Flexural and low-cycle fatigue behavior of atmospheric ice

Accretion of atmospheric ice on power transmission lines may have detrimental effects, sometimes with major socio-economical consequences. The mechanical behavior of this type of ice as an important aspect in the understanding of that issue is still unclear. In the present study, more than 70 tests were conducted using cantilever beams under gradually increasing cyclic load to measure the bending strength of various types of atmospheric ice. Atmospheric ice was accumulated in a closed-loop wind tunnel at −6, −10, and −20 °C, with a liquid water content of 2.5 g m⁻³. Ice samples accumulated at each temperature level were tested at the accumulation temperature, but the ice accumulated at −10 °C was also tested at −3 and −20 °C. Compared to the bending strength results for atmospheric ice under static load, the ice showed less resistance against fracture under cyclic load. It was also revealed that bending strength of atmospheric ice decreases with the test temperature. Another 60 samples of atmospheric ice were also tested under cyclic loads with constant amplitude. The tests revealed that the samples of atmospheric ice accumulated at −10 and −6 °C do not fail under stresses less than 1 MPa after 2000 cycles. At stress levels close to the bending strength of atmospheric ice, however, sometimes the specimen fails after a few hundred cycles. In comparison with the ice accumulated at −10 and −6 °C, atmospheric ice accumulated at −20 °C fails at stresses less than its bending strength. This can be attributed to the colder test temperature and the presence of cavities and cracks in this ice that reduce its bending strength during cyclic stresses.

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The freeze-bond strength in first-year ice ridges. Small-scale field and laboratory experiments

The strength of freeze-bonds in-between blocks in first-year ridges has been investigated through field and laboratory tests. A series of small scale field tests with submerged ice blocks were carried out in Adventfjorden on Svalbard in March–April 2005. An opening was made in the landfast level ice and the ice was sawed into cubes with dimensions of 0.24 m. Some of the cubes were cut in two parts and then frozen together to simulate freeze bonds between the ice blocks. The other blocks were submerged without forming adfreeze bonds. In addition to that, laboratory tests with both laboratory made layered (fresh- and seawater) and sea ice were conducted in February–April 2006 at UNIS. The strength of the freeze bonds, the strength of the submerged ice blocks and their changes with time of submerging, confining pressure, block size and physical properties of ice were investigated. The average strength of freeze bonds was found to be 0.032 ± 0.018 MPa after 48 h of being submerged in the field. The corresponding values from the laboratory tests were 0.067 ± 0.052 MPa for the sea ice testing and 0.274 ± 0.142 MPa for the laboratory made layered freshwater ice up to 60 h of being submerged. The initial physical properties of ice, the confining pressure applied to the ice pieces before and during submerging together with the size of the ice blocks are the main parameters that affect the freeze bond strength.     

High temperature deformation behavior of a near alpha Ti600 titanium alloy

The high temperature deformation behavior of a near alpha Ti600 titanium alloy was investigated with isothermal compression tests at temperatures ranging from 800 to 1000 °C and strain rates ranging from 0.001 to 10.0 s⁻¹. The apparent activation energy of deformation was calculated to be 620.0 kJ mol⁻¹, and constitutive equation that described the flow stress as a function of the strain rate and deformation temperature was proposed for high temperature deformation of Ti600 titanium alloy in the α + β phase region. The processing map was calculated to evaluate the efficiency of the forging process in the temperatures and strain rates investigated and to recognize the instability regimes. High efficiency values of power dissipation over 55% obtained under the conditions of strain rate lower than 0.01 s⁻¹ and temperature about 920 °C was identified to represent superplastic deformation in this region. Plasticity instability was expected in the regime of strain rate higher than 1 s⁻¹ and the entire temperature range investigated.     

Mechanical properties of 3D fiber reinforced C/SiC composites

High toughness and reliable three dimensional textile carbon fiber reinforced silicon carbide composites were fabricated by chemical vapor infiltration. Mechanical properties of the composite materials were investigated under bending, shear, and impact loading. The density of the composites was 2.0–2.1 g cm⁻³ after the three dimensional carbon preform was infiltrated for 30 h. The values of flexural strength were 441 MPa at room temperature, 450 MPa at 1300°C, and 447 MPa at 1600°C. At elevated temperatures (1300 and 1600°C), the failure behavior of the composites became some brittle because of the strong interfacial bonding caused by the mis-match of thermal expansion coefficients between fiber and matrix. The shear strength was 30.5 MPa. The fracture toughness and work of fracture were as high as 20.3 MPa m^1/2 and 12.0 kJ·m⁻², respectively. The composites exhibited excellent uniformity of strength and the Weibull modulus, m, was 23.3. The value of dynamic fracture toughness was 62 kJ·m⁻² measured by Charpy impact tests.     

