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The direct effects of carbon fiber-reinforced polymer (CFRP) composites with a fastener in lightning environments are very complicated. Experimental models were designed to understand the influence of different factors on the damage modes. First, different specimen structures, including unidirectional and woven fabric, were studied. Second, the damage characteristics of the two cases where current injection occurred in the fastener part and the carbon fiber part were experimentally studied. Finally, the different grounding points were studied. The experimental results showed that the woven fabric structure can conduct current better, and the area of lightning damage is smaller than that of the unidirectional ply. The lightning experimental conditions had a significant influence on outgassing, delamination damage characteristics and the lightning phenomenon. A high-speed camera was used to observe the lightning action process. The mechanism of electrical and thermal conversion between fastener and CFRP composites was revealed by discussing the lightning strike process. The damage morphology and lightning phenomena caused by an instantaneous electric field distortion distribution was deduced. The current work provides a reference for effectively designing lightning protection strategies under different lightning strike conditions.

Grain-boundary (GB) precipitation has a significant adverse effect on plasticity of alloys, which easily leads to catastrophic intergranular failure in safety-critical applications under high external loading. Herein, we report a novel strategy that uses the local stress concentration induced by GB precipitates as a driving force to trigger phase transformation of preset non-equiatomic high-entropy solid-solution phase at GBs. This in situ deformation-induced phase transformation at GBs introduces a well-known effect: transformation-induced plasticity (TRIP), which enables an exceptional elongation to fracture (above 38 %) at a high strength (above 1.5 GPa) in a GB precipitation-hardened high-entropy alloy (HEA). The present strategy in terms of “local stress concentration-induced phase transformations at GBs” may provide a fundamental approach by taking advantage of (rather than avoiding) the GB precipitation to gain a superior combination of high strength and high ductility in HEAs.

We demonstrate a strategy to stabilize nanoprecipitates in Al–Cu alloys, based on computational design that identifies synergistic solutes (Sc and Fe) that simultaneously segregate to the θ′-Al2Cu/Al interface and strongly bond to one another. Furthermore, Sc and Fe are predicted to each segregate into a separate atomic plane, forming a sandwiched structure reinforcing the interface. This interfacial architecture was realized through a simple heat treatment in a Sc–Fe–Si triple-microalloyed Al–Cu model alloy. Such a back-to-back layered interface, thermodynamically stable and kinetically robust, is found to suffocate nanoprecipitate coarsening at 300°C, enabling a dramatic reduction in creep rate. IMPACT STATEMENT The segregant architecture of synergistic solute at θ′-Al2Cu/Al interface was guided by computational calculations and artificially realized at atomic scale to achieve an ultra-high thermal stability of θ′-Al2Cu, leading to a high creep resistance at 300°C.

In order to quantify the fracture toughness and reveal the failure mechanism of crystalline/amorphous nanolaminates (C/ANLs), in-situ micro-cantilever bending tests were performed on Ag/Cu–Zr and Mo/Cu–Zr C/ANLs in a scanning electron microscope over a wide range of cantilever widths from several microns to the submicron scale. The results demonstrate that the fracture behavior was strongly influenced by sample size and constituent phases, respectively. The Ag/Cu–Zr micro-cantilevers failed in a ductile manner, with fracture toughnesses higher than the Mo/Cu–Zr samples that exhibited brittle failure. Both materials also displayed different cantilever width-dependences of fracture toughness. The Ag/Cu–Zr beams showed a fracture toughness that increases with the cantilever width, mainly due to a size-dependent constraining effect on the deformation of the crystalline phase. For the Mo/Cu–Zr beams, the fracture toughness decreased gradually to a low plateau as the cantilever width exceeded ∼1500 nm, which can be rationalized by a transition in stress condition. The underlying fracture mechanism of the Ag/Cu–Zr micro-cantilevers was identified as the interconnection of microcracks initiated in the amorphous Cu–Zr layers, compared to a catastrophically penetrating crack propagation in the Mo/Cu–Zr samples. The discrepancy in size-dependent fracture behavior between the two material systems is discussed in terms of plastic energy dissipation of ductile phases, crack tip blunting, crack bridging and the effect of strain gradient in the plastic zone on crack propagation.

Nanostructured crystalline Al/amorphous AlN multilayer films with a wide layer thickness (h) range from ∼10 nm up to ∼200 nm were prepared by using magnetron sputtering. Nanotwins and 9R phase were substantially observed in the Al layers, showing a strong thickness dependence. The 9R phase predominantly penetrated through the Al layer in the II regime of h ≤ ∼20 nm, while mainly terminated within the layer interior in the I regime of h > ∼20 nm. On the contrary, the coherent nanotwins were boosted when h > ∼20 nm and the percentage of twinned Al grains was greatly increased. The formation mechanisms of 9R phase and coherent nanotwins were discussed in terms of the interfacial chemistry/physics modulated by the amorphous AlN layers, which displayed gradient characteristics and hence was sensitive to the layer thickness. A significant thickness dependence of hardness was also evident that the hardness monotonically increased with reducing h in the I regime, while reached a peak value and hold almost unchanged in the II regime. The hardness in the II regime is about 1 GPa greater than the predictions from an interfacial barrier crossing model. This discrepancy is mainly contributed by the layer-penetrating 9R phase rather than the nanotwins. This study provides a new perspective on fabricating nanotwinned Al by utilizing heterophase interfaces.

The aircraft lightning environment consists of four lightning current components with different parameters, which are known as lightning components A, B, C and D. The lightning damage of aeronautic carbon fiber reinforced polymer laminates subjected to multiple continuous sequential lightning current components with different timing combinations was experimentally evaluated. The experimental results indicated that the carbon fiber reinforced polymer laminates suffered serious lightning damage, including carbon fiber fracture, resin pyrolysis and delamination. Through an analysis of the lightning damage properties of carbon fiber reinforced polymers, the influential factors and evaluation methods of the lightning damage in carbon fiber reinforced polymer laminates were studied. Because the lightning damage evaluation method under a single lightning impulse was found to be inapplicable for the multiple continuous lightning strikes, a multi-factor evaluation method was proposed. In the multiple continuous lightning strike test, the damage depth was found to be closely related to lightning components A, B and D and could be estimated based on the amplitudes and rise rates of the applied lightning components. Increases in the damaged area after a lightning strike were driven by lightning component C due to its substantial thermal effects. The damaged area was evaluated on the basis of the parameters of the electrical action integral and the transfer charge. The research on the evaluation methods for carbon fiber reinforced polymer laminate lightning damage presented herein may provide experimental support and a theoretical basis for studying the lightning effect mechanism and optimizing material formulations, manufacturing processes and structural designs to achieve performance improvements for carbon fiber reinforced polymer laminates in the future.

