Assessment of vacuum bag pressure impact on porosity of laminates made with VBO prepregs
Piotr Czarnocki, Tomasz Katz, Piotr Koperniak
Quarterly No. 3, 2015 pages 141-145
DOI:
keywords: porosity, VBO prepregs, ultrasound attenuation
abstract Vacuum bag only (VBO) prepregs allow for manufacturing composite airframe parts without the need for expensive autoclaves since such prepregs can be cured in ovens with the help of vacuum bags. However, the vacuum pressure must be kept at an acceptable level to obtain low porosity products. One of such prepregs is Cytec MTM46/HTS(12K)-150-35% RW carbon/epoxy VBO prepreg designed for airframe applications. The aim of the presented research was to determine an acceptable level of vacuum pressure in vacuum bags, in particular, and the effect it exerts on the porosity of laminates made with the aforementioned prepreg. For this purpose, UD laminate plates were manufactured under 10, 40, 60, 80 kPa and 96kPa vacuum pressure. Next, ultrasound attenuation displayed by every single plate during ultrasound C-scanning was defined in terms of the so-called full screen height percentage and presented in the form of coloured contour plots. Upon counting the pixels corresponding to each colour, it was possible to determine plate area fractions for each attenuation level. Next, a certain number of specimens was cut out of the plate regions that differed in their attenuation and these specimens were x-rayed with the help of a tomograph, then specialized software was used to determine their porosity. Finally, an experimental relationship between the ultrasound attenuation and specimen porosity was determined.