Interpreting Tensile Charts

[QAJA1717]

Hello All,

I'd like to gather some thoughts on interpreting tensile test charts. I've seen a number of examples online as well as on textbooks but as I've started reviewing real world examples, as is often the case, there are some chart behavior that I can't quite explain. I've attached a photo of an example from a metal specimen, "tensile chart example" (excuse the blacked out areas - had to redact certain sensitive info). On the picture, note the vertical line at the point of fracture. Our tensile testing s/w interprets the load at which fracture occurs at the top of this line - 4450 lbf. Being a straight vertical line, it appears this is when the extensometer was removed, however load continued to be applied. The s/w further interprets this as UTS = 86 ksi.

From what I know with tensile charts, it looks to me that the load at which fracture occurs should be closer to 2880 lbf - the point at which the curve ends. This brings the UTS down quite a bit.

Additionally, I'd like to know if anyone knows where I can obtain a document that shows a number of pictures showing typical errors in tensile testing and how they appear on a tensile chart (similar to the attachment, "extensometer slippage"). I'm thinking of collecting these images and putting them on our testing procedures as a quick guide in interpreting errors in tensile tests. Maybe even a poster I can put up in our lab.

Thanks.

 

[SWComposites]

Please attach file directly not in a zip file.
Have you reviewed the applicable ASTM test method?
Have you reviewed the info in MMPDS?

 

[bobjustbob]

Your software is interpreting the UTS correctly. We remove the extensometer to prevent damage when the sample breaks. After we have reached the yield point we are usually not interested in the strain any longer just the stress. The UTS is calculated from the highest stress applied to the sample. After it reaches this point the sample begins to neck down, reducing the cross sectional area. The 2880 would be used to calculate the fracture strength.

I don't know of any collection of photos with errors during tensile testing. What is in the second photo is either the extensometer moving or a error with the extensometer sending a bad signal to the computer. I have seen that before with an older extensometer that needed to be repaired.

Bob