Characterising the impact of surface integrity on the fatigue behaviour of a shot-peened connecting rod

The present study focuses on analysing and modelling the influence on fatigue behaviour of the surface of a hot-forged C70 connecting rod which undergoes a shot-blasting treatment. The shot-blasting heavily affects the surface and thus the fatigue properties. In addition, the forging process introduces large defects which also have an effect on the fatigue strength. So as to be able to determine which aspects of the surface integrity are the most influential in fatigue, additional surface states were generated by shot-peening the as-forged surface. The various surface states were thoroughly characterised and then tested in high cycle fatigue in bending. The various aspects studied are the surface roughness and large defects, residual stresses, and microstructure

Characterising the impact of surface integrity on the fatigue behaviour of forged components

The present study focusses on analysing and modelling the influence on fatigue behaviour of the surface of a hot-forged C70 connecting rod which undergoes a shot-blasting treatment. The shot-blasting heavily affects the surface and thus the fatigue properties. In addition, the forging process introduces large defects which also have an effect on the fatigue strength. So as to be able to determine which aspects of the surface integrity are the most influential in fatigue, various surface states were thoroughly characterised and then tested in high cycle fatigue in bending. The various aspects studied are the surface roughness and large defects, residual stresses, microstructure and hardness

The effect of quenching and defects size on the HCF behaviour of Boron steel

This work investigates the effect of natural and artificial surface defects and quenching on the fatigue strength of a Boron steel (22MnB5). A vast experimental campaign has been undertaken to study the high cycle fatigue behaviour and more specifically the fatigue damage mechanisms observed in quenched and untreated materials, under different loading conditions and with differents artificial defects sizes (from 25 μm to 370 μm radius). In order to test the sheet metal in shear an original test apparatus is used. The critical defect size is determined to be 100 ± 50 μm. This critical size does not appear to depend on the loading type or the microstructure of the material (i.e. ferritic–perlitic or martensitic). However, for large defects, the quenched material is more sensitive to the defect size than the untreated material. For a defect size range of 100–300 μm the slope of the Kitagawa–Takahashi diagram is approximately −1/3 and −1/6 for the quenched and untreated materials respectively. A probabilistic approach that leads naturally to a probabilistic Kitagawa type diagram is developed. This methodology can be used to explain the relationship between the influence of the heat treatment and the defect size on the fatigue behaviour of this steel

A flexible HCF modeling framework leading to a probabilistic multiaxial Kitagawa-Takahashi diagram

This article describes a flexible modeling framework which leads to the construction of a probabilistic, multiaxial Kitagawa-Takahashi diagram. This framework has been developed following experimental observations that clearly indicate that two independent fatigue damage mechanisms can be activated, at the same time, in metallic materials. Specifically, one damage mechanism is associated with crack initiation and the other with crack arrest. It is postulated that these damage mechanisms are more appropriately modeled using two different fatigue criteria or, more specifically, two completely different approaches to fatigue (i.e. a classical multiaxial fatigue criterion and a LEFM type criterion). Hence, the proposed modeling framework provides the possibility of combining any two suitable criteria, in a probabilistic framework based on the weakest link hypothesis and results in the continuous description of the Kitagawa diagram for any multiaxial stress state. It is shown that under certain conditions this approach is equivalent to the classical El Haddad approach to the short crack problem encountered in LEFM. However, the proposed framework is easily extended to multiaxial loading conditions. This modeling framework is demonstrated in detail via its application to multiaxial fatigue data for data taken from the literature

The effect of machining defects on the fatigue behaviour of the Al7050 alloy

During the High Speed Machining (HSM) of aircraft components, geometrical defects, such as mismatches or chatters, can be created. To obtain a high surface quality, an expensive manual grinding operation is systematically done to remove these defects. The aim of this study is to identify the impact of HSM defects on the fatigue behaviour of the aluminium alloy Al7050. After listing and reproducing the most frequently observed surface defects, fatigue tests are conducted under fully reversed plane bending loads. Investigations carried out in previous work showed that residual stresses and the strain hardening introduced by machining under these conditions can be neglected. Therefore, only the geometric aspect of the surface integrity is considered in this study. The results show that the fatigue strength decreases only when the surface roughness is significantly degraded. It is also pointed out that manual grinding allows the effect of the machining defects to be removed from the fatigue behaviour. In order to predict the influence of the surface condition on the fatigue behaviour, a numerical approach based on the real surface topology is also developed. Crack initiation sites that are numerically identified are in agreement with experimental results. Numerical simulation results are compared to the predictions of different fatigue criteria from the literature and discussed over a wide range of surface defects

