Harish Lambadi

Bio: Harish Lambadi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Finite element method & Homogenization (chemistry). The author has an hindex of 1, co-authored 3 publications receiving 6 citations.

Homogenization of Periodic Masonry Using Self-Consistent Scheme and Finite Element Method

Abstract: Masonry is a heterogeneous anisotropic continuum, made up of the brick and mortar arranged in a periodic manner. Obtaining the effective elastic stiffness of the masonry structures has been a challenging task. In this study, the homogenization theory for periodic media is implemented in a very generic manner to derive the anisotropic global behavior of the masonry, through rigorous application of the homogenization theory in one step and through a full three-dimensional behavior. We have considered the periodic Eshelby self-consistent method and the finite element method. Two representative unit cells that represent the microstructure of the masonry wall exactly are considered for calibration and numerical application of the theory.

Monotonic uniaxial and biaxial electromechanical experiments and modeling of uniaxial stretched polyvinylidene fluoride (PVDF)

Abstract: In this study, results from monotonic uniaxial and biaxial stretch experiments carried out on rectangular uniaxially stretched PVDF thin samples, is reported. Both mechanical and electromechanical response of the film is reported in the study. Non-linearity in mechanical and electromechanical response is observed. Anisotropy in mechanical and electromechanical response is also noted from uniaxial and biaxial experiments. Constitutive models that are developed to capture (a) nonlinearity and (b) anisotropy are reported both for a mechanical and electromechanical response.

Cyclic Electro-Mechanical Modelling of Uniaxially Stretched PVDF

Abstract: Polyvinylidene fluoride (PVDF) is a piezopolymer, and it has numerous applications as sensors and actuators. Uniaxially stretched PVDF subjected to cyclic stresses finds usage in different applications. Characterising the cyclic response of PVDF through appropriate models is important. In this study, we used two approaches to model cyclic stress with the number of cycles. In the first approach, the evolution equations are used and adopted to model the variation of the cyclic mechanical response of PVDF to track the cyclic response at each time step. In the second approach, the effect of cyclic loading on the material, in terms of entropy generation for mechanical and electrical response, is considered for modelling and this approach is adopted to model the PVDF response when subjected to cyclic loading. The mean stress and voltage variation with the number of cycles are predicted.

Contribution to the modelling of interfaces in masonry

Abstract: The aim of this study was to model the mechanical behavior of interfaces in masonry structures. In the first part, the characteristics of the materials and interfaces involved are determined experimentally. In the second part, a model based on the adhesion intensity is developed. This model can be used to describe the interfaces between mortar and full or hollow bricks and to describe the damage occuring in the mortar. The mechanical behavior predicted by this model is compared with previously obtained experimental data. The model is then tested in the case of some classical masonry structures (small walls, diagonal compression tests).

A gradient elastic homogenisation model for brick masonry

Abstract: The elastic macro-mechanical properties of masonry are investigated herein by taking into account the presence of a weakly non-local heterogeneity within a simple gradient elasticity model. Masonry has a heterogeneous structure composed of masonry units bound by mortar. The homogenisation of masonry walls is a challenging task but also a very appealing method for modelling heterogeneity effects exhibited by masonry elements. In particular, it allows the use of smeared mechanical properties, thus avoiding the need of knowing the exact unit-to-unit and joint-to-joint geometry. Current codes provide very simplified empirical expressions to estimate an isotropic elastic modulus of masonry on the basis of its strength properties. The respective equations which do not take into account the anisotropy of masonry, present high scatter resulting in ambiguous safety. The homogenization argument employed in this work is based on a simple procedure utilising Aifantis’ gradient elasticity (GradEla) model. The GradEla model is a straight-forward extension of Hooke’s law by enhancing it with the addition of the Laplacian of the classical expression of the Hookean stress multiplied by an internal length accounting for the local heterogeneity. It has been successfully used to eliminate singularities from dislocation lines and crack tips, as well as in interpreting size effects. However its use in masonry structures has not yet been explored. A first step in this direction is attempted in this paper with emphasis on obtaining practical easy-to-use results rather than exhausting all other possibilities and complexities encountered in GradEla and its generalisation, as well as in more involved homogenisation procedures. In our analysis uniform vertical, horizontal and shear loads are assumed to act on the boundaries of the representative volume/surface element. The components of masonry are assumed to follow a gradient elastic stress distribution resulting in a gradient elastic homogenised model (GREHM). GREHM comprises a set of closed-form concise equations which estimate the elastic moduli in the longitudinal and transverse directions, the shear modulus and the Poisson’s ratio. The aforementioned orthotropic material properties are verified using experimental results and also, compared to other homogenisation models. The validation shows that the proposed equations can effectively estimate with considerable precision the elastic properties of masonry walls. To illustrate the resulting estimation of the orthotropic elastic properties, normalised graphs are provided.

