Comment on the paper entitled 'A new cumulative fatigue damage rule based on dynamic residual S-N curve and material memory concept' by Peng Z., Huang H., Zhou J. and Li Y. Published in Metals (2018; 8 (6): 456)

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A numerical framework for determination of stress concentration factor distributions in tubular joints

Fatigue design of welded tubular joints implies the calculation of stress concentration factors at distinct weld toe locations using parametric formulas for basic loading cases. A Python based framework for automated calculation of hot spot stress and stress concentration factor distributions along the entire weld is presented. Hot spot stresses are calculated based on extrapolation of surface stresses extracted from a finite element analysis output database. For each node of the weld toes, the extrapolation direction and location dependent distances are first determined. Next the complete stress tensor in each read-out point is extrapolated towards the weld toe. The hot spot stress is determined as the maximum value of three critical stress values following the guidelines of DNV. A validation study is carried out in which the framework results are compared to both experimental data and parametric equations from literature for three different load cases: axial loading, in-plane bending and out-of-plane bending. The results obtained from the developed framework show good agreement with the experimental results and capture the shape of the stress concentration factor distribution much better than reference parametric equations. Finally, the framework is used to demonstrate the importance of including the weld geometry in the finite element model of the tubular joint. The results show that using a model without a weld can result in overly conservative estimations of stress concentration factors

Cumulative damage and life prediction models for high-cycle fatigue of metals : a review

Fatigue design of engineering structures is typically based on lifetime calculation using a cumulative damage law. The linear damage rule by Miner is the universal standard for fatigue design even though numerous experimental studies have shown its deficiencies and possible non-conservative outcomes. In an effort to overcome these deficiencies, many nonlinear cumulative damage models and life prediction models have been developed since; however, none of them have found wide acceptance. This review article aims to provide a comprehensive overview of the state-of-the art in cumulative damage and lifetime prediction models for endurance based high-cycle fatigue design of metal structures

Modeling nonlinear fatigue damage accumulation in a welded runway girder

Due to its inherent linear nature, Miner’s damage accumulation rule is widely known to produce unsatisfactory results for lifetime prediction under variable amplitude loading. This can be attributed to its incapability of accounting for load sequence and load interaction effects. In this study, one piece-wise linear and three non-linear damage accumulation models have been implemented in a numerical framework for fatigue lifetime assessment of welded details of industrial assets. Lifetime predictions obtained by these models are first compared to lifetime predictions using Miner’s rule and to experimental data of two-level loading sequences. The results reveal that the studied damage models perform better than Miner’s rule for two-level load sequences within the scope of the studied dataset. Finally the different models are used to estimate the fatigue life of a weld detail that is part of a crane runway girder. A much larger (relative) discrepancy is observed between the lifetime predictions of the different models for a realistic load case than for simple two-level block loads

Reliable online social network data collection

Large quantities of information are shared through online social networks, making them attractive sources of data for social network research. When studying the usage of online social networks, these data may not describe properly users’ behaviours. For instance, the data collected often include content shared by the users only, or content accessible to the researchers, hence obfuscating a large amount of data that would help understanding users’ behaviours and privacy concerns. Moreover, the data collection methods employed in experiments may also have an effect on data reliability when participants self-report inacurrate information or are observed while using a simulated application. Understanding the effects of these collection methods on data reliability is paramount for the study of social networks; for understanding user behaviour; for designing socially-aware applications and services; and for mining data collected from such social networks and applications. This chapter reviews previous research which has looked at social network data collection and user behaviour in these networks. We highlight shortcomings in the methods used in these studies, and introduce our own methodology and user study based on the Experience Sampling Method; we claim our methodology leads to the collection of more reliable data by capturing both those data which are shared and not shared. We conclude with suggestions for collecting and mining data from online social networks.Postprin

Evaluation of fatigue crack propagation in steel ESET specimens subjected to variable load spectra

