Finite element simulation

The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of metallic nanodisks has been studied by near-infrared pump-probe diffraction measurements over a temporal range spanning from 100 fs to several nanoseconds. The experiments demonstrate that in these systems a surface acoustic wave (SAW), with a wave vector given by the reciprocal periodicity of the two-dimensional array, can be excited by ̃120 fs Ti:sapphire laser pulses. We unambiguously show that the observed SAW velocity shift originates from the mechanical interaction between the SAWs and the nanodisks, while the correlated SAW damping is due to the energy radiation into the substrate. In order to clarify the interaction between the nanodisks and the substrate, numerical calculations of both the elastic eigenmodes and the time-dynamics of the system, following the impulsive heating excitation by the laser, are performed. Simulations based on finite-elements analysis, together with a wavelet analysis of ...

It is well recognised that superstructure load is transferred to surrounding soil through piled foundation. Consequently, the high stress regime (stress bulb) is generated surrounding of the pile. On the other hand, the excavation in the ground inevitably results in the ground movement due to induced-stress release. These excavations are sometimes inevitable to be constructed adjacent to existing piled foundations. This condition leads to a big challenge for engineers to assess and protect the integrity of piled foundation. This research presents three-dimensional coupled consolidation analyses (using clay hypoplastic constitutive model which takes account of small-strain stiffness) to investigate the responses of an endbearing pile due to adjacent excavation at different depths in soft clay. The effects of excavation depths (i.e., formation level) relative to pile were investigated by simulating the excavation near the pile shaft (i.e., case S) and next to (case T). It was revealed that the maximum induced bending moment in the pile after completion of excavation in all the cases is much less than the pile bending moment capacity (i.e. 800 kNm). Comparing the induced deflection of the end-bearing pile in the case T, the pile deflection in case S is higher. Moreover the piles in cases of S and T were subjected to significant dragload due to negative skin friction.

Steel members with a single-angle cross-section are widely used, but some of their behaviours under loads are not considered by design codes, necessitating related research. This study is carried out on fifty steel single-angle members focused on the stress distribution behaviour and the ultimate axial load capacities under different end deformations through 3-dimensional Finite Element (FE) simulations and comparison with previous experimental findings. FE modeling is capable of modeling steel structures with high accuracy. Based on the results, the length of the angle affects neither the shape of the stress distribution nor the ultimate load capacity of the element. The end deformations affect the stress distribution on the member angle cross-section, including the ultimate load capacity. The end deformations which restricted deformations in the two directions perpendicular to the load axis are found to be optimal, with an average increase in load capacity by a factor of 1.96 for an equal angle and 2.21 for an unequal angle compared with the capacities calculated for single angles with deformations allowed in all directions. The appearance of a compression zone on the unconnected angle leg reduces the ultimate load capacity. The current design code (ANSI/AISC-360) can be adopted to calculate the ultimate load in the case of no deformation in the y-axis direction and no deformations in the xand y-axis directions where the mean ratios of P Num /P code are 1.24 and 1.34 respectively. However, the code does not agree with the end deformations of free deformations and no deformation in the x-axis direction for either equal or unequal angles where the mean ratios of P Num /P code are 0.64 and 0.79 respectively, which is unsafe.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The effect of welding residual and thermal stresses on fatigue crack growth in rail welds was studied. The residual stresses in a flash-butt weld were calculated by means of finite element (FE) analysis, and the results were in good agreement with experimentally determined residual stresses in a welded rail. The redistribution of the residual stresses in the welded rail was simulated using an FE model developed for train-track-rail interaction simulation. It was employed here for train traffic conditions at a straight track during heavy-haul operation conditions. The thermal stresses that occur in the rail due to variations in temperature between winter and summer were also accounted for in this FE model. The results from the stabilised stress response in the rail, after several wheel-rail contact load passages, were used to investigate the sensitivity in crack growth in the weld region using fracture mechanics. A number of parameters were varied, for example, the axle load, crack location, crack size and rail temperature.

