Do metals get old and weakened through time?

[spader]

This spade had been bought new in 1997 from Costco Glasgow. It has worked flawlessly and faithfully for all that years. It was strong like a tank digging and scooping soils, gravels and chips. It dug out many plants, trees, grass patches and weeds. But it suddenly broke yesterday when digging the soil in the corner of the garden. I was so surprised to see a tool that I thought was impossible to destroy and would outlive us broke just like that.

Do some metals get life time for its structural strength? Or is it just one off event in material universe? It didn't come with life time warranty, regretfully.

 

[stonepark]

Need to see the raw edges of the break to identify cause if not corrossion.

Just like a knife being abused, you can get micro fractures that allow corrosion or can cause sudden failures.

 

[Paul_B]

There are several potential modes of faillure. Impossible to tell from the photographs provided. So all we can say is metals can fail due to the material, the design, issues in manufacturing it or simply time and exposure to the elements.

For example the blade looked like it was the usual metal wrapped around the handle with the seam towards the back. An inclusion or dislocation in the structure of the metal could have resuilted in a micro crack which propagated and sudden;y cause rapid failure cracking through this attachment sleeve (if I have remembered elemments of my materials degree correctly, not guaranteed though).

I once had aa tent pole crak through from a hole caused by the crimping of the outer aluminium pole sleeve over the joining pin. Without any extra stress on the pole it just snapped with not external force appplied. The pole was in the tent for about an hour and we were playing football away from it and heard a crack noise and saw it had collapsed. It went from just those three crimp holes to a crack running between two of them in a split second without any clue it would do that. That is the speed of crack propagation for you.

Can I point out that it was a costco spade, likely a cheaper brand and made cheaper. I am afraid I tend to get a good brand with a stainless steel spade blade and attachement sleeve tube, with a wooden handle. In my spades the blade lasts but the handle of the spade tends to split accross thee top of it due to being left out in the rain at times. In the OPs case I think the spade has lasted long enough to have been a good tool for them. It has earnt it money over that time you could say. Just but a new spade perhaps.

 

[Nice65]

Yes, it’s called metal fatigue, and it’s use rather than time. The same effect as the hardening of a bit of steel wire when bent back and forth. It hardens and snaps.

 

[Pattree]

It sounds as if you have been working the spade hard, particularly in tasks involving levering.
There is a process called “work hardening” whereby as metal flexes to and fro the molecules clump forming a more brittle structure which can eventually fail.

When we were planting forest trees we used special “Mansfield” or “Schlich” spades because of this. Both patterns had steel running right up the wooden handle. This is because planting in those days was done in two blows: The first vertical, the second levered sideways. This could happen 1200 times a day for several weeks of the weather held. Bloody heavy to carry around a mountain but it never failed.


Edited to add:
Yes indeed. @Nice65 I couldn’t remember the term “metal fatigue”. but it’s nearly bed time!

 

[spader]

The make of the spade is "Draper", and it was cheap. I recall it was £15 or £20 in 1997 - 1999 around the time. At the time, money was worth more than the now. Petrol was 67p per litre.

Will try to get close-up photo of the raw edge of the breakage. Yes, it has lasted well, and it had done its worth. I have another spade, but with much longer handle, and heavier. I preferred this one for its shorter handle and lighter weight.

It had not been used to leverage slabs or stones. It was mainly used digging the plants out from the soil, or shaping grass patches.

 

[Paul_B]

I really rate a mattock as a "digging" tool too. Heavy, rocky ground it breaks it up and you can scrape it back. You can really lever well with such a tool. Not the same as a pick axe BTW.

Last time I did tree planting it was a simple spade or shovel, create a crack, shove the whip in then plastic tube and perhaps a mat / mulch to protect the roots. Conservation work not pro though. There's probably loads of decent sized trees around Preston and Ribble valley area put in by this quick method. It was well over 25 years ago now.

 

[Nice65]

Edited to add:
Yes indeed. @Nice65 I couldn’t remember the term “metal fatigue”. but it’s nearly bed time!

