Q1. How does a prestressed precast concrete bridge beam work?

Concrete is great in compression, very strong stuff.

Concrete isn't so good in tension, however, so using any concrete slab in such a way that it will experience bending load - as a cantilever, for example, or a flooring slab with a long span - requires something to address that weakness in tension.

The most common solution is simple rebar...but then there's the prestressed option.

In the above video - the first in a series of twelve Shay Murtagh videos exploring prestressed concrete beams in great depth - explains what prestressed concrete is and why it's strong than just reinforced concrete.

In case you aren't aware of Shay Murtagh, they seem to be a company with at least 100 employees - many but not all of whom can line dance.

Micro Tensile Strength Test of Plastic per ASTM D638

I always like to open these posts with a joke or pun of some sort, but I couldn't come up with one for this video that wouldn't be a stretch, so I'll just get cracking.

The inherent simplicity of a tensile test - just stretch a material specimen - belies the actual complexity present in performing one carefully and repeatably. 

Today's video shows the care that must be taken to perform a tensile test according to industry standards - ASTM D638, in this case - and the stress/strain curve that results from a properly conducted test.

In case you were curious what this whole "ASTM" standard was about, check out this video about the ASTM organization.

Discover the Harrison Spinks' Wire Drawing Department

We draw wires in the ASM summer materials science camp, but nothing that we do in camp remotely approaches this level of professionalism.

In terms of drawing a wire, we're an introductory art student, and the Harrison Spinks folks are Picasso.

See, 'cause they can draw wires better than we can.

Get it...Picasso...because he's an artist...he did drawings.

In all seriousness, seeing the very clean, seemingly safe process shown above makes me appreciate the less careful process for a similar result shown below.

Why Japanese Iron Kettles Are So Expensive | So Expensive | Business Insider

Now that's just gorgeous.

I don't drink tea, so I have absolutely no need for one of these kettles...

...but I kinda want one.

They're so simple and so pretty.

The craft that goes into creating them is spectacular to watch, too.

How Sand Made From Crushed Glass Rebuilds Louisiana’s Shrinking Coast | World Wide Waste

I feel like I've posted about Glass Half Full before, but I can't find the post.

Maybe I've just meant to post about them because I think they're just about the coolest folks around.

I like to think of myself as a decently environmentally friendly person. I recycle and compost and all that, but I feel like an utter slacker compared to these folks.

Plastic Recycling Doesn't Work and Never Will Work

 

[T]he plastics industry has waged a decades-long campaign to perpetuate the myth that the material is recyclable. This campaign is reminiscent of the tobacco industry’s efforts to convince smokers that filtered cigarettes are healthier than unfiltered cigarettes.

The above quote is from Judith Enck and Jan Dell's article in The Atlantic and lays it all out fairly straight forwardly.

We use too many man-made polymers.

Man-made polymers are bad for us.

They can't really be recycled.

I'm pretty sure that Everything Into Oil was nothing more than a pipe dream.

COLD HARD SCIENCE: SLAPSHOT Physics in Slow Motion - Smarter Every Day 112

For me, the big payoffs in this video come from the high speed videography at 2:30 and again at 5:20. Seeing the composite hockey stick flex and store up energy then spring forward even ahead of the player's hand when that stored energy is release is just gorgeous and shows the advantages of composite materials in sports as compared to older, wooden sticks.

Plus, I'm down for just about any video that Destin posts.