Question

thermoplastics
thermoplastics are plastics that can be melted and solidified repeatedly.
two 3d printing methods that use thermoplastics are selective laser
sintering (sls) and fused filament fabrication (fff).
layer adhesion:
when printing with thermoplastics, what will a hot new
layer cause the previous layer to do?
crack and split
melt a little bit
completely freeze

Explanation:

Thermoplastics can be melted and solidified repeatedly. When a hot new layer is added during 3D printing with thermoplastics, due to the heat transfer, the previous layer will be affected. Since thermoplastics have the property of being able to melt (as they can be melted and solidified repeatedly), the heat from the hot new layer will cause the previous layer (which is also made of thermoplastic) to melt a little bit. This allows for better adhesion between layers in 3D printing processes like Fused Filament Fabrication (FFF). A new layer being hot won't cause the previous layer (which is made of thermoplastic that can melt) to crack and split (as that would be more characteristic of a brittle material that doesn't have the melt - solidify property) and it won't cause the previous layer to completely freeze (as the new layer is hot and thermoplastics don't 'freeze' in the sense of becoming a completely rigid, non - meltable state in this context).

Answer:

melt a little bit