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Dwell fatigue effect is a long-standing problem threatening the long-term service reliability for fan blades and fan disks of an aircraft engine. To understand the basic mechanism of dwell fatigue damage, pure fatigue and 60 s dwell fatigue properties of bimodal Ti-6Al-4V alloys with different volume fractions of the primary α (αp) phase were examined comparatively. The results showed that both pure fatigue and dwell fatigue life decreased with increasing the volume fraction of the αp phase and the dwell fatigue life was lower than the pure fatigue one. The quasi-in-situ test results and the quantitative characterization of damage behaviors of the local microstructure units defined by the αp-secondary α (αs) combination reveal that the αs phase close to the αp phase with extensively slip activities was gradually damaged under dwell fatigue loading, while that under pure fatigue loading was undamaged, demonstrating that the dwell loading induced the damage of the αs phase, and further reduced the fatigue life. A stress relaxation-based model is proposed to describe the physical mechanism on dwell fatigue damage of the bimodal Ti-6Al-4V alloy, i.e. the elastic deformation of the αs phase caused by the strain incompatibility would be gradually transformed into plastic deformation during the dwell stage, and thus promotes fatigue damage. The model provides new insights into the microscopic process of stress/strain transfer between the soft and hard microstructure units under dwell fatigue loading.

Combined with the topology optimization, additive manufacturing can be used to fabricate metal parts with complex shapes. However, due to the geometrical variations and microstructure heterogeneities of the additively manufactured metal parts, new standards with the use of miniature specimens are required for the evalutation of the spatial distribution of mechanical properties throughout the parts. Here, we conduct a systematic investigation on tensile and fatigue properties of selective laser melted Inconel 718 specimens with different thicknesses ranging from 0.1 mm to 1 mm. A “microstructure unit” that can well reflect the microstructure characteristic of selective laser melted materials is defined. The results reveal that premature necking with a dramatic drop in uniform elongation occurs if the ratio (t/d) of specimen thickness (t) to the "microstructure unit" size (d) is less than one. Premature necking is mainly attributed to the transition of strain localization behavior. We also propose a probabilistic statistical model for fatigue limit prediction based on the available fatigue data. It is recommended that the criterion of t/d ≥ 4 should be satisfied to ensure that the yield strength, the uniform elongation, and the fatigue limit determined by the miniature specimens are comparable with those determined by standard specimens. The findings may provdie a guide to the establishment of miniature specimen-based standards toward the qualification of additively manufactured metal parts.

In this study, we report a new method to prepare highly sensitive monoclonal antibody against α-zearalanol (ZAL) based on a similar antigen determinant structure. Zearalanone (ZAN), structural analogs of ZAL, was modified by oximation to obtain ZAN-O. ZAN-O was then coupled with bovine serum albumin using 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide (EDC) to synthesise the artificial complete antigen ZAN-O-BSA. ZAN-O-BSA was used to immunise the BALB/c mice. The splenocytes of the immunised mice were fused with myeloma NS0 cells. During the process of cell fusion, ZAL was used as an inhibitor instead of ZAN to screen the hybridoma cell lines that can secrete monoclonal antibodies against ZAL. The sensitivity (half inhibitory concentration, IC50) of the prepared monoclonal antibody was 0.475 ng/ml, the limit of detection (LOD) was 0.050 ng/ml, the linear range of detection was 0.066-3.399 ng/ml, the affinity constant Kaff was 6.18×107 l/mol, the cross-reactivity rate with structural analogues, such as β-zearalanol, α-zearalenol, β-zearalenol, ZAN and zearalenone were 28.07, 13.16, 15.83, 60.28 and 7.95% respectively. The cross-reactivity with other mycotoxin and carrier proteins were all less than 0.05%. The prepared monoclonal antibody can be used to establish a highly sensitive immunoassay for the detection of ZAL.

