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1

2D and 3D numerical simulation of fatigue crack growth path and life predictions of a linear elastic

Bashiri Abdullateef H.

Materials Science Poland

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2021

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Vol. 39, No. 2

285--297

EN

This paper describes implementation of the finite element method (FEM) to investigate crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental and numerical data. The approach involved using two different software to compute stress intensity factors (SIFs), the crack propagation trajectory, and fatigue life estimation in two and three dimensions. According to the software, crack modeling might be run in various ways. The first is a developed source code program written in the Visual Fortran language, while the second is the widely used ANSYS Mechanical APDL 19.2 software. The fatigue crack propagation trajectory and the corresponding SIFs were predicted using these two software programs. The crack direction was investigated using the maximum circumferential stress theory, and the finite element (FE) analysis for fatigue crack growth was done for both software based on Paris's law. The predicted results in both software demonstrated the influence of holes on the crack growth trajectory and all associated stresses and strains. The study's findings agree with other experimental and numerical crack propagation studies presented in the literature that reveal similar crack propagation trajectory observations.

2

The fatigue life estimate by the LEFM concept of the tube joints exposed to axial load

Djoković J. M., Nikolić R. R., Bujňák J., Hadzima B.

Roczniki Inżynierii Budowlanej

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2017

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z. 17

35--41

EN

In the tube joints the crack growth usually appears along the weld’s edge, i.e. at the spot where the chord and the brace are connected. The semi-elliptical crack the most frequently develops from the initial flaw that originated during the welding. The abrupt change in the material’s structure and response to loading are increasing the normal stresses in the lateral tube at certain spots around the crossing of the main and lateral tubes, producing the “hot spot” stress. Sensitivity to fatigue depends on combination of the cyclic loading, initial defects, environmental influences and the “hot spot” stresses which are the result of the tube walls bending during the loading of the structure. The principles of the Linear Elastic Fracture Mechanics (LEFM) are applied in this paper to analysis of the crack propagation behavior of a thin tube joints. Influence of various parameters was investigated individually and independently, and the share of the fatigue crack growth and subsequently the working life of the welded joint were estimated.

3

Propagation of cracks in reinforced concrete beams cracked and repaired by composite materials

Benarbia D., Benguediab M.

Mechanics and Mechanical Engineering

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2017

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Vol. 21, nr 3

591--601

EN

Strengthening and repairing existing reinforced concrete structures is often more economical and sustainable than rebuilding them. Today the most commonly used techniques based on reparation by externally bonded Carbon Fiber Reinforced Polymers (CFRP). However, bonding concrete beams, particularly damaged beams, suffer from the pre-existing of open cracks at the bottom face of the beams. This paper presents an investigation by finite element method using the general purpose FE software Abaqus to study the flexural behavior of initially damaged concrete beams repaired with FRP plates. In this study, it is aimed to simulate the phenomenon of propagations of cracks where the beam is initially loaded to introduce damage, then, after bonding the FRP plates. The linear elastic fracture mechanics (LEFM) approach is adopted to pursue the stress intensity factor’s evolution in 3-points bending before and after reparation of RC beams. Many parameters were taken account, such us the thickness of the adhesive layer and reinforcing plate, the stiffness, and young’s modulus. Results were identified and discussed.

4

Prediction of static crack propagation in adhesive joints

Hedayati R, Jahanbakhshi M, Ghorbani Khouzani S

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 4

937--946

EN

In this work, fracture mechanics methodology is used to predict crack propagation in the adhesive joining of aluminum and composite plates. Three types of loadings and two types of glass-epoxy composite sequences: [0/90]2s and [0/45/-45/90]s are considered for the composite plate. Therefore 2 × 3 = 6 cases are considered and their results are compared. The debonding initiation load, complete debonding load, crack face profile and load-displacement diagram have been compared for the six cases.

5

An analysis of the evaluation of the fracture energy using the DCB-specimen

Biel A., Stigh U.

Archives of Mechanics

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2007

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Vol. 59, nr 4-5

311-327

EN

The methods to estimate the fracture energy using DCB-specimens as advocated in common standards. For instance, ASTM D 3433 and BS 7991:2001 are based on a compliance method, i.e. on linear elastic fracture mechanics (LEFM). Since the mechanical properties of almost all adhesives are non-linear, errors are generated. In some of the standards, the non-linear behaviour is compensated for by the use of correction terms generated from the experiments. An analysis of the methods of evaluation the fracture energy from experiments is performed. This analysis is performed first by simulating an experiment using realistic data for an engineering adhesive and then, by analysing the results with different methods. In this way, the correct fracture energy is known beforehand and the error in the evaluated fracture energy can be determined. In the present work it is shown that the magnitude of this error depends on the length of the crack. The results show that some commonly used methods generate substantial errors when a large region of non-linear deformation precedes the crack tip. It is also shown that methods based on nonlinear fracture methods do not produce this kind of error.

6

Tortuous cracks under remote mode I: the statistical LEFM approach

Pokluda J.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2001

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Vol. 269, z. 67

277-296

EN

Principles of the statistical approach to the stability of microtortuous cracks under the remote mode I loading are presented within the framework of linear elastic fracture mechanics. The basic idea of this approach lies in the suggestion that branching occurs only at those sites along the crack front, where the characteristic structural parameter (grain size, interparticle distance) is comparable to or larger than the plastic zone size. By using procedures introduced in the paper, extrinsic contribution to the fracture toughness or to the fatigue threshold can be separated from experimentally obtained KIc or [delta]Kth values. Consequently, it enables to determine the intrinsic resistance against crack initiation and growth as a more relevant measure of materials quality. Moreover, this theory elucidates quantitatively well some interesting phenomena observed in fracture and fatigue of metallic materials.