An Improved Wheeler Residual Stress Model For Remaining Life Assessment of Cracked Plate Panels

In this paper an improved Wheeler residual stress model has been proposed for remaining life assessment of cracked plate panels under variable amplitude loading (VAL). The improvement to the Wheeler residual stress model is in terms of the expressions for the shaping exponent, which is generally obtained through experiments. Simple expressions for the computation of shaping exponent have been proposed for compact tension (CT) specimen and plate panels with a center crack or an edge crack. The remaining life assessment has been carried out by employing linear elastic fracture mechanics (LEFM) principles. In the present study, the degree of influence of overload ratio (OLR) and the shape factor (β) on the shaping exponent have been investigated for remaining life assessment of cracked plate panels under tensile overload. It is observed that the parameters OLR and β have differing influences on the shaping exponent. Crack growth studies have been conducted on CT specimen and plate panels with a center crack or an edge crack subjected to tensile overloads for validating the proposed expressions. It is observed from the studies that the remaining life predicted using the improved Wheeler model for these plate panels are in close agreement with the experimental values reported in literature.     

Explosive desensitization studies via chemical group modification. Nitroso-Derivatives of RDX and 3-Amino-TNT

With aims toward desensitizing RDX and TNT via molecular modification, mono- and trinitroso-derivatives of RDX and 3-amino-TNT were synthesized and subjected to sensitivity tests. Impact and shock sensitivity data show these compounds to be markedly desensitized. Explosive yield measurements indicate that the changes in power output due to these molecular modifications are minor.     

The Pathogen-annotated Tracking Resource Network (PATRN) system: A web-based resource to aid food safety,regulatory science,and investigations of foodborne pathogens and disease

Investigation of foodborne diseases requires the capture and analysis of time-sensitive information on microbial pathogens that is derived from multiple analytical methods and sources. The web-based Pathogen-annotated Tracking Resource Network (PATRN) system (www.patrn.net) was developed to address the data aggregation, analysis, and communication needs important to the global food safety community for the investigation of foodborne disease. PATRN incorporates a standard vocabulary for describing isolate metadata and provides a representational schema for a prototypic data exchange standard using a novel data loading wizard for aggregation of assay and attribution information. PATRN currently houses expert-curated, high-quality “foundational datasets” consisting of published experimental results from conventional assays and next generation analysis platforms for isolates of Escherichia coli, Listeria monocytogenes, and Salmonella, Shigella, Vibrio and Cronobacter species. A suite of computational tools for data mining, clustering, and graphical representation is available. Within PATRN, the public curated data repository is complemented by a secure private workspace for user-driven analyses, and for sharing data among collaborators. To demonstrate the data curation, loading wizard features, and analytical capabilities of PATRN, three use-case scenarios are presented. Use-case scenario one is a comparison of the distribution and prevalence of plasmid-encoded virulence factor genes among 249 Cronobacter strains with similar attributes to that of nine Cronobacter isolates from recent cases obtained between March and October, 2010–2011. To highlight PATRN's data management and trend finding tools, analysis of datasets, stored in PATRN as part of an ongoing surveillance project to identify the predominant molecular serogroups among Cronobacter sakazakii isolates observed in the USA is shown. Use-case scenario two demonstrates the secure workspace available for private users to upload and analyze sensitive data, and for collating cross-platform datasets to identify and validate congruent datapoints. SNP datasets from WGS assemblies and pan-genome microarrays are analyzed in a combinatorial fashion to determine relatedness of 33 Salmonella enterica strains to six strains collected as part of an outbreak investigation. Use-case scenario three utilizes published surveillance results that describe the incidence and sources of O157:H7 E. coli isolates associated with a produce pre-harvest surveillance study that occurred during 2002–2006. In summary, PATRN is a web-based integrated platform containing tools for the management, analysis and visualization of data about foodborne pathogens.     

Low temperature synthesis of nanosized Mn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites and their characterizations

Nanosized Mn_1−x Zn _x Fe₂O₄ (x = 0, 0·1, 0·3, 0·5, 0·6, 0·7, 0·9) mixed ferrite samples of particle size < 12 nm were prepared using the co-precipitation technique by doping the Zn²⁺ ion impurities. Autoclave was employed to maintain constant temperature of 80°C and a constant pressure. The X-ray analysis and the IR spectrum analysis were carried out to confirm the spinel phase formation as well as to ascertain the cation distribution in the ferrite samples. This clearly points to the fact that the Zn²⁺ ion’s presence is not restricted to A-site alone for some of the Mn-Zn ferrite series. The real part of a.c. susceptibility measurements clearly indicated the superparamagnetic behaviour of the ferrite samples. There is a systematic decrease in the particle size, Curie temperature and magnetization with the increase in the Zn²⁺ ion doping, measured using magneto thermal gravimetric analysis (MTGA) and vibrating sample magnetometer (VSM), respectively. The lattice constant is found to be constantly decreasing till x = 0·6 and beyond this an unusual slight increase in the lattice constant is found.     

An Improved Concrete Damage Model for Impact Analysis of Concrete Structural Components by using Finite Element Method

This paper presents the development of an improved concrete damage model for projectile impact on concrete structural components. The improvement is in terms of reduction of input material parameters for nonlinear transient dynamic impact analysis by employing concrete damage model. The experimental data such as pressure vs volumetric strain, triaxial compression failure and pressure vs stress difference have been used for evaluation of the important parameters of concrete damage model. Various contact algorithms have been outlined briefly to model the interface between the projectile and target. The nonlinear explicit transient dynamic analysis has been carried out by using finite element method to compute the responses. It is observed that the computed penetration depth obtained in the present study is in good agreement with those values of corresponding experimental studies and LS-DYNA.     

