Tunable Membrane for Electromagnetic Devices Using Dielectric Elastomers

2008 ◽  
Vol 61 ◽  
pp. 141-146
Author(s):  
Christian Bolzmacher ◽  
Karin Bauer ◽  
Ulrich Schmid ◽  
Helmut Seidel ◽  
Moustapha Hafez
Keyword(s):  
Material Model ◽  
Silicone Membrane ◽  
Creep Data ◽  
Electromagnetic Actuators ◽  
Membrane Behavior ◽  
Electromagnetic Devices ◽  
Dynamic Experiments ◽  
Experimental Creep ◽  
Strain Relationship ◽  
Tunable Stiffness

The amplitudes of miniaturized electromagnetic actuators are clearly enhanced if the eigenfrequencies of the membrane are used for actuation. However, the bandwidth for such operation is very limited. This can be overcome to some extent by the employment of membranes with electrically tunable stiffness. In this context we investigated membranes of dielectric elastomer materials and present experimental results on the ability to change their pre-strain to shift the eigenmodes to lower frequencies upon activation. Furthermore, the viscoelastic properties of an acrylic and a silicone membrane are investigated and compared to dynamic experiments. The parameters for the stiffness and viscoelasticity are derived from the experimental creep data and incorporated in a hyperelastic material model. Using this adapted stress-strain relationship the membrane behavior over time can be evaluated for different loading as well as pre-strain conditions.

Numerical Simulation of Mechanical Effects in Composite Structures by the Finite Element Method

1998 ◽  
Vol 123 (2) ◽  
pp. 248-252
Author(s):  
C. Mu¨ller ◽  
A. Bohmann
Keyword(s):  
Numerical Simulation ◽  
Strain Rate ◽  
Composite Structures ◽  
Failure Strain ◽  
Radial Strain ◽  
Material Model ◽  
Test Facility ◽  
Fiber Reinforced ◽  
Mechanical Effects ◽  
Dynamic Experiments

In electromagnetic railgun experiments at ISL, the composite projectiles are accelerated up to 2000 m/s with a maximal acceleration of 7×106 m/s2. The maximum forces typically will have been achieved after 200 μs. One consequence of this dynamic load is a strain rate in the order of ε˙=2000 s−1, a rate at which metals are also giving up their static properties. The aim of research at ISL is the construction of a fiber-reinforced sabot adapted for dynamic bearing. FE simulations support the construction process as well as allowing a detailed study of the mechanical effects occurring during the acceleration of the sabot. The most important problem of dynamical simulation of composites is an adequate material model. We show in this paper, that the classical homogenized laminate models are insufficient to be used in dynamics. To develop an appropriate material model, we investigated selected materials statically as well as dynamically and we compared the experimental results with those of their numerical simulation. For a first material model approach, we made quasi-static experiments with a special sabot geometry. The quasi-static investigations have revealed that different conditions, e.g., lateral support, involve a completely different system answer. We found that a specimen without radial strain has more than the double strength of a specimen that allows radial strain, whereby the system answer still remains linear elastic and only very little internal delamination occurs. A second step toward a material model consists of dynamic experiments with specimens in a simple cylinder geometry on a Split Hopkinson Pressure Bar test facility. The specimens are made of fiber-reinforced epoxy, as well as metal-matrix composites. The dynamic experiments proved the strain as principal failure criterion for dynamic bearing, whereby the failure strain depends upon the momentary strain rate. Failure strain is also a historical function, so that the deformation history is important. We can show that the viscous polymer matrix plays a very important role for the dynamic toughness of reinforced materials. When the material fails, the stress is far beyond that of static failure: up to two times the static strength has been measured. Experiments with real sabots in railguns have shown that the failure occurs a relatively long time after the stress has achieved its maximum.

Finite Element Analysis of Hyperelastic Material Model for Non-Pneumatic Tire

2018 ◽  
Vol 775 ◽  
pp. 554-559 ◽  
Author(s):  
Ravivat Rugsaj ◽  
Chakrit Suvanjumrat
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Material Model ◽  
Hyperelastic Material ◽  
Element Analysis ◽  
Pneumatic Tire ◽  
Water Jet Cutting ◽  
The Finite Element Analysis ◽  
Strain Relationship ◽  
Relationship Of

This research aimed to find an appropriated hyperelastic material model for the finite element analysis (FEA) of a non-pneumatic tire (NPT). The innovative method involving water jet cutting technique was performed to prepare the tensile and compressive test specimens from the non-pneumatic tire, TWEEL, which was developed by Michelin. The stress-strain relationship of material testing results was fitted to select the suitable constitutive model. The FEA was performed and compared to the physical experiment to validate the hyperelastic material model. The suitable hyperelastic material model can be used in the development of NPT for the further work.

