PSI - Issue 82

Mr. Parthasarathy Iyengar et al. / Procedia Structural Integrity 82 (2026) 309–316 P. Iyengar, J. Mardaras, S. Kyle-Henney / Structural Integrity Procedia 00 (2026) 000–000

313

5

Fig. 4(a) shows specimen failed in fatigue, whereas Fig. 4(b) illustrates what as may be superficially observed. Heat treatment of GD11 to ‘TF’ condition however showed section fatigue failure and is discussed in Chapter 3.

Fig. 4. (a) Specimen failed in fatigue; (b) Superficial observation of failure in fatigue by initiated crack of 7010 compared to AMMC.

3. Mechanical test performance Tensile strength & modulus were found to be significantly higher than commonly used Aircraft Aluminium alloys. Tested coupons were made in accordance with D 3552 by ASTM (2017). GD112 and GD113 were sand blast treated at the external surface. Overall, the following was observed from tensile test of 17 specimen. • GD222 was seen to have a higher tensile strength but significantly lower modulus than GD112 and GD113. • GD222 was seen to strain significantly more but have a more pronounced ‘cliff jump’ breaking point. Curves generally exhibit a ‘flat’ characteristic with only a sympathetic yield point. This point indicates interfacial failure at the section. Extension strain was sensed, leading to (rapid) failure along with decline of the curve. Post yield indicates failure at the fibre, which was physically observed as ‘unzipping’. The specimen-wise performance and Stress-Strain curves are presented as Fig. 5(a) and 5(b) below.

b

a

Fig. 5. (a) Specimen-wise comparison of Young’s modulus and tensile strength; (b) Stress-Strain curves of tested AMMC specimen.