Laser-induced femtosecond demagnetization has attracted a broad attention as a possible candidate for information storage technology. However, whether or not lattice vibration directly participates in demagnetization has been highly controversial over a decade. A recent electron diffraction experiment attributed the demagnetization to the polarized phonon effect, but a similar x-ray diffraction experiment attributed it to the Einstein-de Haas effect. Common to both experiments is that neither the angular momentum of the lattice nor the rotation of the sample was directly probed. Here, we report our first first-principles calculation of forces on atoms induced by an ultrafast laser during ultrafast demagnetization. We employ two complementary methods: (i) the frozen lattice with electronic excitation and (ii) frozen excitation but moving the lattice. We find that the forces on atoms start at -50 fs and peak around 30 fs. The magnitude of the force is far smaller than the empirical estimates. Within the limit of our theory, our results suggest that the polarized phonon effect and the Einstein-de Haas effect are unlikely to be the main course of demagnetization. We expect that our finding has a profound impact on the future direction of laser-induced dynamics in magnetic and quantum materials., Comment: 18 pages, four figures

Through explicit examples we show that twist-4 parton distributions have no parton interpretation in the sense that parton or partons inside a hadron can carry the momentum fraction $x$ of the hadron with $x >1$ or $x1$. The corresponding transverse momentum dependent parton distributions have also no parton interpretation. They are finite. The implications of our results are discussed., Comment: Published version

The porosity and mechanical properties of GH4169 (a precipitation strengthened nickel-base superalloy) specimens fabricated using the laser melting deposition technique at different laser powers were investigated. The results showed that the dendritic structure with the Laves phase and carbides embedded in the Ni-γ matrix formed in the as-fabricated GH4169 due to the strong temperature gradient and the high cooling rates. Porosity remarkably decreased first and slightly increased subsequently as the laser power increased from 300 to 800 W. The lowest porosity of the specimens characterized by 3D X-ray tomography is 0.28%. The specimens fabricated at 600 W tensiled along the direction perpendicular to the building direction exhibit the average yield strength of 587 MPa, the ultimate tensile strength of 903 MPa, and the elongation at fracture of 13.6%. Furthermore, the fatigue limit of the 600 W fabricated specimens is 173.7 MPa corresponding to the fatigue ratio of 0.1. And the relationship among the porosity, laser power and mechanical properties is discussed.

This overview firstly introduces the state-of-the-art research progress in length scale-related fatigue performance of conventionally-fabricated metals evaluated by miniature specimens. Some key factors for size effects sensitive to microstructures including the specimen thickness, grain size and a ratio between them are highlighted to summarize some general rules for size effects. Then, ongoing research progress and new challenges in evaluating the fatigue performance of additive manufactured parts controlled by location-specific defects, microstructure heterogeneities as well as mechanical anisotropy using miniature specimen testing technique are discussed and addressed. Finally, a potential roadmap to establish a data-driven evaluation platform based on a large number of miniature specimen-based experiment data, theoretical computations and the ‘big data’ analysis with machine learning is proposed. It is expected that this overview would provide a novel strategy for the realistic evaluation and fast qualification of fatigue properties of additive manufactured parts we have been facing to.

A bulk in-situ Al/(TiAl3+Al2O3) composite was fabricated by accumulative roll-bonding (ARB) and spark plasma sintering (SPS) from pure Al sheets and TiO2 nanoparticles. The microstructure and mechanical properties of the composite were investigated. A uniform dispersion of TiO2 nanoparticles in Al matrix was first achieved by ARB processing in the primary Al/TiO2 composites. Subsequent SPS resulted in the formation of hierarchical TiAl3 (∼60 nm) and Al2O3 (∼750 nm) particles that were distributed uniformly in the ultrafine-grained Al matrix. Microhardness and strength (at ambient and high temperatures) of the final composite were substantially enhanced compared with those of pure Al and the primary Al/TiO2 composite, reaching ∼198.6 HV, ∼628.8 MPa at room temperature and ∼384.2 MPa at 300 °C, respectively. The high strength of the Al/(TiAl3+Al2O3) composite was attributed to a superimposition of different strengthening mechanisms.

