Failure analysis of Ancient metal artifacts

[IronAgeGeorge]

Hi, I hope I've come to the right place, I'm an archaeology researcher located in England with an engineering background and I've been asked to help a fellow researcher looking into possible reasons for failure of Bronze Age copper alloy artifacts such as axes.

It occurs to me this is a field in which we are in desperate need of some expert help.

One of the object types in question are small bronze wood cutting axes, some of these have failed by a fracture which runs in parallel with the cutting edge, 1-2cm back, either the entire cutting edge is lost or it "hangs off", with a large crack running at least 50% of the blade length.

Some of these axes also show signs of sometimes extreme mis-use and there is a train of thought which suggests these items may have been "ritually" broken.

However, I have a feeling that a great many of these objects hay have failed as a normal part of the product "life cycle". If I remember correctly, an axe, even when used completely normally will eventually fail due to small fractures joining up?

Ideally I'd like to find some failure analysis on similar objects, So something on failure of axes or hammers, and something on failure of copper alloys would be really good.

If anyone is interested I'd also like information on abnormal use failures, it occurs to me that in some cases what we are seeing is damage caused by continuing use after an initial failure. Or that the artifact was used "against the manufacturers instructions".

I hope someone can help, or at least point me in the right direction. Sorry I'm such a novice, I did three months of material science as part of my electronics based apprenticeship, that was a long time ago and the electronics swiftly moved on to computers.

 

[swertel]

Do you have any pictures of these you could share? Maybe post them on a website and give the link here.

It is easier to determine the mode of failure if we can see the cracks and striations <sic> of the piece.

In the meantime, I'll &quot;dig&quot; around and see if I can come up with some good references to material failure.

--Scott

 

[IronAgeGeorge]

Hi Scott,

I'm afraid right now the images I have got do not show the damage in sufficient detail to allow a proper analysis.

However, I will speak to my collegue and see what we can do.

I will get a few of the images that I do have and get them on a web site in the mean time.

I have a feeling we only need to understand a few objects in order to establish if metal fatigue of some sort was a primary reason for failure.

 

[Carburize]

There may also be information available on similar work or contact with specialists through the Historical Metallurgy Society in the UK.

http://www.hist-met.org

 

[TVP]

ASM International offers many references on the topic of failure analysis. Use the following link to browse their catalog on this topic:

http://www.asminternational.org/Tem...yTopic&template=Ecommerce/Topic.cfm&TopicID=8

A good university library will have some of these books in their reference section.

 

[IronAgeGeorge]

I have scanned in one diagram I have showing an axe head which is seen as possibly being ritually broken.

http://www.smartgroups.com/pictures...reID=10490010&Layout=D&Sort=Ordernum&Dir=desc

Sorry it's not much good.

I've emailed my collegue for better pictures.

The text to accompany the axe head goes as follows:

&quot;An axe blade for instance, was probably still shafted when a massive blow landed just below the onset of the haft, tearing the exposed part of the blade downwards, all but breaking it in two. It is significant that, despite further blows shown by dents and cracks on the thin edge of the flanges, the axe stayed in one piece.&quot; Louis Nebelsick.

The author then goes on to say that together with the other damaged objects in the hoard this shows clear evidence of Ritual breaking.

 

[tomwalz]

“A” is the axe head?
It is about 15 cm ( 6” )long and about 4.5 (1.77” ) cm. across at the widest part?

Was there a haft (shaft)? That seems a bit small for a handle but it looks like a good size to be hand held. In addition I don’t see attachments points for a handle but it does look like the ridges on the left and right sides would have been a big help in gripping. In that case I would think the palm of the hand would be on the left side and the fingers on the right side. If there were handle I would expect the long part you grip to be on the right side.

It looks to me as though it might have been gripped with the left hand.

Cast material. Inclusions in it. Guy is holding it and beating on something. Handle starts to give way but his grip serves to keep the two pieces marginally aligned so he can get another couple swings.

I think that it may have broken / ripped where it did because of the arc of the swing. Maybe the user was cutting something below his shoulder, perhaps kneeling and working on the ground. The axe head would have impacted on the fingers side of the head.

Are there ‘tide’ marks on the separation. Tide marks here means curved lines, one after another much like the waves leave marks on the shore. If the metal ripped a bit each time a blow was struck then each blow would have created a separate tide mark.

I don’t know about a ritual breaking but I think that was a valuable tool. If it was cast metal then it should be easy to recast it using an open mold. In any case wouldn’t the metal alone be worth saving?

