The effect of overload on the fatigue crack growth behaviour of 304 stainless steel in hydrogen

Fatigue crack growth (FCG) behaviour and its characteristics following tensile overloads were investigated for AISI 304 stainless steel in three different atmospheres; namely dry argon, moist air and hydrogen. The FCG tests were performed by MTS 810 servohydraulic machine. CT specimens were used for the tests and crack closure measurements were made using an extensometer. FCG rates of 304 stainless steel at both dry argon and moist air atmospheres have shown almost the same behaviour. In other words, the effect of moisture on FCG of this material is very small. However, in a hydrogen atmosphere, the material showed considerably higher crack growth rate in all regimes. In general, for all environments, the initial effect of overloads was to accelerate the FCG rate for a short distance (less than a mm) after which retardation occurred for a considerable amount of time. The main causes for retardation were found as crack blunting and a long reinitiation period for the fatigue crack. Regarding the environmental effect, the overload retardation was lowest in a hydrogen atmosphere. This low degree of retardation was explained by a hydrogen embrittlement mechanism. In a general sense, hydrogen may cause a different crack closure mechanism and hydrogen induced crack closure has come in to the picture. Scanning electron microscope and light microscope examinations agreed well with the above results.     

Electron beam modification of thermoplastic elastomeric blends made from polyolefins

Thermoplastic elastomeric films have been prepared from blends of ethylene vinylacetate copolymer (EVA) with low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP) by electron beam modification in presence of radiation sensitizer. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) have been used to evaluate the structural changes of these blends. Scanning electron microscopy (SEM) indicates the morphological features of the blends. Significant improvements of mechanical, dynamic mechanical and set properties have been obtained by electron beam modification of the blends of EVA with LDPE and HDPE. However, in the case of EVA/PP, degradation of the PP phase has been observed. The effects of ditrimethylol propane tetraacrylate (DTMPTA) as radiation sensitizer have also been evaluated from the mechanical and dynamic mechanical properties.     

Research of core characteristics of the Package-Reactor

A new small reactor concept called the Package-Reactor has been jointly developed by Hitachi, Ltd. and Mitsubishi Heavy Industries, Ltd. The reactor technology was based on that of conventional LWRs. The reactor core consists of 12 cassettes containing fuel rods with a similar design to that of PWR fuel rods. Cassettes are placed in air at atmospheric pressure. Tube-type control clusters placed outside the pressure boundary are used as the core shutdown system. Natural circulation with two-phase flow is employed for the core cooling system and no re-circulation pumps are required. With these concepts the Package-Reactor eliminates any active components that operate in high pressure regions of the reactor and its capital costs can be reduced. The feasibility of reactivity control by using moderator void feedback and burnable poisons was studied to reduce operational and maintenance costs. It was found that a continuous operation of more than 5 years without any operations to control reactivity would be feasible with a UO₂ fuel enrichment of 5.0 wt%, which is the upper limit for UO₂ fuel enrichment under the current regulations in Japan. In addition, we researched the core reflectors' characteristics of the Package-Reactor.     

Latent hardening in polycrystalline copper and comparison with high density polyethylene

When a parallelepiped specimen of polycrystalline copper is compressed in thex-direction (primary direction) while holding thez-dimension unchanged by a vice, the specimen is anisotropically hardened as follows: when thez-direction is subsequently compressed while holding thex-dimension unchanged the yield stress (0.2% offset) is higher than the final flow stress of the primary deformation. This is similar to latent hardening in single crystals. On the other hand, if the second compression is in they-direction instead of thez-direction, the yielding (0.2% offset) occurs at a stress less than the final flow stress of the primary deformation. Both effects are reported here together with the results of two successive compressions in two mutually perpendicular directions without any constraints in either compression. These results are compared with the earlier results of high density polyethylene.     

A dual-parameter multichannel analyzer using a personal computer

The design of a practical system for measuring two-parameter signals is reported. To obtain constantly changing energy spectral of nuclear reactor assemblies due to repeated insertion of pulsed neutron sources, the simultaneous acquisition of time and energy data is needed. A computer-based dual-parameter multichannel pulse-height analyzer was developed. The analyzer uses a personal computer, two analog-to-digital converters (ADCs), and a parallel interface board for handling these signals. The system is simple to operate, and because the memory size and coincidence resolution time can be changed by software operations, it is highly flexible     

Effect of Sb doping on CVT grown SnTe single crystals electrical and thermal properties

Journal of Materials Science: Materials in Electronics - Pure and Sb-doped SnTe single crystals are grown by chemical vapour transport (CVT) technique. Doping of 5%, 10%, and 15% Sb is done in...     

A framework for business process modeling by QoS-based pruning

In this paper, we have proposed a methodology towards improved business process model redesign based on QoS. We have extended an existing framework that generates an exhaustive space of process models from a set of capability library. The solution space is pruned based on goal and constraints considered thereafter. An algebraic framework is deployed that permits integrated multi-dimensional assessments of QoS factors for choosing path from the reduced space towards derivation of an optimal business process model by comparing the QoS values on both quantitative and qualitative scales. The proposed methodology ensures that while deriving a solution, no possible superior business process model is left out. Further, the designs that do not satisfy the given constraints are eliminated. Eventually, the extended and improved framework provides a comprehensive, both syntactically and semantically correct, consistent and improved business process that adheres to the target business goals and constraints specific to a business house. A use case is used to describe our methodology.     

AC impedance analysis and EMI shielding effectiveness of conductive SBR composites

Flexible conductive polymer composites were prepared using styrene–butadiene rubber (SBR) as a matrix and conductive carbon black as filler. The filler loading was varied from 10 to 60 phr. The complex AC impedance and electromagnetic interference shielding effectiveness (EMI SE) of the composites were measured at the microwave frequencies of 7.8–12.4 GHz. The effect of variation in filler concentration and measurement frequency on the AC impedance and EMI SE of the composites were investigated. Equivalent circuits describing the conduction behavior of the composites were determined by means of Nyquist plots. The complex electric modulus of the composites was also determined. Increase in the filler loading increased the capacitive nature of the materials. The composites were better defined by a parallel resistor–capacitor circuit in series with a resistor. The EMI SE was found to pass through a maximum with increase in frequency. However, with the increase in filler loading and sample thickness of the material, the EMI SE was found to increase continuously. POLYM. ENG. SCI., 46:1342–1349, 2006. © 2006 Society of Plastics Engineers.     

Error explanation with distance metrics

In the event that a system does not satisfy a specification, a model checker will typically automatically produce a counterexample trace that shows a particular instance of the undesirable behavior. Unfortunately, the important steps that follow the discovery of a counterexample are generally not automated. The user must first decide if the counterexample shows genuinely erroneous behavior or is an artifact of improper specification or abstraction. In the event that the error is real, there remains the difficult task of understanding the error well enough to isolate and modify the faulty aspects of the system. This paper describes a (semi-)automated approach for assisting users in understanding and isolating errors in ANSI C programs. The approach, derived from Lewis’ counterfactual approach to causality, is based on distance metrics for program executions. Experimental results show that the power of the model checking engine can be used to provide assistance in understanding errors and to isolate faulty portions of the source code.