热轧基板点状氧化铁皮分析

热轧带钢表面氧化铁皮严重影响冷轧生产,为减少带钢表面氧化铁皮,通过对热轧基板表面氧化物分布的形貌分析,验证氧化物形成的原因,最终提高产品表面质量。     

Effect of Oxide Scale on Interfacial Heat Transfer during Slab Hot Rolling

Ｉｎｈｏｔｒｏｌｌｉｎｇｏｆｓｌａｂ ,ｔｈｅｔｈｅｏｒｉｅｓｏｆｈｅａｔｔｒａｎｓ ｆｅｒａｎｄｔｅｍｐｅｒａｔｕｒｅｄｉｓｔｒｉｂｕｔｉｏｎｗｅｒｅｗｉｄｅｌｙｒｅｃｏｇ ｎｉｚｅｄａｎｄｕｓｅｄｉｎｐｒａｃｔｉｃｅ[1 4 ] .Ｈｏｗｅｖｅｒ ,ｔｈｅｑｕａｎｔｉ ｔａｔｉｖｅｃｈａｒａｃｔｅｒｉｚａｔｉｏｎｏｆｔｈｅｉｎｔｅｒｆａｃｉａｌｈｅａｔｔｒａｎｓｆｅｒａｎｄｔｅｍｐｅｒａｔｕｒｅｄｉｓｔｒｉｂｕｔｉｏｎｉｓｓｔｉｌｌｉｎｃｏｍｐｌｅｔｅａｎｄｉｎｃｏｎｓｉｓｔｅｎｔａｎｄｉｎｍｏｓｔｃａｓ…     

热轧高强钢氧化铁皮演变规律的研究

对HY490钢在精轧工艺下氧化铁皮的厚度演变进行了数值模拟。通过热轧试验验证了数值模拟结果,并对热轧试验氧化铁皮的结构进行了检测。采用冷弯试验测定了2种工艺条件下带钢表面氧化铁皮的粘附性。结果表明:数值模拟结果与现场实测值相符。此模拟方法解决了精轧过程中无法直接测量3次氧化铁皮厚度的问题,为通过调整生产工艺参数来控制氧化铁皮厚度提供了参考。热轧试验表明适当地降低开轧温度、终轧温度、卷取温度和缩短轧制道次间隔时间是控制氧化铁皮厚度和结构的有效手段。冷弯试验表明工艺1条件下氧化铁皮与钢板的粘附性较差,弯曲面铁皮呈细片状脱落。工艺2条件下铁皮与钢板结合牢固,弯曲面铁皮呈细粉末状,粘附性好。     

Shear Strength of Fiber-Reinforced Sands

Soil reinforcement using discrete randomly distributed fibers has been widely investigated over the last 30 years. Several models were suggested to estimate the improvement brought by fibers to the shear strength of soils. The objectives of this paper are to (1) supplement the data available in the literature on the behavior of fiber-reinforced sands; (2) study the effect of several parameters which are known to affect the shear strength of fiber-reinforced sands; and (3) investigate the effectiveness of current models in predicting the improvement in shear strength of fiber-reinforced sand. An extensive direct shear testing program was implemented using coarse and fine sands tested with three types of fibers. Results indicate the existence of a fiber-grain scale effect which is not catered for in current prediction models. A comparison between measured and predicted shear strengths indicates that the energy dissipation model is effective in predicting the shear strength of fiber-reinforced specimens in reference to the tests conducted in this study. On the other hand, the effectiveness of the predictions of the discrete model is affected by the parameters of the model, which may depend on the test setup and the procedure used for mixing the fibers.     

Shear Strength and Stiffness of Silty Sand

The properties of clean sands pertaining to shear strength and stiffness have been studied extensively. However, natural sands generally contain significant amounts of silt and∕or clay. The mechanical response of such soils is different from that of clean sands. This paper addresses the effects of nonplastic fines on the small-strain stiffness and shear strength of sands. A series of laboratory tests was performed on samples of Ottawa sand with fines content in the range of 5–20% by weight. The samples were prepared at different relative densities and were subjected to various levels of mean effective consolidation stress. Most of the triaxial tests were conducted to axial strains in excess of 30%. The stress-strain responses were recorded, and the shear strength and dilatancy parameters were obtained for each fines percentage. Bender element tests performed in triaxial test samples allowed assessment of the effect of fines content on small-strain mechanical stiffness.     