What are chances it was broken by someone from a less sophisticated group than the group that made it originally? They didn’t know how to use it so it broke? Once it was broken they had no idea how to fix it or that it could be fixed.

A nice shot of both sides of the rip would really help especially if it shows grain structure.

Interesting question.
Thanks
Tom

 

[IronAgeGeorge]

Hi Tom/All,

Thanks for the feedback/info. I've also posted this on the Materials Information Society forum to see if they can give me a better feel if any books cover these sorts of failures.

Hi Tom, I'm sorry about the picture, as you can see Archy diagrams are often more about art than revealing the function. Can you believe these were the best I have? The others really don't reveal much at all.

 

[tomwalz]

Aw heck, don't worry.

1. It was fun.

2. Typically I am asked to do failure analysis with nothing but a description of the problem over the phone.

3. I am in the tool making business and that was my approach. However I am primarily tool amteri8als. I think I will pass your question onto some real knife experts on Bladeforums and /or Knifeforums. Many of the people there make and / or use knives, axes, etc. Overall they are really nice intelligent folk.

4. Finally, if I helped then I am happy. However all I will promise you is that my opinion here is worth what you paid for it. Since You didn't pay anything then my opinion is worth .........?

As Ami the Finn says “Nice that you exist.”

Tom

 

[IronAgeGeorge]

I have an update.

Firstly, still no photo's of the objects in question.

However, I have now collected a range of Bronze Axe types as well as a reconstruction of a mounted axe (which I think IS very similar to how this axe originally looked). I think this explains your confusion about the handle.

If you go to:

http://www.smartgroups.com/pictures/openalbum.cfm?GID=1414642&AlbumID=2667065

You will see the reconstruction and a number of typical axe designs, I'm still looking for a picture of an axe similar to the damaged one from the article.

Thr Bronze age axes were unique in that the shaft was mounted &quot;in-line&quot;, in other words the handle extended the length of the blade and had to be specially selected to give the correct angle for use. Hopefully the picture should explain more than my words.

It is thought that the final union was made by plunging a correctly shaped handle into a heated axe head thus burning in the exact shape thus removing any movement. The head was then held on the axe by tightly winding rope round it and the shaft. Later models had a loop built into the axe head to make this task easier.

I'd suggest, looking at the reconstruction and at the failed head that a failure of this sort must have been typical, since the reliance on the handle shape to form the axe surely meant it was very difficult to ensure an oblique angle of contact and that this is a form of uneven stress fracture (can I call it that?) in other words the design of the tool is such that in normal use, more impact will be seen on the bottom edge of the axe than the top, and that the end result of this stress would be a fracture exactly as is shown.

The test mentions a heavy blow to the axe which almost severed it, followed by others which failed to separate the two. It's difficult to comment on this since the diagram does not show any particular marks however the interpretation to my mind is dubious, since I'd suggest that the minute this crack opened to this extent the axe immediately became very fragile, and I'm sure I could break it with my hands, so to interpret this as some failed attempt at a ritual breakage seems pretty far fetched to me.

 

[Carburize]

As has been stated in several of the responses, a good low magnification (X5) image of the fracture surface would help to identify the failure process, if such an image could be obtained.

 

[IronAgeGeorge]

I know, I'm waiting for a response from my collegue, she's away from email at the moment, a common event with archaeologists.

 

[tomwalz]

1. The point was raised on knifeforums that a ritual breaking might have been done from an easier direction.

2. Would the rawhide wrap be strong enough so thatit would hold while the metal tore?

 

[EngineerDave]

Fascinating topic. I have my own personal interest in some of these historical matters with regards to metallurgy.

What was the final determination on this?

 

[flames]

You could contact Dr. Wayman at the University of Alberta in Canada (mike.wayman@ualberta.ca) as he specializes in Archaeometallurgy and Historical Metallurgy if you need more help (from the replies to this posting I am not sure you do). He concentrates in various aspects of historical metallurgy as well as being very knowledgeable in failure analysis. I believe his last sabatical was actually at a museum in London, England looking at ancient copper alloys.

 

[jackboot]

Good subject and very interesting:

My thoughts:

I could only imagine that the owners of such tools probably held these items with higher esteem than people hold their cars today.
Could it be that possibly these items just failed due to normal use? Since &quot;blacksmiths&quot; were probably few and far between - maybe these items were saved until someone could make the trip to get them repaired? Like a modern day mechanic in some remote locations - maybe the mechanic/blacksmith had to make the rounds to repair items within traveling distance.
Regardless of the failure mode - I tend to think that if it was my tool/weapon I would protect it to hand it down to my offspring.

My thoughts only-
jackboot