Anomalies in Long-Crack Propagation at Low ΔK in Some Engineering Alloys.

In this article, we discuss an unusual pattern in long-crack behavior at low stress intensity factor ranges ΔK (below ΔK), characterized by an initial dip, followed by a plateau, and then an acceleration in fatigue crack growth (FCG) rate. This unanticipated FCG behavior was first observed experimentally in the IMI 834 alloy and reported by Marci in 1996. Such an anomaly is only reported from experimental observation but cannot be understood or explained using the plasticity, roughness, or oxide-induced crack closure assumptions.

Unusual Fatigue Crack Growth Behavior of Long Cracks at Low Stress Intensity Factor Ranges.

In this article, we characterize and review the unusual lack of threshold in fatigue crack growth (FCG) behavior for some alloys at low values of stress intensity factor ranges ΔK and its implications to damage-tolerant design approaches. This unusual behavior was first observed by Marci in 1996 in IMI 834 alloy. Conventional applications of linear elastic fracture mechanics to FCG analysis at constant R-ratio (or K) assumes that (da/dN) decreases monotonically with decreasing ΔK and approaches the threshold value of ΔK with (da/dN) ≤ 10 mm/cycle for a given R (or K).

Impact of Notches on Additively Manufactured Inconel 718 Tensile Performance.

This study was completed in effort to characterize the notch sensitivity of additively manufactured (AM) Inconel 718 produced by laser powder bed fusion (L-PBF). Three different root radii on V-notched test specimens and smooth specimens were evaluated under tensile conditions for specimens built in vertical and horizontal orientations. Both the total axial strain and localized notch diametral strain were measured.

Discussion and Comments on K and ∆K.

This article addresses online discussions with comments related to K and ∆K used in fatigue crack growth (FCG) analyses and modeling. The author of this article assembled an online discussion pertaining to the critical issues and challenges on Kop and ∆K, which took place during the summer of 2020. The meetings were titled, .