Nonlinear analysis of residual stresses in a rail manufacturing process by FEM

The aim of this paper is to study the residual stresses in an UIC-60 rail and their reduction by means of roller straightening. Both experimental and numerical investigations have been carried out in the past to reveal the formation of dominant longitudinal residual stresses. However, the agreement between both investigations was not particularly good. The finite element method (FEM) has also been used to simulate one, two and three-dimensional analyses of a rail during roller straightening processes. The present model considers the longitudinal movement of a rail through the straightening machine, contact conditions between rail and rollers and kinematic hardening so as to take into account the plastic behaviour of the rail material (steel). These results were compared with the experimental investigations and good agreement was observed. In this respect, this paper presents a novel, more realistic numerical simulation by FEM for the roller straightening process. Finally, an improvement of the straightening process in order to obtain smaller residual stress in the rail section is proposed.     

A consistent implementation for inelastic materials in an ALE formulation for steady state rolling contact

The numerical analysis of rolling contact for rubber materials is a challenging task, especially due to the many nonlinearities inherent to the material, large deformations, friction, and energy dissipation, among others. Industrial applications can be found in ball bearings, rollers, and most commonly in tires of vehicles, applications where reliable numerical simulations lead to the improvement of durability, performance and safety. While a transient analysis stands as a practical and powerful tool for the simulation of rotating bodies, the large amount of computational resources required represents its biggest disadvantage. An alternative frequently used lays in a steady state simulation by means of an Arbitrary Lagrangian Eulerian (ALE) formulation, where the rotational velocity and axial loads are assumed to remain constant. Within this framework, the reference configuration is neither attached to the material particles nor fixed in space and special attention should be paid to the history variables of inelastic materials. In this work, a viscoelastic material model is implemented in an in-house finite element code, based on a generalized Maxwell model. The implementation takes into consideration the contribution of all elements connected in circumferential direction and a consistent linearization is made for each of them, leading to an assembled stiffness matrix with more non-zero values than a standard one. This approach is combined with smeared reinforcement embedded in base elements. The reinforcing layers are described by a hyperelastic material model, providing additional advantages for the modeling and simulation of reinforced rollers and tires. Numerical results for different examples show the capabilities of this implementation and the efficiency of the numerical algorithms is discussed. Important remarks and an outlook for further research concludes this presentation. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A generic approach to measuring the machine flexibility of manufacturing systems

Despite extensive studies on the flexibility of manufacturing systems over the last two decades, a unified measurement approach has not been developed. To this end, we integrate two domains of machine flexibility models from the literature: operational capability-based machine flexibility and time and cost-based machine flexibility, and propose a generic model to measure machine flexibility with consideration of uncertainties in the system. Furthermore, in our approach we include part characteristics such as processing time and processing cost, the number of operations that a machine can perform, and uncertainties in demand and machine-part assignment. The resulting framework to measure machine flexibility is a two-stage model: a super efficiency Data Envelopment Analysis Model and a flexibility model. The results show that the marginal system machine flexibility does not always increase as the number of operations that a machine can perform increases, and the system machine flexibility depends on the demand uncertainty.     

Prediction of the paper path in a laser printer by finite element analysis

A conventional problem of paper handling in a page-printing printer is to design a reliable paper path. Sometimes, this also affects the printing quality. The nonlinear theory of elastica has often been used to model paper deflection shape and to predict the paper path between some guiding rollers. The present paper proposes another method that can solve this problem more efficiently. Considering a piece of paper as a nonlinear beam, finite element analysis with geometric nonlinearity and manipulating the contact gap element between paper and guiding surfaces can be used to simulate the large-deflection behavior of paper. In this paper, the paper path in the vicinity of an OPC (organic photoconductive) drum is investigated with a general purpose finite element package. The effect of the electrostatic force between the OPC drum and the paper is considered, and the deformed shape of the paper for different forces lengths is obtained. According to those results an appropriate paper guide is added for an exact paper path.     

Aggregation and disaggregation in hierarchical production planning

This paper reports on a simulation study of hierarchical planning procedures, which can support a material requirements planning system. Data for this study have been obtained from a Swedish manufacturing company. The three final products considered in the simulations represent a major part of this company.An aggregate plan in terms of product groups and machine groups is derived with the aid of an aggregate model. This plan is then disaggregated by changing order release times obtained from material requirements planning, and by distributing extra capacity among individual machines.The results indicate that our methods in general perform significantly better than a comparable reference case without the supporting hierarchical planning process. In our simulation experiments we evaluate different design features, like disaggregation procedures and methods for aggregating items and machines.     