Microstructures and mechanical properties of homogenized Al-2.5 wt% Cu (Al-Cu), Al-2.5 wt%Cu-0.3 wt%Sc (Al-Cu-Sc) and Al-2.5 wt%Cu-0.3 wt%Sc-0.2 wt% Fe (Al-Cu-Sc-Fe) alloys were comprehensively studied, which allowed to demonstrate the single Sc effect as well as the combined Sc and Fe effect on microstructural evolution during homogenization treatment and hence on mechanical response, respectively. It was clearly revealed that the single minor Sc addition refined the grains of as-cast Al-Cu alloy, and induced Sc enrichment in the micro-sized α-Al/θ-Al2Cu eutectic. During homogenization, the Sc distribution highly affected the formation of micron-sized (Cu,Sc)-rich W-phases and submicro/nano-sized Al3Sc dispersoids. In comparison, the co-addition of minor Fe and Sc produced grains and micro Sc-segregation similar to the single Sc addition. However, the formation of W phase was highly suppressed. This resulted in promoted Al3Sc dispersoid formation during homogenization and led to improved strength. Unfortunately, coarse (Cu, Fe)-rich constituents were newly created in the homogenized Al-Cu-Sc-Fe alloy, and the ductility of alloy was correspondingly reduced.

The mechanical behavior of (Fe40Mn40Co10Cr10)100−xCx (x = 0, 2.2, 3.3 at.%) high entropy alloys (HEA) at various temperatures (298 K, 159 K and 77 K) was investigated. For Fe40Mn40Co10Cr10 HEA, the jointly activated twinning and martensitic phase transformation concurrently increase the strength and ductility at 77 K. In contrast, twinning and phase transformation gradually vanish as temperature decreases for carbon alloyed HEAs, resulting in ductile-brittle transition. Our findings indicate that the additional interstitial carbon atoms increase the f.c.c. phase stability, and inhibit the deformability of Fe40Mn40Co10Cr10 HEA at low temperature.

The microstructure and mechanical properties of powder-forged Fe-C-Cu alloys manufactured at an elevated temperature were evaluated. It was found that the mechanical properties of the alloys were no worse than those in the literature, and the contribution of copper to the strength was quantified: the major strengthening mechanism of copper is grain-refinement strengthening rather than precipitation strengthening. Then, to ensure the safety of the elevated-temperature manufacturing, the hot-deformation behaviour of the Fe-C-2.5Cu alloy was investigated via construction of the constitutive equation and the hot-processing map, which proved that the high-temperature manufacturing was not only safe but also efficient. Finally, fatigue tests were conducted on the powder-forged connecting rods and 5154 wrought steel connecting rods for the same engine application, and the results showed that the powder-forged connecting rods had better fatigue strength and higher reliability.

Optical fiber overhead ground wires (OPGW) is a special power cable that combines communication transmission and lightning protection. Because of its low cost, long working life, high reliability and many other advantages, it is widely used in power systems. In order to study the effect of direct damage caused by lightning, this paper designs a mechanical fixture that can exert a tensile force, and studies the lightning damage under different excitation sources. At the same time, three different lightning damage patterns are defined to quantitatively describe the degree of lightning damage. The results show that under the test conditions of a tungsten copper rod with a diameter of 10mm as the electrode, under the action of different components (A, B, C) of the lightning current, different damage forms to the OPGW strands are shown. The lightning current component C has the most obvious and most serious arc ablation effect on the strands. The lightning damage of the components B and C of the lightning current is relatively slight. The experimental results show the difference in damage of OPGW optical cables caused by different lightning current components, which is helpful to further understand OPGW's lightning damage mechanism, and can provide a theoretical basis for its test methods and standards.

Mobile communication base stations are the basic facilities of telecommunication operation networks. When the communication base station is struck by lightning, a very high overvoltage will appear on the top of pole, which leads the power supply cable of RRU(Remote Radio Unit) directly break through, and a large lightning current will flow through the cable, damaging the communication equipment and the power supply. Therefore, the research on the lightning current distribution characteristics of the mobile communication base station has important theoretical significance and engineering application value for the lightning protection of the mobile communication base station. In this paper, a simulation model of the current distribution characteristics of the communication pole system with overvoltage protective varistor is established, and the influence of the impulse current, the length of the pole and the DC reference voltage on the current distribution characteristics of the pole system is studied. The results show that: (1) When $8 /20\ \mu \mathrm{s}$ impulse current is injected into the 10m long pole system, the dynamic resistance $r$ of varistor decreases with the increase of impulse current peak value, the current distribution ratio of pole and core of power cable gradually approaches to 9:1. (2) As the length of the pole increases, the influence of the varistor on the current waveform parameters of the core branch of the power gradually decreases, and the front time distortion rate through the power line core branch decreases. (3) When the peak value of the impulse current and the length of the pole are the same, the lower the DC reference voltage of the varistor, the smaller the current waveform distortion of the core branch of the power, and the greater the current distribution.

