Effect of laminate configuration and feed rate on cutting performance when drilling holes in carbon fibre reinforced plastic composites

Composites use in the aerospace industry is expanding, in particular carbon fibre reinforced plastics (CFRP) for structural components. Machinability can however be problematic especially when drilling, due to CFRP's inherent anisotropy/in-homogeneity, limited plastic deformation and abrasive characteristics. Following a brief review on composites development and associated machining, the paper outlines experimental results when twist drilling 1.5 mm diameter holes in 3 mm thick CFRP laminate using tungsten carbide (WC) stepped drills. The control variables considered were prepreg type (3 types) and form (unidirectional (UD) and woven), together with drill feed rate (0.2 and 0.4 mm/rev). A full factorial experimental design was used involving 12 tests. Response variables included the number of drilled holes (wear criterion VB_Bmax ≤ 100 μm), thrust force and torque, together with entry and exit delamination (conventional and adjusted delamination factor values calculated) and hole diameter. Best results were obtained with woven MTM44-1/HTS oven cured material (3750 holes) while the effect of prepreg form on tool life was evident only when operating at the higher level of feed rate. Thrust forces were typically under 125 N with torque values generally below 65 Nmm over the range of operating parameters employed. Finally, the delamination factor (F_d) measured at hole entry and exit ranged between ～1.2–1.8 and 1.0–2.1 respectively.     

Microstructure,texture and magnetic properties of strip casting Fe–6.2 wt%Si steel sheet

An Fe–6.2 wt%Si strip with equiaxed grains and mild {0 0 1}〈0 v w〉 fiber texture was produced by twin-roll strip casting process. Then the as-cast strip was treated with or without the hot rolling prior to the warm rolling and annealing. When the hot rolling was not introduced, a fine and heterogeneous warm-rolled microstructure was produced and led to a fine recrystallization microstructure and very weak {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. When the hot rolling was introduced, a coarse and homogeneous warm-rolled microstructure was produced and led to a very coarse recrystallization microstructure and much stronger {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. The annealed sheets with hot rolling showed a higher magnetic induction and a higher core loss than those without hot rolling.     

Long-term monitoring of atmospheric corrosion at weathering steel bridges by an electrochemical impedance method

Weathering steel corrosion was monitored for one to two years under natural atmosphere by an electrochemical impedance technique. Two identical comb-shape weathering steel sheets embedded in epoxy resin were used as monitoring probe electrodes at two different bridges in Japan. Impedances at 10 kHz (Z_10kHz) and 10 mHz (Z_10mHz) were automatically measured every hour. Coupons (50 × 50 × 2 mm³) prepared from the same steel sheets were exposed together to measure the corrosion mass loss. The average (Z_10mHz)⁻¹ value for half to one year exposure correlated well with the average corrosion rate determined from the corrosion mass loss.     

Mechanical properties of micro-sized copper bending beams machined by the focused ion beam technique

Micro-sized bending beams with thicknesses, t, from 7.5 down to 1.0 μm were fabricated with the focused ion beam technique from a copper single crystal with an {1 1 1}〈0 1 1〉 orientation. The beams were loaded with a nano-indenter and the force vs. displacement curves were recorded. A strong size effect was found where the flow stress reaches almost 1 GPa for the thinnest beams. A common strain gradient plasticity approach was used to explain the size effect. However, the strong t^−1.14 dependence of the flow stress could not be explained by this model. Additionally, the combination of two other dislocation mechanisms is discussed: the limitation of available dislocation sources and a dislocation pile-up at the beam centre. The contribution of the pile-up stress to the flow stress gives a t⁻¹ dependence, which is in good agreement with the experimental results.     

