Investigation of creep fracture and bending of arsenical lead alloys for cable sheathing series 1954

Dollins, Curtis W.

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https://hdl.handle.net/2142/112539 Copy

Description

Title

Investigation of creep fracture and bending of arsenical lead alloys for cable sheathing series 1954

Author(s)

Dollins, Curtis W.

Issue Date

1955-01

Keyword(s)

• Creep
• Fracture
• Bending
• Arsenical Lead Alloys
• Cable Sheathing

Abstract

The results of current research on the properties of lead and lead-alloy sheath for underground-power cable are given in this bulletin, which is one of a series of such reports. Special emphasis is placed on the arsenical-lead alloys which have come into commercial use during the last ten years. The data cover creep rates under steady tensile stresses up to 300 psi at 110 and 150 deg, time to fracture under steady stress of 600 to 1800 psi at 110 deg. These properties are important factors in the serviceability of cable sheath. Some of the samples of sheathing for which test results are given herein were manufactured experimentally and represented trials in the development of alloys. Some of them have been accepted for use on cable in commercial orders, while others have been rejected. No classification is given to indicate which materials have been accepted. Small amounts of arsenic in combination with other constituents and with proper production technique are shown to produce a marked improvement in all three properties: creep resistance, life to fracture, and ability to withstand bending. This improvement appears to be due to retardation of recrystallization at the stresses and temperatures that are generally encountered by sheaths in service. At such temperatures in stresses, the reduction in creep rates of arsenical-lead alloys compared with that in commercially pure lead is considerable. However, for some arsenical sheaths that have been produced, at the upper limits of 150 deg and 300 psi which might occur for some cables during short, infrequent periods of ampere-loading in service, there is little difference in creep rate between certain alloys and copper-bearing lead. Some of the other alloys were, nevertheless, considerably better than lead in this respect. In the former cases the retardation of recrystallization appears to be offset by recovery which removes the strain-hardening and thus lowers the creep resistance. The arsenical-lead alloys have good ductility when not too heavily loaded with constituents that form appreciable alpha solid solutions with lead. Unless artificially aged, discontinuous precipitation may render such alloys low in ductility and also low in creep and bending resistance. The alpha solid solutions also lose strength rapidly as the temperature is increased. The constituents that are insoluble or form stable intermetallic compounds impart to lead the best creep and bending resistance for high temperature operation without impairing its ductility. Artificial aging of arsenical-lead sheathing improves it for high temperature operation by preventing discontinuous precipitation due to strain aging, and renders the sheathing in a more stable condition for resting creep by advancing the state of precipitation. The arsenical-lead alloys have outstanding ability to withstand slow bending of the type that occurs in manholes in service because of the daily expansion and contraction of the cable in the duct between manholes. The magnitude of the improvement in this property as well as in others over the properties of copper-bearing lead depends upon the alloy content and aging given the alloys. The alloys with good creep resistance have good bending resistance but they then have lowered creep resistance. Reliable indications of these various properties of cable sheathing of any type are obtainable only from long-time tests. Stopping the press during extrusion greatly affects the creep properties of the sheath, seemingly because of the difference in work hardening and heat treatment that the sheath receives during the stopping, recharging, and starting of the press. This generally causes a narrow ring around the sheath that has very high creep resistance; the adjacent sheath for a foot or more has a little less than normal creep resistance.

Publisher

Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign

Series/Report Name or Number

• TAM R 78
• 1967-0374

ISSN

0073-5264

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/112539

Sponsor(s)/Grant Number(s)

The Edison Research Committee of The Commonwealth Edison Company

Copyright and License Information

Copyright 1955 Board of Trustees of the University of Illinois

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