If I was asked to give the proportional limit, would my answer be the range from yield or strain or would I give the value at that point in either the yield or strain axis?
Hi, Jake. Because there are different ways to report it, I would expect that a request for the Proportional Limit would include a note as to how to reference it (sort of like Yield Strength, at 0.2% Offset). You could also check the units. If the report asks for the Proportional Limit in units of the Y-axis (stress) or the X-axis (strain), then you would have your answer. =]
Hi, Djochiem, thanks for the Kudos. These values are acquired EXPERIMENTALLY. It is possible to develop a theoretical program that models the values from material parameters, and for the most part, this is the goal of computational stress-strain modeling (en.wikipedia.org/wiki/Stress%E2%80%93strain_analysis#Mathematical_methods). But even after using a CADD Program to model stress/strain effects, actual test models must be measured in the lab to get the "real" values. =]
Hi, @Axole, The Proportionality Limit is not a calculation. It is a position on the graph where the straight-line modulus no longer fits the data. From there you can read the Stress value from the vertical axis and the Strain value from the horizontal axis and report those values. It would be reported as "Stress @ Proportional Limit" or "Strain @ Proportional Limit". This informs the user of the material of the Max Stress and Max Strain the material can experience before is undergoes permanent non-elastic deformation....it won't bounce back and that can make the part or the entire assembly fail.
Hysteresis implies that the load is applied in a cyclic manner. This is a "static" test in which the strain is slowly increased (either compression or tension) as the stress is measured until the sample breaks or the testing machine reaches its maximum load. To measure hysteresis, you typically would not leave the proportional region, but any testing procedure can be defined and followed.
Izzy Farmer Then the yield strength is reported as "0" as it has already failed. If an entire class of materials fails before 0.2% offset, then a lower, more appropriate strain value can be chosen and reported. =]
hi! should we be approximating where the proportional limit is located to calculate the slope? I'm just not sure how to determine exactly where that limit is located when I plot given data.
Hi, Caroline, If you are plotting manually with graph paper then the measurement of slope and modulus is a rough approximation. It should be OK to use your best estimate for the proportional limit. If, however, you are using a plotting package, then using a statistical curve-fitting procedure would automate and clear this up. In between, you can use Excel which will use a least-squares fitting routine to find the best fit of a line through the elastic region of your data. If you have digital values, you can only include those datapoints that are clearly before the proportional limit. If you really want to be fancy, you can continue to add more data points that are closer to the observed proportional limit while monitoring the value of the R^2 error. If after adding a point the R^2 value drastically lowers, then you can be assured that you are including data beyond the proportional limit. I hope this helps! =]
William, thanks for your great explanation. Do we have any simple formula to calculate the Yield strength (YS) at 0.2% offset? I.e if i have YS=35,000psi then what is the YS at 0.2% offset (proof strength)?
Hi, Thong, It is my understanding that YS at .2% offset is a measured value, not a calculated value. It depends on the material. Perhaps if one wanted to create a formula, it would include a parameter for each type of material, but that parameter would be based on measured values, so it would be simpler to just quote the YS at .2% by reading from the test. Thoughts?
It is a point on the data curve that is measured BEFORE the part totally fails. Yield is while the point is "giving up" or "in the processes of failing". Before the Yield point or the "proportional limit", the part is considered to be only "stretching" and is elastic and will return to its original shape if the load was removed. The difficulty is pointing to a specific point on the data curve, somewhere after the Yield Point or Proportional Limit. The process is to locate the point on the horizontal strain axis where strain = 0.002 (also represented as strain = 0.2%), and then draw a line up from this point until it crosses the data. But instead of drawing the line vertically (parallel to the Stress Axis), it is drawn parallel to the Modulus. Does this help?
Came here to understand what yield strength meant after looking at specs for extruded aluminum (t slots). Apparently the yield strength for regular and ultra-lite t slotting is the same, somehow.
Hey William, I really enjoyed your video and found it very educating. Could you please give me a shoutout in your next video, I would like to expand my reputation among the engineering community. Cheers.
![[UNCUT] เก็บ "สจ.โต้ง" เอี่ยวมาเฟีย รู้ตัวคนบงการ ก่อนสั่งลั่นไก I คนดังนั่งเคลียร์ I 13 ธ.ค.67](http://i.ytimg.com/vi/o-J_p62D40w/mqdefault.jpg)
i am graful for your affort Thank you Sir
thanks for your great explanation. god bless you
Glad you found it useful. =]
Excellent Explanation! It helped me a lot! Thanksss
I'm glad it helped! =]
Well explained. Thank you!
This is so good💯💯💯
Thank you for a great video!
Thank you! This clarified a lot of questions...
If I was asked to give the proportional limit, would my answer be the range from yield or strain or would I give the value at that point in either the yield or strain axis?
