full-scale girth welds on energy pipelines to ascertain the influence of welding process parameters on welding stresses. Finite element models are developed, and validated with neutron diffraction measurements, to evaluate the welding stresses for under-matched, matched and over-matched welds. The effects of heat input, wall thickness and variable restraint lengths of WIC sample are systematically investigated. As a practical outcome, this work can help in selection of the appropriate restraint length for WIC tests to simulate the specified stress conditions in the pipeline, and, ultimately, reduce the risk of Hydrogen Assisted Cold Cracking (HACC) in high strength low alloy.

Hydrogen assisted cracking (HAC) is a common type of failure mechanism that can affect a wide range of metals and alloys. Experimental studies of HAC are cumbersome due to various intrinsic and extrinsic parameters and factors (associated with stress, hydrogen and the materials microstructure) contributing to the hydrogen crack kinetics. The microstructure of many materials consists of diverse constituents with characteristic features and mechanical properties which only occur in very small material volumes. The only way to differentiate the effect of these individual constituents on the hydrogen crack kinetics is to miniaturise the testing procedures. In this paper we present a new experimental approach to investigate hydrogen assisted crack growth in a microstructural constituent, i.e. acicular ferrite. For this purpose, sharply notched micro-cantilevers were fabricated with a Focus Ion Beam within this selected microscopic region. Acicular ferrite can be found in many ferrous alloys including ferritic weld metal and has specific features that control its intrinsic susceptibility to HAC. These features were characterised via Electron Backscatter Diffraction and the specimens were subsequently loaded under uncharged and hydrogen charged conditions with a nano-indenter. The outcomes of the testing, demonstrated that the threshold stress intensity factor, Kth, to initiate crack propagation in acicular ferrite ranges between 1.56 MPa m1/2 and 4.36 MPa m1/2. This range is significantly below the values of Kth reported for various ferrous alloys in standard macro-tests. This finding indicates that the mechanisms and resistance to HAC at micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

In the present study, the Welding Institute of Canada (WIC) restraint test was used to simulate the restraint conditions of full-scale girth welds on energy pipelines to ascertain the influence of welding process parameters on welding stresses. Finite element models are developed, and validated with neutron diffraction measurements, to evaluate the welding stresses for under-matched, matched and over-matched welds. The effects of heat input, wall thickness and variable restraint lengths of WIC sample are systematically investigated. As a practical outcome, this work can help in selection of the appropriate restraint length for WIC tests to simulate the specified stress conditions in the pipeline, and, ultimately, reduce the risk of Hydrogen Assisted Cold Cracking (HACC) in high strength low alloy.

Hydrogen assisted cracking (HAC) is a common type of failure mechanism that can affect a wide range of metals and alloys. Experimental studies of HAC are cumbersome due to various intrinsic and extrinsic parameters and factors (associated with stress, hydrogen and the materials microstructure) contributing to the hydrogen crack kinetics. The microstructure of many materials consists of diverse constituents with characteristic features and mechanical properties which only occur in very small material volumes. The only way to differentiate the effect of these individual constituents on the hydrogen crack kinetics is to miniaturise the testing procedures. In this paper we present a new experimental approach to investigate hydrogen assisted crack growth in a microstructural constituent, i.e. acicular ferrite. For this purpose, sharply notched micro-cantilevers were fabricated with a Focus Ion Beam within this selected microscopic region. Acicular ferrite can be found in many ferrous alloys including ferritic weld metal and has specific features that control its intrinsic susceptibility to HAC. These features were characterised via Electron Backscatter Diffraction and the specimens were subsequently loaded under uncharged and hydrogen charged conditions with a nano-indenter. The outcomes of the testing, demonstrated that the threshold stress intensity factor, Kth, to initiate crack propagation in acicular ferrite ranges between 1.56 MPa m1/2 and 4.36 MPa m1/2. This range is significantly below the values of Kth reported for various ferrous alloys in standard macro-tests. This finding indicates that the mechanisms and resistance to HAC at micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

In this study functionally gradient metal-ceramic coatings were fabricated using low cost slurry and sintering process. The quality of FGM coatings was evaluated through microstructure analysis, thermal cycling tests (60 minutes at 900 deg C followed by 30 minutes cooling), and post fracture analysis.

A feasibility study of a relatively simple and economical method for producing functionally graded thermal barrier coatings using the Wet Powder (Slurry) and Sintering method showed promising results. This method is relatively undeveloped and under utilised compared to more expensive techniques such as chemical vapour deposition, physical vapour deposition, plasma spraying and powder metallurgy. It utilizes a pressurized spray gun to spray a slurry mixture of the powdered coating material suspended in a liquid solution directly onto a substrate surface followed by sintering using an oxyacetylene torch. The effects of slurry composition, type of ceramic powder, compatibility with substrates, spraying and sintering conditions were studied. Several TBC specimens have been fabricated under various conditions to develop a procedure which produce good quality coatings (of up to 3 layers) with little or no spallation. The optimum time, heat flux and applied pressure level for sintering were deduced. TBCs produced from a 40-45% ceramic, 4% binder and 0.4% dispersant composition and sintered for 30 minutes with an applied pressure of 30 MPa produced good quality coatings with a uniform and very smooth surface. Scanning electron micrographs of the fabricated TBC coatings showed good contact between the grain boundaries of the ceramic powder. In phase 2 of this project, the Wet Powder and Sintering method will be further developed. Improvements to this method include automating the sintering procedure and optimizing the fabrication conditions. A much more extensive micromechanical testing program will be conducted to obtain a more qualitative measure of the quality of the FGM thermal barrier coatings and to develop high temperature constitutive models for input into the FE modeling.