Reaching Breaking Point: Materials, Stresses, & Toughness: Crash Course Engineering #18

Today we’re going to start thinking about materials that are used in engineering. We’ll look at mechanical properties of materials, stress-strain diagrams, elasticity and toughness, and describe other material properties like hardness, creep strength, and fatigue strength.

***

RESOURCES:

***

Thanks to the following Patrons for their generous monthly contributions that help keep Crash Course free for everyone forever:

Mark Brouwer, Trevin Beattie, Satya Ridhima Parvathaneni, Erika & Alexa Saur, Glenn Elliott, Justin Zingsheim, Jessica Wode, Eric Prestemon, Kathrin Benoit, Tom Trval, Jason Saslow, Nathan Taylor, Brian Thomas Gossett, Khaled El Shalakany, Indika Siriwardena, SR Foxley, Sam Ferguson, Yasenia Cruz, Eric Koslow, Caleb Weeks, Tim Curwick, D.A. Noe, Shawn Arnold, Ruth Perez, Malcolm Callis, Advait Shinde, William McGraw, Andrei Krishkevich, Rachel Bright, Mayumi Maeda, Kathy & Tim Philip, Eric Kitchen, Ian Dundore, Chris Peters
--

Want to find Crash Course elsewhere on the internet?

[Razes]

As material engineer this episode makes me happy, thanks for spreading the knowledge

[verdatum]

I can't put into words how much I love this. I'm a hobbyist blacksmith, and far too often in this realm we see these termed used far too loosely. This is because most blacksmiths haven't had the material engineering that evolved out of what the historical blacksmiths came to learn. Giving these words like strength, toughness, and hardness formal definitions makes them all so much more useful, but only to those who have taken the time to learn their proper formalized meanings. Videos like this, make that understanding so very much easier. As a teen, I tried to learn this from things like Modern Marvels on cable TV, and they would almost always get at least one critical aspect almost completely wrong.

[RangerRuby]

This just shows that no matter how strong something is, it always has a breaking point. I liked how you went into so much detail and taught me something new! Thanks for this video! I found it very interesting and I can't wait for the next video! DFTBA!

[HolyKoolaid]

In other words, jet fuel doesn't have to "melt steel beams." It just has to decrease its point of failure under stress.

[fastfoodisgross]

It's funny. I'm in college for ChemE and you guys always seem to release videos as I'm taking each course (just started a semester with Material Sciences)

[dragonbrown]

Your soothing voice really makes these lessons more engaging than it needs to be

[noalear]

YES! I am dealing with this at work constantly. It felt like you were talking to me specifically. That really help me understand.

[Pfhorrest]

Fun fact: all substances are either metals or non-metals, and either organic or inorganic, and while there are no organic metals, there are inorganic non-metals, and those are the ceramics, including glass. Polymers, of course, are organic; so between them, metal, and ceramics, you've basically just said that "for now, the materials engineers work with are [exhaustive list of all possible materials]".

[jaredbourne]

She actually convinces me to do a course civil engineer

[moonscapes]

Thank you for inspiring a lot of people, including myself. You and your friends are the reason I decided to film and edit videos for myself, as some sort of memory. I am very grateful for that and many laughs you have brought to us over this!

[oyahfftlisawsome]

As a Materials Engineering student, I'll have to start sharing this video around whenever people ask me "so, what's that?"

[MarkBlease]

Material failure was my favorite part of my material science course last semester.

[vernyeoh]

5:58-6:06
“But as you apply even more stress... the material will begin to deform and stretch along its cross-section as well as its length”

Just want to suggest adding in some detail here as the above sentence seems a bit ambiguous. Even in the elastic region of the stress-strain graph, all (normal) materials do experience deformation span/transverse-wise, and not just lengthwise before the yield point (see Poisson effect and/or Poisson’s ratio).

In the elastic region, this effect is uniform across the material, as the cross-section area deforms uniformly across the entire length. At the yield point and beyond, this deformation begins to be non-uniform and is localized instead – hence the specimen necking/getting thinner in the middle before failure occurs there. (Also, I feel that defining the yield point as being the point beyond which the material can no longer return to its original shape to be a clearer explanation than the above).

To summarize then, perhaps it would be better to phrase the above as “the material will begin to deform and stretch *non-uniformly* along its cross-section as well as its length” – or something along this tune?

Still, thanks for summarizing a semester’s worth of introductory materials engineering so well! Wanted to add this to prevent any misconceptions of when transverse deformation occurs.

[ArunGoyal]

Very well presented. I did the test of communicability. In the whole length of 11 mins, I had to rewind only once to understand the term. Very well packaged and presented. Congratulations.

[LTDoge-dmjr]

This channel is debatable in the topic of killing it as an act of mercy. Ever since they stopped making philosophy videos. The only reason I subscribed. It truly has been a fun ride. I learned so much about others and about myself. Thanks and goodbye

[Nacur]

Uhul!!!!
So much love for materials engineering

[HolisticApproach]

Be tough even though there so much pressure nowadays.

[nacoran]

In the harmonica world there are metal reeds. Historically they used bell brass. Today there are two main materials... bronze-phosphor and stainless steel (not sure what grade but it's magnetic but still good with moisture). There is a debate over which last longer. People fall into both camps, but I've noticed that the people who say steel lasts long self-describe themselves as hard players. My guess is that the stainless is staying under the fatigue stress levels with gentle players but more vulnerable at higher levels. I've read that under certain levels steel (and titanium) can undergo nearly infinite cycles without breaking. I also know when they are retuning reeds a lot of customizers prefer to polish to remove metal rather than just scratch the reeds because they are worried that scratches will create weak points that could lead to reed failure. (At $40 a pop for a harmonica, with 20 reeds per harp, with 12 harps in your set people worry about details like this!)

[jagadeeshvikramc]

So Good.. Awesome Description and Vivid Explanation.. 👏👌👍❤️💐

[JEOGRAPHYSongs]

Engineering is the creative application of science, mathematical methods, and empirical evidence to the innovation, design, construction, operation and maintenance of structures, machines, materials, devices, systems, processes, and organizations. The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, and types of application.