The effect of scanning strategy, i.e. bidirectional scanning without (SS-X) and with a 90°-rotation (SS-XY) for every layer, on mechanical properties of Inconel 718 fabricated by selective laser melting (SLM) was investigated. The results show that tensile strength and fatigue strength of SS-X specimens are superior to that of the SS-XY ones. Such excellent mechanical properties of the SS-X specimens at room temperature were found to mainly result from the processing-induced fine grain structures compared with void size, crystalline orientation or dendrite structure.

Creep performance of selective laser melting (SLM) fabricated Inconel 718 is studied in comparison with that of as-forged and as-cast Inconel 718 via small punch creep test technique. The results show that the SLM-fabricated samples have a time to rupture approximately equal to that of the as-forged samples but much less than the as-cast sample due to the difference in the microstructures introduced by these manufacture processes. Intergranular fracture occurred in all the samples. For the SLM-fabricated Inconel 718, cracks initiated from the brittle Laves phases at grain boundaries during the creep process and may speed up the creep and lead to the failure of the sample. “Track-track” melt pool boundaries as one of the important interfaces in SLM-fabricated material can lead to a change in the cracking direction.

The first moment the chirality-odd twist-3 parton distribution $e(x)$ is related to the pion-nucleon $\sigma$-term which is important for phenomenology. However, the possible existence of a singular contribution proportional to $\delta(x)$ in the distribution prevents from the determination of the $\sigma$-term with $e(x)$ from experiment. There are two approaches to show the existence. The first one is based on an operator identity. The second one is based on a perturbative calculation of a single quark state with finite quark mass. We show that all contributions proportional to $\delta (x)$ in the first approach are in fact cancelled. To the second approach we find that $e(x)$ of a multi-parton state with a massless quark has no contribution with $\delta (x)$. Considering that a proton is essentially a multi-parton state, the effect of the contribution with $\delta(x)$ is expected to be suppressed by light quark masses with arguments from perturbation theory. A detailed discussion about the difference between cut- and uncut diagrams of $e(x)$ is provided., Comment: Published version

Tensile and fracture behaviors of sandwich-structured composites consisting of a Fe-based amorphous layer with a constant thickness and ultrafine-grained Ni layers with different thicknesses were investigated. The results indicate that the initiation and the stable propagation of the shear band in the amorphous layer was dominated by the Ni layers due to their strong constraint role. The catastrophic fracture of the amorphous layer was postponed in the sandwich composites through properly increasing the constrained Ni layer thickness, which effectively decreased the shear stress on the shear fracture planes of the amorphous layer, and thus led to stable propagation of the primary SB characterized by the increase in the smooth region size of the shear band.

The partitioning effect of Al (α-phase stabilizer) and V elements (β-phase stabilizer) on strength of the primary α phases in the α/β Ti-6Al-4V alloy with the bimodal microstructure was investigated. It was found that partitioning of Al and V elements took place in the Ti-6Al-4V alloy during the recrystallization process, leading to the variation of the content of Al and V elements in the primary α phases with changing the volume fraction of the primary α phase. Nanoindentation tests reveal a general trend that the strength of the primary α phases increases with decreasing the volume fraction of the primary α phases, and such trend is independent on the loading direction relative to the c-axis of the α phase. The enhanced strength is attributed to the increase of the content of Al element in the primary α phase, but it is not dominated evidently by the change of the V content. The solid solution strengthening contributed from both the elastic strain introduced by the solute atoms and the variation of the density of states was estimated theoretically.

Cu/Ni laminated composites with the same total thickness of 128 µm, but different modulation wavelength λ (the sum of monolayer thickness of constituent layers) of 32 µm and 3 µm, respectively were prepared using a dual-bath electrodeposition technique. The tensile testing results and the quantitative characterization of strain gradient in the post-necking region of the composites reveal that the λ = 3 µm composites have the higher tensile strength and the better strain hardening ability, as well as the stronger resistance to post-necking compared with the λ = 32 µm ones. A high density of layer interfaces in the ultrathin laminated composite may play a key role in delaying the development of unstable plastic deformation along the layer thickness direction through periodical strain gradient and a number of geometrically necessary dislocations near the interfaces. Thus, the fatal localized plastic deformation along the through thickness direction has to be spread over along the loading direction, leading to the large neck breadth in the ultrathin laminated composites.

