107

There are two main reasons why glass is still preferred over say PMMA. The first is durability. As long as it isn't broken, the glass in a window can easily last for hundreds of years in good condition. In particular it is a lot more resistant to scratches than comparable plastics and isn't really subject to much in the way of environmental degradation. ...


44

Here is a plastic (most likely PMMA) window, in a boat, after only 37 years. In addition to the obvious scratches, the outer surface has developed a cloudiness : possibly from degradation due to UV light, and (towards the LH end) you can see a cubelike pattern of stress cracks, rather like a toughened glass windscreen after a pebble hit it. You really ...


30

What are the requirements for window glass? Resistance to moisture Resistance to UV radiation Resistance to cleaning agents Very high transmission in the visible spectrum (There are many more, from an engineering point of view) Most transparent plastics are not resistant enough. Plexiglas is one example which fulfills the requirements enough to be used ...


27

There are two reasons why. First, for any glue to stick to something, that something needs to be wettable by the glue. A cured silicone surface is bristling with uncrosslinked silicone units which have extremely low surface energy and hence are very difficult if not impossible to wet by glues like epoxy. This means the cured epoxy exhibits no adhesion to the ...


23

Different gears have different drivers for having holes. One way you can categorize gears is by whether they are used primarily for transferring: motion: transferring angular position and angular velocity (see clockwork) torque: when the gears are used in power transmission Motion Gears that transfer motion don't need to transfer power. So their strength ...


18

The first thing to remember is that the naming of eras such as the Stone Age or the Bronze Age is never done by those living during the period. It was always done by others much later. To a certain degree, the reason why bronze was the first important alloy was luck. For whatever reason, design or mistake, someone at some stage during antiquity mixed copper ...


16

Prince Rupert's drops are an example of a tempered silica glass component: its surface has been cooled more rapidly than its interior. Tempering of glasses is important because it lends toughness to the glass, i.e. an ability to resist fracture under load, which explains why a drop can be hit with a hammer and survive. Silica glass, as is common with other ...


16

Muze had a good answer from the Physics side. From a materials perspective, we see things have grain structure, which explains how different fractures occur. Butter cuts smoothly because its micro-structure is rather loosely held. Butter is primarily composed of triglycerides: These short heads (where all the Os are) bunch up, while the long tails spread ...


15

Keeping things simple, steel is an alloy of iron and carbon, whereas stainless steel is essentially an alloy of iron, carbon and chromium or iron, carbon chromium and nickel. All forms of steel, whether they be ordinary iron and carbon alloy or stainless steel are made from a melt in furnaces. Because of this stainless steel cannot be plated to ordinary ...


14

This will at least depend on the: Rate of Cooling Magnetic field strength Exact composition The magnetic field will alter the microstructure as you can read in, for example, Yudong Zhang, Nathalie Gey, Changshu He, Xiang Zhao, Liang Zuo, Claude Esling, High temperature tempering behaviors in a structural steel under high magnetic field, Acta Materialia, ...


14

This is an admittedly North American response. MGT In the US, how much traffic goes over a given track in a year is measured in Million Gross Tons (MGT) e.g. 1 MGT = 2 000 000 000 lbs [spaces instead of commas to be world-friendly]. This is a measure of the total weight of cargo and vehicles but not necessarily the number of individual trains. Rail Life ...


14

I actually did make windows out of plexiglas for an outbuilding. I could work them to the shape I wanted and they were lightweight. However, I discovered that they indeed scratch easily: just trying to get the protective paper off I both scraped and melted the plastic. We want hard windows for houses and primary buildings. So what you describe would be ...


13

Every time you bend aluminium below the recrystallisation temperature, the macroscopic grains become smaller: this is known as cold work. The sides of the tab are either stretched or compressed. The effect is the same as the rolling example below. This is indeed a plastic deformation: the tab stays in place and doesn't bend back and stays in place. ...


13

We use engineering strain even though it is not the "correct" value because in most cases, specifically in the elastic regime, engineering strain differs negligibly from true strain. For linear elastic, Hookean materials, it is generally the case strain at the elastic limit is very small. Even the strongest steels, for example, have an upper limit when cold ...


13

Precipitation Snow Snow can be a problem for running trains, but it really doesn't affect the rail/ballast. Just like on highways, the snow needs to be moved away, but it doesn't have many other effects. Trains are used to plow through small amounts (Wikipedia): and large amounts (Wikipedia): Ice Ice could cause more of an issue due to adding thickness to ...


