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Because additively manufactured materials are increasingly being used in load-bearing structures, strength research has become critical. Surprisingly, numerous studies have reported the tensile strength measurements, but only a few studies have presented meaningful results for the shear strength measurements of additively manufactured polymers. Hence, this paper proposes a combined experimental and numerical investigation of a new interlayer shear strength measurement approach, and it targeted the applications of the same polyamide (PA12) specimens made with fused deposition modeling (FDM) and selective laser sintering (SLS). A necking-shaped shear specimen was developed to measure the pure shear strengths with the aid of a three-dimensional (3D) finite element analysis. The results showed that the specimens made with FDM and SLS exhibited totally different shear failure behaviors. The ultimate shear strength of the FDM-PA specimens had more than a 32% increase over that of the SLS-PA specimens. An interface mechanics assumption was employed to explore the different shear failure mechanisms with the support of a fractography analysis. [ABSTRACT FROM AUTHOR]

• Commonly used Tsai-Hill strength criterion mainly predicted the yield strength. • Suggested quadratic strength criterion provided a lower bound of the ultimate strength. • These results were verified by anisotropic ultimate strengths of major 3D printing metals. 3D printing metals have an intrinsic building orientation, so they have some anisotropy in their strength due to the failure between the printing layers with direction dependence that was commonly seen in composite materials. Although the Tsai-Hill composite strength criterion predicted the ultimate strengths of some 3D printing metals made with selective laser melting and laser powder bed fusion (SLM/LPBF), the current study showed that the composite strength criterion was not applicable to the ultimate strength predictions of all 3D printing metals. Our suggested quadratic strength criterion without stress interaction provided conservative strength predictions to ensure safe 3D printing metal applications. Moreover, the shear strength plays a critical role in strength predictions and should be measured accurately. [ABSTRACT FROM AUTHOR]