# Experimental Analysis of Welded Rods with a Functionally Graded Material Approach
## 1 Introduction  
Due to its ease of use, electric arc welding has a wide range of applications in the manufacturing industry. Material properties in electric arc welding are affected by high temperature. On the other hand, the structure turns out from indicating ductile material properties and starts indicating brittle material properties. The material feature of the welded structure after cooling down to room temperature depends on which temperature it starts to cool. The higher the temperature at which this structure begins to cool, the more brittle a material property it will have. Since the welding is a process performed at high temperatures, the mechanical properties of the structure from which the welding is made are affected by this process. The high temperature formed during the welding process affects both the welding point and the neighbors of that point. The heat affected zone (HAZ) occurs as a result of these effects caused by this high temperature. This formation is explored in [1, 2]. The microstructure and hardness of HAZ of the MAG (Metal Active Gas)-welded structure is investigated in [3]. The high temperature mechanical properties of weld metals are examined in [4]. The negative effect of temperature on mechanical properties can be seen in [5]. It was investigated how the welding process, by providing heat inputs from an externally applied source, affects the mechanical properties of the structure in [6, 7]. Examples of rotary inertia friction welding applications include compressor rotors and drill bits for aircraft engines. The rapid development shown by the friction welding method is due to the features that differ from conventional welding methods. The first of these features is that no extra heat source is required in the friction welding. In addition, the second feature is that the friction welding process begins when the welding temperature reaches a temperature close to the melting temperature. Microstructure properties of the structures produced by welding processes show the interaction between the high temperature during the process and the material properties of the structure. Friction welding, which is one of the rare welding methods that can be applied to similar materials, has become popular in recent years and many studies have been done on this subject in recent years [8; 9]. Microstructures of specimens produced by friction welding are examined in detail in [10; 11; 12; 13]. In [14; 15; 16; 17; 18] various applications related to friction welding have been studied. In [19; 20], the mechanical properties of the structures produced by using friction welding from parts with different properties are examined by tensile tests. Studies on microstructures and mechanical structures obtained by combining two different materials with arc welding are also available in the literature [21]. In addition, the investigation of both microstructure and mechanical properties of structures obtained by combining different materials with friction welding is another study subject [22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33]. In [34; 35], microstructure properties of materials of the same type are studied. By making a nitrogen reinforcement to the welding zone of the steel used in the manufacture of another structure, the mechanical properties of the structure were tried to be improved and as a result, the structure was made to be hard outside and partially soft inside. The cross section of this structure is taken and if this section is examined, it is concluded that the new structure formed is a functionally graded material (FGM) [21]. It should be noted that, there are many other studies related to FGM in the literature [36; 37; 38]. There are many theoretical examples of the thermal behavior and mechanical analysis (vibration, wave propagation, bending and buckling) of axially FGM in the literature [39; 40; 41; 42; 43]. The purpose of this study is to establish a link between theoretical and experimental studies.