Zahur Ullah

Queen's University Belfast | QUB · School of Mechanical and Aerospace Engineering

Purpose – A variety of meshless methods have been developed in the last 20 years with an intention to solve practical engineering problems, but are limited to small academic problems due to associated high computational cost as compared to the standard finite element methods (FEM). The purpose of this paper is to develop an efficient and accurate a...

An automatic adaptive coupling procedure is proposed for the finite element method (FEM) and the element-free Galerkin method (EFGM) for linear elasticity and for problems with both material and geometrical nonlinearities. In this new procedure, initially the whole of the problem domain is modelled using the FEM. During an analysis, those finite el...

Efficient computational modelling of problems including both material and geometric nonlinearities remains challenging. Often these problems are modelled with adaptive finite element method (FEM). Meshless methods offer the attractive possibility of simpler adaptive procedures involving no remeshing, simply insertion or deletion of nodes. In this s...

A coupled hygro-thermo-mechanical computational model is proposed for fibre reinforced polymers, formulated within the framework of Computational Homogenisation (CH). At each macrostructure Gauss point, constitutive matrices for thermal, moisture transport and mechanical responses are calculated from CH of the underlying representative volume eleme...

A three-dimensional multi-scale computational homogenisation framework is developed for the prediction of nonlinear micro/meso-mechanical response of the fibre-reinforced polymer (FRP) composites. Two dominant damage mechanisms, i.e. matrix elasto-plastic response and fibre-matrix decohesion are considered and modelled using a non-associative press...

A novel Overset Improved Element-Free Galerkin-Finite Element Method (Ov-IEFG-FEM) for solving transient heat conduction problems with concentrated moving heat sources is introduced in this communication. The method is a mesh-less/mesh-based chimera-type approach that utilises a coarse finite element mesh to discretise the problem geometry, while a...

A novel Overset Improved Element-Free Galerkin-Finite Element Method (Ov-IEFG-FEM) for solving transient heat conduction problems with concentrated moving heat sources is introduced in this communication. The method utilises a coarse finite element mesh to discretise the problem geometry, while a separate set of overlapping nodes (patch nodes) move...

Woven fabric reinforced plastic composites are highly favoured in the aerospace and automotive industries for their exceptional impact resistance and ease of manufacture. To design and analyse these structures, it is crucial to determine their elastic properties of woven fabric composites, which can be estimated through analytical, numerical, or ex...

Inter-fibre failure analysis of carbon fibre-reinforced polymer (CFRP) composites, under biaxial loading conditions, has been a longstanding challenge and is addressed in this study. Biaxial failure analysis of IM7/8552 CFRP unidirectional (UD) composites is conducted under various stress states. Two widely accepted failure criteria, the interactiv...

This study presents a data-driven, probability embedded approach for the failure prediction of IM7/8552 unidirectional carbon fibre reinforced polymer (CFRP) composite materials under biaxial stress states based on micromechanical modelling and artificial neural networks (ANNs). High-fidelity 3D representative volume element (RVE) finite element mo...

Carbon Fibre Reinforced Polymer (CFRP) composites are widely used in many engineering applications due to their excellent design flexibility and high stiffness- and strength-to-weight ratios. However, the lack of comprehensive experimental data for the validation of computational failure models, especially for composite structures subjected to mult...

This study assessed the widely used Tasi-Wu and Hashin failure criteria, using high-fidelity finite element-based analysis. Three-dimensional representative volume element models of IM7/8552 CFRP unidirectional composites subjected to biaxial loadings via periodic boundary conditions were constructed. The Drucker-Prager plastic damage constitutive...

In this paper proportional topology optimisation (PTO) with maximum entropy (maxent)-based meshless method is presented for two-dimensional linear elastic structures for both minimum compliance (PTOc) and stress constraint (PTOs) problems. The computation of maxent basis functions are efficient as compared to the standard moving least square (MLS)...

This paper presents a meshless element-free Galerkin method coupled with the radial basis functions (RBFs)-based level set algorithm for topology optimization. The meshless approach provides the structural response and corresponding sensitivities at nodal/grid points, and the solution of RBFs-based level set formulation updates the structural geome...

A finite element mesh, aligned along the fibre direction, has often been purported to yield more accurate results in the modelling of damage in composite structures constructed from unidirectional fibre reinforced polymer laminates. However, there has been a lack of a systematic assessment of this approach. This issue is addressed through modelling...

This paper focuses on the utilization of local radial basis functions (LRBFs) based level set method (LSM) for topology optimization of two-dimensional thermal problems using both concentrated as well as uniformly distributed heat generation. The design domain is embedded implicitly into a higher-dimensional function, which is parametrized with the...

The formulation of a new prism finite element is presented for the nonlinear analysis of solid shells subject to large strains and large displacements. The element is based on hierarchical, heterogeneous, and anisotropic shape functions. As with other solid shell formulations, only displacement degrees of freedom are required to describe the shell...

