控制冷却过程中钢板翘曲的分析

采用一维应力和热弹性材料的梁式模型，对控制冷却过程中钢板的翘曲进行了分析。为了验证这种分析的可靠性，用新设计的实验装置做了试验。在水冷过程中，测定了温度与翘曲的连续变化。（１）通过与试验结果的比较，定量地验证了这种分析的可靠性，预计这种计算方法将被用于控制冷却过程中钢板翘曲的控制。（２）由此分析结果可以得出：引起翘曲的主要因素是相变、屈服应力和导热性。ａ）在低温相变条件下，冷却期间的翘曲和残余翘曲     

控制冷却中钢板的翘曲解析

控制冷却中钢板的翘曲解析［日］吉原直武等１绪言现在，各公司都装有中厚板在线控制冷却设备，生产高强度、高韧性并且焊接性优良的产品。在尺寸大的中厚板在线控制冷却中，不容易获得上下面的冷却平衡，难以避免发生上下方向的翘曲。另外，由于冷却设备通板方面的原因，...     

层流冷却中水量对热钢板冷却能力的影响

进行调查水层流冷却热钢板工艺的试验，并根据试验结果，分析了水流量对冷却能力的影响。其结论要点如下：1）喷嘴与冷却钢板表面的垂直距离几乎不影响冷却能力。2）水流量的增加会提高冷却能力。但是，随着流量的继续增加冷却能力和“黑区”的长大均达到饱和。3）冷却能力的饱和与黑区的直径增大的极限有关。     

厚钢板控制冷却中的翘曲解析

籍助于具有一维应力和热弹塑性材料的梁型开发了一种关于控制冷却期间钢板翘曲的数字解析方法。为证实这种解析的有效性,应用新设计的实验装置进行了实验。测量了温度和翘曲的连续变化。（1）该解析的有效性经与实验结果比较被定量地证实。期待着该计算方法被用于控制冷却过程中钢板和型钢的翘曲控制。（2）根据解析结果,发现翘曲的主要原因是相变、屈服应力和导热系数。①在低温转变场合,冷却期间的翘曲行为和残余翘曲都较大,因为有相变时大的膨胀和低温下高的屈服应力。②较高的屈服应力导致较大的翘曲。③较低的导热系数导致在厚度方向上高的、陡峭的温度梯度,它将引起较高的热应力和较大的翘曲。     

钢板加速冷却的最佳冷却条件

近年来,轧后断续加速冷却设备的问世,使减少管线钢管用钢板的合金含量成为现实。通过采用断续加速冷却工艺,沿板厚断面可获得两种组织结构,即板中部为铁素体加珠光体;板表面附近为回火马氏体加贝氏体。本文阐述了钢板原料厚度、化学成分及欲定量获得钢板表面与中部之间硬度差所必须采用的冷却条件。     

控制冷却对热轧多相钢板机械性能的影响

本文论述了钢的化学成分和热轧后冷却状况对其显微组织及机械性能的影响。生产多相钢最重要的一点是,通过添加Si、Cr合金元素和控制冷却获得期望的马氏体和奥氏体,净化铁素体晶粒。控制初始冷却速率会影响铁素体转变的数量、铁素体净化和残留奥氏体中碳的富集;控制第二冷却速率和卷取温度可改变低温转变产物的特性和溶于铁素体中的碳含量。Si可加速铁素体的转变和净化铁素体,而且可提高抗拉强度与延伸率的积。Cr可提高钢的淬透性和屈强比。轧钢厂对所推荐的C、Mn、Si、Cr成分的钢进行生产试验,是为了进一步证实在实验室得到的成分和工艺参数。还对这些三相钢板的应用如制造轮盘进行了试验。     

高温钢板喷雾冷却时的冷却特性和传热系数

传热系数α是定量表示冷媒冷却能力的参数,是设计冷却设备(钢材轧后控制冷却设备,连铸二次冷却设备及热处理冷却设备等)不可缺少的重要参数。为此,本文进行了高温钢板喷雾冷却时的冷却特性和传热系数的研究,结果如下: 1.在钢板表面温度θ_s为200～260℃区间,传热系数α有极大值。 2.在θ_s为100～250℃区间,随θ_s上升,α单调地增加,在θ_s为250～850℃区间,随θ_s上升,α减小。在整个试验温度区间,α未出现极小值。 3.水流密度W和θ_s对α的影响为 α=A·W~n·10~(?)     

