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Linear programming is now included in algorithm undergraduate and postgraduate courses for computer science majors. We give a self-contained treatment of an interior-point method which is particularly tailored to the typical mathematical background of CS students. In particular, only limited knowledge of linear algebra and calculus is assumed. [ABSTRACT FROM AUTHOR]

The numerical prediction of stretch zone width (SZW) under mixed mode condition is rarely reported in the literature. As in most practical situations structures experience complex loading resulting in mixed mode fracture, thus it is essential to establish a methodology for the numerical assessment of SZW under mixed mode fracture condition. Three dimensional non-linear FEM simulations were carried out to correlate numerical parameters with experimentally determined critical SZW and initiation fracture toughness. The present numerical investigation is able to explain the involved mechanism and numerically predicted SZW, critical SZW and initiation fracture toughness which compares well with experimental results. [ABSTRACT FROM AUTHOR]

The effect of fracture specimen parameters like side grooving magnitude, its root radius and angle on the critical stretch zone width formation studied. It is found that there is maximum limit of side grooving magnitude and a minimum limit of root radius and angle which will provide geometry independent evaluation of critical SZW. It is concluded that side grooving magnitude should not be larger than 0.25 times thickness; root radius should not be less than 100 μm and the side grooving angle should not be less than 70°. [ABSTRACT FROM AUTHOR]

To obtain geometry independent critical stretch zone width there is a need to understand its variation with fracture specimen thickness, initial crack size, fracture specimen geometries and the type of loading. It comes out that minimum tri-axiality quotient value on the un-cracked ligament and the plastic zone size contained within fracture specimen geometry are the two criteria to be considered while choosing the fracture specimen shape and its geometry for the evaluation of valid critical SZW value of the material. The present study also showed the possibility of further improving the minimum thickness criterion of fracture specimen. [ABSTRACT FROM AUTHOR]

Steam turbine blades are the critical component in power plant, specifically low pressure blades are generally found to be more susceptible to failure. A mechanical, metallurgical and FEM based coupled methodology is used in the present failure investigation of low pressure steam turbine blade. The results of each investigation of turbine blade failure were then interpreted that leads to find the location of primary failure, sequence of failure and the root cause of its failure. All the three aspects of failure investigation are important in answering the questions raised for the failure and to avoid any future miss-happening. [ABSTRACT FROM AUTHOR]

Abstract: Among several other definitions, the crack initiation fracture toughness (J i) based on critical stretch zone width (SZWc), called J SZWc, is being considered as a geometry independent material property. The problem in SZWc experimental evaluation is in identifying the size of stretch zone on a blunted crack front as this requires a high degree of precision and expertise in measuring the SZW. The present study addresses finite element determination of SZWc value using tensile test data. The role of stress tri-axiality in standard fracture specimens and the smooth round tensile specimen is also studied. Based on the ASTM-E1820 standard, the present study also showed that fracture specimen thickness greater than the specified size is to be used for numerical prediction of valid SZWc value. The numerically predicted SZWc that leads to J SZWc matches well with experimental values. Using J SZWc, the crack initiation load is also determined in circumferentially through-wall cracked (TWC) elbows and compares well with experimental results. Thus the paper establishes the methodology to predict crack initiation in cracked piping components using numerically obtained valid J SZWc from material’s tensile test data. [ABSTRACT FROM AUTHOR]

Abstract: Using large deformation FEM analyses in SA333Gr.6 carbon steel material, the present study demonstrated the assessment of SZWc value that leads to J SZWc and finally compares with the respective experimental results. It also includes numerical prediction of specimen J–R curve using Gurson–Tvergaard–Needleman parameters obtain from tensile specimen tests. Using numerically predicted results, the crack initiation and instability stages in circumferentially through-wall cracked elbows is finally predicted and compares with experimental results. The present study gives evidence that the non-linear FEM analysis supported with proper tensile test data can be helpful in assessing the safety of bend pipes with through-wall crack. [Copyright &y& Elsevier]

Abstract: The study addresses numerical determination of stretch zone width and its critical value. The proposed method is based on the highly deformed stretch zone that is defined as stretch zone width, expected to be better than the half of the crack tip opening distance which inturn determined using 45° line method. The investigation essentially comprises a number of finite element analyses of compact tension test, using tensile test data. The proposed methodology also provides insight into the mechanism involved in the creation of stretch zone. [Copyright &y& Elsevier]

Abstract: Ductile fracture assessments of circumferentially through-wall cracked elbows, based on the elastic–plastic J-integral concept, are discussed with particular interest in its ability and accuracy to predict experimental results corresponding to the initiation of stable crack growth. 3D non-linear finite element analysis is backed up with experimental results to determine the crack initiation load. Non-linear finite element analyses were performed considering both material and geometrical non-linearity using the advanced fracture analysis code WARP3D. Numerical analyses have been carried out to understand the role of crack tip constraint in standard specimens and the elbow component. An attempt has been made to obtain a unique multiaxiality quotient (q) for evaluation of the level of constraint. The work provides benchmark data to assist in the engineering treatment of cracked piping elbows. [Copyright &y& Elsevier]