Investigation of carbon fiber reinforced polymer (CFRP) sheet with subsurface defects inspection using thermal-wave radar imaging (TWRI) based on the multi-transform technique

A combined theoretical and experimental approach is reported using thermal-wave radar imaging (TRWI) for carbon fiber reinforced polymer (CFRP) with subsurface defects inspection. The multi-transform technique (Fourier transform, FT; Hilbert transform, HT; and cross-correlation, CC) is applied to extract the characteristics of thermal-wave signal. Experimental results indicate that the multi-transform technique of thermal-wave signal is available for detecting the subsurface defect. For the shallow defect (defect depth ≤1 mm), the delay time image of CC exhibits high contrast, and the phase image of FT has high SNR at the right frequency component. For the deep defect (defect depth 2.0 mm), the phase images of HT have both high contrast and large SNR value.     

Effect of milling and reinforcement on mechanical properties of nanostructured magnesium composite

Recycled Mg chips were used to synthesize nanostructured Mg composite of Mg–5 wt%Al reinforced with x wt% (x = 1, 2 and 5) in-situ formed AlN powder. Mechanical milling was employed to produce the composite powder of crystalline size 30–43 nm. The mechanically milled (MMed) powders were subjected to uniaxial pressing, sintering and hot extrusion processes to produce bulk solid samples. After sintering at 400 °C and hot extrusion at 350 °C, the crystalline size of the composite samples still remains in nanometer range from 52 to 84 nm. The effect of milling and the percentage of reinforced AlN on the mechanical properties such as tensile strength and ductility were discussed with the general explanation of deformation mechanisms involved.     

Ductilisation of tungsten (W): On the increase of strength AND room-temperature tensile ductility through cold-rolling

Here we show that cold-rolling is a method to achieve room-temperature ductility in commercial purity, monolithic tungsten (W). Furthermore, we show that a decrease in rolling temperature concomitantly increases the strength and ductility of tungsten. So cold-rolling is a way to overcome the strength–ductility trade-off.In this work, we assess three different cold-rolled microstructures obtained from rolling at (i) 1000 °C (1273 K), (ii) 800 °C (1073 K), and (iii) 600 °C (873 K). Benchmark experiments were performed on a sintered ingot as well as on a hot-rolled plate. From these plates tensile test specimens were cut by spark erosion and tested at room temperature. The results show an increase of total uniform elongation, A_ut, ranging from 1.38% (cold-rolled at 1000 °C (1273 K), and 800 °C (1073 K)) up to 1.47% (cold-rolled at 600 °C (873 K)) and an increase of the total elongation to fracture, A_t, ranging from approximately 3% (cold-rolled at 1000 °C (1273 K), and 800 °C (1073 K)) up to 4.19% (cold-rolled at 600 °C (873 K)) with decreasing rolling temperature.The microstructure of the plates is analysed by means of scanning electron microscopy (SEM) (grain size, subgrains, crystallographic texture) and transmission electron microscopy (TEM) (bright field imaging, scanning TEM). Furthermore, strain-rate jump tests have been performed at 400 °C (673 K) to determine the strain-rate sensitivity, m, (sintered ingot m = 0.088, cold-rolled at 600 °C (873 K) m = 0.011) and the activation volume, V, (hot-rolled W plate V = 191 b³, cold-rolled at 600 °C (873 K) V = 111 b³) of the tungsten sheets.The question of why cold-rolling increases both strength and ductility is discussed against the background of cold-rolling-induced lattice defects. We speculate that the increase of ductility is caused by the ordered glide of screw dislocations, that move with low deformation incompatibility along the high-angle grain boundary (HAGB) channels (confined plastic slip).     

Pressure effect on the electrical resistance of SrSi2

Electrical resistance measurements at temperatures ranging from 4.2 to 300 K and pressures ranging from 0 to 3.6 GPa indicate that pressurization reduces the energy gap E_g with a pressure coefficient, ⅆE_g/ⅆP, of −8.8(4) meV/GPa. The deformation potential of E_g is estimated to be 0.50(2) eV, which is smaller than that of tetrahedrally bonded semiconductors, such as Si (1.46 eV). The reduction of E_g by pressurization is qualitatively consistent with the results of a previously reported calculation [Imai Y, Watanabe A. Intermetallics 2006;14:666].     

