Forming limits of AL 6022 sheets with material damage consideration—theory and experimental validation

Characteristics of localized necking in sheet metals are examined with anisotropic plasticity as well as anisotropic damage developed progressively after load application. The vertex theory is employed to describe basic mechanisms of localized necking. Anisotropic plasticity is accounted for by Hill's quadratic yield criterion. An anisotropic damage model based on Continuum Damage Mechanics is reviewed and expanded. The anisotropic damage model is combined with a modified vertex theory to generate damage-coupled localized necking criteria on both sides of forming limit diagram (FLD). The criteria lead to explicit expressions of critical hardening modulus on both sides of FLD. It is shown that the damage-coupled FLD model can be readily reduced and used to predict the forming limit strains of damage-free materials satisfying power hardening law given by other researchers (Hill, J. Mech. Phys. Solids. (1952)1,19; Zhu et al., ASME J. Eng. Mater. Tech. (2001) 123, 329). Critical damage value at localized necking can be computed from the damage-coupled localized necking criteria as a function of stress/strain states and strain paths. Tests on the formability and material properties of Al 6022, such as hardening and damage law, anisotropic plasticity parameter, have been performed. The measured FLD of the material are compared with the predictions based on the damage-coupled localized necking criteria for validation of the proposed FLD model. Material damage is observed to have a definite effect on the forming limits of Al 6022, thus providing a more accurate prediction than that of the conventional models.     

Book Reviews

Book reviewed in this article: Die Gewebe des Menschen und der Sāugetiere (The Tissues of Man and Mammals) . By R. V. Krsti?. Springer, Heidelberg Laser Spectroscopy: New Developments and Applications . Edited by F. Aussenegg. Springer, Vienna In Vitro Aspects of Erythropoiesis . Editor: M. J. Murphy, Jr; Co-Editors: C. Peschle, A. S. Gordon, E. A. Mirand. Springer, Berlin Electron Microscopy in Human Medicine , Volume 2. Cellular Pathobiology, Metabolic and Storage Diseases . Edited by Jan Vincents Johannessen. McGraw-Hill International Book Company, 1978.     

Numerical modelling of cold compaction of metal powder

A finite element programme has been developed for the analysis of porosity and stress distributions in a powder compact, based on rate-independent finite strain plasticity theory. The strain hardening versions of the Gurson model (J. Engng. Mater. Technol., 1977, 99, 2-15), the more recent FKM model (J. Mech. Phys. Solids, 1992, 40(5), 1139-1162), developed by Fleck, Kuhn and McMeeking, and a combination of the two models are used. The friction between the mould wall and the metal powder is modelled by a combination of Coulomb friction and a constant friction shear stress, since Coulomb friction is not realistic at high normal pressures. The finite element programme has been used to study the effects of friction, compaction method, and material parameters. Analyses for powder compacts of various geometries are presented to illustrate the method.     

The effect of an oscillatory entrainment velocity on the film thickness in thermal EHL point contact

In this study, the mathematical model for transient thermal elastohydrodynamic lubrication (EHL) was established and the effect of tangential vibration on thermal EHL was investigated. The pressure calculation was carried out by a multi-grid technique, the elastic deformation was evaluated by a multilevel multi-intergration method, and the temperature was calculated by a single-direction sequential column sweeping process. The present study aims to explain the multi-dimple phenomenon observed experimentally by Ehret and Bauget [Proc Inst Mech Eng Part J: J Eng Tribol 2001; 215: 289–300]. The results show that a tangential vibration produces significant change of pressure and film thickness and it seems to be the most possible mechanism of the movement of multi-dimples observed by Ehret and Bauget [Proc Inst Mech Eng Part J: J Eng Tribol 2001; 215: 289–300]. Furthermore, the effect of the curvature radius, viscosity–pressure coefficient, load and the parameters of vibration was also investigated.     

Modelling of inelastic bending of a metal sheet with thermal coupling

The modelling and numerical analysis of inelastic bending of a metal sheet are presented. The distribution strains and stresses are found for slow and fast bending while taking into account the geometrical and material non-linearities. The constitutive relation of Klepaczko, (Int. J. Plast. 17 (2001) 87, Comput. Methods Appl. Mech. Eng. 175 (1999) 19) was used which includes strain hardening, strain rate sensitivity and temperature effect in material behaviour. The large strains are assumed under plane strain conditions. The results with complete thermal coupling are compared with solutions obtained in the isothermal conditions of bending.     