钢板水幕冷却的分析

本对钢板轧后水幕冷却时影响对流换热系数和冷却效果的各种因素。冷却时间、冷却区长度、冷却水消耗量、冷却装置的数量与安装形式以及系统的冷却速度进行了分析,这些研究结果可对提供指导和帮助。     

雾化冲击射流冷却热轧钢板的研究

利用有限元耦合场数值模拟计算方法对热轧钢板雾化冲击射流冷却进行模拟计算,结果表明,在其它条件相同的情况下,单喷嘴喷射时,在上喷和下喷的喷嘴附近冷却能力相同;多喷嘴喷射时,横向存在二次冷却,钢板表面横向温度分布总体上呈现逐渐降低的趋势。     

Effect of Fiber Waviness on Buckling Strength of Composite Plates

This paper explores the idea of tailoring the profile of reinforcing fibers to improve the buckling strength of composite plates. This paper analyzes the uniaxial buckling behavior of composite laminates in which fibers are placed along parallel sinusoidal curves, instead of the conventional straight line pattern. The sinusoidal fiber orientation results in variable elastic stiffness and nonuniform prebuckling stress fields, which are shown to have a pronounced influence on the buckling strength. For example, changing the fiber orientation from straight line to a sinusoidal pattern can increase the buckling load of a simply supported laminate by more than 80%. For the analysis, a computerized Rayleigh-Ritz procedure is developed that exploits an analogy between bending and stretching formulations to model a variety of boundary conditions.     

Effect of Longitudinal Stress Gradients on Elastic Buckling of Thin Plates

This paper analyzes the effect of longitudinal stress gradients on the elastic buckling of thin isotropic plates. Two types of thin plates are considered: (1) a plate simply supported on all four edges and rotationally restrained on two longitudinal edges; and (2) a plate simply supported on three edges with one longitudinal edge free and the opposite longitudinal edge rotationally restrained. These two cases illustrate the influence of longitudinal stress gradient on stiffened and unstiffened elements, respectively. A semianalytical method is derived and presented herein to calculate the elastic-buckling stress of both types of rectangular thin plates subjected to nonuniform applied longitudinal stresses. Finite-element analysis using ABAQUS is employed to validate the semianalytical model for plates with fixed and/or simple supports. Empirical formulas are produced to calculate the buckling coefficients of plates with fixed and/or simple supports under longitudinal stress gradients. The results help establish a better understanding of the effect of longitudinal stress gradients on the elastic buckling of thin plates and are intended to aid in the development of design provisions to include these effects in the strength prediction of thin-walled beams under moment gradients.     

Deducing Buckling Loads of Sectorial Mindlin Plates from Kirchhoff Plates

This study presents a relationship between the buckling loads of sectorial plates based on the Kirchhoff (or classical thin) plate theory and the Mindlin plate theory. Whereas the former plate theory neglects the effect of transverse shear deformation, the latter plate theory allows for it. This effect becomes significant when dealing with moderately thick plates and sandwich plates. The relationship allows easy and accurate deduction of the buckling loads of the Mindlin plates from their corresponding Kirchhoff solutions.     

Buckling of Laminated Composite Rectangular Plates

The present study estimates the critical/buckling loads of laminated composite rectangular plates under in-plane uniaxial and biaxial loadings. The formulation is based on the first-order shear deformation theory and von-Karman-type nonlinearity. Chebyshev series is used for spatial discretisation and quadratic extrapolation is used for linearization. An incremental iterative approach is used for estimation of the critical load. Different combinations of simply supported, clamped and free boundary conditions are considered. The effects of plate aspect ratio, lamination scheme, number of layers and material properties on the critical loads are studied.     

Membrane Analogy of Buckling and Vibration of Inhomogeneous Plates

Exact explicit eigenvalues are found for compression buckling, hygrothermal buckling, and vibration of sandwich plates with dissimilar facings and functionally graded plates via analogy with membrane vibration. These results apply to simply supported polygonal plates using the first-order shear deformation theory and the classical theory. A Winkler-Pasternak elastic foundation, a hydrostatic inplane force, hygrothermal effects, and rotary inertias are incorporated. Bridged by the vibrating membrane, exact correspondence is readily established between any pairs of eigenvalues associated with buckling and vibration of sandwich plates, functionally graded plates, and homogeneous plates. Positive definiteness is proved for the critical buckling hydrostatic pressure and, in the range of either tension loading or compression loading prior to occurrence of buckling, for the natural vibration frequency.     

