The factors influencing the occurrence of intergranular fracture during fatigue crack growth tests of quenched and tempered steels have been examined. It is found that failure along prior austenite grain boundaries may be divided into two types. One type is found at high proof strength levels in steels in which impurities have segregated to the grain boundaries and is responsible for increased fatigue crack growth rates. The other is confined to environments containing water vapour and does not appear to significantly influence crack growth rates. The occurrence of the latter mode is thought to be related to hydrogen derived from the water vapour. A model describing hydrogen diffusion to regions of hydrostatic stress ahead of the crack tip can account for the observed variation of intergranular failure with crack velocity, mean load, and steel purity levels.
We present a generalized exposure assessment of 28 disposal options for poultry carcasses in the event of a highly pathogenic avian influenza (HPAI) outbreak. The analysis supports a hereto unverified disposal hierarchy for animal carcasses, placing waste processing (e.g., incineration and rendering) above controlled disposal (e.g., landfill), above uncontrolled disposal (e.g., burial on-farm). We illustrate that early stages of the disposal chain (on-farm) pose greater opportunities for exposure to hazardous agents than later stages, where agents are generally contained, wastes are treated, and residues are managed by regulated processes. In selecting carcass disposal options, practitioners are advised to consider the full range of hazards rather than focusing solely on the HPAI agent, and to give preference to technologies that (i) offer high destruction efficiencies for target pathogens; (ii) do not give rise to significant releases of other pathogenic organisms; and (iii) do not release unacceptable concentrations of toxic chemicals. The approach offers an exposure assessment perspective for carcass disposal, thus providing a risk-informed basis for contingency planning and operational intervention. The authors recognize that relevant legislation, public perception, available capacity, and cost also need to be considered when selecting disposal options in the event of HPAI.
Abstract: Fibre Bragg grating sensors have been developed as a strain measurement technique. With regard to practical applications, there is growing knowledge and experience. However, many application issues remain unsolved. These issues include signal interpretation, confidence in measurement accuracy, calibration, and zero‐strain definition. This paper reports some issues which have been encountered in practical measurements and application trials. The investigation covers various aspects of strain measurement. The measurement accuracy in a composite laminate is found to be influenced by the formation of cracks in adjoined layers, interface between fibre sensor and host materials and nonuniform stress fields.
A total of 2195 T8 samples were designed, and the friction stir weld lines were kept in the sample center. Two kinds of crack retarders were designed and bonded onto the samples in three different positions. Fatigue tests were performed with and without crack retarders bonded on the samples. Crack growth rates and fatigue lives were measured and compared with each other. The effect of crack retarder’s width and position on damage tolerance was studied. Crack paths were observed and studied. It is shown that the wider size crack retarder can improve fatigue life even two times more than the narrower one, and it can make crack paths smooth. The damage tolerance of the panel achieves the best performance when the retarder covers the weld zone completely.
The performance and reliability of Structural Health Monitoring (SHM) techniques remain largely unquantified. This is in contrast to the probability of detection (POD) and sensitivity of manual non destructive inspection methods which are well characterised. In this study factors influencing the rates of emission of Acoustic Emission (AE) signals from propagating fatigue cracks were investigated. Fatigue crack growth experiments were performed in 2014 T6 aluminium sheet to observe the effects of changes in crack length, loading spectrum and sample geometry on rates of emission and the probability of detecting and locating the fatigue crack. Significant variation was found in the rates of AE signal generation during crack progression from initiation to final failure. AE signals at any point in the failure process were found to result from different failure mechanisms operating at particular stages in the failure process.
Welded steel T-sections of different weld fillet geometries coated with water ballast tank protective coatings were subjected to thermal cycling with a temperature range from 60°C to -10°C. Cracks developed in the coatings at the weld line, propagating longitudinally along it. The number of cycles required to create 1 mm cracks was strongly dependent on the weld geometry and the coating Dry Film Thickness (DFT). Finite Element Modelling (FEM) was employed to calculate thermally induced strain fields in the coatings subjected to the same temperature range. FEM predicted that the greatest strain concentrations are present at the coating surface within the weld fillet region. Increased DFT and decreased fillet radius leads to increased maximum principal strains. Numerical analysis predicts that greatest strain ranges promoting the earliest cracking/failure are found in thicker coatings applied to smaller weld radii. Experimental observations confirm this.
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