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Using risk analysis for flood protection assessment
This book explores the benefits of using risk analysis techniques in the evaluation of flood protection structures, and examines the results of the environmental impact assessment for selected planned flood protection projects. The objective of the book is to propose a methodology for environmental impact assessment in water management. In more detail, flood mitigation measures are investigated with the aim of selecting the best option for the approval process. This methodology is intended to streamline the process of environmental impact assessment for structures in the field of the water management. The book?s environmental impact assessment system for water management structures analyzes the respective risks for different options. The results are intended to support the selection of future projects that pose minimum risks to the environment. Comparison of alternatives and designation of the optimal variant are implemented on the basis of selected criteria that objectively describe the characteristics of the planned alternatives and their respective impacts on the environment. The proposed Guideline for environmental impact assessment of flood protection objects employs multi-parametric risk analysis, a method intended to not only enhance the transparency and sensitivity of the evaluation process, but also successfully addresses the requirements of environmental impact assessment systems in the European Union. These modifications are intended to improve the outcomes of the environmental impact assessment, but may also be applied to other infrastructure projects. The case study proves that the primary aim? to improve transparency and minimize subjectivity in the environmental impact assessment process specific to flood protection structure projects? is met for the planned project in Kruézlov, Slovakia.
Book
Low Velocity Impact and Mechanical Behaviour of Shot Blasted SiC Wire-Mesh and Silane-Treated Aloevera/Hemp/Flax-Reinforced SiC Whisker Modified Epoxy Resin Composites
In this research the effect of adding silicon carbide nano whiskers (SiCw) into epoxy resin and the impact of reinforcing surface treated SiC wire-mesh (SiCwm) and woven aloevera/hemp/flax fibers (NF) were studied. The principal aim of this work was demonstrating the importance of adding SiCw (0.5 and 1.0 vol.%) and SiC wire-mesh with economical natural fibres (50 vol.%) and silane surface treatment on natural fibres in mechanical and low velocity impact behavior. The SiCw and natural fibres were surface treated by 3-Aminopropyltriethoxysilane whereas SiC wire-mesh was shot blasted. The composites were cured at room temperature using an aliphatic hardener Triethylenetetramine (TETA). The strength factor results showed that the silane surface modified composite designation ‘H
4
’ gave highest normalized strength of 98%. The highest tensile and flexural strength of 141 and 240 MPa was observed for silane surface modified composite designation ‘H
4
’. The low velocity impact damage behavior of ‘H
4
’ composite designation showed higher resistance against to penetration. Transmission electron microscope (TEM) morphological images showed uniform dispersion of surface-modified SiCw in epoxy resin. Similarly the silane treated natural fibre and shot blasted SiC wire-mesh given improved adhesion with matrix. These high damping polymer composites offers their application in automobile, structural and domestic sector.
Journal Article
Study on Low-Velocity Impact and Residual Compressive Mechanical Properties of Carbon Fiber–Epoxy Resin Composites
Room temperature drop hammer impact and compression after impact (CAI) experiments were conducted on carbon fiber–epoxy resin (CF/EP) composites to investigate the variation in impact load and absorbed energy, as well as to determine the residual compressive strength of CF/EP composites following impact damage. Industrial CT scanning was employed to observe the damage morphology after both impact and compression, aiding in the study of impact-damage and compression-failure mechanisms. The results indicate that, under the impact load, the surface of a CF/EP composite exhibits evident cratering as the impact energy increases, while cracks form along the length direction on the back surface. The residual compressive strength exhibits an inverse relationship with the impact energy. Impact damage occurring at an energy lower than 45 J results in end crushing during the compression of CF/EP composites, whereas energy exceeding 45 J leads to the formation of long cracks spanning the entire width of the specimen, primarily distributed symmetrically along the center of the specimen.