12

Based on it being an EN steel grade: The first number is 100x the carbon content percentage (so 0.11%), the letters are added elements (sulphur and maganese), and the last number is the sulfur content (0.30%). You can see the full details here. The full format seems to be: [X][% carbon][added elements][% of added elements, hyphenated] Note that the X is ...


12

Silicon forms bonds in a similar way to carbon, and has a similar outer-shell electron orbital configuration. Carbon, as you may well know, has the ability to covalently bond with up to four lone pairs of electrons on neighboring atoms in a generally tetrahedral arrangement, giving carbon a large versatility in molecular configuration and conformation. The ...


11

It's common to start with a shorter, stiffer tool such as a center drill or a spotting drill. In addition, using the shortest drill bit that drills the hole you need will increase stiffness. Because of the flutes in a drill, the stiffness goes down geometrically as the length increases. The other variable you have control over is how you are holding the tool....


11

I'd recommend searching for shaft couplings. These are a great option for connecting two rotating shafts in a non-permanent fashion. A set screw (as mentioned) can work in low load cases, but is often best with a flat spot cut into the shaft so that you've got more than just friction between the screw end and shaft to constrain things. The setscrew may also ...


11

How To Read the Graphs The graphs are plots of stress versus position. Stress is the force per unit area exerted on a material. Positive values are tension and negative values are compression. The first (leftmost) plot shows the normal stress vs. position that would be expected from bending if there was no pre-stress. The middle plot shows the pre-...


11

For the explanation of the loss of stress from E to F, I'll refer you to my answer to another question. Basically, the drop in stress seen in the diagram is a consequence of the fact that we use engineering stress (not taking the loss of cross-sectional area into consideration) instead of true stress. In a true stress diagram, there is no such drop. See this ...


11

Flexural capacity is based on the stress at the extreme fiber (the point farthest vertically from the neutral axis). $$\sigma = \frac{My}{I}$$ Or, rearranging $$M = \sigma \frac{I}{y} = \sigma S$$ M = moment capacity $\sigma$ = allowable stress S = I/y = section modulus So the relative capacity of the tubes will be a function of their section moduli. ...


11

UPDATED TL;DR: Cast iron has the advantage, because it has a greater capacity to hold heat, and because of its lower conductivity it releases it more slowly, thus its temperature does not fluctuate as much (thus having a more even and steady heat flow) UPDATE: Answering in terms of the advantage (scroll way down) for the following sections Answer to ...


10

A method which works extremely well and which does not require set screws and/or flats on the shaft and which can be added or removed easily and rapidly is a collet based connector. While any one of these will only work for a limited range of shaft sizes, units are available off the shelf for a wide range of shaft diameters and you can make or modify them ...


10

According to the following two sources, diamond is a ceramic: Ceramic Strength-Density Graphs Ceramics @ Virginia University The graph below, from Ceramic Strength-Density Graphs shows diamond is the strongest ceramic, whereas zirconia is one of the most dense and strongest ceramics The site matweb has a database of all sorts or materials. By specifying ...


10

You could work pure diamond into something shaped like a knife, but it wouldn't make a very good knife. Diamonds are hard, but they're brittle. The blade would break long before its edge went dull, but this is arguably worse: you can resharpen a dull blade, but a broken blade (especially one not made of a material that can be melted and reforged) becomes ...


10

Your best option for wireless communication in this situation is some kind of optical link. Consumer microwaves typically operate at a frequency of 2.45 GHz and Bluetooth operates from 2.4 GHz to 2.485 GHz, so any shield you design for one will be equally effective for the other. You could design a Faraday cage which gives you enough suppression at 2.45 ...


10

Is it indeed possible Yes and reasonable to craft a carriage side of such large single sheet It can be reasonable, but typically isn't. To form an entire side of the carriage from one sheet of steel would require a forming press that is gargantuan. However, one could instead have three more reasonably sized presses and then weld the sections together. ...


10

As already mentioned in many contexts you will make one part essentially consumable in order to reduce wear on an expensive or difficult-to-replace part. Similarly if you have a situation like a shaft mounted in a cast iron casing (eg an engine block) it makes sense to protect both, relatively complex and expensive parts with a cheap, expendable and easily ...


10

One of the mechanism that affect corrosion is known in the literature as Stress Corrosion Cracking (SCC). The idea is that tensile stressed regions are prone to crack development. Crack development essentially maximizes the area that corrosion can develop. Since corrosion, degrades the properties of the material, this accelerates further the crack ...


Only top voted, non community-wiki answers of a minimum length are eligible