FEATURE g…/… Torsional performance and damage tolerance: of different braiding configurations flange with an impact energy of 30 Joules. In order to determine the torsional performance and damage tolerance, the impacted and non-impacted shafts were tested on a standard torsional test-bed. During the tests, the rotation and the torsional moment were plotted into a file for subsequent data reduction. Fig. 5: Polished micrograph section of (a) a biaxial and (b) a triaxial configuration. Torsional performance and impact tolerance A broad test campaign show that the braiding configuration has a considerable influence on both torsional performance and damage tolerance. The characteristic mechanical properties of the triaxial braid were the motivation for the NOBRAZED configuration. For long transmission shafts with high axial stiffness, this configuration is an option. The torsional performance and damage tolerance of the three configurations are compared below. Influence of NOBRAZED fibres on damage tolerance The CT scanner investigation showed that the NOBRAZED fibres operate like a separator during the impact. The “loose” fibres between the biaxial layers and the steep gradient of stiffness between the NOBRAZED and biaxial layers have a negative effect on damage tolerance. Figure 6.2 (a) and (b) shows sectional views of the NOBRAZED32-I and T-32-I impacted shafts. The impact area of the T-32-I shaft is marked by a red line. The sectional view of this shaft shows no visible effect of the impact, contrary to the NOBRAZED-32-I shaft. Here, nearly 50% of the cross-section is delaminated. Test specimens and test setup All tested transmission shafts were 925.78 mm in length and 26.0 mm in inner diameter. The shafts were braided with three layers on a steel mandrel. The braiding angle α was set by regulating the braid haul-off speed va. Equation (1) shows the coherence between these two parameters in relation to the mandrel diameter d and the angular frequency of the carrier ωc. α = arctan d.ωc 2.va (1) The LY 556 resin system from Huntsman was used for all the test specimens. It was infused by a VARI process. Flanges made of 15-5PH steel were used to apply force. These flanges were joined with the 9323 epoxy-based adhesive from 3M with a 50mm overlap length. Table 1 summarizes the transmission shafts tested to investigate the mechanical performance of the braiding configuration. Table 1: Tested drive shaft configurations. Fig. 6: (a) and (b) sectional views of impacted shafts. Shaft type B-32-NOI T-32-NOI T-32-I NOBRAZED-32NOI NOBRAZED-32-I Description biaxial braid; α = 32°; without impact triaxial braid; α = 32°; without impact triaxial braid; α = 32°; impacted biaxial braid; α = 32°; NOBRAZED fibres; without impact biaxial braid; α = 32°; NOBRAZED fibres; impacted In contrast to torsional performance, the NOBRAZED fibres dramatically reduce damage tolerance. Figure 7 shows that the residual strength of the NOBRAZED-32-I shaft is only 35% compared to 87% for the T-32-I. Fig. 7: Influence on damage tolerance. The shafts to be tested for impact damage were assembled before undergoing the torque test on an impact rig. The shafts were fixed by their flanges on both sides, as shown in Figure 1. The impactor was a pendulum with an impact diameter D = 25 mm. All drive shafts were impacted 110 mm from the end of the Effect of different braiding configurations on torsional performance Figure 8 shows that the braiding configuration has an influence on torsional performance. In the triaxial configuration, fibre jec composites magazine / No52 October 2009http://www.jeccomposites.com