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Plastic Parts (plastic + part)
Selected AbstractsIncremental model for fatigue crack growth based on a displacement partitioning hypothesis of mode I elastic,plastic displacement fieldsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007S. POMMIER ABSTRACT The mode I displacement field in the near crack tip region is assumed to be depicted by its partition into an elastic field and a plastic field. Then, each part of the displacement field is also assumed to be the product of a reference field, a function of space coordinates only, and of an intensity factor, function of the loading conditions. This assumption, classical in fracture mechanics, enables one to work at the global scale since fracture criteria can be formulated as a function of the stress intensity factors only. In the present case, the intensity factor of the plastic part of the displacement field measures crack tip plastic flow rate at the global scale. On the basis of these hypotheses, the energy balance equation and the second law of thermodynamics are written at the global scale, i.e. the scale of the K-dominance area. This enables one to establish a yield criterion and a plastic flow rule for the crack tip region. Then, assuming a relation between plastic flow in the crack tip region and fatigue crack growth allows an incremental model for fatigue crack growth to be built. A few examples are given to show the versatility of the model and its ability to reproduce memory effects associated with crack tip plasticity. [source] An arbitrary Lagrangian,Eulerian finite element method for finite strain plasticityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2003Francisco Armero Abstract This paper presents a new arbitrary Lagrangian,Eulerian (ALE) finite element formulation for finite strain plasticity in non-linear solid mechanics. We consider the models of finite strain plasticity defined by the multiplicative decomposition of the deformation gradient in an elastic and a plastic part (F = FeFp), with the stresses given by a hyperelastic relation. In contrast with more classical ALE approaches based on plastic models of the hypoelastic type, the ALE formulation presented herein considers the direct interpolation of the motion of the material with respect to the reference mesh together with the motion of the spatial mesh with respect to this same reference mesh. This aspect is shown to be crucial for a simple treatment of the advection of the plastic internal variables and dynamic variables. In fact, this advection is carried out exactly through a particle tracking in the reference mesh, a calculation that can be accomplished very efficiently with the use of the connectivity graph of the fixed reference mesh. A staggered scheme defined by three steps (the smoothing, the advection and the Lagrangian steps) leads to an efficient method for the solution of the resulting equations. We present several representative numerical simulations that illustrate the performance of the newly proposed methods. Both quasi-static and dynamic conditions are considered in these model examples. Copyright © 2003 John Wiley & Sons, Ltd. [source] A basic thin shell triangle with only translational DOFs for large strain plasticityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2001Fernando G. Flores Abstract A simple finite element triangle for thin shell analysis is presented. It has only nine translational degrees of freedom and is based on a total Lagrangian formulation. Large strain plasticity is considered using a logarithmic strain,stress pair. A plane stress isotropic behaviour with an additive decomposition of elastic and plastic strains is assumed. A hyperelastic law is considered for the elastic part while for the plastic part a von Mises yield function with non-linear isotropic hardening is adopted. The element is an extension of a previous similar rotation-free triangle element based upon an updated Lagrangian formulation with hypoelastic constitutive law. The element termed BST (for basic shell triangle) has been implemented in an explicit (hydro-) code adequate to simulate sheet-stamping processes and in an implicit static/dynamic code. Several examples are shown to assess the performance of the present formulation. Copyright © 2001 John Wiley & Sons, Ltd. [source] Surface texture characterization of injection-molded pigmented plasticsPOLYMER ENGINEERING & SCIENCE, Issue 9 2004Ingrid Ariño An appropriate description of the surface textures deliberately created on injection-molded plastic parts of interior car components is presented. A spatial wavelength-dependent analysis is used as an interesting alternative to the traditional roughness parameters. Auto-correlation functions and power spectral densities are examples of such spectral functions that include parameters both in amplitude and profile directions. Even fractal concepts can be useful descriptors. As an illustration, it is also shown how the effects on the surface topography of the plastic part of after-etching the mold can be assessed by suitable descriptors. An experimental evaluation of injection-molded plaques containing three different surface patterns was carried out using an optical profilometer, supplemented by contact stylus measurements. The ability to assess the topography of these plaques by means of a new fast photometric stereo-technique, denoted OptiTopo, was also evaluated. In its present form, however, this technique does not provide a detailed description of the topography of a pigmented plastic. Reasons for this and possible improvements are discussed. Polym. Eng. Sci. 44:1615,1626, 2004. © 2004 Society of Plastics Engineers. [source] Factors affecting the formation of fingering in water-assisted injection-molded thermoplasticsADVANCES IN POLYMER TECHNOLOGY, Issue 2 2006Shih-Jung Liu Abstract Water-assisted injection-molding technology has received extensive attention in recent years, due to the lightweight of plastic parts, relatively low-resin cost per part, faster cycle time, and flexibility in the design and manufacture. However, there are still some unsolved problems that confound the overall success of this technology. One of these is the water "fingering" phenomenon, in which the water bubbles penetrate outside designed water channels and form finger-shape branches. This study has investigated the effects of various processing parameters on the formation of fingering in water-assisted injection-molded thermoplastic parts. Both amorphous and semicrystalline polymers were used to mold the parts. The influence of water channel geometry, including aspect ratio and fillet geometry, on the fingering was also investigated. It was found that water-assisted injection-molded amorphous materials gave less fingering, while molded semicrystalline parts gave more fingering when compared to those molded by gas-assisted injection molding. For the water channels used in this study, the channels with a rib on the top produced parts with the least water fingering. Water fingering in molded parts decreases with the height-to-thickness ratio of the channels. The water pressure, water injection delay time and short-shot size were found to be the principal parameters affecting the formation of water fingering. In addition, a numerical simulation based on the transient heat conduction model was also carried out to help better explain the mechanism for the formation of fingering in water-assisted injection-molded thermoplastics. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 98,108, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20062 [source] Control of rotational molding using adaptive fuzzy systemsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2005D. I. Abu-Al-Nadi Abstract Rotational molding is a method for manufacturing hollow plastic parts. In the work reported here, adaptive fuzzy logic techniques have been used to relate the machine oven temperature to other manipulated parameters of the process. The objective is to design a reliable control system for the rotational molding process. An adaptive fuzzy network was developed to correlate changes in oven temperature to changes in the opening of the control valve on the fuel system. The network parameters were optimized using real-valued genetic algorithms. This network gave good results when its performance was compared with experimental data from a commercial rotational molding machine. The network was successfully utilized to design a control system, which works well in regard to set point tracking and load rejection. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 266,277, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20047 [source] A review of current developments in process and quality control for injection moldingADVANCES IN POLYMER TECHNOLOGY, Issue 3 2005Zhongbao Chen Abstract Injection molding is one of the most versatile and important manufacturing processes capable of mass-producing complicated plastic parts in net shape with excellent dimensional tolerance. Injection molding process and quality control has been an active research area for many years, as part quality and yield requirements become more stringent. This paper reviews the state-of-the-art research and development in injection molding control. It organizes prior studies into four categories, namely, process setup, machine control, process control, and quality control, and presents the distinction and connection of these different levels of control. This paper further reviews and compares the typical variables, models, and control methods that have been proposed and employed for those control tasks. Strictly speaking, real online quality control without human intervention has yet to be realized, primarily due to the lack of transducers for online, real time quality response measurement, and a robust model that correlates the control variables with quantitative quality measurements. Based on the research progress to date, this paper suggests that the different levels of control tasks have to be integrated into a multilevel quality control system, and that the quality sensor and the process and quality model are the two most important areas for further advancement in injection molding control. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 165,182, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20046 [source] The occurrence of surface roughness in gas assist injection molded nylon compositesPOLYMER COMPOSITES, Issue 2 2000Shih-Jung Liu Gas assist injection molding has increasingly become an important industrial process because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that limit the overall success of this technique. The purpose of this report was to study the surface roughness phenomenon occurring in gas assist injection molded thermoplastic composities. The materials used were 15 % and 35% glass-fiber filled nylon-6 composites. Experiments were carried out on an 80-ton injection molding machine equipped with a high-pressure nitrogen-gas injection unit. Two "float-shape" axisymmetric cavities were used. After molding, the surface quality of molded parts was measured by a roughness meter. Various processing variables were studied in terms of their influence on formation of surface roughness: melt temperature, mold temperature, melt filling speed, short-shot size, gas pressure, and gas injection delay time. Scanning electronic microscopy was also employed to characterize the composites. It was found that the surface roughness results mainly from the exposure of glass fiber in the matrix. The jetting and irregular flows of the polymer melt during the filling process might be factors causing the fiber exposure. [source] Effect of machine compliance on mold deflection during injection and packing of thermoplastic partsPOLYMER ENGINEERING & SCIENCE, Issue 7 2006Brian Carpenter Minimizing mold deflection is essential when manufacturing plastic parts to tight tolerances. Both the mold and the machine are compliant and deform upon loading, which can affect the part quality. Therefore, understanding mold deflection during injection molding is critical for determining the final geometry of the part. It is also critical for secondary processes such as the in-mold coating process. This article presents work in quantifying both mold deflection during an injection-molding cycle and the effect of machine compliance on mold behavior. The mold cavity pressure obtained using MoldFlowÔ was used as input for the subsequent finite element mold deflection analysis. Two different structural models were used: the first model included only the mold, the mold base units and the ejector platen; the second model included the effect of the injection-molding machine compliance. To validate the model, strain gage rosettes were placed on the mold and the machine. Validating experiments were conducted using process parameters identical to those used in the simulations. A comparison of the experimental and simulation results for both models is presented. POLYM. ENG. SCI., 46:844,852, 2006. © 2006 Society of Plastics Engineers [source] Surface texture characterization of injection-molded pigmented plasticsPOLYMER ENGINEERING & SCIENCE, Issue 9 2004Ingrid Ariño An appropriate description of the surface textures deliberately created on injection-molded plastic parts of interior car components is presented. A spatial wavelength-dependent analysis is used as an interesting alternative to the traditional roughness parameters. Auto-correlation functions and power spectral densities are examples of such spectral functions that include parameters both in amplitude and profile directions. Even fractal concepts can be useful descriptors. As an illustration, it is also shown how the effects on the surface topography of the plastic part of after-etching the mold can be assessed by suitable descriptors. An experimental evaluation of injection-molded plaques containing three different surface patterns was carried out using an optical profilometer, supplemented by contact stylus measurements. The ability to assess the topography of these plaques by means of a new fast photometric stereo-technique, denoted OptiTopo, was also evaluated. In its present form, however, this technique does not provide a detailed description of the topography of a pigmented plastic. Reasons for this and possible improvements are discussed. Polym. Eng. Sci. 44:1615,1626, 2004. © 2004 Society of Plastics Engineers. [source] | ||||||||||