Fatigue Life Extension by Crack Repair Using Double Stop-Hole Technique
TL;DR: In this paper, the double stop drill hole method can be used to increase the fatigue life of the cracked components and the results show that fatigue life extension caused by double stop hole method is significantly more than the conventional single stop-hole method, while the distance between the hole centers is the main parameter affecting the efficiency of this method.
Abstract: Drilling holes in the vicinity of the crack tip turns the crack into a notch and reduces the crack tip stress intensity factor. In this paper, a new idea is used in which instead of a single hole, two symmetric and interconnected holes are drilled at the crack tip. The main concept of double stop-hole method is to reduce the stress concentration at the edge of stop-holes in the cracked structural elements. The double stop drill hole method can be used to increase the fatigue life of the cracked components. The fatigue crack growth retardation is examined using an experimental investigation coupled with a stress analysis on the efficiency of proposed double stop-holes. The distance between the hole centers is considered as the main parameter affecting the efficiency of this method. The results show that the fatigue life extension caused by the double stop-hole method is significantly more than the conventional single stop-hole method.
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TL;DR: In this article, the fatigue strength of Ti-6Al-4V blunt V-notched samples produced by the selective laser melting (SLM) process is assessed. But despite the observed fatigue strength reduction induced by the notch, samples showed a sufficient low notch sensitivity that it was not possible to define a critical radius for the material analysed.
101 citations
31 Jul 2017
TL;DR: In this paper, the authors assess the fatigue strength of Ti-6Al-4V smooth and circular notched samples produced by selective laser melting (SLM) and investigate the fracture surface of the broken samples in order to identify crack initiation points and fracture mechanisms.
Abstract: Additive manufacturing (AM) offers the potential to economically produce customized components with complex geometries in a shorter design-to-manufacture cycle. However, the basic understanding of the fatigue behavior of these materials must be substantially improved at all scale levels before the unique features of this rapidly developing technology can be used in critical load bearing applications. This work aims to assess the fatigue strength of Ti–6Al–4V smooth and circular notched samples produced by selective laser melting (SLM). Scanning Electron Microscopy (SEM) was used to investigate the fracture surface of the broken samples in order to identify crack initiation points and fracture mechanisms. Despite the observed fatigue strength reduction induced by circular notched specimens compared to smooth specimens, notched samples showed a very low notch sensitivity attributed both to hexagonal crystal lattice characteristics of tempered alpha prime grains and to surface defects induced by the SLM process itself.
64 citations
TL;DR: In this paper, the EMC-ASED criterion was used to predict the tensile load-carrying capacity (LCC) of U-notched Al 7075-T6 and Al 6061 -T6 plates by combining the equivalent material concept (EMC) with the averaged strain energy density (ASED) criterion.
32 citations
TL;DR: In this paper, the suitability of the combined Equivalent Material Concept-Averaged Strain Energy Density (ECA-ASED) failure criterion, called EMC-ASED, in predicting the load-carrying capacity (LCC) of notched aluminum plates subjected to mixed mode I/II loading was checked.
31 citations
Cites background from "Fatigue Life Extension by Crack Rep..."
..., it is necessary to strictly evaluate the resistance of the aero-aluminum alloys against crack initiation from the notch border, so-called the notch fracture toughness (NFT), experimentally and/or theoretically [13-17]....
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TL;DR: In this paper, a model using the finite element method (FEM) was developed, in order to predict the creep behavior of high pressure turbine (HPT) blades, and the overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade.
Abstract: During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
20 citations
References
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TL;DR: In this article, a comparison of the fatigue behavior between the S355 mild steel and the S690 high strength steel grades, supported by an experimental program of fatigue tests of smooth specimens, performed under strain control, and fatigue crack propagation tests, is presented.
160 citations
"Fatigue Life Extension by Crack Rep..." refers background in this paper
...The specimen was assumed to be made from S690 steel alloy with the elastic modulus of 209.4 GPa and the Poisson’s ratio of 0.3....
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...Although, the related results were obtained for the S690 high strength steel, the same approach can be extended to study the fatigue life improvement of other metallic alloys and also other types of cracked specimens....
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...High strength steel S690 is a quenched and tempered fine-grain structural steel which is intended for structural applications where weight savings is important....
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...The tolerances for S690 plates can be found in EN 10025 standard [12]....
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...The material constants for S690 steel are presented in Table 1 [13]....
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TL;DR: In this paper, the crack growth retardation and the location of fatigue crack initiation from stop-hole edge under different mode-mixities are examined by means of a developed fatigue code.
84 citations
TL;DR: In this article, the authors investigated how the stop drilling procedure improved the crack initiation life and the total fatigue life in specimens of 6061-T651 aluminium alloy and AISI 304 stainless steel.
79 citations
"Fatigue Life Extension by Crack Rep..." refers methods in this paper
...The method has been investigated theoretically and experimentally by some researchers in the past [5-10]....
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TL;DR: In this paper, the authors examined the crack growth retardation using a numerical study on the efficiency of stop holes, which turns the crack into a notch and diminishes the crack tip stress singularity.
51 citations
15 Jul 2000-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effects of inserting an expanded hole or a non-expanded hole at the tip of a fatigue crack on the subsequent delay of fatigue crack propagation was studied, showing that the hole expansion process modifies the condition and properties of the surface layer of materials and affects significantly the length of the nucleation stage of the fatigue process.
Abstract: The purpose of this paper is to study the effects of inserting an expanded hole or a non-expanded hole at the tip of a fatigue crack on the subsequent delay of fatigue crack propagation. Single edge pre-cracked specimens of two aluminum alloys were used to perform the crack arresting tests under cyclic stress loading. An obvious increase in the delay of crack propagation is obtained for the specimens with expanded hole. The compressive residual stresses produced by the hole expansion process play an important role in increasing the fatigue resistance of the material. The observation of micro-structure at the fatigue failure section reveals that the hole expansion process modifies the condition and properties of the surface layer of materials and affects, significantly the length of the nucleation stage of the fatigue process.
37 citations