In this paper, we investigate the impact of an object simplification approach in registration using the Iterative Closest Point (ICP) algorithm. Though the simplification of the objects remarkably reduces the registration time, it also raises a critical issue, whether the simplified version of the object carries sufficient information to recover the proper geometric parameters of registration. Accordingly, we investigate both simulated and real data to test the geometric degradation caused by the simplification. As for computational times, we monitor how much time we can save during the ICP registration using simpler objects. Moreover, we check the times taken by the simplification process itself to see whether simplification can be considered online, as well.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

O objetivo deste trabalho será avaliar uma viga utilizando o método dos elementos finitos codificado na linguagem python sob condições de incêndio. Para tal, serão utilizados modelos
simplificadores de perda de resistência do material ao longo do tempo e distribuição de calor.
O método para o cálculo linear estático a cada etapa da distribuição de calor será o Método
dos Elementos Finitos e a distribuição de calor utilizará o Método das Diferenças Finitas.
Como elemento de escolha para facilitar ambas as resoluções será elegido o elemento linear
de quatro nós retangular ou CSR (Constant Strain Rectangle). Após análise computacional,
foi constatada um deslocamento vertical máximo de 84% contra o software de referência
levando à conclusão que apesar de válida a simulação, a escolha do elemento CSR não
é a mais adequada devido às suas limitações sendo necessários elementos de ordem superior.

Nowadays in the construction of modem buildings, it is necessary to accommodate pipes and ducts necessary services, such as air conditioning, water supply, sewerage, electricity, computer networks, and telephone networks. Cellular memberssteel Ishaped structural elements with circular web openings at regular intervals -have been used as beams for more than 35 years now. Although in the past already a large deal of research was performed into the subject of the behavior of cellular beams, almost no attention has been paid to the application of cellular members as columns. The column will be analyzed using the finite element method to calculate the critical load and compared with the Eurocode3 standard, web-post buckling, and frame using cellular member by FEM.

The computational-costs for finite element simulations of general sheet metal forming processes are considerable, especially measured in time. In combination with optimization, the performance of the optimization algorithm is crucial for the overall performance of the system, i.e. the optimization algorithm should gain as much information about the system in each iteration as possible. Least-square formulation of the object function is widely applied for solution of inverse problems, due to the superior performance of this formulation. In this work focus will be on small problems which are defined as problems with less than 1000 design parameters; as the majority of real life optimization and inverse problems, represented in literature, can be characterized as small problems, typically with less than 20 design parameters. We will show that the least square formulation is well suited for two classes of inverse problems; identification of constitutive parameters and process optimization. The scalability and robustness of the approach are illustrated through a number of process optimizations and inverse material characterization problems; tube hydro forming, two step hydro forming, flexible aluminum tubes, inverse identification of material parameters.

The goal of this study was to develop a mathematical model of the lower extremity capable of predicting injury risk and simulating the kinetic and kinematic response of the pedestrian lower extremity under vehicle impact loading. The hip-to-foot multi-body model incorporates a detailed facet contact surface, 50 th percentile male anthropometric and inertial properties, and stiffness and failure tolerances from the most recent literature. Model validation was achieved using a combination of parameter optimization for component-level kinetic response and full-scale simulations for kinematic response. The three-dimensional kinematic response of the struck-side lower extremity of seven post-mortem human surrogates struck laterally by a sedan at 40 km/h is also presented.

This paper reports a three-dimensional (3D) study of the microstructure and texture below a conical nanoindent in a (1 1 1) Cu single crystal at nanometer-scale resolution. The experiments are conducted using a joint high-resolution field emission scanning electron microscopy/electron backscatter diffraction (EBSD) set-up coupled with serial sectioning in a focused ion beam system in the form of a cross-beam 3D crystal orientation microscope (3D EBSD). The experiments (conducted in sets of subsequent ð1 1 2Þ cross-section planes) reveal a pronounced deformation-induced 3D patterning of the lattice rotations below the indent. In the cross-section planes perpendicular to the (1 1 1) surface plane below the indenter tip the observed deformation-induced rotation pattern is characterized by an outer tangent zone with large absolute values of the rotations and an inner zone closer to the indenter axis with small rotations. The mapping of the rotation directions reveals multiple transition regimes with steep orientation gradients and frequent changes in sign. The experiments are compared to 3D elastic-viscoplastic crystal plasticity finite element simulations adopting the geometry and boundary conditions of the experiments. The simulations show a similar pattern for the absolute orientation changes but they fail to predict the fine details of the patterning of the rotation directions with the frequent changes in sign observed in the experiment. Also the simulations overemphasize the magnitude of the rotation field tangent to the indenter relative to that directly below the indenter tip.

