Hallo fernstudent,
anbei die PTC-Empfehlung. Ich verwende meist 0.01 bei Stahl.
http://www.ptc.com/cs/tpi/22313.htm
mfg
Roland Leiter
Techsoft RAND
Title Estimating the Initial Value for Material Damping Properties.
Product Pro/MECHANICA Module Motion TPI ID 22313 Created 22-SEP-98
Workstation All Reported In Release 21.0 Reported In Datecode
SPR None Resolved In Release Resolved In Datecode
Description
-----------
This document describes how to calculate values that can be used as an initial
estimate for material damping properties in Pro/MECHANICA Motion.
Alternate Technique
-------------------
See Resolution below.
Resolution
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Trying to arrive at accurate values for material damping properties for use
in Pro/MECHANICA Motion is a very difficult undertaking. Material damping
properties are not as well documented, understood, or known as other properties
such as Young's Modulus.
It is important to remember that although Pro/MECHANICA Motion is a predictive
code, it cannot derive material properties. The material properties are an input
to the program. Results based on this input are only as valid as the assumptions
that were used to derive the material properties.
There is no known EXACT relationship to derive Material Damping properties.
The approximate formula given below is simply ONE model of a relationship that
can be used, but must adhere to all the assumptions under which it was derived,
as outlined below.
This approximate relationship is only valid under the following conditions:
1) The materials are impacting such that no permanent deformation occurs as a result
of the impact between the "ball" and the "target" material.
2) The impact occurs in the linear portion of the coefficient of restitution versus
impact velocity curve. That is, the coefficient of restitution remains between
1.0 and approximately 0.8.
Hint: If the analysis requires that material have zero material damping, it is best
to use a small value of 0.01, for example, instead of zero for material damping
to improve the solution accuracy. This is reasonable since no real material
possesses zero damping.
Calculations to determine At.
subscript t = "target" material used in the experiment.
subscript b = "ball" or indenter material used in the experiment.
The formula used to derive these values is:
At ~= [(1/42)*(Kt^2)*(Pb^0.5)] * [(2/Ht^2.5) - (1/Hb^2.5)]
This is an approximate relationship as denoted by the "~=" sign.
Where:
-----
HV = Vicker's hardness
Ht = Corresponding Meyer (projected area) hardness = (HV * 9.806)/0.92) in MPa (target material)
Hb = Ht = Corresponding Meyer (projected area) hardness = (HV * 9.806)/0.92) in MPa (ball material)
Pb = Mass density
Et = Young's modulus
vt = Poisson's ratio
At = Surface damping
vi = critical impact velocity for full plasticity
Kt = Et/(1-vt^2) = Effective stiffness
e = Coefficient of restitution
Again:
subscript t = "target" material used in the experiment.
subscript b = "ball" or indenter material used in the experiment.
Notes:
1) The material damping property is really a function of the surface treatment of
the material. This is due to the fact that surface treatment determines hardness.
Materials such as steel can have widely varying material damping properties
depending on the surface treatment (as demonstrated in the above table).
2) When choosing a hardness value to use in the equation, always
choose a value that corresponds to the material after is has been worked in.
This is the steady-state operating condition of the material after all permanent
deformations have ceased.
3) The material damping equation was derived from an experimental study found in the
literature, it is not based on experiments performed at Parametric Technology
Corporation
4) The coefficient of restitution is defined as the ratio of post to pre-impact
velocity in the contact normal direction.
As an example, the case of a titanium carbide ball impacting a low alloy steel block is considered.
The material properties of the two materials are listed below:
Material Condition HV Ht Pt Et vt vi
(MPa) (kg/m^3)(GPa) (m/s)
--------------------------------------------------------------------------------------
Low alloy steel Q & T 260 2770 7860 211 0.293 0.638
Tungsten carb. As received 1700 18120 15150 534 0.220 23.739
--------------------------------------------------------------------------------------
Using the aforementioned equation for At it follows that:
At ~= [(1/42)*(Kt^2)*(Pb^0.5)] * [(2/Ht^2.5) - (1/Hb^2.5)]
~= [(1/42)*((211e9/(1-0.293^2))^2)*(15150^0.5)] * [(2/2770e6^2.5) - (1/18120e6^2.5)] = 0.770
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