Uniaxial Tensile Strength Research Articles

On the application of a lattice method to configurational and fracture mechanics

This study elucidates the concept of material forces at the tip of an evolving crack in brittle homogeneous materials by using a numerical lattice approach. A 2D lattice with an erosion algorithm is employed in the context of LEFM to investigate two well-known classic fracture problems in Mode I, i.e., a center-cracked rectangular panel with finite dimensions and a three-point bending beam with a notch. Validated by the well-developed analytical solutions for these two configurations, the lattice is used to derive crack tip driving forces in the direction of crack propagation based on the change of global stiffness matrix of the mesh before and after crack growth without any stress calculations, and to obtain the material forces opposing the tip motion utilizing the Eshelby-stress tensor and local force balance law in cracked bodies. Comparing these two distinct approaches, it is observed that the discrete material forces at the crack tip are closely equal to the tip driving forces, but with different signs, confirming that the lattice approach approximates the values of crack tip material forces using Eshelby-stress distributions. Moreover, satisfying C1 continuity by including rotational displacements for the Euler–Bernoulli based frame struts, there is no need for the lattice model to update interior computational point positions in the mesh to eliminate spurious material forces away from the tip, a complication observed in Finite Element formulations. The discrete material forces are then characterized for the two problems by only three material parameters, i.e., Young's modulus, uniaxial tensile strength, and the configurational characteristic width or crack band. After conducting a regression analysis on the material forces with respect to different tensile strength values, a parabolic relationship emerges between the material forces and tensile strengths. This feature is employed to extract the crack band width values by the lattice approach, which are explicitly used to obtain the crack tip material forces of the two classic problems. Being simple in terms of constitutive formulation, failure criterion, and capable of obtaining the configurational characteristic width or crack band for different boundary value problems for brittle homogeneous isotropic materials, the numerical lattice formulation sheds light on the important concept of material force in Configurational and Fracture Mechanics.

Predicting rock burst hazard with incomplete data using Bayesian networks

Rock burst is a dynamic process of sudden, rapid and violent release of elastic energy accumulated in rock and coal masses during underground activities. It can lead to casualties, to failure and deformation of the supporting structures, and to damage of the equipment on site; hence its prediction is of great importance. This paper presents a novel application of Bayesian networks (BNs) to predict rock burst. Five parameters —Buried depth of the tunnel (H), Maximum tangential stress of surrounding rock (MTS) (σθ), Uniaxial tensile strength of rock (UTS) (σt), Uniaxial compressive strength of rock (UCS) (σc) and Elastic energy index (Wet)— are adopted to construct the BN with the Tree augmented Naïve Bayes classifier structure. The Expectation Maximization algorithm is employed to learn from a data set of 135 rock burst case histories, whereas the belief updating is carried out by the Junction Tree algorithm. Finally, the model is validated with 8-fold cross-validation and with another new group of incomplete case histories that had not been employed during training of the BN. Results suggest that the error rate of the proposed BN is the lowest among the traditional criteria with capability to deal with incomplete data. In addition, a sensitivity analysis shows that MTS is the most influential parameter, which could be a guidance on the rock burst prediction in the future.

Improving the simulation of landfast ice by combining tensile strength and a parameterization for grounded ridges

AbstractIn some coastal regions of the Arctic Ocean, grounded ice ridges contribute to stabilizing and maintaining a landfast ice cover. Recently, a grounding scheme representing this effect on sea ice dynamics was introduced and tested in a viscous‐plastic sea ice model. This grounding scheme, based on a basal stress parameterization, improves the simulation of landfast ice in many regions such as in the East Siberian Sea, the Laptev Sea, and along the coast of Alaska. Nevertheless, in some regions like the Kara Sea, the area of landfast ice is systematically underestimated. This indicates that another mechanism such as ice arching is at play for maintaining the ice cover fast. To address this problem, the combination of the basal stress parameterization and tensile strength is investigated using a 0.25° Pan‐Arctic CICE‐NEMO configuration. Both uniaxial and isotropic tensile strengths notably improve the simulation of landfast ice in the Kara Sea but also in the Laptev Sea. However, the simulated landfast ice season for the Kara Sea is too short compared to observations. This is especially obvious for the onset of the landfast ice season which systematically occurs later in the model and with a slower build up. This suggests that improvements to the sea ice thermodynamics could reduce these discrepancies with the data.

