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AN EVALUATION OF FATIGUE AND FRACTURE MECHANICS PROPERTIES OF ULTRA‐HIGH STRENGTH 7XXX SERIES Al‐ALLOYS
Author(s) -
Sanctis M.,
Lazzeri L.
Publication year - 1992
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.1992.tb01268.x
Subject(s) - materials science , grain boundary , ductility (earth science) , ultimate tensile strength , fracture mechanics , fatigue limit , fracture toughness , intergranular fracture , toughness , paris' law , stress concentration , stress (linguistics) , fracture (geology) , composite material , crack closure , metallurgy , microstructure , creep , linguistics , philosophy
— The fatigue and fracture mechanics properties of rapidly solidified ultra‐high strength 7XXX series Al‐alloys have been studied. With respect to conventional high‐strength Al‐alloys, these materials exhibited a better fatigue‐endurance on both plain and notched specimens at low stress amplitude in constant amplitude fatigue tests, whereas the opposite occurred at high stress amplitudes. Fatigue crack growth tests indicated lower crack growth rates at low Δ K ‐levels, but at intermediate and high Δ K ‐values these materials were particularly prone to additional components of “static” crack propagation, which led to steeply inclined d a/ d N vs Δ K curves. Moreover, the increase in tensile strength was linked with some loss of ductility and fracture toughness. Overload regions were characterized by a large amount of intergranular decohesion, possibly facilitated by the presence of incoherent particles at grain boundary regions and by the large strength differential between the matrix and precipitate free zone. The best results in terms of elongation to rupture and toughness were obtained by reducing the amount of Cr/Mn incoherent dispersoid‐forming elements, in order to lessen the tendency towards matrix‐dispersoid interface decohesion at grain boundaries.