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Fatigue failure is invariably the most crucial failure mode for metallic structural components. Most microstructural strategies for enhancing fatigue resistance are effective in suppressing either crack initiation or propagation, but often do not work for both synergistically. Here, we demonstrate that this challenge can be overcome by architecting a gradient structure featuring a surface layer of nacre-like nanolaminates followed by multi-variant twinned structure in pure titanium. The polarized accommodation of highly regulated grain boundaries in the nanolaminated layer to cyclic loading enhances the structural stability against lamellar thickening and microstructure softening, thereby delaying surface roughening and thus crack nucleation. The decohesion of the nanolaminated grains along horizonal high-angle grain boundaries gives rise to an extraordinarily high frequency (≈1.7 × 103 times per mm) of fatigue crack deflection, effectively reducing fatigue crack propagation rate (by 2 orders of magnitude lower than the homogeneous coarse-grained counterpart). These intriguing features of the surface nanolaminates, along with the various toughening mechanisms activated in the subsurface twinned structure, result in a fatigue resistance that significantly exceeds those of the homogeneous and gradient structures with equiaxed grains. Our work on architecting the surface nanolaminates in gradient structure provides a scalable and sustainable strategy for designing more fatigue-resistant alloys.

Biological load-bearing materials, like the nacre in shells, have a unique staggered structure that supports their superior mechanical properties. Engineers have been encouraged to imitate it to create load-bearing bio-inspired materials which have excellent properties not present in conventional composites. To create such materials with desirable mechanical properties, the optimum structural parameters combination must be selected. Moreover, the optimal design of bio-inspired composites needs to take into account the trade-offs between various mechanical properties. In this paper, multi-objective optimization models were developed using structural parameters as design variables and mechanical properties as optimization objectives, including stiffness, strength, toughness, and dynamic damping. Using the NSGA-II optimization algorithm, a set of optimal solutions were solved. Additionally, three different structures in natural nacre were introduced in order to utilize the better structure when design bio-inspired materials. The range of optimal solutions that obtained using results from previous research were examined and explained why this collection of optimal solution ranges is better. Also, optimal solutions were compared with the structural features and mechanical properties of real nacre and artificial biomimetic composites to validate our models. Finally, the optimum design strategies can be obtained for nacre-like composites. Our research methodically proposes an optimization method for achieving load-bearing bio-inspired materials with excellent properties and creates a set of optimal solutions from which designers can select the one that best suits their preferences, allowing the fabricated materials to demonstrate preferred performance. [ABSTRACT FROM AUTHOR]

The influence parameters (Π1 and Π2) of the stable hydraulic geometry of the channel were found based on the dimensional analysis,namely π theorem.In addition,a set of calculation formulas for stable channel width BR and stable channel depth hR were proposed,with multiple linear regression conducted on 303 sets of sample data from prototype measurements and flume experiments.Yalin and da Silva methods were selected as standard methods to test and compare the formula in this paper,and the results show that the channel width and the channel depth calculated in the scatter plots with both methods are all close to the measured values.In general,the error indexes of the formula in this paper are slightly better than those of the Yalin and da Silva methods,while the difference between them is not significant in terms of the values of the error indexes.Therefore,it can be considered that the calculation accuracy of the two methods is equivalent,and the formula in this paper can be applied to engineering practice.

In order to facilitate the use of the discharge coefficient table of broad crest weir in the current design code for Spillway of water conservancy,the discharge coefficient formula of broad crest weir is obtained by fitting the data in the current water conservancy code with bivariate rational function approximation.By Comparing the fitting formula with the current power code formula,the results show that the fitting formula is better than the current power code formula.By comparing the error indexes of fitting formula and power code formula,it is found that the error indexes of fitting formula are in the better range under each value of r/H,while the deviation of each error index of power code from the optimal value is small when r/H≥0.20.The fitting formula is used to calculate a series of discharge coefficients corresponding to water head at different fillet radii of a spillway broad crest weir.Through the analysis of the calculation results,it can be seen that the fitting formula can be used to calculate the discharge coefficient of broad crest weir in engineering design instead of consulting the water conservancy code table.