Mechanical Properties of First-Year Sea Ice at Tarsiut Island

This paper deals with the interpretation of small-scale first-year sea ice strength and property test data collected in 1982 during several field trips at Tarsiut Island N-44 location in the Canadian Beaufort Sea. Measurements of flexural, horizontal, and vertical uniaxial compressive and confined plane strain and borehole jack strengths are presented. Mathematical relationships representing the variation of these mechanical properties with temperature; salinity; strain and stress rates; and crystal structure (depth) are analyzed. Uniaxial unconfined compressive strength data of horizontal sea ice samples are compared with triaxially confined borehole jack strength data. Flexural strength data obtained from laboratory tests are compared with full-thickness cantilever beam tests performed in the field. The measured flexural strength of first-year sea ice is also provided in a statistical format. The apparent elastic modulus of sea ice is presented as a function of salinity and temperature.     

Field-Scale In-Situ Compliance of Arctic First-Year Sea Ice

This paper presents the experimental results and analysis of the creep recovery and cyclic loading crack-opening-displacement measurements recorded on level first-year sea ice at Barrow, Alaska. This was the third of a three-trip program to track the seasonal evolution of the mechanical and physical properties of first-year S2 sea ice. Seven large-scale in-situ experiments were completed covering a size range of 1:30 with the largest test having dimensions of 30 m × 30 m. The creep recovery response from the largest test specimen is examined in this paper to determine the compliance of a precracked square-plate test geometry via a nonlinear viscoelastic∕viscoplastic formulation. This model is then applied to the cyclic loading, and a monotonic ramp to fracture, to quantify its ability to predict the behavior for a variety of loading paths.     

Evolution of crystallographic alignment in Tb-Fe-B melt-spun ribbons

Ternary Tb-Fe-B ribbons were prepared via melt-spun technique under different wheel speeds of 5-25 m/s.Effect of wheel speed on the crystal structure and microstructure of the ribbons was investigated.All the ribbons quenched under different wheel speeds crystallized in single Tb2Fe14B phase with tetragon structure.Different crystallographic alignment evolutions were observed in the free side surface and wheel side surface of the ribbons.On the free-side surface,an in-plane c-axis crystal texture of Tb2Fe14B phase was found in the ribbons quenched at 5 m/s.However,with the increase in the wheel speed,the direction of the c-axis texture turns to perpendicular to the ribbon surface.On the wheel-side surface,a strong c-axis texture perpendicular to the ribbon surface was observed in the ribbons quenched at 5 m/s,and then weakened gradually with the increase in the wheel speed.Further investigation showed that the competition of the two types of temperature gradients during the quench process was responsible for the crystallographic alignment evolution in the ribbons.     

Fatigue and fracture behavior of a fine-grained lamellar TiAl alloy

The fatigue and fracture resistance of a TiAl alloy, Ti-47Al-2Nb-2Cr, with 0.2 at. pct boron addition was studied by performing tensile, fracture toughness, and fatigue crack growth tests. The material was heat treated to exhibit a fine-grained, fully lamellar microstructure with approximately 150-μm grain size and 1-μm lamellae spacing. Conventional tensile tests were conducted as a function of temperature to define the brittle-to-ductile transition temperature (BDTT), while fracture and fatigue tests were performed at 25 °C and 815 °C. Fracture toughness tests were performed inside a scanning electron microscope (SEM) equipped with a high-temperature loading stage, as well as using ASTM standard techniques. Fatigue crack growth of large and small cracks was studied in air using conventional methods and by testing inside the SEM. Fatigue and fracture mechanisms in the fine-grained, fully lamellar microstructure were identified and correlated with the corresponding properties. The results showed that the lamellar TiAl alloy exhibited moderate fracture toughness and fatigue crack growth resistance, despite low tensile ductility. The sources of ductility, fracture toughness, and fatigue resistance were identified and related to pertinent microstructural variables.     