The damage behavior of soft-hard grain combinations in a pure Ti subjected to pure fatigue and dwell fatigue loading was investigated in-situ using the digital image correlation technique combined with the electron backscattering diffraction technique. The results show that the basal slip of hard grains only occurred under dwell fatigue loading, revealing that the basal slip is strongly time-dependent. The facet formation is mainly attributed to the time-dependent basal slip assisted by the locally high stress. The soft orientation also influenced the deformation degree of the hard grains under pure fatigue loading via the strain incompatibility between the soft and hard grains. These findings have significant implications in further understanding the effect of grain orientation-dependent strain rate sensitivity of the pure Ti on the dwell effect.

Fatigue strength of the Cu/Ni laminated composites with different thickness ratios of the Ni layer to the Cu layer was investigated. The result reveals that the Cu/Ni laminated composite with the thickness ratio of the Ni layer to the Cu layer of 9.0:1 not only has an ultrahigh strength (1361.80 MPa), but also is of a relatively high fatigue ratio approaching to 0.30 compared with ultrafine-grained and nanocrystalline Ni. The introduction of the ultrathin Cu layers into the ultrafine-scale Ni leads to alternate variation of local delamination and crack deflection crossing the layers in the Cu/Ni laminated composites subjected to fatigue loading, maximizing the cracking resistances in spatial directions.

Microstructures and service performance (mechanical and electrical properties) of the commercially pure Al conductor wires subjected to different cold drawing strains were investigated. The results show that the microstructures of the cold-drawn Al wires along the radial direction were inhomogeneous, i.e. the texture in the center region was strong and weak components, while that in the surface region shifted from the initial cubic texture to a component and finally developed into a strong component. The volume fraction of the high angle grain boundaries in the surface region was higher than that in the center region. The cold-drawing process greatly enhanced the yield strength of the pure Al wires while retained the acceptable electrical resistivity. The strengthening mechanism and the variation of electrical conductivity of the cold-drawn Al wires are discussed through correlating with microstructure evolution.

Atmospheric wet deposition plays an important role in the supply of nutrients and toxic substances to terrestrial and aquatic environments. Although long-term (e.g. annual, multi-year) wet deposition is recorded well, pronounced and short-term changes in precipitation chemistry are less well investigated. In the present study, the precipitation chemistry and scavenging ratio of air pollutants were observed during an extreme torrential rain event (325.6 mm at the observation site) that occurred over 19–21 July 2016 in the North China Plain (NCP). The scavenging ratio of particles showed a similar spatial distribution to that of the precipitation amount in the NCP, indicating the efficient removal of particulate matter due to the large amount and precipitation intensity of the storm. In addition, the scavenging ratio of water soluble ions was larger than that of organics and gaseous pollutants such as SO2 and NO2, likely due to their differences in water solubility. Consequently, raindrops incorporated more aerosol sulfate than gaseous compounds. Due to the heavy precipitation amount, almost all species in rainwater during this storm showed their lowest concentration but the highest flux compared with other rain events, indicating an important role played by this storm in terms of the substances received by the terrestrial and marine ecosystems of the region. However, the contribution of this storm to the annual chemical flux was lower than that of precipitation amount, indicating that the atmospheric compounds were scavenged below-cloud first and were then diluted by the cloud/rainwater. Future studies are needed in the context of the occurrence of extreme rainfall events in the NCP from the perspective of climate variability.

Quantitative investigation was performed to understand effects of length scales (film thickness) on grain growth and corresponding fatigue damage behaviors in the nanocrystalline Au thin films on flexible substrates with a film thickness ranging from 930 nm to 20 nm. In thicker films ( h ≥ 90 nm), abnormal grain growth happened due to the local high stress, while in thinner films uniform grain growth occurred. Such length–dependent grain growth mechanisms was found to be associated with the film strength and the film thickness. Consequently, the main damages in thicker films exhibited the applied load range-related competition between the intergranular cracks and the intragranular cracks along the localized slip. In the thinner film, fatigue damage is associated with GB-related behaviors, such as intergranular cracking and deformation twinning.