Preparation of MoO2 sub-micro scale sheets and their optical properties

MoO₂ sub-micro sheets have been synthesized in a large scale on silicon substrate with MoO₃ and C powders as raw materials using a novel chemical vapour deposition method. The lengths and widths of MoO₂ sheets are in the range of several to dozens micrometers, and the thickness of MoO₂ sub-micro sheets is ～200 nm. Transmission electron microscopy and high-resolution electron microscopy show that the MoO₂ sheets are of single crystal with a monoclinic structure. The sheets exhibit fluorescent emissions at 304.4, 343.5 and 350.6 nm when the 220 nm light excitation is applied at room temperature, and the emissions result from some defects and the electron transition between valence band and conduction band. UV–vis spectrum shows the MoO₂ sub-micro sheets have absorption peaks between 200and 300 nm and the emissions should be attributed to the defect states of MoO₂. Furthermore, the band-gap is estimated to be approximately 4.22 eV. The growth mechanism of the two-dimensional MoO₂ sub-micro scale sheets is also discussed.     

Nanoscale characterisation and clustering mechanism in an Fe–Y2O3 model ODS alloy processed by reactive ball milling and annealing

Reactive ball milling and annealing is proposed as a new production method for oxide dispersion strengthened (ODS) steels. A highly concentrated Fe–38 atm.% Y₂O₃ ODS model alloy was processed by reactive ball milling and annealing of YFe₃ and Fe₂O₃ powders so as to induce the chemical reaction 2YFe₃ + Fe₂O₃ → 8Fe + Y₂O₃. The model alloy was characterised after milling and annealing by complementary techniques, including atom probe tomography. Ball milling up to the stationary state results in the formation of two metastable nanometric interconnected phases: super-saturated α-iron and an yttrium and oxygen rich phase. Annealing leads the system towards equilibrium through: (i) a chemical evolution of each phase to nearly pure α-Fe and Y₂O₃ oxide slightly sub-stoichiometric in oxygen; and (ii) growth of the phases. A pure iron matrix reinforced by nanometric Y₂O₃ particles was successfully synthesised by reactive ball milling and annealing.     

Observation of two separate charge density wave transitions in Gd2Te5 via transmission electron microscopy and high-resolution X-ray diffraction

Gd₂Te₅ is a layered material consisting of alternating single and double square planar Te sheets. At room temperature the material hosts a complex lattice modulation characterized by multiple in-plane wavevectors. Diffraction measurements performed via transmission electron microscopy and high-resolution X-ray scattering reveal two distinct transitions at T_c1 = 410(3) and T_c2 = 532(3) K, associated with an on-axis incommensurate lattice modulation and an off-axis commensurate lattice modulation respectively. Our results show that the two lattice modulations are separate in origin but that there is some coupling between them.     

Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples: Effect of Y-doping

Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y³⁺-doped, were studied in the temperature regime 1250–1400 °C to determine the effect of Y³⁺ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of ～5 (at 1300 °C), and increases the corresponding activation enthalpy for oxidation from 407 ± 20 to 486 ± 34 kJ mol^?1. Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 °C, the presence of Ni alone enhances transport by a factor of ～2 relative to undoped alumina.     

Low cycle fatigue behaviour of a low interstitial Ni-base superalloy

The low cycle fatigue behaviour of precipitation strengthened nickel-base superalloy 720Li containing a low concentration of interstitial carbon and boron was studied at 25, 400 and 650 °C. Cyclic stress response at all temperatures was stable under fully reversed constant total strain amplitude (Δε/2) when Δε/2 ? 0.6%. At Δε/2 > 0.6%, cyclic hardening was followed by softening, until fracture at 25 and 650 °C. At 400 °C, however, cyclic stress plateaued after initial hardening. Dislocation–dislocation interactions and precipitate shearing were the micromechanisms responsible for the cyclic hardening and softening, respectively. The number of reversals to failure vs. plastic strain amplitude plot exhibits a bilinear Coffin–Manson relation. Transmission electron microscopy substructures revealed that planar slip was the major deformation mode under the conditions examined. However, differences in its distribution were observed to be the cause for the bilinearity in fatigue lives. The presence of fine deformation twins at low Δε/2 at 650 °C suggests the role of twinning in homogenization of cyclic deformation.     