A Unified View of Engineering Creep Parameters

2008 ◽  
Author(s):  
D. R. Eno ◽  
G. A. Young ◽  
T.-L. Sham
Keyword(s):  
General Framework ◽  
Likelihood Estimation ◽  
Material Model ◽  
Efficient Estimation ◽  
Upper And Lower Bounds ◽  
Model Parameters ◽  
Creep Data ◽  
Special Cases ◽  
Temperature Interaction ◽  
Model Recognition

Creep data are often analyzed using derived engineering parameters to correlate creep life (either time to rupture, or time to a specified strain) to applied stress and temperature. Commonly used formulations include Larson-Miller, Orr-Sherby-Dorn, Manson-Haferd, and Manson-Succop parameterizations. In this paper, it is shown that these parameterizations are all special cases of a common general framework based on a linear statistical model. Recognition of this fact allows for statistically efficient estimation of material model parameters and quantitative statistical comparisons among the various parameterizations in terms of their ability to fit a material database, including assessment of a stress-temperature interaction in creep behavior. This provides a rational basis for choosing the best parameterization to describe a particular material. Furthermore, using the technique of maximum likelihood estimation to estimate model parameters allows for a statistically proper treatment of runouts in a test database via censored data analysis methods, and for construction of probabilistically interpretable upper and lower bounds on creep rate. Comparisons are made to a generalization of the commonly used Larson-Miller parameterization (namely, the Mendelson-Roberts-Manson parameterization), which is comparable in complexity to the Manson-Haferd parameter, but utilizes a reciprocal temperature dependence. The general framework for analysis of creep data is illustrated with analysis of Alloy 617 and HAYNES® 230® alloy (Alloy 230) test data.

A New 1000kv Electron Microscope

1969 ◽  
Vol 27 ◽  
pp. 100-101
Author(s):  
J.L. Williams ◽  
K. Heathcote ◽  
E.J. Greer
Keyword(s):  
Electron Microscope ◽  
Direct Observation ◽  
High Voltage ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Specimen Thickness ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Dynamic Experiments ◽  
Conventional Instrument

High Voltage Electron Microscope already offers exciting experimental possibilities to Biologists and Materials Scientists because the increased specimen thickness allows direct observation of three dimensional structure and dynamic experiments on effectively bulk specimens. This microscope is designed to give maximum accessibility and space in the specimen region for the special stages which are required. At the same time it provides an ease of operation similar to a conventional instrument.

A tilting high temperature gas reaction chamber for the JEM 7A T.E.M.

1978 ◽  
Vol 36 (1) ◽  
pp. 70-71
Author(s):  
Brian L. Rhoades
Keyword(s):  
Cross Section ◽  
Reaction Chamber ◽  
Objective Lens ◽  
Reduced Cross Section ◽  
Cross Sectional ◽  
Structural Investigations ◽  
Transmission Electron ◽  
Dynamic Experiments ◽  
Successful Design ◽  
Thermocouple Junction

A gas reaction chamber has been designed and constructed for the JEM 7A transmission electron microscope which is based on a notably successful design by Hashimoto et. al. but which provides specimen tilting facilities of ± 15° aboutany axis in the plane of the specimen.It has been difficult to provide tilting facilities on environmental chambers for 100 kV microscopes owing to the fundamental lack of available space within the objective lens and the scope of structural investigations possible during dynamic experiments has been limited with previous specimen chambers not possessing this facility.A cross sectional diagram of the specimen chamber is shown in figure 1. The specimen is placed on a platinum ribbon which is mounted on a mica ring of the type shown in figure 2. The ribbon is heated by direct current, and a thermocouple junction spot welded to the section of the ribbon of reduced cross section enables temperature measurement at the point where localised heating occurs.

Delamination in the scoring and folding of paperboard

TAPPI Journal ◽  
2012 ◽  
Vol 11 (1) ◽  
pp. 61-66 ◽  
Author(s):  
DOEUNG D. CHOI ◽  
SERGIY A. LAVRYKOV ◽  
BANDARU V. RAMARAO
Keyword(s):  
Finite Element ◽  
Plane Deformation ◽  
Strain Analysis ◽  
Local Strain ◽  
Uniaxial Stress ◽  
Material Model ◽  
Element Model ◽  
Plastic Behavior ◽  
Stress Strain ◽  
Strain Fields

Delamination between layers occurs during the creasing and subsequent folding of paperboard. Delamination is necessary to provide some stiffness properties, but excessive or uncontrolled delamination can weaken the fold, and therefore needs to be controlled. An understanding of the mechanics of delamination is predicated upon the availability of reliable and properly calibrated simulation tools to predict experimental observations. This paper describes a finite element simulation of paper mechanics applied to the scoring and folding of multi-ply carton board. Our goal was to provide an understanding of the mechanics of these operations and the proper models of elastic and plastic behavior of the material that enable us to simulate the deformation and delamination behavior. Our material model accounted for plasticity and sheet anisotropy in the in-plane and z-direction (ZD) dimensions. We used different ZD stress-strain curves during loading and unloading. Material parameters for in-plane deformation were obtained by fitting uniaxial stress-strain data to Ramberg-Osgood plasticity models and the ZD deformation was modeled using a modified power law. Two-dimensional strain fields resulting from loading board typical of a scoring operation were calculated. The strain field was symmetric in the initial stages, but increasing deformation led to asymmetry and heterogeneity. These regions were precursors to delamination and failure. Delamination of the layers occurred in regions of significant shear strain and resulted primarily from the development of large plastic strains. The model predictions were confirmed by experimental observation of the local strain fields using visual microscopy and linear image strain analysis. The finite element model predicted sheet delamination matching the patterns and effects that were observed in experiments.

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