Shear Strength of Municipal Solid Waste

A comprehensive large-scale laboratory testing program using direct shear (DS), triaxial (TX), and simple shear tests was performed on municipal solid waste (MSW) retrieved from a landfill in the San Francisco Bay area to develop insights about and a framework for interpretation of the shear strength of MSW. Stability analyses of MSW landfills require characterization of the shear strength of MSW. Although MSW is variable and a difficult material to test, its shear strength can be evaluated rationally to develop reasonable estimates. The effects of waste composition, fibrous particle orientation, confining stress, rate of loading, stress path, stress-strain compatibility, and unit weight on the shear strength of MSW were evaluated in the testing program described herein. The results of this testing program indicate that the DS test is appropriate to evaluate the shear strength of MSW along its weakest orientation (i.e., on a plane parallel to the preferred orientation of the larger fibrous particles within MSW). These laboratory results and the results of more than 100 large-scale laboratory tests from other studies indicate that the DS static shear strength of MSW is best characterized by a cohesion of 15?kPa and a friction angle of 36° at normal stress of 1?atm with the friction angle decreasing by 5° for every log cycle increase in normal stress. Other shearing modes that engage the fibrous materials within MSW (e.g., TX) produce higher friction angles. The dynamic shear strength of MSW can be estimated conservatively to be 20% greater than its static strength. These recommendations are based on tests of MSW with a moisture content below its field capacity; therefore, cyclic degradation due to pore pressure generation has not been considered in its development.     

Reduction of Oxide Scale with Hydrogen

During hot rolling process metals will inevitably oxidize because of high temperature and air condition.In order to guarantee the surface quality,acid pickling is applied to remove the oxide scale while waste acid will do harm to the environment.Faced with the problem,by means of reduction process of hot-rolled plates,the oxide scale will be reduced to iron,so that acid pickling is unnecessary.One pass cold rolling procedure was applied.The compression ratios of hot-rolled plates with oxide scale were 10%,18%,26%and 31%,respectively.After that,samples mentioned above including a sample without deformation were separately reduced under hydrogen atmosphere condition(5% H2 +95% Ar in volume percent)at 600-1 000℃.The thermal gravimetric apparatus(TGA)was used to establish accurate experimental condition and obtain complete mass loss data.Field emission electron probe microanalysis(EPMA)was applied to analyze scale morphology change and composition distribution through the oxide scale.It was found that the sample with 26%compression ratio could be reduced completely at 900℃ which was favorable to galvanization.     

回转式飞剪机刀轴强度分析

分析了回转式飞剪机上刀轴在剪切过程中的受力状况,分别利用弯扭合成强度计算方法和安全系数法校核了改进设计的回转式飞剪机上刀轴疲劳强度和静强度。理论计算结果表明,上刀轴危险截面的弯曲应力均小于刀轴材质的许用弯曲应力,并具有足够的静强度安全系数。通过实际生产的检验,证明了改进设计的飞剪机能够满足生产线的使用要求。     

Shear Fracture of Advanced High Strength Steels

Failure experiments were carried out through a stretch-bending test system for advanced high strength steels, i.e. dual-phase （DP） steels and martensitic steels （MS）. The die radius in this system was designed from 1 to 15 mm to investigate the failure mode under different geometries. Two failure modes were observed during the ex- periments. As a result, critical relative radii （the ratio of inner bending radius R to sheet thickness t） for DP590 and DP780 steels were obtained. The stretch-bending tests of DP980 display some trends unlike DP590 and DP780 steels, and curve of DP980 in different thicknesses does not coincide well. High blank holder force exhibits more possibility of shear fracture tendency than low blank holder force. The unique character of high strength martensitic steel （1500MS） is that no shear fracture is found especially over small bending radius （R =2 mm） under the same experi- mental conditions. Microstructure analysis indicates that there are obviously elongated grains on shear fracture sur- face. It shows smaller diameter and shallower depth of the dimples than the necking failure.     

Objective Oriented Multistage Ring Shear Test for Shear Strength of Landslide Soil

Ring shear tests were conducted on five samples of different nature with a modified Imperial College type ring shear machine. The three different testing methods used, (1) individual sample testing for each normal stress, (2) increasing load multistage ring shear test, and (3) reducing load multistage ring shear test, all showed similar effective residual internal friction angle for the samples, irrespective of testing method. However, effective residual shear intercept was different according to the testing methodology. The internal friction angle did not vary, particularly after the first minimum point in the stress displacement curve, although the residual shear intercept decreased with increase in the displacement. The thickness of the shearing zone increased along with the displacement. The remolded peak shear strength for saturated conditions at field dry density varied with the consolidation history. Measurement of remolded peak shear strength was possible in a single sample using the increasing load multistage ring shear test at normal consolidation. The equilibrium water content of the sample after the ring shear test was nearly equal to the plastic limit.     

