# Experimental Investigation on Effect of Temperature on FDM 3D Printing Polymers: ABS, PETG, and PLA
## 1 Introduction
This includes the use of stimuli-responsive polymers, shape memory materials, and functional inks [4; 13]. In these efforts, the materials and properties when exposed to the desired stimuli are studied. Additionally, 4D printing has not been limited to only FDM 3D printing with the time variant added to it. Four-dimensional printing has been explored in inkjet-based, stereolithography, and direct laser writing, each with its own advantages and limitations [10; 14]. The main challenge to this day has been the ability to predict the behavior of 4D-printed material. Therefore, there is an extensive effort in the field to develop accurate models and optimize design and simulations to have precision and control over fabricated structures [12]. As discussed by [PERSON] in 2013, shape memory polymers (SMPs) exhibit reversible shape changes in response to stimuli like temperature, light, or moisture, enabling complex and programmable 4D structures [8]. SMPs and hydrogels have been widely investigated for 4D printing applications [2; 15]. Hydrogels, which can respond to environmental conditions, have shown potential for applications in soft robotics and biomedical engineering [10]. Four-dimensional printing introduces an innovative approach to crafting intricate 3D structures. Unlike conventional methods that directly build 3D geometric features, 4D printing allows for the creation of initially flat precursor structures that can be morphed into the desired 3D shape when triggered by external stimuli. This methodology offers substantial advantages in engineering applications, notably in terms of efficiency and adaptability. Firstly, additive manufacturing can experience significant reductions in build time and process complexity when working with flat-configured printed objects. Moreover, the compact nature of the flat precursor structure facilitates transportation and storage. The design of precursor structures hinges on active units, pivotal components that govern the ultimate 3D architecture through their out-of-plane deformations. However, generating non-uniform out-of-plane deformations using pure active materials (e.g., hydrogels or liquid crystal elastomers), which inherently prefer homogeneous responses to external stimuli, poses a challenge. To transform the homogeneous deformation of individual materials into non-uniform deformations within the overall structure, the deliberate pre-embedding of internal strain mismatch within active units is necessary, guided by mechanical principles. Thus, the formulation of a mechanical design strategy is crucial for determining the functional attributes of 4D-printed products. Recent years have witnessed comprehensive reviews of 4D printing advancements, examining various facets such as printing materials [16; 17; 18; 19], techniques [16; 19; 20], and programming pathways [21; 22; 23]. For instance, [PERSON] et al. [17] conducted a material-focused review categorizing existing 4D printing endeavors into those achieved with a single material versus multiple materials. [PERSON] et al. [20] summarized 4D printing methods based on additive manufacturing techniques. However, a thorough exploration of mechanics-driven design strategies guiding the active transformation of 4D-printed structures is noticeably absent from the literature. Bending stands as the predominant method for inducing out-of-plane transformations in 4D printing. In this type of design, the central concern revolves around inducing strain mismatch throughout the thickness of the flat active unit upon exposure to external stimuli. The strain gradient possesses the potential to disrupt the original force equilibrium and drive the active unit into a new equilibrium state characterized by minimized potential energy. Because of all the above-mentioned strengths and capabilities of 4D printing, it has found applications in various fields including aerospace, architecture, biomedical engineering, and wearable technology [4; 19].