Abstract in English:Abstract Interface strength is considered as one of the most influential factors in the long-term durability of the replaced joint in cemented total hip replacement. Several researchers have suggested that the damage initiation in a replaced joint is a mechanical phenomenon primarily taking place in the vicinity of cement-prosthesis interface. In this study, the fracture behavior of a crack at the interface of cement-prosthesis was investigated both experimentally and theoretically under static loading conditions. The finite element method, and then the maximum tangential stress (MTS) and the generalized MTS (GMTS) criteria were used for theoretical study of interface fracture. Some experiments were also carried out to investigate the effect of cement mixing methods (hand mixing and vacuum mixing) on crack growth pattern. The results showed that the vacuum-mixed cement led to self-similar crack growth along the cement-prosthesis interface, while the crack kinked into the cement in the samples prepared by hand-mixed cement. Then some experiments were performed to verify the theoretical results obtained for mixed mode fracture angles in the samples prepared by hand-mixed cement. The sandwich Brazilian disk model was used in both finite element and experimental approaches to simulate the cement-prosthesis interface. The experimental results were found to be in good agreement with those predicted by the GMTS criterion.
Abstract in English:Abstract In this paper, at first the attenuation of Lamb waves in three-layer adhesive joints, including two elastic plates bonded together by a viscoelastic adhesive layer, is investigated using Global matrix method and then suitable incidence angle is theoretically calculated to generate low-attenuation Lamb waves using angle beam transducer. Theoretical boundary value problem in three-layer adhesive joints with perfect bond and traction-free boundary conditions on their outer surfaces is solved to find a combination of frequencies and modes with lowest attenuation. Characteristic equation is derived by applying continuity and boundary conditions in three-layer joints using Global matrix method. Phase velocity dispersion curves and attenuation intensity plot in high and low frequencies are obtained with numerical solution of this equation by a computer code for a three-layer joint, including an aluminum repair patch bonded to the aircraft aluminum skin by a layer of viscoelastic epoxy adhesive. To validate the numerical solution results of characteristic equation, wave structure curves are plotted for a special mode in two different frequencies in the adhesive joint. Also, transducer incidence angle is calculated in terms of frequency for different modes using theoretical method to generate Lamb wave modes with low attenuation level by angle beam transducer. These modes are recognizable by transducers in inspections with Lamb waves because of low attenuation level.
Abstract in English:Abstract This paper presents an extension of BATTINI´s formulation to two-dimensional analysis of nonlinear dynamical problems. The main interest of the co-rotational approach is to separate rigid body motions from pure deformations at the local element level through co-rotated framework. Employing co-rotated framework to derive both internal and inertial terms is the objective of the formulation presented in this study. Numerical examples are presented to illustrate the ability of the proposed co-rotational formulation.
Abstract in English:Abstract Despite the availability of large number of empirical and semi-empirical models, the problem of penetration depth prediction for concrete targets has remained inconclusive partly due to the complexity of the phenomenon involved and partly because of the limitations of the statistical regression employed. Conventional statistical analysis is now being replaced in many fields by the alternative approach of neural networks. Neural networks have advantages over statistical models like their data-driven nature, model-free form of predictions, and tolerance to data errors. The objective of this study is to reanalyze the data for the prediction of penetration depth by employing the technique of neural networks with a view towards seeing if better predictions are possible. The data used in the analysis pertains to the ogive-nose steel projectiles on concrete targets and the neural network models result in very low errors and high correlation coefficients as compared to the regression based models.
Abstract in English:Abstract The protective capability of the Kevlar fibre-reinforced rubber composite armour (KFRRCA) at different obliquities is studied using depth-of-penetration experiments method against a 56 mm-diameter standard-shaped charge. Efficiency factors are calculated to evaluate the protection capability of the KFRRCA at different obliquities. Meanwhile, an X-ray experiment is used to observe the deformation, fracture, and scatter of the shaped-charge jet as it penetrates the composite armour. Finally, scanning electron microscopy (SEM) is used to analyse the effect of the Kevlar fibre-reinforced rubber for the composite armour to resist jet penetration. The results showed that the KFEECA can be used as additional armour, because it has excellent protection capability, and it can disturb the stability of the middle part of the shaped charge jet (SCJ) obviously especially when the armour at 30°and 68° obliquities.