Evolution of crystallographic alignment in Tb-Fe-B melt-spun ribbons

Ternary Tb-Fe-B ribbons were prepared via melt-spun technique under different wheel speeds of 5-25 m/s. Effect of wheel speed on the crystal structure and microstructure of the ribbons was investigated. All the ribbons quenched under different wheel speeds crystallized in single Tb₂Fe₁₄B phase with tetragon structure. Different crystallographic alignment evolutions were observed in the free side surface and wheel side surface of the ribbons. On the free-side surface, an in-plane c-axis crystal texture of Tb₂Fe₁₄B phase was found in the ribbons quenched at 5 m/s. However, with the increase in the wheel speed, the direction of the c-axis texture turns to perpendicular to the ribbon surface. On the wheel-side surface, a strong c-axis texture perpendicular to the ribbon surface was observed in the ribbons quenched at 5 m/s, and then weakened gradually with the increase in the wheel speed. Further investigation showed that the competition of the two types of temperature gradients during the quench process was responsible for the crystallographic alignment evolution in the ribbons.     

Dynamic deformation and fracture behaviors of two Zr-based amorphous alloys

Dynamic deformation and fracture behaviors of Zr-based amorphous alloys were investigated in this study. Quasi-static and dynamic compressive tests were conducted using a universal testing machine and a compressive Kolsky bar, respectively, and then the test data were analyzed in relation to microstructure and fracture mode. Quasi-static compressive test results indicated that the compressive strength of the amorphous alloy containing dendritic β phases was similar to that of the amorphous alloy, while the ductility was better. Under dynamic loading, the maximum shear stress and ductility of the amorphous alloys were considerably lower than those under quasi-static loading because of the decreased resistance to fracture. The deformation and fracture behaviors occurring under quasi-static and dynamic loading conditions were explained by fracture mechanisms observed on fractured surfaces.     

In situ Sea Ice Experiments in McMurdo Sound: Cyclic Loading, Fracture, and Acoustic Emissions

The breakup of first-year sea ice plays an important role in the dynamics and thermodynamics of polar ice covers. A recent research program has studied the in situ mechanical properties of the annual ice in Antarctica to support the development of physically based models of the breakup process. As part of this effort, two field trips were conducted to McMurdo Sound, and the present paper describes the experimental work and presents selected results. The in situ experiments investigated the constitutive and fracture behavior of edge-notched, square plate specimens of first-year ice and involved a detailed characterization of the physical properties and thermal state of the ice. Acoustic emissions, which are generated by microcracking, were monitored in the crack tip vicinity and provide insight regarding the size of the process zone. The paper describes the physical properties and microstructure of the sheet, the cyclic-loading response, and the acoustic emissions activity from an extensive series of experiments conducted on one of the in situ specimens. Varying the cyclic-loading frequency and amplitude provided a means to examine rate effects on the anelastic and viscous components of strain and the extent of microcracking near the crack tip. The viscous deformation rate estimated from the experiments exhibited an increasing power-law exponent with values between one and three. Acoustic emissions monitoring indicated that microcracking occurred in a process zone near the crack tip, and the size of the process zone increased with decreasing cyclic loading frequency. Practical aspects of the experiments are considered, and the results are put into context with the overall modeling goals of the project.     

降低氰化钠消耗的研究

本文就我国现行的氰化法提金工艺中普遍存在的NaCN消耗过高的问题,在小型试验的基础上,经过理论研究,在大型生产中得到成功的应用,降低了NaCN消耗,创造的经济效益可观。     