The damage behavior of carbon fiber reinforced polymer (CFRP) composites subjected to lightning component A (20–100 kA) was studied based on the analysis of the dynamic conductive properties of CFRPs. The dynamic conductivities were introduced into the coupled multifield model for CFRP lightning damage simulation for the first time. The simulated damage results were obtained from the numerical models which established based on different conductivities. The rationality of these simulation models was analyzed. The comparison between experiment and simulation results showed that the dynamic conductivity simulation model can more realistically simulate the conductive state of CFRPs subjected to actual lightning impulse. The dynamic conductivity model can reduce the deviation of damage areas and depths between the calculation and experiment from + 304% and −39.2% (in DC conductivity simulation model) to −4.9% and + 2.9%, respectively. Lightning damage area increased as the in-plane and in-thickness conductivities decreased. The anisotropic distribution of the damaged area was also affected by the ratio of the longitudinal and transverse conductivities. The lightning damage depth had the non-monotonic variation characteristics that increased first and then decreased as the in-thickness conductivity decreased.

The lightning damage depths and areas of carbon fiber reinforced polymer (CFRP) laminates subjected to multiple continuous sequential lightning current components with different timing combinations were experimentally evaluated. The experimental results indicated that the CFRP laminates suffered serious lightning damage, including fracture of the carbon fibers and layer delamination. After a multiple lightning strike composed of lightning components A, B and C, the surface temperature of the CFRP laminates, which was projected from the measured temperature with lower magnitude, can exceed 1600 °C. The damage area and depth were approximately 2790 mm2 and 1.28 mm in the “ABCD” test mode. The damage depth was found to be closely related to lightning components A, B and D, which are accompanied by the shockwave and the overpressure effect, the dielectric breakdown effect and the local thermal effect. The increases in the surface temperature and damage area after lightning strike were mainly affected by the lightning component C with substantial thermal effect. The application sequence and material properties are important factors for evaluating the damage effect of the newly added lightning component on samples that have suffered from multiple continuous lightning components. The influencing factors and analysis method for CFRP laminate lightning damage subjected to multiple continuous sequential lightning components may provide both experimental support and a theoretical basis for studying the mechanism of the lightning effect and the refinement and improvement of a lightning direct effect test method for CFRP laminates in the future.

Previous studies demonstrated that the He ion irradiation damage tolerance of nanostructured metallic multilayers (NMMs) was closely dependent on the layer thickness (h): smaller h led to lower irradiation hardening. Here in Mo/Zr NMMs, we uncovered that the h-dependent irradiation hardening and corresponding plastic deformation characteristics are also sensitive to the He+ irradiation fluences. At a low irradiation fluence of 1.0 × 1016 He+·cm−2, the irradiation hardening decreased monotonically with reducing h. While at a high irradiation fluence of 1.0 × 1017 He+·cm−2, a non-monotonic h-dependence was unexpectedly displayed with the minimum irradiation hardening at h of ∼25 nm. The irradiation fluence also affects the strain rate sensitivity (m) remarkably. Irradiation of 1.0 × 1016 He+·cm−2 induced a transition in SRS m from positive in the as-deposited Mo/Zr NMMs to negative SRS in their irradiated counterparts. This transition was rationalized in terms of dynamic strain aging that considered dislocation-bubble interactions. Irradiation of 1.0 × 1017 He+·cm−2, however, resulted in a non-monotonic h-dependence of m, with the bottom located at a turning point of h ∼50 nm. Coupling effect of the layer thickness and the applied fluence on irradiation hardening and plastic deformation characteristics was quantitatively elucidated by employing a strengthening model and a thermally activated model, respectively, where parameters of the characteristic microstructural features, i.e., the layer thickness and irradiation (He) defects, were both included.

The lightning test method with a single lightning component C was found to be inappropriate to simulate the lightning effect on optical-fiber overhead ground wires (OPGWs). This study establishes a multiple lightning current test system, including intermediate current component B and continuing current component C, to investigate the lightning test method for OPGWs. The lightning characteristics and damage performance of OPGWs with different test conditions under multiple sequential lightning currents were experimentally evaluated via visual inspection and infrared temperature measurement. The test results indicated that the lightning damage of OPGWs was not only related to the parameters of the applied lightning current but also the experimental method. The lightning erosion degree and surface temperature of OPGWs increased as the transfer charge of current component C increased. When the transfer charge was approximately 200 °C, the surface temperature exceeded 3600 °C. Moreover, as the discharge gap increased from 5 cm to 6 cm, the temperature decreased, and the lightning damage degree, particularly the number of broken strands, decreased accordingly. The research on the lightning test method in this paper may provide experimental support and a theoretical basis for a proper evaluation of the lightning protection performance OPGWs and the study of the lightning effect mechanism.

Grain boundary (GB) engineering via alloying opens a pathway to design the interfaces in alloys for tuning their mechanical properties, thus it is quite critical to determine the optimum addition of alloying element. Here, we prepared immiscible Cu-Cr alloyed thin films by non-equilibrium magnetron sputtering deposition to study Cr alloying effects on the microstructure and mechanical properties of Cu thin films. It is found that Cr doping can notably refine the grains and promote the formation of fully nanotwinned columnar grains at low Cr volume concentrations (≤∼3.7 at.%) associated with the average GB Cr concentrations ≤ ∼15 at.%, beyond which the formation of nanotwins is significantly suppressed. The role of Cr atoms/clusters played in the twinning process is rationalized in terms of dislocation rebound-promotion mechanism. Importantly, a maximum hardness is discovered at the optimum Cr addition of ∼2.0 at.%. The Cr concentration-dependent hardness of Cu-Cr alloyed films was quantified by a combined strengthening model. The achievement of the maximum hardness was related to the greatest GB solute segregation-induced strength contribution. It is further uncovered that the Cu-Cr system exhibits strain rate sensitivity (SRS, m) monotonically reduced with increasing the Cr concentration, ranging from a positive m of 0.0314 (for pure Cu) to a negative m of −0.0245, which is attributed to a competition between the dislocation-boundary interactions (increasing m) and the dislocation-solute atoms interactions (decreasing m). These findings provide valuable insights into tuning the composition of alloyed thin films to achieve optimized mechanical performance.

