Образование в контексте идентификационных процессов (Субъект образования как следствие концептуальной рамки)

The available models for the prediction of fatigue crack growth in adhesive bonds rely on the similitude principle. In most cases, one of three similitude parameters based on the strain energy release rate (SERR) is used; i.e. Gmax, (Δ√G)2, or ΔG. In all cases it is usually observed that keeping the similitude parameter constant, and changing the R-ratio, results in a different crack growth rate. In this paper it is shown that this apparent ‘R-ratio’ effect is caused because the selected similitude parameter does not define a unique load cycle; a single value of the similitude parameter could correspond to infinitely many load cycles. The strain energy dissipation approach is used to show that the resistance to fatigue crack growth is related to the maximum applied load. The amount of energy available for crack growth is shown to be related to the applied cyclic work. With these relationships the R-ratio effects reported in literature can be qualitatively explained, purely in terms of the actual applied load cycle. Although it is possible that the material behaviour also depends on the R-ratio, the magnitude of these effects can only properly be determined if the applied load cycle is correctly described first.Structural Integrity & CompositesAerospace Structures & Material

The Challenge of Reversing Theories to Hybridize Structures with Fiber Metal Laminate Design Concepts

To further optimize aeronautical structures, an increased level of material hybridization is required. Optimization efforts aim to identify optimal design solutions that satisfy prescribed requirements. However, this demands reversal of currently available knowledge on hybrid structural technologies, which are often formulated as theories predicting performance based on known load cases and selected material configurations. After briefly reviewing the available fundamental theories for strength, fatigue, and damage tolerance of hybrid structures, this paper discusses the challenges in reversing these theories. Solutions are proposed in which theories can be approximated to significantly reduce the computational time while maintaining the required level of accuracy.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.Structural Integrity & Composite

How proper similitude principles could have improved our understanding about fatigue damage growth

This paper discusses similitude parameters for predicting fatigue damage growth, and demonstrates that proper principles exploiting the strain energy release could have improved our knowledge on fatigue damage growth. The paper demonstrates how the original Stress Intensity Factor concept introduced by Irwin has been introduced inconsistently for describing fatigue crack growth. Subsequently, it illustrates how this has led to misinterpretation of certain phenomena, like for example plasticity induced crack closure. Using proper similitude in agreement with the physics of observed fatigue damage phenomena, it is demonstrated how the average strain energy release over a single load cycle should relate to the crack surface extension in that same load cycle. The paper concludes with illustrating how phenomena like for example plasticity and fibre bridging in composites can be understood and quantified.Aerospace Structures and MaterialsAerospace Engineerin

Introduction to Aerospace Structures and Materials

This book provides an introduction to the discipline of aerospace structures and materials. It is the first book to date that includes all relevant aspects of this discipline within a single monologue. These aspects range from materials, manufacturing and processing techniques, to structures, design principles and structural performance, including aspects like durability and safety. With the purpose of introducing students into the basics of the entire discipline, the book presents the subjects broadly and loosely connected, adopting either a formal description or an informal walk around type of presentation. A key lessons conveyed within this book is the interplay between the exact science and engineering topics, like solid material physics and structural analysis, and the soft topics that are not easily captured by equations and formulas. Safety, manufacturability, availability and costing are some of these topics that are presented in this book to explain decisions and design solutions within this discipline.Creative Commons license CC BY-NC-SA 4.0 https://creativecommons.org/licenses/by-nc-sa/4.0/Structural Integrity & Composite

How proper similitude can improve our understanding of crack closure and plasticity in fatigue

The appropriateness of some common similitude principles with respect to describing and predicting fatigue damage propagation is discussed. Linear elastic fracture mechanics have provided a basis to describe damage growth using stress intensity factors or strain energy release rates, both related to the work of Griffith and Irwin. The fatigue crack growth equations presented in the literature are discussed, and it is demonstrated that the principles of similarity in current methodologies have not yet been well established. As a consequence, corrections for the stress ratio effect are misunderstood. An alternative principle of similitude using cyclic work and strain energy release is proposedStructural Integrity & Composite

Fatigue delamination of composite materials: Approach to exclude large scale fibre bridging

This paper proposes a straightforward methodology to generate fatigue delamination curves without the influence of fibre bridging using test data obtained on unidirectional double cantilever beam specimens with fibre bridging.Structural Integrity & Composite

Fatigue crack propagation and delamination growth in Glare

Fibre Metal Laminate Glare consists of thin aluminium layers bonded together with pre-impregnated glass fibre layers and shows an excellent fatigue crack growth behaviour compared to monolithic aluminium. The fibres are insensitive to the occurring fatigue loads and remain intact while the fatigue cracks occur in the aluminium layers. As a consequence, part of the load is transferred through the fibre layers instead of around the crack tip in the aluminium layers, reducing the crack growth rate. The major concept in this thesis is the stress intensity at a crack tip in the metal layers of a Fibre Metal Laminate being the factor determining the extension of that crack under cyclic loading. The stress intensity factor consists of a crack opening contribution of the far field stresses in the aluminium layers, similar to monolithic aluminium, and a crack closing contribution of the intact fibres in the wake of the crack. An analytical model has been developed based on the crack opening relations. Validation with a wide range of test data, reveals a good correlation between predicted and experimental crack growth rates, crack opening contours and delamination shapesAerospace Engineerin

The energy dissipation during fatigue crack growth in metallic materials

An energy equation for fatigue crack growth was proposed. It equates the total external work per cycle (dW/dN) to the sum of plastic dissipation (dUpl/dN), change in strain energy stored (dUe/dN) and the energy dissipated in new crack surface formation (dUa/dN). Fatigue crack growth experiment of 7075-T6 was used to derive the relation between fatigue crack growth rate (da/dN) and variables in this equation. The result shows dUpl/dN and dUe/dN are not straightforwardly related to da/dN. The dUa/dN, whose value cannot be obtained sufficiently precise experimentally, can be the variable straightforwardly related to da/dN within the range of test.Structural Integrity & Composite

Method for fabrication of a fiber metal laminate

Aerospace Materials & ManufacturingAerospace Engineerin

Impact fatigue, multiple and repeated low-velocity impacts on FRP composites: A review

A review of experimental evidence from the literature in relation to “impact fatigue”, “multiple impacts”, and “repeated impacts” on FRP composites, along with articles discussing theoretical and numerical simulations, is provided. A new terminology and definition is presented to clear the meanings of these types of loadings. Experimental investigations about the impact fatigue, have been categorized in terms of the impact energy and the number of impacts. Also, many parameters are considered to illuminate their effects during the repeated impacts on FRP laminates. Discussion of the reported results will be presented along with a recommendation for future explorations and research paths to fill in the knowledge gaps.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.Structural Integrity & Composite