Irradiation effects on the stable and unstable deformation behavior and fracture properties of SA533B steel have been studied in detail based on the equivalent true stress versus true strain curves. An iterative finite element simulation technique was used to obtain the equivalent true stress-true strain curves from experimental load-displacement data. The results showed the localized necking occurs without diffuse necking for high dose irradiated cases that showed negligible uniform ductility in engineering stress-strain curves. Slope of true stress-strain curves was still positive during the unstable necking deformation regardless of irradiation dose level, and the slope considerably varied with necking mode change rather than with irradiation dose level. The equivalent fracture stress decreased with increase in dose level up to 0.1dpa and slightly increased above dose level. The equivalent fracture strain decreased with increasing dose level up to 0.1dpa and then decreased at lower rate, but it was still high after high dose irradiation exposure even if uniform ductility was almost zero. These dose dependences of tensile fracture stress and fracture strain are related with the fact that density of irradiation induced defects increases with increasing dose and is saturated at dose around 0.05dpa.

The torsional mode of the atomic force microscope (AFM) cantilevers has been widely used in various measurements where the high sensitivity of the AFM [1,2,3]. The approximated frequency and mode shape of the overhang-shaped cantilevers are usually used and give rises to several inconsistency between the calculated values and the experimental results. In this talk, we present the calculation of the frequency and mode shape of the width-varying cantilevers so that the frequency and modeshape of any higherorder mode could be obtained. This gives fruitful method for the experimentalist to choose the suitable geometric parameters for the cantilever targeting a specific frequency.

References:
[1] Le Tri Dat, Chi Cuong Nguyen, Nguyen Duy Vy and Amir F. Payam, Tuning the flexural frequency of overhang-/T-shaped microcantilevers for high harmonics, Japanese Journal of Applied Physics 62(10) 107002 (2024).
[2] Nguyen Duy Vy, Alessio Morelli, Vinh N.T. Pham, Dewar Finlay, Amir Farokh Payam, Dynamics analysis of width-varying microcantilevers: Interplay between eigenfrequencies, contact stiffness and interaction forces, International Journal of Solids and Structures 259, 112027 (2022).
[3] Le Tri Dat, Vinh N. T. Pham, Nguyen Duy Vy, Amir F. Payam, Frequency equation and semi-empirical mechanical coupling strength of microcantilevers in an array, Microscopy Research & Technique 85(9)
3237-3244 (2022).

AM&act-The Welding Institute Level-3 crack tip opening displacement (CTOD) method was ezpanded to be applicable to plane strain (Planbstrain Level-3 CLOD method). The delinition of the reference strain is a major source of uncertainty in the application of the Level-3 CTOD method. Two different measures of the reference strain were proposed. Applied CTOD estimates of the surface cracked wide plate in bending were performed using the Level-3 CLOD methods. It was found that the proposed Plane-strain Level-3 CTOD method can provide highly accurate predictions of applied CIOD with a safety factor approximately equal to 1.0 for the surface crack in bending.

This paper presents a plasticity model for deep axial surface cracks in pressurised pipes. The model is used in an investigation of the relative merits of fracture criteria based on COD and plastic instability. Recent investigations have shown that the inconsistency of the singular bending stress field in an axially cracked cylindrical shell arising from use of classical eighth order shallow shell theory is removed when use is made of a tenth order shell theory which accounts for transverse shear deformations. Although the membrane stresses are only moderately affected, the influence on the bending stresses is considerable. In the case of surface cracks moments are induced due to the eccentricity of the crack and transverse shear effects should therefore be included. A plasticity model for a rectangular axial surface crack is developed. Like a previous surface crack model by Erdogen and Ratwani, 3 -5 it generalises Dugdale's assumption of a concentrated yield zone in the plane of the crack but, contrary to that model, transverse shear effects are included and a continuous stress distribution is assumed in the yield zone. The inherent difficulties arising from the use of shell theory to model a three-dimensional problem can be overcome when the crack is sufficiently deep and the material is so ductile that full yield of the section around the crack develops before failure. In that case the calculations confirm the initial assumption of separation of the crack surfaces and the sides of the yield zone. The model is' used to analyse published test data on surface cracked pressurised pipes. The analysis consists in COD evaluation and estimate of failure as a consequence of plastic instability. A method is proposed which deals with the problem by simultaneous analysis of a number of cracks with increasing depth. The method avoids iterations and enables, for any load and crack length, calculation of the smallest crack depth which would cause instability.

We describe a new algorithm for 3D, and potentially higher, volume rendering. This algorithm takes advantage of the shear-warp factorization technique to reduce matrix computing and a hierarchical data structure for better utilization of spatial coherence. The algorithm represents an improvement over existing algorithms in terms of performance, with little compromise in image quality. The algorithm benefits 3D volume rendering as well as multi-modality volume rendering. Initial work on comparison and validation of algorithm are done. The results and analysis show that the algorithm is promising. Our preliminary work in using this method for medical simulation is also discussed. This method is particularly suitable for PC-based medical simulation where the computation load is high and the raw computing power is limited.

