A dynamic programming approach for minimizing the number of drawing stages and heat treatments in cylindrical shell multistage deep drawing

Deep drawing is an important sheet metal forming process that appears in many industrial fields. It involves pressing a blank sheet against a hollow cavity that takes the form of the desired product. Due to limitations related to the properties of the blank sheet material, several drawing stages may be needed before the required shape and dimensions of the final product can be obtained. Heat treatment may also be needed during the process in order to restore the formability of the material so that failure is avoided. In this paper, the problem of minimizing the number of drawing stages and heat treatments needed for the multistage deep drawing of cylindrical shells is addressed. This problem is directly related to minimizing manufacturing costs and lead time. It is required to determine the post-drawing shell diameters along with whether heat treatment is to be conducted after each drawing stage such that the aforementioned objectives are achieved and failure is avoided. Conventional computer-aided process planning (CAPP) rules are used to define the search space for a dynamic programming (DP) approach in which both the post-drawing shell diameter and material condition are used to define the states in the problem. By discretizing the range of feasible shell diameters starting from the initial blank diameter down to the final shell diameter, the feasible transitions from state to another is represented by a directed graph, based upon which the DP functional equation is easily defined. The DP generates a set of feasible optimized process plans that are then verified by carrying out finite element analysis in which the deformation severity and the resulting strains and thickness variations are investigated. Two case studies are presented to demonstrate the effectiveness of the developed approach. The results suggest that the proposed approach is a valuable, reliable and quick computer aided process planning approach to this complicated problem.     

A method for measuring the thermal geometric parameters of large hot rectangular forgings based on projection feature lines

The online dimensional measurement of large hot forging is an important procedure in the forging process. Because of different production demands, the final geometrical shapes of large forgings are usually different (e.g. cylindrical columns, rectangular prisms). Forgings of different geometric shapes need to be measured along different dimensions. For rectangular forgings, the lengths primarily need to be measured. A generalized measurement system for different geometric shapes of forgings cannot provide the accuracy of measurement systems targeted at measuring a known shape. Based on the characteristics of the rectangular forgings, a thermal dimensional measurement system is proposed in this paper. The localization, rapid extraction of feature points and method for measuring the dimensions of rectangular forgings are presented. The proposed methods can easily and efficiently extract the feature points of the forging. The experiment results show that the method proposed in this paper has the advantages of high precision and high efficiency, which is appropriate for online measurement.     

A finite element study of the effect of the angle between two intersecting cylindrical shells subjected to internal pressure

The results of a study of the critical region of two intersecting cylindrical shells due to internal pressure loading are presented as a function of the angle between the two axes. The investigation was performed using the thin shell element of a three-dimensional finite element program. Three models with the angle between the axes of the two cylindrical shells equal to 30, 60, and 90°, were analyzed. In all of the three models, the diameter ratio of the two shells was 0.5283; the diameter to thickness ratio of the larger or main shell was 44.76, while the same ratio for the smaller or attached shell was 15.487. The results of these analyses show that the stresses in the critical intersection region are least when the two axes are perpendicular to each other; for other angular configurations, the stresses increase as the acute angle between the two axes decrease. This effect of inclination for pressure loading is just opposite of the effect found by authors [1] for external moments. In that case, for in-plane as well as out-ofplane moments, the stresses are larger for normally intersecting shells as compared to other angular configurations.     

功能梯度薄壁圆柱壳的自由振动

研究了由功能梯度材料制成的薄壁圆柱壳的自由振动.采用幂律分布规律描述功能梯度材料沿厚度的梯度性质,根据Donnell壳体理论,导出了功能梯度材料薄壁圆柱壳线性振动的简化控制方程.基于此理论分析了功能梯度圆柱壳的自由振动特性,给出了两端简支功能梯度材料薄壁圆柱壳小挠度固有振动的频率公式.以简支圆柱壳作为算例,与前人结果及有限元法对比验证了该简化功能梯度薄壁圆柱壳理论的正确性,同时讨论了周向波数及梯度指数对其频率的影响.     

双路扫描式激光测径仪系统设计

针对企业对小型零部件生产线上的工件线径检测精度和稳定性问题,研制了一款基于ARM+FPG A的双路扫描式激光测径系统,用于解决扁平形漆包线线径的精确测量问题。该测径系统采用标准棒法测量原理,运用累加求和取平均值的处理算法,实现了工件线径的厚度和宽度双向检测,克服了单路激光测径系统测量范围受限等缺点。实验结果表明,该测径仪精度可达到0.001 mm,示值误差不超过±0.005 mm,稳定性能好,测量精度高,适合于生产线上小尺寸工件线径的精度检测。由于FPGA的快速数据处理能力,本系统特别适用于动态线材的尺寸监测。     

Free vibration analysis of multi-symmetric stiffened shells

The application of structural symmetry techniques to the free vibration analysis of cylindrical and conical shells for the prediction of natural frequencies and mode shapes is described. Appropriate boundary conditions have been developed for the analysis of only a part of the shell and have been shown to yield results comparable to the full shell analysis. Half and quarter models of the shell have been developed and analysed using semi-loof and facet shell finite elements. Unstiffened and stiffened circular cylindrical shells and stiffened conical shells have been considered.     

