Apparatus and Method for Strain Energy Based Resiliency Measurement of Loss Control Materials

Loss of circulation is one of the greatest challenges that are frequently encountered while drilling. Various types of LCM products are used by the industry to combat loss of circulation. Characterization of these LCM products is very important to select the most suitable products to improve the success rate of LCM treatment jobs. This paper describes the theoretical basis of the application of strain energy along with the development of a strain energy-based mathematical model to create a dedicated software driven novel method and test apparatus for quick and reliable measurement of the coefficient of resiliency of various LCM products to improve the likelihood and probability of success rate of LCM treatment jobs. The simple but reliable method and apparatus provide a fit-for-purpose solution for additional characterization of LCM products. The design and construction of the test device and the development of the method considered the most critical technical factors that have high impact on data reliability, data accuracy, repeatability and data sensitivity. The components of the test device were selected based on technical, economical, portability and ease of operation using a dedicated software driven method and data acquisition system. Experimental results generated by loading and unloading a particular mass of a LCM product under a constant displacement rate of the loading foot of the test apparatus demonstrated the suitability of the method and the apparatus in determining the coefficient of resiliency of LCM products. Based on the area below the loading curve i.e. the strain energy absorbed during the loading cycle and the area below the unloading curve i.e. the strain energy desorbed during the unloading cycle, the data acquisition software automatically calculates the coefficient of resiliency of the LCM products. The resilient characteristic of LCM products is one of the critical factors that is very important for high performance pill or slurry design to enhance the seal/plug stability. Hence, the newly developed method and apparatus will play a positive role to improve the probability and the likelihood of creating a stable and lasting seal/plug in the loss zones. As loss control materials with good resilient properties are highly adaptable in changing stress and pressure conditions, this method can provide appropriate guidelines to mud chemists, mud engineers and mud consultants in designing high performance LCM blends or slurries to combat moderate and severe loss of circulation.

Installation for measuring the dielectric anisotropy of liquid crystals at low frequencies by the bridge method with constant displacement

Installation designed to measure the dielectric anisotropy in laboratory studies of liquid crystal polymer films is described. The installation operates on the principle of a balanced alternating current (AC) bridge, allowing the application of a direct external current (bias) to the liquid crystal cell. The internal resistance of the direct current (DC) source, which affects the equilibrium condition of the bridge, is compensated. The frequency of the AC current feeding the bridge and the offset voltage of the cell is regulated within a wide range, which makes it possible to study various functional dependences of the dielectric parameters of liquid crystals and their modifiers.Introduction

Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode

Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.

Formation of Amorphous Materials Causes Parallel Brittle-viscous Flow of Crustal Rocks

<p>Relative motion of tectonic plates is accommodated along lithosphere-scale shear zones. The strength and stability of these shear zones control large scale tectonics and the location of earthquakes. It is widely accepted that rocks undergo a “brittle-to-viscous” transition as depth increases, however the details of how this transition is achieved are a topic of active research.</p><p>To study this transition in polymineralic rocks, we sheared bi-mineralic aggregates with varying ratio (30:70, 50:50 & 70:30 vol%) of quartz (Qtz) and potassium feldspar (Kfs) at temperature, <em>T </em>= 750˚C and pressure, <em>Pc </em>= 800 MPa under either constant displacement rate or constant load boundary conditions. Under constant displacement rate, samples reach high shear stress (τ ≈ 0.4 - 1 GPa, depending on mineral ratio) and then weaken. Under constant load, the strain rate shows low sensitivity to stress below shear stresses of 400 MPa, followed by a high stress sensitivity at higher stresses irrespective of mineral ratio (stress exponent, <em>n</em> = 9 - 13, assuming that<em> strain rate ∝ stress <sup>n</sup>)</em>.</p><p>Strain is localized along "slip zones" in a C and C’ orientation in all experiments irrespective of mineral ratio. These zones delimit larger cataclastic lenses, which develop a weak foliation. Quartz in the lenses shows pervasive Dauphiné twinning that leads to clear CPO patterns in the {r} and {z} rhomb planes. The {r} maxima (and {z} minima) are sub-parallel to the loading direction and rotate synthetically with increasing finite strain suggesting that they track the local σ<sub>1</sub> direction. The material in the slip zones shows extreme grain size reduction, no porosity and flow features. At peak strength, 1-2 vol% of the sample is composed of slip zones that are straight and short. With increasing strain, the slip zones become anastomosing and branching and occupy up to 9 vol%; this development is concomitant with strain-weakening of the sample. The best developed slip zones are observed in samples with high Kfs contents (70 & 50 vol%). We infer that the material in the slip zones is formed of nanocrystalline to partly amorphous material (PAM) that is predominantly derived from Kfs. By compiling literature data on PAM development, we show that the volume of PAM increases with increasing homologous temperature and work done (stress x strain per unit volume) on the sample in rocks containing feldspars.</p><p>Our results suggest that strain localization leads to microstructural transformation of the rocks from a crystalline solid to an amorphous, fluid-like material in the slip zones. This material forms over a broad range of <em>P-T</em>, stress and strain conditions suggesting that it should form readily in nature. The measured rheological response is a combination of viscous flow in the slip zones and cataclastic flow in coarser-grained lenses and can be modeled as a frictional slider coupled in parallel with a viscous dashpot.</p>