An experimental study was performed to investigate the ultimate strength and modes of failure of axially loaded channel rack columns with rear flanges. A total of 16 column specimens fabricated by press-brake forming method were tested up to failure. The material properties of the column specimens were determined using standard tensile coupon tests. The deformation and stress behavior of the tested columns were monitored using displacement transducers and strain gauges. The effects of column slenderness ratio, thickness, perforation, and end conditions on the column ultimate strength and mode of failure were studied. The test failure loads were compared to the ultimate load predictions of the 2001 AISI North American Specification. The comparison showed that the AISI procedure overestimates the failure load, which suggests that the proportioning of the cross-sectional dimensions of the lipped channel sections with rear flanges has a direct effect on the capacity of the columns.

Classical plasticity theories generally assume that the stress at a point is a function of strain at that point only. However, when gradients in strain become significant, this localization assumption is no longer valid. These conventional models fail to display a 'size effect'. This effect is seen experimentally when the scale of the phenomenon of interest is on the order of several microns. Under these conditions, strain gradients are of a significant magnitude as compared to the overall strain and must be considered for models to accurately capture observed phenomena. The mechanics community has been actively involved in the development of strain gradient theories for many years. Recently, interest in this area has been rekindled and several new approaches have appeared in the literature. Two different approaches are currently being evaluated. One approach considers strain gradients as internal variables that do not introduce work conjugate higher order stresses. Another approach considers the strain gradients as internal degrees of freedom that requires work conjugate higher order stresses. Experiments are being performed to determine which approach models material behavior accurately with the least amount of complexity. A key difference between the two models considered here is the nature of the assumed boundary conditions at material interfaces. Therefore, we are investigating the deformation behavior of aluminum/sapphire interfaces loaded under simple shear. Samples are fabricated using ultra-high vacuum diffusion bonding. To determine the lattice rotations near the boundary, we are examining the samples with both electron backscatter diffraction methods (EBSD) in the scanning electron microscope and with a variety of diffraction techniques in the transmission electron microscope. The experimentally found boundary conditions shall be subsequently used to determine whether the simpler internal variable model is adequately descriptive or if the greater complexity associated with the internal degree of freedom approach is warranted.

For the first time, lateral-extensional micromachined resonators fabricated on highly n-type doped silicon substrates and aligned to the [100] crystalline orientation are shown to exhibit an adjustable turnover temperature. This behavior commonly observed in quartz resonators is a key to achieving exceptional temperature stability in oven-controlled crystal oscillators. To demonstrate the effect of doping concentration and resonator alignment to different crystalline orientations, the thinfilm piezoelectric-on-silicon (TPoS) platform is utilized. It is shown through combined theoretical analysis and finite element simulation that the turnover temperature is a sensitive function of doping concentration and also can be adjusted by changing the thickness of the resonant structure. In order to experimentally validate these results, similar resonators are fabricated on three silicon-on-insulator (SOI) substrates and the temperature variation of frequency for several devices are measured and the trends are shown to agree with theory. The minimum temperature variation of frequency is measured for a ~25MHz TPoS resonator aligned to the [100] crystalline orientation showing a maximum frequency variation of 148ppm over the -40°C to 85°C temperature range. This is more than 20x reduction compared to the earlier results from similar uncompensated devices.

The effect of total length and presence of bearings towards torsional stiffness of Low Stiffness Resilience Shaft (LSRS) in Semi Active Steering (SAS) is discussed in this paper. LSRS, an integral component of the SAS is a flexible shaft that can replace the conventional rigid shaft of the steering system and allows active control to be performed. Static structural torsional test simulations using ANSYSTM were performed on arrangements of 4 wire rope strands with different lengths in order to select the best one for the optimum performance of the LSRS. With the total length of the wire ropes equal to their lay lengths being the defining factor, three different LSRS namely LSRS A, LSRS B and LSRS C were modelled and then analyzed. LSRS A was found out to be the stiffest with an average torsional stiffness of 12.30 N.m/rad and LSRS C the most torsionally flexible, having the least average stiffness of 4.93 N.m/rad. Furthermore, LSRS I, II and III were modelled based on the number of b...

