m_visco, mvisco

SDT-visc Contents Functions

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m_visco, mvisco_3m

Purpose

Material function for support of viscoelastic materials

This function is part of the viscoelastic tools.

Syntax

 out = m_visco('command',model);

Description

Viscoelastic materials are described by a structure with fields

.pl	Reference elastic properties used for initial model assembly. This should include the loss factor.
.name	Reference name for the material.
.type	Always set to m_visco since this is the material handling function.
.unit	Unit system see fe_mat convert.
.T0	Reference temperature.
.G	Description of the modulus as a function of frequency. This can be a matrix with three columns giving frequencies, real and imaginary parts of the modulus, or a string that will be evaluated to determine the modulus. To sort frequencies use mat.G=sortrows(mat.G).
.at	Description of the frequency shift as a function of temperature. This can be a matrix with two columns giving temperature and frequency shift α_T, or a string that will be evaluated to determine the shift factor.
.nomo	is a cell array containing information need to create the nomogram. See details under the nomo command.

Accepted commands are

database,default,info,dbval

These commands are used to select materials. Info lists available materials. Default gives the first material. m_visco searches its own database and for mvisco_*.m functions in the MATLAB search path. The mvisco_3m function is given to illustrate the contents of a user database file.

To start a selection process use cf=feplot;m_visco('database',cf). This will give you a list of materials in the database. In the Mat tab, select materials you want to see, use the delete key (or the Remove material ... context menu) to remove entries. You can also add materials to the stack manually with

m_visco('database -unit TM Densil',cf);
m_visco('database -unit TM Smactane 50_G',cf);

By default, the maximum loss factor and associated modulus and frequency are displayed for the material reference temperature. You can order the list by giving a target InfoTarg freq temp sort (frequency, temperature, sort by modulus 1 or loss factor 2). Thus

>> m_visco('info wtarg 30 ttarg=20')
     CorningGlass0010   (G 2.87e+009 Pa e 0.02 3.00e+001 Hz 20 C)
ChicagoVitreous-CV325   (E 1.03e+008 Pa e 0.06 3.00e+001 Hz 20 C)
    Soundcoat-DYAD609   (G 6.21e+008 Pa e 0.08 3.00e+001 Hz 20 C)
   BarryControl-H-326   (G 5.90e+006 Pa e 0.08 3.00e+001 Hz 20 C)
...

You can also select your material by opening an feplot figure with all materials and selecting graphically. The InfoTarg command can then be used to select materials in a plots. For example giving a target frequency and a range of temperatures is achieved with

cf=feplot;cf.mdl='reset';
m_visco('database',cf);% open FEPLOT figure with database
RO=struct('wtarg',20,'ttarg',[-10 5 20 40 60 80]');
mat=[stack_get(cf.mdl,'mat','#ISD'); % Get selected materials
     stack_get(cf.mdl,'mat','#Smac')];
cf.mdl.Stack=mat; 
% Once you have all desired entries, redraw
m_visco('info -modmin 1e6 -etamin .2 -cf1',cf,RO);

Figure 5.2: Material selection diagram.

mat=m_visco('database Name') tries to find an optimal match for Name in the database and returns the associated material. mat=m_visco('database -unit TM Name') converts to unit system TM (see fe_mat Convert). Command option -matid can be used to specify a MatId for the material. Without output argument material is added to the stack of the feplot figure (one can give the cf pointer as a second input argument). If Name is not given, all materials are returned.

mat=m_visco('dbval') is used to generate equivalent elastic materials. This is not currently functional.

The 3ParWLF material is a standard viscoelastic model with WLF type temperature dependence. Its constitutive law is the characterized by

(5.10)

The parameters retained to characterize this model are G0, etamax, wmax, c1, c2, T0.

DispMat

m_visco('dispmat',mat) is used to generate a text display of a viscoelastic material describe by the mat data structure.

RefMat

m_visco('refmat',mat,model) uses data on temperature range and frequency in the model to create a

nomo

The nomo command generates a standard nomogram plot. The following entries in the cell array mat.nomo are used. If using a mat.G table that contains raw experimental data that is non smooth, mat=m_visco('nomo -smooth',mat) will generate a smooth table.