Here we report the effects of Zr addition (0.1–0.3 at.%) on the multi-scale second-phase particles and fracture behavior for Mg-3Gd-1Zn (at.%) alloys. Microstructural features of the alloys in the as-cast, solutionized, and aged conditions have been investigated in detail. The results have revealed that the cast alloys are mainly composed of α-Mg matrix, eutectic phase (Mg, Zn)3Gd, 14H long period stacking ordered (LPSO) structure and cuboid shaped GdH2 phase. After solution heat treatment, the eutectic phase (Mg, Zn)3Gd has transformed to X phase with 14H-LPSO structure, which has different distributions and morphologies due to different Zr additions. When the Zr addition is 0.3 at.%, a large amount of microscale Mg(Gd, Zn, Zr) particles appear along the grain boundaries. After aging heat treatment, Mg-3Gd-1Zn alloy with basal precipitates γ '' exhibits poor age-strengthening response. In contrast, Zr addition to the Mg-3Gd-1Zn alloy gave rise to a strong age-strengthening response. The strength improved significantly due to dense distribution of nanoscale prismatic plate β ' and β 1 precipitates, which are not observed in the Zr-free alloys. One key finding of this study is that Zr contributes to formation of the prismatic precipitates, and their amount increase with increase of Zr addition. The mechanical damage for these alloys is a sequence of microscale GdH2 or Mg (Gd, Zn, Zr) particles cracking, followed by fracture of the surrounding particles, and finally the growth/coalescence of micron-voids in the α-Mg matrix. The fracture of microscale particles was quantitatively analyzed by a Weibull model.

Coarse-grained (CG), fine-grained (FG), and ultrafine-grained (UFG) Al-2.5 wt% Cu (Al-Cu) alloys were respectively prepared, with and without 0.3 wt% Sc addition, for comparison. The influences of minor Sc addition on the microstructural evolution, tensile mechanical properties and pitting corrosion resistance were systematically studied at different grain scales. A significant Sc microalloying effect on the precipitation was observed that the minor Sc addition promoted the dispersion of finer θ′-Al2Cu precipitates in the CG alloy and favored the intragranular θ′-Al2Cu precipitation in the FG and UFG alloys, with the smaller grain size leading to a stronger Sc microalloying effect. The Sc addition induced convincing increases in the yield strength at all the three grain scales, and improved (in the CG and UFG Al-Cu alloys) or retained (in the FG Al-Cu alloy) the pitting corrosion resistance at the same time. This indicates that the inverse strength-pitting corrosion correlation as usually observed can be broken by minor Sc addition. The strengthening mechanisms were discussed and the grain size-dependent pitting corrosion resistance mediated by the Sc addition was rationalized in terms of a competition between the positive influence derived from the interfacial Sc segregation and the negative influence come from the deformation-induced dislocations. The present findings provide a possible approach to break the inverse strength-pitting resistance correlation in heat-treatable Al alloys by modifying the precipitate/matrix interfaces through the suitable microalloying atom segregation.

Al-XCu (X = 1.0, 1.5, and 2.5 wt%) alloys with and without 0.3 wt% Sc addition were prepared respectively. The effects of composition and heat treatment processes on the microstructural evolution were systematically investigated by using transmission electron microscope and atom probe tomography (APT). Both Al3Sc dispersoids and θ′-Al2Cu precipitates coexisted after artificial aging, and a strong Sc segregation at θ′-Al2Cu/matrix interfaces was detected and quantified through APT examinations. A Sc solute partitioning was demonstrated between in the Al3Sc dispersoids and at the θ′-Al2Cu/matrix interfaces, mediated by the Cu content. Increasing the Cu content, both the size and volume fraction of the Al3Sc decreased after solid solution treatment. As a result, the interfacial Sc segregation was accordingly intensified during subsequent aging treatment. A parameter of reduction in interfacial energy (Δγ), derived from APT analyses, was proposed to characterize the degree of interfacial Sc segregation. The coupling effect of Al3Sc dispersoids and θ′-Al2Cu precipitates on ductile fracture was discussed, where a micromechanical model was developed to describe a quantitative relationship between the fracture strain with Δγ as well as parameters of the Al3Sc dispersoids.

The effects of carbon content on the microstructure and room-temperature mechanical properties of Fe40Mn40Co10Cr10 high-entropy alloy (HEA) were systematically investigated. The results showed that heavy carbon alloyed HEA could possess supreme combination of high tensile strength (935 MPa) and high ductility (~ 74%). The excellent mechanical properties were ascribed to as follows: the high content interstitial carbon atoms strengthens the matrix greatly through suppressing dislocation motion and promoting the deformation-induced twinning at room temperature, which enhance the strength and ductility. Simultaneously, the ductility is further secured for single FCC structure maintained due to appropriate carbon alloying. Our findings provide a novel strategy for developing HEAs with excellent mechanical properties.

Crystalline/amorphous interfaces (CAIs) confer outstanding mechanical properties on crystalline/amorphous nanostructured multilayers (C/ANMs), which are widely used in micro/nanodevices, because their unique interfacial structure possesses high strain compatibility. In this study, Cu/X (X = Cu–Ti, HfO2) C/ANMs with equal layer thicknesses (h) were comparatively investigated in terms of size-dependent hardness (H) and thermal stability to uncover the fundamental difference(s) between Cu/Cu–Ti and Cu/HfO2. It was found that both as-deposited Cu/Cu–Ti and Cu/HfO2 C/ANMs exhibited a maximum hardness at a critical thickness of h ∼30 nm, which was caused by a transition from confined dislocation gliding to dislocation transmission across the interface. Specifically, the Cu/Cu–Ti C/ANMs exhibited annealing hardening, whereas the Cu/HfO2 C/ANMs exhibited annealing softening associated with a minimum softening at h ∼ 30 nm, which was closely correlated with their thermal stability. In comparison with monolithic amorphous X thin films, the glassy X nanolayers in the present Cu/X C/ANMs exhibited reduced thermal stability and a trend that smaller sizes led to higher stability. The underlying mechanism of the size-dependent crystallization behavior of X nanolayers is discussed in terms of the constraining effects of the interface. These findings provide deep insights into the design of Cu/metallic-glass and Cu/ceramic-glass C/ANMs with optimal performance.