The design and modeling of Low Stiffness Resilience Shaft (LSRS) for the Semi-Active Steering (SAS) system using wire ropes is discussed in this paper, along with the static structural torsion test simulation of the wire ropes in order to determine the best possible configuration which serves the purpose of an LSRS. The importance of this study arises due to the unidirectional torsional properties of a wire rope. For an effective operational LSRS, the wire ropes need to have similar angular deflection in both the clockwise and anti-clockwise direction. LSRS, an integral component of the SAS is a flexible shaft that can replace the conventional rigid shaft of the steering system and allows active control to be performed. 3D solid models of the simple strand and the 4 strand wire ropes used in finite element analysis were generated in CAD software SolidWorksTM. The single strand and the different configuration of wire ropes required to function the LSRS effectively were then analyzed using Finite element simulation in ANSYSTM. A single wire rope could not be used because its construction has inconsistency in the torsional stiffness in clockwise and anti-clockwise direction. The single-strand right-direction lay wire rope is found to have 16.05% angular deflection percentage difference in the clockwise and anticlockwise directions which indicates that using a single strand wire rope for the LSRS will cause the vehicle to have a variable response in the clockwise and anti clockwise direction upon turning the steering wheel. Due to this inconsistency, two variations namely Variation 1 and Variation 2 with arrangement of 4 strand wire rope were devised so that the angular deflection percentage difference would be negligible. Simulation results indicated that Variation 1 of the two variations with an angular deflection percentage difference of 0.34% in the clockwise and anti-clockwise direction respectively is best suited for the use in LSRS as it has almost negligible angular deflection percentage difference and will allow the vehicle to have similar steering response in the clockwise and anti-clockwise direction.

The aim of this work is to see whether supports defined as stable by deterministic calculations can automatically be reliable in the geotechnical sense, as is often considered in Senegal. The analysis was carried out on an building project that had to rest on a two-level subsoil in a site requiring underpinning. A deterministic calculation of the project is carried out to verify the stability of the retaining wall with a safety factor. Then, a probabilistic calculation is made to take into account the variability of the characteristics of the soils that will house the retaining structure, with a coefficient of variation of 10%. The reliability index is determined by considering a safety factor threshold value of 1.5. The length of the sheet with reliable stability is then determined. The results show that for a plug length of 1.8 m, both the secant pile wall and the cast wall are stable with a safety factor greater than 1.7. However, the probabilities of failure and the reliability index remain below their thresholds for both the secant pile wall and the cast wall when the plug is 1.8 m long. The supports are stable and reliable when the plug length is 2.8 m for the same materials. In conclusion, a safety factor greater than the limit does not guarantee a reliable structure in deterministic studies.

In this paper two of the main variables involved in machining processes have been experimentally measured in order to supply reliable data for Finite Element simulation assessing. The implemented strategy is based on the split tool technique which permits to isolate the contribute of the investigated variables different zones of the tool.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Finite Element simulation of orthogonal cutting is nowadays assuming a large relevance; in fact a very large number of papers may be found out in technical literature on this topic. In recent years, numerical simulation was performed to investigate various phenomena such as chip segmentation, force prediction and tool wear. On the other hand, some drawbacks have to be highlighted; due to the geometrical and computational complexity of the updated-Lagrangian formulation mostly used in FE codes, a cutting time of only a few milliseconds can be effectively simulated. Therefore, steady-state thermal conditions are not reached and the simulation of the thermal phenomenon may be ineffective. In order to overcome such problem two different approaches are proposed in this paper. The former is based on a pure thermal simulation once the thermal flow on the tool is properly calculated. The latter, on the contrary, is based on an artificial modification of the heat transfer coefficient at the interface between the chip and the tool in the thermo-mechanical simulation. Both of the proposed methodologies are discussed in the paper, highlighting the advantages and the drawbacks of each of them.

Winged porphyroclasts are often used as kinematic or strain indicators in shear zones. In particular, it has been suggested that the geometry of d-clasts in mylonites can give information about the rheological behaviour of the matrix around the Ž . clast Passchier et al., 1993 . We tested this hypothesis with a numerical finite element simulation of the flow field of a viscous matrix around a relatively rigid clast. Power-law viscous flow properties of the matrix with stress-exponents of 1 Ž . linear viscous , 3 and 5 were tested, as well as three different sets of approximately simple shear boundary conditions, which are relevant to experimental andror natural situations. The simulations show that the flow field is primarily determined by the boundary conditions. The stress-exponent is of secondary importance. In general, the different boundary conditions produce two types of flow fields about the rigid clast: an eye-shaped flow field and a bow-tie shaped flow field. The former is produced by boundary conditions that approximate simple shear applied at an infinite distance from the rigid clast, and the latter is produced by boundary conditions which are equivalent to a shear box or ring shear apparatus. Although both the shear-box and ring-shear boundary conditions produce bow-tie flow patterns, the wing geometries which result from the flow patterns for these two cases can be significantly different. The geometry of the wings that develop on a d-clast is a direct function of the flow field around the clast. For linear and Ž non-linear rheologies, only the ring-shear boundary conditions produce wings that show ''stair-stepping'' i.e. wings that are . parallel but not in the same plane . In natural shear zones, d-clasts both with and without stair-stepping are observed. In comparing geologic observations with experimental or numerical modelling, it is essential to understand which boundary conditions are appropriate.

