The subject of the thesis is to compare layered model and tomographic model. These models are used for description of low velocity layer in seismic survey. The goal of the work was to find out the conditions whether to prefer tomographic model instead of layered model. Program Geostar was used for modelling of low velocity layer. This program is a part of software package produced by CGG Veritas company. Geostar is available at department of Applied Geophysics for study purposes. Four synthetic models were created for comparison of tomographic and layered models. Models of low velocity layer were computed for layered an tomographic model in Geostar environment. Original models were compared to created models. Accuracy was estimated on root mean square error and static correction which was exactly known. In all cases, layered model showed better results then tomographic model. 1

A major concern affecting the efficient use of composite laminates in aerospace industry is the lack of understanding of the effect of low-velocity impact (LVI) damage on the structural integrity. This project aims to develop further knowledge of the response and damage mechanisms of composite laminates under LVI, and to explore the feasibility of assessing the internal impact damage with a visually inspectable parameter. The response and damage mechanisms of composite laminates under LVI have been investigated experimentally and numerically in this project. Various parameters including the laminates thickness, lay-up configuration, repeated impact, and curing temperature have been examined. The concept and the phenomena of delamination threshold load (DTL) have been assessed in details. It was found that DTL exists for composite laminates, but the determination of the DTL value is not straightforward. There is a suitable value of range between the impact energy and the laminates stiffness/thickness, if the sudden load drop phenomenon in the impact force history is used to detect the DTL value. It is suggested that the potential menace of the delamination initiation may be overestimated. The composite laminates tested in this project demonstrate good damage tolerance capacity due to the additional energy absorption mechanism following the delamination initiation. As a result, the current design philosophy for laminated composite structure might be too conservative and should be reassessed to improve the efficiency further. To explore the feasibility of linking the internal damage to a visually inspectable parameter, quasi-static indentation (QSI) tests have been carried out. The dent depth, as a visually inspectable parameter, has been carefully monitored and assessed in relation to the damage status of the composite laminates. It is proposed that the damage process of composite laminates can be divided into different phases based on the difference in the increasing rate of dent depth. Moreover, the internal damage has been examined under the optical microscope (OM) and the scanning electron microscope (SEM). Residual compressive strength of the damaged specimen has been measured using the compression-after-impact (CAI) test. The results further confirm the findings with regard to the overestimated potential menace of the delamination initiation and the proposed damage process assumption. The proposed damage process assumption has great potential to improve the efficiency and accuracy of both the analytical prediction and the structural health monitoring for damages in composite laminates under low-velocity impact.

The aim of this thesis is to investigate Ti/APC-2 nanocomposite laminates mechanical properties after low velocity impact. The finite element analysis with software ANSYS/LS-DYNA is used to analyze the size of damage and plastic zone and internal energy of laminates during low velocity impact. Finally, the numerical results and experimental data are in good agreement. The work can be divided into two parts: the first is to fabricate the hybrid composite laminates and place the samples on the floor, subjected to the free drop of a rigid steel ball of 1m and 2m high. Then, the samples after impact were due to static tensile and fatigue tests to obtain mechanical properties. Using the optical microscopy the impact defects of laminate surface were measured. The second, ANSYS/LS-DYNA was used to simulate a laminate impacted by a steel ball. The energy change of steel ball impact and internal energy of laminates during impact were also discussed. From the experimental data, the mechanical properties, such as ultimate strength and stiffness, of virgin samples are better than those of impacted samples due to free drop. In addition, no matter the laminates were added nanoparticles SiO2 or not, the strength of laminates reduces after impact, however, the fatigue resistance of impacted samples does not lose much. Compare with the data of penetration depth and plastic zone due to free drop. The errors of numerical results are 5.4%~12.4% for the penetration depth and the errors 5.21%~8.98% for plastic zone respectively. That is acceptable. The numerical method ology provides a reference to realize the energy change in laminates after impact. Also, from the experimental measurement it is obvious to see damage area after impact and the mechanical properties do not reduce significantly due to low velocity impact generally in Ti/APC-2 composite laminates.

Impact induced dynamic cracks are produced with a Split Hopkinson Pressure Bar (SHPB) apparatus in two rocks (Kuru granite and Flamboro limestone) with impact velocities ranging from 8 to 12 m/s. Impact bit (tungsten carbide) diameters range from 8mm to 15mm. Dye impregnation combined with UV imaging, CAT scans and Optical scans were employed to study the resulting crack patterns. The resulting damage is quantified in terms of radial crack density on impact surface, crater, crushed zone and crack density with depth. In both rocks ‘total’ damage obtained is directly proportional (exponential) with bit diameter and impact velocity. The ‘total’ damage in Kuru granite is found to be greater than Flamboro limestone at all impact velocities; however, the crushed zone in the latter is found to consistently greater than the former. 2D simulations of dynamic fractures with AUTODYN have also been carried out showing good qualitative agreement with experimental results.