This study aimed to reveal the lightning-induced conduction characteristics and improve the lightning damage simulation of carbon fiber-reinforced polymer (CFRP) composites. The real-time conductivity of CFRPs under lightning impulses was investigated. A potential barrier model of “fiber-resin-fiber” units was established based on the electron hopping and tunneling effect to clarify the nonlinear conduction mechanism. An impulse equivalent circuit model of CFRPs was constructed and experimentally verified. The effective resistance was proposed and incorporated into the coupled thermoelectrical damage analysis of CFRPs under lightning component A. The simulated damage based on different conductivity models was compared with the experimental results, indicating that the adoption of effective resistance can advance the simulation study of lightning-induced damage in actual lightning environments. This adoption can decrease the maximum deviation in simulated in-plane damage from −42.8% to −8.86% and decrease the deviation in the predicted through-thickness damage from 2 to 3 layers to within 1 layer.

Lightning strike damage has become a primary issue limiting the extensive application of carbon fibre-reinforced polymer (CFRP) composites in the aerospace field. A detailed understanding of the physical interactions involved in the lightning strike process is still lacking, especially regarding the lightning-induced mechanical effects that potentially contribute to fracture and ply delamination in CFRP structures. This paper presents research on shock wave pressure induced by impulse currents on CFRP laminates. A novel method that exploits a polyvinylidene fluoride (PVDF) piezoelectric sensor was developed to directly measure the pressure induced by arc channel expansion. The influences of discharge polarity, strike distance and surface condition on the shock wave pressure were investigated. The results showed that the shock wave pressure produced by negative discharge was greater than that produced by positive discharge, the difference between which was reasonably explained based on the polarity effect concept. Increases in current amplitude and strike distance both contributed to larger measured pressures. A woven copper mesh protection could diminish the shock wave pressure to some extent, while an additional insulating epoxy resin layer enhanced it. Analysis results demonstrated that the pressure imposed on the laminated samples was related to the energy injected into the arc channel. In addition, the energy consumed by vaporized materials at the interface between the arc root and sample was defined as another source of shock wave pressure. The presence of an insulating layer confined the diffusion of the plasma channel at the arc root, as confirmed by high-speed imaging observations.

Experimental evidence demonstrated that equal channel angular pressing (ECAP) at cryogenic temperature, in comparison with ECAP at room temperature, led to promoted strength-ductility synergy in an Al-2.5wt.%Cu alloy. The simultaneous improvement is related to microstructural hierarchy of multimodal grains, low angle grain boundaries, and inter/intragranular precipitates, which was tuned by aging treatment in match with the low-temperature ECAP. The artificial aging could maintain multimodal grain size distribution, introduce a large number of low angle grain boundaries and produce intragranular precipitates to improve strength/ductility. A minor 0.3wt.% Sc addition was effective in optimizing the precipitations and further boosting the strength/ductility combination. The underlying mechanisms for higher strength and greater ductility were rationalized in terms of the low-temperature ECAP.

In this study, a 3D printed nickel-plated carbon fiber mesh is proposed as an interconnected lightning strike protection (LSP) layer. The conductive nickel coating provides the fibers with sufficient electrical and thermal conductivity. The continuous carbon fibers maintain their appealing features of low density, and high strength and modulus. The 3D printing technology offers low process costs and enables rapid manufacturing of LSP layers for complex and large-scale structures. Herein, simulated lightning experiments at 100 kA were performed. The lightning-induced electric arc was recorded to observe its evolution during the contact, expansion, and attenuation stages. The in-plane and cross-sectional damage analysis demonstrated that the nickel-plated carbon fiber mesh achieved effective arc dissipation and load suppression, which limited the damage area and depth within the surface layer. These results indicate that the proposed method can be employed as a potential LSP candidate in future aviation applications.

In this work, we investigate the plastic deformation characteristics (hardness, strain rate sensitivity and activation volume) of nanotwinned AlxCoCrFeNi (x = 0, 0.1, 0.3) high entropy alloy thin films (HEAFs). The extremely thin nanotwins with thickness of ~ 2 nm soften these HEAFs, but enhance their strain rate sensitivity. We combine the detwinning softening process with conventional strengthening mechanisms to elucidate the mechanical properties of AlxCoCrFeNi HEAFs. These findings provide deep insights into design strategies to explore the promising high entropy alloys, especially the nanotwinned HEAFs at micro- and nano-scale.

A series of nanoindentation tests were performed on a Zr-based bulk metallic glass at different peak-loads and strain rates. It is observed that the strain rate sensitivity index gradually decreases from positive to almost zero with increasing peak-load. Furthermore, at a fixed strain rate, the indentation hardness firstly shows a dramatic reduction and then becomes stable with increasing peak-load. These observations can be well understood in the framework of the activation and the accumulation of free volume via shear transformation zones. The current work may provide a practical way to tailor the hardness of the metallic glass.

A direct relationship between the yield strength and the atomic ratio of solvent (Zr) atoms in the Zr-Cu-Al-Ni metallic glasses system is firstly uncovered. It is found that either shear modulus or yield strength decreases almost nearly with the increase in atomic ratio of Zr. The origin of this relationship is ascribed to the preferential straining of the weakest configurations, which consist of the solvent-solvent bonds and the free volume concentrated in them. It is suggested that a higher atomic ratio of Zr corresponds to a larger amount of weakest configurations, which will facilitate the activation and the accumulation of the shear transformations and finally results in the lower yield strength. This finding may provide an effective strategy for designing high-strength metallic glasses by modifying the chemical composition.

To clarify the evolution of damage for typical carbon woven fabric/epoxy laminates exposed to lightning strike, artificial lightning testing on carbon woven fabric/epoxy laminates were conducted, damage was assessed using visual inspection and damage peeling approaches. Relationships between damage size and action integral were also elucidated. Results showed that damage appearance of carbon woven fabric/epoxy laminate presents circular distribution, and center of the circle located at the lightning attachment point approximately, there exist no damage projected area dislocations for different layers, visual damage territory represents maximum damage scope; visible damage can be categorized into five modes: resin ablation, fiber fracture and sublimation, delamination, ablation scallops and block-shaped ply-lift; delamination damage due to resin pyrolysis and internal pressure exist obvious distinguish; project area of total damage is linear with action integral for the same type specimens, that of resin ablation damage is linear with action integral, but no correlation with specimen type, for all specimens, damage depth is linear with logarithm of action integral. The coupled thermal–electrical model constructed is capable to simulate the ablation damage for carbon woven fabric/epoxy laminates exposed to simulated lightning current through experimental verification.

