## 1 Introduction  
Currently, increasing attention is being given to additive manufacturing techniques [1; 2] compared to traditional processing techniques in order to promote competitiveness in the manufacturing market. Material extrusion (ME) technique, the term used here according to the standard of ISO/ASTM 52900:2015 to include the fused filament fabrication (FFF) or fused deposition modeling (FDM) technique, can fabricate products almost without geometrical limitations. It is an increasingly growing additive manufacturing technique in modern manufacturing industry, and the built end-use parts have been used in a wide range of applications, such as automotive, dentistry, electronic and aerospaceindustry [3; 4]. In this technique, the raw material filament is first melted in an extrusion head. It is then extruded out from the nozzle, which moves in a scheduled mode. The molten filament then cools, solidifies and bonds with the extruded material layer beneath it. A three-dimensional model or part entity is finally completed by repeating this procedure until the last layer. During the past few years, extensive research has been carried out in studying various quality characteristics of ME products, such as mechanical property, surface roughness and build quality [PERSON] [5] developed new composite filaments mixing the acrylonitrile butadiene styrene (ABS) thermoplastic with copper and iron particles. The thermo-mechanical properties of the ME samples made of these filaments were investigated. It was found that the tensile strength was decreased with the loading of metal particles, but the thermal conductivity was improved. [PERSON] [6] studied the effects of key processing parameters (the layer height, infill density and postprocessing heat-treatment time at 100 \({}^{\circ}\)C) on the material properties of ME polylactic acid (PLA) parts tested in torsion. It was concluded that to improve the fabricated parts' strength while preserving their ductility and reliability needs low levels of heat treatment. The layer height and infill density were important for optimizing strength, and ductility was significantly affected by infill and heat treatment. [PERSON] [7] evaluated the shock mitigating properties of the polymeric structures fabricated by an ME device. The effect of layer height, infill pattern and density on the energy dissipation properties was examined. The results showed that the impact absorption capacity was influenced a lot by the infill density, whereas the effect of the other two factors was small. [PERSON] [8] studied the effects of layer height, deposition velocity and infill rate on ME parts' mechanical properties, and summarized the quantitative relationship between these processing parameters and the parts' tensile strength. The proposed theoretical model gave accurate predictions of the tensile strength, and it could reveal the work mechanism of these parameters. [PERSON] [9] compared the effect of layer height, infill density and build direction on the mechanical performance of PLA and ABS test samples, which included tensile yield stress, tensile strength, nominal strain at break, and modulus of elasticity. This work provided assistance in selecting proper filament materials for ME. [PERSON] et al. [10] thoroughly reviewed different experimental, analytical and computational studies for characterizing the mechanical properties of ME parts under different loading conditions. The applicability and limitations of these studies were summarized. The three approaches were recommended to be used together for accurately estimating the mechanical properties. The predictive tools, able to predict the mechanical performance, deformation and failures of ME parts, deserve further research. [PERSON] [11] investigated the selection of proper build directions and raster angles to achieve the optimum surface roughness and mechanical property of ME parts. The results showed that the direction has a more significant effect than the raster angle.