The Ingenious Structure of Scorpion Armor Inspires Sand-Resistant Surfaces

Erosion is so widespread and undesirable in various engineering applications such that it is so incumbent to find anti-erosion means to address it. In previous researches (Han et al. in J Bionic Eng 7(09):S50–S58, 2010; J Wuhan Univ Technol Mater Sci Ed 26(2):305–310, 2011; Langmuir 28(5):2914–2921, 2012; Adv Colloid Interface Sci 234:27–50, 2016; Surf Coat Technol 313:143–150, 2017; Zhang et al. in Adv Mater Sci Eng 2013(5):1–9, 2013), people found that the surface of desert scorpion Androctonus australis, which belonged to the parabuthus, had very complex microstructures that had the strong anti-erosion qualities in the blown sand environment. Here, through further research, a new microstructure, hexagonal pit structure, was firstly discovered on the back of desert scorpion. These microstructures were applied in the design of biomimetic samples, which were fabricated by 3D printer using EOS stainless steel GP1. These biomimetic samples were used to test the erosion rate under the impact of quartz sand of three different sizes. The experiment was carried out using a blasting jet machine with injection angle, velocity and time of 30°, 25 ms^?1 and 90 s, respectively, and the results showed that the biomimetic samples with different microstructures had better anti-erosion performance. The hexagonal pit structure, whose depth was 200–300 μm and the length was 200–500 μm, had also good anti-erosion performance. The physical model was established to express the mechanism of anti-erosion by controlling the motion direction and impacting velocity of the particles. The anti-erosion performance of all these biomimetic samples can be quantified by the erosion rate and improvement rate. On the whole, these microstructures all have good anti-erosion effect; hence, this paper research is of great practical significance.     

A note on “A comparative evaluation of assembly line balancing heuristics”

SALBP-1 is the assembly line problem most represented in the literature. Many exact and heuristic procedures have been designed to solve it, and several papers comparing them have been published. Since Ponnanbalam et al. (Int J Adv Manuf Technol 15:577–586, 1999) is often referred, it is worth noting that the definition of “positional weight” given there is not right, since it does not coincide with that was originally published in Helgeson and Birnie (J Ind Eng 12(6):394–398, 1961). This implies that the conclusions in Ponnanbalam et al. (Int J Adv Manuf Technol 15:577–586, 1999) should be revised.     

Upper-bound modelization of an ironed three-layered polymer-coated steel strip

Global beverage can and food container consumption is very high, with billions of cans produced annually worldwide. There are several steps in can manufacturing, but ironing is the most crucial. In a previous work (Sellés et al., J Mater Process Technol 202:7–14, 2008), a series of ironing experiments were reported using a new material and an ironing simulator. This material was a three-layered polymer-coated steel, and it was seen that under some process conditions, it survived the ironing process with no damage in any of the three layers. The critical die angle was determined as well as specimen quality surface tests. In this paper, an associated theoretical ironing model is described, using the upper-bound theorem and considering the cases of successful ironing or shaving. It is possible to give insight into how to design a material that irons well. For example, the optimal layer thicknesses are also found.     

A note on “A multi-objective genetic algorithm for solving assembly line balancing problem”

Assembly line balancing has a considerable place in industrial importance. Hence, a lot of researchers are interested in this subject and several papers have been published so far. Many exact, heuristic, metaheuristic, and hybrid approaches have been used to solve this type of problems. Recently Ponnanbalam et al. (Int J Adv Manuf Technol 16:341–352, 2000) have considered a multi-objective genetic algorithm utilizing several simple heuristic rules for solving the simple assembly line balancing problems, one of these rules was “rank positional weight (RPW)” originally published in Helgeson and Birnie (J Ind Eng 12(6):394–398, 1961). Through providing two possible justifications, this note suggests that the mentioned rule can be mistakenly utilized and some revisions in Ponnanbalam et al. (Int J Adv Manuf Technol 16:341–352, 2000) seem to be necessary.     

复合材料疲劳损伤演化的两阶段模型

针对复合材料疲劳损伤的特征,将损伤过程分为减速损伤和加速损伤两个阶段;基于连续介质损伤力学的概念,建立了疲劳损伤演化两阶段模型。并用此模型描述了ＳｉｌｉｃｏｎｅＸ２３８、Ｃｈｌｏｒｏｐｒｅｎｅ、Ｎｏｒｙｌ ＧＴＸ８３０等复合材料的疲劳损伤。结果表明,提出的两阶段模型与试验结果吻合较好。     

高性能偏振膜的研制

综述了国内外科研人员在高性能偏振膜的研制方面开展的工作,主要涉及偏振膜光谱性能、抗激光损伤阈值和膜层应力控制等方面的研究。针对我国神光系列装置对偏振膜的性能要求,简述了中国科学院上海光学精密机械研究所采用电子束沉积技术在光谱性能、损伤阈值和面形精度三个方面开展的研究工作。给出了在薄膜设计、制备和后处理等方面进行的研究和取得的进展。结合上述研究成果,得到了低缺陷密度、低应力的高性能偏振膜。由本科研团队研制的布儒斯特角薄膜偏振器在在2012年和2013年SPIE激光损伤国际会议(SPIE Laser Damage)组织的全球性偏振膜激光损伤阈值水平竞赛中连续取得了p分量损伤阈值和平均损伤阈值最佳的结果。另外,通过解决应力诱导膜层龟裂的重大技术问题,在国内首先推出了大口径偏振片,该大口径偏振片满足透射率TP98%,反射率RS99%的光谱性能要求和17J/cm2(9ns)的通量运行要求,有力支撑了我国SGII-UP大型激光装置的稳定运行。     

A static friction model for tube bulge forming using a solid bulging medium

In a metal working process, the friction between the material and the tools influences the process by modifying the strain distribution of the workpiece. From a numerical point of view, a constant coefficient of friction (Coulomb’s friction) is commonly used in finite element simulations to model the frictional behaviour of contacting solids. However, friction coefficient varies in time and space with many parameters. We presented here a theoretical model of static friction in rubber/metal contact which allows the determination of the static coefficient of friction as a function of local contact conditions. Simulations using finite element software ABAQUS/Explicit were carried out for an axisymmetric tube bulging operation using the defined friction model. We compared the computed tube thickness related to the constant coefficient of static friction with the defined friction model. The results clearly showed that the new friction model provides better agreement between experiments (Girard, Grenier, Mac Donald, J Mater Process Technol 172:346–355, 2006) and results of numerical simulations.     

Cutting force prediction in ball-end milling with inclined feed by means of geometrical analysis

A geometrical model for the analysis of cutting forces in ball-end milling has been presented in a previous work (Tsai CL, Liao YS, J Mater Process Technol 205:24–33, 10), which can be used to analyze cutting forces in vertical or horizontal feed. In this paper, the three-dimensional geometrical analysis is depicted with different interacting relations among cutting edge, undeformed chip and shear zone along nonhorizontal cutting direction, and a general geometrical model of inclined feed in ball-end milling is presented. According to the geometrical analysis, the cutting directions of horizontal, vertical, inclined downward, and inclined upward feed are defined with a feed angle. A general force model is derived, and the three-dimensional cutting forces are predicted. Experiments are conducted to verify the geometric force model. The influences of different feed angle and helix angle on cutting forces in inclined downward and inclined upward feed are discussed and simulated.     

An approximate method for the solution of an influence function foil rolling model

Fleck and Johnson (Int. J. Mech. Sci. 29 (1987) 507) and Fleck et al. (Proc. Inst. Mech. Eng. 206 (1992) 119) have developed foil rolling models which allow for large deformations in the roll profile, including the possibility that the rolls flatten completely. However, these models require computationally expensive iterative solution techniques. A new approach to the approximate solution of the Fleck et al. (1992) Influence Function Model has been developed using both analytic and approximation techniques. The numerical difficulties arising from solving an integral equation in the flattened region have been reduced by applying an Inverse Hilbert Transform to get an analytic expression for the pressure. The method described in this paper is applicable to cases where there is or there is not a flat region.     