Hi, Jake. Because there are different ways to report it, I would expect that a request for the Proportional Limit would include a note as to how to reference it (sort of like Yield Strength, at 0.2% Offset). You could also check the units. If the report asks for the Proportional Limit in units of the Y-axis (stress) or the X-axis (strain), then you would have your answer. =]
@@WilliamLWeaver I just realized I was saying yield instead of stress whoops. I will just assume stress because there is no clarification. Thank you
Great explanation, Question though, can this be calculated without a chart using datapoints ?
Hi, Djochiem, thanks for the Kudos. These values are acquired EXPERIMENTALLY. It is possible to develop a theoretical program that models the values from material parameters, and for the most part, this is the goal of computational stress-strain modeling (en.wikipedia.org/wiki/Stress%E2%80%93strain_analysis#Mathematical_methods). But even after using a CADD Program to model stress/strain effects, actual test models must be measured in the lab to get the "real" values. =]
Thank you soo much Sir!!
Thanks for the Kudos! =]
how do you calculate the limit of proportional
Hi, @Axole, The Proportionality Limit is not a calculation. It is a position on the graph where the straight-line modulus no longer fits the data. From there you can read the Stress value from the vertical axis and the Strain value from the horizontal axis and report those values. It would be reported as "Stress @ Proportional Limit" or "Strain @ Proportional Limit". This informs the user of the material of the Max Stress and Max Strain the material can experience before is undergoes permanent non-elastic deformation....it won't bounce back and that can make the part or the entire assembly fail.
Sir for hysteresis graph corresponding to which strain we will find the yield load.
Hysteresis implies that the load is applied in a cyclic manner. This is a "static" test in which the strain is slowly increased (either compression or tension) as the stress is measured until the sample breaks or the testing machine reaches its maximum load. To measure hysteresis, you typically would not leave the proportional region, but any testing procedure can be defined and followed.
thanks!! this is super helpful.
what happens when the yield strength at strain offset at 0.2% when the material has already failed by that point?
Izzy Farmer Then the yield strength is reported as "0" as it has already failed. If an entire class of materials fails before 0.2% offset, then a lower, more appropriate strain value can be chosen and reported. =]
thankyou!
hi! should we be approximating where the proportional limit is located to calculate the slope? I'm just not sure how to determine exactly where that limit is located when I plot given data.
Hi, Caroline, If you are plotting manually with graph paper then the measurement of slope and modulus is a rough approximation. It should be OK to use your best estimate for the proportional limit. If, however, you are using a plotting package, then using a statistical curve-fitting procedure would automate and clear this up. In between, you can use Excel which will use a least-squares fitting routine to find the best fit of a line through the elastic region of your data. If you have digital values, you can only include those datapoints that are clearly before the proportional limit. If you really want to be fancy, you can continue to add more data points that are closer to the observed proportional limit while monitoring the value of the R^2 error. If after adding a point the R^2 value drastically lowers, then you can be assured that you are including data beyond the proportional limit. I hope this helps! =]
William, thanks for your great explanation. Do we have any simple formula to calculate the Yield strength (YS) at 0.2% offset? I.e if i have YS=35,000psi then what is the YS at 0.2% offset (proof strength)?
Hi, Thong, It is my understanding that YS at .2% offset is a measured value, not a calculated value. It depends on the material. Perhaps if one wanted to create a formula, it would include a parameter for each type of material, but that parameter would be based on measured values, so it would be simpler to just quote the YS at .2% by reading from the test. Thoughts?
good explanation😀😀
I don't understand if it's deformation=0,002 or 0,2% of the last obtained value of deformation (failing point). Can you please explain?
It is a point on the data curve that is measured BEFORE the part totally fails. Yield is while the point is "giving up" or "in the processes of failing". Before the Yield point or the "proportional limit", the part is considered to be only "stretching" and is elastic and will return to its original shape if the load was removed.
The difficulty is pointing to a specific point on the data curve, somewhere after the Yield Point or Proportional Limit. The process is to locate the point on the horizontal strain axis where strain = 0.002 (also represented as strain = 0.2%), and then draw a line up from this point until it crosses the data. But instead of drawing the line vertically (parallel to the Stress Axis), it is drawn parallel to the Modulus. Does this help?
Came here to understand what yield strength meant after looking at specs for extruded aluminum (t slots). Apparently the yield strength for regular and ultra-lite t slotting is the same, somehow.
what do you meat Yield Strength at 0.2% Offset?
It is explained at 3:00
Great!
Thanks a lot
Hey William, I really enjoyed your video and found it very educating. Could you please give me a shoutout in your next video, I would like to expand my reputation among the engineering community. Cheers.
Well explained. Thank you!