Effect of strain rate on the tensile behavior of a single crystal nickel-base superalloy

The effect of various strain rates on the tensile behavior of a single crystal nickel-base superalloy was studied. Single crystals with 0 0 1 crystal orientation were tested at 800 and 1000 °C under three kinds of strain rate of 10⁻³, 10⁻⁴ and 6 × 10⁻⁵ s⁻¹. The yield strength increased with the increase of strain rate, while the configuration of the stress–strain curves was independent of strain rate. Additionally, fracture surface was related to strain rate at two temperatures. At 800 °C the amount of cleavage surface was different at three strain rates, which resulted from the difference of activated slip systems. The elongation increased with the decrease of strain rate, which was influenced by the heterogeneous ductile deformation. At 1000 °C the difference of fracture surface was attributed to the microvoid at higher strain rate, while the γ/γ′ interfaces also played an important role at lower strain rate; elongation rate was independent of strain rate.     

Deformation behavior of two Mg alloys during ring hoop tension testing

Ring hoop tension testing (RHTT) was performed on circumferential samples taken from two Mg-based (+Al, Zn, Mn) alloy tubes. Two initial strain rates, 0.001 and 0.1 s⁻¹, were used during these tests. The experiments were conducted at temperatures from ambient to 300 °C. The microstructural evolution during deformation was examined by optical microscopy and electron backscattered diffraction (EBSD) techniques. At moderate temperatures and/or high strain rates, the accompanying c-axis strains were mainly accommodated by twin formation. Contraction twins were formed in grains containing radial basal poles and extension twins in those with circumferential basal poles. At temperatures above 200 °C and the lower strain rate (0.001 s⁻¹), the formation of voids in the partially dynamically recrystallized regions caused premature fracture. The unusual types of twinning behavior displayed under these conditions are responsible for the ductility and work hardening differences observed when the present results are compared with those of previous tension tests carried out along the longitudinal direction.     

Lightweight polyethylene non-woven felts for ballistic impact applications: Material characterization

The polyethylene non-woven felt, Dyneema Fraglight, has excellent capabilities to stop bomb fragments. According to the manufacturer, a felt with an areal density of 1.2 kg/m² stops a 17-grain projectile at 450 m/s. The research presented in this paper aims at improving our understanding of how non-woven felts work. Static tensile tests were performed at different strain rates and temperatures. The static tensile tests showed that there is an important size effect: the strength of the specimens decreases when increasing the size of the specimen, for lengths of 5 cm or less. This effect is expected since the felt is made by mixing, combing and needle punching of 5-cm-long fibers. The tests also showed that the felt is anisotropic and that at a temperature of 100 °C it loses a significant part of both its strength and strain to failure. Tensile tests at medium (1 s⁻¹) and high strain rates (1000 s⁻¹) did not show any evidence of strain rate dependence. Out-of-plane punching tests, designed to help with the modeling, were also performed and the results are presented.     

Structural, electrochemical and optical comparisons of tungsten oxide coatings derived from tungsten powder-based sols

Tungsten trioxide (WO₃) electrochromic coatings have been formed on indium tin oxide-coated glass substrates by aqueous routes. Coating sols are obtained by dissolving tungsten powder in acetylated (APTA) or plain peroxotungstic acid (PTA) solutions. The structural evolution and electrochromic performance of the coatings as a function of calcination temperature (250 °C and 400 °C) have been reported. Differential scanning calorimetry and X-ray diffraction have shown that amorphous WO₃ films are formed after calcination at 250 °C for both processing routes; however, the coatings that calcined at 400 °C were crystalline in both cases. The calcination temperature-dependent crystallinity of the coatings results in differences in optical properties of the coatings. Higher coloration efficiencies can be achieved with amorphous coatings than could be seen in the crystalline coatings. The transmittance values (at 800 nm) in the colored state are 35% and 56% for 250 °C and 400 °C-calcined coatings, respectively. The electrochemical properties are more significantly influenced by the method of sol preparation. The ion storage capacities designating the electrochemical properties are found in the range of 1.62–2.74 × 10^− 3 (mC cm^− 2) for APTA coatings; and 0.35–1.62 × 10^− 3 (mC cm^− 2) for PTA coatings. As a result, a correlation between the microstructure and the electrochromic performance has been established.     

