Info Favorites Register Log in
myArmoury.com Discussion Forums

Forum index Memberlist Usergroups Spotlight Topics Search
Forum Index > Off-topic Talk > Can tempered steel loosen up more from shock force trauma? Reply to topic
This is a standard topic  
Author Message
Christopher B Lellis




Location: Houston, Texas
Joined: 01 Dec 2012

Posts: 268

PostPosted: Wed 21 May, 2014 10:58 am    Post subject: Can tempered steel loosen up more from shock force trauma?         Reply with quote

I was testing the durability and overall quality of a sword by whacking the broad side of the blade on an object to see if it kept it's shape and stayed straight. I probably hit each side about 30 times with a strong amount of force and I might be mistaken because I have no way to actually prove it but it seems to me like the entire sword is slightly more flexible, especially where I thought it was too stiff in the middle. The sword did not bend, at least to the naked eye.

Can you actually loosen the steel up by just putting it under stress, or I am just imagining this?
View user's profile Send private message
Peter Lyon
Industry Professional



Location: New Zealand
Joined: 20 Nov 2006
Reading list: 39 books

Posts: 229

PostPosted: Wed 21 May, 2014 11:53 am    Post subject:         Reply with quote

I hope it is just your imagination, otherwise it is possible the increased flexibility is due to stress micro cracking. I don't know of any way that the heat treat would change otherwise. Maybe the more metalurgically inclined could give other ideas.
Still hammering away
View user's profile Send private message
Christopher B Lellis




Location: Houston, Texas
Joined: 01 Dec 2012

Posts: 268

PostPosted: Wed 21 May, 2014 12:00 pm    Post subject:         Reply with quote

Peter Lyon wrote:
I hope it is just your imagination, otherwise it is possible the increased flexibility is due to stress micro cracking. I don't know of any way that the heat treat would change otherwise. Maybe the more metalurgically inclined could give other ideas.


Well, that's not very good at all is it
View user's profile Send private message
Timo Nieminen




Location: Brisbane, Australia
Joined: 08 May 2009
Likes: 1 page
Reading list: 1 book

Posts: 1,494

PostPosted: Wed 21 May, 2014 5:12 pm    Post subject:         Reply with quote

Unless you hit hard enough to flatten a mid-blade ridge (or similar), then cracks. Or imagination.

Next time, measure the flexibility before and after. Clamp the base of the blade, and hang a weight from the tip, and see how far the blade bends under the load. Whack-test, and repeat. Expect no difference, and if you see one, suspect cracks. This is a real-life crack-detection technique; see https://biblio.ugent.be/publication/3140766 and http://www.sciencedirect.com/science/article/...8306005580

You could load the blade like this, and feel whether the upper surface is smooth when bent. I don't know whether cracks would open up enough to feel, but you could try. At least a negative result might reassure.

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
View user's profile Send private message Visit poster's website
Luka Borscak




Location: Croatia
Joined: 11 Jun 2007
Likes: 7 pages

Posts: 2,229

PostPosted: Thu 22 May, 2014 3:42 am    Post subject:         Reply with quote

I don't think you really cracked your blade, but I would advice against such rigorous tests next time. A few whacks on each edge and flat against an object is ok to see if there is a weak spot in the blade, but 30 strikes each side is maybe a bit too abusive.
View user's profile Send private message
Eric W. Norenberg





Joined: 18 Jul 2008

Posts: 265

PostPosted: Thu 22 May, 2014 12:18 pm    Post subject:         Reply with quote

Sounds like metal fatigue to me... I could wildly speculate that repeated rapid flexing, due to impact, in a very restricted area could create enough heat to alter the temper in that zone. But my money is on metal fatigue, stress micro-fractures.

I don't think you'll find much info on that related directly to sword blades but you might find some stuff on this internet thing about car leaf springs, written in more-or-less laypersons' terms, by people with some material science/engineering/metallurgy pedigree. You'll find some parallel insights perhaps.

Stress micro-fractures aren't the end of a piece of metal's life but many will argue that it is the beginning of the end. What this really means to you depends on what you really use the sword for - if you are into test cutting heavy targets I would have serious concerns.

I think that an instinctive understanding of this is why there aren't more historical blades out there to be found - a certain amount of hard use/ abuse and a fighting man might start to worry about how much life was left in a blade.
View user's profile Send private message
Timo Nieminen




Location: Brisbane, Australia
Joined: 08 May 2009
Likes: 1 page
Reading list: 1 book

Posts: 1,494

PostPosted: Thu 22 May, 2014 5:49 pm    Post subject:         Reply with quote

Eric W. Norenberg wrote:
I could wildly speculate that repeated rapid flexing, due to impact, in a very restricted area could create enough heat to alter the temper in that zone.


This won't change the flexibility. That is, the elastic modulus (Young's modulus) doesn't depend on the heat treatment. The elastic limit (how far it can bend before it permanently deforms), and whether failure is plastic (taking a set) or fracture (breaking) depends on the heat treatment.

(OK, there will be a small effect due to heat treatment - the density depends on heat treatment - but it's small. Even the composition of a steel alloy only has a small effect on the elastic modulus; the effect of heat treatment is much smaller.)

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
View user's profile Send private message Visit poster's website
Eric W. Norenberg





Joined: 18 Jul 2008

Posts: 265

PostPosted: Fri 23 May, 2014 8:03 am    Post subject:         Reply with quote

Ah, excellent Timo. Thank you for that explanation, that is something new to me. So relative stiffness / wiggly-ness is determined by other factors (material density, or cross section?), heat treating and tempering mostly effecting failure resistance and the nature of the failure?
View user's profile Send private message
Timo Nieminen




Location: Brisbane, Australia
Joined: 08 May 2009
Likes: 1 page
Reading list: 1 book

Posts: 1,494

PostPosted: Sat 24 May, 2014 5:18 pm    Post subject:         Reply with quote

Basically, yes. Heat treatment determines failure point and mode of failure.

Density for various steel alloys and iron doesn't vary much; it's the cross-section that matters for stiffness. For side-to-side stiffness, the stiffness is proportional to the width, and the cube of the thickness. That cubic dependence is why diamond-section blades, especially hollow diamond with high ridges, are so stiff.

IIRC, there's less than 10% variation in elastic modulus (Young's modulus) over most steels, including stainless steels with about 30% of the alloy being other than iron. (Cast iron can have a much lower elastic modulus.)

A handy table: http://www.engineeringtoolbox.com/young-modulus-d_773.html

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
View user's profile Send private message Visit poster's website


Display posts from previous:   
Forum Index > Off-topic Talk > Can tempered steel loosen up more from shock force trauma?
Page 1 of 1 Reply to topic
All times are GMT - 8 Hours

View previous topic :: View next topic
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum






All contents © Copyright 2003-2018 myArmoury.com — All rights reserved
Discussion forums powered by phpBB © The phpBB Group
Switch to the Basic Low-bandwidth Version of the forum