ANALYSIS OF MULTIPLE CO-PLANAR SURFACE BREAKING FLAWS LOADED IN TENSION UNDER CLEAVAGE FAILURE CONDITIONS

ABSTRACT In procedures such as R6 and BS 7910 for assessing the structural integrity of structures, complex multiple flaws located in close proximity to each other are generally characterised as one, larger, single flaw. Recent studies have shown that the current characterisation rules may be non-conservative under some circumstances. Concurrent experimental and analytical programmes are being undertaken in order to further investigate this potential non-conservatism for situations where the possibility of cleavage failure has to be taken into account when assessing structures or components containing multiple flaws. The analytical work has involved inelastic finite element modelling in conjunction with numerical analysis based on the weakest link methodology for cleavage initiation to determine the probability of cleavage failure. This has allowed the probability of failure for the situation of multiple adjacent flaws to be compared with that for the single characterised flaw to determine whether the characterisation rules are conservative. Initial results from the cases studied so far indicate that

Whole Body Screening Using High-Temperature Superconducting MR Volume Resonators: Mice Studies

High temperature superconducting (HTS) surface resonators have been used as a low loss RF receiver resonator for improving magnetic resonance imaging image quality. However, the application of HTS surface resonators is significantly limited by their filling factor. To maximize the filling factor, it is desirable to have the RF resonator wrapped around the sample so that more nuclear magnetic dipoles can contribute to the signal. In this study, a whole new Bi2Sr2Ca2Cu2O3 (Bi-2223) superconducting saddle resonator (width of 5 cm and length of 8 cm) was designed for the magnetic resonance image of a mouse's whole body in Bruker 3 T MRI system. The experiment was conducted with a professionally-made copper saddle resonator and a Bi-2223 saddle resonator to show the difference. Signal-to-noise ratio (SNR) with the HTS saddle resonator at 77 K was 2.1 and 2 folds higher than that of the copper saddle resonator at 300 K for a phantom and an in-vivo mice whole body imaging. Testing results were in accordance with predicted ones, and the difference between the predicted SNR gains and measured SNR gains were 2.4%∼2.7%. In summary, with this HTS saddle system, a mouse's whole body can be imaged in one scan and could reach a high SNR due to a 2 folds SNR gain over the professionally-made prototype of copper saddle resonator at 300 K. The use of HTS saddle resonator not only improves SNR but also enables a mouse's whole body screen in one scan

Failure of A Novel, Rapid Antigen and Antibody Combination Test to Detect Antigen-Positive HIV Infection in African Adults with Early HIV Infection

BACKGROUND: Acute HIV infection (prior to antibody seroconversion) represents a high-risk window for HIV transmission. Development of a test to detect acute infection at the point-of-care is urgent. METHODS: Volunteers enrolled in a prospective study of HIV incidence in four African cities, Kigali in Rwanda and Ndola, Kitwe and Lusaka in Zambia, were tested regularly for HIV by rapid antibody test and p24 antigen ELISA. Five subgroups of samples were also tested by the Determine Ag/Ab Combo test 1) Antigen positive, antibody negative (acute infection); 2) Antigen positive, antibody positive; 3) Antigen negative, antibody positive; 4) Antigen negative, antibody negative; and 5) Antigen false positive, antibody negative (HIV uninfected). A sixth group included serial dilutions from a p24 antigen-positive control sample. Combo test results were reported as antigen positive, antibody positive, or both. RESULTS: Of 34 group 1 samples with VL between 5x105 and >1.5x107 copies/mL (median 3.5x106), 1 (2.9%) was detected by the Combo antigen component, 7 (20.6%) others were positive by the Combo antibody component. No group 2 samples were antigen positive by the Combo test (0/18). Sensitivity of the Combo antigen test was therefore 1.9% (1/52, 95% CI 0.0, 9.9). One false positive Combo antibody result (1/30, 3.3%) was observed in group 4. No false-positive Combo antigen results were observed. The Combo antigen test was positive in group 6 at concentrations of 80 pg/mL, faintly positive at 40 and 20 pg/mL, and negative thereafter. The p24 ELISA antigen test remained positive at 5 pg/mL. CONCLUSIONS: Although the antibody component of the Combo test detected antibodies to HIV earlier than the comparison antibody tests used, less than 2% of the cases of antigen-positive HIV infection were detected by the Combo antigen component. The development of a rapid point-of-care test to diagnose acute HIV infection remains an urgent goal

Early Diagnosis of HIV Infection in Infants - One Caribbean and Six Sub-Saharan African Countries, 2011-2015.

Pediatric human immunodeficiency virus (HIV) infection remains an important public health issue in resource-limited settings. In 2015, 1.4 million children aged 50% decline. The most common challenges for access to testing for early infant diagnosis included difficulties in specimen transport, long turnaround time between specimen collection and receipt of results, and limitations in supply chain management. Further reductions in HIV mortality in children can be achieved through continued expansion and improvement of services for early infant diagnosis in PEPFAR-supported countries, including initiatives targeted to reach HIV-exposed infants, ensure access to programs for early infant diagnosis of HIV, and facilitate prompt linkage to treatment for children diagnosed with HIV infection

Investigation into the effect of residual stress on crack-tip constraint and brittle fracture

It is well known that the level of constraint of material at a crack-tip during loading can affect the apparent fracture toughness of components and structures. The effects of geometry and loading on the development of constraint are well defined. Recent research has shown that residual stresses, defined as stresses existing in a material when it is under no primary load, present in the crack-tip region can also affect constraint. However, the effects of this on fracture toughness are not, currently, well understood. The aim of this paper is to investigate the use of constraint based fracture mechanics to quantify unique material fracture toughness curves in two-parameter fracture mechanics type analyses. A novel method for generating residual stresses in single edge notch bend specimens, with minimal associated crack-tip plastic strain, has been devised analytically. Experimental validation has been undertaken to investigate the applicability of constraint based fracture mechanics to characterise the effect of residual stress on brittle fracture of a pressure vessel steel. The results suggest that the use of a unique material toughness curve is possible, certainly when there is a negligible effect of prior plastic strain in the crack-tip region.</jats:p

Magnitude and distribution of retained residual stresses in laboratory fracture mechanics specimens extracted from welded components

Quantifying material fracture toughness properties is an important step in ensuring structural integrity of industrial components. Welding of structural components can cause large magnitudes of residual stress to be generated, which can be defined as a stress that exists in a material when it is under no primary loading. These stresses can be retained in laboratory fracture mechanics testing specimens removed from non-stress relieved welds, making the quantification of valid material fracture toughness difficult. The aim of this paper is to investigate, analytically, the levels and distributions of residual stresses retained in fracture mechanics specimens taken from welded components. This was achieved using parametric finite element analyses. Furthermore, in order to ensure the validity of fracture toughness measurements derived from components that contain residual stress, a robust method for the design of stress-free fracture mechanics specimens is proposed. Significant weld residual stresses have been shown to be retained in certain laboratory specimens post extraction from non stress-relieved welds. The magnitude and distribution of retained residual stress has been shown to be dependant on material properties, specimen size, specimen type and removal location. In addition, the stress partitioning method has been shown to provide a useful approach for estimating the levels and distributions of residual stresses retained in fracture mechanics specimens extracted in certain orientations.</jats:p