Prediction of Fatigue Crack Growth in Metallic Specimens under Constant Amplitude Loading Using Virtual Crack Closure and Forman Model

Abstract

This paper considers the applicability of virtual crack closure technique (VCCT) for calculation of stress intensity factor range for crack propagation in standard metal specimen geometries with sharp through thickness cracks. To determine crack propagation rate and fatigue lifetime of a dynamically loaded metallic specimen, in addition to VCCT, standard Forman model was used. Values of stress intensity factor (SIF) ranges ΔK for various crack lengths were calculated by VCCT and used in conjunction with material parameters available from several research papers. VCCT was chosen as a method of choice for the calculation of stress intensity factor of a crack as it is simple and relatively straightforward to implement. It is relatively easy for implementation on top of any finite element (FE) code and it does not require the use of any special finite elements. It is usually utilized for fracture analysis of brittle materials when plastic dissipation is negligible, i.e., plastic dissipation belongs to small-scale yielding due to low load on a structural element. Obtained results showed that the application of VCCT yields good results. Results for crack propagation rate and total lifetime for three test cases were compared to available experimental data and showed satisfactory correlation.

Numerical Investigation of Asymmetric Strain Controlled Fatigue Behaviour Using Kinetic Theory of Fracture and Peridynamics

“…( 13), cycle energy losses can be expressed proportional to each cycle hysteresis loop area A and then the term kT in Eq. ( 13) becomes 𝑘𝑇 + 𝜓𝐴 resulting KTF modified low cycle fatigue damage equation: 2 ℎ 𝑁 𝛾𝑓𝜎 max _𝑥𝑥′ ( (24) where 𝜓proportional constant, 𝐴 𝜎 𝑦hysteresis loop area at material yield limit. Fatigue process activation energy U and activation volume γ in Eq.…”

“…FE governing equations of motion are cast in terms of spatial derivatives of displacement which is not valid for the case of discontinuity, e.g., fatigue crack. Although special FE methods, such as Extended Finite Element Method (XFEM) [1]), Virtual Crack Closure Technique (VCCT) [2], Cohesive Zone Models (CZM) [3] or even a combination of them [4], can be applied to cope with the discontinuity problem caused by fatigue cracking, the numerical fatigue model complexity and possible uncertainty increase, especially for 3D cracking. This aforementioned problem also results that the fatigue crack in FE model cannot be simulated directly, e.g., without previously defining the crack path.…”

A Model Based Study of Fatigue Life Prediction for Multifarious Loadings

“…Some other models which analytically found crack closure/opening loads by using cycle by cycle method, details are given in [128][129][130]. [131] shows virtual crack closure method for determination of effective stress intensity prediction is in good agreement. Crack closure is extensively used method for life prediction.…”