Impact induced dynamic cracks are produced with a Split Hopkinson Pressure Bar (SHPB) apparatus in two rocks (Kuru granite and Flamboro limestone) with impact velocities ranging from 8 to 12 m/s. Impact bit (tungsten carbide) diameters range from 8mm to 15mm. Dye impregnation combined with UV imaging, CAT scans and Optical scans were employed to study the resulting crack patterns. The resulting damage is quantified in terms of radial crack density on impact surface, crater, crushed zone and crack density with depth. In both rocks ‘total’ damage obtained is directly proportional (exponential) with bit diameter and impact velocity. The ‘total’ damage in Kuru granite is found to be greater than Flamboro limestone at all impact velocities; however, the crushed zone in the latter is found to consistently greater than the former. 2D simulations of dynamic fractures with AUTODYN have also been carried out showing good qualitative agreement with experimental results.

Low-velocity impact damage in IM7/977-3 carbon fiber reinforced polymer (CFRP) composites was investigated using 3D computed tomography (CT). 32-ply IM7/977-3 symmetric cross-ply composites were impacted at different impact energy levels and with different impactors (DELRIN® resin flat-ended cylindrical and tool steel hemispherical strikers) using an Instron 8200 Dynatup drop-weight impact machine. The impact energies were chosen to produce slightly visible damage, characterized by short cracks on the impacted surface and little delamination on the non-impacted surface (29.27 J), and barely visible damage, characterized by indentation on the impacted surface but no visible delamination on the back surface of the specimens (20.77 J). Internal damage was assessed using the Zeiss METROTOM 1500 industrial CT scanning system, and CT images were reconstructed using VGStudio MAX and the MyVGL 2.2 viewer. To determine the extent of the damage zone, impacted 152.4 mm square composite plates were initially scanned. As the relatively large specimen size did not allow for evaluation of internal cracks and isolation of delamination at ply interfaces, smaller specimens that enclosed the damaged region (45 mm square plates) were cut out and imaged. The CT scan results showed that volume of the impact damage zone had a generally positive correlation with impact energy, maximum load, and maximum deflection, but that the relationship was generally weak. Absence of a definite correlation between damage volume and impact energy was unexpected, as the difference in the impact energy was up to 30%.

Diploma thesis deal with measuring air-jet generated by low-velocity outlet. Diploma thesis piles of several part. First part includes velocity measurment (flow volumes) single ventilators. Follows measuring velocity distribution in air-jet generated by low-velocity outlet, his vizualization by the smoke method. Last point is problems errors and uncertainties measuring. Thesis likewise includes appendices, where there are mentioned tables from single maesuring and setting frequency transducers.

A new high-resolution 3-dimensional P-wave velocity model for Mt. Pinatubo volcano was developed by tomographic inversion of P-wave arrivals from 3,007 earthquakes recorded during a four month period from May to August, 1991. The arrivals were recorded by a network of seismic stations, consisting of seven pre-eruption stations and seven post-eruption stations. Two stations survived the June eruptions. First-arrival travel times were calculated using a finite-difference solution to the eikonal equation. An iterative, linearized approximation of the nonlinear tomography problem was used to solve separately for both velocity structure and hypocenter locations. Several inversions performed with different initial parameters and convergence schemes, and synthetic checkerboard reconstructions indicate a horizontal spatial resolution of velocity perturbations near 4 km. However, the network sparseness allows for a substantial trade-off between focal depth, origin time, and the vertical velocity profile. Many hypocenter clusters collapse from diffuse clouds into tighter features after 3-D relocation. These bands of earthquakes appear to represent fault-related structures. Three low-velocity (relative to the horizontal average) anomalies exist within the well-resolved portion of the velocity model. These anomalies are spatially associated with pre- and post-eruption earthquakes oriented along mapped surface fault zones. Similar anomalies observed at different volcanoes have been previously interpreted as magma related. The low-velocity anomalies at Pinatubo are interpreted as highly fractured, hot volumes of mostly competent rock, which may contain partial melt. / Master of Science