In recent years, using electromagnetic fields as a targeted therapy for tumors has become a new idea. This paper aims to study the response of rat glioma cells (C6) when the external electromagnetic field parameters change and to obtain a complete working range of magnetic field parameters. Four-day, 4-h daily millisecond magnetic field exposure experiments were performed with C6 cells. The peak values of magnetic field intensity were 260 mT, 90 mT, 19 mT and 6 mT. Each day after exposure, cell morphology and cell viability assay (MTT method) were measured. The response of C6 cells shows a significant window effect and time cumulative effect on the cell, and it is non-destructive. The working inhibited magnetic field range of magnetic field increase rate dB/dt (T/s) is [34, 119.5] and [166.75, 527.25], the magnetic field amplitude B (mT) is [6, 260], the magnetic field integral Bt (mT·s) is [0.1649, 0.8085] and the energy integral B2t (mT2·s) is [2.317, 53.328]. Our findings provide the theoretical and experimental basis for clinical applications of electromagnetic fields.

According to the mathematical analysis model constructed on the basis of energy-balance relationship in lightning strike, and accompany with the simplified calculation strategy of composite resin pyrolysis degree dependent electrical conductivity, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate suffered from lightning current was established based on ABAQUS, to elucidate the effects of lighting current waveform parameters and thermal/electrical properties of composite laminate on the extent of ablation damage. Simulated predictions agree well with the composite lightning strike directed effect experimental data, illustrating the potential accuracy of the constructed model. The analytical results revealed that extent of composite lightning strike ablation damage can be characterized by action integral validly, there exist remarkable power function relationships between action integral and visual damage area, projected damage area, maximum damage depth and damage volume of ablation damage, and enhancing the electrical conductivity and specific heat of composite, ablation damage will be descended obviously, power function relationships also exist between electrical conductivity, specific heat and ablation damage, however, the impact of thermal conductivity on the extent of ablation damage is not notable. The conclusions obtained provide some guidance for composite anti-lightning strike structure-function integration design.

A transmission electron microscope and an atom probe tomography were used to quantitatively characterize the microstructural evolution of Al-XCu alloys (X = 1.0, 1.5, and 2.5 wt%) with 0.3 wt% Sc addition. A dual solute alloying/microalloying effect on the microstructural evolution was demonstrated. On the one hand, the nucleation and coarsening of Al 3 Sc dispersoids displayed a Cu alloying effect . By increasing the Cu content, both the Al 3 Sc disperoid size and the volume fraction decreased after solution treatment. On the other hand, the precipitation of θ′ -Al 2 Cu strengthening particles during aging treatment was promoted by Sc segregation at the θ′ /matrix interfaces, showing a notable Sc microalloying effect . The strongest interfacial Sc segregation was generated in the Al-2.5 wt%Cu-Sc alloy, resulting in the most promoted θ′ precipitation. The Sc partitioning between Al 3 Sc dispersoids and Sc segregation at the θ′ /matrix interfaces, tailored by the Cu content, impacted the mechanical properties and deformation behavior at both room temperature and high temperature. The Al-2.5 wt%Cu-Sc alloy had a room temperature yield strength of approximately 2.2 times that in its Sc-free counterpart and approximately 1.8 times that in the Al-1.5 wt%Cu-Sc alloy, which is rationalized by strengthening models. In addition, the improvement in the high-temperature mechanical properties after Sc addition was discussed in terms of the Sc segregation-induced high coarsening resistance of θ′ precipitates.

Quasi-static and dynamic tensile experiments were conducted on a Zr-based bulk metallic glass at room temperature. A significant ductile-to-brittle transition was identified with increasing strain rate, based on the changes in the macroscopic fracture mode from shear to normal tension and in the microscopic fracture feature from vein patterns to fine dimples and/or nanoscale periodic corrugations. According to the Mohr-Coulomb criterion, it is revealed that such a transition is due to the competition between the intrinsic critical shear and tensile strengths at different strain rates. Microscopically, the strain-rate-induced transition is attributed to the change in the motion of local atomic groups from shear transformation zone to tension transformation zone, in which the characteristic volume of shear transformation zone is a key parameter.

This study aims to reveal the damage properties and mechanism of carbon fiber-reinforced polymer (CFRP) composites subjected to lightning current component A by artificial lightning tests and simulation analysis. The lightning strike process was observed by using a high-speed camera and infrared temperature measurements. The surface damage and internal damage were inspected via ultrasonic and 3D X-ray scanning. The damage behavior of CFRP composite was deduced and the damage regions were quantitively analyzed by detecting the surface morphology and microstructural changes and analyzing the lightning strike process. The results indicated that the lightning-induced damage included lightning attachment damage due to direct contact with the lightning arc, laminate peeled-off damage caused by the explosive gas impact, and internal delamination induced by expanding pyrolysis gas. A coupled thermal-electric CFRP model, which first introduces the dynamic conductivity of CFRP materials, was established. The comparison results indicated that the Joule heating-based numerical model can simulate the evolution of thermal damage well, although the laminate peeled-off damage resulting from the mechanical impact was not included in the simulation scope. A temperature field criterion and a pyrolysis degree field criterion were proposed and verified for evaluating in-plane and in-depth damage with acceptable deviations.

