Mixed mode fatigue crack propagation behaviour of aluminium F357 alloy. (August 2018)

• Record Type: Journal Article
• Authors: Grasso, Marzio; Xu, Yigeng; Russo, Roberto; Rosiello, Vincenzo
• Is Part Of: Engineering failure analysis. Volume 90(2018)
• Page Start: 463
• Page End: 475
• Publication Date: 2018-08
• Subjects: Mixed-mode fatigue and fracture -- Linear elastic fracture mechanics (LEFM) -- Fatigue crack growth; System failures (Engineering) -- Periodicals; Fracture mechanics -- Periodicals; Reliability (Engineering) -- Periodicals; Pannes -- Périodiques; Rupture, Mécanique de la -- Périodiques; Fiabilité -- Périodiques; Fracture mechanics; Reliability (Engineering); System failures (Engineering); Periodicals; Electronic journals; 620.112
• DOI: 10.1016/j.engfailanal.2018.04.010
• Languages: English
• ISSNs: 1350-6307

Abstract

Abstract: Manufacturing defects are often not in the plane perpendicular to the loading direction and will propagate under mixed mode fatigue loading condition. This paper presents a numerical study of mixed mode crack growth behaviour in H-shaped specimens made of aluminium F357 alloy. The size and orientations of the crack are based on the fractographic observation of defects in F357 specimens manufactured by foundry. Equivalent values of the stress intensity factor (SIF) and the maximum circumferential tensile stress criterion have been adopted to simulate growth of cracks at angles of 90°, 60° and 45° to the loading direction, respectively. Mixed mode fatigue crack growth behaviours are analysed in terms of the shape of crack front, SIF variation, and kink angle. The mixity of SIFs of three modes is complex at early stage of growth with the maximum mode III SIF value at the two ends and the maximum mode II SIF value at the middle of the crack front. The crack surface rotates during the mixed mode crack growth, becoming normal to the loading direction regardless of the initial orientation of the crack. The simulated crack front agrees well with the final elliptical shape of the crack front observed in the physical test specimens. The initial crack orientated at 45° to the loading direction has the longest fatigue life compared with other two crack orientations. Highlights: The mixed mode in aluminium F357 alloy is investigated considering three different inclinations for the crack surface; Fractographic investigations show that defects nucleate close to the external surface with circular shapes; The initial phase of the fatigue crack growth process is affected by the third mode at the two ends of the crack front; The effect of mode III combined with the free surface changes the crack shape from circular to elliptical; Out of the three inclinations of the crack discussed in the paper the 45 0 orientation has the longest fatigue life;