Papers by Keyword: SIF

Abstract: Bonding metallic structures with composite materials is widely considered to be the most optimal method for joining damaged and fractured structures. This method offers important advantages, such as reducing the stress intensity factor (SIF) and increasing the lifetime of the joined structure. However, hygrothermal aging is a phenomenon that can reduce the lifetime of reinforced structures made of glass fiber-reinforced polymer (GFRP). This study used numerical modeling to investigate a cracked stainless steel pipe operating in a hygrothermal environment and repaired with three patches. The main objective of this work is to determine the effect of adhesive aging due to hygrothermal damage on the repair efficiency of a cracked SA312 type 304 stainless steel pipe. The Finite Element Method (FEM) is used to evaluate the SIF as a function of applied load for different immersion times and at two different temperatures. First, the developed model was validated against literature results. A parametric study was then carried out. The obtained results showed that the adhesive maintains its stiffness for 7.5 months of immersion and that the mechanical properties of the adhesive are acceptable even at temperatures of 90°C or lower and internal pressures less than or equal to 50 bar. However, when the pressure load exceeds 50 bar (p_int > 50 bar), the degradation of the adhesive becomes more significant, and the hygrothermal aging leads to variations in the mechanical properties of the joined structure. It is important to note that these results can contribute to the improvement of the existing composite repair design standard and can provide reliability for the application of GFRP in different humid environments.

Abstract: In service condition rail joints, especially the weldments are under the action of various loadings which are not only working in multiple axis direction but also time-dependent having a cyclic and mixed-mode in nature and non-relative to each other. The surface of the rail and its weldment is acted by very high repetitive stress through the wheel and because of this contact stress the running surface or subsurface may have cracks or fractures due to fatigue. This work is based on numerical simulation of an aluminum thermite weldment on a UIC 60 rail under multi-axial fatigue crack propagation under the friction with surficial interaction between weldment and wheel with bending load due to vertically applied load through the wheel on the weld. Since contact is highly influenced by vertical load and also for minimizing the simulation time the lateral and longitudinal traction forces are not included in this study. The work formulation and discretization have been done with the finite element method and a non-linear lagrangian algorithm solver is applied. A 3-D rail-weld wheel model assembly and a semi-elliptical crack as a flaw on the weld surface are used to identify 3-Modes of SIFs along with its graphical plot generation. Simulation is performed under multi-axial weld wheel surface contact at different locations on weld running surface, taking into account varying position of fracture crack on weld 3-D model to calculate fracture life of weld joint and observation of fatigue crack propagation. This work involves the numerical and theoretical approach of fracture mechanics on created FE fatigue model using the Linear Elastic Fracture Mechanics (LEFM) method following Paris law for fracture mechanics. All the numerical simulation for critical fracture dimension and cycle count with stress intensity factor for weld failure data is estimated using software ANSYS 2020 academic and plotted, then comparison of predicted and observed transverse crack growth behavior and fatigue life of weld, based on Millions Gross Tonnes (MGT) is discussed.

Abstract: The cracked blade in L-0, L-1 governor side, and L-1 generator side were found when A 220 MW low-pressure steam turbine was checked in the serious inspection. However, the crack population more dominant at L-1 Gen compared to L-0 Gov and L-1 Gov. Most of the cracks were located on 300-400 mm from the root of the blade span, and it did not associate with the pitting defect. In this study, the root cause of L-1 blade failure was investigated. There is three-stage of analyzing process, firstly capturing the airfoil and dimension of L-1—secondly, the material properties analysis, and finally stress analysis of L-1 by the finite element analysis software. L-1 is the blade with the chord length on the tip L-1 blade longer than root as 2.1% and the angle of an airfoil from root to tip twisted as 24 degrees. The type of material did not look precisely similar to AISI 422 because its hardness-strength is lower than AISI 422 as 5.1%. The finite element analysis shows that there was a symptom of the imprecise shroud gap that promoted maximum stress at 300-400 mm from the root area of the L-1 blade span. Moreover, a lack of hardness-strength material cannot accommodate the excessive movement of the blade and promoted the initial crack of L-1. A crack length blade as 16 mm shows a lower number of cyclic (N_f) to failure tremendously compared to standard blades such as 32,367 of the number cyclic for regular blade and 42.6 for the crack blade. Increasing 2 mm of initial crack will decrease significantly the number of cyclic N_f of the blade. It was tearing mode crack propagation of L-1 results a significant stress intensity factor compared to other modes, especially at 16 mm length of the crack.