Optical fiber ground wires (OPGWs) are used to protect power transmission lines from lightning strikes. A lightning test system with a tension device was established to study the properties and influence factors of lightning damage for OPGWs under multiple consecutive lightning strikes composed of current impulse and continuous current. The lightning damage can be divided into arc sweeping damage, melting damage and ablation damage. The lightning energy injected through a W-Cu electrode was the most concentrated, leading to the most serious ablation damage and the smallest sweeping damage area. As the action integral and external tensile force increased, the lightning damage became more severe. The broken strands and ablation damage volume decreased as the discharge gap increased from 20 to 40 mm. In addition, a 3D finite element simulation of lightning melting damage was conducted considering the lightning test conditions. When 1850 K, which is close to the melting point of steel, was selected as the criterion temperature for melting damage, the deviations between the simulation and experimental results were less than 10%.

Cancer treatment is a challenge in modern medicine. Several novel modalities have been invented to selectively treat cancer cells. The reactive species such as reactive oxygen species and reactive nitrogen species play important role in the anti-cancer capacity of several modalities, such as cold atmospheric plasma. In this study, we first demonstrated that a nanosecond-pulsed magnetic field (NMF) generator could sensitize the melanoma cell line B16-F10 to the cytotoxicity of an important ROS, H2O2. The magnetic field strength and the frequency were two key factors to control the activation level of NMF treatment. This study provided a novel strategy to use electromagnetic modality in cancer treatment particularly for the treatment on deep tumors such as brain, pancreatic, etc.

Wind-turbine blades are more vulnerable to lightning strikes as they lack a protection system for large-scale glass fiber reinforced polymer (GFRP) composite structures. A low-energy electron beam (EB) cured printing process for fabricating a continuous carbon fiber-reinforced thermoset resin as a non-metallic lightning protection mesh on a GFRP composite surface was carried out in this study. During the proposed process, a continuous carbon fiber mesh was printed through a Fused Filament Fabrication that integrates the rapid curing of an epoxy resin with low-energy EB irradiation. The printing process was analyzed and optimized by examining the correlation between the EB exposure dose and the printing height. Results from artificial lightning strikes showed that the printed carbon fiber mesh prevented damage, and the structure remained relatively intact with residual strength reaching 90.1 % at 100 kA maximum peak current. The protection mechanism was investigated using a high-speed camera, which revealed that the carbon fiber mesh spreads the striking current outside the laminate instead of penetrating inside.

Commercial precipitation-hardened Al-Cu alloys are normally used at temperatures below its ageing temperature of ∼225°C, to avoid thermally induced precipitate coarsening and resultant softening. Making such popular Al alloys creep resistant at or above 300°C is thus challenging. Here we present a modified precipitation protocol, exploiting Sc-microalloying and a carefully designed three-step heat treatment to enhance Sc segregation at the matrix/θ′-Al2Cu precipitate interfaces. The stabilized nanoprecipitates enable an order-of-magnitude reduction in creep rate at 300°C, demonstrating the room for microstructure improvement and the potential for property elevation in traditional engineering alloys through innovative processing coupled with synergetic alloying elements. A carefully designed precipitation protocol produces stable nanoprecipitates in Sc-microalloyed Al-Cu alloys, rendering an order-of-magnitude elevation of creep resistance at 300°C.

The hardness, tensile ductility, and strain rate sensitivity of crystalline Cu/amorphous Cu–Zr nanolaminates (Cu/Cu–Zr C/A NLs) have been measured as a function of modulation ratio (η). With reducing η, the tensile ductility first decreased and subsequently increased, leaving a minimum value at η ∼ 1.0. However, the strain rate sensitivity (m) increased monotonically with reducing η and spanned from a negative value at η over ∼1.0 to a positive one at η below ∼1.0, indicating a tunable strain rate sensitivity in engineered C/A NLs. Careful microstructural examinations reveal that a deformation-induced devitrification (DID) in the amorphous nanolayers is the key factor responsible for the aforementioned experimental phenomena. For thinner amorphous nanolayers, the DID becomes more intense. The size-dependent DID drives the pure Cu–Zr amorphous single layer films to (i) exhibit a thickness-dependent tensile ductility opposite to that of pure Cu single layer films, and (ii) have a negative m contrary to the positive m in their pure Cu counterpart. When the two layers are engineered into C/A NLs, a competition exists between the two inverse constituent nanolayers. This competition is strongly η-dependent, resulting in a non-monotonic evolution in tensile ductility and significant change in m when η spans from 9.0 to 0.1. The fracture mode of the C/A NLs transformed from shearing at small η to opening at large η; this can be rationalized by considering the competition between the two constituent nanolayers as a microcrack initiator. In addition, the strengthening mechanisms of the C/A NLs were analyzed and the η-dependent hardness was quantitatively described using a modified mechanistic model.

Nanoindentation methodology was used to measure the hardness, strain rate sensitivity (SRS) and activation volume of Cu/Cu–Zr crystalline/amorphous nanolaminates (C/ANLs) with layer thickness ( h ) spanning from 2.5 to 150 nm before and after He ion-implantation at room temperature. It is interestingly to uncover that the ion radiation-induced devitrification (RID) occurs in the glassy Cu–Zr nanolayers, in which the nanocrystallites transit from the Cu 10 Zr 7 intermetallics at large h to the fcc Cu–Zr solid solution at small h . Compared with the as-deposited Cu/Cu–Zr C/ANLs associated with monotonic increase in hardness and SRS (or a monotonic decrease in activation volume) with reducing h , the irradiated Cu/Cu–Zr manifested enhanced hardness in the form of two hardness plateau and an unexpected non-monotonic variation in SRS (similarly in activation volume). It was clearly unveiled that the SRS of irradiated Cu/Cu–Zr firstly decreased with reducing h down to a critical size of ∼50 nm and subsequently increased with further reducing h to ∼10 nm, below which a SRS m plateau emerges (The activation volume of irradiated Cu/Cu–Zr had exactly an opposite variation). These phenomena are rationalized by considering a competition between dislocation-interface and dislocation-bubble interactions. A thermally activated model based on the depinning process of bowed-out dislocations pinned by obstacles was employed to quantitatively account for the variation of SRS with h in Cu/Cu–Zr C/ANLs before and after radiation. Our findings not only provide fundamental understanding of the effects of radiation-induced defects on plastic characteristics of C/ANLs, but also offer guidance for their microstructure sensitive design for performance optimization at extremes.

