JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 47

Tab.1: Critical points prepreg curesystem

Prepreg sample

Critical point

Value

Time

CP(1) Critical viscosity

8.25

15.53 min

CP(2) Minimum viscosity

5.7

41.87 min

CP(3) Maximum slope ion viscosity

0.18

53.95 min

CP(4) Critical slope ion viscosity

0.03

87.12 min

40 minutes is an expected artifact of data filtering and should be
ignored.
As mentioned earlier, the crosslinking reaction stops at the
end of cure because all monomers have reacted. In this case,
at constant temperature the loss factor and ion viscosity are
also constant, and the slope of Log(ion viscosity) vs. time
(dLog(IV)/dt) ideally equals zero. A positive slope indicates
that cure is still ongoing. Although temperature fluctuations in
Figure 5 complicate the evaluation of slope, even after 120 minutes it is still positive and the cure is still proceeding. In reality,
much time may pass before the slope is truly zero. As a practical
matter, the user would typically choose a small, non-zero value
to indicate the end of cure as, defined by requirements of the
application.

Fig. 4: Typical ion viscosity behaviour of a curing thermoset

The critical points, which quantitatively characterize the prepreg cure, are shown above in Table 1.
Fig. 5: Ion viscosity and slope data at 10 Hz from prepreg cure

monomers diminishes to the point where the reaction rate
begins to decrease; consequently, the slope of ion viscosity also
decreases, and eventually will have zero slope when cure has
stopped completely.

Results of single-frequency cure monitoring
A second sample of the epoxy-graphite prepreg was cured and
data was recorded at a single frequency to allow CureView to
calculate critical points. Figure 5 shows the Log(ion viscosity)
and the slope of Log(ion viscosity) curves at 10 Hz.
The data were averaged and filtered to reduce noise and
enhance the extraction of critical points. The data processing
parameters were:
- Data averaging: 4
- Slope span: 8
- Data filtering: 4
- Slope filtering: 10
- Slope filtering start time: 40 minutes
Discussing the mathematical purpose of these parameters is
beyond the scope of this report; the parameters are listed here
to allow later reproduction of the following results from raw
data. Note that the spike in the slope of Log(ion viscosity) at

For purposes of clarity, a critical slope of 0.03 was arbitrarily
chosen for CP(4). The end of cure is a user-defined condition,
and the user must determine the appropriate slope of CP(4) for
his application.

Conclusion
It was possible to make dielectric measurements of an epoxygraphite prepreg because a filter prevented shorting of the MiniVaricon sensor. Cure monitoring data show very little noise, and
the resulting Log(ion viscosity) and slope of Log(ion viscosity)
curves clearly show the progress of cure. The CureView software
was able to extract critical points to quantitatively characterize
the cure. These critical points can be used to compare and study
changes in cure time as a result of changes in resin formulation
or processing (time and temperature) conditions.
The critical slope of ion viscosity - CP(4) - can be used in
manufacturing or quality assurance/quality control to confirm
that the composite has cured to the proper state. Dielectric cure
monitoring is the only method that can study and document
thermoset cure using the same technique in R&D, QA/QC and
manufacturing. n
More information: http://lambient.com
Contact: slee@lambient.com

No85 November - December 2013 /

jec composites magazine 47


http://www.lambient.com

JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013

Cover
Edito
Point of view: bespoke equipment
Contents
Agenda of Events
COMPANY & BUSINESS In Brief
APPLICATIONS
Large parts
Skateboard
Second life
Truck
Pipe
MARKET Process
FEATURE CONSTRUCTION
Roofing
PFRP house
Sandwich panels
GFRP grid
Gelcoat
Windows
Bridge
RESEARCH & DEVELOPMENT
Cure monitoring
Design
TECHNOLOGY & INNOVATIONS
NDC
Simulation
CBeam
Index
In the world
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Cover
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 2
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Edito
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Point of view: bespoke equipment
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 5
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Contents
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 7
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Agenda of Events
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 9
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - COMPANY & BUSINESS In Brief
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 11
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Large parts
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 13
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Skateboard
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 15
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Second life
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 17
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Truck
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 19
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Pipe
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 21
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 22
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - MARKET Process
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 24
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 25
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 26
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 27
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Roofing
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 29
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 30
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - PFRP house
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 32
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Sandwich panels
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 34
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 35
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - GFRP grid
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 37
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Gelcoat
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 39
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Windows
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 41
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Bridge
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 43
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 44
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Cure monitoring
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 46
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 47
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Design
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 49
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 50
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 51
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - NDC
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 53
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Simulation
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 55
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - CBeam
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - Index
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - In the world
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 59
JEC COMPOSITES MAGAZINE - Issue #85 - November/December 2013 - 60
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