Three-dimensional elastic properties of masonry by mechanics of structure gene

Abstract: Masonry is a composite material formed by units and joints, highly anisotropic and difficult to characterize. This paper presents the application of Mechanics of Structure Gene (MSG) to the homogenization of masonry. Since it is a semi-analytical technique, MSG considerably reduces the computational cost and maintains the same precision of three-dimensional (3D) analyses, for example, by the Finite Element Method. Other interesting features are the possibility of obtaining 3D properties from the solution of 1D or 2D problems and the absence of necessity of applying boundary conditions. In the analyzed examples, the 3D elastic constants of the masonry, considered as an anisotropic material, are calculated from Young’s modulus and Poisson’s ratio of the blocks (or units) and the mortar joints, considered as isotropic. The results obtained are compared with numerical or theoretical methods by different authors, including a 3D finite element analysis, and present agreement, even for large ratios between Young’s moduli of blocks and mortar. Thus, the results presented in the paper show that the MSG method can be successfully applied in the homogenization of masonry and presents advantages over other methods for the same purpose.

Finite Element Homogenization of Periodic Block Masonry by the Effective Moduli Method

Abstract: The study is devoted to the determination of the effective material properties of masonry based on its internal structure. Masonry is considered as a periodic composite consisting of bricks and mortar. According to the classical method of determining effective moduli for composites, in order to describe internal microstructure we consider a representative volume cell, which enables us to determine effective properties of an equivalent anisotropic material. The problem for the representative volume cell is simulated and analyzed using finite element method.

An improved mean-field homogenization model for the three-dimensional elastic properties of masonry

Abstract: Accurate assessment of the overall mechanical behavior of masonry, composed of bricks and mortar joints, remains challenging due to its inhomogeneous and orthotropic nature. In this study, the feasibility of various mean-field homogenization schemes for the three-dimensional orthotropic elastic properties of masonry is comprehensively investigated. Three kinds of masonry patterns are considered, including the stack bonded pattern, the running bonded pattern and the double-leaf Flemish bonded pattern that has received limited attention so far. Special attention is paid to the homogenization schemes which have not been applied to the masonry case, such as Lielens’ interpolative double inclusions (D-I) and the interaction direct derivative (IDD) schemes. After a comparison between the well-known mean-field homogenization schemes, an improved micro-mechanical model is proposed by combining the advantages of the IDD and D-I models. The validation of the proposed model is conducted through a comparison against experimental data from literature and numerical results obtained via finite element analyses (FEA). The results show that the proposed model can accurately evaluate the orthotropic elastic properties of the three masonry typologies for a wide range of stiffness ratios between brick and mortar, ranging from 1 to 1000. The proposed model also shows better performance than the classical schemes especially when the stiffness ratios between brick and mortar are higher than 10, which is of major importance for the application of mean-field homogenization based multiscale methods to the nonlinear analysis of masonry. Furthermore, the presented homogenization method can be of interest for other anisotropic materials, e.g., laminate materials.