Hydraulic Conductivity of MSW in Landfills

This paper presents a laboratory investigation of hydraulic conductivity of municipal solid waste (MSW) in landfills and provides a comparative assessment of measured hydraulic conductivity values with those reported in the literature based on laboratory and field studies. A series of laboratory tests was conducted using shredded fresh and landfilled MSW from the Orchard Hills landfill (Illinois, United States) using two different small-scale and large-scale rigid-wall permeameters and a small-scale triaxial permeameter. Fresh waste was collected from the working phase, while the landfilled waste was exhumed from a borehole in a landfill cell subjected to leachate recirculation for approximately 1.5 years. The hydraulic conductivity tests conducted on fresh MSW using small-scale rigid-wall permeameter resulted in a range of hydraulic conductivity 2.8×10?3–11.8×10?3?cm/s with dry unit weight varied in a narrow range between 3.9–5.1?kN/m3. The landfilled MSW tested using the same permeameter produced results between 0.6×10?3–3.0×10?3?cm/s for 4.5–5.5?kN/m3 dry unit weights. The hydraulic conductivity obtained from large-scale rigid-wall permeameter tests decreased with the increase in normal stress for both fresh and landfilled waste. The hydraulic conductivity for fresh MSW ranged from 0.2 cm/s for 4.1?kN/m3 dry unit weight (under zero vertical stress) and then decreased to 4.9×10?5?cm/s for 13.3?kN/m3 dry unit weight (under the maximum applied normal stress of 276 kPa). The hydraulic conductivity of the landfilled MSW decreased from 0.2 cm/s to 7.8×10?5?cm/s when the dry unit weight increased from 3.2 to 9.6?kN/m3. The results clearly demonstrated that the hydraulic conductivity of MSW can be significantly influenced by vertical stress and it is mainly attributed to the increase in density leading to low void ratio. In small-scale triaxial permeameter, when the confining pressure was increased from 69 to 276 kPa the hydraulic conductivity decreased from approximately 10?4?to?10?6?cm/s, which is much lower than those determined from rigid-wall permeameter tests. The published field MSW hydraulic conductivities are found to be higher than the laboratory results. Landfilled MSW possesses lower hydraulic conductivity than fresh MSW due to increased finer particles resulting from degradation. The decreasing hydraulic conductivity with increasing dry unit weight is expressed by an exponential decay function.     

Effects of Long-Term Dynamic Loading and Fluctuating Water Table on Helical Anchor Performance for Small Wind Tower Foundations

The application of this study is to use helical anchors as a foundation system for small wind tower (1–10?kW) guyed cables. Helical anchors are currently used to anchor guyed cables of cell or transmission towers. However, the increased dynamic vibrations a wind turbine adds to the tower and foundation system under working loads, as well as extreme environmental conditions (e.g., straight line winds, ice load, or sudden furling shocks), require additional knowledge about the behavior of helical anchors. These field conditions were simulated in this study from tower-instrumented field data on wind speed and tower response. These tower responses were then transmitted to the helical anchors through an extensive, large-scale testing program that included monitoring the performance of the helical anchor foundation under dynamic loads, subject to natural variations in both wind regimes, precipitation (water level) and variations in helical anchor geometry. This paper compares the uplift prediction methods used in helical anchor design as well as discusses the effects of long-term dynamic loading and fluctuating water table on helical anchor performance.     

Influence of microstructure on crack-tip micromechanics and fracture behaviors of a two-phase TiAl alloy

The tensile deformation, crack-tip micromechanics, and fracture behaviors of a two-phase (γ + α₂) gamma titanium aluminide alloy, Ti-47Al-2.6Nb-2(Cr+V), heat-treated for the microstructure of either fine duplex (gamma + lamellar) or predominantly lamellar microstructure were studied in the 25 °C to 800 °C range.In situ tensile and fracture toughness tests were performed in vacuum using a high-temperature loading stage in a scanning electron microscope (SEM), while conventional tensile tests were performed in air. The results revealed strong influences of microstructure on the crack-tip deformation, quasi-static crack growth, and the fracture initiation behaviors in the alloy. Intergranular fracture and cleavage were the dominant fracture mechanisms in the duplex microstructure material, whose fracture remained brittle at temperatures up to 600 °C. In contrast, the nearly fully lamellar microstructure resulted in a relatively high crack growth resistance in the 25 °C to 800 °C range, with interface delamination, translamellar fracture, and decohesion of colony boundaries being the main fracture processes. The higher fracture resistance exhibited by the lamellar microstructure can be attributed, at least partly, to toughening by shear ligaments formed as the result of mismatched crack planes in the process zone.     

Electrochemical evaluation of a corrosion fatigue failure mechanism in a duplex stainless steel

Laboratory corrosion fatigue studies on smooth and precracked samples indicated that two duplex stainless steels would have similar service lives in a paper-processing environment; but, in service, one of these alloys has exhibited premature failures. Since corrosion fatigue experiments had proven unable to detect this failure mechanism, electrochemical measurements and slow strain rate tensile tests were used to evaluate four alloy composition-dependent failure mechanism hypotheses. No significant differences were found in the dissolution rates or hydrogen fugacities produced when mechanical processes expose bare surface, and slow strain rate tensile tests found no indication of a difference in cracking susceptibility for the same hydrogen fugacity. Electrochemical experiments found that pits nucleate in one phase of the duplex microstructure at lower potentials in the failure prone alloy, but do not propagate beyond the microscopic dimensions of this phase. These microstructurally limited “micropits” were found to nucleate fracture in slow strain rate tensile tests, and examination of a service failure confirmed the presence of microscopic pits at crack initiation sites. The premature failures are attributed to the lower pitting resistance of the failure prone alloy, and the failure of laboratory experiments to predict this behavior is attributed to the slow kinetics of pit nucleation in these experiments. A laboratory testing methodology is suggested that will ensure detection of similar susceptibilities in future corrosion fatigue testing programs.     