That is called ‘human fatigue’ and involves a softening of the brain when it’s bedtime.

 

[TLM]

Work hardening of ferritic steels is not quite the same as fatigue but as it involves plastic deformation it can easily lead to it.
Plastic deformation tends to cause fairly fast fatigue.

 

[C_Claycomb]

Also, the spade was stainless steel. Nothing that old looks that shiny otherwise.

 

[spader]

Yes, it is stainless steel. There is no rust anywhere on the metal part of the spade at all.
The blade is also hard metal. I tried to sharpen the spade edge with angle grinder years ago. The edge was so hard, it wouldn't sharpen, and the grinder pad in the angle grinder just wore out.

 

[spader]

 

[Pattree]

Now that’s interesting!!
The shaft is completely hollow.
As far as I can see, it is not showing signs of collapse that I would expect if the metal has bent.
I’m pretty certain this is metal fatigue (cumulative micro fractures) exacerbated by work hardening as the shaft flexed. The break point is ragged. If that is rust on the face of the fracture then it’s been coming apart for a while.

 

[spader]

Now that’s interesting!!
The shaft is completely hollow.
As far as I can see, it is not showing signs of collapse that I would expect if the metal has bent.
I’m pretty certain this is metal fatigue (cumulative micro fractures) exacerbated by work hardening as the shaft flexed. The break point is ragged. If that is rust on the face of the fracture then it’s been coming apart for a while.

The metal seems to be some sort of stainless steel or alloy steel, which don't get rusty easy.
The fractured area doesn't seem to have rust.

 

[Pattree]

 

[spader]

View attachment 90394

Aha. OK.

 

[Paul_B]

With metal fatigue do you get the same small rough area with most of the break being the granular surface like fast fracture? Not described well I know.

I have forgotten more about this than I care to admit to. It is a long time since I got my materials engineering masters and I never actually used it. Just shows that if you don't use it you lose it!!

 

[Pattree]

With metal fatigue do you get the same small rough area with most of the break being the granular surface like fast fracture? Not described well I know.

I have forgotten more about this than I care to admit to. It is a long time since I got my materials engineering masters and I never actually used it. Just shows that if you don't use it you lose it!!

So many variables. Alloy, impurities, stress patterns etc. In this case there seems to be surface rusting around the same area that shows discolouration at the fracture suggesting that this area opened to air/moisture some time before the cleaner section (and the tool) failed.

I’m not an engineer at all but I have some practical experience of metal (and other materials) failure.

 

[Paul_B]

So many variables. Alloy, impurities, stress patterns etc. In this case there seems to be surface rusting around the same area that shows discolouration at the fracture suggesting that this area opened to air/moisture some time before the cleaner section (and the tool) failed.

I’m not an engineer at all but I have some practical experience of metal (and other materials) failure.

My thought on the discoloured section is a crack allowing moisture in over time. This crack could have propagated quickly to fail when it did. I had a crimped tend pole and the resulting crimp just caused the pole to shatter suddenly. As in perfectly ok as new (not surprising it was a brand new tent which I had only used for three nights before it failed). It showed no issues but looking at the other poles the rectangular crimps formed tabs that dug into the section joining pins and this was actually made with cracks at the corners either side of the tabs that coould easily be expected to fail quickly through catastrophic crack propagation. This happens quickly.

I think the main thing is the OP had about 15 years of good use from it so it has earnt its investment. As a TV valuer might say, "it has washed its face!"

I trained as an engineer in two different disciplines as a BEng and Masters. The last was in materials engineering so I really should know about all this. It is however very easy to lose knowledge if it is not used.

 

[TLM]

It looks like there is solid corrosion products all over the inside of the tube. I guess the rust colour on the sides is from there, of course with cracks it could have been from outside water too.

It looks to me that it has cracked on the sides first, which is a bit strange, unless it has been over bent so that it has slightly flattened and the sides cracked. The final fracture looks kind of typical, mostly brittle but some shear lips on the tension (?) side.

If it took 15 years of solid service to break it it was certainly worth the price.