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  • 2000-2004  (4)
  • 1
    Electronic Resource
    Electronic Resource
    PO Box 1354, 9600 Garsington Road, Oxford OX4 2XG, UK. : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 27 (2004), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Quantification of the enhancement in cleavage fracture toughness of ferritic steels following warm pre-stressing has received great interest in light of its significance in the integrity assessment of such structures as pressure vessels. A Beremin type probability distribution model, i.e., a local stress-based approach to cleavage fracture, has been developed and used for estimating cleavage fracture following prior loading (or warm pre-stressing, WPS) in two ferritic steels with different geometry configurations. Firstly, the Weibull parameters required to match the experimental scatter in lower shelf toughness of the candidate steels are identified. These parameters are then used in two- and three-dimensional finite element simulations of prior loading on the upper shelf followed by unloading and cooling to lower shelf temperatures (WPS) to determine the probability of failure. Using both isotropic hardening and kinematic hardening material models, the effect of hardening response on the predictions obtained from the suggested approach has been examined. The predictions are consistent with experimental scatter in toughness following WPS and provide a means of determining the importance of the crack tip residual stresses. We demonstrate that for our steels the crack tip residual stress is the pivotal feature in improving the fracture toughness following WPS. Predictions are compared with the available experimental data. The paper finally discusses the results in the context of the non-uniqueness of the Weibull parameters and investigates the sensitivity of predictions to the Weibull exponent, m, and the relevance of m to the stress triaxiality factor as suggested in the literature.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 24 (2001), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The purpose of this paper is to revisit the maximum tensile stress (MTS) criterion to predict brittle fracture for mixed mode conditions. Earlier experimental results for brittle fracture of polymethylmethacrylate (PMMA) using angled cracked plates are also re-examined. The role of the T-stress in brittle fracture for linear elastic materials is emphasized. The generalized MTS criterion is described in terms of mode I and II stress intensity factors, KI and KII and the T-stress (the stress parallel to the crack), and a fracture process zone, rc . The generalized MTS criterion is then compared with the earlier experimental results for PMMA subjected to mixed mode conditions. It is shown that brittle fracture can be controlled by a combination of singular stresses (characterized by K ) or non-singular stress (T-stress). The T-stress is also shown to have an influence on brittle fracture when the singular stress field is a result of mode II loading.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Alimentary pharmacology & therapeutics 15 (2001), S. 0 
    ISSN: 1365-2036
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: : 5-aminosalicylic acid (5-ASA) has been associated with renal complications in inflammatory bowel disease. Renal function is typically monitored using serum creatinine; however, significant disease may predate increases in creatinine.〈section xml:id="abs1-2"〉〈title type="main"〉Aims: To identify whether markers of early renal disease (urinary albumin, α-1-microglobulin [α-1-M] and N-acetyl-β-D-glucosaminidase [NAG], and serum cystatin C) are useful in the assessment of renal function in inflammatory bowel disease patients receiving 5-ASA.〈section xml:id="abs1-3"〉〈title type="main"〉Methods: Twenty-one patients with a new diagnosis of inflammatory bowel disease were investigated. Samples were taken at diagnosis, and at 3-monthly intervals after the commencement of 5-ASA, for 1 year.〈section xml:id="abs1-4"〉〈title type="main"〉Results: Mean creatinine clearance was 100 mL/min and did not change following treatment. Inflammatory bowel disease was not associated with albuminuria. Urinary N-acetyl-β-D-glucosaminidase and α-1-microglobulin at diagnosis were increased in 10 (48%) and 11 (52%) patients, respectively: treatment was not associated with consistent changes in urinary protein excretion. There was a significant correlation between cystatin C and creatinine clearance both at diagnosis (r=–0.533, P=0.0275) and combining the initial and follow-up data (r=–0.601, P 〈 0.01), but not between creatinine and creatinine clearance (P 〉 0.05).〈section xml:id="abs1-5"〉〈title type="main"〉Conclusions: Tubular proteinuria is an extra-intestinal manifestation of inflammatory bowel disease irrespective of 5-ASA treatment. Tubular proteins are not useful predictors of an adverse renal response to 5-ASA. Serum cystatin C may be an improved marker of glomerular filtration rate in this setting.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Alimentary pharmacology & therapeutics 16 (2002), S. 0 
    ISSN: 1365-2036
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Aim : To establish whether bone disease is present at diagnosis in inflammatory bowel disease and to identify contributory metabolic abnormalities.Methods : Newly diagnosed patients with inflammatory bowel disease (19 males, 15 females; mean age, 44 years; range, 17–79 years; 23 ulcerative colitis, 11 Crohn's disease) were compared against standard reference ranges and a control group with irritable bowel syndrome (eight males, 10 females; mean age, 40 years; range, 19–64 years). Bone mineral density (g/cm2, dual-energy X-ray absorptiometry: lumbar spine and femoral neck) and biochemical bone markers were measured.Results : Femoral neck bone mineral density, T- and Z-scores (mean ± s.d., respectively) were lower in inflammatory bowel disease patients than in irritable bowel syndrome controls (0.78 ± 0.12 vs. 0.90 ± 0.16, P = 0.0046; − 0.88 ± 0.92 vs. 0.12 ± 1.17, P = 0.0018; − 0.30 ± 0.89 vs. 0.61 ± 1.10, P = 0.0030). Lumbar spine bone mineral density and T-scores were also significantly lower in patients than controls (0.98 ± 0.15 vs. 1.08 ± 0.13, P = 0.0342; − 1.05 ± 1.39 vs. − 0.14 ± 1.19, P = 0.0304). Compared with controls, the urinary deoxypyridinoline : creatinine ratio was increased (7.66 vs. 5.70 nmol/mmol, P = 0.0163) and serum 25-hydroxy vitamin D was decreased (18.7 vs. 28.5 µg/L, P = 0.0016); plasma osteocalcin and serum parathyroid hormone did not differ (P 〉 0.05).Conclusions : The bone mineral density is reduced at diagnosis, prior to corticosteroid treatment, in both Crohn's disease and ulcerative colitis. Our data suggest that this is attributable to increased resorption rather than decreased bone formation.
    Type of Medium: Electronic Resource
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