Realistically, if one was to only use the engineering stress and strain values you would get a more conservative results in your design. This is because the values of stress and strain are calculated lower which is beneficial in cases where your loading conditions aren't well known.
Thank you for such a great series of lectures. Question: The "Ultimate Tensile Strength" of the material is increased when we compare the graphs of the original specimen and the elongated specimen. How does it happen within the material? Because, in the original case, we assumed constant area (even after deformation)by which we calculated the stress. Now when we plot the sceond graph, we correct that area value and thereby observe the increase in ultimate tensile strength. So, technically, there is no increase in the strength. All we have done is make the values more accurate by considering the true area at that point. Correct?
I use Shigley's Mechanical Engineering Design. I teach two courses out of this book, and I have a lot of videos from those courses collected in these playlists: MEEN361: ua-cam.com/play/PL1IHA35xY5H5AJpRrM2lkF7Qu2WnbQLvS.html and MEEN462: ua-cam.com/play/PL1IHA35xY5H5KqySx6n09jaJLUukbvJvB.html Check them out if you're interested! Thanks for watching!
dear sir,when we reach UTS why engineering stress began to decrease?I mean as the specimen is held in UTM,how stress is decreased bcz area is constant,It means load applied by UTM, is decreased after uts,If it is the case,how UTM managed to increase or decrease load? My second question is that why some materials like yield mild steel have two yield points?
The yield point phenomenon occurs due to the segregation of impurity solute atoms(C and/ or N in Fe) around dislocations so as to reduce the strain energy associated with the distorted atomic arrangement (maximum in bcc metals, less in hcp metals and least in fcc metals). This additional stress required to free the dislocations and set them in motion needed for plastic deformation is called the upper yield point. Once dislocations have been freed, the stress needed for their motion drops abruptly and is called the lower yield point. There comes slight variation in its value due to the interaction of moving dislocations with the impurity solute atoms obstructing their paths
The hexagonal closest packed (hcp) has a coordination number of 12 and contains 6 atoms per unit cell. The face-centered cubic (fcc) has a coordination number of 12 and contains 4 atoms per unit cell. The body-centered cubic (bcc) has a coordination number of 8 and contains 2 atoms per unit cell.
after necking, the area becomes soo small that it requires less and less stress to strain ..... as we talk about engineering stress strain diagram ... stress = Force / Area
Due to Necking phenomenon, the cross section area is narrowed and can't take the stress. Actually true stress increases as area decreases. The reason why MS has two yield stress is due to phenomenon of strain hardening and slippage that results upper yield point and lower yield point. Strain hardening can be visually observed when you take a glass of rice granules and continuosly stab it with chop sticks, at one point granules get tightly aligned and chop stick get stuck. Slippage is where atoms slide over one another similar to dislocation
Thanks for simplifying the concepts.
Glad you enjoy the videos!
Dear Sir,
How many times can the strengthening mechanism be performed? Is there a limit?
Realistically, if one was to only use the engineering stress and strain values you would get a more conservative results in your design. This is because the values of stress and strain are calculated lower which is beneficial in cases where your loading conditions aren't well known.
In 56:50, Is the green line’s slope same as the 0.2% offset line?
Thank you so much :) hugs from Portugal
We'll have to do a fist-bump instead... COVID and all :)
Thank you for such a great series of lectures.
Question: The "Ultimate Tensile Strength" of the material is increased when we compare the graphs of the original specimen and the elongated specimen. How does it happen within the material?
Because, in the original case, we assumed constant area (even after deformation)by which we calculated the stress. Now when we plot the sceond graph, we correct that area value and thereby observe the increase in ultimate tensile strength. So, technically, there is no increase in the strength. All we have done is make the values more accurate by considering the true area at that point.
Correct?
by strain hardening
You are fantastic 🎉🎉🎉🎉🎉🎉🎉🎉🎉
I appreciate the encouragement! Glad you enjoyed it!
Which Textbook you have referred to?
I use Shigley's Mechanical Engineering Design. I teach two courses out of this book, and I have a lot of videos from those courses collected in these playlists:
MEEN361: ua-cam.com/play/PL1IHA35xY5H5AJpRrM2lkF7Qu2WnbQLvS.html and
MEEN462: ua-cam.com/play/PL1IHA35xY5H5KqySx6n09jaJLUukbvJvB.html
Check them out if you're interested! Thanks for watching!
perfect sir saved my degree,from south africa
I'm glad I could help! Thanks for watching!
can't the revised yield stress be calculated the same way as the ultimate stress is computed, using the Cold work factor?
thank you very much
You're welcome, I'm glad it was helpful! Thanks for watching!
Which book you are referring.where can i get the formula someone help me
In this video, I am referring to Shigley's Mechanical Engineering Design, 10th edition. Thanks for watching!
dear sir,when we reach UTS why engineering stress began to decrease?I mean as the specimen is held in UTM,how stress is decreased bcz area is constant,It means load applied by UTM, is decreased after uts,If it is the case,how UTM managed to increase or decrease load?
My second question is that why some materials like yield mild steel have two yield points?
The yield point phenomenon occurs due to the segregation of impurity solute atoms(C and/ or N in Fe) around dislocations so as to reduce the strain energy associated with the distorted atomic arrangement (maximum in bcc metals, less in hcp metals and least in fcc metals).
This additional stress required to free the dislocations and set them in motion needed for plastic deformation is called the upper yield point. Once dislocations have been freed, the stress needed for their motion drops abruptly and is called the lower yield point.
There comes slight variation in its value due to the interaction of moving dislocations with the impurity solute atoms obstructing their paths
The hexagonal closest packed (hcp) has a coordination number of 12 and contains 6 atoms per unit cell.
The face-centered cubic (fcc) has a coordination number of 12 and contains 4 atoms per unit cell.
The body-centered cubic (bcc) has a coordination number of 8 and contains 2 atoms per unit cell.
Aluminum FCC
Nickel FCC
Cadmium HCP
NiobiumBCC
ChromiumBCC
PlatinumFCC
CobaltHCP
SilverFCC
CopperFCC
TitaniumHCP
GoldFCC
VanadiumBCC
IronBCC
ZincHCP
LeadFCC
ZirconiumHCP
MagnesiumHCP
after necking, the area becomes soo small that it requires less and less stress to strain ..... as we talk about engineering stress strain diagram ...
stress = Force / Area
Due to Necking phenomenon, the cross section area is narrowed and can't take the stress. Actually true stress increases as area decreases.
The reason why MS has two yield stress is due to phenomenon of strain hardening and slippage that results upper yield point and lower yield point.
Strain hardening can be visually observed when you take a glass of rice granules and continuosly stab it with chop sticks, at one point granules get tightly aligned and chop stick get stuck.
Slippage is where atoms slide over one another similar to dislocation