Research on the hot deformation behavior and graphite morphology of spheroidal graphite cast iron at high strain rate

The hot deformation behavior of spheroidal graphite cast iron (SGCI) was investigated quantitatively from 600 °C to 950 °C at high strain rate of 10 s⁻¹ by compression tests on a Gleeble-1500 simulator. The results show that the peak strain increases gradually with increasing deformation temperatures in the range of 600–800 °C and decreases when the temperature is raised to 800 °C and above. The optimum deformation temperature range is determined at 700–900 °C. The graphite particles become spindles or flakes after deformation, even some graphite collapse in the compressed specimens with about 0.7 peak strains. The graphite area fraction decreases as the temperature increases, at the same time, the high peak strain promotes the dissolving of carbon.     

Solid phase epitaxy on N-type polysilicon films formed by aluminium induced crystallization of amorphous silicon

In this work, undoped amorphous silicon layers were deposited on n-type AIC seed films and then annealed at different temperatures for epitaxial growth. The epitaxy was carried out using halogen lamps (rapid thermal process or RTP) or a tube conventional furnace (CTP). We investigated the morphology of the resulting 2 µm thick epi-layers by means of optical microscopy. An average grain size of about 40 µm is formed after 90 s annealing at 1000 °C in RTP. The stress and degree of crystallinity of the epi-layers were studied by micro-Raman Spectroscopy and UV–visible spectrometer as a function of annealing time. The presence of compressive stress is observed from the peak position which shifts from 520.0 cm^− 1 to 521.0 cm^− 1 and 522.3 cm^− 1 after CTP annealing for 10 min and 90 min, respectively. It is shown that the full width at half maximum (FWHM) varies from 9.8 cm^− 1 to 15.6 cm^− 1, and the magnitude of stress is changing from 325 MPa to 650 MPa. Finally, the highest crystallinity is achieved after annealing at 1000 °C for 90 min in a tube furnace exhibiting a crystalline fraction of 81.5%. X-ray diffraction technique was used to determine the preferential orientation of the poly-Si thin films formed by SPE technique on n⁺ type AIC layer. The preferential orientation is 100 for all annealing times at 1000 °C.     

Electrical and optical properties of 12CaO·7Al2O3 electride doped indium tin oxide thin film deposited by RF magnetron co-sputtering

12CaO·7Al₂O₃ electride (C12A7:e⁻) doped indium tin oxide (ITO) (ITO:C12A7:e⁻) thin films were fabricated on a glass substrate by an RF magnetron co-sputtering system with increasing number of C12A7:e⁻ chips (from 1 to 7) and at various oxygen partial pressure ratios. The optical transmittance of the ITO:C12A7:e⁻ thin film was higher than 70% in the visible wavelength region. In the electrical properties of the thin film, a decrease of the carrier concentration from 2.6 × 10²⁰ cm^− 3 to 2.1 × 10¹⁸ cm^− 3 and increase of the resistivity from 1.4 × 10^− 3 Ω cm to 4.1 × 10^− 1 Ω cm were observed with increasing number of C12A7:e⁻ chips and oxygen partial pressure ratios. It was also observed that the Hall mobility was decreased from 17.27 cm²·V^− 1·s^− 1 to 5.13 cm²·V^− 1·s^− 1. The work function of the ITO thin film was reduced by doping it with C12A7:e⁻.     

Three-dimensional measurement of ice crystals in frozen beef with a micro-slicer image processing system

A novel technique has been developed for measuring the three-dimensional (3-D) structure and distribution of ice crystals formed in frozen beef by using a micro-slicer image processing system (MSIPS). The system has functions to reconstruct the 3-D image based on the image data of exposed cross-sections obtained by multi-slicing of a frozen sample with the minimum thickness of 1 μm and to display the internal structure as well as an arbitrary cross-section of the sample choosing observation angles. The size and distribution of ice crystals can be determined from the 2-D quantitative information, such as the periphery and area of the crystals. The effects of freezing conditions on the morphology and distribution of the ice crystals were demonstrated quantitatively from the observations of raw beef stained by fluorescent indicator. For the samples frozen at −15 °C, the network structure of ice crystals were observed mainly at intercellular space, having approximately 100 μm in cross-sectional size, while that prepared at −120 °C showed the spherical crystals of 10–20 μm in diameter within the cells. The 3-D image of the sample demonstrated that the growth of ice columns was restricted by the intrinsic structure of muscle fibers. The proposed method provided a new tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.     