Same same but different: Code-Switching in Schweizer SMS – ein Vergleich zwischen vier Sprachen

This study examines the formal and functional aspects of code-switching (CS) in a Swiss corpus of 26'000 text messages (SMS). Four corpora (Swiss-German, French, Italian and Romansh) are compared with regard to the absolute number of CS, the languages used for CS, the grammatical properties of the CS elements and their potential functions. The aim is to find out: a) which patterns are representative of one or more individual lan-guages and b) which patterns are characteristic for SMS-communication in general and/or are valid for Switzerland as a whole. With regard to the differences in the number of CS and the languages used, the respective patterns seem to mirror the different lan-guage contact situations in Switzerland. As for the described CS-types, the corpora under scrutiny seem to share the extensive use of one-token alternations (isolated items) that carry out framing functions and may point out a shared type of minimal multilingual practice

A new methodology for designing heat treated components in fatigue

This study is dedicated to the effect of the heat treatment on the fatigue strength of an automobile rear axle beam and aims to propose a suitable and reliable methodology for the fatigue design. The rear axle beam is made of sheet metal (22MnB5); the microstructure is initially ferrito-pearlitic before the heat treatment and is martensitic after. A vast experimental campaign has been undertaken to investigate the behaviour, and more specially, the fatigue damage mechanisms observed for both treated and non-treated material, under different loading conditions: tension and shear test with different load ratios. In order to test the sheet metal in shear an original fatigue test apparatus is used. A probabilistic approach using the weakest link concept is introduced to model the fatigue behaviour. This approach leads naturally to a probabilistic Kitagawa type diagram, which in this case explains the relationship between the influence of the heat treatment and the microstructural heterogeneities. Integrate in a numerical model, this methodology permit to predict the effect of a local heat treatment on the fatigue strength of the components

Annexin A2 binding to endosomes and functions in endosomal transport are regulated by tyrosine 23 phosphorylation

The phospholipid-binding annexin A2 (AnxA2) is known to play a role in the regulation of membrane and actin dynamics, in particular in the endocytic pathway. The protein is present on early endosomes, where it regulates membrane traffic, including the biogenesis of multivesicular transport intermediates destined for late endosomes. AnxA2 membrane association depends on the protein N terminus and membrane cholesterol but does not involve the AnxA2 ligand p11/S100A10. However, the precise mechanisms that control AnxA2 membrane association and function are not clear. In the present study, we have investigated the role of AnxA2 N-terminal phosphorylation in controlling association to endosomal membranes and functions. We found that endosomal AnxA2 was partially tyrosine-phosphorylated and that mutation of Tyr-23 to Ala (AnxA2Y23A), but not of Ser-25 to Ala, impaired AnxA2 endosome association. We then found that the AnxA2Y23A mutant was unable to bind endosomes in vivo, whereas a phospho-mimicking AnxA2 mutant (Y23D) showed efficient endosome binding capacity. Similarly, we found that AnxA2Y23D interacted more efficiently with liposomes in vitro when compared with AnxA2Y23A. To investigate the role of Tyr-23 in vivo, AnxA2 was knocked down with small interfering RNAs, and then cells were recomplemented with RNA interference-resistant forms of the protein. Using this strategy, we could show that AnxA2Y23D, but not AnxA2Y23A, could restore early-to-late endosome transport after AnxA2 depletion. We conclude that phosphorylation of Tyr-23 is essential for proper endosomal association and function of AnxA2, perhaps because it stabilizes membrane-associated protein via a conformational change

The effect of machining defects on the fatigue behaviour of the Al7050 alloy

During the High Speed Machining (HSM) of aircraft components, geometrical defects, such as mismatches or chatters, can be created. To obtain a high surface quality, an expensive manual grinding operation is systematically done to remove these defects. The aim of this study is to identify the impact of HSM defects on the fatigue behaviour of the aluminium alloy Al7050. After listing and reproducing the most frequently observed surface defects, fatigue tests are conducted under fully reversed plane bending loads. Investigations carried out in previous work showed that residual stresses and the strain hardening introduced by machining under these conditions can be neglected. Therefore, only the geometric aspect of the surface integrity is considered in this study. The results show that the fatigue strength decreases only when the surface roughness is significantly degraded. It is also pointed out that manual grinding allows the effect of the machining defects to be removed from the fatigue behaviour. In order to predict the influence of the surface condition on the fatigue behaviour, a numerical approach based on the real surface topology is also developed. Crack initiation sites that are numerically identified are in agreement with experimental results. Numerical simulation results are compared to the predictions of different fatigue criteria from the literature and discussed over a wide range of surface defects