## 1 Introduction  
For the past few decades, the technology of 3D printing has developed significantly in many engineering fields, such as automotive, metal manufacturing, construction, chemical, aerospace, biomedical, and consumer product fields [1; 2; 3; 4]. Three-dimensional printing can be a good solution, which can be easily evaluated in terms of performance characteristics. Therefore, 3D printing technologies are often referred to in the manufacturing of many complex structures and components. A 3D-printed bolt is one of them. It is obvious that bolts are the simplest solution for fixing together mechanical components, and today 3D-printed bolts are commonly used in real life applications such as toy manufacturing, biomedical engineering and industrial engineering [5; 6; 7]. Additive manufacturing has also changed the medical industry and medical education. Since then, composite-based bolts have replaced the titanium screws that were previously employed. In addition, it has been revealed that 3D-printed screws outperform titanium bolts in terms of efficiency and strength for knee surgery implants [5]. Therefore, investigations on 3D-printed bolts cannot be neglected. It is well known that one of the primary disadvantages of bolts is self-loosening. Self-loosening occurs in bolted joints when a transversal load that is perpendicular to the axis of the bolt is applied to them. Then, the result of the loosening of the joint can lead the structure to failure [8]. If a rotational load or dynamic axial load is applied to a bolted joint, loosening can take place in the joint [9; 10]. Even if there are no external loads on bolted joints, they may loosen gradually under cyclical temperature changes [11; 12]. This self-loosening phenomenon depends on the initial preload and amplitude of temperature variations. If the amplitude of the temperature changes is high enough corresponding to the initial preload of the joint, the force of a clamped part can decrease slowly under cyclical temperature changes [13]. Three-dimensional printing filaments play a key role in additive manufacturing because the reliability of a 3D-printed product is mainly dependent on a material. Acrylonitrile butadiene styrene (ABS) and poly lactic acid (PLA) materials are used widely in additive manufacturing because of their good mechanical properties [14,15]. Many investigations have been conducted by researchers on metal bolts [16, 17, 18], for example, [PERSON] and et al. [19,20] conducted investigations on metal-ceramic composite bolts, but very few studies have been carried out on 3D-printed bolts. For instance, [PERSON], and [PERSON]. [21] conducted an investigation on ISO standard 3D-printed bolts and nuts. They used two types of fusion deposition modeling 3D printer materials such as PLA and ABS. The result of their study has shown that PLA bolts are stronger than ABS bolts in sheer stress and equivalent stress. Therefore, PLA materials are often referred to in printing bolts. [PERSON] et al. [22] studied the self-loosening behavior of 3D-printed bolts under transversal vibration experimentally, and they compared the test results to a steel bolt. They proved that a steel bolt is more durable than a 3D-printed bolt in the first stage of loosening. However, a 3D-printed bolt is advantageous in a specific complex fastening condition. Three-dimensional-printed bolts might be used in conditions that there are temperature changes. Owing to the nature of plastic, plastic materials are very sensitive to temperature. Therefore, to choose a suitable material for bolts is very important in terms of self-loosening under cyclical temperature changes. As mentioned above, self-loosening may occur in bolted joints under cyclical temperature changes and this has been investigated by researchers for steel bolts [12,13], but self-loosening of a 3D-printed bolt under cyclical temperature changes has not been investigated before. Therefore, 3D-printed bolts under cyclical temperature changes were investigated experimentally in this study.