Materiales.Compuestos at 19:56, 12 December 2022

2022-12-12T19:56:40Z

Scipediacontent at 17:15, 7 May 2022

2022-05-07T17:15:17Z

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Scipediacontent: Scipediacontent moved page Draft Content 503207951 to Torres et al 2021b

2022-03-31T19:35:40Z

Scipediacontent moved page Draft Content 503207951 to Torres et al 2021b

Scipediacontent: Created page with "== Abstract == Nowadays, manufacturing of composite parts using out-of-Autoclave (OoA) processes is gaining importance because it allows a reduction of initial investments an..."

2022-03-31T19:35:37Z

Created page with "== Abstract == Nowadays, manufacturing of composite parts using out-of-Autoclave (OoA) processes is gaining importance because it allows a reduction of initial investments an..."

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== Abstract ==

Nowadays, manufacturing of composite parts using out-of-Autoclave (OoA) processes is gaining importance because it allows a reduction of initial investments and recurring costs. Among these technologies, the consolidation of out-of-autoclave prepregs using vacuum bag only technologies (VBO) is proven to provide high-quality composite structural parts without the need of autoclaves.  OoA prepregs are designed to be semi-impregnated creating engineered channels within the tows to evacuate internal air or volatiles generated during the cure cycle.
The aim of this work is to understand and explain the void formation mechanisms, their spatial distribution and transport mechanisms during the consolidation of OoA prepregs using vacuum bag only methods. This work includes parallel studies carried out using X-ray computed tomography (XCT) to determine the most important factors for air removal process in laminated composites produced by hand lay-up (HLU) and automated fiber placement (AFP).
A big challenge is the accurate monitoring of the evolution of porosity during composite curing, which has not been done so far and even less with a 3D visual technique. This combination of monitoring the dynamics of pore evolution by laboratory XCT and synchrotron tomography (SXCT) at different resolutions during a cure process will provide a profound understanding of the pore evacuation process which is strategic for the further development of OoA materials.

== Full document ==
<pdf>Media:Draft_Content_503207951native-articles-525.pdf</pdf>

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 ==1 Introduction==
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 Some of the panels were partially cured to visualize the residual void content at a semicured state. The cure cycle of the individual panels was interrupted at the points of the cure cycle highlighted in <span id='cite-_Ref82525769'></span>[[#_Ref82525769|Figure 5]]a. The dynamic viscosity evolution of the M56 neat epoxy resin across the cure cycle is shown in <span id='cite-_Ref82525769'></span>[[#_Ref82525769|Figure 5]]b. The minimum viscosity level of η<sub>min</sub> ≈ 10Pa·s is obtained after point t<sub>2</sub>. The degree-of-cure α through the cure cycle is also plotted for comparison purposes. Point t<sub>1</sub> was placed at the beginning of the first dwell to allow the resin viscosity to decrease, thus providing the necessary resin mobility to allow pore evacuation. Points t<sub>2</sub> and t<sub>3</sub> were selected according to the dynamic resin viscosity profile to study laminate microstructure during the period in which the resin viscosity remains at minimum value, called processing window. Lastly, point t<sub>4</sub> was selected at the end of the second heating ramp to study the transition from low to high viscosity. A vacuum release to 0.5bar was applied at t<sub>2</sub>.
+[[File:Torres_et_al_2021b-image9.png|centre|600x600px]]
-[[Image:Torres_et_al_2021b-image9.png|600px]]
 <div id="_Ref82525769" class="center" style="width: auto; margin-left: auto; margin-right: auto;">
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 <div id="_Ref82526492" class="center" style="width: auto; margin-left: auto; margin-right: auto;">
-<span style="text-align: center; font-size: 75%;">'''Figure 10.''' Interply, intraply and total void content evolution during the cure cycle obtained from XCT tomograms: a) HLU, b) AFP</span></div>
+<span style="text-align: center; font-size: 75%;">'''Figure 10.''' Interply, intraply and total void content evolution during the cure cycle obtained from XCT tomograms: a) HLU, b) AFP.</span></div>
 Regarding the reinforced prepregs, the intratow void removal was also very effective in laminates with particles and evacuation channels were completely filled after point t<sub>1</sub>. However, the high value of the porosity detected by XCT is attributed to the high content of voids arrested by the presence of the particles that remained from the initial state and were not guided to the evacuation channels. In addition, the initial interply porosity in laminates interleaved with veils was higher than the laminate with particles and this effect was attributed to the open fiber network structure of the veil that is able to accommodate more air entrapments. However, after consolidation, all these values were considerably lower.
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 <div id="_Ref82617439" class="center" style="width: auto; margin-left: auto; margin-right: auto;">
-<span style="text-align: center; font-size: 75%;">'''Figure 13.''' Intraply and interply porosity distribution along the relative thickness position in the HLU laminate IM7/M56 [+45/0/-45/90]3s at different points during the cure cycle</span></div>
+<span style="text-align: center; font-size: 75%;">'''Figure 13.''' Intraply and interply porosity distribution along the relative thickness position in the HLU laminate IM7/M56 [+45/0/-45/90]3s at different points during the cure cycle.</span></div>
 In reinforced AFP laminates, the particles, however, act as a bridge in the interface and preclude that the applied vacuum pressure reduces the pore volume. Even more, rather than migrating, the pores remain in their original position as the particles block their path and higher pressures are necessary to make them move in the interface. Pore movement towards the evacuation channels was hardly observed (<span id='cite-_Ref82619125'></span>[[#_Ref82619125|Figure 14]]).

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Torres et al 2021b - Revision history

Materiales.Compuestos at 19:56, 12 December 2022

Scipediacontent at 17:15, 7 May 2022

Scipediacontent: Scipediacontent moved page Draft Content 503207951 to Torres et al 2021b

Scipediacontent: Created page with "== Abstract == Nowadays, manufacturing of composite parts using out-of-Autoclave (OoA) processes is gaining importance because it allows a reduction of initial investments an..."