Experimental Study of Interfacial Shear Stresses in FRP-Strengthened RC Beams

This paper presents the results of an experimental study on the distribution of shear stresses along the interface between concrete and the carbon fiber-reinforced polymer (FRP) in 29 plate-strengthened beams, where the primary test variables are: Clear cover, plate length, plate thickness (area), and compressive strength of concrete. FRP strain measurement was accomplished using either the photographic technique of digital image correlation or a series of electrical-resistance strain gages, both providing similar results. The distribution of shear stresses is found to be smoother than predicted by several analytical expressions available in the literature. Another substantial observation is the existence of a second region of peak stress, occurring near the center of the shear span in all of the beams with longer plate lengths, which the authors believe is associated with the singular application of shear corresponding to the point load, as well as the transition from elastic to plastic behavior occurring in the rebar. Because the overall nature of the stress distribution is sufficiently smooth, it is very reasonable to approximate it as a constant stress.     

Maximum Shear Strength of RC Beams Retrofitted in Shear with FRP Composites

In reinforced concrete (RC) beams strengthened in shear with fiber-reinforced polymer (FRP), crushing of the web can be a potential mode of failure. The guidelines provided by codes and standards for the design of structures strengthened with externally bonded FRP recommend limiting the maximum shear strength to avoid such an undesirable failure scenario. However, these limitation provisions are not based on specific research studies performed on beams strengthened in shear with FRP. Rather, they simply duplicate provisions used in conventional concrete codes and standards. The main objective of this research study is to assess the suitability of the limits specified by the guidelines, and propose, if necessary, an alternative equation as an upper limit for shear strength against web crushing failure in such structures. To this end, an analytical approach was developed based on the static theorem of the theory of plasticity. The predictions of the equations resulting from this approach were compared with those obtained from tests reported in the literature and with those predicted by ACI Committee 440-02, Canadian Standard S6-06, and the European recommendations fib TG 9.3. The study shows that the current ACI Committee 440-02 and Canadian Standards provisions are overly conservative and therefore need to be reviewed.     

Influence of Shear Rate on Undrained Vane Shear Strength of Organic Harbor Mud

Dredging operations in European harbors for maintenance of navigable water depth produce vast amounts of harbor mud. Between 2005 and 2007, the second largest harbor construction project in Germany was designed as a pilot study to use dredged harbor mud as backfill material to avoid expensive disposal or ex situ treatment. During this project, a partial collapse of the backfill highlighted the need for an improved assessment of undrained shear strength of naturally occurring liquid harbor mud. Using vane shear testing, this study evaluates the effect of shear rate on the undrained shear strength of harbor mud. It is shown that measured values for both peak and residual shear strength are significantly influenced by shear rate effects. Furthermore, the influence of shear rate on the peak shear strength is found to be independent of water content while the influence of the shear rate on the residual shear strength strongly depends on water content. New shear rate dependent correction factors μ are proposed using the test results and the observed time to failure in the harbor basin. The proposed correction leads to significant lower design undrained shear strengths than the classical Bjerrum correction and would have predicted the failure during the construction.     

Shear Strength of Normal Strength Concrete Beams Reinforced with Deformed GFRP Bars

This paper evaluates the shear strength, Vc, of intermediate length (2.5 < a∕d < 6) simply supported concrete beams subjected to four-point monotonic loading and reinforced with deformed, glass fiber-reinforced polymer (GFRP) reinforcement bars. Six different overreinforced GFRP designs, ρ > ρb, were tested with three replicate beams per design. All samples failed as a result of diagonal-tension shear. Measured shear strengths at failure are compared with theoretical predictions calculated according to traditional steel-reinforced concrete procedures and recently published expressions intended for beams reinforced with GFRP. Recommendations are made regarding the adequacy of shear strength prediction equations for GFRP-reinforced members. The study concludes that shear capacity is significantly overestimated by the “Building Code Requirements for Structural Concrete and Commentary” (ACI 318-99) expression for, Vc, as a result of the large crack widths, small compression block, and reduced dowel action in GFRP-reinforced flexural members. Shear strength was found to be independent of the amount of longitudinal GFRP reinforcement. A simplified empirical equation for predicting the ultimate shear strength of concrete beams reinforced with GFRP is endorsed.     