Structure control classification and optimization model of hollow carbon nanosphere core polymer particle based on improved differential evolution support vector machine

The structure of core polymer particle is an important index of efficiency in hollow carbon nanosphere. How to control and optimize the structure of core polymer particle has been investigated using pattern recognition method in this research. A novel method of pattern recognition material design based on differential evolution support vector machine was proposed. The control model was established and software was adopted to carry out a digital simulation for the model. Using the model, we found the control criteria and optimized conditions for pore structure of composite polymer. Then, the results are compared to other classification methodologies. Experimental results show this model has higher classification accuracy in most of data sets. Experimental and dynamics results show that the properties of hollow carbon nanosphere have been greatly improved.     

Unsupervised and semi-supervised extreme learning machine with wavelet kernel for high dimensional data

Extreme learning machine (ELM) not only is an effective classifier in supervised learning, but also can be applied on unsupervised learning and semi-supervised learning. The model structure of unsupervised extreme learning machine (US-ELM) and semi-supervised extreme learning machine (SS-ELM) are same as ELM, the difference between them is the cost function. We introduce kernel function to US-ELM and propose unsupervised extreme learning machine with kernel (US-KELM). And SS-KELM has been proposed. Wavelet analysis has the characteristics of multivariate interpolation and sparse change, and Wavelet kernel functions have been widely used in support vector machine. Therefore, to realize a combination of the wavelet kernel function, US-ELM, and SS-ELM, unsupervised extreme learning machine with wavelet kernel function (US-WKELM) and semi-supervised extreme learning machine with wavelet kernel function (SS-WKELM) are proposed in this paper. The experimental results show the feasibility and validity of US-WKELM and SS-WKELM in clustering and classification.     

Scheduling orders on either dedicated or flexible machines in parallel to minimize total weighted completion time

We are interested in the problem of scheduling orders for different product types in a facility with a number of machines in parallel. Each order asks for certain amounts of various different product types which can be produced concurrently. Each product type can be produced on a subset of the machines. Two extreme cases of machine environments are of interest. In the first case, each product type can be produced on one and only one machine which is dedicated to that product type. In the second case, all machines are identical and flexible; each product type can be produced by any one of the machines. Moreover, when a machine in this case switches over from one product type to another, no setup is required. Each order has a release date and a weight. Preemptions are not allowed. The objective is minimizing the total weighted completion time of the orders. Even when all orders are available at time 0, both types of machine environments have been shown to be NP-hard for any fixed number (≥2) of machines. This paper focuses on the design and analysis of approximation algorithms for these two machine environments. We also present empirical comparisons of the various algorithms. The conclusions from the empirical analyses provide insights into the trade-offs with regard to solution quality, speed, and memory space. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. This research is supported by the National Science Foundation through grants DMI-0300156 and DMI-0245603.     

Optimal maintenance of two stochastically deteriorating machines with an intermediate buffer

We consider a manufacturing system in which an input generating installation transfers a raw material to a subsequent production unit. Both machines deteriorate stochastically with usage and may fail. For each machine the deteriorating process is described by some known transition probabilities between different degrees of deterioration. A buffer has been built between the two machines in order to cope with unexpected failures of the installation. A discrete-time Markov decision model is formulated for the optimal preventive maintenance of both machines. The maintenance times are geometrically distributed and the cost structure includes operating costs, storage costs, maintenance costs and costs due to the lost production. It is proved that for fixed buffer content and for fixed deterioration degree of one machine, the average-cost optimal policy initiates a preventive maintenance of the other machine if and only if its degree of deterioration exceeds some critical level. We study, by means of numerical results, the effect of the variation of some parameters on the optimal policy and on the minimum average cost. For the case in which the maintenance times follow continuous distributions, an approximate discrete-time Markov decision model is proposed.     

关于钻尖的变导程拟螺面磨法的研究

本文介绍了确保钻尖质量的变导程拟螺面磨法、相应的几何优化模型及其算法,由于经过实例计算和3659开刃机上的试验的验证,因而本文为磨得高质量钻尖提供了可靠依据。     

从支持向量机到非平行支持向量机

非平行支持向量机是支持向量机的延伸,受到了广泛的关注.非平行支持向量机构造允许非平行的支撑超平面,可以描述不同类别之间的数据分布差异,从而适用于更广泛的问题.然而,对非平行支持向量机模型与支持向量机模型之间的关系研究较少,且尚未有等价于标准支持向量机模型的非平行支持向量机模型.从支持向量机出发,构造出新的非平行支持向量机模型,该模型不仅可以退化为标准支持向量机,保留了支持向量机的稀疏性和核函数可扩展性.同时,可以描述不同类别之间的数据分布差异,适用于更广泛的非平行结构数据等.最后,通过实验初步验证了所提模型的有效性.     