Deformation and fracture in graphene with divacancies of the 555–777 type

The deformation and fracture of graphene sheets containing 555–777 defects have been investigated by molecular dynamics simulations. Each such defect is a divacancy forming a localized configuration of three pentagonal and three septangular cells of carbon atoms in a hexagonal graphene lattice. An emphasis is made on the influence of 555–777 defects in graphene on its mechanical characteristics (stress–strain curve, uniaxial tensile strength, and maximum elastic strain).

Relationship between tensile Young’s modulus and strength of fly ash high strength concrete at early age

This paper presents an experimental investigation on the tensile properties of hardening fly ash HSC at different ages and quantifies the uniaxial tensile strength and tensile Young’s modulus of fly ash HSC. Test results showed that: (1) the axial compressive strength of hardening fly ash HSC at early age was lower than cubic compressive strength at the identical age; (2) the uniaxial tensile strength of hardening fly ash HSC at early age was lower than splitting tensile strength at the identical age; (3) the tensile Young’s modulus of the hardening fly ash HSC at early age was approximately 1.06–2.02times of the compressive Young’s modulus at the identical age; (4) the tensile Young’s modulus of hardening fly ash HSC at early age increased with the increase of uniaxial tensile strength. The prediction models showed good accuracy with the experimental results.

Multiscale homogenization for nearly periodic structures

In this paper, we propose a new numerical multiscale homogenization method for nearly periodic structures, where perfect periodicity is disturbed due to unintended geometrical imperfections. Geometrical imperfection is introduced as an input to the calculation, and the calculation is always done using the idealized perfect geometry. This has a distinct advantage in numerical calculations where the same mesh can be used for a series of imperfect geometries. The method is implemented using commercially available finite element code ABAQUS. The proposed method is validated by comparing the results to those of a conventional calculation. The results demonstrate that the proposed method can accurately capture the stress distribution when the amplitude of the imperfection is small. Finally, the method is applied to the analysis of the effect of fiber waviness on the mechanical properties of a low cost CFRP. The simulation results reveal that the fiber waviness has little effect on the macroscopic stiffness, but significantly degrades the uniaxial tensile strength.

Electrospun elastic acrylonitrile butadiene copolymer fibers

Abstract Nitrile rubber (NBR) is an unsaturated copolymer of acrylonitrile and butadiene. Due to its excellent oil-resistance, NBR products are widely used such as in the automotive and aerospace industries. This paper discusses the fabrication of acrylonitrile butadiene copolymer fibers via electrospinning. A transition from electrospray to electrospinning mechanism was observed and investigated by varying the solution composition. Diameter distributions and average diameters of the electrospun fibers from solutions of various copolymer weight concentrations were determined and compared. Water contact angles of both raw material and electrospun fiber mats were measured. Results indicated that the copolymer material was intrinsically hydrophobic, and the electrospun fiber mats showed higher hydrophobicity due to increased surface roughness. These properties were found to be strongly dependent upon the solution concentration. As the solution concentration increased, average fiber diameter increased and water contact angle decreased. Fiber mats of three different basis weights prepared from solutions of 5% copolymer concentration were prepared. Some of the mats were rolled into yarns. The flat mats and yarns were tested for uniaxial tensile strength to obtain data on their stress-strain performance. Comparison the stress-stain data for the flat mats and yarns showed similar properties. Evaluations of the performances of the fiber mats and yarns accounted for the fiber mat basis weights (mass of fibers per area of mat) and mat porosities through application of an idealized parallel fiber mat model. For small strains the stress-strain curves followed similar paths, but at large strains the paths deviated as fiber-fiber bonds slipped or fibers ruptured. For different basis weights, maximum tensile strengths of the flat mats and yarns were close, but slightly varied due to the more complex fiber structures compared to the idealized model. The yarns held larger stresses before rupture and possessed higher maximum tensile strengths than the flat mats attributed to the lower porosity of the yarns and additional bonds between fiber layers that are absent in the flat mats.

Simulation and experiment of soft-tissue deformation in prostate brachytherapy.

Soft-tissue deformation is one of the major reasons for the inaccurate positioning of percutaneous needle insertion process. In this article, simulations and experiments of the needle insertion soft-tissue process are both applied to study soft-tissue deformation. A needle deflection model based on the mechanics is used to calculate the needle deflection during the interaction process. The obtained needle deflection data are applied into finite element analysis process as the system input. The uniaxial tensile strength tests, compression tests, and static indentation experiments are used to obtain the soft-tissue parameters and choose the best strain-energy function to model in the simulation. Magnetic resonance imaging is used to reconstruct the prostate, establishing both prostate three-dimensional finite element model and artificial prostate model. The needle-soft tissue interaction simulation results are compared with those of the needle insertion experiment. The displacement data of the mark point in the experiment are comparable to the simulation results. It is concluded that, using this simulation method, the surgeon can predict the deformation of the tissue and the displacement of the target in advance.

