Failure Analysis Approach to Fracture Studies in Powder Metallurgy Parts

This paper presents a failure analysis of tool steel and brass powder metallurgy (P/M) parts that failed during service. A detailed failure investigation of fractured tool steel and brass parts was carried out to assess the causes for their premature failures. The fractured surfaces of the broken pieces and the component surfaces were subjected to detailed examination. Investigations were carried out by visual methods, microhardness measurements, and using optical and scanning electron microscopes. In the case of the brass sample, visual examination of the surface indicated flat surface features. Detailed optical and electron microscopic studies corroborated by microhardness indentations have conclusively established that the failure was mainly due to the presence of very small impurities in the brass component material. In the case of the tool steel sample, the fractured surfaces of the component were subjected to destructive and nondestructive tests. Representative fractured pieces were examined visually and tested for their yield strength using simple tensile tests. Optical and scanning electron microscopies at appropriate magnifications were also performed to characterize its microstructure and fracture morphology. Detailed investigations of the tool steel part established that the failure was mainly due to inferior yield strength of the component resulting from improper heat treatment.     

Modelling and experimental investigation of devolatilizing wood in a fluidized bed combustor

A two-dimensional model is developed for the determination of devolatilization time and char yield of cylindrical wood particles in a bubbling fluidized bed combustor. By using the concept of shape factor, the model is extended to particles of cuboid shape. The model prediction of the devolatilization time agrees with the measured data (present and those reported in the literature) for cylindrical and cuboidal shaped particles within ±20% while the char yield is predicted within ±17%. Influence of some important parameters namely, thermal diffusivity, external heat transfer coefficient and shrinkage, on the devolatilization time and char yield are studied. Thermal diffusivity shows noticeable influence on devolatilization time. The external heat transfer coefficient shows little influence beyond a value of 300 W/(m² K). However particle shrinkage shows negligible effect on the devolatilization time but has a significant influence on the char yield.     

Machining characteristics and fracture morphologies in a copper-beryllium (Cu-2Be) alloy

The technology of materials removal is improved greatly by the introduction of advanced cutting tools like cubic boron nitride, ceramics, polycrystalline diamond and the more recent whisker-reinforced materials. In this paper, the influence of cutting temperature on machinability, mechanical properties, microstructure, and fracture morphology of Cu-2Be alloy using a polycrystalline diamond cutter is investigated. The information on machining, microstructure, and fracture morphology of Cu-2Be alloy are very useful to understand their fabrication characteristics and the basic mechanisms of its deformation and fracture. The machinability (in terms of surface finish) of Cu-2Be alloy is evaluated as a function of cutting temperature, resulting from wet and dry cutting. Machining is carried out on a Hardinge Cobra 42 CNC machine (Hardinge Inc., Elmira, NY), and the machining parameters used—cutting speed, depth of cut, and feed rate—are kept constant during both wet and dry cutting. The machined surface finish on Cu-2Be alloy is measured using a surface finish analyzer (Surftest 401, series 178) technique. The machined specimens are examined for their strength and hardness properties using a standard Universal Testing Machine and Rockwell hardness tester, respectively. Wet cutting (using coolants) produced a smooth surface finish when compared with dry cutting of the Cu-2Be alloy. The machined specimens are examined for their microstructural features using a Nikon optical microscope. The specimens are etched using a suitable etchant solution for revealing such microstructure constituents as grain size, phase proportions, and the possible overheated areas (especially in dry cutting). The fractured surfaces from the tensile and impact toughness tests are investigated for their fracture morphologies (dry and wet cutting) using a microprocessor-controlled scanning electron microscope (Jeol Model JSM 5910 LV). A detailed analysis is also made to understand and interpret the basic fracture mechanisms responsible for crack initiation and crack propagation. The Cu-2Be alloy showed relatively higher mechanical properties in wet cutting in comparison to dry cutting operations. Fracture studies demonstrated intergranular and ductile fractures as dominant modes of fracture mechanisms in Cu-2Be alloy.     

TeraGrid Science Gateways and Their Impact on Science

The Science Gateways program seeks to provide researchers with easy access to TeraGrid's high-performance computing resources. A look at four successful gateways illustrates the program's goals, challenges, and opportunities.     

