Solid Phase Sheet Forming of Thermoplastics—Part II: Large Deformation Post-Yield Behavior of Plastics

1986 ◽  
Vol 108 (2) ◽  
pp. 113-118 ◽  
Author(s):  
H. F. Nied ◽  
V. K. Stokes
Keyword(s):  
Solid Phase ◽  
Large Strain ◽  
Amorphous Polymers ◽  
Sheet Forming ◽  
Point Of View ◽  
Large Strains ◽  
Polybutylene Terephthalate ◽  
Forming Process ◽  
Yield Behavior ◽  
Stable Manner

This paper examines the phenomenology of the large strain, post-yield behavior of the three thermoplastics—polycarbonate, polybutylene terephthalate and polyetherimide—from the point of view of the sheet forming process. A photographic technique is utilized to measure the large nonhomogeneous strains observed in polymers. This technique makes possible the mapping of the strain field for flat specimens in the form of strain contours. Amorphous polymers polycarbonate and polyetherimide are shown to behave differently from semicrystalline polybutylene terephthalate. All three polymers are shown to neck in a stable manner, with the necked regions undergoing very large strains. The mechanical properties of the necked/drawn polymer are shown to be substantially different from the properties of the virgin polymer.

Solid Phase Sheet Forming of Thermoplastics—Part I: Mechanical Behavior of Thermoplastics to Yield

1986 ◽  
Vol 108 (2) ◽  
pp. 107-112 ◽  
Author(s):  
V. K. Stokes ◽  
H. F. Nied
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Solid Phase ◽  
Hold Time ◽  
Sheet Forming ◽  
Temperature Deformation ◽  
Polybutylene Terephthalate ◽  
Forming Process ◽  
Time Periods ◽  
Insight Into

The detailed mechanical behavior to yield of three thermoplastics—polycarbonate, polybutylene terephthalate, and polyetherimide—subjected to simulated forming histories, is examined in order to gain an insight into the sheet forming process for thermoplastics. The phenomenology of yield is shown to be quite different for semicrystalline polybutylene terephthalate when compared with amorphous polycarbonate and polyetherimide. The dependence of the mechanical properties of thermoplastics on temperature, deformation rate and hold-time periods are shown to be important for understanding and controlling the solid phase sheet forming process.

Incremental Sheet Forming with an Industrial Robot – Forming Limits and Their Effect on Component Design

2005 ◽  
Vol 6-8 ◽  
pp. 457-464 ◽  
Author(s):  
L. Lamminen
Keyword(s):  
Sheet Metal ◽  
Industrial Robot ◽  
Forming Limit Diagram ◽  
Sheet Forming ◽  
Incremental Sheet Forming ◽  
Point Of View ◽  
Forming Limit ◽  
Forming Process ◽  
3D Cad ◽  
Component Design

Incremental sheet forming (ISF) has been a subject of research for many research groups before. However, all of the published results so far have been related to either commercial ISF machines or ISF forming with NC mills or similar. The research reported in this paper concentrates on incremental sheet forming with an industrial robot. The test equipment is based on a strong arm robot and a moving forming table, where a sheet metal blank is attached. The tool slides on the surface of the sheet and forms it incrementally to the desired shape. The robot is capable of 5-axis forming, which enables forming of inwards curved forms. In this paper the forming limit diagram (FLD) for ISF with the robot is presented and it is compared with conventional forming limit diagrams. It will be shown that the conventional FLD does not apply to incremental forming process. Geometrical accuracy of sample pieces is also studied. Cones of different shapes are formed with the robot equipment and their correspondence with the 3D CAD model is evaluated. The results are compared with other results of accuracy of incremental sheet forming, reported earlier by other researchers. The third issue covered in this article is a product development point of view to incremental sheet forming. In addition to fast prototyping and low volume production of sheet metal parts, ISF brings new possibilities to sheet metal component design and manufacturing. These possibilities can only be exploited if design rules, that will take the possibilities and limitations of the method into account are created for ISF.

scholarly journals A generalized mechanical model using stress–strain duality at large strain for amorphous polymers

2020 ◽  
pp. 108128652095846
Author(s):  
CA Bernard ◽  
D George ◽  
S Ahzi ◽  
Y Rémond
Keyword(s):  
Mechanical Model ◽  
Mechanical Response ◽  
Amorphous Polymer ◽  
Large Strain ◽  
Amorphous Polymers ◽  
3D Models ◽  
Experimental Results ◽  
Large Strains ◽  
Stress Strain ◽  
Numerical Predictions

