When it comes to determining the suitability of a 3D printing material for a project, you need to know how hard, how strong and how flexible that material is. These things are referred to as the ‘mechanical properties’ of a material.
The phrase “good mechanical properties” is widely used in the 3D printing industry. However, it is a generic phrase that fails to describe the unique characteristics of a material. It is also important to consider that “good” does not mean “suitable”, since all materials have different properties for different applications.
Pictured above: A snapshot of the mechanical properties of Ultimaker CPE+, taken from the material’s technical data sheet.
You can find out the mechanical properties of a 3D printing material, by downloading its ‘data sheet’. Data sheets, or technical data sheets, provide data on the mechanical and thermal properties of a material. However, they don’t make it clear what each data set means. With that in mind, we have provided some useful information about mechanical properties below, to help you better understand what they are and how they translate to a material’s character.
Material Hardness
The hardness of a 3D printing material is usually measured using the Rockwell scale, or the Shore durometer. For instance, Ultimaker CPE+ has a hardness of 111 on the Rockwell scale, while Ultimaker ABS has a hardness of 97 on the Shore durometer. Both tests measure the hardness of a material, by testing its resistance to indentation. The harder a material is, then the more resistant it will be to changes in shape when a compressive force is applied.
The hardness of a material is measured using the Rockwell scale, or the Shore hardness scale.
Tensile strength at yield
Tensile strength at yield refers to the amount of stress a material can withstand before permanent deformation. A good example of this is if you imagine a rubber tube that is being stretched out. If you removed the pressure on the tube, then it would return to its original shape. However, if the stress on the tube kept increasing, then it would reach a point of deformation, rendering it incapable of springing back to its original shape.
The tensile strength at yield of a material is measured in megapascals (MPa).
Tensile strength at break
Tensile strength at break refers to the amount of force that can be applied to an object or material before it breaks. Coming back to our rubber tube example, if you kept increasing the pressure on it, then it would go beyond the point of deformation and break, because the molecules of the material would be unable to counter the external forces being applied. The force required to break the rubber tube is then used as that material’s tensile strength at break rating.
The tensile strength at break of a material is measured in megapascals (MPa).
In the video below, you can see a carbon fibre chain link printed by a Markforged 3D printer being put to the test. If you watch the video closely, you can see the chain link slowly deform, before breaking.
Elongation at yield
Elongation at yield, or tensile elongation at yield, refers to the ratio between the initial length and the increased length of a material at its yield point (which as we covered above, is the point that a material deforms – but does not break). In the simplest terms, elongation at yield is a measurement of a material’s ability to resist changes in shape before it deforms permanently. A good example would be if you stretched an elastic band out. Eventually, the band would deform.
The elongation at yield rating of a material is measured as a percentage.
Elongation at break
Elongation at break, or tensile elongation at break, refers to the ratio between the initial length and the increased length of a material at its break point. So, this is a measurement of a material’s ability to resist changes in shape before it breaks. For example, if you were to stretch an elastic band out as far as you could, it would eventually break. With both elongation at break and elongation at yield ratings, the more flexible a material is, the higher its elongation will be.
The elongation at break rating of a material is measured as a percentage.
Flexural strength
Flexural strength, also known as bend strength, is a measurement used to define a material’s tendency to bend. It is a ratio of stress to strain in flexural deformation. This measurement is widely used with materials that deform significantly, but will not break. It is a useful measurement to know, since it defines a material’s ability to resist failure in bending. An example of a test to find a material’s flexural strength, would be to bend a plastic stick with your hands until it deformed.
The flexural strength of a material is measured in megapascals (MPa).