Fluid pressure driven by tectonic loading at marine convergent margins mediates the effective normal stress at subduction fault, affecting a wide range of processes including the aseismic-seismic transition, accretionary wedge morphology, coseismic rupture propagation, etc. The mechanical coupling between sediment frame deformation and fluid flow controls the generation of overpressure and thus is affected by both the frame rheologic behavior and sample permeability. In this study, we simulate the mechanical coupling using lab-constrained rheologic and hydraulic properties, and successfully reproduce the experimental results of both the synthetic samples and natural sediments recovered from the Nankai subduction zone. We establish a method to extract frame viscous behavior from the porosity data of a saturated uniaxial-strain creep test. A poro-visco-elastic FEM model is then presented to properly simulate the viscous behavior and evaluate the role of frame viscous strain in mitigating overpressure. Finally, with the consideration of sediment viscous deformation, we upscale the model to margin scale to infer pore pressure evolution within the Nankai accretionary prism over a geological timescale.

The purpose of this work was to explore the possibility of measuring properties of viscoelastic materials by nanoindentation. Indentation is not a common method for determining properties of viscoelastic materials and nanoindentation is a very new, state-of-the art technology. Therefore, this research is one of very few works in this area. This study includes nanoindentation experiments on viscoelastic materials, determining bulk properties of the same materials by conventional rheological techniques, suggesting of physical models to measure properties of viscoelastic solids and viscoelastic liquids by nanoindentation and numerical simulations of the nanoindentation process. The experimental part includes nanoindentation tests of viscoelastic solids and viscoelastic liquids and comparing measured local properties with the bulk ones. The bulk properties were measured with SAOS and Torsion tests. For this investigation polybutadiene was selected as an example of a viscoelastic liquid and silicon cross-linked rubber as a viscoelastic solid. It was found that the local properties of solid polymers vary widely. However, by averaging data collected from various locations, the bulk properties can be determined accurately for the viscoelastic solids. For the physical modeling we validated the Sneddon & Sakai model of indentation of viscoelastic solids and suggested a model for the indentation of viscoelastic liquids, based on Stoke's theory of a potential flow around a sphere. Also nanoindentation of a viscous liquid was simulated using the FLUENT commercial code. It was found that for the indentation of viscoelastic materials with dominantly viscous properties, the indentation model developed from Stoke's theory gives realistic values for shear forces, but predicts a smaller than actual compression force, acting on the surface of the indenter. The comparison of the results of the mentioned above different approaches allowed us to draw conclusions about the advantages and limitation of the technology and theoretical analysis of nanoindentation and its application in rheometry. It was shown that nanoindentation can be successfully used for investigation of viscoelastic materials. Because of its unique abilities nanoindentation will become an irreplaceable tool in such areas as the testing of thin films, study of materials in a transient states, and biomedical research. However, there are number of technical and theoretical issues that need to be addressed. We outlined issues that need to be resolved and suggested direction for further research and development. Among them are: selection of a proper model to simulate behavior of particular viscoelastic material, further improvement of indentation control and data acquisition system, manufacturing new indenters of optimum shape and material.

The forced vibration probjlem of a finite sphere with an exciting source embedded inside it was treated. The source is assumed to oscillate sinusoidally and the complex dilatational modulus is used to describe the motion inside the sphere. If the outer surface of the sphere is restrained from radial displacement, the ratio of the amplitude of a mid-point to the amplitude of a point on the exciting source could be used as an indication of the dilatational properties of the sphere. From the criterion of maximum amplitude ratio in conjunction with the frequency, the dilatational properties of a testing material can be determined. This method can be applied to visco-elastic fluids as well as solids. (Author).

Today, we are living in a polymeric era where thousands of daily used products are manufactured from some polymeric materials with different tasks and under a wide range of ambient conditions, including time duration of loading and working condition temperature. This leads to focusing light spot on behavior of such specific materials and investigating the strain associated with the applied stress to understand both of creep and stress relaxation behavior of the loaded polymeric components. Hence, this chapter deals with the estimation of induced strain allied with the applied force on a polymeric material via establishing the so-called mechanical equivalent models starting from the simple elastic element (spring with a modulus of elasticity E), simple viscous element (damper or dashpot with fluid viscosity Œ∑), Maxwell model, Voigt model, modified Maxwell model, modified Voigt model, and Maxwell-Voigt model. The theoretical analysis was built on derivation of the prompted deformation, as a function of time in each of the employed models, as a result of the applied external load (force) and then by depending on Hook,Äôs law transforming the gained expressions into stress (œÉ) and strain (Œμ) notation, followed by comparing the obtained equation with the general formula of the Hook,Äôs law to find exact values of the constant and as coefficients of the stress and strain. Final theoretical analysis showed that Maxwell,Äôs modified model was the best describing behavior of a loaded polymeric material to some extent followed by the other models.

Complex fluids from biological systems to polymeric solutions and gels experience elevated pressures due to environmental and processing conditions, which may impact the fluid performance. Tunable pressure-dependent fluid behavior is desirable for oilfield applications to optimize hydrocarbon recovery. Oilfield fluids are used to help transport and suspend solids, reduce friction pressure, and prevent fluid loss. Key to these fluid performance metrics is the fluid rheology. Depending upon the composition and flow conditions, the fluid can behave as a purely viscous or viscoelastic fluid. By selecting the composition, the flow properties can be optimized for specific functions, such as, suspending proppants to keep fractures open or retaining fluid downhole. ☐ High-pressure measurements may be performed using falling body, pressure-driven, and rotational devices. Falling body rheometers use a stationary object in a moving fluid or a stationary fluid with a mobile object to obtain viscosity measurements. Pressure-driven devices force a fluid through a capillary and obtain pressure drop and volumetric flow rate to obtain the viscosity. These techniques are restricted in the material properties that may be obtained and their application to non-Newtonian fluids. Rotational rheometers apply a shear or oscillatory stress or strain to the fluid to obtain viscoelastic properties, however, this technique is often pressure-limited. Overall, high-pressure viscoelastic measurements can be challenging for mechanical rheometers. ☐ To address these shortcomings, a passive microrheology experiment has been designed and validated to measure the linear viscoelasticity of complex fluids at high pressures. The apparatus incorporates a steel alloy sample chamber with dual sapphire windows into a simple diffusing-wave spectroscopy (light-scattering) device and is capable of both transmission and backscattering geometries. The measured light intensity correlation from the Brownian motion of polystyrene probe particles dispersed in the sample is interpreted using the Generalized Stokes-Einstein Relation to determine the material linear viscoelasticity. This high-pressure microrheology instrument is validated by measuring the viscosity change of water and 1-propanol over pressures from 0 to 172.4 MPag at ambient temperature. ☐ Complimentary mechanical and microrheology measurements are performed at ambient pressure on stimulation fluids containing a crosslinked guar gum biopolymer before the measurement is performed at elevated pressures. We investigate the effect of crosslinker density on rheological properties at frequencies up to 1 MHz and pressures of 200 MPag, expanding the accessible range of experimental conditions beyond those of existing rheological measurement techniques.

This report describes an innovative method for measuring the complex Young's modulus, complex shear modulus, and complex Poisson's ratio of a viscoelastic cylinder. The new nonresonant technique is based on measured transfer functions that are obtained by vibrating the cylinder linearly and rotationally with two different-size masses on its free end. Both masses have their own individual transfer functions, which can be measured and combined to yield the unknown Young's modulus and shear modulus values at every frequency where a measurement is made. Once these moduli are determined, Poisson's ratio can be calculated. The test method is subjected to Monte Carlo simulations to show that it is relatively unaffected by external noise in the data.