Blade-Integrated Disk is a perspective one-piece design strategy of turbine engine components with high efficiency of air compression. In this work, a functionally graded material composed of GH4169 and K418 is processed by laser melting deposition technique, followed by suitable heat treatment to optimize the microstructures and mechanical properties. Microstructure characterization, tensile and small punch creep tests of the functionally graded GH4169/K418 specimens were conducted. It is found that the as-built functionally graded material exhibits the continuous microstructure and the gradual composition transition region without sharp interfaces and hot cracks. The tensile yield strength, ultimate strength and elongation of the graded specimens at fracture achieved 726 MPa, 1044 MPa and 13.2%, respectively after the specimens were heat-treated through homogenization at 1100 °C for 1.5 h, solution treatment at 980 °C for 1 h and standard double aging. The creep life of the GH4169/K418 graded specimens at 650 °C and 850 N was mainly affected by the microstructure formed at different build heights of the as-built and heat-treated specimens. The relationship between the microstructures and tensile as well as creep properties of the graded specimens is elucidated.

The high frequency of new particle formation (NPF) events observed under polluted atmospheric conditions is still poorly understood. To improve our understanding of NPF and its effects, the particle number size distribution (3-1000 nm) and submicron particle chemical composition were measured from 4 November 2017 to 17 January 2018 in suburban Beijing. During this intense campaign, 22 NPF events were identified with a frequency of 29%, including 11 cases that occurred under "clean" conditions (C-NPF) and 11 cases that occurred under "polluted" conditions (P-NPF). The observed formation rate (J(3)) and condensation sink were 4.6-148.9 cm(-3).s(-1) and 0.01-0.07 s(-1), and the majority of NPF events occurred when the condensation sink (CS) values below 0.03 s(-1), indicating that condensation vapor likely constitutes the critical limiting factor for NPF events. The correlations between log J(3) and [H2SO4] that close to previous CLOUD experimental results in the majority of NPF events (68%) suggest the high nucleation rates (up to 100 cm(-3).s(-1)) would be attributed by the amines that enhancing sulfuric acid nucleation, while the reminding cases (32%) possibly attributed to the H2SO4-NH3 clustering mechanism, which is supported by the theoretical expectations for H2SO4 nucleation with NH3 simulated by the MALTE_BOX model. The observed growth rate varied from 4.9 to 37.0 mm.h(-1), with the dominant contribution (>60%) from sulfuric acid during the early phases of growth (similar to 4 nm), which was also sufficient to explain the observed Q(GR) for 50 nm)

Fatigue strength and cracking behavior of ultrathin Ag films on flexible polyimide substrates were investigated. The experimental results show that the enhanced fatigue strength of the 50 nm-thick Ag films not only is caused by the increase in the yield stress and the suppression of cyclic strain localization, but also results from the severe crack deflection induced by the formation of nanotwins, which delays the fatigue crack initiation and enhances the resistance to the fatigue crack growth. The fatigue cracking mechanism for the nanocrystalline metal films is evaluated.

Cu/Ni laminated composites with a thickness ratio of the Cu layer to the nanocrystalline Ni layer of 1:20 are prepared by the dual-bath electrodeposition technique. Tensile and fatigue tests are performed at room temperature. The results show that the laminated composites not only have a better synergy of the tensile strength and ductility, but also the higher fatigue strength than the pure Ni counterpart sheets. The introduction of the ultrathin Cu layer into the composite may play a key role in enhancing the ductility and the fatigue cracking resistance. The basic mechanisms for the blunting at the crack tip in the laminated composites are discussed.

In nanocrystalline (nc) metals, it is still not clear how local grain boundary (GB) structures accommodate GB migration at atomic scales and what dominates the motion of atoms at the inherently unstable GB front. Here, we report the adjustment of the local GB structures at atomic scales during self-driven GB migration, simultaneously involving GB dissociation, partial dislocation emission from GB, and faceting/defaceting in the nc Cu. Furthermore, we reveal that the fundamental of GB migration ability is closely related to the local structure, i.e. the GB segment consisting of “hybrid” structural units and delocalized GB dislocations is relatively unstable.

