Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Electrical Conductivity and Wire Bending

Name: Joe
Status: student
Grade: 6-8
Location: PA
Country: USA
Date: Fall 2011


Question:
Is wire conductivity affected by bending?



Replies:
Hi Joe,

No, a wire's electrical conductivity is not measurably affected by bending. Regards,

Bob Wilson


Hi Joe The short answer is yes, there is a change in conductivity because bending the wire causes a change in the internal structure (lattice) of the conductive material. The long answer is, you will probably never notice it because the change results in very very minor differences in conductivity. So, practical considerations say that any change resulting from a bend in the conductor is negligible. Hope this helps.

Bob Froehlich


Yes ! it can be affected. Three things: - work-hardening - cracks - small changes of width & length

So if you take a new pure copper electrical wire and bend it at all points along its length by winding it around a round pen, then unroll it against a flat table-top to straighten it, I think it might: - increase in length by 1% and decrease in cross-section by 1%, (keeping about the same volume) and the resistance would increase ~2% from those changes in shape; - become a little harder to bend next time from a bunch of defects now worked into the metal, called work-hardening, which might increase its resistance by more than 5%, or maybe a lot less. You never know with work hardening; - start growing a crack at some point where your bending and unbending was not carefully well-distributed which only affects one short part of the length of wire, so it does not increase resistance much until the wire is almost broken...

One might have to repeat the exercise several times if the metal is very tolerant. If it breaks, try it again with: a) better distributed bending; b) do not go that far, the metal was sufficiently damaged before that point. c) try a thinner wire or a fatter winding mandrel, so the effective bending intensity is less. I think the ratio of mandrel to wire diameters should be ~5-10%. This sets the percentage of stretching or compressing that happens on each side of the wire as it is bent.

Different metals have different degrees of ductility and work-hardenability. galvanized iron wire or stainless steel wire might be more susceptible than copper. It depends most on the amount of carbon in the steel. Rigid steel piano wire is more hardenable because it is made with higher carbon percentage, You can buy it in an annealed state (relatively soft, bendable, compared to its own hard state), or in already-hardened state (very hard and springy, often breaks rather than taking a permanent bend) I think steel guitar strings are hard steel too. High-carbon spring steel can definitely differ by ~20% between the hardened and annealed states.

Copper has many hardenable alloys too - phosphor-bronze and beryllium copper for example.

Jim Swenson


Electrical conductivity in a wire is not effected by bends, unless the bend interrupts the continuity of the wire. Such is not the case in coaxial or fiber cable. Sharp bends in coaxial and fiber cable could pinch off the signal.

Sincere regards, Mike Stewart



Click here to return to the Engineering Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory