Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Fatigue Crack and Delamination Growth in Fibre Metal Laminates under Variable Amplitude Loading

This thesis presents the investigation into the fatigue propagation and delamination growth of Fibre Metal Laminates under variable amplitude loading. As explained in the first chapter, the motivation of the research is twofold: first, to obtain a clear understanding and detailed characterization of the failure mechanisms in GLARE under variable amplitude loading (selective and flight load spectra). Second is to obtain an accurate prediction model for fatigue crack propagation in GLARE accounting for fibre bridging, delamination and influence of plasticity. The major concept in this thesis is that the stress intensity at the crack tip in the metal layers of a Fibre Metal Laminates (FMLs) is the factor determining the extension of that crack under cyclic loading. This implies that the stress intensity factor can be described with Linear Elastic Fracture Mechanics, including the contribution of the fibre layers and the with the crack growth associated delamination behaviour. The investigation presented in this thesis, covers the theoretical analysis of the crack growth phenomena and experiments to support and validate the developed prediction model. This investigation has been restricted to through-the-thickness cracks with the same crack length in all metal layers. In the second chapter, the various GLARE grades and lay-ups are defined together with a description of the manufacturing process, quality assurance procedures and fatigue crack growth phenomena. The aspects introduced are the fatigue crack growth in the aluminium layers, controlled by the stress intensity factor at the crack tip, and the delamination of the aluminium and prepreg layers, which occurs in the wake of the propagating crack. The crack opening is constrained by the bridging fibre layers, while the stress redistribution to these fibre layers determines the delamination growth. In addition, this chapter discusses the effects of variable amplitude loading in metals, together with the models developed so far to predict fatigue crack growth. The influence of variable amplitude loading on the delamination growth (i.e. a major phenomenon contributing to the slow fatigue crack growth in FMLs) is discussed in chapter 3. An extensive test programme is presented in this chapter utilizing double and multiple block loads, and flight load spectra to validate the hypothesis that delamination in FMLs is independent of retardation effects under variable amplitude loading. Furthermore, the use of scanning electronic microscopy is presented to study the delamination growth striations on the disbonded fracture surfaces. Chapter 4 presents the effect of variable amplitude loading on delamination shapes. These delamination shapes influence the bridging stresses and the crack tip stress intensity factor. The change in the delamination shape due to variable amplitude loading is understood, and the hypothesis on the reason of this change in delamination shapes has been validated. The use of Digital Image Correlation (DIC) is presented to observe delamination shapes and crack tip plastic zones in-situ fatigue testing. Although a change in delamination shape can be observed, its effect on the bridging stress profile is observed to be negligible. Crack tip plasticity and shear-lip formation both were investigated, as presented in chapter 5. Difference in shear-lip morphology was observed in monolithic metals, adhesively bonded metal laminates and FMLs. Monolithic metals revealed typical shear-lip profiles with the early tensile mode followed by a transition mode and finally the transverse shear mode. For metal laminates (without fibres), the mode transition happened quite late during fatigue crack growth, but the transition length was smaller than those of monolithic metals. In FMLs the shear lip profiles were rather difficult to see with the naked eye or optical microscope. However, the straight appearance of the crack when observed from the specimen side, implied a flat cracked fracture surface without shear lips. Plastic zone sizes are compared in the same chapter. In case of monolithic metals and metal laminates, a big difference is observed between the predicted plastic zone sizes (using Irwin’s relation) and the sizes measured with DIC. However, comparing these sizes for FMLs revealed only a small difference. In FMLs, the plastic zone sizes are observed to be independent of the crack length which corresponds to the constant crack tip stress intensity factors. Chapter 6 presents the development and validation of three different types of prediction models. These models include a linear damage accumulation (non-retardation) model, a yield zone model and a crack closure model. The predictions using these models correlated with experimentally observed crack growth behaviour. Chapter 7 outlines the sub-routine added to the prediction model for post-stretched laminates. This routine has been validated with the data from post-stretched GLARE 1 and ARALL from the literature. Chapter 8 summarizes the conclusions of the investigation. It can be concluded that with the proposed prediction model, the mechanism of crack propagation and delamination growth in GLARE is fully described and understood. The prediction model has been validated with experimental crack growth data, and is considered accurate. In its implemented form, the model has the potential to be extended to other material-, geometrical- and test parameters.Aerospace Structures and MaterialsAerospace Engineerin

Understanding the Fatigue Behavior of FML Structures and Materials under Complex Variable Amplitude Loading

This paper presents various failure mechanisms in FMLs, highlights the presence or absence of interaction effects, and describes how the failure mechanisms can be described for predicting damage growth under arbitrary complex load spectra.Aerospace Engineerin

