## 1 Introduction  
Multi-material parts manufactured by additive manufacturing (AM), also known as 3D printing, demonstrate a vast potential regarding the integration of multiple, material-specific functions. For example, differences in stiffness of two different materials can be used in such a way that damping functions are locally integrated [1; 2]. Moreover, conductive materials can be combined with conventional build materials in order to realize conductivity inside specific areas of the part, so that the assembly and maintenance of radiant heat surfaces [3] or 3D printed circuits would be omitted [4]. Using AM technologies to generate multi-material parts enables the possibility of achieving custom-designed requirements by means of functional integration via local material variations and a specific design of material properties. Hence, in contrast to traditional manufacturing processes (e.g., milling or casting), the designer has entirely new opportunities in product design. Consequently, there are two big challenges. On the one hand, the design engineer needs to be supported to ensure a consideration of these new design potentials in conceptual design. On the other hand, standardized test methods for analyzing both the compatibility and the bonding quality of two materials printed together have to be established. The latter research gap is focused on in this contribution.  
Whereas only a few AM technologies are capable of processing multiple materials within the printing process, the AM technique material extrusion (ME) is due to its process principle (discrete material transition) predestinated in this regard [5]. In fact, only the number of extruders integrated into the ME machine limits the number of processable materials--even within one layer [6]. A multi-material part design framework supporting the selection of suitable material combinations for additively manufactured parts has already been proposed by [PERSON] et al. [7]. However, the quantification of the interface strength (bonding quality) between two different polymeric materials and a compatibility in general are inadequately discussed. As the compatibility is closely linked to the corresponding mechanical properties in the interface zone, a quantification of those is indispensable for designing multi-material parts for ME. Yet, standardized test methods and test specimens for multi-material ME parts are not available. As a consequence, users have no common basis on which mechanical properties of two combined thermoplastic materials can be determined. A standard that shall enable an efficient and clear communication between users (here, suppliers of additively manufactured parts and their customers) is addressed in DIN EN ISO/ASTM 52901 [8], but multi-material parts are not considered.  
In this paper, novel specimens for the three exemplary load types, namely, tensile, lap-shear, and compression-shear, are proposed. With ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid), two standard materials from the prototyping sector are used as reference materials. The proposed test methods, including the development of novel tests specimens for characterization of multi-material ME parts, are experimentally validated.