We report the unique thermal and mechanical stability of a metastable B2 phase embedded in a metallic glass matrix at liquid-nitrogen temperature. The B2 phase is stabilized by the constraints of the hard amorphous matrix, which result from the increasing hydrostatic pressure during cryogenic cooling. The stability of the B2 phase contributes to the high strength and ductility of CuZr-based bulk metallic glass composites at cryogenic temperature. This discovery is expected to provide new strategies for designing strong and ductile materials containing a metastable phase.

An experiment platform was established for direct current resistance testing methods of carbon fibre reinforced polymer composites in this paper. Drastic differences have been found in the volume resistance of carbon fibre reinforced polymers between the theoretical values and testing values obtained with a classic three-electrode testing method for solid dielectric materials. Thus, on the basis of the experimental circuit and structures of carbon fibre reinforced polymers, an improved three-electrode testing method was put forward. The experimental results, which reflect the electric characteristics, surface coating materials and internal layer structures of carbon fibre reinforced polymers were subsequently obtained and can be well explained by the inferred conduction model, in which the electric field extension and surface current effect were considered comprehensively. This work provides a theoretical support for further research of electric characteristics, thermal degradation and weight loss...

Nanolayered materials exhibit unique plastic deformation behavior, i.e. , a bulk-like to small-scale plasticity transition and a scaling behavior of extremely small activation volume ( V * b 3 ) with intrinsic size. This unusual plastic transition phenomenon likely stems from the dislocations respectively emit from interfaces and Frank–Read-type bulk sources below and above a critical intrinsic size ∼20 nm. We quantitatively capture the scaling relationship between strain rate sensitivity and intrinsic size by a phenomenological model based on the Orowan–Frank–Read process.

How to defeat the conflict of strength vs. toughness and achieve unprecedented levels of damage tolerance within either metallic crystalline or metallic glassy family is a great challenge for designing structural materials. The combination of glassy with crystalline nanolayers can manifest extraordinarily high toughness, i.e. superior strength in conjunction with high ductility, when the constituent layers approach a critical internal feature size. Three-point bending and uniaxial microcompression tests were performed on Cu/Cu–Zr crystalline/amorphous nanolaminates (C/ANLs) with equal layer thicknesses ∼50 nm to investigate their toughening behaviors. The dislocations absorbed by the amorphous phase not only render defect-free nanocrystals, but also create nanocrystallites in glassy nanolayers. It is revealed that the Cu/Cu–Zr C/ANLs self-toughen via the combination of the extrinsic shielding effect of crystalline/amorphous interfaces on a crack growth accommodated by an extensive shear-band sliding process and the intrinsic deformation-induced devitrification mechanism associated with the brittle-to-ductile transition of glassy nanolayers. The findings indicate that the high damage tolerance potentially accessible to glassy materials can extend beyond the benchmark ranges towards levels previously inaccessible to metallic crystalline–amorphous composites.

The microstructural evolution and hardness of He-irradiated Nb/Zr crystalline/crystalline multilayers with a wide range of layer thickness h from 5 to 100 nm were investigated under three different ion dose Φ of 1.0 × 1016, 1.0 × 1017 and 5.0 × 1017 ions·cm−2 at room temperature. Careful microstructural examinations found the occurrence of a radiation-induced amorphization phenomenon near the interface. Besides, He bubbles were distributed within the Nb layers and at the interface. Both the amorphization and He bubble distribution were highly dependent on h and Φ, which caused the mechanical properties sensitive to h and Φ. With reducing h, the hardness of as-deposited Nb/Zr multilayers showed a maximum at h = 10 nm. While the He-irradiated samples manifested a hardening behavior at Φ = 1.0 × 1016 ions·cm−2, a softening behavior at Φ = 5.0 × 1017 ions·cm−2 and a transition from hardening to softening at Φ = 1.0 × 1017 ions·cm−2 with reducing h. These strengthening behaviors were rationalized by a coupling effect of dislocation-amorphous and dislocation-bubble interactions. Modified mechanistic models based on interactions of dislocations with obstacles were employed to quantitatively describe the underlying strengthening mechanisms.

The creep behavior of free-standing Cu films with bimodal grain size distribution was investigated at room temperature. It is found that the higher loading rate, the greater the primary creep strain rate and the smaller the steady-state creep strain rate. This unique creep behavior was explained by considering the competition between dislocation activities and dislocation stress fields. Given the grain size distribution, a modified phase-mixture model is proposed to predict the scaling behavior of creep rate and applied stress.

For small-scale metallic single crystals, systematic studies have established that external sample size ( ϕ ) has an obvious influence on the apparent strength, following a “smaller is stronger” fashion. In the present nanocrystalline (NC) Zr micropillars, deformation crossover leads to the strongest external size emerging at a critical ϕ ≈ 400 nm , similar to that of bulk-scaled NC metals. Above the critical external size the NC Zr pillars failed via highly inhomogeneous single-shear offset, below which they deformed via relative homogeneous shear.

The initial plasma and its spread speed have obvious influence on the dynamic characteristics of triggered vacuum switch (TVS). A special sensor is designed for measuring the initial charge of the trigger device of TVS in this paper, and the initial plasma diffusion characteristics are researched. The experimental results show that the diffusion velocity of the initial plasma charge increases with the increase of the steepness of the trigger current. When trigger current steepness increases 2 kA/μs, the maximum diffusion velocity of initial plasma increases reached to 150 cm/μs about.

Lightning can cause severe damage to aircraft, lightning direct effect test is very important for research of spacecraft material, design of structure of aircraft, but the limitation of the measuring technology and special test apparatus has become the technical bottleneck. Lightning current components for lightning direct effect test consist of component A (initial strode), component B (Intermediate current), component C (Continuing current) and component D (Restrike). Lightning current components A and D can be produced by the type of RLC circuit and crowbar circuit. The efficiency of the conventional RLC circuit in generating long duration time impulse current wave is relative low. To solve this problem, a replaceable electrodes triggered vacuum switch is designed and researched and then a high efficiency crowbar circuit which produces lightning current component A is designed in this paper.