Orientation dependence of local lattice rotations at precipitates: Example of κ-Fe3AlC carbides in a Fe3Al-based alloy

Local lattice rotations and in-grain orientation gradients at κ precipitates in matrix grains with orientations near the 45° rotated cube {0 0 1}〈1 1 0〉 (RC) and the γ-fiber components {1 1 1}〈1 1 2〉 were investigated in a Fe₃Al alloy warm-rolled to reductions of between 10% and 60%. Near-RC grains showed larger local lattice rotations at precipitates than γ-fiber grains. In RC-oriented grains the local lattice rotations about the transverse direction (TD) were dominant at low reductions, but rotations about the rolling direction (RD) also occurred at higher strains. In the γ-fiber grains the axes of the in-grain lattice rotations were scattered between TD and RD. The rotations around the particles and their orientation dependence were analyzed using 3-D crystal plasticity finite-element simulations of a spherical inclusion in a plane strain deformed matrix of different orientations, namely RC, {1 1 1}〈1 1 2〉 and {1 1 1}〈0 1 1〉.     

Mechanical anisotropy and deep drawing behaviour of AZ31 and ZE10 magnesium alloy sheets

The influence of the initial microstructure on the deep drawability and the associated microstructural evolution in two different magnesium alloy sheets, AZ31 and ZE10, has been examined. Tensile testing at room temperature shows that the AZ31 sheet has high plastic strain ratios, r = 2–3, which are caused by strong basal-type texture. The ZE10 sheet shows lower r values, r ～ 1, as a result of its weak texture. Deep drawing experiments carried out over the temperature range 100–300 °C revealed that the ZE10 sheet can be successfully deep-drawn at lower temperatures than the AZ31 sheet. The ZE10 cups show earing despite the weak texture and low normal anisotropy, while earing of the AZ31 cups is negligible. In the ZE10 cups, deformation is accommodated mainly by 〈a〉 slips and by compression as well as secondary twinning. The occurrence of dynamic recrystallization is observed in successfully deep-drawn AZ31 cups.     

Phenothiazine conjugated bipyridine as ancillary ligand in Ru(II)-complexes for application in dye sensitized solar cell

A new high molar extinction coefficient ruthenium(II)-bipyridine complex “cis-Ru(4,4′-bis((E)-2-(10-decyl-10H-phenothiazin-3-yl)vinyl)-2,2′-bipyridine)(4,4′-dicarboxylic acid-2,2′-bipyridine)(NCS)₂ PTZ1″ was synthesized through conjugation of phenothiazine unit with bipyridine and characterized by FT-IR, ¹H-NMR and ESI-MASS spectroscopes. Absorption measurements and time dependent-density functional theory (TD-DFT) calculations show increased spectral response for the ancillary ligand and the corresponding complex. The dye upon anchoring onto mesoporous nanocrystalline TiO₂ solar cells exhibited solar-to-electric energy conversion efficiency (η) of 3.77% short-circuit photocurrent density (J_SC) = 7.79 mA/cm², open-circuit voltage (V_OC) = 640 mV, fill factor = 0.750) under air mass 1.5 sunlight, the reference Z907 and HRS1sensitized solar cells, fabricated and evaluated under identical conditions exhibited η-value of 7.02% (J_SC = 15.25 mA/cm², V_OC = 650 mV, fill factor = 0.705) and 3.05% (J_SC = 8.20 mA/cm², V_OC = 610 mV, fill factor = 0.620) respectively. The lower film absorption of PTZ1on TiO₂ surface could be probably due to larger molecular diameter and planarity of phenothiazine prone to aggregate in solution as well as on TiO₂ surface. The DFT calculations show that the first three HOMOs of PTZ1 have t2g character as observed in case of Z907, while HOMO-4 and HOMO-5 have π-orbitals with major component on phenothiazine moieties of L1.     

