Thank you all very much for the responses, it is much appreciated. It has been definitely educational and I am looking forward to learning more about the mechanical properties of wood from all of you. I have also found several interesting scientific articles in this regard and hope to be able to get a better understanding of the compression failure mechanism in wood of which string follow and set seems to be a mild form of it. One of the articles I have read is called "Compression failure mechanism in small scale timber specimens".
It describes it as follows:
Under a compression load parallel to the grain, small clear-wood specimens undergo four main deformation steps: linear elastic (a), incipient kinking (b), transient kinking (c) and steady-state kinking (d). The incipient kinking is the plastic shearing and buckling of the fibres, localised close to the resin canal region where the fibres are misaligned [I am assuming this is where string follow / set happens]. The transient kinking phase is defined as the unification of all the incipient kinking areas in a unique kinkband that goes through the entire width of the specimen and starts when the peak stress is reached. This step is also characterised by a decrease in the stress, which eventually reaches a plateau when the fibres inside the kinkband can no longer rotate (lock-up angle). The process that takes place during this step is a broadening of the kinkband at a constant stress level (steady-state kinking).
The Swedish article has many illustrations and was primarily written to further the understanding of failure modes in glulam beams.
Cheers,
Phil