A new approach to rock brittleness and its usability at prediction of drillability

Rock brittleness is one of the most important issues in rock drilling and cutting. The relations between drillability and brittleness will assist engineers in excavation works. The demand for representative rock parameters related to planning of underground excavations is increasing, as these parameters constitute fundamental input for obtaining the most reliable cost and time estimates. In rock cutting mechanics, the effects of the rock and brittleness on the efficiency of drilling and excavation are examined by many researchers. In this study, 41 different rock types were tested in laboratory to investigate the relations between the drilling rate index and different brittleness values. Firstly, the relations defined in literature are tested. Strength tests are made according to International Society for Rock Mechanics standards. In addition Norwegian University of Science and Technology standards are used to determine drilling rate index. Then, a new brittleness index is proposed which is the arithmetic average of uniaxial compressive strength and tensile strength. Considering the regression analysis carried out, it was seen that the proposed formula showed good correlation for these samples handled in this study. As a result of this study, a high correlation is obtained between the proposed index and drilling rate index values (R:0.84). The results are found to be at least reliable as well as other brittleness equations given in literature.

Modeling of concrete spallation with damaged viscoelasticity and retarded damage

• High strain-rate stresses by far exceed quasi-static strength as a material property. • High strain-rate stresses are maintained only for short periods followed by failure. • Energy dissipation is much higher under high strain-rates compared to quasi-statics. • A model with damaged viscoelasticity and retarded damage is suitable for these effects. A proposal for a triaxial constitutive law is developed to model strain-rate sensitivity of quasi-brittle materials like concrete. It is based on a standard isotropic quasi-static damage law which is extended with damaged viscoelasticity and retarded damage to consider the physical mechanisms of strain-rate sensitivity. Dynamic uniaxial compressive and tensile stress–strain relations are derived as a special case. The material parameters for strain-rate sensitivity are calibrated to reproduce experimental increase factors for uniaxial compressive and tensile strength. A fully triaxial setup is used for modeling of stress wave propagation in cylindrical concrete specimens with spallation of fragments as part of modified Split–Hopkinson–Bar configurations. The validation of the material model is performed with the comparison of computed and experimental pull-back velocities of the specimen’s free end. It is shown that the validation is only possible considering both damaged viscoelasticity and retarded damage in the material model. The numerical computations yield stresses far beyond quasi-static strength, but high stresses are maintained only for short periods before material destruction. Furthermore, the computations show that the amount of dissipated energy due to dynamic spallation is much higher compared to quasi-static crack energy.

STUDY OF THE TARGETING ERROR FOR PERCUTANEOUS NEEDLE INSERTION INTO SOFT PHANTOM MATERIAL

Percutaneous needle insertion is widely used in minimally invasive procedures, in which the flexible needle is steered to reach a specific target inside the human body. The targeting error is due to a combination of flexible needle deflection and target displacement in soft tissue and only a very limited number of studies have focused on both two factors. This paper presents a targeting error calculation method which incorporates an energy-based needle deflection model into a soft tissue finite-element (FE) model. The needle insertion process is discretized into several increments on the basis of the quasi-static method. Needle deflection in each step is obtained by the needle-soft tissue interaction model which is applied into the FE model as the displacement input. A 2D-planar FE model is used to model the target displacement by imposing needle distribution forces and needle deflection at different steps on the appointed reference nodes. The soft tissue is modeled as a non-linear hyperelastic material with geometrical non-linearity. Uniaxial tensile strength tests are utilized to determine the soft tissue parameters. Needle targeting experiments are conducted to validate the simulation results. Results show that the proposed method can predict the needle targeting errors while the averaged prediction error stays below 0.4[Formula: see text]mm. At last, we conduct different experiments to compensate the obtained targeting error and thus, reaching preferable effects.

Study of rock splitting failure based on griffith strength theory

It is argued here that often-cited result that the Griffith theory leads to a uniaxial compressive strength that is twelve times greater than uniaxial tensile strength is erroneous. A uniaxial compressive load can lead to the maximum tensile stress at longitudinal crack tips when the ratio of minor axis to major axis of the Griffith's crack is finitely small, but it is smaller than the maximum tensile stress of inclined crack under the same pressure. According to the characteristics of the maximum tensile stress distribution on the perimeter of the Griffith's crack, and the splitting characteristics of rock failure process, the conditions of axial splitting failure of rock specimens are proposed, and the mechanism of splitting fracturing of rock specimens is clarified as well.

