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.     

Core-Based SCB Fracture of Aligned First-Year Sea Ice (Phases III and IV)

This paper provides the results of two small-scale testing programs linked to large-scale field programs carried out by the writers and others. The large-scale in-situ sea ice testing program was part of the Office of Naval Research's (ONR's) Sea Ice Mechanics Initiative (SIMI). Three field trips to Barrow, Alaska, were completed to examine the seasonal evolution of the first-year sea ice growing on Elson Lagoon. Trips were made in November, March, and May, when significant changes in thickness and temperature profile were evident. The experiments were designed to determine the fracture behavior of sea ice in situ and make comparisons with small-scale lab tests. Due to the unique microstructure of the sea ice tested, it was necessary to complete small-scale (0.1 m) tests for comparative purposes. A detailed study of the ice fabric at the site revealed a very strong alignment of the c-axis. This prompted a study of the fracture properties parallel (hard-fail) and perpendicular (easy-fail) to the preferred c-axes orientation plane in both the largeand small-scale tests. The effects of c-axis alignment, temperature and microstructure on the fracture toughness and tensile strength are investigated.     

Bohai Sea Ice Conditions

Oil and gas exploration and production and other maritime activities are rapidly increasing in the Bohai Sea. Since sea ice occurs every winter in this region, it poses serious threats to these activities. The presence of sea ice has caused severe damages to offshore structures and losses of production in this region. Sea ice is an important marine environmental factor to be considered in the planning, design, and construction of offshore structures in the Bohai Sea and northern Yellow Sea. This paper gives an overview of ice conditions in the Bohai Sea and the northern Yellow Sea.     

Modeling and Forecasting of Bohai Sea Ice

The sea ice model for simulating ice growth, decay, and drift in the Bohai Sea was developed based on the ice conditions in the Sea and on existing sea ice models. Both dynamic and thermodynamic processes of sea ice are incorporated into the model. The viscous-plastic constitutive law is applied to estimate the internal ice stress. The thermodynamic growth rates are determined from the effect of thermodynamic forcing from atmosphere and ocean, which are parameterized according to the heat exchanges at the air∕ice, air∕water, and ice∕water interfaces. This model is coupled with an oceanic model and is linked to a numerical weather prediction model for forecasting ice conditions in the Bohai Sea and the northern Yellow Sea. Statistical verification was used to make an objective assessment of the model. This paper summarizes the development of the sea ice model and its application in Bohai Sea ice forecast.     

Bohai Sea Ice Monitoring Using Satellite Images

Sea ice monitoring and forecasting in the Bohai Sea is an operational task of the National Research Center for Marine Forecasts (NRCMEF), China. An overview of current satellite image receiving and processing systems at NRCMEF in relation to the Bohai Sea ice monitoring, including the use of NOAA-AVHRR, GMS, SAR of ERS-1, Radarsat, and SeaWiFS data, is presented.     

Wave-Ice Interactions in Barents Sea Marginal Ice Zone

The motion of two ice floes in a wave field were simultaneously measured with two six degree of freedom instruments in the Barents Sea Marginal Ice Zone. The heave motion amplitude was used to interpret the wave amplitude. The response of the floes in a wave field relative to the wave amplitude at several different frequencies was investigated through spectral analysis. Comparison of the calculated wave amplitude at these two locations gave the wave attenuation coefficient, which was somewhat larger than those reported from previous field experiments; this is perhaps due to both the relatively higher concentration and the types of ice found during the investigation. The heave, sway, surge, pitch, roll, and yaw amplitudes were compared with the wave amplitude. The nondimensional response amplitude operators have similar values in the directions parallel and perpendicular to the wave direction; the response amplitude operators in pitch, heave, and surge agree with the predictions from previous theoretical studies. Similar responses in the sway, roll, and yaw directions indicate significant floe-floe interactions. These floe interactions may also contribute to the observed wave attenuation. Finally, there was essentially no difference between the floe energy attenuation and the wave attenuation.     

Flexural Behavior of Model Sea Ice in a Centrifuge

An experimental program was devised for the production of saline ice sheets in a centrifuge and the determination of flexural strength and elastic modulus of this ice through in situ cantilever beam testing. A cold box, in which dry ice acted as a heat sink, was used for this purpose. The ice beams were produced by lowering a heated brass frame through the ice cover. The load and beam deflections were recorded during indentation. The results of this analysis showed that inertial acceleration did not affect the flexural strength of the thin ice sheets required for this type of simulation. The data obtained were consistent with previously published strength values for thicker ice. The effective modulus showed a dependency on brine volume and inertial acceleration. The values obtained are substantially lower than those from conventional 1g tests and increase with the level of inertial acceleration. This is attributed to the confining stress.     

