Sometimes, when we look at the data-sheet of a particular material, we take for granted the material properties and its associated units without understanding their physical relevance. For e.g., one of the most important properties associated with any material is its Tensile Strength, but how many of us really know the physical significance of 1 MPa. Of course I am not talking about the conversion, here. We all know that 1 MPa is 1,000,000 Pa. But then again, how much exactly is one Pascal? What does one Pascal look/feel like? Wouldn’t it be great if we could imagine how much 1 MPa or 1 Pa pressure would be, with respect to analogies derived from everyday things? For instance, if someone asks me how much 30 cm is, I can quickly point to a foot ruler and say, “Well, 30 cm is that much.” But if not for the foot ruler, it would be really difficult to fathom what 30 cm would look like, wouldn’t it? Similarly, when one sees the material data-sheet, one can see the unit and its conversion. But to understand the physical sense of the measurement, it is important that there is some reference, so that it becomes easy to fathom the magnitude of the scale.
On similar lines, we have tried to come up with easy-to-understand analogies for some of the most famous units and material properties:
Micrometer (µm): I would like to explain the relevance of a micrometer with the help of a 3D Printing parameter called Layer thickness. In 3D Printing, layer thicknesses are usually mentioned in micrometers(µm), and people often find it difficult to fathom how small or big the layer thickness value is. To put things into perspective, different 3D Printing technologies have different layer thickness values. The layer thickness in FFF/FDM technology, on an average, is around 180 µm. Whereas in SLS and SLA technologies, the layer thickness on an average is around 100 µm. To give an analogy, a human red blood cell is about 5 µm (across). A human hair, on an average, is around 75 µm (across).
We have a technology in 3D Printing called as Polyjet. The layer thickness in Polyjet technology is around 16 µm. So you can imagine how fine the layer thickness in some of the 3D Printing technologies really is! You can see a comparative diagram below that truly highlights the scale at which we are dealing!
Elongation at break (%): Elongation at break is always calculated as % of the total part elongation. It is the measurement of how much a material can elongate before it fractures. There is a material in 3D Printing called Tango-elastic, it has an elongation at break of around 200-220% . That is, if the part has 10 mm length, it will stretch to about 20 mm before it fails.
Shore Hardness: Hardness is defined as the ability of a material to resist indentation. There are different ways of measuring hardness, and Shore hardness is one such method. Read more about what Shore hardness is and what it signifies, here.
The other day, while I myself was trying to make sense of 1 MPa, I stumbled across this answer on Quora by Andrew Corradini. It went something as follows. (I have paraphrased it.)
While we don’t notice it, we are dealing with the weight of the air stretching from the top of the atmosphere to the ground, and it is about 14.7 pounds for an imaginary column of 1 x 1 inches. Air is actually exerting pressure on us from all the sides, all the time. We call this as Atmospheric pressure, and it is equal to 14.7 psi or about 1/10th of a MPa. To put it simply, 1 MPa pressure would be 10 times of what we are experiencing right now.
To give another analogy, your car tire pressure is usually around 30-35 psi, which is approximately twice of what we are currently experiencing (14.7 psi). Tire pressure in racing bicycles can be as high as 120 psi, which would be almost 8 times the atmospheric pressure. Thus a full 1 MPa is a bit over that (145 psi). To put it succinctly, 1 MPa pressure is about the pressure in a well-inflated bicycle tire, plus a little bit more.
Another way to ‘imagine’ it is this: Think of one square inch. Something like the end joint of your thumb. Imagine a person weighing 120-145 lbs (55-65 kgs) standing on the end of your thumb. We’re talking about the entire weight of that person focused through a nice flat heel, entirely on the last joint of your thumb. That’s a fairly graphic way to imagine 1 MPa of force.
We hope you found this helpful. Kindly let us know which other material properties or material units you’d like us to cover. You may drop down a comment below or write to us at firstname.lastname@example.org