Eeta	gives the log10 of Emin,Emax,etamax. Note that for units in Pa, a shift to MPa is performed in the plot.
w	gives the log10 of Wmin,WRmin,WRmax. Increasing Wmin shifts the show isotherms right.
file	gives the name of the bitmap file used to digitize the nomogram. When this file is in the current directory, the nomogram and the bitmap are overlaid. This allows editing of tabular values as described under fevisco handnomo.
T	is used to specify isotherm positions in the nomogram.

For example

 m_visco('nomo','isd112 (1999)',4)
 mat=m_visco('isd112 (1993)'); 
 mat=sdsetprop(mat,'nomo','w',[-1 0 12],'Eeta',[4 8 2],'type','G', ...
  'unit','SI','T',[-20:20:120]);
 m_visco('nomo',mat)

Figure 5.3: Nomogram of the ISD112.

at

The at command is used to generate shift factor using calls of the form

 at=m_visco('at',T,mat)

where mat can be a data structure or a string matched against the m_visco database.

interp [,-unit SI] [,showrange]

The interp command is used to generate the modulus at arbitrary frequency-temperature design points using calls of the form G=m_mvisco('interp',w,T,mat) where mat can be a data structure or a string matched against the m_visco database. Accepted options are

-unit SI an optional unit conversion code (see fe_mat('convert') can be given when needed.
ToE uses the assumption that G=E/E(1+ν) to estimate the Young modulus.
-rel generates the relative coefficient such that G(ω,T)=coefG₀.
ShowRange generates a standard display giving modulus variations for a given frequency/temperature range. This allows the user to validate the usefulness of a particular material for the operating conditions given by this range.
cf=1 selects the figure for display
yscale=log,lin selects linear or log scale for display.

For example

 w=logspace(1,3,100);  % default : cf.Stack{'info','Freq'} in Hz
 T=[0:10:50];          % default : cf.Stack{'info','Range'}
 mat=m_visco('isd112 (1993)');
 G=m_visco('interp -unit MM',w,T(:),mat);
 m_visco('interp ShowRange',w,T(:),mat);
 %m_visco('interp',cf,'MatName') is also acceptable

Figure 5.4: Modulus vs. frequency and temperature. Horizontal blue lines show the physical frequency range (indicated in the legend) at the temperature shown by the text.

WriteNastran

This utility is meant to help users generate complex modulus tables for use in NASTRAN. The tables are generated as two TABLED1 bulk entries if only one ID is specified in the command, the real and imaginary parts are written with sequential numbers. The command specifies the table identifier (default 1) and file name. Note that this only supports a single temperature, since NASTRAN does not handle multi dimensional tables.

For more details on writing TABLED1 entries see naswrite WriteCurve.

 fname=horzcat(nas2up('tempname'),'.blk');
 m_visco(horzcat('WriteNastran 101 201',fname), ...
   10:10:100,10,'isd112 (1993)');
 type(fname)

HandNomo FileName

Displays the bitmap image of a nomogram and guides the user through the process needed to obtain a tabular version suitable for inclusion in m_visco. The main steps of the procedure are as follows

Rect : define the location of the axis in the bitmap by selecting two of its corners.
Elim : click on the text of ytick labels on the left of the axis to define the modulus range and the maximum axis value for the loss factor range.
wlim : click on the text of ytick labels on the right of the axis to define the minimum frequency displayed on the true frequency axis (left y axis) and the min and max values for the reduced frequency (x axis).
at : click on the isotherm that is always generated to enter the isotherm edition mode. You can then use the following keys to edit the at values. n to add new isotherm values. Left and right arrows to move the offset of the current isotherm. Up and down arrow to select a different isotherm.
If the isotherm slope is not correct, check the Elim and wlim values and possibly adjust the axis rectangle using : uU to move the rectangle along -x or +x; vV to move the rectangle along -y or +y; xXyY to resize the rectangle.
eta click on the green line with circle markers. Adjust values with your mouse. Use left and right arrows to select the points and q to exit.
G click on the blue line with circle markers. Adjust values with your mouse. Use left and right arrows to select the points and q to exit.

At any point during the procedure, you can press the i key to generate a screen printout of the material. This can then be included in m_visco or a mvisco_*.m database file.

With a material saved in a database, can superpose the original figure and the nomogram using m_visco('HandNomo MatName') while having the image file in the current directory.