We present the first experimental evidence supported by simulations of kinetic effects launched in the interpenetration layer between the laser-driven hohlraum plasma bubbles and the corona plasma of ...the compressed pellet at the Shenguang-III prototype laser facility. Solid plastic capsules were coated with carbon-deuterium layers; as the implosion neutron yield is quenched, DD fusion yield from the corona plasma provides a direct measure of the kinetic effects inside the hohlraum. An anomalous large energy spread of the DD neutron signal (∼282 keV) and anomalous scaling of the neutron yield with the thickness of the carbon-deuterium layers cannot be explained by the hydrodynamic mechanisms. Instead, these results can be attributed to kinetic shocks that arise in the hohlraum-wall-ablator interpenetration region, which result in efficient acceleration of the deuterons (∼28.8 J, 0.45% of the total input laser energy). These studies provide novel insight into the interactions and dynamics of a vacuum hohlraum and near-vacuum hohlraum.
General relationship between strength and hardness Zhang, P.; Li, S.X.; Zhang, Z.F.
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
11/2011, Letnik:
529
Journal Article
Recenzirano
► The hardness is not an intrinsic property but reflects the hardening state in CG. ► The ratio of hardness to strength can also be reflected by indentation morphology. ► The ratio of hardness to ...strength increases with increasing parameter
α. ►
H
V
=
3
σ
UTS
is valid for materials with relatively high strength and better toughness.
Both hardness and strength are the important properties of materials, and they often obey the three times empirical relationship in work-hardened metals and some bulk metallic glasses (BMGs). But the relationships between strength and hardness are quite different for those coarse-grained (CG) and ultrafine-grained materials, brittle BMGs and ceramics. In the present work, some Cu alloys with different microstructures, Zr-, Co-based BMGs and Al
2O
3 were employed to analyze the general relationship between hardness and strength. Several different relationships could be gotten from the experimental results of different materials available, and three types of indentation morphologies were observed. Indentation with “sink-in” morphology always represents a state of material and one third of hardness is in the range from yield strength to ultimate tensile strength. The other two indentation morphologies induced the fully hardening of material, so hardness could represent the intrinsic mechanical property of materials. The ratios of hardness to strength are found to be affected by the piled-up behaviors and their ability of shear deformation. Combined effect of the two aspects makes hardness approximately be three times of strength in the work-hardened crystalline materials and the shearable BMGs, but higher than three times of strength in the brittle-, annealed BMGs and ceramics.
The cyclic deformation and damage behaviors of the Fe–Mn and Fe–Mn–C TRIP/TWIP steels are comprehensively studied in a wide range of strain amplitude (from 0.3% to 8.0%). It is found that with ...increasing C content, the dislocation structures change from wavy slip to planar slip after cyclic deformation. In order to evaluate the low-cycle and extremely-low-cycle fatigue (LCF and ELCF) properties, a fatigue life prediction model, Nf = (Wa/W0)β, with a hysteresis energy-based criterion is used and developed. The model reveals that the LCF and ELCF damage mechanisms can be controlled by the material's damage capacity (the intrinsic fatigue toughness W0) and its ability of transforming mechanical work into effective damage (the damage transition exponent β). From a macroscopic point of view, W0 is related to the match of strength and ductility (approximately the static toughness U), and β mainly has a negative correlation with the cyclic strain hardening exponent n′. On the micro-scale level, W0 represents the defect-accommodated ability of the materials, and β is determined by the uniformity and reversibility of plastic deformation. For the current Fe–Mn(–C) TRIP/TWIP steels with increasing C content, the cooperation between an increasing damage capacity and an incremental damage accumulation rate leads to a higher ELCF property and a lower LCF property.
The low-cycle fatigue (LCF) damage mechanisms may be controlled by the material's damage capacity and damage accumulation rate. The influences of planar slip caused by short-range order (SRO) on fatigue damage and cracking are quite different from those caused by lowering the stacking fault energy (SFE), which has its origin from the various effects on damage accumulation rate. Display omitted
The extremely-low-cycle fatigue (ELCF) behaviors of pure Cu and Cu–Al alloys are comprehensively studied following the cyclic push–pull loading tests with extremely high strain amplitudes (up to ...±9.5%). Compared with the common low-cycle fatigue (LCF) region, several unique features in the ELCF regime can be noticed, including the deviations of fatigue life from the Coffin–Manson law, the non-negligible proportion occupied by the cyclic hardening stage of the whole fatigue life, special microstructures formed by cyclic loading containing deformation twins, shear bands and ultra-fine grains and the transformation of fatigue cracking modes. All these characteristics indicate the existence of special interior fatigue damage mechanisms of ELCF. To help discover the new damage mechanisms under ELCF, a model of fatigue life prediction with a hysteresis energy-based criterion is proposed. Based on the analysis of the experimental and modeling results, two intrinsic factors determining the ELCF properties were concluded: the capacity of ELCF damage, and the defusing and dispersion ability of the external mechanical work. The former can be evaluated by a parameter of the model called the intrinsic fatigue toughness W0, which is related to the microstructure evolution condition, the cyclic hardening ability, the deformation homogeneity and possibly the static toughness. The latter can be represented by the damage transition exponent β, which can be enhanced by improving the planarity, reversibility and uniformity of plastic deformation, reflecting the decline in the degree of surface damage and the dispersion of fatigue cracks. For Cu–Al alloys with increasing Al content, cooperation between an increasing damage capacity and a decreasing damage accumulation rate leads to a comprehensive improvement in the ELCF properties.
