提高冷轧高强度钢板屈服强度控制水平的研究

在高强度钢板中,超低碳烘烤硬化钢板(简称BH钢板)是新型优质汽车用薄板.在生产BH钢板时,需要有效地控制屈服强度,以保证较好的深冲性能.采用四方图识别了影响屈服强度的关键因素,包括化学成分、热轧参数、冷轧参数等;基于大量的生产过程历史数据,分别用回归分析、神经元网络、决策树三种不同方法进行分析,建立各关键输入变量(KIV)对屈服强度(KOV)影响的多变量模型.以神经元网络模型为例,进行了模型评价.以该模型为基础,在已知某些KIV取值的情况下,能够较为准确地预测BH钢成品的屈服强度,合格率提高7个百分点,取得了较好的经济效益.     

Bond Strength of Fiber Reinforced Polymer Rebars in Normal Strength Concrete

The bond behavior of reinforcing bars in concrete is a critical issue in the design of reinforced concrete structures. This study focuses on the bond strength of fiber reinforced polymer (FRP) rebars in normal strength concrete. Four different types of rebars were tested using the pullout method: aramid FRP (AFRP); carbon FRP (CFRP); glass FRP (GFRP), and steel. This involved a total of 151 specimens containing 6, 8, 10, 16, and 19?mm rebars embedded in a 203?mm concrete cube. The test embedment lengths were five, seven, and nine times the rebar diameter (db). For each rebar, the test results include the bond stress–slip response and the mode of failure. The test results showed that the bond strength of an FRP rebar is, on average, 40–100% the bond strength on a steel rebar for pullout failure mode. Based on this research, a proposal for the average bond strength of straight FRP rebars in normal strength concrete is made, which verifies an existing bond strength relationship (GFRP) and extends its application to AFRP and CFRP. It is an expression that is a function of the rebar diameter, and the concrete compressive strength.     

Strength of Low-Dimensional Objects

Filaments, films, tubes, membranes, and shells are considered as a general class of low-dimensional objects, the thickness of which is much smaller than their length and possible displacements. The strength of such materials almost achieved the theoretical limit, and their bearing capacity is restricted by macroscopic elastic (or viscoelastic) loss of stability rather than fracture. The generality of the phenomena of the loss of bearing capacity in low-dimensional objects and elastic (or viscoelastic) instability and its modes (wrinkles and focuses in twisting of a wire and a ribbon and in buckling, corrugation, curvature condensation of tubes and shells and plastic folds in flicking) is analyzed.     

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.     

提高低合金高强度钢强韧性的措施

本文通过对提高低合金高强度钢强韧性措施的探讨，结合舞钢的具体生产情况，提出了提高低合金高强度钢强韧性的工艺方法。     

Optimization Evaluation Test of Strength and Toughness Parameters for Hot-Stamped High Strength Steels

Use of hot-stamped high strength steels (HSHSS) not only reduces the vehicle weight, but also improves the crash safety, therefore more and more mentioned steels are used to produce automobile parts. However, there are several problems especially the low ductility and toughness, which have restricted the application of HSHSS in automobile body. Suitable process parameters are very crucial to improve strength and toughness. In order to study the effect of austenization temperature, soaking time and start deformation temperature on strength and toughness of boron steel 22MnB5, an L9 (3⁴) orthogonal experiment which was analyzed by means of comprehensive evaluation was carried out based on Kahn tear method to obtain the value of fracture toughness. The results indicate that the excellent formability, high strength and toughness of boron steel 22MnB5 with 1.6 mm in thickness are obtained when the austenization temperature is in the range of 920 — 950 °C, the soaking time is 1 min and the start deformation temperature is in the range of 650 — 700 °C. The optimal parameters were used for typical hot stamping structural parts tests. Properties of samples such as tear strength, unit initiation energy and ratio of strength to toughness (RST) were improved by 10.91%, 20.32% and 22.17%, respectively. Toughness was increased substantially on the basis of a small decrease of strength.     

高强度H型钢的研究与开发

研究了控制轧制中各相关因素和铌、钒等微合金元素在钢中的作用机制;阐述了微合金化和控制轧制技术在高强度H型钢开发过程中的应用效果;开发出了400 MPa以上级别的高强度H型钢。     

Tensile Strength of Unsaturated Sand

A theory that accurately describes tensile strength of wet sand is presented. A closed form expression for tensile strength unifies tensile strength characteristics in all three water retention regimes: pendular, funicular, and capillary. Tensile strength characteristically increases as soil water content increases in the pendular regime, reaches a peak in the funicular regime, and reduces with a continuing water content increase in the capillary regime. Three parameters are employed in the theory: internal friction angle (at low normal stress) ?t, the inverse value of the air-entry pressure α, and the pore size spectrum parameter n. The magnitude of peak tensile strength is dominantly controlled by the α parameter. The saturation at which peak tensile strength occurs only depends on the pore size spectrum parameter n. The closed form expression accords well with experimental water retention and tensile strength data for different sands.     

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.     

Strength of silicone breast implants

Rupture and leakage are recognized problems associated with silicone breast implants. Data are scarce about the durability of the silicone shell, and the life span of this device is unknown. The purpose of this study was to investigate the strength of silicone breast implants. Thirty implant shells were subjected to mechanical testing. Twenty-nine of the shells were tested after explanation, and one unused implant served as a control to validate the testing method. Implantation time varied from 4 months to 20 years, and all shells were tested, regardless of condition. Fourteen implant shells were intact, eight were leaking, and seven were ruptured. All ruptured implants had been in place for 10 years or longer. The breaking force of all excised shell specimens ranged from 2.6 to 22.4 N (0.6 to 5.0 lb.). Specimens from the control "high performance" shell required 15.5 to 25.6 N (3.5 to 5.8 lb) of force to fail. The weakest group was from thin-shelled implants between 10 and 16 years of age. More than half these specimens failed with less than 1 lb of force. The average breaking force of ruptured shell material was less than that of intact shells. A comparison of strength data in this study with manufacturers' data suggests that breaking force is dependent on implant type, shell thickness, and implantation time.     

提高球团矿强度的实践

弓长岭矿业公司球团一厂通过采取一系列措施,包括:精细配料,强化造球,改善链篦机布料均匀性,制定合理的热工制度,调整热工参数,查堵漏风等,在不增加煤耗的前提下,使球团矿抗压强度逐年提高。2009年达到创纪录的2932N/个,为强化高炉冶炼创造了条件。