How to Read Safety Data Sheets Page Categories
Time to read: 9 min
To most people, plastics might seem all the same, simply to an engineer, plastics come in families, have cousin materials, and accept other materials that are as different as cats are from dogs. Of grade, our clients await the states to worry nigh these details, and as nerds, the minute differences betwixt materials are a source of fascination.
Just even the nerdiest among us won't have all the material properties memorized for many types of plastics (and if y'all do, then maybe you need to get out more), and not everyone who needs to select materials for a pattern has a technical background. And with new materials being released all the fourth dimension, we need a mode to look at the key material properties: This is where material data sheets become invaluable. So, how exercise you interpret these valuable references and choose the right cloth for your design?
Tensile Backdrop
Tensile strength is the nigh common measure of strength in materials and also the most likely number for the nerds in your life to have memorized, and for this reason, it appears at the top of most data sheets. For older engineers, such equally all of our professors, any report of force of materials used to focus on the tensile test for all the useful data it provided, peculiarly in looking at metal backdrop. With polymers taking over in design, we need to perform other tests to get the same depth of data on plastic materials, only this remains the all-time starting point for deciding if a cloth is correct for your application.
The tensile strength exam is straightforward: A small piece of material is held betwixt two clamps on a hydraulic press, and 1 of the clamps pulls on the material until it breaks. From this unproblematic test, we tin can discover the ultimate tensile forcefulness (UTS—how much stress it can take when it breaks), the tensile strength at yield (how much stress the material tin can stand before it starts to deform permanently), the modulus of elasticity (also called Young's Modulus, meaning how much it deforms under stress), and the elongation at yield (basically, how much it stretches earlier it snaps).
Oh, no! We can hear the yawns from here. What do these terms hateful, and why should yous care?
In their direct form, they give you lot an piece of cake mode to compare forcefulness between materials. For example: ABS is a nice strong plastic and has a UTS of 40 MPa. Steel is a squeamish strong metal and has a UTS of 400 MPa. Wow—steel is ten times as strong as ABS for the aforementioned size. I didn't know that. (See! I'chiliad not that nerdy!) At present, of course that doesn't mean that you should carelessness plastics for steel, merely it does mean that parts of the same forcefulness volition need to be much thicker.
Similarly, the modulus of elasticity allows u.s.a. to accept an at-a-glance idea of how "springy" the cloth is, whether very stiff (steel – YM of around 200 GPa) or quite flexible (ABS —effectually 2 GPa), and the elongation at yield (or sometimes at break) volition give y'all an thought of merely how far you can pull the material earlier it becomes an upshot (here steel and ABS compare well, with 20-30% for each, depending on the specific material). Run across? Useful. You should definitely keep a nerd effectually for interpreting these things.
Flexural Backdrop
Flexural properties are similar to tensile backdrop, and in many materials can be approximated from the aforementioned measurement. However, for accuracy, specially in plastics, information technology's best to perform a three-point flexural forcefulness test, where a bar of the material is placed across ii supports, with a hydraulic head pressing in the centre, which gives us flexural forcefulness and flexural modulus, which in homogenous materials are the same as the tensile strength and modulus, simply…look, look, come dorsum!
Let's pause that down a bit. Essentially, if a textile is perfectly the same all the way through, the way most steel is, then the flexural exam will requite y'all the same numbers as the tensile examination. Simply plastics are almost never the same throughout the cross section—because of injection molding, the material will form a skin of material that doesn't match the remainder of the material.
While that can occasionally exist a bad thing, in some cases it works out really, really well, like in the case of rigid structural foam: The interior of the part is super lightweight (foam-similar), while the outside skin is solid plastic (the peel), which results in lightweight, strong parts. This material property allows for the structure of ladders, play equipment, and hand carts that are both cheap and lightweight.
But yous should be careful, considering these properties tin besides work to your disadvantage, such every bit when fabric surface roughness or surface imperfections result in a much lower flexural force than tensile strength. This can happen with quite a few printed materials, like those produced with SLS or FDM. Go on in heed when prototyping with these materials that care should be taken when designing parts that flex.
Touch on Backdrop
Many of us remember ourselves to be Titanic experts (or at least, Leonardo DiCaprio experts), merely here'south a lesser-known fact: If the Titanic had been hit by similar touch of a rock in the tropics instead of an iceberg in the Arctic, it may not have sunk. Why? Impact strength.
Steel is uncommonly strong (see tensile numbers higher up), but at low temperatures, it becomes very brittle, so force that would bounce off a steel plate in warm weather, or at worst paring information technology, will cause the sinking of an ocean liner at colder temperatures (and give millions of teenage girls the all-time movie feel of their lives 86 years afterward). Luckily, we've since been more than careful well-nigh measuring the bear on forcefulness of materials before using them in our designs.
This test, like the other mechanical tests, is beautifully unproblematic: The sample is secured in a clamp beneath a heavy pendulum arm, the arm is raised, and so the arm swings down and breaks the sample. (Not just educational, but fun.)
The tests are done on either notched or unnotched samples. A notched examination is a realistic indicator of impact force when there may be some flaws on the surface of the product (an iPhone example gets tossed into a pocket with some keys, and flaws are bound to result), while an unnotched test is better for situations where the fabric volition be in less demanding environments.
