What typically happens to the bottom layers of a bridge in Fused Deposition Modeling as the length increases?

In Fused Deposition Modeling (FDM), as the length of the printed object increases, particularly for bridging sections, the bottom layers can face challenges in maintaining their structural integrity. When a bridge gets longer, the material has to span a greater distance without direct support underneath, which can lead to drooping or sagging. This is primarily due to the weight of the material itself and the thermal behavior of the layers during the printing process.

If the bottom layers lack sufficient adhesion to the upper layers, the material may not maintain its intended shape, resulting in a bridge that droops rather than holds firm. This phenomenon occurs because the extruded filament needs enough time to cool and solidify before the next layers are applied. If the lower layers do not set properly, they may struggle to support the additional weight of the layers being printed above them.

In contrast, the other options do not accurately describe what typically happens to the bottom layers. Rigid strengthening and improved adhesion are not guaranteed outcomes when dealing with extended lengths in bridging, and solidification rates can vary; it's the adherence to structural integrity that is most crucial in this context. Thus, the observation regarding drooping and insufficient adherence is the most relevant and accurate outcome when discussing the behavior of