Does wood become brittle with age?

[glenn k]

Wood does not fatige like metal but does it change with age?
In a recent thread someone said cypress becomes brittle with age.
I have been trying to find if this is true. Sure the trees do; the older wood gets plugged with resens etc and sap wood has less lignin than heartwood.
But does the chemical structure of the wood change over time?
To become more brittle wouldn't the cellulose have to break down?
If it does change over time would it matter if it was milled or not or would it go off still in the log?

[echnidna]

I've never seen wood go brittle from age

[glenn k]

neither have I echnidna.
But perhaps it does change my 1st house built ~1870 had studs that were so hard I had to drill then to nail the plaster on. Present house ~1840 had what looked like ironbark studs mega hard (unfortunatly couldn't get the hand made iron nails out, it must have been soft to get them in perhaps green). I had to drill my new sugargum floor to get nails through so maybe the studs were hard to start with.
I read somewhere that softwoods get weaker over time and hardwoods get stronger but no idea if it is true.

[glen boulton]

i think cypress gets dry and hard as a result it tends to crack easier. what i mean by that is... if you nail down cypress flooring withing a month of being milled, it nails easy. but if you were to pull that floor up in 15 years time.... it will snap and shatter without letting go of that bloody nail. i have done many extensions and it is very hard to reuse the old flooring.

i wouldn't call it brittle as it doesn't shatter and fail easily. but is hard to break and when it does it prefers to break along the grain.

so i think it gets dry and hard and this makes it lose its flexibility thats all.

i would understand that in the definition of "brittle" would involve the lessening (if there is such a word) of strength. not that i would know.

this is not a clinically proven fact, its just me and a hammer.

[PAH1]

There is the distinct possibility that it could, cellulose consists of sugars with hydroxyl groups that could become aldehyde groups and react with things over time. I would expect that there would be woods that would go easier with time, Richard Raffan certainly believes so, and just to be perverse I am pretty sure there would be others that went the other way and became harder and more brittle with time.

[Colin Howkins]

Maybe it does, maybe it does not. But what effect does it have on its serviceability? I would argue, not much. there is too much 'old' woodwork around - like centuries old and some stretching back a millennium or two, and it still is functional.

Timber certainly gets harder over time, but I don't think brittle

[weisyboy]

as wood dryes it becomes more brittle or hard in ironbarks case.:2tsup:

[pjt]

In general terms (if I remember correctly) matl's are classed as brittle when they fail suddenly when under load, cast iron, concrete, glass are typical brittle matl's.
A brittle mat'l will show no or very little yeild point when tested in a tensile testing machine.
google stress strain curve for further reading
An article in Wood Review a while back featured Kennedy's Aged Timbers in Bris, they tested sample large section timbers to destruction to ascertain whether the timber properties had changed or not (and from memory) the testing regularly shows that the timber is as good as the day it went into service.
Is timber brittle? It does break suddenly when under load! we have all probably grabbed a bit of stick and bent it round our knee untill it breaks and it usually breaks suddenly, green stuff is a whole lot more flexable tho.
Is it safe to use? there's enuff of it about holding up houses and bridges and things to safely say it is, you just cant go past it safe load limit or it will fail (suddenly)
peter.

[markharrison]

I am not a materials technologist but my experience with certain old timbers seem to suggest that something is going on. Australian Red Cedar is a case in point. My c1880 ARC chairs seem to be prone to catastrophic failure. One tipped over backwards. Where the balloon top joined the legs, there is a dowel. The balloon top shattered like china around this join.

Another one snapped a turned front leg almost clean through.

I doubt that this is technically "brittle" but I think you can be forgiven for using the word to describe events like these.