Variable Amplitude Fatigue of FMLs On Developing a Mechanistic Understanding

Presentation on conferenceAerospace Engineerin

Demographic Evaluation and Parametric Assessment of Air Pollutants over Delhi NCR

The impact of air pollution on people and the environment is a severe issue that has recently been the subject of extensive research. This study has looked at the factors that contribute to the seasonal and spatial variability of pollutant concentration over Delhi NCR from 2019 to 2021. Additionally, the causes of changes in air quality during the COVID-19’s lockdown period in 2020 have been discussed, along with comparisons to the pre-lockdown year (2019) and the post-lockdown year (2021). Seven pollutant parameters, viz., (PM2.5, PM10, NOx, CO, SO2, NH3, and O3) were retrieved from the air quality monitoring stations spread over Delhi NCR. The results show a significant temporal (seasonal) and spatial variability in the air pollutants’ concentration. The highest pollutant level was observed in winter and the lowest in summer seasons. The results suggest that the concentration of atmospheric pollutants was already lower (20–30%) before the implementation of the lockdown. Meteorology played an important role in emission reduction during the lockdown, in particular, and seasonal, in general. The results also suggest that Bhiwadi is not the most polluted city, as claimed in the World Air Quality Report 2022. The most polluted sites in terms of pollutant concentration were observed over Delhi in all the years considered.Space Systems Egineerin

Fault detection and diagnosis to enhance safety in digitalized process system

The increased complexity of digitalized process systems requires advanced tools to detect and diagnose faults early to maintain safe operations. This study proposed a hybrid model that consists of Kernel Principal Component Analysis (kPCA) and DNNs that can be applied to detect and diagnose faults in various processes. The complex data is processed by kPCA to reduce its dimensionality; then, simplified data is used for two separate DNNs for training (detection and diagnosis). The relative performance of the hybrid model is compared with conventional methods. Tennessee Eastman Process was used to confirm the efficacy of the model. The results show the reduction of input dimensionality increases classification accuracy. In addition, splitting detection and diagnosis into two DNNs results in reduced training times and increased classification accuracy. The proposed hybrid model serves as an important tool to detect the fault and take early corrective actions, thus enhancing process safety.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Safety and Security Scienc

Emerging Themes and Future Directions of Multi-Sector Nexus Research and Implementation

Water, energy, and food are all essential components of human societies. Collectively, their respective resource systems are interconnected in what is called the “nexus”. There is growing consensus that a holistic understanding of the interdependencies and trade-offs between these sectors and other related systems is critical to solving many of the global challenges they present. While nexus research has grown exponentially since 2011, there is no unified, overarching approach, and the implementation of concepts remains hampered by the lack of clear case studies. Here, we present the results of a collaborative thought exercise involving 75 scientists and summarize them into 10 key recommendations covering: the most critical nexus issues of today, emerging themes, and where future efforts should be directed. We conclude that a nexus community of practice to promote open communication among researchers, to maintain and share standardized datasets, and to develop applied case studies will facilitate transparent comparisons of models and encourage the adoption of nexus approaches in practice.Water Resource

Fracture Toughness Evaluation of Powder Metallurgical ASP2030 High-Speed Steels Using Flexural Specimens and Finite Element Method

In the present study, the fracture toughness of hardened and tempered powder metallurgical (PM) high-speed steel ASP 2030 was investigated using notched and unnotched bending specimens and the finite element method. The normal flexural strength of notched and unnotched specimens marquenched by austenitizing at 1150, 1170, and 1185°C, followed by quenching to room temperature is measured after triple tempering at 560°C for 2 h. The finite element method (FEM) analysis is performed to observe the true stress distribution and calculate the critical fracture stress in the specimens under the experimental conditions of the bending test. The microstructural features of the specimens were investigated by X-ray diffraction (XRD) and a field emission scanning electron microscope (FESEM) with an electron backscatter detector (EBSD). No retained austenite was detected in the tempered specimens, and according to the results of the EBSD analysis and XRD tests, the microstructure of the matrix consists of martensitic ferrite laths. It can be observed that with the increase of austenitizing temperature from 1150 to 11850C, the normal flexural strength of the specimens decreases. The decrease in flexural strength of the specimens is due to the increase in the prior austenite grain size and consequently the martensitic ferrite laths after tempering. In addition, as the austenitizing temperature increases, the volume fraction of the undissolved carbides decreases, which causes the size of the undissolved carbides to increase and the flexural strength to decrease. According to FEM, the critical crack length calculated from the critical fracture stress is approximately equal to the average diameter of undissolved carbides.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.(OLD) MSE-