We model the pressure distribution around cylindrical objects in simple shear deformation using the ®nite element method in two dimensions and present an analytical solution for a special case. Parameter space is explored numerically for viscosity contrast between object and matrix, h, and for the non-linearity of ¯ow, as expressed by n. We show that the geometry and size of the pressure shadow is independent of h, but strongly dependent on n. For example, at n 1, pressure shadows are roughly circular in shape, while for n . 1, pressure shadows disintegrate into two branches. We also show that pressure may only exceed 100 MPa in pressure shadows at resolvable distances from the object if h . 4 for strain rates of 10 214 s 21 and matrix viscosities around 10 22 Pa s. As these values for strain rate, viscosity and viscosity contrast are geologically reasonable, we emphasise that it is conceivable that geobarometric results obtained from syndeformational mineral parageneses near rigid porphyroblasts may be in¯uenced by non-lithostatic components of pressure.

We model the acoustics of rocks partially saturated with hydrogen. We compare the acoustic properties of H 2 (hydrogen), CO 2 (carbon dioxide) and CH 4 (methane) and those of rocks saturated with these gases and brine. The gas properties are obtained from the Peng-Robinson equation of state, and we consider the pressure-temperature conditions based on a linear basin modeling with a constant geothermal gradient. The bulk and shear moduli of the dry rock are obtained with the Krief model, while the Athy equation is used to calculate the porosity as a function of depth. Mesoscopic attenuation and velocity dispersion due to fluid effects is quantified using the Johnson model. The viscoelastic Cole-Cole model is used to describe the velocities and attenuation predicted by the Johnson model when synthetic seismograms with an equivalent viscoelastic rheology are to be calculated. In this case, the P-wave velocity as a function of gas saturation is obtained with the Gassmann equation and an effective fluid modulus based on the Brie equation.

The injection of CO 2 into a saline aquifer induces changes in pore pressure and fluid saturation, which in turn induce variations in the petrophysical properties of the storage site. Thus, numerical modeling of CO 2 sequestration combining multiphase fluid flow and wave propagation simulators requires determining the time steps at which the flow parameters (porosity and absolute permeability) need to be updated during the simulation of CO 2 injection. For this purpose, this work presents a sensitivity analysis of the seismic response of the Utsira formation (where CO 2 is being injected) due to variations in its petrophysical properties. A multiphase fluid flow simulator is used to determine the spatio-temporal distribution of CO 2 and brine during injection. The porosity and absolute permeability are assumed to be dependent of saturation and pore pressure. In the wave propagation simulator the Lamé parameters include effects of mesoscopic losses due to the presence of CO 2 in the pore space. The numerical experiments allow to define the time step at which the flow parameters need to be updated to obtain accurate seismic images of the spatial distribution of CO 2 after injection, with a more precise definition of the zone where the pushdown effect is observed.

Capture and storage of Carbon dioxide in aquifers and reservoirs is one of the solutions to mitigate the greenhouse effect. Geophysical methods can be used to monitor the location and migration of the gas in the underground. To perform this task properly, a suitable geological model is important, which simulates the geometry and petro-elastical properties of the different formations. In this work we integrate numerical simulators of CO2-brine flow and seismic wave propagation to model and monitor CO2 storage in saline aquifers. We also build a petrophysical model of a shaly sandstone based on porosity and clay content and considering the variation of properties with pore pressure and fluid saturation. The pressure map before the injection of CO2 is assumed to be hydrostatic for which a reference porosity map is defined. The permeability is assumed to be anisotropic and is obtained from first principles as a function of porosity and grain sizes. The density is the usual arithmetic av...