A note on factor substitution in industrial production processes

Summary An industrial production process turns out a single product, the inputs being raw material, machine services, labour, and power. The machine is operated by one worker. The rate of output can be increased by speeding up the machine. Since this requires not only more raw material per hour but also more power as well as harder work and increased wear and tear, it has been argued that partial factor variation, and thus also factor substitution, is impossible. It is shown by a mathematical model that, if labour and machine service are measured in hours of effective operation per period, the case is actually characterized by substitution between this factor complex and power input, with raw material as a limitational shadow factor.

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Zusammenfassung In einem industriellen Produktionsprozeß werde ein Produkt aus einem Werkstoff unter Verwendung einer von einem Arbeiter bedienten Maschine hergestellt. Durch eine Erhöhung der Arbeitsgeschwindigkeit der Maschine kommt ein höherer Ausstoß zustande. Dies erfordert nicht nur erhöhte Material- und Treibstoffmengen, sondern auch zusätzlichen Arbeitseinsatz und größere Maschinenbeansprunchung (Verschleiß, Reparatur), was dem Anschein nach bedeutet, daß der Grenzertrag jedes einzelnen Faktors Null ist, so daß Faktorsubstitution ausgeschlossen ist. Diese Schlußfolgerung erweist sich jedoch als irrig. In einem mathematischen Modell des Prozesses sind Arbeits- und Maschinenstunden sowie Treibstoff substitutionale Faktoren; nur Rohstoff ist ein limitationaler Schattenfaktor.

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Vorgel. v.:M. Beckmann     

A new approach towards integrated cell formation and inventory lot sizing in an unreliable cellular manufacturing system

This paper presents a comprehensive mathematical model for integrated cell formation and inventory lot sizing problem. The proposed model seeks to minimize cell formation costs as well as the costs associated with production, while dynamic conditions, alternative routings, machine capacity limitation, operations sequences, cell size constraints, process deterioration, and machine breakdowns are also taken into account. The total cost consists of machine procurement, cell reconfiguration, preventive and corrective repairs, material handling (intra-cell and inter-cell), machine operation, part subcontracting, finished and unfinished parts inventory cost, and defective parts replacement costs. With respect to the multiple products, multiple process plans for each product and multiple routing alternatives for each process plan which are assumed in the proposed model, the model is combinatorial. Moreover, unreliability conditions are considered, because moving from “in-control” state to “out-of-control” state (process deterioration) and machine breakdowns make the model more practical and applicable. To conquer the breakdowns, preventive and corrective actions are adopted. Finally, a Particle Swarm Optimization (PSO)-based meta-heuristic is developed to overcome NP-completeness of the proposed model.     

Simulation of powder metallurgical coating by radial axial ring rolling

The process integrated powder coating by radial axial rolling of rings is expected to provide a new hybrid production technique to apply different kinds of powder metallurgical functional surfaces to ring–shaped work pieces. The main advantages compared with conventional manufacturing processes in this field can be found in lower costs, shorter process cycles and larger producible work pieces. In order to meet the requirements for an industrial application of this new process it is important to proof its capability particularly with regard to reproducibility and to investigate its boundaries. A reliable process simulation will provide a deeper insight into the governing parameters and reduce the money and time consuming experimental tests. Considering a numerical simulation using the FE method two challenges can be named. First one requires a material model to describe the compaction of metal powder at different elevated temperatures. As second the simulation of the ring rolling process itself is still very time consuming. A fine spatial discretization due to large deformations in the rolling gap and contact interaction between workpiece and rollers are the most prevailing factors in this context. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear modeling and analysis of a rolling element bearing with a clearance

Rolling element bearings are the key components in many rotating machinery. For efficient performance of the machine it is necessary to accurately predict the effect of various parameters and operating conditions on the machine’s behavior. This paper deals with the development of a nonlinear model of the rotor-bearing system on rolling element bearings with clearance. Clearance is an important nonlinearity which can cause bifurcations and chaos as has been shown in this paper. In this paper a detailed model for clearance is developed. In this model the inner race center and the outer race center are not assumed to be collinear when relations for deflections in the rolling element are developed. The model is non-dimensionalized and then analyzed to reveal rich nonlinear phenomena. Further, for better performance of any machine it is necessary to identify and stay out of chaotic regimes of operation. Hence, Lyapunov exponents and Poincaré mappings are used to analyze the system and determine the regions of chaotic response.     

