Shear deformable beams in contact with an elastic half-plane

The present work deals with the contact problem of a Timoshenko beam bonded to an elastic semi-infinite substrate under different loading conditions. The analysis allows investigating the effects induced by shear compliance of the beam, the stress intensity factors ad the beam edges as well as the singular nature of the interfacial stresses

Improved Drilling Efficiency via Enhanced Water Based Mud in the Niger Delta

This study focuses on latest advances in water based mud as a potential for the Niger Delta, its impact on drilling efficiencies and well productivity. Recently, New mud additives are been developed to enhance the rheology of water based mud to deliver the same characteristics and reliability of an oil based mud when considering the Niger Delta geology. Due to the challenges with Water Based Mud in respect to chemistry and suitability, Oil Based Mud (OBM) has become the main type of drilling fluid in deeper sections during drilling campaign in the Niger Delta. But the use of OBM as come with some challenges that has necessitated the further research and development of Water Based Mud rheology that can deliver the same results as OBM. Some of the challenges associated with the use of OBM include but not limited to high cost and management, contamination of OBM in the storage site during drilling activities, logistics complexity, environmental impact from spills and disposal, and impact on well productivity and reservoir management. In countries such as Ghana, Columbia, Oman, Mexico, Enhanced WBM mud has been used and is still being used in drilling to deep depths (8000ft-10000ft)TVD in formations with similar geology with that of the Niger Delta. Sample wells will be reviewed from one of these regions for the project and they will be used to show the evolving new technologies and techniques in WBM rheology formulation. This study is channeled to label the engineered properties of the mud, mud composition, its effects on drilling efficiency and well productivity, challenges encountered, the concept for an enhancement, added advantage in comparison to OBM, comparative cost advantage. It was discovered that Enhanced WBM has an added advantage hence leading to a reduction in pollution trends in the Niger Delta and cost effectiveness. Other advantages include addressing to an extent the challenges encountered with WBM such as (inhibition, hydration and solids control) leading to an enhanced well productivity and ultimately affects the overall cost of well delivery

The Bending Theory of Fully Nonlinear Beams

This book presents the bending theory of hyperelastic beams in the context of finite elasticity. The main difficulties in addressing this issue are due to its fully nonlinear framework, which makes no assumptions regarding the size of the deformation and displacement fields. Despite the complexity of its mathematical formulation, the inflexion problem of nonlinear beams is frequently used in practice, and has numerous applications in the industrial, mechanical and civil sectors. Adopting a semi-inverse approach, the book formulates a three-dimensional kinematic model in which the longitudinal bending is accompanied by the transversal deformation of cross-sections. The results provided by the theoretical model are subsequently compared with those of numerical and experimental analyses. The numerical analysis is based on the finite element method (FEM), whereas a test equipment prototype was designed and fabricated for the experimental analysis. The experimental data was acquired using digital image correlation (DIC) instrumentation. These two further analyses serve to confirm the hypotheses underlying the theoretical model. In the book’s closing section, the analysis is generalized to the case of variable bending moment. The governing equations then take the form of a coupled system of three equations in integral form, which can be applied to a very wide class of equilibrium problems for nonlinear beams

Modified hinged beam test on steel fabric reinforced cementitious matrix (SFRCM)

An experimental campaign based on modied hinged beam test (MhBT) set-up has been reported in the present study. The samples consist of two concrete blocks coupled by a proper hinge device and laminated with steel wire fabrics embedded in a cementitious mortar layer. Two kinds of fabrics, made of galvanized steel strands with dierent mesh spacing, have been used to reinforce the concrete joists. With the aid of a DIC monitoring system, slippage prole at the interface between the concrete support and the mortar laminate along the contact region has been assessed, together with the fracture opening. Force vs slippage at the interface has been retrieved for the sampled tested according to the MhBT set-up. With the aim to obtain predictive ultimate load design formulas, a novel classication of laminate here proposed will be argued and related to a MhBT design formula. The in influence of peel and shear stresses interaction on the ultimate strength of the system has been discussed in detail

Finite Torsion of Compressible Circular Cylinders: An Approximate Solution

This paper deals with the equilibrium problem of circular cylinders under finite torsion. A three-dimensional kinematic model, where the large twisting of the cylinder is accompanied by transverse contraction and longitudinal extension, is formulated. Following a semi-inverse approach, the displacement field prescribed by the above kinematic model contains as unknowns the longitudinal displacement, the rigid rotation and the transverse stretch of cross sections. To simplify the mathematical formulation, the transverse stretch is assumed to be constant, as it radially undergoes very low variations. This hypothesis produces some approximations in the field equations, but the equilibrium solution obtained is however characterized by a satisfactory accuracy, as shown by the comparisons performed using the numerical techniques of the Finite Element Method (FEM). A Lagrangian analysis is performed and the compressible Mooney-Rivlin law is assumed for the stored energy function. Once evaluated the Piola-Kirchhoff stresses, the unknowns are determined by imposing the equilibrium conditions and the boundary conditions. For the end base of the cylinder two different boundary conditions have been considered, according to which the longitudinal translation of this surface is allowed or prevented. Once the kinematic unknowns have been determined, explicit formulae for displacements, stretches and stresses are provided, which show the role of the geometric and constitutive parameters, as well as of the twisting angle. The results provided by the proposed solution are shown by a series of graphs. The same torsion problem has been addressed with FEM. A very good agreement was found between the results obtained with the two different analyses. Finally, the nonlinear torsion problem was linearized by introducing the hypothesis of smallness of the displacement and deformation fields. With this linearization, the classical solution for the infinitesimal torsion problem was fully retrieved