Effects of Random Material Properties on Buckling of Composite Plates

Composites exhibit a considerable amount of variation in their material properties because their fabrication∕manufacturing process involves a large number of parameters that cannot be controlled effectively. In the present study, the material properties have been modeled as random variables for better prediction of the system behavior. The classical laminate theory and first-order and higher-order shear deformation theories have been employed in deriving the governing equations for buckling of laminated rectangular plates. A mean-centered first-order perturbation technique has been used to find the second-order statistics of the buckling load. The approach has been validated by comparison with results of Monte Carlo simulation. Typical results have been presented for a plate with all edges simply supported. The effectiveness of the theories in predicting the buckling load dispersions has been examined. The sensitivity of buckling loads to change in the standard deviation of random material properties and to system parameters—side-to-thickness ratio and aspect ratio—has been examined for cross-ply symmetric and antisymmetric laminates.     

Exact Solutions for Buckling of Multispan Rectangular Plates

This paper presents exact solutions for buckling of multispan rectangular plates having two opposite edges simply supported and the other two edges being either free, simply supported, or clamped. The Levy solution procedure is employed to develop an analytical approach for buckling analysis of multispan plates. The Levy solution for each span is derived and the continuity along the interface of two spans is ensured through the implementation of the essential and natural boundary conditions at the interface. Extensive buckling factors, most of which are first-known exact solutions, are given in tabular and design chart forms for two- and three-unequal-span square plates subjected to uniaxial in-plane load in the x or y directions and biaxial in-plane load. The influence of the span ratios and plate boundary conditions on the buckling factors is discussed. Buckling factors are also obtained for two-, three-, and four-equal-span rectangular plates with various edge support conditions. The exact buckling solutions presented in this paper are of benchmark values for such plates.     

Bounds on Flexural Properties and Buckling Response for Symmetrically Laminated Composite Plates

Nondimensional parameters and equations governing the buckling behavior of rectangular symmetrically laminated plates are presented that can be used to represent the buckling resistance, for plates made of all known structural materials, in a very general, insightful, and encompassing manner. In addition, these parameters can be used to assess the degree of plate orthotropy, to assess the importance of anisotropy that couples bending and twisting deformations, and to characterize quasi-isotropic laminates quantitatively. Bounds for these nondimensional parameters are also presented that are based on thermodynamics and practical laminate construction considerations. These bounds provide insight into potential gains in buckling resistance through laminate tailoring and composite-material development. As an illustration of this point, upper bounds on the buckling resistance of long rectangular orthotropic plates with simply supported or clamped edges and subjected to uniform axial compression, uniform shear, or pure in-plane bending loads are presented. The results indicate that the maximum gain in buckling resistance for tailored orthotropic laminates, with respect to the corresponding isotropic plate, is in the range of 26–36% for plates with simply supported edges, irrespective of the loading conditions. For the plates with clamped edges, the corresponding gains in buckling resistance are in the range of 9–12% for plates subjected to compression or pure in-plane bending loads and potentially up to 30% for plates subjected to shear loads.     

Effect of Cooling Patterns on Microstructure and Mechanical Properties of Hot-Rolled Nb Microalloyed Multiphase Steel Plates

 The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstructure containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns Ⅰ, Ⅱ and Ⅲ were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values (547 MPa, 37.2% and 28384 MPa·%, respectively) for the steel plate processed by cooling pattern Ⅲ.     

Ritz Buckling Analysis of Rectangular Plates with Internal Hinge

This paper presents the Ritz method for buckling analysis of rectangular plates with an internal line hinge. The Ritz method involves the domain decomposition method to cater for the discontinuity of slope at the hinge line. The correctness of the Ritz formulation and solutions is confirmed by the exact solutions derived using the Levy method for plates with two opposite sides simply supported. Based on the Ritz method, buckling factors are generated for rectangular plates of various aspect ratios, hinge locations, and support and loading conditions.