RE: Recognizing when a material has failed in Compression from a Stress - Strain Curve

[MatthewMansfield]

Hello all

This is a new question but it linked to a previous post.

The question is, when interpreting a stress strain for compressive testing how do you know when a material has failed?

I have been given a plot of 3 x compressive tests of some wooden samples.

I am trying to figure out from looking at the graph when the material fractured - is there a formal definition i.e. when the moment stress decreases but strain increases is when the material is said to havew failed?

I have attached a copy of the plot in question.

Your thoughts?

Thank you.

https://files.engineering.com/getfi...2-24b8-4491-8994-efde1d73a152&file=Failed.png

 

[r13]

The is my interpretation. The failure is defined as the sharp loss in stress with minor strain change. The orange line is in plastic region/zone, in which the strain increases rapidly with little change in stress.

 

[Compositepro]

The point where the stress starts to go down with added strain is the maximum allowable stress. The specimen may not have failed yet, but if this were a structure it would collapse at this point. In real life you can have parts of the structure go past this stress and it will still be supporting load as long as the excess load can transfer to other parts of the structure. This flexibility is what makes wood structures fairly robust.