Mechanisms of fatigue crack growth – a critical digest of theoretical developments

Abstract

A B S T R A C T Recent advances in the processing technology are permitting the manufacture of novel metallic materials with superior fatigue properties via microstructure tailoring. In the light of these promising developments, there is a rising need for establishing a synergy between state-of-the-art experimental characterizations and physically based theoretical underpinnings. A revisit to the existing predictive literature is thus a timely requirement prior to furthering new design guidelines against cyclic damage. To that end, this paper recounts an overview of the key mechanistic and analytical theories on the fatigue crack growth mechanisms. Emphasis is placed on categorizing the proposed modelling endeavours based on their fundamental principles. In doing so, contributions and limitations thereof are carefully examined on the basis of most updated experimental revelations. The objective is to provide a perspective to the current generation of engineers and researchers alike. This concise yet critical narrative would essentially assist in formulating even more advanced microstructure-damage relationships in the modern context. A commentary is added at the end outlining the promising avenues for future research.CTOD, FCG = crack tip opening displacement, fatigue crack growth MD, DFT = molecular dynamics, density functional theory RVE = representative volume element LEFM, EPFM = linear elastic and elastic plastic fracture mechanics E, H = Young's modulus, plastic modulus GB = grain boundary K max , K min , K open , = maximum, minimum and opening stress-intensity factors K c = fracture toughness under mode I loading ΔK eff th , ΔK th = (effective) threshold stress intensity factor range da/dN = fatigue crack growth rate per cycle (a is the crack length and N is the number of cycles) L deflect , θ deflect = length and angle of a deflected crack respectively θ = angle between slip and crack paths σ yield , σ cyclic yield , σ fracture = monotonic, cyclic yields strengths and static fracture strength σ ′ f , ε ′ f = strength and ductility coefficient in Coffin-Manson-Basquin rule: Δε plastic ¼ 2ε ′ f 2N f ð Þ c σ eff , σ hydro = effective and hydrostatic stress ρ * = effective radius of a sharp crack ρ slip , _ ρ vacancy , ρ interface = dislocation density, vacancy generation rate and interface density P H 2 , P O 2 = partial pressures of hydrogen and oxygen m, C = Paris exponent, Paris proportionality constant m Schmid = Schmid factor τ friction , τ forward friction , τ reverse friction = friction (Peierls) stress for free (unobstructed), forward and reverse dislocation glide

On the formation of ridges and burnished debris along internal fatigue crack propagation in 42CrMo4 steel

“…This also explains that the diameter of most burnished debris particles, observed in present work, is in the range of 3.5–10 μm starting from the average martensite block size. Along with further fisheye growth, r c value overlaps more grains/blocks, forming bigger ridges (Figure 5B) up to Stage 2 stable crack growth 58 …”

Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

“…Stage II: Crack propagation (d) The plastic blunting process [24][25][26][27] has asymmetrical effects in the tensile and compressive loading cycles. This mechanism describes crack-growth behaviour in one loading cycle.…”

“…The crack-growth process of creep fatigue is mainly discussed under the second stage of crack growth, and this discussion is based on the idea of the plastic blunting process [24][25][26][27].…”

Short review on multiscale short fatigue crack growth model

“…Nevertheless, this law is appropriate for relatively LC at macroscopic scale. When it comes to short fatigue crack, this empirical law becomes inadequate, especially in MSC stage . The phenomenon of MSC was firstly discovered by Pearson in 1975 when studying the FCG of aluminum alloy .…”

“…When it comes to short fatigue crack, this empirical law becomes inadequate, especially in MSC stage. [7][8][9] The phenomenon of MSC was firstly discovered by Pearson in 1975 when studying the FCG of aluminum alloy. 10 It was found out that the MSC could propagate even below the threshold of LC and at the same nominal SIF range ΔK, the crack growth rate of MSC was higher than that of LC.…”