Papers by Keyword: Fracture Mechanics

Abstract: An interface crack between two semi-infinite piezoelectric/piezomagnetic media under out-of-plane mechanical load and in-plane electric and magnetic fields parallel to the crack faces is examined. A portion of the faces is electrically conducting and kept at a uniform magnetic potential, while the remaining portion is electrically and magnetically permeable. The coupled fields are represented by functions analytic in the plane outside the crack. With these representations, the mixed crack-face conditions lead to a combined Dirichlet–Riemann and Hilbert boundary-value problem, which is solved in closed form for arbitrary conductive versus permeable segment lengths. The solution yields explicit expressions for stresses, electric and magnetic fields, and the crack-face sliding (displacement jump). The singular behavior at both crack tips and at the transition between conducting and permeable zones is characterized, and intensity factors are defined accordingly. Parametric results illustrate how applied electric and magnetic fields modulate the fracture driving force; in particular, suitable magnetic loading can markedly reduce the mechanical stress intensity at the permeable tip. The formulas supply benchmark data for verification and enable design guidelines for tailoring electrode coverage and field application to mitigate interface fracture. The approach provides an analytic framework for mixed electromagnetic conditions in magnetoelectroelastic interface fracture.

Abstract: This study aims to address these challenges by evaluating the displacement and interfacial damage of acetabular components with auxetic inner structures under cyclic loading conditions. Aseptic loosening of the acetabular cup is one of the primary causes of implant failure in hip replacements. However, assessing the damage behavior of implants in vivo remains a significant challenge, particularly when evaluating implant displacement and interfacial damage. A cantilever device for displacement measurements was designed and calibrated using a laser displacement sensor. The cantilever device successfully measured the displacement of the acetabular cup by monotonic and cyclic loading up to-2.3kN. Both AE sensors and cantilever devices could measure the increasing displacement in both the rotational and embedding directions. Finally, the loosening mechanism of the acetabular cup with an auxetic texture was discussed.

Abstract: This study presents a detailed analysis of the catastrophic failure of a Pelton turbine bucket, revealing a complex mechanism involving multiple interacting factors. Through a root cause analysis (RCA), the primary crack was identified to have originated in a high-stress concentration zone, exacerbated by pre-existing discontinuities. The turbine runner had accumulated approximately 90,000 service hours, suggesting a low-stress, high-cycle fatigue as the initial damage mechanism. However, the rapid crack propagation was driven by an abrupt shift in the fatigue regime, transitioning to high-stress, low-cycle fatigue induced by severe impact loads during counter-jet entry. This phenomenon led to the fracture of the bucket segment. This work emphasizes the importance of considering the synergistic interaction of accumulated fatigue, pre-existing discontinuities, and changes in the loading regime in the design and maintenance of Pelton turbines, to prevent premature failures and ensure the structural integrity of these critical components.

Abstract: The role of welding in fracture mechanics development is considered from historical point of view. Starting point was analysis of Schenectady ship failure during the II World War, leading to development of linear elastic, as well as elastic-plastic fracture mechanics, soon afterwards. Two case studies are described to illustrate weldment fracture mechanics and structural integrity assessment.

Abstract: Repeated loading on the railroad tracks will result in fatigue failure. Fatigue failure combined with a defect in the form of a crack in the railroad track will result in a decrease in strength. Defects in the form of cracks are formed due to improper manufacturing and treatment processes. One treatment that can cause the formation of defects in the form of cracks is thermite welding. Improper and non-standard thermite welding techniques can trigger the formation of defects in the form of cracks in the railroad joints. Based on these problems, this simulation aims to obtain information about the value of maximum stress, SIF, J-Intergal, number of cycles, and crack extension from variations in crack size to repeated loading. The method consists of preprocessing, processing and postprocessing. Preprocessing begins with the design of the UIC 54 railroad crack which consists of 3 variations of crack length, namely 10 mm, 15 mm, and 20 mm. The design was tested through static structural simulation using the ANSYS 2021 R2 application. Meshing is configured using an element size of 5 mm and uses curvature capture. The results of the simulation obtained maximum stress values, SIF, J-Integral, number of cycles, and crack extension. Based on the simulation of SIF 1 and J-Integral values on the specimen design with a crack length of 10 mm it shows 362.03 Mpa.mm^1/2 of 0.5708 mJ/mm², for an initial crack length of 15 mm that is equal to 482.81 Mpa.mm^1/2 and 0.91738 mJ/mm², and for an initial crack length of 20 mm, it is 600.54 Mpa.mm^1/2 and 1.4465 mJ/mm². The results show that the increase in SIF 1 and J-Integral will be proportional to the increase in the initial crack length value. .