Upper-bound and lower-bound solutions for the axisymmetric compression of a concrete plug

Deep radioactive waste deposits require specific solutions to close underground galleries and avoid any radioactive migration in the environment. One investigated solution consists of a swelling clay plug that induces a swelling pressure of approximately 7MPa on the walls of the galleries. The clay plug is confined by a concrete plug to maintain and drive the swelling pressure towards the walls of the galleries. The concrete plug must therefore be designed to endure such a pressure. This paper addresses the mechanical strength of a cylindrical concrete plug with a ring-shaped tooth, a free face and a uniform compressive stress over the other face. Two experimental tests over 1/43 reduced samples are first performed and show two collapse mechanisms: dome collapse and tooth-shear collapse. Upper- and lower-bound solutions are investigated based on the Mohr–Coulomb criterion from nonlinear criteria of concrete. The choices of parameters for the friction angle (φ) and cohesion (C) are discussed in relation to the uniaxial compressive and tensile strength of the concrete and the magnitude of the stresses in the model. The results of the simplified analytical, numerical and experimental approaches are then compared, with good agreement found between the approaches.

Electrospun poly(L-lactide-co-caprolactone) blended with fibrinogen as an artificial tendon for achilles tendon repair

Event Abstract Back to Event Electrospun poly(L-lactide-co-caprolactone) blended with fibrinogen as an artificial tendon for achilles tendon repair Hongbing He1, 2* and Xujun Wu2, 3* 1 Fudan University, Institute of Peripheral Vascular Surgery, China 2 P&P Biotech Co., Ltd, R&D, China 3 Shanghai Jiaotong University, School of Materials Science and Engineering, China Introduction: Achilles tendon rupture is the most common type of sports-related injury. Incomplete healing of such tendon injuries can result in marked dysfunction and disability. The gold standard clinical treatment is surgical repair using an autograft. However, autograft repair has several disadvantages including limited availability of autograft tissues, and donor site complications. Implantation of a bioresorbable prosthesis into a tendon defect may be a useful alternative method to facilitate [AP1] the repair and regeneration of tendon. Methods: The aim of the present study was to determine the effects of electrospun poly(L-lactide-co-caprolactone) blended with fibrinogen as an artificial tendon on the healing of canine Achilles tendon defects. An Achilles tendon defect (Figure 1) was created by laterally resecting 2 cm of the Achilles tendons from 24 beagle dogs that were randomly assigned to either the experimental or control group. The experimental group was repaired with the electrospun poly(L-lactide-co-caprolactone) blended with fibrinogen artificial tendon, while the control group was repaired with an autologous tendon graft. At 14, 30, 90, and 180 days after implantation, the tendons were dissected and examined grossly, and using histology and immunohistochemistry. In addition, the micromorphology, uniaxial longitudinal tensile strength, and biochemical properties were also evaluated. Results: The tendon diameters, peri-tendinous adhesion, and inflammation scores for the experimental and control groups were compared over the course of the study. The fibrillogenesis, diameter, density, and alignment of the collagen fibrils, and the hydroxyproline content, maximum load, and modulus of elasticity were significantly improved with the electrospun poly(L-lactide-co-caprolactone) blended with fibrinogen artificial tendon treatment compared with the autologous tendon treatment. Conclusion: The electrospun poly(L-lactide-co-caprolactone) blended with fibrinogen artificial tendon was biocompatible and showed appropriate biomechanical performance, suggesting that it is a suitable candidate for future clinical use. Figure 1. Achilles tendon defect. (A) Creation of a 2 cm defect, and (B) the defect after implantation of an Achilles tendon prosthesis. Keywords: Regenerative Medicine, Scaffold, Smart material, Biodegradable material Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Regenerative medicine: biomaterials for control of tissue induction Citation: He H and Wu X (2016). Electrospun poly(L-lactide-co-caprolactone) blended with fibrinogen as an artificial tendon for achilles tendon repair. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.01567 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. * Correspondence: Dr. Hongbing He, Fudan University, Institute of Peripheral Vascular Surgery, Shanghai, China, Email1 Dr. Xujun Wu, Shanghai Jiaotong University, School of Materials Science and Engineering, Shanghai, China, wxj@shsongli.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Hongbing He Xujun Wu Google Hongbing He Xujun Wu Google Scholar Hongbing He Xujun Wu PubMed Hongbing He Xujun Wu Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Correlation of Mineralogical and Textural Characteristics with Engineering Properties of Granitic Rock from Hulu Langat, Selangor

