Explicit local buckling analysis and design of fiber–reinforced plastic composite structural shapes

Pultruded fiber–reinforced plastic (FRP) composite structural shapes (beams and columns) are thin-walled open or closed sections consisting of assemblies of flat plates and commonly made of E-glass fiber and either polyester or vinylester resins. Due to high strength-to-stiffness ratio of composites and thin-walled sectional geometry of FRP shapes, buckling is the most likely mode of failure before material failure. In this paper, explicit analyses of local buckling of rectangular orthotropic composite plates with various unloaded edge boundary conditions (i.e., (1) rotationally restrained along both unloaded edges (RR), and (2) one rotationally restrained and the other free along the unloaded edges (RF)) and subjected to uniform in-plane axial action at simply-supported loaded edges are first presented. A variational formulation of the Ritz method is used to establish an eigenvalue problem, and explicit solutions of plate local buckling coefficients in term of the rotational restraint stiffness (k) are obtained. The two cases of rotationally restrained plates (i.e., the RR and RF plates) are further treated as discrete plates of closed and open sections, and by considering the effect of elastic restraints at the joint connections of flanges and webs, the local buckling of different FRP shapes under uniform axial compression is studied. The approximate expressions of the rotational restraint stiffness (k) for various common FRP sections are provided, and their application to sectional local buckling predictions is illustrated. The explicit local buckling formulas of rotationally restrained plates are validated with the exact transcendental solutions. The analytical predictions for local buckling of various FRP profiles based on the present discrete plate analysis and considering the elastic restraints of the flange–web connections are in excellent agreements with available experimental results and finite element eigenvalue analyses. A design guideline for local buckling prediction and related performance improvement is proposed. The present explicit formulation can be applied effectively to determine the local buckling capacities of composite plates with elastic restraints along the unloaded edges and can be further used to predict the local buckling strength of FRP shapes.     

Starting solutions for some unsteady unidirectional flows of a second grade fluid

Exact solutions corresponding to the motions of a second grade fluid, due to the cosine and sine oscillations of an infinite flat plate as well as those induced by an oscillating pressure gradient are determined by means of the Fourier sine transforms. These solutions, presented as sum of the steady-state and transient solutions, satisfy both the governing equations and all associate initial and boundary conditions. In the special case when α₁ → 0, they reduce to those for a Navier-Stokes fluid.     

间接蒸汽加热时二元连续精馏塔提馏段操作线方程

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安钢高强板AH60的生产实践

本文论述了高强度低合金钢板AH60的试制过程，结合产品技术要求和生产实际设计合理的成分体系和工艺路线。     

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介绍电液变阻起动器的结构设计、性能特点、工作原理及系统构成，详细介绍了电液变阻起动过程的可编程控制技术。与其他传统的降压起动方式相比，该系统由于在起动过程中两极板的距离均匀缩短，阻值线性降低，因此电机具有良好的软起动性能。     

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从显微组织、断口形貌、原材料状态、加工工艺和装配等方面对燃油泵弹性薄元件在生产中常见的断裂原因进行了分析；并对其进行了工艺试验的对比分析。认为其失效模式主要与氢脆、回火脆及原材料组织状态有关。提出了预防措施。     

落锤试验测定船板的无塑性转变温度

无塑性转变温度是安全设计的重要参量，广泛应用于材料研究和产品质量控制过程。利用落锤试验方法，测定了AH36级船板的无塑性转变温度为-25℃，并对试验结果进行了评定。结果表明，落锤试验方法简单，试验数据重复性好，当船板的服役温度高于NDTT时，基本保证船板不会发生脆断。     

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作者介绍了气动标记机的作用、基本构成和工作原理,指出目前标记机控制系统中存在的一些不足,在此基础上研究了气动标记机系统中的若干关键算法,提出了NURBS曲线插补、加工轨迹优化的一种实现算法。     

异齿宽齿轮泵的研究

概述了直齿轮泵和斜齿轮泵的困油特性及目前解决困油问题的方法。通过对齿轮泵的结构调整，得出消除齿轮泵的困油现象的新方法。通过与卸荷槽法进行比较，总结出异齿宽齿轮泵的优点及其技术要点，并给出了轴套的结构尺寸。     

数控车床加工效率的优选研究

以齿轮零件为例,介绍了数控车床加工时对怎样合理安排加工顺序,走刀路线、刀具的选择及切削要素的确定进行了分析,对在数控车床上加工类似零件有一定的参考价值。