We develop a petro‐elastical numerical methodology to compute realistic synthetic seismograms and analyze the sensitivity of the seismic response when injecting carbon dioxide (CO2) in a depleted gas reservoir. The petro‐elastical model describes the seismic properties of the reservoir rock saturated with CO2, methane and brine, and allows us to estimate the distribution and saturation of CO2 during the injection process. The gas properties, as a function of the in‐situ pressure and temperature conditions, are computed with the Peng‐Robinson equation of state, taking into account the absorption of gas by brine. Wave attenuation and velocity dispersion are based on the mesoscopic loss mechanism, which is simulated by an upscaling procedure to obtain an equivalent viscoelastic medium corresponding to partial saturation at the mesoscopic scale. Having the equivalent complex and frequency‐dependent bulk (dilatational) modulus, we include shear attenuation and perform numerical simulatio...

Lightweight and miniaturized weapon systems are driving the use of new materials in design such as microscale materials and ultra low-density metallic materials. Reliable design of future weapon components and systems demands a thorough understanding of the deformation modes in these materials that comprise the components and a robust methodology to predict their performance during service or storage. Traditional continuum models of material deformation and failure are not easily extended to these new materials unless microstructural characteristics are included in the formulation. For example, in LIGA Ni and A1-Si thin films, the physical size is on the order of microns, a scale approaching key microstructural features. For a new potential structural material, cast Mg offers a high stiffness-to-weight ratio, but the microstructural heterogeneity at various scales requires a structure-property continuum model. Processes occurring at the nanoscale and microscale develop certain structures that drive material behavior. The objective of the work presented in this report was to understand material characteristics in relation to mechanical properties at the nanoscale and microscale in these promising new material systems. Research was conducted primarily at the University of Colorado at Boulder to employ tightly coupled experimentation and simulation to study damage at various material size scales under monotonic and cyclic loading conditions. Experimental characterization of nano/micro damage will be accomplished by novel techniques such as in-situ environmental scanning electron microscopy (ESEM), 1 MeV transmission electron microscopy (TEM), and atomic force microscopy (AFM). New simulations to support experimental efforts will include modified embedded atom method (MEAM) atomistic simulations at the nanoscale and single crystal micromechanical finite element simulations.

The present work discusses the use of model asperities as a method for studying asperity flattening in metal forming. Asperity flattening and the resulting real contact area largely influence friction in metal forming. In order to gain a fundamental understanding of asperity flattening, a method of choice often is to use model asperities. Here, macroscopic model surfaces are emulating real surface topographies. The work presents the method in a historic context, explains the method, lists advantages and disadvantages, and discusses the method in terms of whether the insights gained on model asperities are of qualitative or quantitative nature. In conclusion, the method is a valid tool to fundamentally study asperity flattening. It is, however, not always possible to transfer obtained conclusions quantitatively from model surfaces to real surfaces.

This paper reports on quantitative measurements of strain in a 7.5 nm compressive strained Ge/5.1 nm tensile strained Si bi-layer grown by reduced pressure chemical vapour deposition on top of a relaxed Si 0.5 Ge 0.5 virtual substrate. Geometric phase analysis of high resolution transmission electron microscopy images acquired using the SACTEM-Toulouse, an aberration-corrected transmission electron microscope, is used to quantify the strain within s-Ge and s-Si layers. Finite element simulations are carried out to estimate the impact of strain relaxation in thin areas of a TEM specimen. Experimental results are compared with the predictions of elasticity theory and finite element simulations.

An 11 m-deep basement structure in London SW1 was left vacant from 1968 to 1989. The basement heaved significantly during this period due to the lack of a superstructure, providing a unique opportunity to study the development of long-term heave in London Clay. May (1975) presented the monitoring results from 1968-73 and excerpts of site data collected after 1973 have also been circulating informally in the industry since the 1990s. However, the full set of monitoring data remains hitherto unpublished. This paper was initially drafted in the early 1990s when three of the authors (Nicholson, Chapman, and Solera) were working together with Arup. The paper somehow never got published as people and circumstances changed. More recently, the first author (Chan) started postgraduate research on heave and pressure beneath slabs in excavations in over-consolidated clays, using the heave monitoring data from the draft paper to complement centrifuge test results. For this reason, it was decide...

A thermodynamics based damage mechanics coupled constitutive model is used to simulate the nanoindentation experiment on eutectic commercial Pb/Sn solder alloys. The study is aimed at explaining the apparent size dependent behavior observed at small indentation depths for this class of highly rate dependent materials. Interest is at small depths of indentation and a small-strains small-displacements theory is used. The study is motivated by the fact, that in the case of rate independent materials such a size dependence of the response is explained in terms of storage of the so-called geometrically necessary dislocations. Presently it is not clear if this is the source of size effects in a rate dependent material. Moreover, the storage of dislocations is difficult in eutectic solder alloys due to thermally activated diffusion processes that promote dislocation mobilization as opposed to storage. Therefore, a classical theory constitutive model should be able to capture such a size dependent feature of the response. The paper describes the constitutive model and its integration scheme. Simulations of the nanoindentation problem are performed at different temperatures and indentation strain rates and numerical results are compared with experiments.

