ISBT212-04_3 - Stress and Strain: Proportional Limit and Yield Strength
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- เผยแพร่เมื่อ 5 ก.ย. 2024
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I have developed and taught a course in Materials over the past few years and this iteration exists as a series of video lectures that are accompanied by online quizzes and face to face laboratory activities. The objective of the course is to provide a broad overview of Materials to students so that they may begin a deeper examination of the topics and technology presented.
I am sharing the video lectures with the hope that you may find them useful and to ask for your comments and questions on how to correct and improve the course. Thanks for watching!
Video Lecture Component of 2016 ISBT212 - Technology Foundations II: Materials offered at La Salle University to majors in the B.S. Integrated Science, Business, and Technology department.
www.lasalle.edu...
This video series may contain mistakes and errors of fact. While presenting the unscripted material, I may confuse names, facts, and figures. Please check the information for accuracy before you use it to win a bet or design a complex, potentially dangerous device.
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i am graful for your affort Thank you Sir
Excellent Explanation! It helped me a lot! Thanksss
I'm glad it helped! =]
thanks for your great explanation. god bless you
Glad you found it useful. =]
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
Well explained. Thank you!
This is so good💯💯💯
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.
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 for a great video!
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.
Thank you! This clarified a lot of questions...
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!
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?
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?
Thank you soo much Sir!!
Thanks for the Kudos! =]
what do you meat Yield Strength at 0.2% Offset?
It is explained at 3:00
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! =]
good explanation😀😀
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!