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• 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]

Unlike isotropic homogenous materials, 3D printing polymers are anisotropic in terms of their strength and fracture toughness properties, according to previous research. Therefore, the lowest strength must be accurately measured before the extensive application of any 3D printing materials. Certain 3D printing materials have been increasingly employed in large structures; therefore, the size effect of their strengths has become very important. In this work, we performed a systematic experimental investigation on the minimum strengths and size effects of four common 3D printing polymers made by fusion deposition modeling and injection molding. Three types of tensile specimens with very different cross-sectional areas were selected. For each material system, two types of specimens with different printing surface angles were employed. The results from 200 specimens demonstrated that the minimum tensile strengths in the build direction of some specimens were only 25% that of the other directions in the same specimens, and 59% of the injection-molded specimens composed of the same material. No general conclusion on the size effects of the tensile strengths could be made for most specimens. Only the strengths along the build direction decreased up to 72% in two types of specific specimens if their cross-sectional areas increased by 60 times. Although their strengths were anisotropic, the stiffness properties of the 3D printing polymers were isotropic. Digital image correlation measurements showed that the Young's moduli of all specimens composed of the same material were similar. A dual-notch mechanics model was employed to explain the anisotropic strengths, and a fractography analysis supported the size effect. [Display omitted] • Tensile strength along the build direction was the minimum strength. • No general conclusion on the size effects of the tensile strengths could be made. • Strengths decreased 72% in only PLA and PC specimens if their areas increased by 60 times. [ABSTRACT FROM AUTHOR]

The present work investigated the development of sand bed scour by submerged circular impinging vertical turbulent jets over a wide regime of jet diameters, exit velocities and impinging distances. The scour hole profiles were recorded with the optical method in order to present dynamic scour hole characteristics and their variation with any time. The results revealed that the scour profiles in the equilibrium state are similar and the geometries of the sour hole in the jet central region are only determined primarily by jet momentum flux. A semi-empirical equation has been developed for the maximum dimensionless scour depth in equilibrium state based on the obtained experimental data and theoretical analysis. The evolution of scour hole is found to be logarithmic, and three phases of temporal evolution were further distinguished. Finally, models for the prediction of variation of scour depth with time have been developed and validated, which could be used to assess the scour effects generated by impinging turbulent jets. The overall temporal evolution of the scour depth can be predicted by the erosion parameter E c and the dimensionless time to reach equilibrium τ ∞ , which is superior to existing models in predicting the scouring process. • The scour hole profiles were recorded with the optical method in order to present dynamic scour hole characteristics. • A semi-empirical equation has been developed for the maximum dimensionless scour depth in equilibrium state. • Models for the prediction of variation of scour depth with time have been developed and validated. [ABSTRACT FROM AUTHOR]

New branched benzothiadiazole-cored conjugated oligomers with terminal carbazoles 1 and 2 have been synthesized. It was found that no obvious shifts of the maximal absorption bands for 1 and 2 were detected in the films compared with those in solutions, indicating weak π-π stacking occurred in the solid states on account of site isolation effect of the branched architectures. Hence, the synthesized oligomers could emit strong red light in the films. Notably, the emission of the films based on 1 and 2 could be quenched obviously upon exposed to gaseous TNT and DNT. The fluorescence quenching efficiency of the oligomer 2 -based film reached 91% when exposed to the saturated vapor of DNT for 3 min at 55 °C. The linear Stern–Volmer plot and the decrease of the fluorescence lifetime of 2 induced by DNT suggested the fluorescence sensing mechanism was due to the photo-induced electron transfer. [ABSTRACT FROM AUTHOR]