In this study, the effect of strain rate on the tensile deformation behavior of Fe–22Mn–0.6C–(1.5Al) (wt%) twinning-induced plasticity (TWIP) steel was investigated. The experimental results ...indicated that the work hardening exponent (n), ultimate tensile strength (σu) and the uniform elongation (δu) decreased with increasing strain rates (from 10−4 to 100s−1). This phenomenon exhibited negative strain rate sensitivity (NSRS), and the strain rate sensitivity value (m) was observed to be higher in the aluminum added FeMnC TWIP steel. In order to gain an in-depth understanding of this sensitivity and the subsequent effect of aluminum, the present research focused on the deformation twins and conducted comparative studies on their influence in terms of fractions (F), thickness (t) and spacing (s). Additionally, a twin boundary affected zone (TBAZ) model was proposed, where the relation between higher strain rates were directly applicable to the reduction of interfaces between the matrix and deformation twins. These result indicated that fewer sessile dislocations could be accommodated at high strain rates, thus weakening the work hardening ability. Finally, model calculations were performed to validate the findings, where TBAZ region fractions in FeMnC–Al were observed to be higher than that in FeMnC, corresponding to the increased strain rate sensitivity.
We predict theoretical existence of intrinsic two-dimensional organic topological insulator (OTI) states in Cu–dicyanoanthracene (DCA) lattice, a system that has also been grown experimentally on Cu ...substrate, based on first-principle density functional theory calculations. The p z -orbital Kagome bands having a Dirac point lying exactly at the Fermi level are found in the freestanding Cu–DCA lattice. The tight-binding model analysis, the calculated Chern numbers, and the semi-infinite Dirac edge states within the spin–orbit coupling gaps all confirm its intrinsic topological properties. The intrinsic TI states are found to originate from a proper number of electrons filling of the hybridized bands from Cu atomic and DCA molecular orbitals based on which similar lattices containing noble metal atoms (Au and Cu) and those molecules with two CN groups (DCA and cyanogens) are all predicted to be intrinsic OTIs.
► Effects of LSP on mechanical properties of stainless steel ANSI 304 are evaluated. ► LSP can clearly enhance the values of mechanical properties in the shocked region. ► Martensite transformation ...does not take place in the surface layer subjected to LSP. ► Enhancement mechanisms of LSP on mechanical property of stainless steel are revealed. ► The results can provide some insights on the surface modification of stainless steel.
The aim of this article is to address the effects of a single laser shock processing (LSP) impact on the nano-hardness, elastic modulus, residual stress and phase transformation of ANSI 304 austenitic stainless steel. Residual stress distribution of the LSP-shocked region is determined by X-ray diffraction (XRD) with sin
2
ψ method, and the micro-structural features in the near-surface layer are characterized by using cross-sectional optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). By comparing with the untreated samples, LSP can clearly improve nano-hardness, elastic modulus, and residual stress in the LSP-shocked region. The underlying enhancement mechanisms of LSP on nano-hardness, elastic modulus and residual stress of stainless steel ANSI 304 are also revealed. These studies may provide some important insights into surface modification for metal materials.
The tensile and high-cycle fatigue tests of Fe-30Mn-0.9C twinning-induced plasticity (TWIP) steel after 30%, 60% and 70% pre-straining were performed. Meanwhile, the surface damage morphologies of ...post-fatigue specimens and microstructure evolutions of pre-strained and post-fatigue pre-strained specimens were also investigated. It is found that the fatigue properties of the TWIP steel can be effectively improved through pre-straining, because the pre-straining can change the fatigue strength coefficient and exponent, respectively. The improvement of fatigue strength coefficient may be attributed to the strengthening mechanisms induced by both twin boundaries and dislocations; while the variation of fatigue strength exponent should be resulted from the combined effects of deformation homogeneity and slip reversibility, as well as the internal damages. Furthermore, the detailed mechanisms associated with the variations of fatigue strength coefficient and exponent were discussed. This study may enrich the fundamental knowledge about how to improve the high-cycle fatigue properties of TWIP steels.
This experiment was conducted to investigate the efficacy of Lactobacillus acidophilus, Bacillus subtilis, and Clostridium butyricum supplementation in broilers. A total of 400 one-day-old mixed sex ...Ross 308 broilers with an initial average BW of 46 ± 0.5 g were randomly allotted into 4 treatments with 5 replicate pens per treatment and 20 broilers in each pen for 35 d. Dietary treatments were (1) an antibiotic-free diet (CON), (2) CON + 5 mg/kg of avilamycin, (3) CON + 1 × 105 cfu of multistrain probiotics/kg of diet (P1), and (4) CON + 2 × 105 cfu of multistrain probiotics/kg of diet (P2). Broilers fed the P1 and P2 diets had greater BW gain than broilers fed the CON diet during d 22 to 35 (P = 0.01) and overall (P = 0.02). Feed conversion ratios in P1 and P2 were decreased (P = 0.03) compared with that in CON from d 22 to 35. Ileal digestibility of most essential amino acids, with the exception of His and Phe, were increased (P < 0.05) in P1 and P2 compared with CON. Serum IgA and IgM concentrations in P2 were higher (P < 0.05) than those in CON. The cecal Lactobacillus numbers were increased (P = 0.02), and the counts of Escherichia coli were decreased (P = 0.03) in P1 and P2 compared with CON. Dietary supplementation with multistrain probiotics decreased (P < 0.05) the excreta NH3 content compared with the CON. In conclusion, dietary supplementation with multistrain probiotics improved broiler growth performance, ileal amino acids digestibility, and humoral immunity. Furthermore, the probiotics decreased the cecal numbers of E. coli and decreased the NH3 content of excreta.
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