## 4 Conclusions  
This study investigated the mechanical properties of additively manufactured metal materials, including 316L and 17-4 PH stainless steel, under static and cyclic loading in tensile mode. The full-solid and infill specimens were fabricated by MAM using the BMD technique. The infill density of 16%, 20%, and 24% was set for the infill specimens, corresponding to a relative density of 50% to 75%, approximately. The full-solid specimen considered to have a 100% relative density equivalent was investigated to obtain the properties of the base materials. The results showed that the 17-4 PH full-solid specimens behave as a brittle material and have higher strength than the 316L full-solid specimens. In contrast, the 316L specimens have more elongation and ductility. For the infill specimens, as expected, a higher relative density produces stronger specimens with a higher elastic modulus. However, this behavior is not entirely linear. The relationship between the mechanical properties and the relative density is linear when the specimen has a low relative density and rapidly increases when the relative density approaches a full-solid. The analytical methods described in Section 2.4 were used to validate the experimental results in this study by comparing the values of an elastic modulus and yield strength of 316L and the values of the elastic modulus of 17-4 PH infill specimens. Good agreement is observed between both methods for the specimens with a low relative density, while more discrepancy presents when the relative density increases. Since the formulas were derived using the Euler-Bernoulli beam theory, it cannot be used to predict the mechanical properties of the infill specimens with a high value of the ratio between \(b\) and \(l\), namely a high relative density. However, this analytical procedure can be satisfactorily used in the initial evaluation to determine the mechanical properties of the infill specimens with a low relative density. Regarding the cyclic test, 316L stainless steel was selected for the test specimens because of its ductility and widespread application. The fatigue test was performed with the maximum stress, ranging from 30% to 90% of the ultimate tensile strength of each specimen with different relative densities. The results showed that the fatigue behavior is similar to the tensile strength one; the infill specimens with a higher relative density have a higher fatigue strength for every stress level. The fatigue behavior is also a non-linear function of the relative density, especially when the specimens have a high relative density. The specimens with 16% and 20% infill densities yield slightly different weight efficiency, while those with 24% infill density show an outstanding weight efficiency. As a result, in terms of weight efficiency, the AM parts with a low relative density cannot compete with those that have a relative density. If lightweight AM parts are required, their relative densities between 50% and 60% of the full-solid counterparts can be considered. In contrast, a high relative density close to the full-solid one is recommended if the strength of AM parts is needed. However, the dense parts affect the time and costs in the manufacturing process. Thus, a specific core design requirement is vital for making a decision. Conceptualization, P.S. and T.F. ; Methodology, I.T., P.S. and T.F. ; Software, I.T. and Y.M. ; Validation, I.T. and P.S. ; Formal Analysis, I.T. and P.S. ; Investigation, I.T. and P.S. ; Resources, T.F. ; Data Curation, I.T. and Y.M. ; Writing--Original Draft Preparation, I.T. and P.S. ; Writing--Review and Editing, P.S. ; Visualization, I.T. and P.S. ; Supervision, T.F. ; Project Administration, P.S. ; Funding Acquisition, P.S. and T.F. All authors have read and agreed to the published version of the manuscript. This work (Grant No. RGNS 64-070) was supported by Office of the Permanent Secretary, Ministry of Higher Education, Science, Research and Innovation (OPS MHESI), Thailand Science Research and Innovation (TSRI) and Chiang Mai University.