SPHC钢薄板坯的高温力学性能

用Gleeble热模拟试验机对SPHC钢(%:0.02C、0.18Mn、0.03Si、0.04Als)70 mm×1250 mm板坯进行600～1 350℃的力学性能的研究,并借助扫描电子显微镜和能谱仪分析了拉力试样的断口。结果表明,SPHC薄板坯的第Ⅰ和第Ⅲ脆性区分别为1 200℃～固相线及600～850℃,850～1 200℃薄板坯的塑性最好;第Ⅲ脆性区试样为沿晶界断裂;晶界处夹杂物及γ→α相变中形成的片状铁素体造成了晶界脆性,降低了第Ⅲ脆性区材料塑性。     

Index for Estimating Physical and Mechanical Parameters of Model Ice

A series of experiments on the physical and mechanical properties of ethanol model ice were conducted to determine the basis for quality control of fine grain model ice. The measured physical parameters of the model ice included the ethanol solution freezing point, air temperature profiles in an ice basin, ice temperature profiles, solution temperature profiles, unfrozen liquid in ice, and ice density. The measured mechanical parameters of the model ice were compressive strength, flexural strength, and characteristic length and strain modulus. Based on these measurements, the dominating factor influencing the physical and mechanical parameters of model ice is found to be the amount of unfrozen liquid in ice. Therefore, a new index of quality control for the physical and mechanical parameters of ice is developed. The statistical relationships of these measured physical and mechanical parameters with the new index are shown.     

Modeling Ice Passage at Navigation Locks

Physical and numerical models were used to assess ice passage at navigation locks, focusing on key factors such as the design of the lock filling and emptying system and the intakes to the lock filling culverts. Unconventional ice passage techniques such as manifolds in the miter gates were also evaluated. Physical model results were compared to field observations and to a parallel series of tests using the DynaRICE ice-hydraulic numerical model. The study focused on three general ice processes at locks: (1) ice accumulating near culvert intakes during lock filling; (2) drawing ice into the lock chamber; and (3) flushing ice out of the lock. Ice accumulation thickness in the upper lock approach was found to be the most important parameter affecting ice passage into the lock chamber. Physical and numerical model results compared reasonably well, proving DynaRICE to be a useful tool for assessing ice passage for new lock designs.     

Formation of Breakup Ice Jams at Bridges

Bridges can impede the passage of river ice during the breakup event and promote formation of ice jams, with adverse socioeconomic and ecological impacts. Design for ice passage at bridges has largely been empirical and qualitative so that avoidance of ice-jam instigation is often uncertain. It is thus important to develop rational design criteria, based on a thorough understanding of the factors governing the interaction between bridges and ice. This concern is quantified by utilizing recent advances on breakup initiation and comparing driving and resisting forces when the sheet ice cover is about to be set in motion. Retention of ice sheets by in-stream piers can lead to jamming via accumulation of ice rubble that may be arriving from upriver. The resulting methodology is applied to two case studies and yields results that are in full accord with local experience. Though the present findings pertain to the obstruction created by in-stream piers, similar reasoning can be applied to constrictions that may be caused by protruding bridge abutments.     

高温下奥—贝蠕铁的组织与性能

奥—贝蠕铁是继奥—贝球铁之后发展起来的新型工程材料之一，也是世界上正在开发的材料。本文系统地提供了奥—贝蠕铁的制取工艺，奥—贝蠕铁的组织特征及其在常温及随温度提高力学性能变化的规律。研究表明，以稀土硅铁为蠕化剂，所制取的蠕化率大于９０％、基体以铁素体为主的蠕墨铸铁，经等温淬火后，可稳定地获得奥氏体—贝氏体基体（以下简称奥—贝蠕铁），它有较好的综合性能，在常温下σｂ＝８２０～９３７．５ＭＰａ，δ＝０．４０％～０．７８％；在６００℃时，σｂ＝１５８～１８７ＭＰａ，δ＝４．００％～７．８４％，仍超过ＨＴ１５０的常温性能。当低于３００℃时组织和性能稳定性较好，是适宜的工作温度范围     