Assessing Frost Resistance of Concrete Aggregates in Minnesota

This study was undertaken to identify test procedures capable of reliably assessing concrete aggregate freeze-thaw durability and establish appropriate acceptance criteria for the same. Highway condition surveys were performed to document the field freeze-thaw performance of selected aggregate sources representing a range of frost resistance. Cores were obtained for laboratory testing and evaluation, and samples of the original aggregate sources were obtained for use in performing environmental simulation tests [i.e., variations of ASTM C 666 and the Virginia Polytechnic Institute (VPI) single-cycle slow-freeze test] and correlative tests (e.g., absorption capacity, Iowa pore index test, X-ray diffraction and fluorescence analysis, and hydraulic fracture test). Petrographic examination was used to correlate aggregate geological and engineering properties with the results of environmental and correlative tests. A suite of tests was developed for more accurately assessing the probable field performance of any given aggregate as a function of its original geological origin and probable environmental exposure. Petrographic examination is used first to identify aggregate composition and provide a basis for selecting subsequent durability tests, which may include the hydraulic fracture test, VPI single-cycle slow-freeze test, and ASTM C 666 Procedure B (modified to use salt-treated aggregates).     

Effect of heterogeneous microstructure on magnetization reversal mechanism of hot-deformed Nd-Fe-B magnets

The hot-deformed(HD) Nd-Fe-B magnets show heterogeneous microstructure composed of coarse and fine grain regions. It is significant to fully understand the influence of this complex microstructure on the magnetization reversal process which can give the guidance for the enhancement of the magnetic properties. In this paper, the heterogeneous microstructure of the(HD) Nd-Fe-B magnets were characterized from the morphology, size, macro-texture and micro-structure. In addition, the magnetization reversal process of the HD Nd-Fe-B magnets was systematically analyzed by magnetic measurement, insitu domain evolution observation and micromagnetic simulation. The results indicate that the HD NdFe-B magnets mainly consist of fine grain regions(FGRs) and coarse grain regions(CGRs). The FGRs show plate-like grains with fine grain size and strong c-axis texture, while the CGRs show equiaxial grains with large grain size and weak c-axis texture. In particular, it is worth noting that the texture in homogeneity exists not only between FGRs and CGRs, but also inside both the FGRs and CGRs. The dominant coercivity mechanism of the HD Nd-Fe-B magnets is domain wall pinning. Also, the experimental analysis shows that the reverse domain is formed and expanded in the CGRs at low reverse applied field, while the reverse domain occurs in the FGRs at higher reverse applied field. The micromagnetic simulation results also confirm the above magnetization reversal process. In addition, micromagnetic simulation results also show that the orientation of the grains also affects the pinning strength, besides the grain size.     

Evaluation of Live-Load Lateral Flange Bending Distribution for a Horizontally Curved I-Girder Bridge

This paper focuses on levels of live-load lateral bending moment (bimoment) distribution in a horizontally curved steel I-girder bridge. Work centered primarily on the examination of (1) data from field testing of an in-service horizontally curved steel I-girder bridge and (2) results from a three-dimensional numerical model. Experimental data sets were used for calibration of the numerical model and the calibrated model was then used to examine the accuracy of lateral bending distribution factor equations presented in the 1993 Edition of the (AASHTO) Guide Specifications for Horizontally Curved Bridges. It is of interest to examine these equations for potential use in preliminary design even though they have been eliminated during recent AASHTO specification modifications that addressed curved bridge analysis, the 2005 Interims to the AASHTO LRFD Bridge Design Specifications. In addition, they were developed using idealized computer models and small-scale laboratory testing with very few field tests of in-service full-scale curved steel bridges conducted to support or refute their use. Results from such experimental and numerical studies are presented and discussed herein.     