Numerous models have been developed in the literature to simulate the thermomechanical behavior of amorphous polymers at large strain. These models generally show a good agreement with experimental results when the material is submitted to uniaxial loadings (tension or compression) or in the case of shear loadings. However, this agreement is highly degraded when they are used in the case of combined load cases. A generalization of these models to more complex loads is scarce. In particular, models that are identified in tension or compression often overestimate the response in shear. One difficulty lies in the fact that 3D models must aggregate different physical modeling, described with different kinematics. This requires the use of transport operators complex to manipulate. In this paper, we propose a mechanical model for large strains, generalized in 3D, and precisely introducing the adequate transport operators in order to obtain an exact kinematic. The stress–strain duality is validated in the writing of the power of internal forces. This generalized model is applied in the case of a polycarbonate amorphous polymer. The simulation results in tension/compression and shear are compared with the classical modeling and experimental results from the literature. The results greatly improve the numerical predictions of the mechanical response of amorphous polymers submitted to any load case.

Core Criteria I

2018 ◽  
Author(s):  
Sanford C. Goldberg
Keyword(s):  
Cognitive Processes ◽  
Point Of View ◽  
Infinite Regress ◽  
Belief Formation ◽  
Forming Process ◽  
Epistemic Criteria ◽  
Problem Of The Criterion

Chapter 3 deals with the first issue one faces in the task of articulating the explicit epistemic criteria for belief: the problem of the criterion. It is tempting to suppose that a belief can be normatively proper from the epistemic point of view only if the believer can certify for herself the reliability of every belief-forming process on which she relied. But insisting on this quickly leads to the threat of an infinite regress. This chapter defends a foundationalist response to this problem, according to which we enjoy a default (albeit defeasible) permission to rely on certain cognitive processes in belief-formation. These are processes that satisfy what the author calls the Reliabilist Rationale. Importantly, our permissions here are social: any one of us is permitted to rely on any token process that satisfies this rationale, whether the token process resides in one’s own mind/brain or that of another epistemic subject.

Analytical Solutions for Circular Bars Subjected to Large Strain Plastic Torsion

1990 ◽  
Vol 57 (2) ◽  
pp. 298-306 ◽  
Author(s):  
K. W. Neale ◽  
S. C. Shrivastava
Keyword(s):  
Closed Form ◽  
Analytical Solutions ◽  
Large Strain ◽  
Kinematic Hardening ◽  
Flow Theory ◽  
Constitutive Laws ◽  
Isotropic Hardening ◽  
Large Strains ◽  
Inelastic Behavior ◽  
Rate Dependent

The inelastic behavior of solid circular bars twisted to arbitrarily large strains is considered. Various phenomenological constitutive laws currently employed to model finite strain inelastic behavior are shown to lead to closed-form analytical solutions for torsion. These include rate-independent elastic-plastic isotropic hardening J2 flow theory of plasticity, various kinematic hardening models of flow theory, and both hypoelastic and hyperelastic formulations of J2 deformation theory. Certain rate-dependent inelastic laws, including creep and strain-rate sensitivity models, also permit the development of closed-form solutions. The derivation of these solutions is presented as well as numerous applications to a wide variety of time-independent and rate-dependent plastic constitutive laws.

scholarly journals Strain effects on polycrystalline germanium thin films

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Toshifumi Imajo ◽  
Takashi Suemasu ◽  
Kaoru Toko
Keyword(s):  
Thin Films ◽  
Solid Phase ◽  
Growth Promotion ◽  
Large Strain ◽  
Compressive Strain ◽  
Substrate Material ◽  
Large Crystal ◽  
Solid Phase Crystallization ◽  
Strain Effects ◽  
Thin Film Devices

AbstractPolycrystalline Ge thin films have attracted increasing attention because their hole mobilities exceed those of single-crystal Si wafers, while the process temperature is low. In this study, we investigate the strain effects on the crystal and electrical properties of polycrystalline Ge layers formed by solid-phase crystallization at 375 °C by modulating the substrate material. The strain of the Ge layers is in the range of approximately 0.5% (tensile) to -0.5% (compressive), which reflects both thermal expansion difference between Ge and substrate and phase transition of Ge from amorphous to crystalline. For both tensile and compressive strains, a large strain provides large crystal grains with sizes of approximately 10 μm owing to growth promotion. The potential barrier height of the grain boundary strongly depends on the strain and its direction. It is increased by tensile strain and decreased by compressive strain. These findings will be useful for the design of Ge-based thin-film devices on various materials for Internet-of-things technologies.