Journal Article
Comparison of X-ray Computed Tomography and Ultrasonic C-Scan Techniques and Numerical Modelling of Impact Damage in a CFRP Composite Laminate
Two different experimental techniques are employed to visualize the impact damage generated by a low-velocity impact on a carbon-fibre reinforced-polymer (CFRP) composite laminate. At the relatively low impact-velocity of 1.69 m.s−1, and a corresponding impact energy of 7.5 J, used in the present work the damage induced in the CFRP panel is barely visible to the naked eye but the techniques of ultrasonic C-scan and X-ray computed tomography (CT) can detect the damage that has occurred. This damage is mostly interlaminar damage, i.e. delaminations, between the plies due to a change in modulus from one ply to the next in the laminate. This interlaminar damage is usually accompanied by intralaminar damage, e.g. matrix cracking, in the ply itself. The type and extent of damage detected from using these two techniques is discussed and the relative merits of these techniques are compared. In general, the CT gave the better resolved picture of damage but the lateral extent of the damage was underestimated relative to C-scan which was more sensitive to very fine delamination cracks. In addition, a numerical approach, based on a finite-element analysis model, is employed to predict the type, location and extent of damage generated by the impact event and the modelling predictions are compared to the experimental results.
Journal Article
Experimental and Simulation Study on Low-velocity Impact Damage of Composite Laminates under Temperature Environment
The composite material casing of aero-engine operates in different temperature environments and is inevitably impacted by external objects during use. The resin matrix composite materials are sensitive to temperature, which leads to more complex damage propagation and failure modes of materials under temperature environment. The influence of temperature environment on low-velocity impact damage of composite materials needs to be studied. In this paper, the T300/QY8911 composite laminates were subjected to low-velocity impact test and simulation study under three different temperature environments of 20°C, 120°C, and 180°C. The impact damage detection was carried out by visual inspection and ultrasonic C-scan to analyze the influence of temperature on the damage of composite laminates. Finite element simulation analysis was also conducted on the gradual expansion process of impact damage of composite laminates under different temperature environments to predict the impact damage area of laminates. The results show that the main damage forms are matrix cracking and delamination and the temperature has a significant effect on the low-velocity impact damage of composite laminates. Under the same impact energy, the length of the back crack and the cracking damage of the matrix of the laminate decreases as the temperature increases; the impact damage area and the delamination damage of the laminate increases as the temperature increases.
Journal Article
Cyclic Impact Damage and Water Saturation Effects on Mechanical Properties and Kaiser Effect of Red Sandstone Under Uniaxial Cyclic Loading and Unloading Compression
In this study, the influence of cyclic impact loading damage and water saturation on mechanical behavior and Kaiser effect of rock samples was investigated through a series of uniaxial cyclic loading and unloading compression tests. The test results showed that the cyclic loading and unloading strength of rock samples in dry condition gradually decreased with the increase of previous damage, while the cyclic loading and unloading strength of rock samples in saturated condition showed a decrease in cyclic loading strength of 10.95% (3 times), − 5.40% (6 times), and 0.87% (9 times) compared to those not subjected to cyclic impact loading. We have elucidated the mechanism underlying this phenomenon from the perspective of water–rock interaction. Statistical analysis of the Felicity ratio values further revealed that the valid response stress interval of rock acoustic emission (AE) Kaiser effect is negatively affected by previous damage and water saturation. Moreover, the relationship among AE signal energy decay rate and previous damage and water saturation was discussed, negatively impacting the valid response stress interval of rock AE Kaiser effect. The results suggest that drilling of cores from stress-disturbed areas should be avoided as much as possible during the measurement of in situ stress using the rock AE Kaiser effect. The tests should also be conducted with dry rock samples to have a larger response stress interval for the AE Kaiser effect.HighlightsThe wave velocity change rate and porosity were used to characterize the previous damage of rock.The influence of previous damage and water saturation on rock failure mode was evaluated.The strengthening mechanism of water-rock strength was discussed.The influence of previous damage and water saturation on Kaiser effect was studied.