The effects of lithology, fracturing, and gouge zone mineralization on the geophysical properties of fault zones are not very well understood. In situ seismic data collected over the exhumed San Gregorio Fault at Moss Beach, CA were used to relate in situ compressional wave velocity to internal fault zone properties. This active strike-slip fault is exposed in cross section on an uplifting and actively eroding wave-cut platform. It cuts shallow marine sediments that have been buried to depths of a few kilometers. The unweathered exposure containing seawater makes it a unique analog of subsurface faults. Previous structural analysis over this exposure observed damage caused by faulting over a ~100 m wide zone in cross-section. The fault zone is centered at a 10-17 m wide clay-rich fault core flanked by a ~30 m wide brecciated gouge zone. These gouge zones are bordered on either side by 30-40 m wide fractured zones. Resolving to a scale of a few meters, the seismic survey produced a continuous P-wave velocity profile analogous to a horizontal well log across the fault. Lateral variations in the velocity profile correlate exactly to previously mapped fault zone structure. The clay core and adjacent brecciated gouge create a ~50 m wide very low velocity zone, 25-50% slower than the surrounding host rock. Fractured bedrock on either side of the core causes a wider zone of 5-10% slow velocity, for a total fault signature ~100 m wide. Fault parallel fracture anisotropy was observed in the fractured zones, but surprizingly anisotropy was not observed in the strongly foliated gouge zones. The field measurements differ significantly from laboratory measurements at zero pressure and in some cases from expected values for saturated rock of this porosity, perhaps due to biased rock sampling, the long wavelength effects of macrofractures, frequency dispersion, and partial saturation. The velocity profile is similar in width and consistent in velocity contrast to low S-wave velocity zones derived from fault zone guided waves in other strike-slip faults. The traveltime delay across the fault zone is not large enough to cause the 2-3 km wide crustal low velocity zones modeled by refraction studies. Synthetic reflection seismograms in the typical frequency range show that the fault zone acts as a thick bed or as a constructively interfering thin bed. The models suggest that very large reflection coefficients observed across accretionary prism faults can be explained by fracturing, brecciation and clay content without elevated pore pressures. Comparison with a refraction study across the Punchbowl Fault shows a similar structural zonation of these two well-studied examples of brittle fault zones. This suggests that high-resolution seismic velocity models can be used to directly interpret internal deformation structure of brittle faults. / Master of Science

Ce travail s’inscrit dans la problématique de réduction de masse, de sécurité inhérent au domaine aéronautique, il concerne plus spécifiquement les sièges de pilotes d’avion de ligne. Un nouveau concept d’assise composite sandwich multifonctionnel est proposé. Il est composé d’une peau carbone, d’une âme nid d’abeille Nomex et d’une peau hybride Kevlar/lin. L’assemblage de plusieurs matériaux engendre des comportements parfois complexes et rend difficile la prédiction de la ruine de la structure. Une démarche expérimental/numérique est mise en place pour appréhender l’endommagement de l’assise et ainsi permettre un pré-dimensionnement via un outil numérique.Tout d’abord, des essais de caractérisation permettent d’élaborer les lois de comportement des différents matériaux constituant le sandwich. Le composite hybride présente un comportement élasto-plastique-endommageable-anisotrope. Le nida Nomex est représenté par un réseau de ressort et une loi couplant le comportement en compression et en cisaillement qui est implémentée dans ABAQUS. Des essais d’impacts permettent d’évaluer les modes de rupture et l’énergie dissipée par les concepts d’assises réalisés. Des simulations numériques intégrant les comportements matériaux identifiés sont mises en places pour corréler l’essai d’impact. L’analyse couplée des résultats expérimentaux et numériques permet d’identifier les couplages entre les différents mécanismes. Enfin, le modèle est utilisé pour dimensionner une assise composite qui s’avère sans optimisation fine, comparable à une assise existante en aluminium de l’A350. / This work is part of the problem of mass reduction, safety inherent in the aeronautical field, it concerns more specifically the seats of pilots of airliner. A new multi-functional sandwich composite seat pan is proposed, composed by a carbon skin, a Nomex honeycomb core and a Kevlar/flax hybrid skin. The assembly of several materials generates complex behaviors and makes the ruin of the structure difficult to predict. An experimental/numerical approach is used to understand the damage mechanism of the seat and to create a pre-dimensioning numerical tool.Firstly, characterization tests allow identifying the mechanical behaviors of each material and constituting a database for the creation of material laws. The hybrid composite shows an elastoplastic-damaging-anisotropic behavior. The honeycomb is represented by a spring network and a law coupling the compression and shear behavior is implemented. Impact tests are used to evaluate the failure modes and the energy dissipated by the different concepts. The impact tests are correlates by numerical simulation using the identified material behaviors. The analysis of the experimental and numerical results makes it possible to identify the coupling between the different mechanisms. Finally, the model is used to design a new composite seat pan. This one is comparable to the existing aluminum seat pan without optimization phase.