Fuzzy Based Ant Colony Optimization Scheduling in Cloud Computing

Cloud computing is an Information Technology deployment model established on virtualization. Task scheduling states the set of rules for task allocations to an exact virtual machine in the cloud computing environment. However, task scheduling challenges such as optimal task scheduling performance solutions, are addressed in cloud computing. First, the cloud computing performance due to task scheduling is improved by proposing a Dynamic Weighted Round-Robin algorithm. This recommended DWRR algorithm improves the task scheduling performance by considering resource competencies, task priorities, and length. Second, a heuristic algorithm called Hybrid Particle Swarm Parallel Ant Colony Optimization is proposed to solve the task execution delay problem in DWRR based task scheduling. In the end, a fuzzy logic system is designed for HPSPACO that expands task scheduling in the cloud environment. A fuzzy method is proposed for the inertia weight update of the PSO and pheromone trails update of the PACO. Thus, the proposed Fuzzy Hybrid Particle Swarm Parallel Ant Colony Optimization on cloud computing achieves improved task scheduling by minimizing the execution and waiting time, system throughput, and maximizing resource utilization.     

A cascaded scheme for eye tracking and head movement compensation

The authors previously (1995) proposed an efficient method for tracking the eye movements. The proposed algorithm did not address the issue of compensating for head movements. Head movements are normally much slower than eye movements and can be compensated for using another tracking scheme for head position. In this paper, a hybrid method employing the two tracking schemes is developed. To this end, first a measurement model for the compensation of the head movement is formulated and then the overall tracking scheme is implemented by cascading two Kalman filters. The tracking of the iris movement is followed by the compensation of the head movement for each image frame. Experimental results are presented to demonstrate the accuracy aspects and the real-time applicability of the proposed approach     

Influence of Osmotic Suction on the Soil-Water Characteristic Curves of Compacted Expansive Clay

Unsaturated clays are subject to osmotic suction gradients in geoenvironmental engineering applications and it therefore becomes important to understand the effect of these chemical concentration gradients on soil-water characteristic curves (SWCCs). This paper brings out the influence of induced osmotic suction gradient on the wetting SWCCs of compacted clay specimens inundated with sodium chloride solutions/distilled water at vertical stress of 6.25 kPa in oedometer cells. The experimental results illustrate that variations in initial osmotic suction difference induce different magnitudes of osmotic induced consolidation and osmotic consolidation strains thereby impacting the wetting SWCCs and equilibrium water contents of identically compacted clay specimens. Osmotic suction induced by chemical concentration gradients between reservoir salt solution and soil-water can be treated as an equivalent net stress component, (pπ) that decreases the swelling strains of unsaturated specimens from reduction in microstructural and macrostructural swelling components. The direction of osmotic flow affects the matric SWCCs. Unsaturated specimens experiencing osmotic induced consolidation and osmotic consolidation develop lower equilibrium water content than specimens experiencing osmotic swelling during the wetting path. The findings of the study illustrate the need to incorporate the influence of osmotic suction in determination of the matric SWCCs.     

The Effect of Gradual Fluorination on the Properties of FnZnPc Thin Films and FnZnPc/C60 Bilayer Photovoltaic Cells

Motivated by the possibility of modifying energy levels of a molecule without substantially changing its band gap, the impact of gradual fluorination on the optical and structural properties of zinc phthalocyanine (F_nZnPc) thin films and the electronic characteristics of F_nZnPc/C₆₀ (n = 0, 4, 8, 16) bilayer cells is investigated. UV–vis measurements reveal similar Q‐ and B‐band absorption of F_nZnPc thin films with n = 0, 4, 8, whereas for F₁₆ZnPc a different absorption pattern is detected. A correlation between structure and electronic transport is deduced. For F₄ZnPc/C₆₀ cells, the enhanced long range order supports fill factors of 55% and an increase of the short circuit current density by 18%, compared to ZnPc/C₆₀. As a parameter being sensitive to the organic/organic interface energetics, the open circuit voltage is analyzed. An enhancement of this quantity by 27% and 50% is detected for F₄ZnPc‐ and F₈ZnPc‐based devices, respectively, and is attributed to an increase of the quasi‐Fermi level splitting at the donor/acceptor interface. In contrast, for F₁₆ZnPc/C₆₀ a decrease of the open circuit voltage is observed. Complementary photoelectron spectroscopy, external quantum efficiency, and photoluminescence measurements reveal a different working principle, which is ascribed to the particular energy level alignment at the interface of the photoactive materials.