Comparison of the simulation and experimental fatigue crack behaviors in the aluminum alloy HS6061-T6

AbstractThis work deals with rotating bending fatigue tests on aluminum alloy HS6061-T6. Results have been obtained for two sizes of narrow section diameter for specimens with one hole. Results show that fatigue endurance is reduced in the case of the hole. In order to explain this behavior, numerical analysis by FEM were carried out to determine the stress concentrations for the two types of specimens. It is found that the important factor affects fatigue life is the narrow section diameter of the specimens, and the maximum damage occurs in the outer part of the specimen at the first stages of loading, however, it moves toward the center of the bar under uniaxial loading. The number of cycles to failure predicted numerically is higher than the experimental one. This difference is attributed mainly to an upper stage of fatigue crack growth, particularly, the interaction between fatigue crack growth and growth that can not be accounted for in the numerical model

On Vanishing Theorems For Vector Bundle Valued p-Forms And Their Applications

Let $F: [0, \infty) \to [0, \infty)$ be a strictly increasing $C^2$ function with $F(0)=0$. We unify the concepts of $F$-harmonic maps, minimal hypersurfaces, maximal spacelike hypersurfaces, and Yang-Mills Fields, and introduce $F$-Yang-Mills fields, $F$-degree, $F$-lower degree, and generalized Yang-Mills-Born-Infeld fields (with the plus sign or with the minus sign) on manifolds. When $F(t)=t, \frac 1p(2t)^{\frac p2}, \sqrt{1+2t} -1,$ and $1-\sqrt{1-2t},$ the $F$-Yang-Mills field becomes an ordinary Yang-Mills field, $p$-Yang-Mills field, a generalized Yang-Mills-Born-Infeld field with the plus sign, and a generalized Yang-Mills-Born-Infeld field with the minus sign on a manifold respectively. We also introduce the $E_{F,g}-$energy functional (resp. $F$-Yang-Mills functional) and derive the first variational formula of the $E_{F,g}-$energy functional (resp. $F$-Yang-Mills functional) with applications. In a more general frame, we use a unified method to study the stress-energy tensors that arise from calculating the rate of change of various functionals when the metric of the domain or base manifold is changed. These stress-energy tensors, linked to $F$-conservation laws yield monotonicity formulae. A "macroscopic" version of these monotonicity inequalities enables us to derive some Liouville type results and vanishing theorems for $p-$forms with values in vector bundles, and to investigate constant Dirichlet boundary value problems for 1-forms. In particular, we obtain Liouville theorems for $F-$harmonic maps (e.g. $p$-harmonic maps), and $F-$Yang-Mills fields (e.g. generalized Yang-Mills-Born-Infeld fields on manifolds). We also obtain generalized Chern type results for constant mean curvature type equations for $p-$forms on $\Bbb{R}^m$ and on manifolds $M$ with the global doubling property by a different approach. The case $p=0$ and $M=\mathbb{R}^m$ is due to Chern.Comment: 1. This is a revised version with several new sections and an appendix that will appear in Communications in Mathematical Physics. 2. A "microscopic" approach to some of these monotonicity formulae leads to celebrated blow-up techniques and regularity theory in geometric measure theory. 3. Our unique solution of the Dirichlet problems generalizes the work of Karcher and Wood on harmonic map

Investigation of Fiber Reinforced Composite Using Multi-Material 3D Printing

Fiber reinforced composite materials have been commonly fabricated by laying and curing the stiff and high strength fibers within tough matrix to enhance the elastic modulus. The strength and elasticity of the fiber reinforced polymers are dependent on the intrinsic mechanical properties of matrix and fiber, the fiber layup pattern as well as the volume percentage of the matrix and fiber. In this paper, the effects of these factors on the 3D printed fiber reinforced composite materials were investigated. The fiber reinforced polymers were fabricated using multi-material inkjet printer with rubbery material as matrix and rigid strong polymer as the fiber reinforcement. Two types of fiber layup configurations and fiber/matrix volume ratios were designed for this study. The experimental result shows that both tensile strength and elastic modulus of the fiber reinforced polymers could be largely enhanced by varying the fiber/matrix ratio and layup pattern.Mechanical Engineerin

Re-evaluation of Sympoventuriaceae

Sympoventuriaceae (Venturiales, Dothideomycetes) comprises genera including saprophytes, endo-phytes, plant pathogens, as well as important animal or human opportunistic pathogens with diverse ecologies and wide geographical distributions. Although the taxonomy of Sympoventuriaceae has been well studied, generic boundaries within the family remain poorly resolved due to the lack of type materials and molecular data. To address this issue and establish a more stable and reliable classification system in Sympoventuriaceae, we performed multi-locus phylogenetic analyses using sequence data of seven genes (SSU, ITS, LSU, act1, tub2, tef1 and rpb2) with increased taxon sampling and morphological analysis. The molecular data combined with detailed morphological studies of 143 taxa resolved 22 genera within the family, including one new genus, eight new species, five new combinations and one new name. Finally, we further investigated the evolutionary history of Sympoventuriaceae by reconstructing patterns of lifestyle diversification, indicating the ancestral state to be saprophytic, with transitions to endophytic, animal or human opportunistic and plant pathogens

Characterization of starch synthetic genes and starch granule during seeds development between synthetic hexaploid wheat and its parents

To study the development of starch granules in polyploid wheats, we investigated the expression of starch synthetic genes between the synthetic hexaploid wheat SHW-L1, its parents T. turgidum AS2255 and diploid Ae. tauschii AS60. The synthetic hexaploid wheat SHW-L1 showed significantly higher starch content and grain weight than its parents. Scanning electron microscopy (SEM) showed that SHW-L1 rapidly developed starch granules than AS2255 and AS60. The amount of B-type granule in AS60 was less than that in SHW-L1 and AS2255. RT-qPCR result showed that the starch synthetic genes AGPLSU1, AGPLSU2, AGPSSU1, AGPSSU2, GBSSI, SSIII, PHO1 and PHO2 expressed at earlier stages with larger quantity in SHW-L1 than in its parents during wheat grain development. The expression of the above mentioned genes in AS60 was slower than in SHW-L1 and AS2255. The expression pattern of starch synthase genes was also associated with the grain weight and starch content in all three genotypes. The results suggested that the synthetic hexaploid wheat inherited the pattern of starch granule development and starch synthase gene expression from tetraploid parent. The results suggest that tetraploid wheat could plays more important role for starch quality improvement in hexaploid wheat

Non-contrast MR imaging of blood-brain barrier permeability to water

Neuro Imaging Researc