Fatigue life scattering and prediction of Inconel 718 fabricated by selective laser melting were investigated using miniature specimen tests combined with statistical method and machine learning algorithms. The relationship between pore features and fatigue life of the selective laser melting-fabricated specimens was analyzed statistically. The results show that the increase in the size and/or the number of the pores in the specimens, and/or the decrease in the distance from a pore center to the specimen surface degraded the fatigue life. The machine learning and statistical analysis results reveal that the fatigue life are most closely related to the location of the pores compared with the size and the number of pores in the specimens. The finding may provide a potential way to get high-throughput statistical data helping in evaluating defect-dominated scattering and prediction of fatigue life of additive manufactured metallic parts using miniature specimen testing assisted by the machine learning approach.

Creep performance of additively-manufactured components is strongly related to additive manufacturing process-induced microstructures and loading direction. Here, the creep life and the cracking behavior of Inconel 718 fabricated by selective laser melting were investigated systematically at 650°C and 400 N by means of the small punch creep testing method. The results show that the periodic and spatially heterogeneous microstructures composed of V-shaped grains and columnar grains are produced, and play an important role in the creep performance. Under the same heat-treatment condition, the creep resistance of the specimens loaded along the scanning direction is much higher than that of the ones loaded along the building direction. While under the same loading direction, homogenization/aging-treated specimens have the longest creep life and the solution/aging-treated specimens are of the shortest creep life. The creep cracking mechanism of the alloy associated with the spatially heterogeneous microstructures was elucidated. The theoretical calculation suggests that the higher energy input or the larger overlap ratio of the melting pools may decrease the area fraction of the V-shaped grains to enhance the creep life. The finding provides a potential strategy to design microstructures for the high creep performance of selective laser melting-fabricated Inconel 718.

It has been expected that mechanical properties of a composite can be enhanced effectively by increasing the content of reinforcing particles to high levels, for which a simultaneous fulfillment of high content and uniform distribution of reinforcing particles is key. In this study, we fabricated Al-TiAl3-Al2O3 composites from starting materials of Al sheets and TiO2 nanopowders by combining accumulative roll-bonding and spark plasma sintering processes. The microstructure and mechanical properties of the samples were investigated. The as-prepared samples contain hybrid TiAl3 and Al2O3 particles with total volume fractions up to 66.1–81.5 % that were formed in situ by the reaction of Al and TiO2 with much smaller volume fractions (6.7–13.9 %). The composites exhibit a microhardness up to ∼532 HV and high strengths up to ∼1312 MPa at room temperature, ∼919 MPa at 300 °C and ∼565 MPa at 600 °C. The superior mechanical properties of the composites at ambient and elevated temperatures can be attributed to the high volume fraction of reinforcing particles with meanwhile uniform distribution, for which different strengthening mechanisms were discussed.

45CrMoVA steel bar specimens were pre-twisted at different angles (θpre) ranging from 8.3° to 16.3°. Torsion fatigue properties of the pre-torsion specimens were investigated. The results indicate that the torsion fatigue life of the specimens increases first, and then decreases with increasing θpre. A model was established to predict torsion fatigue life for the pre-torsion shaft components, and the desired θpre of 11.4° corresponding to the longest fatigue life for the pre-torsion 45CrMoVA steel bars was obtained. It is expected that the model may provide a guideline for the pre-torsion process of the steel shaft parts.

Effects of the surface roughness and the build thickness on fatigue properties of selective laser melted Inconel 718 were investigated at 650 °C. The result indicated that fatigue strength was enhanced by ~50% after surface machining and polishing. The thinner un-machined specimens exhibit a longer fatigue lifetime than the thicker ones, while the opposite trend appears in the machined specimens. Finite element simulations reveal that the defect shape has more evident influence on fatigue properties than the defect depth when it is less than 200 μm. Safety thresholds of the stress concentration factor and the defect depth are 2 and 50 μm, respectively.

