Influence of electric discharge machining on fatigue limit of high strength aluminum alloy under finish machining

Abstract

The aim of this study was to investigate the fatigue limit of the electric discharge machined aluminum alloy 2024 T6. Machining was performed at 3, 6, 9, and 12 A discharge current values while all other parameters were kept constant. The fatigue tests were performed on a four-point rotating bending machine at the frequency of 50 Hz and at ambient temperature. Fatigue limits at 10⁷ cycles were determined using staircase (up-and-down) method and the obtained data was analyzed statistically. For reference purposes, fatigue strength of the conventionally turned specimens was also found by the same technique. The EDM surface is characterized by its morphology, roughness, hardness, and thickness of the resolidified layer. The effects of discharge current values on these surface characterizing parameters and subsequent influence on fatigue limit have been discussed.     

Developing the Processing Maps Using the Hyperbolic Sine Constitutive Equation

Hot compression tests were performed on a duplex stainless steel at temperatures ranging from 1223 K to 1473 K (950 °C to 1200 °C) and strain rates from 0.001 to 100 s^?1. The constitutive analysis of flow stress was carried out using the hyperbolic sine function, and the material constants were determined at two typical strains of 0.3 and 0.7. The power dissipation map, instability map, and processing map for the material were developed for strains of 0.3 and 0.7. The developed processing maps were based on the hyperbolic sine as well as the conventional power-law constitutive equations. The efficiency of power dissipation (η) varied from 12 to 60 pct over the studied temperature and strain rate. The highest value of η was obtained at strain rates below 0.01 s^?1, whereas the lowest value of η was observed at the intermediate strain rates. The instability region in sin h-based processing map was only observed in the range of 1423 K to 1473 K (1150 °C to 1200 °C) and at a strain rate of 100 s^?1, while the conventional processing map did not predict any instability region. Optical microscopy observations were more consistent with the results of the sin h-based processing map and indicated that the instability regime at high temperatures and high strain rates was due to the development of adiabatic shear bands.     

Pre-hardened tool steels failure analysis in die-casting

Heat checking is one of the principal causes of termination die-casting molds life. Thermal fatigue cracking of dies because of thermal and mechanical loads may condense the lifetime of the die. The surface quality of dies and as a result the surface of castings is degraded due to cracks. New pre-hardened tool steel known as TOOLOX44, addresses the issue by improving the elimination of heat treatment and optimization of impact toughness. This research investigates thermal fatigue cracking of dies by applying TOOLOX44 in the die casting mold specimen. The surface defect during experimental test was identified by visual analysis of the surface and potential causes of the undesirable effect were analyzed and shown by Cause effect diagram. In addition, microstructures of Toolox44 were analyzed by Light optical microscope and Scanning electron microscope. Finally, chemical compositions of typical TOOLOX44 compared TOOLOX44 sample in 20000 cycles test.     

HANDY: a hybrid association rules mining approach for network layer discovery of services for mobile ad hoc network

Mobile ad hoc network (MANET) is an infrastructure-less network formed between a set of mobile nodes. The discovery of services in MANET is a challenging job due to the unique properties of network. In this paper, a novel service discovery framework called hybrid association rules based network layer discovery of services for ad hoc networks (HANDY) has been proposed. HANDY provides three major research contributions. At first, it adopts a cross-layer optimized design for discovery of services that is based on simultaneous discovery of services and corresponding routes. Secondly, it provides a multi-level ontology-based approach to describe the services. This resolves the issue of semantic interoperability among the service consumers in a scalable fashion. Finally, to further optimize the performance of the discovery process, HANDY recommends exploiting the inherent associations present among the services. These associations are used in two ways. First, periodic service advertisements are performed based on these associations. In addition, when a response of a service discovery request is generated, correlated services are also attached with the response. The proposed service discovery scheme has been implemented in JIST/SWANS simulator. The results demonstrate that the proposed modifications give rise to improvement in hit ratio of the service consumers and latency of discovery process.     

Experimental investigation on CO2-light crude oil interfacial and swelling behavior

A systematic series of experiments are designed and performed including interfacial tension(IFT) measurements concomitant with Bond(BN,the ratio of gravity forces to capillary forces) and swelling/extraction measurements.Dynamic IFT, BN and swelling/extraction are measured as a function of pressure at temperatures of 30,50 and 80 ℃.In addition, in the light of measured IFT the minimum miscibility pressure(MMP) of CO_2 and light crude oil is determined based on a method called vanishing interfacial tension(VIT). The obtained results interestingly revealed that equilibrium IFT decreases linearly with pressure in two distinct pressure intervals while equilibrium BN shows an increasing trend as a function of pressure for all of the studied cases while no obvious trend is observed for swelling of crude oil and extraction of light-components regarding time, temperature and pressure.     

Influence of cold rolling degree and ageing treatments on the precipitation hardening of 2024 and 7075 alloys

In the present work, the precipitation hardening of 2024 and 7075 aluminum alloys is investigated as a function of cold rolling degree, ageing time and temperature using Vickers microhardness measurements and differential scanning calorimetry (DSC). It is found that a variation in such parameters can improve the hardness and plays an important role in the precipitation hardening process. At specific ageing temperature, the large cold rolled 7075 alloy exhibits two peaks of hardness. Moreover, for both alloys, the increment of hardness during ageing decreases with increasing the cold rolling degree. While in some cases microhardness measurements give impression that the precipitation reaction is slowed down by deformation, DSC analysis indicates that the precipitation is much accelerated since only a slight deformation decreases strongly the temperatures of reactions. However, the degree of cold rolling does not play a crucial role.     

Concurrent outbreaks of Shigella sonnei and enterotoxigenic Escherichia coli infections associated with parsley: implications for surveillance and control of foodborne illness

In recent years, the globalization of the food supply and the development of extensive food distribution networks have increased the risk of foodborne disease outbreaks involving multiple states or countries. In particular, outbreaks associated with fresh produce have emerged as an important public health concern. During July and August 1998, eight restaurant-associated outbreaks of shigellosis caused by a common strain of Shigella sonnei occurred in the United States and Canada. The outbreak strain was characterized by unique pulsed-field gel electrophoresis patterns. Epidemiologic investigation determined that the illness was associated with the ingestion of parsley at four restaurants; at the other four restaurants, the majority of the people who contracted the illness ate parsley. Isolates from patrons in two unrelated restaurant-associated enterotoxigenic Escherichia coli (ETEC) outbreaks in Minnesota shared a common serotype and pulsed-field gel electrophoresis (PFGE) pattern. Parsley was the implicated or suspected source of both ETEC outbreaks. In each of the outbreak-associated restaurants, parsley was chopped, held at room temperature, and used as an ingredient or garnish for multiple dishes. Infected food workers at several restaurants may also have contributed to the propagation of the outbreak. The sources of parsley served in outbreak-associated restaurants were traced, and a 1,600-acre farm in Baja California, Mexico, was identified as a likely source of the parsley implicated in six of the seven Shigella outbreaks and as a possible source of the parsley implicated in the two ETEC outbreaks. Global food supplies and large distribution networks demand strengthened laboratory and epidemiologic capacity to enable state and local public health agencies to conduct foodborne disease surveillance and to promote effective responses to multistate outbreaks.