锅炉筒节匹配算法系统设计和实现

通过调研焊接车间锅炉筒节匹配现状,发现目前的方法是根据工人的经验测量几个点进行匹配.这样的匹配方法不仅不够精确,并且不利于追溯匹配记录.因此,提出锅炉筒节匹配算法的系统设计和实现方法.系统使用激光测距仪代替人工测量,用优化匹配算法代替传统的根据工人经验进行匹配的方法,使筒节匹配过程更精确.首先,利用激光测距仪代替人工测...     

可组态多通道实时测控系统的设计与实现

针对激光实验室现场需要对实验过程进行实时精确测控的要求，设计并实现了一种高效实时测控系统。文章介绍了系统的体系结构，阐述了其模块化设计方法和可组态特性。经实际应用表明，系统实时性强，可靠性高，满足实验现场对采集数据和控制时间的精度要求。     

轴向载荷作用下圆柱壳的屈曲仿真

本文采用非线性有限元方法，在经典刚塑性理论的基础上，考虑了材料非线性、大变形效应对材料的影响，利用大型通用程序LS—DYNA对圆柱壳轴向冲击屈曲过程进行了计算机仿真分析。分析表明，利用非线性有限元数值仿真方法，可以对圆柱壳屈曲这一复杂的力学过程进行真实有效的模拟再现。     

High-precision finite element analysis of cylindrical shells

This paper presents the finite element formulation to study the free vibration of cylindrical shells. The displacement function for the high-precision shell element with 16 degrees of freedom is approximated by a Hermitian polynomial of beam function type. The explicit formulation for the high-precision element is extremely efficient. For the purpose of comparison, the subject element is used to study the sample case of free vibration of a shell structure. The results are in good agreement with those published. The study shows that solution accuracy with fewer elements is assured and that accurate solutions are obtainable in the high-frequency range.     

A three-dimensional state space finite element solution for laminated composite cylindrical shells

On the basis of the theory of three-dimensional elasticity, this paper presents a state space finite element solution for stress analysis of cross-ply laminated composite shells. This is a continuation of the authors’ previously published work on laminated plates [Compos. Struct. 57 (1–4) (2002) 117; Comput. Methods Appl. Mech. Engrg. 191 (37–38) (2002) 4259]. Once again a state space formulation is introduced to solve for through-thickness stress distributions, while the traditional finite elements are used to approximate the in-surface variations of state variables. A three-dimensional laminated shell element is established in an arbitrary orthogonal curvilinear coordinate system, while the application of the element is shown by calculating stresses in laminated cylindrical shells. Compared with the traditional finite element method, the new solution provides accurate continuous through-thickness distributions of both displacements and transverse stresses.     

Reliability-based optimum design of a welded stringer-stiffened steel cylindrical shell subject to axial compression and bending

The economy of stiffened shells vs the unstiffened version depends on loading, type of stiffening and stiffener profile. The stiffening is economic when the shell thickness can be decreased in such a measure that the cost savings caused by this decreasing is higher than the additional cost of stiffening material and welding. The present work deals with cylindrical shell columns fixed at the bottom and free at the top subject to axial compression and horizontal force acting on the top of the column. The shell is stiffened outside with stringers welded by longitudinal fillet welds. Half rolled I-section (UB) stiffeners are used to reduce welding cost. The cost function to be minimized includes the costs of the materials, forming of shell elements into the cylindrical shape, assembly, welding and painting. The design variables are the shell thickness, number and profile of stiffeners for the stiffened shell, but only the first type of variable in the unstiffened case. Randomness is considered both in loading and material properties. A level II reliability method (first-order reliability method) is employed. Individual reliability constraints related with shell buckling, stringer panel buckling and the limitation of the horizontal displacement of the column top are considered. The overall structural reliability is obtained by using Ditlevsen's method of conditional bounding. The costs of both the stiffened and unstiffened shells designed to ensure a stipulated probability of failure will be compared with the solutions obtained for a code-based method, which employs partial safety factors. Results are given illustrating the influence of the constraint on the horizontal displacement.     

Optimization of the crushing characteristics of triangulated aluminum beverage cans

In this study, a cylindrical shell body of the aluminum cans is triangulated and optimized for being folded down easily and safely for recycling. The triangulated cylindrical shell is constructed by a family of triangular surfaces based on one set of helical strips and circles lying on a cylindrical side surface. The intersections of helical strips and circles are used as the vertexes of the triangular surfaces. By changing the helical angle of the strips, the number of the strips, and the number of the circles, various triangulated cylindrical shells with different crushing characteristics can be developed. On the basis of the numerical simulation, the minimization problem of the crushing force of the triangulated cylindrical shells is solved using the crashworthiness maximization technique for tubular structures that combines the techniques of design of experiment, response surface approximation as well as usual mathematical programming.     