Abstract: Ductile fracture assessments of circumferentially through-wall cracked piping components performed on the basis of the elastic–plastic -integral concepts are discussed with particular interest in its ability and accuracy to predict actual experimental loads corresponding to initiation of stable crack growth and failure stages. Possible source of uncertainty in the modeling of material behaviour is treated separately, comparing results with each other and with experimental data. Especially estimation schemes for evaluating applied -integral are checked against 3D non-linear finite element analysis (FEM) using the advanced fracture analysis code WARP3D. The influence of stress–strain curve used as an input to the FEM analysis on the predicted results of crack initiation and maximum loads is examined in circumferentially through-wall cracked pipes. The elastic–plastic fracture mechanics based -integral combined with analysis is found to give an accurate and complete description of component behaviour. An approximation of material stress–strain curve is given based on the interpretation of experimental results. [Copyright &y& Elsevier]

In order to evaluate the structural integrity of power plants, it is required to know the load carrying capacity of a piping system. J-integral based elastic-plastic fracture mechanics (EPFM) has become a useful analytical technique for dealing with ductile materials. It is important to see how accurately we can predict the stages of leak-before-break demonstration using EPFM. Current efforts are focussed on verifying previously developed J-estimation schemes for through-wall cracked (TWC) straight pipes with the calculated elastic-plastic J-integral values that are obtained by conducting a rigorous 3D non-linear finite element analysis using advanced fracture analysis code WARP3D. This includes the validation and benchmarking of J-estimation schemes with the present 3D non-linear finite element analysis results and with the experimental results at crack initiation stage. The results corresponding to crack initiation results calculated by estimation schemes are too conservative. Thus, in order to perform J-integral based EPFM analysis more accurately and conveniently, there is a need to develop an efficient estimation scheme that can represent material behaviour closely. The crack initiation load calculated by the present finite element analysis results is shown to provide a more reasonable prediction. [Copyright &y& Elsevier]

• A solution to accurately predict compressive deformation behavior of metallic foam material up-to densification region. • Proposed to choose the correct constitutive relation while defining crushable foam model parameters for metallic foam material while designing composite structure. • Quantify the effect of crushable foam model input parameters in terms of predicting accurately the experimental load- displacement behavior of metallic foam. Closed cell metallic foam material has immense potential to use it as core material in composite structures. In the design of such structures and to understand numerically its deformation behaviour there is a difficulty of choosing the correct constitutive behaviour of metallic foam due to its porous structure. A solution has been proposed to accurately predict the experimental behavior of a closed-cell metallic foam up-to densification region by the use of a crushable foam model under compressive loading condition. The effect of using different stress-strain material curves and other input parameters of the crushable foam model is quantified in terms of predicting experimentally determined compressive load-displacement behavior of the metallic foam. It has been found that for predicting accurate compressive behavior of metallic foam using a crushable foam model, the hardening behavior of metallic foam may be defined by engineering stress vs. true strain values. [ABSTRACT FROM AUTHOR]

Herein we report the synthesis, PDE-4B and TNF-α inhibitory activities of a few dibenzo[ b , d ]furan-1-yl-thiazole derivatives. The hydroxycyclohexanol amide derivatives 14 , 18 , 24 , 29 , 31 and 33 exhibited promising in vitro PDE-4B and TNF-α inhibitory activities. Compound 24 showed good systemic availability in preclinical animal models and was also found to be non-toxic (exploratory mutagenicity test). Further it exhibited promising results in in vivo asthma/COPD and Uveitis models. [ABSTRACT FROM AUTHOR]

Bone histology in patients with nephrotic syndrome and normal renal function. Background. The prevalence of metabolic bone disease in patients with nephrotic syndrome (NS) at normal level of renal function remains uncertain. Methods. To address this issue, we studied 30 patients (20 men and 10 women, mean age 27.3 ± 11.7 years) with NS who had normal renal function (mean creatinine clearance 103 ± 4 ml/min). We evaluated their serum calcium, phosphorus, alkaline phosphatase, immunoreactive parathyroid hormone (iPTH), vitamin D metabolites, urinary calcium, and skeletal survey. The extent of bone mineralization was analyzed by histomorphometric analysis of iliac crest bone biopsy specimens in all patients. The findings on bone histology were correlated with biochemical parameters. Results. The mean duration of NS was 35.5 ± 26.9 months, with a protein excretion of 7.3 ± 3.2 g/24 hr and a serum albumin of 2.2 ± 0.8 g/dl. Total serum calcium was 7.8 ± 0.8 mg/dl, whereas ionized calcium was 5.7 ± 0.7 mg/dl, phosphorus 3.2 ± 1.2 mg/dl, and alkaline phosphatase 149 ± 48.6 U/liter. Serum iPTH levels were normal in all except two patients. The mean serum 25-hydroxyvitamin D [25(OH)D] level was 3.9 ± 1.2 ng/ml (normal 15 to 30 ng/ml), whereas 1,25-dihydroxyvitamin D was 24 ± 4.7 pg/ml (normal 16 to 65). There was an inverse correlation between serum levels of 25(OH)D and the magnitude of proteinuria &formmu1;. The mean 24-hour urinary calcium excretion was 82 ± 21 mg/day. The skeletal survey was normal in all patients. Bone histology was normal in 33.3% of the patients, whereas 56.7% had isolated osteomalacia (OSM), and 10% had an increased bone resorption in association with defective mineralization. The severity of OSM measured by mineralization lag time correlated linearly with the duration &formmu2; and the amount &formmu3; of proteinuria. All patients with NS for more than three years had histological changes. Patients with OSM had lower 25(OH)D and serum albumin as compared with those with normal histology (P < 0.005). Bone mineralization had no significant correlation with serum iPTH, divalent ions, or vitamin D levels. Conclusions. OSM is a frequent finding in adult patients with NS, even at a normal level of renal function. Its severity correlates with the amount and duration of proteinuria. [ABSTRACT FROM AUTHOR]