This paper reports on an experimental study of fatigue crack growth in steel specimens. First, block loading tests (sequences of low and high stress intensity factor ranges ΔK) are discussed. Limited crack growth retardation occurs at transitions from low to high load ranges; significant retardation or crack arrest are observed in high-low transitions. Next, semi-random load spectra are created, processed using a peak-and-valley analysis and further reduced by removing the load ranges below the stress intensity factor threshold ΔKth. Rainflow counting is performed to obtain load profiles consisting of a sequence of blocks with constant ΔK. For the semi-random and the (reduced) peak-and-valley spectra no significant load interaction is observed. Pronounced crack growth retardation is observed in an ordered spectrum obtained by rainflow counting. The strong reduction in number of cycles of the (reduced) peak-and-valley spectra allows for exploration of accelerated fatigue testing. Experimental results of fatigue crack propagation are compared to results of calculations using a Python based numerical framework

A numerical framework for fatigue lifetime prediction of complex welded structures

Ageing infrastructure has been a significant concern for different industrial sectors across Europe. Fatigue cracking is one of the most important damage mechanisms that affect structural health of welded steel structures. Fatigue assessment of welded details in large, complex structures is a difficult and time consuming task. In this paper a numerical framework for fatigue assessment of welded details is presented. In view of industrial applications, automated hot spot stress algorithms for plate and tubular joints were developed and integrated in the framework. The framework provides practicing engineers with an effective tool for fatigue assessment of different components in conformity with leading design codes. Furthermore, apart from Miner’s rule the framework allows easy implementation of different non-linear damage accumulation models in order to account for load interaction and load sequence effects

Investigation of baker’s yeast production robustness

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Assessment of HCC response to Yttrium-90 radioembolization with gadoxetate disodium MRI: correlation with histopathology.

Transarterial <sup>90</sup> Y radioembolization (TARE) is increasingly being used for hepatocellular carcinoma (HCC) treatment. However, tumor response assessment after TARE may be challenging. We aimed to assess the diagnostic performance of gadoxetate disodium MRI for predicting complete pathologic necrosis (CPN) of HCC treated with TARE, using histopathology as the reference standard. This retrospective study included 48 patients (M/F: 36/12, mean age: 62 years) with HCC treated by TARE followed by surgery with gadoxetate disodium MRI within 90 days of surgery. Two radiologists evaluated tumor response using RECIST1.1, mRECIST, EASL, and LI-RADS-TR criteria and evaluated the percentage of necrosis on subtraction during late arterial, portal venous, and hepatobiliary phases (AP/PVP/HBP). Statistical analysis included inter-reader agreement, correlation between radiologic and pathologic percentage of necrosis, and prediction of CPN using logistic regression and ROC analyses. Histopathology demonstrated 71 HCCs (2.8 ± 1.7 cm, range: 0.5-7.5 cm) including 42 with CPN, 22 with partial necrosis, and 7 without necrosis. EASL and percentage of tumor necrosis on subtraction at the AP/PVP were independent predictors of CPN (p = 0.02-0.03). Percentage of necrosis, mRECIST, EASL, and LI-RADS-TR had fair to good performance for diagnosing CPN (AUCs: 0.78 - 0.83), with a significant difference between subtraction and LI-RADS-TR for reader 2, and in specificity between subtraction and other criteria for both readers (p-range: 0.01-0.04). Radiologic percentage of necrosis was significantly correlated to histopathologic degree of tumor necrosis (r = 0.66 - 0.8, p < 0.001). Percentage of tumor necrosis on subtraction and EASL criteria were significant independent predictors of CPN in HCC treated with TARE. Image subtraction should be considered for assessing HCC response to TARE when using MRI. • Percentage of tumor necrosis on image subtraction and EASL criteria are significant independent predictors of complete pathologic necrosis in hepatocellular carcinoma treated with <sup>90</sup> Y radioembolization. • Subtraction, mRECIST, EASL, and LI-RADS-TR have fair to good performance for diagnosing complete pathologic necrosis in hepatocellular carcinoma treated with <sup>90</sup> Y radioembolization