1,720,966 research outputs found
A Robust Design approach for error reduction in Thermoelastic Stress Analysis on Ti6Al4V alloy in presence of unknow biaxial residual stresses
Full text linkIn this study, a general model for Thermoelastic Stress Analysis (TSA) was employed in conjunction with simulated random noise sources to evaluate errors in the experimental technique using a robust design approach as a preliminary analysis. This facilitated the identification of an optimal experimental setup and anticipated ranges of measurement errors for TSA reducing testing time and errors. The model's validity was confirmed through TSA experiments conducted on AA2024 samples exhibiting biaxial residual stresses, as measured by a standard testing method. ANOVA (Analysis of Variance) and ANOM (Analysis of Means) analyses were conducted to explore the impact of parameters describing the analytical relationship between thermoelastic response and stresses in the presence of noise factors. The Robust Design approach was applied to the TSA measurement methodology, involving simulations of various noise sources and potential errors in the process, along with the application of different calibration methods
Considerations on the thermoelastic effect in proximity of crack tips on Titanium and Aluminium: A new formulation
No full textThermoelastic Stress Analysis (TSA) is an experimental technique used for describing the stress state and the mechanical behaviour of materials subjected to linear-elastic deformations. The classic TSA theory consists of a simple relation between temperature and stress variations and was successfully applied in fracture mechanics for SIF and crack tip evaluation. This theory for some materials, such as titanium and aluminium, is no longer valid since the mechanical properties of the material cannot be neglected. The research framework lies in the field of the validity hypothesis of thermoelastic stress analysis, in this regard, the aim of this work is to present a new thermoelastic formulation that includes the second-order effects to investigate the thermoelastic effect in the proximity of crack tips, on Titanium and Aluminium. Moreover, error analysis has been carried out for investigating the differences between the proposed approach and the classical one
A thermoelastic stress analysis general model: Study of the influence of biaxial residual stress on aluminium and titanium
No full textAll the studies on the thermoelastic behaviour of materials, including the revised higher order theory on the thermoelastic effect, are based on several assumptions that limit the application of such theory to the cases of isotropic materials in the presence of uniaxial residual stresses and undergoing uniaxial applied loads. These assumptions lead to some discrepancies in the description of the real thermoelastic behaviour of materials in the presence of residual stresses. In this work, by rewriting the thermoelastic equation in a different way, it was possible to study the behaviour of homogeneous and non-isotropic materials undergoing any loading conditions and residual stresses. Firstly, the error made by the calibration procedures of thermoelastic stress analysis (TSA) data in the presence of residual stresses has been investigated. Then, a statistical analysis was carried out to determine the minimum value of residual stress which would lead to significant and measurable variations in the thermoelastic signal. The simulations involved two non-ferrous metals: AA6082 and Ti6Al4V, which exhibit a specific thermoelastic behaviour
Investigation of the residual stress effect on thermoelastic behaviour of a rolled AA2024
No full textThe Thermoelastic Stress Analysis (TSA) is a contactless technique based on the thermoelastic effect that consists of the generation of small temperature variations caused by the volume variations induced by stresses applied in the linearelastic range. Recent works demonstrated the capability of the TSA for the characterization of materials behaviour in presence of residual stresses. The use of a general TSA analytical expression allows the researchers to find a relationship between the amplitude of the thermal signal varying at the same frequency as the applied load and the characteristics of the residual stress tensor in terms of principal stresses and their direction. The just said relationship, under certain conditions, can be also affected by the uncertainty in the knowledge of the thermo-physical properties of the material which can enhance or blur the presence of residual stresses. In this work, the effect of the main variables, such as the material properties and the presence of residual stress on the TSA were investigated by applying a sensitivity analysis to the analytical general model. The analytical results were then verified and compared with TSA experimental measurements performed on AA2024 samples affected by biaxial residual stresses and the residual stresses measured with a standard test method
Study of the thermo-elastic stress analysis (TSA) sensitivity in the evaluation of residual stress in non-ferrous metal
No full textThe Thermoelastic Stress Analysis (TSA) is a contactless technique able to determine the superficial stress of a component subjected to a dynamic load in a linear elastic field. In these conditions the thermoelastic effect shows the generation of small reversible temperature variations. In this work, a general equation was obtained for the evaluation of the thermoelastic signal. The proposed equation is valid under adiabatic and isentropic conditions, for generalized homogeneous and anisotropic materials in any load condition. By using the proposed generalized equation, TSA sensitivity to the variation of the physical and mechanical material characteristics and TSA sensitivity in the determination of residual stresses were studied. The case studies for performing numerical simulations were represented by AA6082 and Ti6Al4V non-ferrous metals. The results were then compared with the data obtained from experimental tests performed on AA 6082 samples
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Crack tip position evaluation and Paris' law assessment of a propagating crack by means of temperature-based approaches
No full textThis paper investigates the possibility to evaluate the crack tip position, crack growth rate and stress intensity factor (SIF), in order to derive the Paris law by starting from the temperature distribution measured by means of an infrared camera, with high geometrical resolution. In more detail, constant amplitude, fully reversed, stress controlled, crack propagation fatigue tests were carried out on two single edge notch tension specimens machined from 4-mm-thick, hot-rolled AISI 304L stainless steel sheets. The temperature maps were then processed by using a signal reconstruction algorithm based on the least square method in order to extract the maps of the amplitude and phase signal components of the first and second harmonics. In particular, the amplitude maps of the thermoelastic signal allowed the estimation of the stress intensity factor (SIF) using well-established methods, while the thermoelastic phase and second harmonic phase maps were used for estimating the crack-tip position. As for the determination of the crack tip using the phase maps, an experimental approach based on the evaluation of the inversion point of a phase profile (parallel to the crack propagation direction) was adopted. Such a point would represent the beginning of the reverse plasticity zone in the first and second harmonics phase maps. The crack tip position based on temperature maps was systematically compared to that measured by means of a digital microscope. Similarly, experimental SIF values derived from the thermoelastic signals were compared with the relevant numerical values from linear elastic FE analyses. The resulting Paris laws were critically compared. The good agreement between the preliminary data suggest further investigations regarding the applicability of these methods in all load conditions
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