Abstract: In large-sized metal structures, various stress concentrators are often present, which affects the operation of the material. These are intermittent bonds, holes, welded joints, material defects, etc. As a result of overloads under the action of an external cyclic load on structures in the area of stress raisers, the cycle asymmetry, the level of maximum stresses and deformations increase. In this case, the determination of the limit values of the stress cycles can be performed using a diagram of the limit stress amplitudes. The paper presents an engineering method for calculating the limiting stress amplitudes and constructing Hay’s diagrams. It is based on the use of mathematical models of classical linear and structural-mechanical fracture mechanics. Analytically and by calculation, the validity of the method is shown, which consists in determining the endurance limits and limiting stress amplitudes under high-cycle loading in a wide range of variation of the cycle asymmetry coefficient for ferrite-pearlite steels with a yield strength of up to 400 MPa. Thus, a generalized calculation method has been developed for determining the endurance limits for high values of cycle asymmetry and cycle stresses. The error of the method is estimated in the area of low-cycle load. The influence of constant and average load in a cycle on the endurance limit has been investigated both for high-cycle and low-cycle loading. The proposed approach allows to construct Smith and Hay’s fatigue diagrams for the tensile region, taking into account the structural characteristics of the material and the error allowed for engineering calculations.

Abstract: Laser welding is an innovative technology of joining metallic materials. In comparison with conventional arc welding, it has numerous advantages, like high energy of laser beam and high effectiveness, very good reproducibility, possibilities of automation, low energy consumption etc. High pressure vessels and high pressure pipeline industry represent perspective new fields of application. However, since pressure vessels and pipelines are usually operated at conditions of repeated or cyclic loading, an acceptable resistance to fatigue loading of the welds has to be demonstrated. In this contribution, results of an experimental programme aimed at an evaluation of high-cycle fatigue resistance in and near laser welds of a P355 pressure vessel steel are presented and discussed. Particular attention is paid to evaluation of crack initiation mechanisms in connection to laser weld character and welding imperfections. The programme is completed by measurement of fatigue crack growth rates and threshold values in the weld. Results of high-cycle fatigue tests of some groups of specimens were characteristic by a considerable scatter. The reason of the scatter was found in welding defects in some parts of the welds. Fatigue results are discussed also from the viewpoint of fracture mechanics and threshold values of fatigue crack growth.

Abstract: The Brazilian disc test with central notch is widely used to evaluate mixed mode I/II fracture resistance of brittle materials such as rocks and concrete. An analytical evaluation is used based on the maximum tangential stress (MTS) criterion and the generalised maximum tangential stress (GMTS) criterion. In this contribution two concrete types, a C 50/60 and a high strength concrete, were compared using the GMTS criterion. Also, the influence of critical distance r_C on the fracture resistance under the mixed mode I/II was studied.

Abstract: In this paper, the work is based on the application of probabilistic fracture mechanics models (PFM) to predict the reliability of nuclear reactors pipes under pressure. Cracking simulation of a stainless steel piping under the conditions of intergranular stress corrosion cracking (IG-SCC) is based on the general methodology recommended in the modified software M-PRAISE. IG-SCC is characterized by a unique damage parameter depending on residual stresses, environmental conditions, and sensitization degree. This parameter can be used to evaluate the structural reliability and identify the majority of efficient approaches to improve the piping reliability: effect of a corrosive medium on the reliability, which is analyzed in this present work.

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.