Dealing with the 'French Supersonic Aircraft Research Program', thermal cycling tests in four environments, neutral (vacuum, nitrogen) and oxidative (air, oxygen), were performed on carbon/epoxy cross ply laminates [03/903]s. This experimental study was conducted following a local approach through optical and scanning electron microscopy observations and X radiographs and showed a significant effect of the oxygen level on the damage development. Moreover, coefficient of moisture expansion (CME) tests were performed on the same material to characterize the influence of moisture on the sample expansion. The observations performed during five hundred cycles on carbon/epoxy composite laminates, between -50 deg C and 180 deg C, under vacuum, in nitrogen, air and oxygen showed an influence of the test atmosphere on the damage mechanisms. In nitrogen and under vacuum, where there is no oxidation, the damage is composed of only few short cracks no deformation of the matrix is observed. This small damage is only due to thermal stresses created by the mismatch of coefficient of thermal expansion between layers of various orientations. But when these thermal stresses are combined with oxidation, in air and oxygen, the damage is much more developed, quasi saturated, and deep hollows corresponding to matrix shrinkage on the polished edges are observed. These important residual deformations of the matrix are probably due to its oxidation which induces a weight loss, associated to a density increase. The experimental results of coefficient of moisture expansion tests showed that this new equipment is well adapted to perform these measurements of the CME with a very high accuracy. It remains difficult to measure in the width direction along fibres due to the short distance between lasers and mirrors and the position of these mirrors. The results found perpendicular to the fibres are in accordance with results found in the literature for CFRP materials. Therefore, the use of cross-ply laminates is recommended to minimise the CME effect, to have a good stability and a precise geometry.
Thermal cycling under vacuum and CME evaluation of carbon/epoxy laminates
Auswertung von Wärmezyklen im Vakuum und Ausdehnungskoeffizienten bei Feuchtigkeit von Kohlenstoff/Epoxidharz-Laminaten
Materialwissenschaft und Werkstofftechnik ; 34 , 4 ; 354-358
2003
5 Seiten, 9 Bilder, 6 Quellen
Article (Journal)
English
Polymermatrix-Verbundwerkstoff , kohlenstofffaserverstärkter Kunststoff , Epoxidharz , Gasatmosphäre , Sauerstoff , Luft , Stickstoff , zyklische Belastung , Vakuum , Ausdehnungskoeffizient , Feuchtigkeit , Luft- und Raumfahrtindustrie , Tieftemperatur , Hochtemperatur , Rissbildung , Rasterelektronenmikroskopie , Schichtwerkstoff
Damage Effect of Hygrothermal Cycling on Carbon/Epoxy Laminates
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