Functional Stability: An Experimental Knee Joint Cadaveric Study on Collateral Ligaments Tension

Introduction Applying proper tension to ligaments during Total-Knee-Arthroplasty surgery is fundamental for optimal implant performance: low tensions lead to joint instability, over-tensioning to pain and stiffness. “Functional stability” must then be defined and achieved. An experimental cadaveric activity was performed to measure the minimum tension required to achieve this stability. Methods Ten knee specimens were investigated; femur and tibia were clamped to a loading-frame; constant displacement rate was applied and resulting tension force was measured. Joint stability was determined as the slope change in the force/displacement curve, representing the ligaments’ elastic-region activation; the tension required to reach functional stability is the span between ligaments toe-region and this point. Intact, ACL(Anterior-Cruciate-Ligament)-resected and ACL&PCL(Posterior-Cruciate-Ligament)-resected knees were tested. Different flexion angles were tested. Results Results demonstrated an overall tension of 40-50N to be enough to reach stability in intact knees. Similar values are sufficient in ACL-resected knees; higher tension is required (up to 60N) after ACL&PCL resection; slightly higher values were found for 60° flexion. Results agree with other experimental studies, showing that the tensions required to stabilize the joint are lower than the ones currently applied via surgical tensioners. Conclusion To reach functional stability, surgeons should consider such results intraoperatively to avoid ligament laxity or over-tensioning.

Molecular Dynamics Studies of Hydrogen Effect on Intergranular Fracture in α-Iron

In the current study, the effect of hydrogen atoms on the intergranular failure of α-iron is examined by a molecular dynamics (MD) simulation. The effect of hydrogen embrittlement on the grain boundary (GB) is investigated by diffusing hydrogen atoms into the grain boundaries using a bicrystal body-centered cubic (BCC) model and then deforming the model with a uniaxial tension. The Debye Waller factors are applied to illustrate the volume change of GBs, and the simulation results suggest that the trapped hydrogen atoms in GBs can therefore increase the excess volume of GBs, thus enhancing intergranular failure. When a constant displacement loading is applied to the bicrystal model, the increased strain energy can barely be released via dislocation emission when H is present. The hydrogen pinning effect occurs in the current dislocation slip system, <111>{112}. The hydrogen atoms facilitate cracking via a decrease of the free surface energy and enhance the phase transition via an increase in the local pressure. Hence, the failure mechanism is prone to intergranular failure so as to release excessive pressure and energy near GBs. This study provides a mechanistic framework of intergranular failure, and a theoretical model is then developed to predict the intergranular cracking rate.

Related Rule Study of Subcritical Crack Growth and Threshold Values in Transversely Isotropic Slates

Elastic parameters and the subcritical crack growth of different bedding angle slate specimens were studied using uniaxial compression testing and the double torsion constant displacement load relaxation method using SANS and MTS Insight machines. To study the relations of the mode-I stress intensity factor K I versus the subcritical crack growth velocity V , the fracture toughness K I C , the stagnation speed, and the threshold values, the double torsion constant displacement load relaxation method was carried out. The related rules between the bedding angles (β) and the uniaxial compressive strength, fracture toughness, and threshold values were investigated. Experimental results show that the uniaxial compression, the fracture toughness, and the threshold value curves move to the bottom then increase with the increase of the β angle. In addition, its fracture toughness is minimal when the β angle of the slates is 45°, and crack initiation and crack propagation are generated under load, which can lead to the failure of the slate. lg K I - lg V relations of transversely isotropic slates measured by this method are in accordance with linear rules, which is in good agreement with the Charles theory. The range of K 0 / K I C for these different bedding angle slates is from 0.511 to 0.789. The test results would provide the basis for studying seepage and time-dependency of rock engineering stability.

Impact of Government Security on Pastoralist Pupils’ Participation in Regular and Mobile Primary Schools in Turkana County, Kenya

One of the major hindrances to education access in arid and semi-arid lands is lack of security. In recognition of this challenges, the Kenya government has tried to provide interventions through mobile schools and security services in places like Turkana County. Therefore, the research explored the effectiveness of security interventions on pastoralists’ children's participation in regular and mobile primary schooling in Turkana County, Kenya. The research used both descriptive survey and mixed methods. It relied on a sample of 75 school heads, 225 instructors, 375 learners, 85 parents, 3 education officers (1 from every sub-county), 1 County Director of Education and 1 County Commissioner. For data collation, the research used questionnaires, interview schedules and focus groups. Quantitative data was coded and entered into the Statistical Package for Social Science (SPSS) program. To test for effectiveness of security intervention, regression (inferential statistics) was calculated. The analysed data was presented using tables. Qualitative data from interviews and focused groups was analysed and presented thematically. Hypotheses were analysed using regression analysis. Single and multiple regression were calculated to gauge the relative effect of the security interventions on pupils' participation in schooling. The results of the inquiry showed that insecurity around schools in Turkana County was rampant and some schools had suffered attacks. Incidences of insecurity had led to many pupils not attending school thus making many pastoralists pupils not participate in school in the County. Based on these findings, it is evident that insecurity also contributes to constant displacement which makes it difficult for children to pursue educational opportunities. Therefore, it was recommended that all schools should be provided with security officers, including the KPR comprised of the locals who understand the terrain and the people in the security.