Three-dimensional measurement of ice crystals in frozen dilute solution

A Micro-Slicer Image Processing System (MSIPS) has been applied to observe the ice crystal structures formed in frozen dilute solutions. Several characteristic parameters were also proposed to investigate the three-dimensional (3-D) morphology and distribution of ice crystals, based on their reconstructed images obtained by multi-slicing a frozen sample with the thickness of 5 μm. The values of characteristic parameters were determined for the sample images with the dimension of 530×700×1000 μm. The 3-D morphology of ice crystals was found to be a bundle of continuous or dendrite columns at any freezing condition. The equivalent diameter of ice crystals were in the range of 73–169 μm, and decreased exponentially with increasing freezing rate at the copper cooling plate temperature of −20 to −80 °C. At the T_cp −40 °C, the volumes of ice crystals were in the range of 4.6×10⁴ μm³ to 3.3×10⁷ μm³, and 36 ice columns were counted in the 3-D image.     

Strength distributions of warm frozen clay and its stochastic damage constitutive model

There are many defects, such as fissures and cavities, in warm frozen clay and in warm ice-rich frozen clay. These defects are distributed randomly, which make some mechanical properties of these clays exhibit great uncertainty. Thus it is unreasonable to take some deterministic values as the mechanics parameters of these frozen clays. Furthermore, warm frozen clay and warm ice-rich frozen clay are less stable than clays at colder temperatures. Therefore, it is necessary to determine the strength and constitutive relationship of these clays using probabilistic methods. In this paper, based on the characteristics of the random distribution of defects in the warm frozen clay and warm ice-rich frozen clay, the strength distribution laws for both clays are investigated at − 0.5 °C, − 1.0 °C and − 2.0 °C through a series of experimental data, respectively. The investigated results show that the Weibull distribution can more closely reflect the strength distribution law than other probability distributions. Based on the results mentioned above, a stochastic damage model for the warm frozen clay and warm ice-rich frozen clay was developed using the continuous damage theory and probability, as well as statistic theory. Comparing theoretical results of the model with experimental data at these three temperatures, respectively, it is found that the stress-strain relationships of the two kinds of frozen clays, especially their deformation characteristics after failures, could be described by the model very well. Since the range of strength variation for both kinds of frozen clays is very large, it is unsafe and unreasonable for engineering design to use the average strengths of frozen clay soils. The reliability of the strength of these two clays was investigated and discussed on the basis of the fact that the strength of warm frozen clay and warm ice-rich frozen clay satisfy the Weibull distribution.     

Effect of temperature and strain rate on tensile behavior of ultrafine-grained aluminum alloys

Ultrafine-grained Al–4Y–4Ni and Al–4Y–4Ni–0.9Fe (at.%) alloys were synthesized by the consolidation of atomized powders and subsequent hot extrusion. The mechanical behavior of these two alloys has been studied by performing uniaxial tension tests ranging from room temperature to 350 °C. These alloys, with high volume fraction of second-phase particles, exhibited ambient temperature tensile strength ranging from 473 to 608 MPa and plastic elongation ranging from 6.7 to 9.6% at an initial strain rate of 1 × 10⁻³ s⁻¹. However, lower ductility was observed with decreasing strain rate at the intermediate temperature ranging from 150 to 250 °C for Al–Y–Ni–Fe alloys due to limited work hardening.     

The influence of dynamic strain aging on the low cycle fatigue behavior of near alpha titanium alloy IMI 834

Total strain controlled low cycle fatigue tests on IMI 834 have been conducted in air in the temperature range between 375 and 500 °C at a temperature interval of 25 °C at the nominal strain rate of 6.67 × 10⁻⁴ s⁻¹. The observed maximum peak stress ratio, minimum half-life plastic strain range and lower fatigue life at 425 °C indicates the occurrence of dynamic strain aging (DSA). Pronounced deformation bands, increased dislocation density and non-uniform dispersion of dislocations inside primary α grains observed by the study of transmission electron microscopy supports the occurrence of dynamic strain aging. Initial cyclic softening was attributed to shearing of Ti₃Al precipitates as revealed by TEM evidences.     

Investigation of the physical and chemical parameters affecting biodegradation of diesel and synthetic diesel fuel contaminating Alaskan soils