Observations of a〈0 1 0〉 dislocations during the high-temperature creep of Ni-based superalloy single crystals deformed along the [0 0 1] orientation

A NASAIR-100 superalloy single crystal was tested in tension creep at 1000 °C at a stress of 148 MPa, for a time period of 20 h and to a strain of 1.1%. Analysis of the resulting dislocation structures after rafting was completed reveals the frequent presence of all three types of a〈0 1 0〉 dislocations in the γ′ particles. Two of these families experience no resolved forces due to the applied stress. It is proposed that these a〈0 1 0〉 dislocations form as a result of the combination of two dissimilar a/2〈0 1 1〉 dislocations entering from γ channels. The possible driving forces for the movement of these a〈0 1 0〉 dislocations are discussed, and a novel recovery mechanism during creep of rafted microstructures is introduced on the basis of these observations.     

Strengthening gold thin films with zirconia nanoparticles for MEMS electrical contacts

Thin gold films can be strengthened by the incorporation, during reactive sputtering, of nanosized dispersions of monoclinic zirconia. Micron-thick films containing ∼2 vol.% zirconia particles having a particle size of 1–3 nm are found to have an indentation hardness of 3.8 GPa after annealing for 60 h at 500 °C in air. Sputtered gold films of the same thickness and annealed under the same conditions had a hardness of 2.3 GPa. The nanoparticles of zirconia resist coarsening with no change in diameter between deposition and after 60 h at 500 °C. They also suppress grain growth of the gold grains. The electrical resistivity of the strengthened gold films was 4.5 μΩ cm, about 55% higher than gold films. The temperature coefficient of resistivity was unaffected.     

Texture memory and variant selection during phase transformation of a zirconium alloy

The texture evolution of cold-rolled Zircaloy-2 sheets during the α → β → α phase transformation was characterized in situ using high-energy synchrotron X-ray diffraction. It was found that the strong rolling texture is initially modified during heating, evidencing recrystallization, after which it is weakened by a complete phase transformation. Hardly any variant selection was observed during α → β phase transformation. When the material was rapidly cooled back from above the β-transus, the α texture exhibited moderated variant selection. In a study of the effect of maximum heating temperature on the inherited α texture, it was found that incomplete transformations, even with peak temperatures nearing the β-transus, resulted in a perfect texture memory in spite of dramatic morphological changes in the microstructure.     

On-machine dry electric discharge truing of diamond wheels for micro-structured surfaces grinding

Precision grinding with diamond wheels gives a promising alternative to achieve high quality micro-structured surfaces on optical molds. However, it is difficult to true these diamond wheels efficiently, because of the remarkable resistance property and the geometrical limitation of small wheel profile. In this paper, an on-machine dry-EDT method to precision shape and prepare diamond wheels with various profiles was proposed for micro-structured surface grinding. Firstly, the fundamental truing errors were analyzed based on the dry-EDT kinematics. And then the capabilities of dry-EDT truing for high abrasive concentration metal bonded diamond wheels were presented. Next, the effects of kinematic parameters variables on trued wheel profile accuracy were investigated. Finally, the micro-structured surfaces on SiC ceramic and tungsten carbide WC were ground by these trued diamond wheels. The experiments results showed that the arc-shaped diamond wheel (diameter of 200 mm) with 4 μm profile error (PV) and 1.0023 mm profile radius, and the V-shaped diamond wheel with 22.5 μm V-tip radius and 120.03° profile angle could be obtained by on-machine dry EDT. The kinematic parameters of dry-EDT have an important influence on truing profile accuracy of diamond wheels, especially for the tip of V-shaped wheel. The subsequent grinding show that the edge radius of V groove array on SiC is less than 2 μm, while the radius of included corner is around 55 μm. The PV error of ground arc groove array on WC is less than 5 μm. The surface roughness of ground micro-structured surface R_a is 142 nm and 97 nm for SiC and WC, respectively.