Environmentally assisted cracking behaviour of Al-Zn-Mg-Cu-Cr alloy bonded with polymer matrix composite stiffener

Studies were conducted to investigate the effect of polymer matrix composite stiffener (patch) on environmentally assisted cracking (EAC) susceptibility of pre-cracked alclad Al-Zn-Mg-Cu-Cr alloy in 3.5 wt.% NaCl environment. The EAC threshold stress intensity of the peak and two-step aged alloy was reduced from 26 to 7 MPa m1/2 and 31to 8 MPa m1/2 respectively under the influence of patch. The plateau crack velocity was increased from 2.5 × 10−9 to 5.1 × 10−9 m/s for peak aged and 1.2 × 10−9 to 2.0 × 10−9 m/s for two-step aged tempers in patched condition. The significant increase in EAC susceptibility was attributed to crevice effect generated by the stiffener.