Experimental Investigation and Simulation of Magnetic Flux Leakage from Metal Loss Defects

Journal of Failure Analysis and Prevention - Magnetic flux leakage (MFL) principle is widely used in detecting defects in cross-country pipelines. The tools based on the MFL techniques termed as...     

Pre-disaster investment decisions for strengthening a highway network

We address a pre-disaster planning problem that seeks to strengthen a highway network whose links are subject to random failures due to a disaster. Each link may be either operational or non-functional after the disaster. The link failure probabilities are assumed to be known a priori, and investment decreases the likelihood of failure. The planning problem seeks connectivity for first responders between various origin–destination (O–D) pairs and hence focuses on uncapacitated road conditions. The decision-maker's goal is to select the links to invest in under a limited budget with the objective of maximizing the post-disaster connectivity and minimizing traversal costs between the origin and destination nodes. The problem is modeled as a two-stage stochastic program in which the investment decisions in the first stage alter the survival probabilities of the corresponding links. We restructure the objective function into a monotonic non-increasing multilinear function and show that using the first order terms of this function leads to a knapsack problem whose solution is a local optimum to the original problem. Numerical experiments on real-world data related to strengthening Istanbul's urban highway system against earthquake risk illustrate the tractability of the method and provide practical insights for decision-makers.     

Varying relaxation parameters in nonlinear successive overrelaxation

We derive here a generalization to nonlinear problems of the “free steering theorem” of Ostrowski on sufficient conditions for convergence of linear SOR with varying relaxation parameters.     

Effect of cold rolling on the elastic properties of (Al2O3)p-Al composite

Mechanical shaping of an aluminium alloy reinforced with Al₂O₃ particulates, (Al₂O₃)_p-Al, was carried out by a cold rolling operation. Rolling was performed unidirectionally in a direction perpendicular to the extrusion direction of the composite, until edge cracks formed. Cold rolling was found to cause particulate cracking and interfacial debonding, as wellas the redistribution of (Al₂O₃)_p. These parameters have significant roles in determining the elastic properties of the resultant composite.     

Precipitation behavior in a medium carbon,ti-v-n microalloyed steel

The precipitation behavior of a medium carbon steel microalloyed with Ti, V, and N has been studied by analytical transmission electron microscopy in the as-cast and isothermally heat-treated states, as well as at different stages in the thermomechanical processing of the steel. Mixed (Ti,V) nitrides were found in all the structures, but there was no evidence for mixed carbonitride formation. The Hillert-Staffansson model was used to predict the composition of the nitrides as a function of tem-perature. Upon prolonged aging many of the precipitates became “fragmented” and were no longer single crystals. At the same time, the volume fraction of precipitates dropped, while their average Ti content increased. Possible explanations for this unexpected behavior are discussed in this article.     

Electrical properties of Ln2Mo2O7 pyrochlores (Ln=SmYb,Y)

Cubic oxide pyrochlores, Ln₂Mo₂O₇, Ln=SmYb,Y, (Nd_1?xA_x), A=Er and Yb; 0 < x < 1.0, have been synthesized and electrical properties were examined in the range 77-600K. Semiconductor behavior is observed for Ln=EuYb, Y but the resistivity and E_a are low. Sm₂Mo₂O₇ and Nd_1?xYb_xMo₂O₇ (0.05 ≤ x ≤ 0.1) exhibit semimetallic or metallic behavior. The mechanism of conduction in these compounds is explained on the basis of band model proposed by Sleight et al.     

Age Replacement In Simple Systems With Increasing Loss Functions

Some age replacement policies are investigated and conditions for the unique existence of an optimum policy are derived. The optimum policy is the one which minimizes the expected cost per unit time over an infinite time span or maximizes the proportion of time during which the system is in operation. Losses have been expressed through increasing operating cost, if the objective is to minimize the expected total cost per unit time and through increasing renewal times if the objective is to maximize the availability of the system.     

Complex two-unit system with preventive maintenance

A two-unit warm standby redundant system with repair and preventive maintenance is considered. The pdf of the life time of a unit while in standby is assumed to be Erlangian. The pdfs of all the other random variables are arbitrary. Identifying suitable regeneration points, expressions for the Laplace transforms of the availability and reliability of the system are derived.