In this study, the study area was at Hulu Langat in order to study the relationship between mineralogical characteristics and mechanical properties of rock. The type of rock found is granitic rocks. In order to study and determine the mineralogical characteristics of the rocks, thin section of rocks were prepared. Some minerals that abundance was observed in the rocks are quartz, feldspar, mica, clay-rich minerals and accessory minerals. The same rock samples that were collected from 10 tunnel distances then tested to determine point load strength index, uniaxial compressive strength and tensile strength. The relationships between these properties and mineralogical characteristics are described by simple regression analyses.

Macro/Microtesting and Damage and Degradation of Sandstones under Dry-Wet Cycles

In terms of the degradation of mechanical parameters of rock mass in the hydrofluctuation belt of a reservoir bank slope arising from rainfall and the reservoir level fluctuation, the moderately weathered sandstone in a side slope of the Three Gorges Reservoir Region is selected as a research object to carry out “drying-saturation-drying” tests for disks with two thicknesses (h=25 mm,h=50 mm) in different cycles; a spiral CT machine, an ultrasonic velocity meter, and a light Schmidt hammer are utilzed to conduct nondestructive testing on dry-wet cycles; through the Brazilian splitting test, the uniaxial tensile strength of “dry” and “saturated” sandstones under different dry-wet cycles is obtained. The research shows that, with the increase of the dry-wet circles (n), the longitudinal wave velocity and the rebound strength of sandstones are linearly decreased withn; the uniaxial tensile strength of sandstones and the mean CT number of cross sections are logarithmically decreased withn; the fitting equation of macro/micromechanical parameters and dry-wet cycles (n) of sandstones is raised, which is provided as a reference basis for the weathering process of sandstones under dry-wet cycles.

Study on Tensile Damage Constitutive Model for Multiscale Polypropylene Fiber Concrete

Polypropylene fibers perform well in roughness enhancement and corrosion resistance. They can dissipate energy when cracks occur in concrete. Furthermore, they can improve the concrete tensile properties by synergistic work with it. To study the tensile properties of the multiscale polypropylene concrete, uniaxial tensile strength of 18 fiber reinforced and 3 plain concrete specimens was experimentally tested using the paste steel method. The test results indicate that both the strength and the peak strain can be substantially improved. Based on the results, a tensile damage constitutive model was proposed and implemented into FLAC3D for numerical experimentation. The numerical results are consistent with the experimental observations in general and some discrepancies are discussed.

Electrospinning with benign solvents: feasibility study and versatile use of poly(epsilon-caprolactone) fibers

Event Abstract Back to Event Electrospinning with benign solvents: feasibility study and versatile use of poly(epsilon-caprolactone) fibers Liliana Liverani1 and Aldo R. Boccaccini1 1 University Erlangen-Nuremberg, Institute of Biomaterials, Department for Materials Science and Engineering, Germany Introduction: The electrospinning is a well-established technique widely used for the fabrication of fibrous mats for tissue engineering applications. A huge number and varieties of polymers could be processed by the electrospinning technique, but often the use of organic toxic solvents is required. Recently, the introduction of the “Green Electrospinning” concept[1] and the awareness about the disadvantages related to the use of toxic solvents have raised the interest in the use of less or not toxic solvents (benign solvents) for electrospinning[2]. In this framework, the aim of the present work has been the optimization of the electrospinning of poly(epsilon-caprolactone) (PCL) using acetic acid as solvent. The suitability of this solvent has been tested also for the fabrication of patterned mats and for the fabrication of composite electrospun mats, obtained with the addition of bioactive glass (BG) particles. Materials and Methods: Electrospun mats were obtained starting from a 20% w/v PCL (80kDa, Sigma Aldrich) solution in acetic acid (VWR). For the composite mats BG particles (Schott Vitryxx®, size 2μm) have been homogeneously dispersed (20wt% respect to PCL) in the polymer solution before electrospinning. For the electrospinning process the solution was fed with a flow rate of 0.4 mL/h, the applied voltage was 15kV and the needle-target distance was 11cm. Samples morphology was assessed by SEM observations and ATR-FTIR analysis was used for the assessment of the influence of the solvent in the obtained mats chemical composition and for the evaluation of the presence of BG inside the sample. The mechanical characterization of selected fibrous mats was performed by uniaxial tensile strength test. Results and Discussion: SEM micrographs showed an homogeneous beads-free fibrous structure, as reported in figure 1A, having an average fiber diameter of 1.2 ±0.1μm. Figure 1: SEM micrographs of electrospun pure PCL random oriented mats (A), electrospun mats of PCL with BG particles (B), PCL electrospun macroporous pattern (C) and light microscope image of PCL macroporous pattern (D). ATR-FTIR analysis showed the absence of solvent in the electrospun mats, confirming the suitability of the solvent. A composite PCL-BG electrospun beads-free fibrous mat, having an average fiber diameter of 0.6±0.2μm was obtained as reported in figure 1B. A reduction in the average fiber diameter was observed possibly due to the presence of BG particles in the PCL solution. A patterned PCL electrospun mat, containing macroporosity, which could be useful to increase cell adhesion and infiltration inside the electrospun structure was successfully obtained, as showed in figures 1C and 1D, without relevant alteration in the fibers average diameter. It was also observed that when using a patterned target, the duration of the electrospinning process is crucial as it affects the macropore size, as reported in figure 2. Figure 2: Light microscope images of the electrospun PCL patterned mats, varying the time of the electrospinning process: 15 minutes (A), 30 minutes (B) and 45 minutes (C). Conclusions: Homogeneous electrospun PCL fibrous mats were obtained with a less toxic solvent. This system has been investigated also for the fabrication of electrospun composite mats and for obtaining electrospun patterned scaffolds. Further works will be focused on the use of the obtained mats as layers of complex multilayered structures with zonal incorporation of BG particles, which are intended for interface tissue engineering applications. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 657264.