The North China Plain has been identified as a global hotspot for ammonia (NH3). To date, NH3 surface observations in the region have mostly been obtained by passive samplers with a time resolution of weeks (e.g., AMoN-China), and few studies have been performed with fast-response instruments. Thus, the detailed temporal variations of NH3 concentrations are still unclear in the region. From December 2017 to February 2018, NH3 concentrations were observed at a high-temporal resolution of 1 Hz by using the Picarro online instrument at the Xianghe, a rural site between the megacities of Beijing and Tianjin. During the campaign, the hourly NH3 concentrations ranged from 0.8 to 483.3 ppb, with an overall mean of 16.7 ± 19.7 ppb, which was considerably higher than those reported at other sites. In addition, the diurnal profile showed a notable increase of NH3 concentrations in the morning, which was likely due to dew evaporation. While the monthly difference of NH3 concentrations in winter was most likely driven by temperature, the elevated biomass burning may have also a considerable effect. The presented observations could provide insights into the dynamic characteristics of NH3 during haze pollution and provide a unique dataset to validate atmospheric chemistry and transport models at high-temporal resolutions.

Tensile properties of GH4169 fabricated by selective laser melting under stripe and chessboard scanning strategies were investigated. The results show that the GH4169 specimens fabricated by the chessboard scanning strategy have higher tensile strengths and more evident tensile anisotropy than that of the specimens fabricated by the stripe scanning strategy. The strain hardening ability of the chessboard specimens superior to that of the stripe specimen is mainly attributed to the difference in residual stress magnitude arising from different scanning strategies and the unique processing-induced heterogeneous grain structure in the chessboard specimens.

The sandwich-structured ultrafine grained (UFG) Ni/Fe78B13Si9 amorphous alloy/UFG Ni composite were prepared through the electrodeposition technique. Tensile testing of the sandwich composites was conducted and fracture behavior of the composites was characterized. The results show that the yield and ultimate tensile strengths decrease gradually, while the ductility of the sandwich composite increases with increasing UFG-Ni layer thickness. The fracture mode of the sandwich-structured composite varies with changing the constraint UFG-Ni layer thickness. The local necking of the UFG-Ni layers plays an important role in fracture mode of the sandwich composites. The coupling effect of the UFG-Ni layer and amorphous layer on mechanical performance of the sandwich composites is discussed. Keywords: Ultrafine grain, Amorphous alloy, Laminated composite, Shear band, Strength, fracture

The 6063 aluminum alloy is a candidate for fitting clamps to fasten and connect the Al alloy overhead conductor lines. The Al alloy fitting clamps with different extents of stress concentration may become quite dangerous under cyclic loading due to the wind-induced swing of the conductor lines. In this study, fatigue properties and cracking behavior of the 6063 aluminum alloy were investigated using three-point-bending specimens with different notch angles. The relationship between the nominal fatigue cracking resistance and the notch angle of the Al alloy specimens was obtained. Fatigue damage and notch angle-dependent cracking behaviors were evaluated. Fatigue reliability of the 6063 alloy specimens with different stress concentration factors was discussed combined with a grain size of the alloy. Keywords: 6063 Al alloy, Fatigue, Crack growth, Stress concentration, Stress concentration

Fundamental Research Funds for the Central University of China [N110105001, N120505001]; National Natural Science Foundation of China (NSFC) [51231002, 51271054]

We clearly show that fatigue-induced grain growth is suppressed in the annealed nanocrystalline Cu films, which leads to the enhanced resistance to fatigue cracking compared with that of the as-deposited ones. Annealing-stabilization of the nanograin boundaries may provide a potential way to enhance fatigue reliability of nanoscale film-based flexible devices.

Compression workability of the 6063 aluminum alloy for fitting clamps to fasten and connect the aluminum alloy conductor lines was investigated under different height reductions and strain rates at room temperature. The deformation map for compression workability is obtained, which provides the critical deformation conditions related to deformation reduction and strain rate below which the 6063 alloy can be safely processed without cracking damage. Cracking damage behavior was investigated by electron backscattering diffraction technique, revealing that the compression-induced cracking of the 6063 alloy tends to occur at the grain boundaries with grain boundary misorientation angles more than 47°.

