Papers by Keyword: Linear Elastic Fracture Mechanics (LEFM)

Abstract: Bone fracture can occur in all parts of human skeletal cortical bone including phalanx bone of finger bone. Sometime, it leaves permanent damage and a long period of recovery. This situation can be prevented if we understand the mechanics and the process of the bone fracture. This study aims is to evaluate stress shielding induced by crack interaction using a simple model on Linear Elastic Fracture Mechanics (LEFM). Numerical simulation had been carried out in this study to understand the stress shielding induced by crack interaction. The results revealed that the interaction of two cracks is directly proportional to the stress intensity factor (SIF) magnitude at crack tips. Finally, as the crack-to-width ratio increase and the strain energy release rate also increased.

Abstract: Bone fracture is an injury not uncommon to everyday life. Most of the time, it leaves permanent damage and a long period of recovery. This situation can be prevented if we understand the mechanics and the process of the bone fracture. This study aim is to evaluate stress shielding induced by crack interaction using a simple model based on Linear Elastic Fracture Mechanics (LEFM). This simulation based on the determination of the Stress Intensity Factor (SIF) and the changes of stress shielding in different crack interval towards the human phalanx bone. Numerical simulation had been carried out in this project to understand the stress shielding induced by crack interaction. The results revealed that the interaction of two cracks is directly proportional to the SIF magnitude and interaction factor at the crack tips. The parallel cracks have experienced increasing shielding effect as the crack interval increase. The crack interaction limit (CIL) and crack unification limit (CUL) also had been accomplished for every range of crack interval in this project. Several improvements will be conducted for future development of this study, including various stresses loading subjected to the model, porous element added in the model, different planes of the model and use various methods in calculating the stress intensity factor (SIF).

Abstract: One approach to limiting CO₂ emissions from oxidation of carbon-based fuels is to capture the CO₂ and store it, possibly in onshore or offshore subsurface geologic formations. From the CO₂ transportation structure perspective, a critical component of this approach is the pipeline transportation of supercritical or dense CO₂. In CCS, the pipelines undertaking a CO2 transportation task suffer various loads, the effects of which is easily aggravated due to the existence of a high working pressure (above 7.4MPa) and inner corrosion. For the application of anthropogenic CO₂ pipe transportation technique, this paper will address a LEFM-based finite element method which can evaluate fatigue life for a CO₂ transmission pipeline containing a semicircle inner defect. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis. Under the inner pressure fluctuation scenarios, an FRANC2D finite element procedure is generated to simulate mode-I crack extension from a given inner edge crack, which initiates from the half circle defect,and the corresponding stress intension factors(SIFs), , and its increment, , varied with different cracking depths, are calculated and compared. Afterwards, the fatigue lives for the pipeline with the defects of different sizes are obtained by using a modified Paris formula which can analyze the influence of crack closure and stress ratio. Thus, the relation between the fatigue life of CO₂ pipelines and the dimension of the inner defect can be determined by performing the proposed fatigue crack growth analysis.

Abstract: Abstract. The fatigue crack propagation life-span of the engineering structure is studied. Linear elastic fracture mechanics is applied to analyze the life-span of fatigue crack growth of specimen, which is under constant amplitude load. The software of Fatigue is used to calculate the life-span of a center crack plate steel specimen. The result show that the calculated values of the life-span are basically well with the experimental data.

Abstract: Natural or anthropogenic CO₂ pipelines have been in operation in USA, Europe and North Africa for almost three decades, which are aimed at implementing EOR(enhanced oil recovery) technology and (more importantly) developing CCS(carbon capture and storage) technology. At present, there is no specific pipe standard for CO₂ transportation pipelines. Instead, oil & gas pipeline system is directly introduced into the field of CO₂ transportation piping. Therefore, the technical details for oil & gas pipelines transporting supercritical CO₂ should be carefully taken into consideration due to the relevant effects of different impurities in the transported CO₂ and the different transportation environment for these two mediums, i.e. oil&gas mixture and CO₂. For the application of anthropogenic CO₂ pipe transportation technique, this paper will address a FE-based method which can evaluate fatigue life of a supercritical CO2 transmission pipeline containing an inner crack. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis. And under the inner pressure fluctuation scenarios, an FRANC2D finite element procedure is generated to simulate mode-I crack extension from a given inner edge crack and to calculate the corresponding stress intension factors(SIFs) varied with different cracking depths. Afterwards, considering the effects of crack closure, the Paris equation is modified to build an integral analysis method for the fatigue life evaluation of CO₂ pipeline. Thus, the relation between the fatigue life and the inner pressure fluctuation range can be determined by performing the proposed fatigue crack growth analysis, which can also provide a LEFM-based pipeline selection method in terms of fatigue durability other than the conventional method coming from the structural strength theory.

Abstract: This paper proposes a new three-layer artificial neural network (ANN) to predict the fatigue crack length under constant amplitude mode I cyclic loading. It is shown that the proposed model predicts the crack length with an error of less than 0.05%, and more accurately than the current commonly-used models.

Abstract: This paper presents the extensions of newly developed finite element (FE) formulation to evaluate fracture behavior of parallel edge cracks problems. The numerical formulation used Barsoum singular finite elements to compute fracture parameters in two dimensional finite element models subjected to different crack-width ratio and cracks interval ratio. Mixed mode stress intensity factors (SIFs) of parallel edge cracks are computed in extending of FE formulation for pure Mode I formulation proposed by authors. In 2D linear elastic problem under mixed mode condition, the variation of SIF value near crack tips are discussed comprehensively. The newly finite element formulations are resulted with remarkable agreement with energy release rate based method compared to analytical solution available in the literatures.

Abstract: The simplification of two dimensional approaches in singular finite elements has promoted the method to be used in the formulation of stress intensity factor (SIF) of multiple cracks in finite body. The effect of shielding and amplification are considered in defining the SIF. As been observed, the current available analytical approximations are more restricted to several assumptions. The more accurate and less restricted method has motivated this study. This paper presents the investigation of singular finite elements applied in two dimensional finite element models subjected to different crack-width ratio and cracks interval ratio. The newly finite element formulations are resulted with good agreement with theoretical statement compared to analytical solution. The weak points of presented analytical solution are discussed regards to the influence of crack width ratio and cracks interval ratio.

Abstract: This paper explores the initial potential of theory of critical distance (TCD) which offers essential fatigue failure prediction in engineering components. The intention is to find the most appropriate TCD approach for a case of multiple stress concentration features in future research. The TCD is based on critical distance from notch root and represents the extension of linear elastic fracture mechanics (LEFM) principles. The approach is allowing possibilities for fatigue limit prediction based on localized stress concentration, which are characterized by high stress gradients. Using the finite element analysis (FEA) results and some data from literature, TCD applications is illustrated by a case study on engineering components in different geometrical notch radius. Further applications of TCD to various kinds of engineering problems are discussed.

Abstract: The indentation method is able for use in determining the fracture properties of materials. In the present work, a source code programme for two-dimensional finite element method has been applied to simulate cracking behaviour during indentation on brittle specimens under static loading conditions. The study also aims to predict the crack propagation trajectories under Linear Elastic Fracture Mechanics (LEFM). The source code is written in FORTRAN language. The FE mesh is generated using an advancing front method, where the generation of the background mesh and the construction of singular elements are also added to this developed programme to realise the fracture analysis. In evaluating the accuracy of the crack path predictions, the results are compared and validated with the sets of experimental data of relevant published research work. Upon comparison, it is proven that this developed source code programme is capable of demonstrating the crack indentation in terms of predicting the crack trajectories as well as the evaluation of the stress intensity factors.