Evaluation of Undrained Shear Strength Using Full-Flow Penetrometers

Full-flow penetrometers (the T-bar and ball) are increasingly used on sites with thick deposits of soft clays, particularly prevalent offshore. Full-flow penetration tests were performed at five international well-characterized soft clay test sites to assess the use of full-flow penetrometers to estimate undrained shear strength. Field vane shear data were used as the reference undrained strength. Statistical analyses of strength factors indicates that full-flow penetrometers provide an estimate of undrained shear strength at a similar level of reliability compared to the piezocone. Relationships for estimating the strength factor and soil sensitivity using only full-flow penetrometer data obtained during initial penetration and extraction are developed. A strong dependence of the strength factor on sensitivity was identified and can be used for the estimation of undrained strength. The effectiveness and use of the developed correlations are demonstrated through their application at an additional test site.     

低压等离子喷涂涂层膜基界面结合能的研究

用努氏界面印痕法 ,对铁基Ni/Fe、镍基Cu/Ni低压等离子喷涂涂层的膜基界面进行界面结合能的研究 ,分析得到涂层界面的断裂表面能。分析得出铁基纯镍Ni/Fe涂层界面的断裂表面能比镍基铜Cu/Ni涂层的断裂表面能高。界面微观分析表明 ,镍基铜Cu/Ni涂层材料疏松 ,膜基界面存在较多裂纹 ,另外涂层和基体观察不到元素扩散层。Ni/Fe涂层界面结合致密 ,约有 2～ 3 μm的元素扩散层。     

Shear Strength of Compacted Soil under Infiltration Condition

Landslides in residual soil slopes are commonly induced by rainfall infiltration. These residual soils are typically in an unsaturated state with negative pore-water pressures or matric suctions since the groundwater tables in steep slopes are often deep. The net normal and shear stresses of the soil remain essentially constant during rainwater infiltration into the slope. Failure of the slope during rainfall can be primarily associated with the decrease in the matric suction of the soil. The objective of the study was to investigate the strength and deformation characteristics of a residual soil of the Bukit Timah Granitic Formation during infiltration that leads to slope failure. There were two modified direct shear apparatuses used. One apparatus was used for the determination of shear strength under controlled suction conditions while the other apparatus was used for shearing-infiltration tests. The shearing-infiltration test results were compared with the shear strength values obtained from the shearing tests under constant suction. The shearing-infiltration test results indicate a close relationship between the decreasing matric suction and the increasing displacement rate of the soil specimen. At the initial part of the infiltration process, there is a rapid reduction in matric suction that is accompanied by little movement in the soil. When failure of the soil is imminent, the soil movement will accelerate.     

Dilatancy and Shear Strength of Sand at Low Confining Pressures

Sand dilates with shearing at a rate that increases with increasing relative density (DR) and decreases with increasing effective confining stress (σc′). The peak friction angle of a sand depends on its critical-state friction angle and on dilatancy. In this paper, we develop a simple correlation between peak friction angle, critical-state friction angle, and dilatancy based on triaxial compression and plane-strain compression test data for sand for a range of confining pressures from very low levels to approximately 196 kPa.     

Time Effect on Shear Strength and Permeability of Fly Ash

This paper investigates the effect of time on the shear strength and the permeability of fly ash, a major solid by-product of thermoelectric power plants. Direct shear tests using Mikasa's apparatus, conventional permeability tests, and consolidation tests were conducted on two silt-size fly ashes, with low free lime contents, obtained from two different power plants. The results show that the immediate settling of both fly ashes takes place in a short period of time during consolidation and does not change with time. The rate of increase in shear strength with time is different depending on the pozzolanic reactions taking place for the two ashes. The permeability tests under constant stresses of 49 and 98 kPa for 12 days show that the coefficient of permeability for the tested ashes is between 10?6 and 10?7 m∕s. During this period the coefficient of permeability either remains constant (for the case of the ash with a lower free lime content) or is slightly reduced (for the ash with a higher free lime content). The practical implications and the limitations of using low lime silt-size fly ash in vertical drains in the stabilization of soft ground are also discussed.     

连铸坯表面氧化铁皮除不尽原因及对策

 采用SEM对连铸坯表面氧化铁皮除鳞除不尽的原因进行分析。分析结果表明：Q235B、Q345B和SPA-H连铸坯内层氧化铁皮呈楔形嵌入钢基体中,嵌入钢基体中的氧化铁皮主要为铁橄榄石—Fe2SiO4相,随着钢基体中硅含量的增加,嵌入钢基体中的铁橄榄石相增加,使得内层氧化铁皮与钢基体的附着力增加,造成连铸坯表面氧化铁皮除鳞除不尽。针对连铸坯氧化铁皮除鳞除不尽的原因,提出相应的研究对策：一方面,优化加热炉工艺,控制高压水除鳞前连铸坯温度在1173℃以上;另一方面,优化高压水除鳞系统参数,增加高压水除鳞效果。