# Experimental Study of Compression Behavior on Monolayer FFF Samples
## 1 Introduction  
The use of additive manufacturing (AM) techniques, such as Fused Filament Fabrication (FFF)--also referred to as Fused Layer Modeling (FLM) or Fused Deposition Modeling (FDM)--enables the production of components with an exceptionally high stiffness-to-weight ratio [1]. In order to obtain FFF parts with suitable mechanical properties for load-bearing applications, it is important to conduct systematic mechanical tests on suitable test specimens. The tensile behavior of additively manufactured materials has been widely studied in the literature [2; 3; 4], but the compression performance of thermoplastic components produced via additive manufacturing remains less thoroughly explored. Polylactic acid (PLA), a biodegradable thermoplastic derived from renewable resources, plays a pivotal role in Fused Filament Fabrication (FFF) applications and has recently attracted attention in studies focusing on the compression properties of reinforced materials [5; 6]. Nevertheless, most existing research emphasizes solid, semi-solid, or porous specimens [7; 8; 9; 10], rather than thin-walled structures. Thin walls, however, are frequently utilized in weight-reduction designs and are a defining feature of structures optimized through topology-based methodologies. Also, an AM part does not necessarily have to have several layers. A part comprised of only one layer is called a \"monolayer\" in this publication. Single rasters and monolayers are the basic elements of most AM parts (Figure 1). Understanding the behavior of monolayers is fundamental in order to predict the mechanical behavior of AM multilayer parts. If a methodology can be established which links the properties of monolayers to those of multilayer parts, simple mechanical tests could be performed on monolayers instead of on the more complex multilayers. Monolayers are faster and cheaper to manufacture than multilayer parts. The monolayer properties could then be used to accurately predict the multilayer mechanical behavior. The design of monolayer or thin-walled AM compression specimens without infill has not been explored in detail so far by other authors. For example, [PERSON] and [PERSON] [11] studied thin-walled FFF cylinders with infill, but not without. [PERSON], [PERSON], and [PERSON] [12] tested the compression properties of extremely thin-walled cylinders made by FFF, but did not explore the specimen design in detail. For all these reasons, in additive manufacturing, particularly with FDM, there is significant prior knowledge about mechanical properties. However, this knowledge primarily focuses on the tensile behavior of specimens. Moreover, the information is highly fragmented, as any variability can influence the final outcome of the process, such as the material itself, the pigments in the material, the equipment, the deposition paths, etc. At the same time, controlling these parameters can enable the production of parts with specific characteristics [13], such as mechanical properties tailored to their intended use. For this reason, recently published studies have sought to analyze the influence of many of these parameters on compression properties. These studies have clearly shown that layer thickness is one of the most critical parameters [14]. Therefore, the behavior of a single layer is critical and must be studied, as it is a topic of significant scientific interest. Figure 1: Rasters and several monolayers form a multilayer AM part. However, there are no studies analyzing the compression properties of a single deposited layer. Nonetheless, previous articles have shown that understanding the behavior of a single layer is crucial for understanding the behavior of an entire part. The internal structure of an FDM part is not significantly different from that of a fiber-reinforced composite material, as it can be interpreted as a composite structure with layers of thermoplastic polymer fibers stacked vertically in different arrangements, along with a small amount of air [15,16].