write:The left skin panel bucklefailure was angled mostly in a downward 45º direction aft of hinge attachment fittingnumber 5 although a branch was also present upward along the leadin

at the aft half of the chord
a 45º branch angled downward. The left skin panel bucklefailure was angled mostly in a downward 45º direction aft of hinge attachment fittingnumber 5
although a branch was also present upward along the leading edge spar.1.16.3.2 Materials Testing and Microstructural ExaminationAt the Safety Board’s request
NASA-Langley conducted materials testing andmicrostructural examination of the vertical stabilizer and rudder.107 Samples were selectedfrom multiple locations on the vertical stabilizer and rudder to determine chemicalcomposition
extent of cure
glass transition temperature
fiber and void volume fractions
and ply stacking sequence (layup).The chemical composition of each sample from the vertical stabilizer was assessedusing infrared spectroscopy
which measured the total attenuated reflectance through amicroscope. The results were typical for CFRP material with no significant variances inthe spectrums for each specimen.The extent of cure and the glass transition temperature of one area from the upperend of the right skin panel were analyzed using modulated differential scanningcalorimetry
dynamic mechanical analysis
and differential scanning calorimetry in boththe as-received condition and in the dry condition.108 The moisture content for theas-received condition was approximately 0.58 percent. The modulated differentialscanning calorimetry results corresponded to an extent of cure greater than 97 percent.The dynamic mechanical analysis results showed that
in the as-received condition
theonset glass transition temperature measured 134° C
which was between the qualificationvalues of 144° C for the dry condition and 122° C for the 50 percent relative humidity(0.7percent moisture content) condition. The portion of the sample that was tested in thedry condition had an onset glass transition temperature of 149° C. The differentialscanning calorimetry results showed no significant variance among the extent of cure andthe glass transition temperature of all samples
and the results indicated that the extent ofcure was sufficient.106 The most severe damage to the rudder occurred near hinge attachment fitting numbers 2 through 4
but the skin panels near these fittings were difficult to image. The most prominent facesheet-to-honeycombfracture damage to the upper two-thirds of the rudder was the large buckles near hinge attachment fittingnumber 5.107 Some testing and microscopy were completed at Airbus’ composites technology division in Bremen
Germany.108 The curing temperature for the vertical stabilizer CFRP material is specified to be 250° F. Accordingto Airbus materials qualification data
the onset glass transition temperature should be 144° C in the drycondition and 122° C after exposure to a climate of 50 percent relative humidity (corresponding to amoisture content of 0.7 percent weight).