Features of ultrasonic wave propagation to identify defects in composite materials modelled by finite element method

A two-dimensional plane strain finite element model with absorbing boundary condition has been developed to investigate the ultrasonic wave propagation in isotropic and orthotropic media. It is capable of simulating the experimental pulse echo technique to obtain A-scan data, when a short duration pulse is transmitted into a domain with or without a flaw. The flaw can either be a crack or an inclusion of different material such as a Teflon insert or a resin rich zone. After performing FFT on the A-scan data, frequency domain feature analysis is done. The study provides a guideline regarding the suitability of certain harmonics sensitive to certain types of flaw. The simulation shows other important artifacts of wave propagation such as mode conversion and scattering due to the presence of flaws.     

Nitrogen plasma source ion implantation of AISI S1 tool steel

Significant economic savings can be achieved by improving the wear lifetime of precision manufacturing tools through nitrogen-ion implantation. This near-ambient temperature, surface modification process preserves dimensional integrity and surface finish while eliminating delamination problems that are often associated with overlay coatings. Conventional ion implantation is a line-of-sight process which requires elaborate manipulation and masking to uniformly implant components of complex shapes. A recently developed process, plasma source ion implantation (PSII), circumvents this line-of-sight restriction and makes ion implantation more attractive economically. In this article, the effects of PSII of nitrogen at a target bias of 50 kV, to a dose of 0.3 × 10¹⁸ atoms/cm² on the surface microstructure and mechanicalproperties of AISI S1 tool steel are presented.     

Structural and electrical measurements of CdZnSe composite

TheI—Vcharacterization and the electrical resistivity of selenium rich Se₈₅Cd_15-xZn_x (x = 0, 3, 7, 11 and 15) system at room temperature have been studied. Samples were obtained using melt cooling technique. So prepared samples were then characterized in terms of their crystal structure and lattice parameter using X-ray diffraction method. The materials were found to be poly crystalline in nature, having zinc blend structure over the whole range of zinc concentration. The measurements ofI—V bdcharacteristics have been carried out at different temperatures from room to 140°C. The electrical resistivity of the samples with composition at room temperature has been found to vary between maximum 2.7 x 10⁸ Ωm and minimum 7.3 x 10⁵ Ωm and shows a maximum at 3 at. wt.% of Zn. The carrier activation energy of the samples with composition has also been determined and found to vary from 0.026 eV to 0.111 eV.     

Deceleration of a porous rotating disk in a viscous fluid

The flow due to a rotating disk decelerating with an angular velocity inversely proportional to time with either surface suction (or injection) which again varies with time is investigated. The unsteady Navier-Stokes equations are transformed to non-linear ordinary differential equations using similarity transformations. The resulting equations are solved numerically using a globally convergent homotopy method. The flow depends on two non-dimensional parameters, namely an unsteadiness parameter $\text{S}$ and a suction (or injection) parameter $\text{A}$. Some interesting numerical results are presented graphically and discussed.     

Short‐beam three‐point bend test study in syntactic foam. Part III: Effects of interface modification on strength and fractographic features

Syntactic foam slabs having uncoated microballoons and paraffin oil surface‐treated microballoons were fabricated and tested for short‐beam three‐point bend test. The work points to the role of paraffin oil coating first weakening the interface between the microballoons and the matrix and hence lowering the efficiency of load transfer from matrix to the fillers (i.e., microballoons). This led to an overall decrement of 71% in the experimentally measured strength value compared to the deduced value for uncoated microballoons' specimens. The large strengths for uncoated microballoons specimens can be traced to the presence of the curvilinear marks in the matrix that, incidentally, are absent in the case of paraffin oil coated specimens. These observations are revealed distinctly in the microscopy of test‐failed specimens. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 687–693, 2005     

Short beam three point bend tests in syntactic foams. Part I: Microscopic characterization of the failure zones

Scanning Electron Microscopic (SEM) studies were carried out on the failure surface of syntactic foam material tested in a short beam three point bend test (SBT) by employing 21 × 15 × 3 mm³ dimension bearing specimens. The syntactic foams were fabricated using glass microballoons in epoxy binder. The failure of the tensile, compression, and shear dominated regions were studied by SEM at different magnifications. The tensile region had characteristic features, such as partial debonding of the microballoons from the matrix and cracking of glass microballoons, apart from matrix cracking and some river pattern features. The compression side was characterized by crushing and collapsing of microballoons, resulting in accumulation of debris with no apparent river pattern for matrix‐rich regions. The midway positions of the SBT failed surface comprised of deformation bands in the matrix and occasional debonding of microballoons. The morphology recorded in the tensile and compression regions corroborated well with the results obtained on these foam samples in those specimens that were subjected to pure uniaxial tension and compression, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 673–679, 2005     

Scheduling a dynamic job shop production system with sequence-dependent setups: An experimental study

This paper presents the salient aspects of a simulation-based experimental study of scheduling rules for scheduling a dynamic job shop in which the setup times are sequence dependent. A discrete event simulation model of the job shop system is developed for the purpose of experimentation. Seven scheduling rules from the literature are incorporated in the simulation model. Five new setup-oriented scheduling rules are proposed and implemented. Simulation experiments have been conducted under various experimental conditions characterized by factors such as shop load, setup time ratios and due date tightness. The results indicate that setup-oriented rules provide better performance than ordinary rules. The difference in performance between these two groups of rules increases with increase in shop load and setup time ratio. One of the proposed rules performs better for mean flow time and mean tardiness measures.     

Utility of 18 F‐FDG PET/CT scan to diagnose the etiology of fever of unknown origin in patients on dialysis

Introduction: Studies on fever of unknown origin (FUO) in patients of chronic kidney disease and end stage renal disease patients on dialysis were not many. In this study, we used 18 F‐FDG PET/CT scan whole body survey for detection of hidden infection, in patients on dialysis, labelled as FUO. Methods: In this retrospective study, 20 patients of end stage renal disease on dialysis were investigated for the cause of FUO using 18F‐FDG PET/CT scan. All these patients satisfied the definition of FUO as defined by Petersdorf and Beeson. Any focal abnormal site of increased FDG concentration detected by PET/CT, either a solitary or multiple lesions was documented and at least one of the detected abnormal sites of radio tracer concentration was further examined for histopathology. Findings: All patients were on renal replacement therapy. Of these, 18 were on hemodialysis and two were on peritoneal dialysis. 18F‐FDG PET/CT scan showed metabolically active lesions in 15 patients and metabolically quiescent in five patients. After 18F‐FDG PET/CT scan all, but one patient had a change in treatment for fever. Anti‐tuberculous treatment was given in 15 patients, antibiotics in four patients and anti‐malaria treatment in one patient. Discussion: The present study is first study of 18F‐FDG PET/CT scan in patients of end stage renal disease on dialysis with FUO. The study showed that the 18 F FDG PET/CT scan may present an opportunity to attain the diagnosis in end stage renal disease patients on dialysis with FUO.