Fatigue properties of the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy sheets containing different numbers of α/β Widmanstatten colonies in the thickness direction of the sheets were investigated by tension–tension fatigue testing. It is found that fatigue properties of the Ti alloy either in low- or high-stress amplitude regimes become more sensitive to the sheet thickness of the Ti alloy as the sheet thickness is comparable to the length scale of the Widmanstatten colonies. The basic mechanism of such length scale-sensitive fatigue properties in the Ti alloy was elucidated.

Strengths of microstructure units (i.e. α/β lamellae, colony boundary and prior β grain boundary) in the α/β lamellar-structured Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy were examined using microindentation testing. Combining with the EBSD characterization, the relationship between the strength and the crystallographic orientation of the microstructure units was analyzed. The results show that the orientation of the α phase in α/β lamellae dominates the strength of the colony. The strength of the colony boundary can be determined by the strengths of the bilaterial colonies, following a rule of mixtures. Furthermore, the critical resolved shear stresses for the prismatic and the basal slip systems in the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy are evaluated based on the microindentation data.

Tensile properties of ultrafine grained Cu/Ni laminated composites prepared by dual-bath electrodeposition technique were investigated by tensile tests at different strain rates ranging from 1 � 10 � 5 to 1 � 10 � 2 s � 1 . The results show that the stress gradient close to heterogeneous interfaces established at high strain rates may influence mechanical properties of the ultrafine-grained Cu/Ni laminates, leading to a simultaneous increase in strength and ductility as the strain rate increases from 1 � 10 � 5 to 1 � 10 � 2 s � 1 . The effect of such stress gradient in the laminated composites is analyzed to understand the abnormal increase in ductility with strain rate.

The experimental observations on dislocation structures in the micron-thick cantilever beam-type samples of copper single crystals subjected to symmetrically-reversed bending load and the theoretical simulations using the modified reaction–diffusion model were conducted. It was found that strain-gradient introduced by inhomogeneous deformation has a strong influence on dislocation patterning behavior, cyclic deformation response and fatigue life of the micron-thick copper single crystal beams. The simulation results provide a deep insight into the effects of the geometrical scale and the strain gradient on fatigue behaviors in micron-thick metal foils subjected to symmetrically-reversed bending load.

Bio-inspired (nanocrystalline TiO 2 /polyelectrolyte (PE)) 4 nanolayered composites were synthesized by the layer-by-layer self-assembly and chemical bath deposition methods. The results show that the thicknesses of the TiO 2 and PE layers in the as-synthesized are 41.3 nm and 9.6 nm, respectively, and the grain size of the TiO 2 layer is about 5 nm. For the type I cracking, the fracture toughness (K IC = 1.18 ± 0.67 MPa m 1/2 ) of 41.3 nm TiO 2 /9.6 nm PE composite is larger than that of the bulk TiO 2 . For the type II cracking, the crack deflection occurred in the composite. This toughening behavior was attributed to the low interfacial fracture energy and the large ratio of the crack deflection length to the crack penetration length. Our finding demonstrates that the crack deflection is an effective way to toughen the bio-inspired nanocrystalline TiO 2 /PE nanolayered composites.

Grain size and initial dislocation density introduced by different mechanical processing methods may have a strong influence on fatigue behavior of polycrystalline metals. Using the reaction-diffusion model developed by Walgraef and Aifantis, we examined the ability of fatigue dislocation patterning and the evolution of dislocation density in the materials with different grain sizes (100 nm-10 μm) and initial immobile dislocation densities (IIDD, 1 � 10 12 m � 2 -1.58 � 10 15 m � 2 ). The results show that there is a clear relation among the necessary length scale for dislocation patterning, the grain size and the IIDD. Furthermore, the nominal life for fatigue damage initiation of these materials was evaluated based on the evolution of dislocation density and the ability of the dislocation patterning, showing good consistency with the experimental findings.