Effect of Abutment Total Occlusal Convergence and Cement Type on Retention of Cement Retained Implant-Supported Restorations

The purpose of this study was to evaluate the effect of abutment total occlusal convergence (TOC), and cement type on the uniaxial tensile resistance to dislodgment of cement-retained, implant-supported metal copings. Six titanium implantabutmnets were constructed using CAD-CAM technology. Two abutments have TOC 6˚, Two abutments have TOC 8˚, and Two abutments have TOC 12˚. Identical copings were cast to fit each abutment with a loop incorporated that was engaged by the testing unit. The copings were cemented using either a resin-modified glass ionomer (RMGI) (Rely™ X U 200 Automix) or self adhesive resin cement that contained a 10 Methacryloyloxydecyl dihydrogen phosphate (MDP) monomer (Multilink® N). Each of the experimental groups had a unique combination of abutment TOC, and cement.Specimens were aged using a thermocycling unit with water between 5 and 55 degrees Celsius with 15 seconds in each bath and a 5 seconds dwell time, for 540 cycles. A universal testing machine was used to test uniaxial tensile strength. Cement was cleaned using thermal, mechanical, and physical methods, and surface finish was reestablished.This procedure was repeated to obtain different measurements for each group. Surface area for each abutment was calculated and used for the calculation of the tensile strength. One way ANOVA followed by pair-wise Newman-Keuls post-hoc tests were performed to detect significance between subgroups. Pair-wise student t-test was performed to detect interaction between variables of significant effect.P values ≤ 0.05 are considered to be statistically significant in all tests. Regardless of the cement type, totally it was found that Group A recorded the highest retentive force meanvalues followed by Group B while Group C recorded the lowest retentive force mean values. The difference between all groups was statistically significant (p 0.05). Irrespective of convergence groups, totally it was found that Multilink N group recorded statistically significant (p<0.05) higher retentive force mean values than Rely X U200 one.

Geological and Geotechnical Characterisation Using Geophysical Logs - An Example from Adriyala Longwall Project of Singareni Collieries, India

The studies conducted at Adriyala longwall block of Singareni Collieries Company Limited (SCCL) in the state of Telangana, India conclude that geophysical logs comprising electrical, density, neutron, caliper, Full Waveform Sonic (FWS) and acoustic images can provide reliable geological and geotechnical models required for longwall mining. The P wave velocities obtained from sonic logs are correlated with the lab determined strength parameters such as uniaxial compressive strength (UCS), Tensile Strength (TS) and Young’s Modulus. The empirical equations provided a means to construct UCS map of interburden strata of coal seams from sonic data. The integrated study of various maps prepared from geological and geophysical inputs provided an effective means to analyse the competency of immediate overburden and roof of Seam-I, which is considered for longwall mining.Back analysis of behaviour of strata will allow developing of predictive models and appropriate strata control strategies to be applied at Adriyala and other mines and also for multiseam extraction.