JEC COMPOSITES MAGAZINE - Issue #112 - April/May 2017 - 34

AERONAUTlCS software

Fig. 2: CheFEM thermodynamic output with a selection of parameters for layer 2
Tab. 1: CheFEM mechanical output for RTD and
RTW conditions

Unit

RTD
(0% RH)

RTW
(100% RH)

Orientation

[p/4]

Volume

vol%

Property
Filler

Matrix
Water
absorption

wt%

0.00

1.51

°C

104

E @ T*

GPa

4.6

3.5

S @ T*

GPa

0.078

0.060

e @ T*

1.70

1.71

GPa

60 (-3%)

GPa

60 (-3%)

Gxy

GPa

23 (-4%)

GPa

0.42

0.40 (-5%)

GPa

-0.36

-0.27 (-25%)

0.42

0.40 (-5%)

GPa

-0.36

-0.27 (-25%)

Composite
stiffness

Composite
strength

Fig. 3: Tsai-Wu failure envelopes generated by CheFEM. Inlay image: CheFEM
data can be imported in other FEA packages for further fracture and application-oriented analysis

in Figure 2. The 50+ thermodynamic
output properties include chemical
uptake isotherm, chemical solubility,
chemical-thermal
swelling,
glass
temperature depression, diffusion
coefficient, permeation rate, saturation
times and eventual chemical degradation kinetics.
Mechanical output
CheFEM's mechanical output generates, among other properties, the
chemically exposed stiffness and
tensile parameters for the layer. A
selection of this output for RTD (room
temperature dry) and RTW (room
temperature wet) conditions is listed
in Table 1.
Note that T* (°C) is the temperature at
which the matrix unexposed mechanical input properties (stiffness, strength
and yield strain) must be taken. T*
is derived from CheFEM thermodynamics, and based on the simulated
matrix plasticizing and eventual chemical (equilibrium) reaction kinetics. As
such, the described matrix properties
are the only temperature-dependent
mechanical input data that are needed
for CheFEM. This data can usually
be obtained from the matrix material
producer or an experiment. All other
properties, such as fibre stiffness and
strength, can usually be determined at
room temperature.

jec composites magazine / No112 April - May 2017

Failure envelopes
As a direct consequence of the above
generated thermo-mechanical data,
CheFEM can produce failure envelopes according to several failure
criteria, such as maximum stress,
maximum strain and Tsai's quadratic
criteria. Figure 3 shows an example
of the generated Tsai-Wu envelope.
Moreover, CheFEM data can be
imported in other (FEA) software
packages. An example is the Abaqus
Materials Library Manager, which can
be used in conjunction with CheFEM.
Conclusion
The results demonstrated in this
article correlate highly with the experimental work carried out on Thornel
300/Fiberite 934 composites in the
1970s and 1980s. Hence, CheFEM is
definitely a useful tool to get a grip
on the effects of environmental conditions (not only water) on composite
materials. Besides aerospace, CheFEM
is also used in other industries, e.g. for
the analysis of seals, polymers and
composites for oil & gas applications.
The chemical-thermal cycling features
of CheFEM will be discussed in the
forthcoming part 2 of this article.
More information:
www.composite-agency.com

http://www.composite-agency.com

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #112 - April/May 2017