Finite element simulations of PLC effects in notched and CT (compact tensile) specimens of aluminium alloys are presented, based on a macroscopic PLC constitutive model. They predict the formation and propagation of intense strain rate localization bands. In particular, the predicted size of the plastic zone around the crack tip in a pre-cracked CT specimen is compared to the value found when using a standard elastoplastic model neglecting PLC effects.

The aim of the present work is to use an available constitutive model for the description of the Portevin-Le Châtelier effect to simulate the deformation of notched specimens in tension (smooth and sharp U-notched specimens). This model can be used to account for dynamic strain ageing as suggested by Estrin et al. [Acta Mater. 49 (2000) 1087] but also static strain ageing as suggested by Kubin et al. [Acta Metall. Mater. 40 (1992) 1037]. The experimental material studied is an Al-Cu alloy, displaying dynamic strain ageing at room temperature. Regarding Lüders band propagation, the experimental material studied is a mild steel. This work shows that the PLC serrations disappear progressively on the macroscopic curve when the notch radius decreases. However, strain localization still takes place in the deformed notched zone, and can escape from the notched zone. Regarding the Lüders behavior, the computed spreading of deformation bands is in agreement with experimental observations.

Single incremental metal forming SPIF and deep drawing process are similar technologies and SPIF can be used to build a prototype for additional analysis and later construction. In this paper the selection of parameters needed for SPIF process production with software Solidcam are shown. A consideration to strain hardening has been given. Experiment on a thin sheet metal TH435 CA ST E2.8/2.8 of 0.19 mm thickness has been conducted in order to understand basics of the technology.

directeur du mémoire Département de génie mécanique à l'École de technologie supérieure M. Jacques Lanteigne, codirecteur Institut de Recherche d'Hydra-Québec M. Marc Thomas, président du jury Département de génie mécanique à l'École de technologie supérieure M. Hakim Bouzid, membre du jury Département de génie mécanique à l'École de technologie supérieure

We evaluate and discuss the relevance of fiber anisotropy in estimating the effect of transcranial magnetic stimulation (TMS) on the human brain. Finite element simulations were carried out on a threedimensional model of the head that included anisotropic conductivity information derived from diffusion tensor imaging (DTI). The results show that anisotropy has minor effects both on the position of the main locus of activation and on its intensity. It has considerably more effect on the spatial distribution of the induced electric field, yielding differences of the order of 10% of the maximum induced field. Moreover the area affected by magnetic stimulation is slightly larger when we include fiber anisotropy in the calculations than in an isotropic model. We also show that the induced field observed in the anisotropic model does not always align with the local fiber orientation but rather follows specific patterns of parallelity. These findings will help to improve the estimation of the areas involved in magnetic stimulation.

With the increase in operating frequencies of wireless communication standards, Thin Film Bulk Acoustic Resonators (FBAR's) are expected to become a key technology to provide miniature, high-performance and high-frequency filters. In this paper we briefly describe some models for simulating FBARs. We also discuss device optimization in terms of electromechanical coupling and characterization of fabricated devices. Finally, we show the interest of taking the exact geometry of devices into account.

Kinetik enerjiye sahip mermilere karsi, tek veya cok katmanli metal zirh sistemlerinin gosterdigi balistik davranis, cok sayida deneysel, teorik ve sayisal calismayla arastirilmistir. Bu calismada, 9 mm mermilerle uzerine atis yapilan 6061 T651 aluminyum levhalar incelenmistir. Mikroyapi incelemesi optik mikroskop kullanilarak gerceklestirilmistir. Levhalarin mukavemet davranislarinin belirlenmesinde mikrosertlik degerleri kullanilmistir. Levha kalinligi ve carpma hizinin mikroyapi uzerindeki etkisi degerlendirilmistir. Calisma sonucunda; ince levhalarin, dusuk carpma hizlarinda bile yuksek nufuziyet derinligiyle deformasyon sertlesmesine daha duyarli oldugu, kalin levhalarin ise dusuk nufuziyeti derinligiyle termal yumusamaya egilimli oldugu degerlendirilmistir. Maksimum sertlik degerleri her iki levha kalinliginda da carpma bolgesinin hemen altinda elde edilmistir.