An Integrated Model for Tension Stiffening and Reinforcement Corrosion of RC Flexural Members

An integrated model is proposed to describe tension stiffening in reinforced concrete (RC) flexural members that are undergoing uniform corrosion of reinforcement. The tension stiffening model is taken as base to incorporate the effects of reinforcement corrosion. The model is developed in two steps. In the first step, tension stiffening of concrete is modelled using an exponential stress-strain curve defined as function of a decay parameter. Modular ratio and reinforcement ratio are considered in the definition of the decay parameter. In the second step, the effects of uniform corrosion of reinforcement are integrated with the tension stiffening model. For this, fractional reduction in bar diameter is included as an additional parameter in the model. Later, global damage indicator of a structure is defined based on the secant stiffness calculated from its nonlinear load-displacement response. Performance of the proposed model is demonstrated through numerical studies using two RC beams whose details as well as responses are available in literature. Subsequently, the calculated values of damage indicator are shown useful to quantify reduction in load-carrying capacity of the beams. Based on such quantification, effect of assumed corrosion rates of reinforcement bar on capacity loss of the beam is studied in detail.     

A simple correlation for estimation of economic thickness of thermal insulation for process piping and equipment

Where the sole object of applying insulation to a portion of plant is to achieve the minimum total cost during a specific period (evaluation period), the appropriate thickness is usually termed as the economic thickness. The principle is to find at what thickness further expenditure on insulation would not be justified by the additional financial saving on heat to be anticipated during the evaluation period. Although an increase in the amount of insulation applied will raise the initial installed cost, but it will reduce the rate of heat loss through the insulation. Therefore it is necessary to reduce the total cost during the evaluation period. In this work, simple-to-use correlation, employing basic algebraic equations which are simpler than current available models involving a large number of parameters, requiring more complicated and longer computations, is formulated to arrive at the economic thickness of thermal insulation suitable for process piping and equipment. The correlation is as a function of steel pipe diameter and thermal conductivity of insulation for surface temperatures at 100 °C, 300 °C, 500 °C and 700 °C. A simple interpolation formula generalizes this correlation for wide range of surface temperatures. The proposed correlation covers pipeline diameter and surface temperature up to 0.5 m and 700 °C, respectively. The average absolute deviation percent of proposed correlation for estimating the economic thickness of the thermal insulator is 2% demonstrating the excellent performance of proposed simple correlation.     

A comparative evaluation of low cycle fatigue behavior of conventional and modified INCONEL 718

Structural stability of the Inconel 718 is reported to enhance at temperatures above 650°C, with increase in Al/Ti and Al + Ti/Nb atomic ratios. However, no report is available on low cycle fatigue behavior of the modified compositions of the Inconel 718. The present investigation deals with comparative study of LCF behavior of the conventional and modified 718 with Al + Ti/Nb ratios of 0.294 and 0.459 respectively at 650°C. It was observed that fatigue life of the modified alloy, in terms of Coffin-Manson relationship was higher than that of the conventional one.     

Computational Studies on Nitro,Nitramino, and Dinitramino Derivatives of 1‐Aminoazadiboridine as High Energetic Material

Computational studies were performed to determine the thermodynamic and explosive characteristics of high energy materials formed by placing explosophores such as nitro (−NO₂), nitramino (−NHNO₂), and dinitramino (−N(NO₂)₂) groups on 1‐aminoazadiboridine. G3 level calculations were made to determine the gas phase heat of formation of the designed species. In addition to the above, condensed phase heat of formation was also determined by evaluating the sublimation enthalpy. Crystal densities of title compounds were predicted with the help of a wave function analysis (WFA) program and were found to be in the range of 1.55–1.83 g cm⁻³. Bond dissociation energies of various possible bond rupture routes of the designed molecules were calculated at DFT‐B3LYP/6‐311G(d,p) level and attempt was made to identify the trigger linkage. Impact sensitivity was evaluated theoretically by employing a method based on statistical parameters determined from electrostatic potential data. Results show that the designed molecules are highly energetic and their corresponding detonation properties place them in the category of safe and high performance explosive materials.     

Inclusion of covalent triazine framework into fluorinated polyimides to obtain composites with low dielectric constant

Polyimides possess good mechanical properties, favorable dielectric properties, and chemical inertness, which enabled them to find applications in microelectronic industries. The dielectric constant of the polyimides varies between 2.5 and 4, which is rather high for such applications. Hence, synthesizing polyimides with still lower dielectric constant has become one of the critical research confronts. As the properties of a terpolyimides (TPI) could be altered as per the requirement, it was synthesized by combining the dianhydrides 3,3′,4,4′-biphenyldianhydride, 3,3′,4,4′-oxydiphthalicdianhydride, and 4,4′-(hexafluoroisopropylidene) with a diamine 4,4′-(hexafluoroisopropylidene)dianiline or 2,2-bis[4-(4-amino phenoxy)phenyl]hexafluoropropane. As porous covalent triazine framework (CTF-1) is capable of capturing much air within its pores and interfacial voids, it was combined with the TPI matrix in different loadings to obtain CTF-1/TPI composite films with low dielectric constant. The composites exhibited high thermal stability, as their thermal decomposition occurred above 520°C. The tensile properties and the dielectric constant of the composites declined with the raise in CTF-1 loading up to 4%. The decrease in dielectric constant is essentially due to the incorporation of air voids (dielectric constant of air ~1) in the TPI matrix due to the inclusion of porous CTF-1.