A fast algorithm for high accuracy gauging using computer vision

A vision-based inspection system capable of measuring convex-profile cylindrical objects has been developed. Both vertical and horizontal measurements are possible as well as cross-sectional reconstructions. A new algorithm has been developed that minimizes the number of camera views needed to obtain accurate reconstructions. This increases the speed of the analysis procedure. A production version of the inspection system has been installed in a forging plant; for this application camera lenses and other equipment dimensions give a measurement accuracy of ±1.0 mm on length and ±1.5 m² on cross-sectional area.     

用于冷原子干涉仪激光时序控制的DDS跳频系统设计与实现

为了满足冷原子干涉实验对时序控制的需求,设计并实现了一个基于LABVIEW软件的激光时序控制DDS系统,其工作过程为通过设计的LABVIEW上位机软件输入需要产生的频率和频率间隔时间,ARM芯片根据LABVIEW软件发送来的控制信息实现对射频信号芯片的控制,CPLD芯片用来控制射频信号之间的时间间隔,最后DDS芯片产生与控制信息相对应的射频信号。与目前同类装置相比,系统实现了跳频时间和频率更加精确和工作稳定性更好。经过系统的调试分析以及性能测试,DDS跳频系统能够满足原子干涉仪激光时序控制需求。通过测试DDS装置,DDS装置能够输出准确输出射频频率值,并且射频频率时间间隔能精确到微秒。DDS装置可以有效控制冷原子干涉仪的激光时序,在探询时间为120毫秒且重复率为2.2赫兹的情况下,冷原子重力仪的重力测量灵敏度达到 。     

Influence of edge conditions on the modal characteristics of cross-ply laminated shells

The dynamic and static behavior of cross-ply laminated shells are investigated using the third-order shear deformation shell theory of Reddy. The theory is a modification of the Sanders shell theory and accounts for parabolic distribution of the transverse shear strains through the thickness of the shell and does not require shear correction coefficients. The Lévy-type exact solutions for bending, buckling and natural vibration are presented for doubly curved, cylindrical and spherical shells under various boundary conditions.     

Numerical investigation on a laser based localised joining with a glass frit intermediate layer

Localised laser bonding using a glass frit intermediate layer is an ideal technology to hermetically package miniature devices without heating the function components. In this paper, we investigated from a device level packaging perspective, the influence of the laser ring diameter and width, copper boss (heat sink) diameter and misalignment of laser ring in a laser based localised bonding with glass frit intermediate layer. The conclusions are: (1) laser ring diameter and width have slight influence on the bonding process however a system with smaller laser ring diameters achieves better performance compared to that with larger ring diameters. (2) The copper boss (heat sink) diameter has significant influence on the laser power level required to achieve a particular glass frit curing temperature within the glass frit ring. Selection of an appropriate copper boss diameter is determined by the maximum allowable temperature for the temperature-sensitive devices under protection. (3) Misalignment of the laser ring has significant influence on the localised laser bonding and the recommended misalignment deviation for the laser ring should be less than 100 μm.     

封闭空间消防灭火实验中的温度场测量系统

温度场测量系统用于封闭空间消防灭火实验需满足两个条件:测温量程大,系统响应灵敏.介绍了用K型热电偶、高增益数据采集卡和虚拟仪器软件组成的测温系统,去掉热电偶感温端部外壳改进了其响应灵敏性,最后对实际细水雾灭火过程进行实验测量.     

Elastic buckling of double walled cylindrical storage tanks—numerical and analytical estimates

This paper is concerned with estimating the elastic buckling pressures of large liquid natural gas (LNG) storage tanks which are used by the British Gas Corporation for seasonal demand peak shaving. They consist of two concentric ring stiffened cylindrical shells separated by substantial thermal insulation which maintains the LNG within the inner shell at − 165°C with minimal boil off. There is natural gas vapour above the LNG and throughout the tank interior which is normally at just above atmospheric pressure. The shell walls increase in thickness from the top to the bottom and are fabricated from very thin steel or aluminium alloy plates (diameter to thickness ratio ~4000 at the top) since they are usually in hoop tension, but under certain conditions this can become compressive making elastic buckling a possible mode of failure. The individual buckling pressures for the two shells can be estimated using standard procedures but in these LNG tanks the annular insulation transfers loads between the shells enhancing their individual strengths. A numerical method using the finite difference code BOSOR4 and a simple analytical method have been used to estimate these pressures.     

Analysis of laminated shells with laminated stiffeners using rectangular shell finite elements

A finite element analysis of laminated shells reinforced with laminated stiffeners is described in this paper. A rectangular laminated anisotropic shallow thin shell finite element of 48 d.o.f. is used in conjunction with a laminated anisotropic curved beam and shell stiffening finite element having 16 d.o.f. Compatibility between the shell and the stiffener is maintained all along their junction line. Some problems of symmetrically stiffened isotropic plates and shells have been solved to evaluate the performance of the present method. Behaviour of an eccentrically stiffened laminated cantilever cylindrical shell has been predicted to show the ability of the present program. General shells amenable to rectangular meshes can also be solved in a similar manner.