Distributed flexible reconfigurable condition monitoring and diagnosis technology

As manufacturing becomes increasingly decentralized, flexible and reconfigurable, more research needs to be done on monitoring and diagnosis technology that accommodate these new trends. The distributed condition monitoring and diagnosis technology based on the “flexible and reconfigurable” concept is studied here. A condition monitoring diagnosis model based on the distributed flexible and reconfigurable idea is proposed in this paper. The component makeup and functions of this model are discussed in detail. The model can fulfill in most instances the manufacturing system requirements for changing the configuration of the monitoring diagnosis system according to different manufacturing system configurations. This model also realizes the flexibility and reconfigurability of the monitoring diagnosis system in some degree. The model has already spawned a successful prototype for monitoring a chemical plant in accomplishing monitoring and control of the production process and equipment. Finally, some future research work is pointed out. __________ Translated from Chin. J. Mech. Eng., 2004, 40 (3) (in Chinese)     

Effective heuristics for the no-wait flow shop scheduling problem with total flow time minimization

The no-wait flow shop scheduling problem with total flow time criterion has important applications in industrial systems. Heuristics that explore specific characteristics of the problem are essential to find good solutions in limited computational time for many practical applications. This paper first presents two constructive heuristics, namely improved standard deviation heuristic (ISDH) and improved Bertolissi heuristic (IBH), by combining the standard deviation heuristic (Gao et al., Int J Adv Manf Technol 56:683–692, 2011) and Bertolliso heuristic (Bertolissi, J Mater Process Technol 107:459–465, 2000) with the procedure of the constructive heuristic of Laha (Int J Adv Manf Technol 41:97–109, 2009). Then, four composite heuristics, i.e., ISDH with local search, IBH with local search, ISDH with iteration, and IBH with iteration, are separately proposed using the insertion-based local search method and iteration operator to improve the solutions of the ISDH and IBH. Extensive computational experiments are carried out based on a set of well-known flow shop benchmark instances that are considered as no-wait flow shop instances. Computational results and comparisons show that the proposed composite heuristics perform significantly better than the existing ones, and the proposed composite heuristics further improve the presented constructive heuristics for the no-wait flow shop scheduling problem with total flow time criterion.     

Damage evolution and thermal coupled effects in inelastic solids

Mechanical degradation and ductile failure in metal forming operations can be successfully modelled using Continuum Damage Mechanics. In addition to elastic-plastic deformations, heat transfer affects material behaviour, imposing further effects upon damage evolution. This paper addresses modelling aspects and presents a numerical discussion of the coupled effects between ductile damage and temperature evolution. The heat transfer problem is formulated based on a transient heat conduction approximation, in which heat transfer at the free surfaces and heating due to dissipation of the inelastic work are accounted for. Damage is modelled using an elastic-plastic fully coupled approximation, in which differences in tensile and compressive stress states are included.     

The forging of helical gears (II): comparisons of the forging processes

In this study, the forging processes of helical gears have been investigated wherein they have been classified into two types: the guiding type and the clamping types. These two types of forgings of helical gears have been analyzed by using the upper-bound method. New kinematically admissible velocity fields of the clamping-type forging of helical gears have been proposed, where an involute curve has been introduced to represent the tooth profile of the gear. The proposed velocity fields of the clamping-type forging of helical gears have been applied to the non-symmetric lateral extrusion forging and the result has been compared with the solution proposed by Plancak et al. [J. Mater. Process. Technol. 1992; 34:465–472]. Numerical calculations have been carried out to investigate the effects of various parameters, such as modules, number of teeth, helix angles and friction factors on the clamping-type forging of helical gears. For the forging of helical gears, the results of the upper-bound analysis of the clamping type have been compared with those of the guiding ones. Some experiments of the clamping-type forging were carried out with commercial aluminum alloy to show the validity of the analysis. Good agreement was found between the predicted values of the forging load and the experimental forging load.     

疲劳损伤演变方程与寿命估算—连续损伤力学的应用

基于连续损伤力学理论阐述了有关损伤和疲劳损伤的某些基本概念，包括连续性，损伤度，损伤演变和脆性破坏过程等。关于低周和高周疲劳，分别扼要说明了若干疲劳伤理论模型与方程。最后，依据疲劳过程中损伤演变与残余强度关系，作者建立了实用的疲劳损伤演变方程（包括四种函数形式）。