Abstract: The investigation of static crack and its growth is essential issue as to confirm reliability and to avoid catastrophic consequences which leads to the loss of life in case of engines, reactors, aerospace other industrial applications since most of the failures start from the crack. In this study, an edge crack in 3D elastic functionally graded material (FGM) is solved by extended finite element method (XFEM). Linear elastic fracture mechanics (LEFM) theory is used to determine the stresses near the crack front. Stress intensity factor (SIF) is calculated using interaction integral at the crack front.

Abstract: On the basis of using CFRP (Carbon Fiber Reinforced Polymer) to reinforce steel materials and structures, this paper focused on the reinforcement method of box girder steel structure. Firstly, FEM models were set up to discuss the reinforce method, stress distribution between overall strengthening of flange and locally strengthening. Secondly, typical crack model was raised on the basis of mechanics characteristic, reinforcement effects under different methods was analyzed. The results showed that locally strengthening method to reinforce the certain fatigue areas could improve stress concentration phenomenon and SIF effectively. This paper offered a significant basement for reinforcing box girder steel structures and repairing fatigue cracks using CFRP.

Abstract: Composite patch adhesively bonded repair is an advanced repairing method for damaged metallic structure, and patch designing is important before repairing, which decides final repairing effect. Based on 3D FEM, the model of aluminum plate with a central through crack adhesively bonded repaired with composite patch was established, which can take into account residual thermal stress and bending deformation caused by differences of thermal expansion coefficient. SIF was calculated using virtual crack closure technology and compared to evaluate patch designing. The results show that for through centrally cracked aluminum plate, rectangle boron/epoxy patch is the best, and more plies whose fiber direction is parallel to loading direction are, better repairing can be got.

Abstract: Composite patch adhesively bonded repair is an advanced repairing method for damaged metallic structure, and in patch designing, it is important to choose appropriate geometrical parameters, which decides mechanical properties of repaired structure. Based on 3D FEM, the model of aluminum plate with a central through crack adhesively bonded repaired with carbon/epoxy composite patch was established, which can take into account residual thermal stress and bending deformation caused by differences of thermal expansion coefficient. SIF was calculated using virtual crack closure technology and compared to evaluate effects of patch geometrical parameters on mechanical properties of repaired structure. The results show that there is optimal patch length and thickness which can make best repairing effect and an effective patch width can reduce SIF significantly, beyond which it is helpless.

Abstract: The objective of this study is examining the level of degradation caused by the welding process, the influence of defects by third parties and the speed of loading on the integrity of the pipeline. The use of Charpy instrumented pendulium coupled with the the volumetric method analysis allowed us to calculate the dynamic fracture toughness of the API 5L X52 pipeline steel in presence of a real defect characterized by its notch radius but also, to show the need for a second parameter to overcome the problem of fracture toughness transferability.

Abstract: A 2D FE model of cracked aluminum plates repaired with adhesively bonded composite patches was established in this paper, and then the model was validated by comparing the calculated SIF and fatigue life of repaired structure with existing results. The result shows that the model is accurate enough to be used to analyze the mechanical property of cracked aluminum plates repaired with adhesively bonded composite patches.

Abstract: In this study, the FEA static and dynamic analysis for one type of piston are carried out by using software ANSYS to obtained the cranny origin position and stress range value of the dangerous part of the piston, respectively. The critical crack length is analyzed based on the fatigue theory; the stress intensity factors (SIF) are computed, and the expression of the shape geometry factor of the piston is obtained according to the least squares method. An estimated formula of the fatigue life is developed by amending the Paris formula on the basis of studying the fatigue behavior of pistons. Finally, the fatigue cracked life of the piston is calculated using these parameters and the Amending Paris formula.