In either instance, the impact backdrop of plastics are especially interesting, as we so often want to know not necessarily how stiff something is, but how it'southward going to hold up when in an accident or dropped off a table. (Or balcony, which as I swore to my girlfriend, was an accident. Incidentally, difficult case or no, iPhone aren't good afterwards a 3-story autumn. Boyfriends, beware.) Take two mutual clear plastics: polycarbonate and acrylic. They both have similar tensile force (around 40 MPa), but polycarbonate withstand upwardly to 40 times as much impact. Acrylic may make for very dainty clear lenses, but information technology'due south clear which is better for safety glasses.
Thermal Backdrop
In the same way yous have to worry near materials becoming brittle when it's cold, or snapping when a load is sudden instead of gradual, for some applications, you'll also demand to think about what happens when it's actually hot. You lot know what I mean if yous always came back to the car from shopping with your parents to find that the car had melted your favorite Barbie.
While this is less of a business concern for metals, plastic properties dictate that for the most part, when they get hot, they get soft. Fortunately, this is covered on material information sheets, likewise, nether the thermal backdrop section, where yous'll typically find several notes on heat deflection temperature, and sometimes a glass transition temperature.
Estrus deflection is straightforward: The testing will show you at what temperature the material begins to deflect at what stress. Find a pressure similar to the stress you'll need in your blueprint, and then check to make sure that the temperature where deflection happens is well outside your planned use. Like shooting fish in a barrel.
Drinking glass transition is a little more complicated, and only applies to amorphous materials: materials that don't have a crystalline structure (such as polycarbonate and polystyrene, as opposed to crystalline polymers similar nylon and polypropylene). Basically, when an baggy material gets warm, it goes from being brittle to being rubbery, and that happens at the glass transition temperature.
You lot'll have to care about this for two reasons: You don't want your rubbery parts to become breakable, and you lot don't want your hard parts to get rubbery. For instance, if tire rubber gets much beneath minus 100 F, you have to worry about shattering information technology; if ABS is heated above 220 F, it starts to behave like flubber (minus the dancing). And speaking of rubbery materials…
Hardness
Even though from a chemical engineer's perspective elastomers (rubbers) and plastic polymers are essentially the aforementioned, everyone knows that on a practical level, they're just not the same, and we larn this from the time nosotros develop a gustation for pacifiers. Though stretch (call back elongation at suspension/yield) and elastic modulus are very different, for most people, the biggest difference in classification comes down to hardness.
The hardness test for materials is fortunately elementary, consisting of a pocket-size ball-ended or cone-ended rod pressing into the cloth with a specific force. If it barely presses into the material, information technology gets a high hardness number; if it presses in far, information technology gets a depression hardness number. Unfortunately, because we take to measure hardness of everything from rubber bands to diamonds, the scales we apply for these measurements are anything merely simple, with ii mutual scales (Rockwell and Shore), which each have several subcategories, as well as some less common scales (Vickers, Leeb and Brinell, which nosotros volition completely ignore from here on).
Rockwell is the scale used for measuring difficult things, from difficult plastics (like nylon and polycarbonate) to gemstones. For plastics, the nearly common scales are Rockwell Eastward, Rockwell R and Rockwell M; polycarbonate has a hardness of about Rockwell 70M.
When measuring soft things, like rubbers and soft plastics, we use the Shore scale (which likewise has many messages after it to add together to the confusion), and we most often utilize either the Shore A calibration (very soft—rubber bands are Shore A 20 and car tires Shore A 60) or the Shore D scale (firm to hard—a hard hat is Shore D eighty).
A true nerd would desire to swoop farther into the details of the history of the different scales and how to use the Shore OO scale, and if that's you lot, well, then y'all should really detect some other source. Or maybe another hobby. For anybody else, check out our article on prototyping soft materials and elastomers, and our free downloadable chart that shows the hardness of different materials on both Shore A and Shore D scales.
Limitations to Textile Data Sheets
As with every type of technical data, fabric data sheets take their limitations. You'll typically find all the information listed higher up and ordinarily detect extra information (like density), but some data e'er requires farther excavation.
For instance, when you're designing food products, you'll demand to look at the FDA guidelines and besides look for information from the manufacturer as to whether or not the planned material is nutrient safe. In addition, you'll need Cloth Condom Data Sheets (MSDS) to look at health hazards. Similarly, if the material will come into contact with other materials, y'all'll need to find out how the properties volition be altered; it's very common for the outgassing of sure adhesives to cause brittle cracking in acrylics and polycarbonates, for example. Material data sheets are a great starting signal for choosing a material, simply the journey shouldn't end in that location—keep excavation until you're confident in your material choice.
Using Material Information Sheets for Your Blueprint
Textile data sheets provide an amazing amount of information at a glance, but as with all types of engineering knowledge, information technology takes background cognition on what the numbers mean to interpret that information and a skilful engineer to evaluate the backdrop and choose the correct cloth for a design.
Want to learn more than about specific materials to use in your upcoming prototype? Check out our textile data sheets for CNC machining, 3D printing, and Urethane Casting. And want more than engineering noesis coming your style every week? Exist certain to sign upwards here for more articles!
Source: https://www.fictiv.com/articles/how-to-read-material-data-sheets
0 Response to "How to Read Safety Data Sheets Page Categories"
Post a Comment