退火工艺对780 MPa冷轧多相钢组织及性能影响

为了研究退火工艺对780 MPa冷轧多相钢组织及性能影响,采用万能试验机、场发射扫描电镜(SEM)、综合成形试验机及电子探针(EPMA)对两种具有相同成分、抗拉强度均为780 MPa但具有不同屈强比和扩孔性能的多相钢进行了相关研究,结果表明热处理工艺对试验钢组织、力学性能及扩孔性能有着重要影响,采用两相区退火时马氏体岛...     

Investigation of Elongation at Fracture in a High Speed Sheet Metal Forming Process

This paper investigates the dynamic elongation at fracture of conventional steels, advanced high strength steels and nonferrous metals, such as aluminium and magnesium alloys. Dynamic tensile tests were carried out using a high speed material testing machine at various strain rates ranging from 0.001/s to 200/s. The results show that the elongation at fracture of sheet metals does not simply decrease with the increase of the strain rate. The elongation of SPCC, SPRC450R, TRIP600 and AZ31 decreases when the tests are carried out under the quasi‐static state at the strain rate of 0.1/s, but increases again when the tests are carried out at the strain rate of 0.1/s up to the strain rate of 200/s. Furthermore, DP600 and AA7003‐T7 show the tendency that the tensile elongation increases as the strain rate increases. This tendency is related to the microstructure and forming history of the sheet metal. It is concluded that localized strain rate hardening in the necking region induces the enlargement of the necking region and thus the increased elongation. This phenomenon is worth being considered to predict the fracture of sheet metal products in high speed sheet metal forming.     

Behavior of Large-Scale Rectangular Columns Confined with FRP Composites

This paper focuses on axially loaded, large-scale rectangular RC columns confined with fiber-reinforced polymer (FRP) wrapping. Experimental tests are conducted to obtain the stress-strain response and ultimate load for three field-size columns having different aspect ratios and/or corner radii. Effective transverse FRP failure strain and the effect of increasing confining action on the stress-strain behavior are examined. Existing strength models, the majority of which were developed for small-scale specimens, are applied to predict the structural response. Since some of them fail to adequately characterize the test data and others are complex and require significant calculation, a simple design-oriented model is developed. The new model is based on the confinement effectiveness coefficient, an aspect ratio coefficient, and a corner radius coefficient. It accurately predicts the axial ultimate strength of the large-scale columns at hand and, when applied to the small-scale columns studied by other investigators, produces reasonable results.     

Effects of Corrosion of Steel Reinforcement on RC Columns Wrapped with FRP Sheets

This study investigated the effectiveness of carbon fiber-reinforced polymer (CFRP) sheets in protecting reinforced concrete (RC) columns from corrosion of steel reinforcement. Thirty small-scale RC columns and four midscale RC columns were used in this study. The small-scale columns were used for a comprehensive parametric study, whereas the midscale columns were used to evaluate design guidelines proposed based on the results of the small-scale column tests. The test columns were conditioned under an accelerated corrosion process and then tested under uniaxial compression up to failure. The test results showed that although CFRP sheet wrapping decreased the corrosion rate, the corrosion of steel reinforcement could continue to occur, eventually showing a decrease in ultimate axial compression capacity. Design guidelines were proposed based on the small-scale RC column tests and evaluated through a comparison with the test results of midscale RC columns. The proposed design guidelines introduced a concept of effective area to account for the corrosion damage, such as internal cracking and cross-sectional loss of steel reinforcement.     

Ф50mm大规格HRB500钢筋冷弯裂纹组织研究

针对Ф50 mm大规格HRB500钢筋沿横肋根部冷弯裂纹试样,进行化学成分、夹杂物级别、组织特征和断口形貌等检测后发现,钢筋表面树枝状组织是钢筋冷弯开裂的主要原因。热处理试验表明:l 000℃保温50 min,树枝状组织开始均匀化;保温90 min,可以获得F+P为主的均匀组织。通过降低连铸钢水过热度、二冷水冷却强度及控制拉速和轧制节奏、延长加热保温时间等工艺改进措施,能有效改善大规格钢筋边部树枝状组织。