Stress/Strain Curve from a few values?

  • #1

Main Question or Discussion Point

Hi all,

I am trying to ensure that some supporting welds for a structure will meet the impact requirement of 1.3kJ.

I have the following information for the weld deposit:
UTS: 759 MPa
0.2% Proof: 598MPa
18.6% El
69.9% RofA

Is there any formulas that I can use to create a fairly accurate stress strain curve? I need the curve so that I can estimate the energy absorbtion of the material.

I cannot just over engineer this weld as with an impact of 3.6kJ the weld must break.

Any help on this matter will be greatly appreciated as this is the first time I have done anything like this.

Thanks

Kieren
 

Answers and Replies

  • #2
9
0
so u have a ductile material in ur hands. i can tell u how to find 3 points on the curve. i dont knw wat RofA means but i guess it'll help u get a more accurate shape or more points for the curve.

To draw the whole curve, u hav the EL i dont what the unit in %age means but i guess u can direcly plot it on the graph. if u cant then u can use the relation EL=stress/strain and just plot the point (1,EL).

u have 0.2% proof = 598Mpa. so u plot 0.2% point on the strain axis and draw a line parallel to the proportional line (the line from origin to the EL). u have the corresponding stress at 598Mpa and so now u have the yield point.

next u have the ultimate tensile stress, you divide it by the EL and you get the corresponding strain at that point. and then you plot the point.

so u have 3 points on the curve (EL, YP, UTS). u draw a straight line connecting the origin to the EL. i dont know how u would join the other points :(. mayb plot it in excel and see wat it shows. anyway, a straight line will give u an approximate value and can be easily calculated, area under a curve would be a pain to calculate. if u knw MATLAB then u can use tht.

now this area under the curve will be your strain energy density (u).we have the relation u= energy/volume. volume=area*length. you probably have this data from your structure. calculate the energy corresponding to the area under the graph.

now you have your impact requirement of 1.3kJ, so the energy that you had calculated earlier should be greater than this (take a suitable FOS), but less than or equal to 3.6KJ. if it isnt then u probably need a different weld joint.

correct me if m wrong, and i hope this helps. :)
 

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