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Behaviour of Materials
Selected, peer reviewed papers from the fourth edition ACMA 2012, May 9-12, 2012, Fez, Morocco.
eBook
Internal friction of materials
The author presents important new results for the relationship between internal friction and the defect of the elasticity modulus with many principal processes such as plastic deformation, effect of temperature of plastic deformation, effects on the structural stability of alloys and composites up to cyclic microplasticity. The existence of critical strain amplitudes is discussed and supported by experiments, and attention is given to the link of cyclic microplasticity with dislocation density and activation volume of plastic deformation up to the effect of individual factors on the cyclic plastic response of the material. The relationship of the process of mechanical fatigue of the material with internal friction and the defect of the elasticity modulus is discussed. The author proposes a new fatigue life equation which has been verified by a large number of experiments.
eBook
Hypervelocity Gouging Impacts
Description
When materials interact at hypervelocity—on the order of Mach 8.5 and above—unexpected results can occur. This book addresses the effects of hypervelocity impact, summarizing past and present research efforts as well as setting out the theoretical foundation for understanding material interactions at such velocity. It focuses on research conducted at the Holloman Air Force Base High Speed Test Track (HHSTT), which is working toward a test vehicle speed above Mach 10. Researchers have found that as the sled’s speed has increased to Mach 8.5, a material interaction has developed that causes “gouging” in the rails and the sled’s “shoes”—which can lead to catastrophic failure.The author evaluates the HHSTT gouging phenomenon and offers recommendations to mitigate the occurrence of hypervelocity gouging. His insights and recommendations will also find wide applicability in other areas, such as railguns, orbital debris, and weapon design.
eBook
Materials and structures under shock and impact
In risk studies, engineers often have to consider the consequences of an accident leading to a shock on a construction. This can concern the impact of a ground vehicle or aircraft, or the effects of an explosion on an industrial site. This book presents a didactic approach starting with the theoretical elements of the mechanics of materials and structures, in order to develop their applications in the cases of shocks and impacts. The latter are studied on a local scale at first. They lead to stresses and strains in the form of waves propagating through the material, this movement then extending to the whole of the structure. The first part of the book is devoted to the study of solid dynamics where nonlinear behaviors come into play. The second part covers structural dynamics and the evaluation of the transient response introduced at the global scale of a construction. Practical methods, simplified methods and methods that are in current use by engineers are also proposed throughout the book. The aim of this book is to present theoretical elements regarding solids and structures, as well as modeling tools in order to study the vulnerability of a structure to a short duration action, generally of accidental nature. The book takes the point of view of an engineer seeking for the modeling of the physics at stake to relevantly carry out his study. The book originality is that it gathers elements from various fields of engineering sciences, for the purpose of a practical objective.
eBook
Mechanical properties of bio self-healing concrete containing immobilized bacteria with iron oxide nanoparticles
Concrete is arguably one of the most important and widely used materials in the world, responsible for the majority of the industrial revolution due to its unique properties. However, it is susceptible to cracking under internal and external stresses. The generated cracks result in a significant reduction in the concrete lifespan and an increase in maintenance and repair costs. In recent years, the implementation of bacterial-based healing agent in the concrete matrix has emerged as one of the most promising approaches to address the concrete cracking issue. However, the bacterial cells need to be protected from the high pH content of concrete as well as the exerted shear forces during preparation and hardening stages. To address these issues, we propose the magnetic immobilization of bacteria with iron oxide nanoparticles (IONs). In the present study, the effect of the designed bio-agent on mechanical properties of concrete (compressive strength and drying shrinkage) is investigated. The results indicate that the addition of immobilized Bacillus species with IONs in concrete matrix contributes to increasing the compressive strength. Moreover, the precipitates in the bio-concrete specimen were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The characterization studies confirm that the precipitated crystals in bio-concrete specimen were CaCO3, while no precipitation was observed in the control sample.
Journal Article
Concrete Damage under Fatigue Loading in Uniaxial Compression
Despite rigorous efforts in the derivation of various fatigue damage models for concrete, damage predictions of sufficient accuracy are still limited to loading conditions similar to those of the experiments used for developing the models. Most models are void of salient factors affecting the fatigue behavior of concrete such as frequency, stress ratio, and loading waveform, and the approaches used in developing such models tend to be rudimentary. Therefore, further investigation is required. In this study, damage models are expressed for residual concrete strength and fatigue secant modulus using experimental data from tested cylindrical specimens, a damage function, and a stress-life model in the literature. The number of cycles leading to failure, required for normalizing the fatigue cycles for each specimen, is obtained using a proposed secondary strain rate model. The aforementioned influencing factors incorporated into the damage function result in robust models that account for variations in loading parameters.
Journal Article
Structural Behavior of Reinforced Concrete Frames Subjected to Progressive Collapse
This paper presents an experimental program on structural behavior of four reinforced concrete frames under column removal scenarios, simulating progressive collapse. The specimens were designed with conventional non-seismic and seismic detailing in terms of stirrup arrangement and different boundary conditions. Each specimen, consisting of a two-bay beam, a middle joint, and two side columns, was quasi-statically tested by increasing the beam deflection until the complete failure. The load-deflection relationships show the sequential mobilization of compressive arch action and catenary action in the beams. Test results indicate that beam-column connections are the most critical components in developing catenary action, and confirmed the concern in current engineering practice that the longitudinal reinforcement in beams may fail to function as effective ties due to fracture of bars under large rotations. The bar fracture was ascribed to local rotations at the connections heavily dependent on the development of fixed-end rotation.
Journal Article
Behaviour of Carbon and Basalt Fibres Reinforced Fly Ash Geopolymer at Elevated Temperatures
This paper presents the behaviour of potassium activators synthesized fly ash geopolymer containing carbon and basalt fibre at ambient and elevated temperature. Six series of fly ash based geopolymer were cast where carbon and basalt fibre were added as 0.5, 1 and 1.5% by weight of fly ash. One extra control series without any fibre was also cast. Each series of samples were tested at ambient temperature and also heated at 200, 400, 600 and 800 °C and thus a total of 35 series of samples were tested in this study. The result shows that the geopolymer containing 1 wt% basalt and 1 wt% carbon fibre exhibited better compressive strength, lower volumetric shrinkage and mass loss than other fibre contents. Among two fibres composites, the carbon fibre geopolymer exhibited better performance than its basalt fibre counterpart regardless of temperature. The microstructure of carbon fibre reinforced geopolymer composite is more compact containing fewer pores/voids than its basalt based counterpart at elevated temperatures. The results also support the fact that carbon fibre is better than basalt fibre at elevated temperature and showed better bonding with geopolymer at elevated temperature.
Journal Article