In cold regions, biodegradation of fuel spills can take a prolonged period of time. Conventional fuels and crude oil contain contaminants such as aromatics and PAH which can pose risks to humans and the environment. The goal of the present study was therefore to investigate the biological degradation of an alternative synthetic fuel, Syntroleum, which is less toxic and, as shown in this study, more easily biodegradable than conventional diesel fuel. Use of alternative fuels such as Syntroleum would be especially beneficial in sensitive regions where spills of conventional fuel are highly undesirable. Gravel and sand from Interior Alaska were spiked with diesel and synthetic diesel fuel (arctic-grade Syntroleum). After adding an inoculum, samples were incubated in the laboratory at different temperatures (6 °C and 20 °C), contamination levels (2000 mg and 4000 mg of fuel/kg dry soil), nutrient dosages (300 mg N/kg soil and 0 mg N/kg soil) and moisture contents (2%, 4%, 8% and 12% gravimetric water content). The objective of this research was to investigate the effect of physical and chemical environmental conditions on the biodegradability of contaminants and to determine optimal conditions for biodegradation by indigenous microorganisms. The respiration rate (CO₂ production) was measured as an indicator of microbial activity and mineralization of contaminants, and complemented by analysis for hydrocarbons at the end of the experiment by gas chromatography/mass spectrometry. Both fuel types were biodegraded, with up to 75% mineralization after 17 weeks. The faster degradation rate was achieved in Syntroleum-contaminated soils with a degradation-rate constant of 0.0064–0.0106 d^− 1 at 20 °C. At 6 °C, diesel fuel showed minimal degradation during several short-term studies (4–6 weeks), less than 5% total mineralization of the hydrocarbons in the fuel. The average degradation-rate constant for Syntroleum at 6 °C was 0.0016 d^− 1 during a 4-week study, while the degradation-rate constants became much higher (0.0045–0.005 d^− 1) for the long-term experiments (12–17 weeks), resulting in significant mineralization of total carbon present. The different moisture contents in the sandy soil showed no significant impact on respiration. The addition of fertilizer was essential to achieve good degradation rates. After the end of the 17-week experiment, the recovered contaminant was approximately 50% less in the case of Syntroleum when nutrients were added to the soil as compared with nutrient-deficient conditions. Respiration rates were higher in sand than in gravel, which may be due to differences in soil porosity and the available surface area for more even hydrocarbon distribution. Degradation rates varied significantly over time. A first-order model, which used different rate constants for three growth phases, was able to model cumulative carbon dioxide production quite well over a period of four months. In the carbon mass balance, the sum of the diesel range organics recovered from the soil plus the produced carbon dioxide accounted for approximately 30–85%. The remaining amount of carbon either was incorporated into biomass, degraded incompletely, or evaporated.     

Application of hydrocarbon mixtures in small refrigerating and cryogenic machines

Application of hydrocarbon mixtures enables the creation of simple, reliable and durable refrigerating and cryogenic Joule–Thomson micro coolers for the temperature range of −73 to −183 °C. The temperature, thermal, power and hydraulic performances of a series of prototypes are presented. The results of tests demonstrate that small, single stage, sealed, lubricated compressors can be applied to these purposes. The start up and steady operation hydraulic performance of those machines are quite similar to the performance of domestic refrigerators. The last, together with the fact that in the studied micro coolers the lubricated compressors are used at temperatures down to −183 °C, ensures a large resource of operation. That is just the reason that holds out a hope for prospects in a broad field of applications for the studied prototypes, despite their lower power performances in contrast to gas micro coolers.     

Hot deformation behavior of SiCp/AZ91 magnesium matrix composite fabricated by stir casting

The uniaxial compressive deformation behavior of a 10 vol.% SiC particulate reinforced AZ91 magnesium matrix composite (SiCp/AZ91) fabricated by stir casting is investigated at elevated temperature (250–400 °C). Peak stresses and flow stresses decrease as temperatures increase and strain rates decrease. The extent of dynamic recrystallization (DRX) becomes less as temperatures decrease at 250–350 °C or strain rates increase, and recrystallization occurs mainly within the intergranular regions rich of particles. Dynamic recrystallization accomplishes at 400 °C even at the strain rate of 1 s⁻¹. An analysis of the effective stress dependence on strain rate and temperature gives a stress exponent of n = 5 and a true activation energy of Q = 99 kJ/kJ. The value of Q is close to the value for grain boundary diffusion in Mg. It is concluded that the deformation mechanism of SiCp/AZ91 composite during hot compression is controlled by the dislocation climb.     

New powellite type oxides in Ca–R–Nb–Mo–O system (R = Y, La, Nd, Sm or Bi)—Their synthesis, structure and dielectric properties

New complex oxides having powellite (CaMoO₄) type structure in the Ca–R–Nb–Mo–O system (R = Y, La, Nd, Sm or Bi) were prepared employing the method of solid state reaction between the component oxides at high temperature (1000–1100 °C). The new compounds, CaRNbMoO₈ (R = Y, La, Nd, Sm, Bi) are colorless and electrical insulators. The dielectric constants (K at 1 MHz) of these compounds are in the range 14–33 and K shows very little variation in the temperature range 30–100 °C. Their temperature coefficient of dielectric constant (TCK) is negative, which varies from − 21 to − 220 ppm/°C.