The activation energy for lattice

A phenomenological formula for the calculation of the activation energy for lattice self-diffusion is proposed. Use of the Engel-Brewer theory to determine the valence of an element provides an unambiguous means of calculating the activation energy from the formulaQ = RT_m(16 +V), where R is the gas constant,T _m the melting temperature, andV the Engel-Brewer valence [1 for body-centered cubic (bcc) structures, 2 for close-packed hexagonal (cph) structures and 3 for face-centered cubic (fcc) structures]. The approach works well for the great majority of metals and correctly predicts the activation energy for diffusion in fcc argon and xenon. Dif-fusion coefficients for elements with other structures, elements with anomalous diffusion coef-ficients and semiconductors, are also discussed.     

Alternative for Quantifying Field-Overhead Damages

The context of delays significantly affects delay responsibility. Among other things, recoverable damages for a delay should be related to the timing of the corresponding delay and its effect on indirect costs. This paper presents an alternative and integrated approach for quantifying and apportioning delay responsibility. It considers the context of a delay in terms of its timing and the degree of suspension during the course of a project. The proposed approach allocates project-site overhead costs onto schedule activities. It then helps track site overhead damages in a “real-time” manner while schedule-window analysis is employed to analyze the delay. A case study is used to illustrate its application. Results infer that the conventional daily overhead rate-based method can cause double payments because conventional recovery possibly covers parts of field overhead already paid from the original contract. This new approach also enables the application of the comparative negligence doctrine when concurrent delays occur by fairly sharing delay damages between the project parties. Practitioners can employ the proposed approach for reasonably quantifying and apportioning delay damages while researchers may further explore its applications in the industry.     

Spheroidization cycles for medium carbon steels

An investigation has been made of spheroidization of medium carbon steels used in the bolt industry. Two process cycles were considered. One was the intercritical cycle, widely used in industry, in which the steel was heated above the lower critical, A1, temperature for approximately 2 hours; then cooled below it; and held for various periods to allow the austenite to transform and carbides to spheroidize. The other process was a subcritical cycle, which involved heating to below the A1 for various times. Wire samples of two steels were studied: AISI 1541, which is high in manganese and considered difficult to spheroidize, and AISI 4037, which is considered easier to spheroidize and is used extensively in industrial applications. Both cycles produced similar drops in hardness. However, 1 hour of the subcritical cycle yielded greater ductility than 32 hours of the intercritical process, as measured by tensile tests. Results of a new flare test designed to evaluate formability also indicated much faster spheroidization in the subcritical cycle. The level of spheroidization was defined in this study to be the percentage of carbide particles with aspect ratios less than 3. In 30 minutes, the subcritical cycle produced the same percentage of particles with an aspect ratio of less than 3 as produced by the intercritical cycle in 32 hours. The fast spheroidization in the subcritical process is attributed to the fine pearlite generated by the current practice of rapid cooling off the hot mill. This advantage is lost in the intercritical process as the original pearlite is dissolved above the A1 temperature.