Bending device and anticlastic surface measurement of solids under large deformations and displacements

Large bending of elastic bodies gives rise to significant transverse effects. Based on a recent theoretical model in the context of finite elasticity, both the longitudinal and anticlastic curvatures in bent solids under large deformation and displacement can be accurately assessed. In order to experimentally investigate the anticlastic deformation induced by large inflexion and corroborate the theoretical predictions, a properly designed mechanical bending device is here proposed. By imposing a rotation at the ends of the sample, both the longitudinal and anticlastic curvatures are measured by DIC (digital image correlation) monitoring instrumentation and compared with the theoretical results, finding good agreement. Compact analytical formulae for assessing the radii of curvature within the thickness of the sample are provided. Conversely to existing studies of the anticlastic surface induced by infinitesimal bending, the present analysis takes into account large through-to-thickness curvature variations, whose knowledg can plays a key role for a wide class of mechanical applications

Double lap shear test on steel fabric reinforced cementitious matrix (SFRCM)

The present work deals with the experimental characterization of the mechanical behaviour of a galvanized steel fabric reinforced cementitious matrix (SFRCM).The present work deals with the experimental characterization of the mechanical bond behaviour of a galvanized steel fabric reinforced cementitious matrix (SFRCM) laminated on concrete support. The specimens, made of two low strength concrete blocks connected with a galvanized steel fabric embedded in a geo-polymeric mortar layers, have been tested according to double lap test (DLT) set-up. Six different groups of specimens have been tested varying both the lamination length and the steel fabric density. In order to reproduce the load-slip or bond-slip curves, a tri-linear bond slip model together with its parameters identification has been proposed. For some specimens, the slip profile and the slip distribution has been analysed and split into the substrate laminate slip and inner laminate layers slip. This distinction has been used as a measure of the fabric-matrix compatibility. In addition, the effect induced by the rigid blocks rotation occurred during the DLT has been argued. The DIC optical system monitoring has been used to asses both the force-slip distribution and the crack opening displacement (COD)

Large Deformations and Stability of the Two-Bar Truss Under Vertical Loads

Analytical formulations for the static equilibrium of truss structures are often based on concepts of linear elasticity. Geometric nonlinearities are taken into account, but the nonlinear constitutive behavior of the material is not considered. However, the assumption of linear elastic material is not consistent with the response of solids subjected to large deformations. In light of this, accurate models must take into account both geometric and constitutive nonlinearities. In the present work, we investigate the problem of the von Mises (or two-bar) truss subjected to a vertical load. The bars of the truss are composed of rubber so as to observe large displacements and deformations. We propose a theoretical model that is entirely developed in three-dimensional nonlinear elasticity. A compressible Mooney-Rivlin law is employed for the constitutive behavior of the rubber. Experimental tests on the von Mises truss subjected to a vertical load are carried out. Snap-through is observed and good agreement is found with the analytical predictions. Finally, a simple formulation to predict the critical Euler buckling load is presented and validated through experimental observation

Snap-through and Eulerian buckling of the bi-stable von Mises truss in nonlinear elasticity: A theoretical, numerical and experimental investigation

In this paper, the equilibrium and stability of the von Mises truss subjected to a vertical load is analyzed from theoretical, numerical and experimental points of view. The bars of the truss are composed of a rubber material, so that large deformations can be observed. The analytical model of the truss is developed in the fully nonlinear context of finite elasticity and the constitutive behavior of the rubber is modeled using a Mooney–Rivlin law. The constitutive parameters are identified by means of a genetic algorithm that fits experimental data from uniaxial tests on rubber specimens. The numerical analysis is performed through a finite element (FE) model. Differently from the analytical and FE simulations that can be found in the literature, the models presented in this work are entirely developed in three-dimensional finite elasticity. Experiments are conducted with a device that allows the rubber specimens to undergo large axial deformations. For the first time, snap-through is observed experimentally on rubber materials, showing good agreement with both theoretical and numerical results. Further insights on Eulerian buckling of the rubber specimens and its interaction with the snap-through are given. A simple formulation to determine the critical load of the truss is presented and its accuracy is validated through experimental observation. Comparisons with a linear elasticity based approach demonstrate that an accurate prediction of snap-through and Eulerian buckling requires nonlinear formulations, such as the ones proposed in this work