Magnesium Sheet Metal Forming Considering its Specific Yield Behavior

2005 ◽  
Vol 6-8 ◽  
pp. 771-778 ◽  
Author(s):  
M. Redecker ◽  
Karl Roll ◽  
S. Häussinger
Keyword(s):  
Sheet Metal ◽  
Elevated Temperatures ◽  
Flow Behavior ◽  
Specific Yield ◽  
Forming Limit ◽  
Forming Process ◽  
Local Flow ◽  
Yield Behavior ◽  
Magnesium Sheet ◽  
Testing Procedures

In recent years very strong efforts have been undertaken to build light weight structures of car bodies in the automotive industry. Structural technologies like Space Frame, tailored blanks and relief-embossed panels are well-known and already in use. Beside that there is a large assortment of design materials with low density or high strength. Magnesium alloys are lighter by approximately 34 percent than aluminum alloys and are considered to be the lightest metallic design material. However forming processes of magnesium sheet metal are difficult due to its complex plasticity behavior. Strain rate sensitivity, asymmetric and softening yield behavior of magnesium are leading to a complex description of the forming process. Asymmetric yield behavior means different yield stress depending on tensile or compressive loading. It is well-known that elevated temperatures around 200°C improve the local flow behavior of magnesium. Experiments show that in this way the forming limit curves can be considerably increased. So far the simulation of the forming process including temperature, strain rates and plastic asymmetry is not state-of-the-art. Moreover, neither reliable material data nor standardized testing procedures are available. According to the great attractiveness of magnesium sheet metal parts there is a serious need for a reliable modeling of the virtual process chain including the specification of required mechanical properties. An existing series geometry which already can be made of magnesium at elevated temperatures is calculated using the finite element method. The results clarify the failings of standard calculation methods and show potentials of its improvement.

Topology Optimization of Blank Geometry for the Sheet Forming Process

2012 ◽  
Author(s):  
Saber DorMohammadi ◽  
Mohammad Rouhi ◽  
Masoud Rais-Rohani
Keyword(s):  
Topology Optimization ◽  
Volume Fraction ◽  
Structural Response ◽  
Sheet Forming ◽  
Forming Process ◽  
Exchange Method ◽  
Forming Simulation ◽  
Blank Shape Optimization ◽  
Blank Shape ◽  
Consistent Subset

The newly developed element exchange method (EEM) for topology optimization is applied to the problem of blank shape optimization for the sheet-forming process. EEM uses a series of stochastic operations guided by the structural response of the model to switch solid and void elements in a given domain to minimize the objective function while maintaining the specified volume fraction. In application of EEM to blank optimization, a sheet forming simulation model is developed using Abaqus/Explicit. With the goal of minimizing the variability in wall thickness of the formed component, a subset of solid (i.e., high density) elements with the highest increase in thickness is exchanged with a consistent subset of void (i.e., low density) elements having the highest decrease in thickness so that the volume fraction remains constant. The EEM operations coupled with finite element simulations are repeated until the optimum blank geometry (i.e., boundary and initial thickness) is found. The developed numerical framework is applied to blank optimization of a benchmark problem. The results show that EEM is successful in generating the optimum blank geometry efficiently and accurately.

Concurrent Engineering Design of Sheet Stamping by Using an Inverse FE Approach

1997 ◽  
Author(s):  
Shiyong Yang ◽  
Kikuo Nezu
Keyword(s):  
Finite Element ◽  
Concurrent Engineering ◽  
Process Simulation ◽  
Three Dimensional ◽  
Sheet Forming ◽  
Design Stage ◽  
Forming Process ◽  
Element Analysis ◽  
Preliminary Design Stage ◽  
Product And Process

Abstract An inverse finite element (FE) algorithm is proposed for sheet forming process simulation. With the inverse finite element analysis (FEA) program developed, a new method for concurrent engineering (CE) design for sheet metal forming product and process is proposed. After the product geometry is defined by using parametric patches, the input models for process simulation can be created without the necessity to define the initial blank and the geometry of tools, thus simplifying the design process and facilitating the designer to look into the formability and quality of the product being designed at preliminary design stage. With resort to a commercially available software, P3/PATRAN, arbitrarily three-dimensional product can be designed for manufacturability for sheet forming process by following the procedures given.

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