Journal Article
Impact Damage Detection Using Chirp Ultrasonic Guided Waves for Development of Health Monitoring System for CFRP Mobility Structures
When impact damage occurs in carbon fiber-reinforced plastic (CFRP) structures, it is barely visible but may cause significant degradation in the mechanical properties of the structure. Hence, a structural health monitoring (SHM) system that can be installed in CFRP mobility structures and is sensitive to impact damage is needed. In this study, we attempted to establish an SHM system based on ultrasonic guided waves, which are generated by inputting a broadband chirp signal into a film-like piezoelectric actuator. The relationship between impact damage size and maximum time-of-flight (ToF) delay was investigated for three types of CFRP plates: woven, non-woven, and hybrid laminates. As a result, it was found that the maximum ToF delay increased linearly with an increase in the damage size for all CFRP laminates. Moreover, the amplitude of the A0 mode was found to be significantly affected by the damage length in the wave propagation direction. Thus, this SHM method using chirp ultrasonic waves can quantitatively evaluate the size and extent of the impact damage in CFRP laminates.
Journal Article
Classification of barely visible impact damage in composite laminates using deep learning and pulsed thermographic inspection
With the increasingly comprehensive utilisation of Carbon Fibre-Reinforced Polymers (CFRP) in modern industry, defects detection and characterisation of these materials have become very important and draw significant research attention. During the past 10 years, Artificial Intelligence (AI) technologies have been attractive in this area due to their outstanding ability in complex data analysis tasks. Most current AI-based studies on damage characterisation in this field focus on damage segmentation and depth measurement, which also faces the bottleneck of lacking adequate experimental data for model training. This paper proposes a new framework to understand the relationship between Barely Visible Impact Damage features occurring in typical CFRP laminates to their corresponding controlled drop-test impact energy using a Deep Learning approach. A parametric study consisting of one hundred CFRP laminates with known material specification and identical geometric dimensions were subjected to drop-impact tests using five different impact energy levels. Then Pulsed Thermography was adopted to reveal the subsurface impact damage in these specimens and recorded damage patterns in temporal sequences of thermal images. A convolutional neural network was then employed to train models that aim to classify captured thermal photos into different groups according to their corresponding impact energy levels. Testing results of models trained from different time windows and lengths were evaluated, and the best classification accuracy of 99.75% was achieved. Finally, to increase the transparency of the proposed solution, a salience map is introduced to understand the learning source of the produced models.
Journal Article
Localizing impact damage of composite structures with modified RAPID algorithm and non-circular PZT arrays
Detecting and localizing impact damage of composite structures is one of the key expectations towards development of structural health monitoring (SHM) systems. In this paper, a method intended to meet these requirements is presented. The developed method is based on guided waves actuation in a monitored structure. One of the methods used for damage localization with guided waves is the RAPID/PRA algorithm. This algorithm is mostly used for circular arrays of PZT piezoelectric transducers. In the paper a modification of this approach, adopted to be used for more general geometries of PZT networks is presented. Its main improvement is that predicted location of damage is less biased by inhomogeneous distributions of sensing paths, i.e. lines connecting pairs of transducers of a network, than for RAPID algorithm. The developed method was verified experimentally on composite laminated specimens with introduced damage caused by low energy impact. Detailed description of the developed algorithm as well as the results of impact damage localization tests are delivered in the paper.
Journal Article
Investigation of the Mechanical Behaviors and Damage Mechanism of C/C Composites Impacted by High-Velocity Jets
Carbon/Carbon (C/C) composites exhibit excellent mechanical properties at high temperatures, making them widely used in aerospace, such as the leading edges of spaceplane wings and the nose cones of hypersonic aircraft. However, damage caused by rain erosion to C/C composites affects their mechanical properties and poses significant challenges during operational service periods. A jet impingement test platform was employed to conduct single and multiple water-jet erosion tests on three-dimensional orthogonal C/C composite materials and to investigate the residual mechanical properties of the specimens after jet impact. The damage was characterized using optical microscopy, scanning electron microscopy, and X-ray computed tomography. The results showed that the damage types of the C/C composite materials under water-jet impingement included fiber bundle fracturing, delamination, and debonding. The extent of erosion damage was positively correlated with the jet velocity and diameter. The changes in the multi-jet damage indicated a cumulative expansion process, and z-directional fiber bundles exhibited superior resistance to jet impact damage propagation. The results of the three-point bending tests showed that the greater the initial impact damage, the lower the residual mechanical properties of the materials, and the residual strength of the specimen suddenly decreased when damage occurred at the back of the specimen.
Journal Article