Size Effect on Strength of Floating Sea Ice under Vertical Line Load

The size effect on the nominal strength of a floating ice plate subjected to a vertical uniform line load is analyzed. The cracks produced by the load, which are parallel to the load line, are treated as softening inelastic hinges. The problem is one dimensional in the direction normal to the load line, equivalent to a beam on elastic foundation provided by buoyancy of ice in water. The softening moment-rotation diagram of inelastic hinges is simplified as linear and its dependence on structure size (ice thickness) is based on the energy dissipated by fracture. For thick enough plates, no two hinges (on one side of the line load) can soften simultaneously, in which case a simple analytical solution is possible. In that case, the load-deflection diagram has multiple peaks and troughs and consists of a sequence of spikes that get progressively sharper as the plate thickness increases. In terms of a dimensionless nominal strength, the effect of a finite fracture process zone at ice surface leads to an up-and-down size effect plot, such that each load peak decreases with the size at first but then asymptotically approaches a rising asymptote of the type (thickness)1/4 (which implies a reverse size effect, caused by buoyancy). The energy dissipation when the crack in the hinge gets deep causes a strong monotonic size effect, such that the dimensionless troughs between two spikes, in the case of thick enough plate, decrease asymptotically as (thickness)?1/2. For thin enough plates, more than one hinge soften simultaneously and, in the asymptotic case of vanishing ice thickness, the plasticity solution, which has no size effect, is approached. In the intermediate size range with hinges softening simultaneously, the exact solution is complicated and only approximate formulas for the size effect are possible. They are constructed by asymptotic matching.     

Effect of δ Phase on Mechanical Properties of GH4169 Alloy at Room Temperature

Tensile tests of GH4169 alloy were performed at room temperature. Different fractions, distributions and shapes of δ phase was prepared by aging treated at 880 °C, 930 °C and 980 °C for 5 h or 10 h. The effect of δ phase on the mechanical properties of GH4169 alloy was investigated. The results show that 0.2% yield strength and ultimate tensile strength of GH4169 alloy increase by 61 MPa and 78 MPa respectively when the fraction of δ phase increases from 2.20% to 5.21%. Then, the ultimate tensile strength remains at 1 012 MPa even when the fraction of δ phase reaches 7.56%. The fraction effect of δ phase on the strength improvement of GH4169 alloy is more significant than morphology, and the critical fraction value is 5.21%. In addition, the elongation decreases by 14.1% when the fraction of δ phase increases from 2.20% to 7.56%. Excessive needle or short rod shaped δ phase is responsible for the reduction of elongation.     

镍对09CuPCrNi耐候钢高温力学性能的影响

采用Gleeble 3000热模拟实验机测试和研究了CCT曲线以及镍含量对09CuPCrNi耐候钢(%:0.08C、0.34～0.35Cu、0.091～0.099P、0.53～0.55Cr、0.02～0.27Ni)的700～1 300℃塑性和抗拉强度的影响。结果表明,当钢中Ni含量由0.27%降至0.02%时,Ar₁、Ar₃分别由670.2℃和860.0℃升至710.0℃和882.5℃,并且贝氏体和马氏体相变也提前发生,800℃高温脆性温度区增宽,950℃高温脆性区消失。0.02%Ni耐候钢09CuPCrNi室温抗拉强度475～485 MPa,伸长率32%～34%,冲击功72～84 J,满足该耐候钢力学性能使用要求。     

氮对GCr15轴承钢高温力学性能的影响

实验用钢GCr15(%:0.97～1.03C、1.43～1.59Cr)用10 kg真空感应炉熔炼,在充氩情况下,使用氮化硅向钢中加0.1%～0.3%氮。通过Gleeble-1500热模拟试验机对该钢的锻材在700～1150℃进行拉伸试验,并用光学显微镜、扫描电子显微镜观察断口形貌和纵向组织。结果表明,氮在钢中以固溶形式存在,随氮含量增加,高温下钢的断面收缩率有较大提升,峰值应力提升不明显。     

高应变率下纯钛动态压缩力学性能各向异性

利用Instron电子拉伸机和分离式霍普金生（SHPB）压杠实验装置,研究了准静态和动态压缩条件下织构多晶纯钛板TA2的力学性能,对织构多晶纯钛板法向ND、轧向RD、横向TD等三个方向进行了压缩实验,得到了不同应变率下的应力-应变曲线。结果表明对于轧制和退火纯钛板,准静态和动态压缩力学性能均表现出明显的各向异性,且规律一致：均为ND方向屈服强度最大,TD次之,RD方向最小。     

Mechanical Properties of Ausformed Carbide-Free Bainite

Metallurgical and Materials Transactions A - In this study, the effect of ausforming temperature and strain on the bainite transformation in a model alloy containing 0.39 pct C, 2.0 pct Mn, 1.9 pct...