Crack Growth In Presence Research Articles

Investigation of fatigue crack growth in engineering components containing different types of material irregularities by XFEM

The extended finite element (XFEM) has been applied to investigate fatigue crack growth in engineering components containing different types of material irregularities. The standard approximations of finite element method are enriched with additional functions by employing the partition of unity approach. In order to keep track of discontinuities in the domain, level set method is employed. Fatigue crack growth in presence of different material irregularities, such as elliptical, rectangular, hexagonal and octagonal discontinuities, has been the main focus of the study. The effect of geometry, position and material properties of these discontinuities on fatigue behavior of the cracked specimen has been addressed. The fatigue life of the cracked component has been estimated by the generalized Paris law. The mixed mode stress intensity factors have been evaluated by the domain-based interaction integral approach. Several numerical problems are solved by XFEM to study the fatigue crack growth behavior of cracked specimens containing different types of material irregularities.

Effect of material irregularities on fatigue crack growth by enriched techniques

The present study investigates the behaviour of propagating cracks in engineering materials containing different material irregularities like bi-material interfaces and holes by employing enriched numerical techniques. Three enriched techniques like the extended finite element method, the element free Galerkin method and the Coupled finite element-element free Galerkin method have been used for analysis. The enriched techniques provide strong numerical tools for modelling different discontinuities independent of the mesh or the grid due to which the problems of conformal meshing, mesh adaption and remeshing do not occur. The level set method has been used to represent different types of discontinuities present in the domain. Several numerical problems, involving fatigue crack growth in presence of bi-material interfaces and holes, are solved to illustrate the applicability, efficiency and accuracy of the three enriched techniques in modelling such problems.

Fatigue crack growth analysis of cracked specimens by the coupled finite element-element free Galerkin method

ABSTRACTThis paper presents a novel approach based on the coupled finite element (FE) and element free Galerkin (EFG) method to model fatigue crack growth in 2-D specimens containing different types of material discontinuities like holes and bi-material interfaces. In this approach, EFGM is used to discretize the domain near the crack whereas the conventional FEM is employed in the rest of the domain. The shape functions of the transition elements have been obtained by using the ramp function. The level set method has been used to track different discontinuities present in the domain. Finally, several two dimensional numerical problems are presented to demonstrate the applicability and efficiency of the proposed technique in modelling fatigue crack growth in presence of material discontinuities. The effect of various material irregularities on fatigue life, critical crack length and crack growth paths has been investigated in the present study. The results show that the critical crack length and the fatigue life of the cracked component reduce due to the presence of a weak bi-material discontinuity in it. The weaker discontinuities increase the fatigue life of the cracked specimen, whereas the stronger discontinuities slightly increase the fatigue life of the cracked component. The presence of holes in a cracked specimen reduces the fatigue life and the critical crack length at final failure. It was also observed that the holes and the weaker discontinuities exert some sort of attractive effect on the crack during its propagation through the domain.

Hydrogen Enhanced Fatigue Crack Growth Rates in a Ferritic Fe-3wt%Si Alloy

It is well known that the presence of hydrogen in ferrous materials promotes both static fracture and affect the material fatigue crack growth rates. The latter is often referred to as Hydrogen Enhanced Fatigue Crack Growth Rate (HE-FCGR) which defines the reduction of crack growth resistance of the material under cyclic stresses when hydrogen is present. When it comes to the determination of the life of components exposed to hydrogen it is therefore of paramount importance to establish such hydrogen induced variation in crack speed in the material in order to avoid unexpected catastrophic failures. In this study the fatigue crack growth rate was determined for a Fe-3wt%Si alloy. Compact tension specimens were used to determine the Paris regime of the fatigue crack growth rate curve of the material. Two environmental conditions were investigated: laboratory air and in-situ electrochemically charged hydrogen. Different mechanical conditions, in terms of load ratio (R=0.1 and R=0.5) and test frequency (f=0.1 Hz, 1 Hz and 10 Hz), were used under electrochemically charged hydrogen conditions. The results show that compared to the specimens tested in air, there is a clear detrimental effect of H for the specimens tested in hydrogen, in terms of accelerated crack growth. The strength of the impact of hydrogen in enhancing the fatigue crack growth rates of the Fe-3wt%Si alloy clearly depends on the test conditions. Fractographic investigations were also used to unveil the mechanisms involved in the process leading to accelerate crack growth in presence of hydrogen.

Experimental study on the fracture capacity and fatigue life reduction of the tensioned cracked plate due to the local buckling

Using a special fixture, the effect of symmetric, and for the first time, anti-symmetric buckling on the fracture and fatigue behaviour of tension cracked plates was studied experimentally. A subroutine was also developed in ABAQUS environment to model the fatigue crack growth in presence of the buckling. Results showed that the buckling can reduce the fracture capacity and the fatigue life by 35% and 59% respectively. The anti-symmetric buckling has more effect on the fracture capacity loss due to mix mode of I-III but it has an opposite effect on the fatigue crack growth due to the sliding crack closure.

Fatigue crack growth in presence of material discontinuities by EFGM

In this paper, the element free Galerkin method has been used to model and simulate the fatigue crack growth phenomenon in cracked specimens containing material discontinuities like holes and bi-material interfaces. The appropriate enrichment functions are added to the standard EFGM approximation in order to take into account the effect of various discontinuities present in the domain. The level set method is used to track different discontinuities present in the domain. Finally, several numerical problems are solved to demonstrate the effect of these material discontinuities on fatigue crack growth.

On the Development of a Prediction Methodology for Crack Growth in Fibre Metal Laminates with MSD Scenario

Multiple-site Damage (MSD) is a dangerous scenario for aircraft structures due to the interaction of adjacent cracks in one structural element. Despite their excellent fatigue crack growth resistance, Fibre Metal Laminates (FMLs) may also encounter this damage scenario. However, only few studies on fatigue crack growth in presence of MSD in FMLs has been reported. An overview of the relevant methods for predicting the crack propagation properties of MSD in FMLs is given and discussed in this paper. The fatigue crack growth of MSD in FMLs was experimentally studied and is reported in this paper. A new analytical methodology, based on the superposition principle and displacement compatibility method, is proposed.

Structural evolution model of damage accumulation processes in modern metallic and polymer nanomaterials

The complex evolution and hierarchical approach to the modeling of the heterogeneous viscous-plastic damaging media fracture process were considered. The model of stochastic crack growth in presence of other defects discussed here allows one to address the process of crack propagation on the basis of microdefects nucleation mechanism, the small cracks growth and coalescence under the external stress and hydrogen effect. Macroscopic model based on the deterministic approach simulates the damage accumulation process and fracture of metal during the hydrogen induced delayed fracture. We also model damage accumulation up to the critical state of a material. Statistical parameters can be estimated experimentally, by the optical and electronic probes, by fractography and by the scanning tunneling "in situ" microscopy methods. Applications to modeling of hot tearing of an aluminum alloy during the solidification process are discussed.