基于特征正交分解的材料微结构参数化表征模型及等效性能优化设计

随着计算能力的不断发展,近年来基于材料微结构图像的材料等效性能数值模拟越来越受到学者们的重视.在此背景下,提出了一种针对材料微结构图像的高效参数化表征模型.通过特征正交分解(proper orthogonal decomposition,POD)对已有材料微结构图像数据进行特征分析,得到近似描述该类材料微结构的特征缩减基.应用移动最小二乘(moving least squares,MLS)法建立特征缩减基映射系数的响应面模型,拟合得到任意给定参量相应的缩减基映射系数.利用拟合缩减基系数可获得任意给定参量对应的微结构图像矩阵.该参数化表征模型被用于表征含椭球夹杂的两相材料(2-phase composite)的二维情形, 并进一步应用于这类复合材料宏观等效力学性能的优化设计.     

基于故障树和混沌粒子群算法的锻压机床故障诊断方法

锻压机床由于生产效率高和材料利用率高的特点,被广泛应用于各领域.然而,锻压机床发生故障时,其故障种类繁多、故障数据量大,所以对锻压机床故障源的快速、准确诊断较困难.针对该问题,文章提出一种将故障树分析法和混沌粒子群算法相融合的方法,对锻压机床的故障源进行故障诊断.该方法是先通过故障树分析法对锻压机床的故障进行分析从而得到故障模式及其故障概率,然后由得到的故障模式和已知的故障维修经验分析归纳出故障模式的学习样本,再根据得到的故障概率运用混沌粒子群算法的遍历性快速、准确地诊断出锻压机床发生故障的精确位置.文章提出的方法以锻压机床的伺服系统为例进行了故障诊断实验,将该实验结果与遗传算法、粒子群算法进行对比.实验结果表明,文章的算法在锻压机床伺服系统的故障诊断中准确度更高、速度更快.     

Evaluation of self-activating temperature influence on cracks initiation in GRP laminates

The paper deals with problems of fatigue processes of GRP laminates under the influence of cyclic loads. An important aspect which takes place in laminate fatigue with polymer matrix is self-activating temperature generated by friction. As it has been shown in previous authors' research, the phenomenon has significant influence on laminate behavior, also, when self-activating temperature comes to glass-transition temperature, which begins transition from elastic to viscoelastic material model. After passing over of this temperature the stiffness decreasing is supervised, that can lead to more quick propagation of faults (especially delaminations) and decreasing of life cycle of composite laminate element. The aim of the presented paper is simulation research of fatigue processes with taking into consideration self-activating temperature and rheology of material. In the research four cases are analyzed, in which layers rotation, self-activating temperature increasing and changes of rheological model were taken into consideration. As the research shows, the self-activating temperature has significant influence on fatigue processes, because it can cause transition of the rheological model of the material. In the future research an experimental verification of the model is planned. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A material model of nonlinear fractional viscoelasticity

Multiscale methods are frequently used in the design process of textile reinforced composites. In addition to the models for the local material structure it is necessary to formulate appropriate material models for the constituents. While experiments have shown that the reinforcing fibers can be assumed as linear elastic, the material behavior of the polymer matrix shows certain nonlinearities. These effects are mainly due to strain rate dependent material behavior. Fractional order models have been found to be appropriate to model this behavior. Based on experimental observations of Polypropylene a one-dimensional nonlinear fractional viscoelastic material model has been formulated. Its parameters can be determined from uniaxial, monotonic tensile tests at different strain rates, relaxation experiments and deformation controlled processes with intermediate holding times at different load levels. The presence of a process dependent function for the viscosity leads to constitutive equations which form nonlinear fractional differential equations. Since no analytical solution can be derived for these equations, a numerical handling has been developed. After all, the stress-strain curves obtained from a numerical analysis are compared to experimental results. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation model for anisotropic fibrous materials

Paper and paper–based materials such as cardboard are used in a wide variety of applications and in the development of new applications such as boxes an accurate simulation model is of major importance. Industrially made paper material typically has an orthotropic fibrous structure, due to the manufacturing process, where the fibers tend to align in the direction of motion in the machine. In this work a plasticity–based material model allowing for finite strains is developed. The model is suitable for materials with an anisotropic fibrous structure such as paper. The general framework is based on separate mappings describing the deformations of the continuum and the substructure and a multiplicative split of these mappings into elastic and plastic parts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)