Abstract in English:Abstract This work presents a numerical model to simulate the failure behavior of slender reinforced concrete columns subjected to eccentric compression loads. Due to the significant influence of the lateral displacements on the loading state provided by an eccentric load, geometric nonlinearity is considered. The responses of the concrete in tension and compression are described by two scalar damage variables that reduce, respectively, the positive and negative effective stress tensors, which lead to two different damage surfaces that control the dimension of the elastic domain. To describe the behavior of the reinforcements, truss finite elements with elastoplastic material model are employed. Interaction between the steel bars and concrete is modeled through the use of interface finite elements with high aspect ratio and a damage model designed to describe the bond-slip behavior. The results showed that the numerical model is able to represent the nonlinear behavior of slender concrete columns with good accuracy, taking into account: formation of cracks steel yielding crushing of the concrete in the compressive region and interaction between rebars and concrete.
Abstract in English:Abstract Deflection is an important design parameter for structures subjected to service load. This paper provides an explicit expression for effective moment of inertia considering cracking, for uniformly distributed loaded reinforced concrete (RC) beams. The proposed explicit expression can be used for rapid prediction of short-term deflection at service load. The explicit expression has been obtained from the trained neural network considering concrete cracking, tension stiffening and entire practical range of reinforcement. Three significant structural parameters have been identified that govern the change in effective moment of inertia and therefore deflection. These three parameters are chosen as inputs to train neural network. The training data sets for neural network are generated using finite element software ABAQUS. The explicit expression has been validated for a number of simply supported and continuous beams and it is shown that the predicted deflections have reasonable accuracy for practical purpose. A sensitivity analysis has been performed, which indicates substantial dependence of effective moment of inertia on the selected input parameters.
Abstract in English:Abstract A numerical method is developed for the buckling analysis of moderately thick plate with different boundary conditions. The procedure use the finite strip method in conjunction with the refined plate theory (RPT). Various refined shear displacement models are employed and compared with each other. These models account for parabolic, hyperbolic, exponential, and sinusoidal distributions of transverse shear stress, and they satisfy the condition of no transverse shear stress at the top and bottom surfaces of the plates without using a shear correction factor. The number of independent unknown functions involved here is only four, as compared to five functions in the shear deformation theories of Mindlin and Reissner. The numerical results of present theory are compared with the results of the first-order and the other higher-order theories reported in the literature. From the obtained results, it can be concluded that the present study predicts the behavior of rectangular plates with good accuracy.
Abstract in English:Abstract This paper presents a finite element formulation for the analysis of two dimensional reinforced elastic solids developing both small and large deformations without increasing the number of degrees of freedom. Fibers are spread inside the domain without the necessity of node coincidence. Contact stress analysis is carried out for both straight and curved elements via two different strategies. The first employs consistent differential relations and the second adopts a simple average calculation. The development of all equations is described along the paper. Numerical examples are employed to demonstrate the behavior of the proposed methodology and to compare the contact stress results for both calculations.
Abstract in English:Abstract This paper aims to set up the ball systematic slipping model and analyze the slipping characteristics caused by different factors for a ball screw operating at high speeds. To investigate the ball screw slipping mechanism, transformed coordinate system should be established firstly. Then it is used to set up mathematical modeling for the ball slipping caused by the three main reasons and the speed of slipping can be calculated. Later, the influence of the contact angle, helix angle and screw diameter for ball screw slipping will be analyzed according to the ball slipping model and slipping speeds equation and the slipping analysis will be obtained. Finally, curve of slipping analysis and that of mechanical efficiency of the ball screw analysis by Lin are compared, which will indirectly verify the correctness of the slipping model. The slipping model and the curve of slipping analysis established in this paper will provide theory basis for reducing slipping and improving the mechanical efficiency of a ball screw operating at high speeds.