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.
Fast radio bursts (FRBs) are immensely energetic millisecond-duration radio pulses. Observations indicate that nearby FRBs can be produced by old stellar populations, as suggested by the localization ...of the repeating source FRB 20200120E in a globular cluster of M81. Nevertheless, the burst energies of FRB 20200120E are significantly smaller than those of other cosmological FRBs. Here, we report the detection of a bright burst from FRB 20200120E in 1.1 – 1.7 GHz, with a fluence of approximately 30 Jy ms, which is more than 42 times larger than the previously detected bursts near 1.4 GHz frequency. It reaches one-third of the energy of the weakest burst from FRB 20121102A and is detectable at a distance exceeding 200 Mpc. Our finding bridges the gap between nearby and cosmological FRBs and indicates that FRBs hosted in globular clusters can be bright enough to be observable at cosmological distances.Repeating fast radio burst, FRB 20200120E, has been localized to a globular cluster M81. Here, the authors show detection of a burst from FRB 20200120E that is 42 times stronger than the previously detected bursts.
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.
Bulk nanostructured (NS) materials processed by severe plastic deformation (SPD) have received considerable attention for several decades. The physical origin of this processing philosophy is to ...enable substantial grain refinement from a micrometer to a nanoscale level mainly through the activation of fundamental deformation mechanisms: dislocation glide, deformation twinning, and their sophisticated interactions. The formation of nanostructures in NS metallic materials is significantly governed by the quintessential dominance of these two plasticity carriers during SPD, and their mechanical properties are thereby correspondingly affected. According to conventional crystal plasticity, the stacking fault energy (SFE) of materials is one of the most crucial factors primarily controlling which deformation mechanism plays an overwhelming role in accommodating the plasticity. Therefore, a profound understanding of the vital significance of SFE in NS materials can extend and enrich our comprehension of their structure-property relationship, lead to the design of NS metallic materials with superior properties, and pave the path for their perspective applications. Choosing Cu and its binary alloys as model systems, this review extensively surveys the principal influences of SFE on the preferred choice of deformation mechanisms during SPD, microstructural evolution, grain refinement, deformation behavior, and mechanical properties of NS material including tensile properties and cyclic deformation responses.
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