Textile reinforced polymer composites have excellent structural performance including mechanical properties and thermal properties, which are benefited from their relative complex architecture of the reinforcement. Tailoring the geometry of the fabric can achieve desired material properties, but the complex geometry imposes some challenges to explo...

This paper presents a hierarchic finite element-based computational framework for the multi-scale modelling of composite laminates. Hierarchic finite elements allow changing the approximation order locally or globally without changing the underlying finite element mesh. Both micro- and macro-level structures are discretised with these elements. The...

A three-dimensional hierarchic finite element-based computational framework is developed for the investigation of inter-laminar stresses and displacements in composite laminates of finite width. As compared to the standard finite elements, hierarchic finite elements allow to change the order of approximation both locally and globally without modify...

The current work is mainly about the implementation of the local radial basis functions (LRBFs) within the level set framework for structural optimization of two-dimensional linear elastic problems. The implicit representation of the structural geometry is accomplished through the LRBFs based level set function (LSF), and the geometry modification...

This paper extends the applications of a novel and fully automated multi-scale computational homogenisation framework, originally proposed by the authors (Ullah, et al. (2017)) for uni- directional and 2D-textile composites, to 3D-textile composites. 3D-textile composites offer many advantages over 2D-textile composites but their highly complicated...

Keywords: Fiber reinforced polymer composites, 3D textile/woven composites, Finite element analysis, Multiscale computational homogenization. This paper presents a multiscale computational homogenisation approach for the calculation of homogenised structural level mechanical properties of 3D textile/woven based fiber reinforced polymer (FRP) compos...

The mortar contact formulation is a well-established technique to tie non-conforming finite element meshes in domain decomposition and is also the basis of many well-known contact algorithms. Mortar contact formulation allows for a variationally consistent treatment of contact conditions including mesh tying, non-penetration, frictionless and frict...

This paper proposes a novel multi-scale approach for the reliability analysis of composite structures that accounts for both microscopic and macroscopic uncertainties, such as constituent material properties and ply angle. The stochastic structural responses, which establish the relationship between structural responses and random variables, are ac...

This paper presents a formulation for brittle fracture in 3D elastic solids within the context of configurational mechanics. The local form of the first law of thermodynamics provides a condition for equilibrium of the crack front. The direction of the crack propagation is shown to be given by the direction of the configurational forces on the crac...

This paper investigates two critical issues, namely propagation of multi-scale uncertainty, and selection of failure criteria, related to reliability analysis of composites by using multi-scale methods. Due to the multi-scale architecture of composites, uncertainties exist in both microscale and macroscale parameters. It is necessary, therefore, to...

Fibre reinforced polymer composite structures are expected to experience a range of hygro-thermal environmental conditions during their service life. Since the presence of moisture and temperate can cause plasticization of the polymer matrix, alter the stress state, and degrade the fibre/matrix interface, an understanding of moisture diffusion and...

A three-dimensional multi-scale computational homogenisation framework was developed for the prediction of nonlinear micro-mechanical response of the fibre-reinforced polymer (FRP) composite. Two dominant damage mechanisms, i.e. matrix damage and fibre-matrix decohesion were considered and modelled using a non-associative pressure dependent thermod...

Quantifying uncertainty in the overall elastic properties of composite materials arising from randomness in the material properties and geometry of composites at microscopic level is crucial in the stochastic analysis of composites. In this paper, a stochastic multi-scale finite element method, which couples the multi-scale computational homogeniza...

In this paper, a stochastic homogenization method that couples the state-of-the-art computational multi-scale homogenization method with the stochastic finite element method, is proposed to predict the statistics of the effective elastic properties of textile composite materials. Uncertainties associated with the elastic properties of the constitue...

Technical Report from Engineering and Computing Sciences at Durham University

A fully coupled hygro-thermo-mechanical computational framework based on the multi-scale computational homogenisation is proposed for fibre reinforced polymers. At each macrostructure Gauss point, constitutive matrices for thermal, moisture transport and mechanical responses were calculated from the computational homogenisation of underlying repres...

This paper presents an initial computational multiscale modelling of the fibre-reinforced composite materials. This study will constitute an initial building block of the computational framework, developed for the DURCOMP (providing confidence in durable composites) EPSRC project, the ultimate goal of which is the use of advance composites in the c...

A variety of meshless methods have been developed in the last fifteen years with an intention to solve practical engineering problems, but are limited to small academic problems due to associated high computational cost as compared to the standard finite element methods (FEM). The main objective of this thesis is the development of an efficient and...

Three-dimensional problems with both material and geometrical nonlinearities are of practical importance in many engineering applications, e.g. geomechanics, metal forming and biomechanics. Traditionally, these problems are simulated using an adaptive finite element method (FEM). However, the FEM faces many challenges in modeling these problems, su...

Most of the real world solid mechanics problems are three-dimensional with material and geometrical nonlinearities and their numerical solution is computationally very expensive, therefore it is more convenient to solve these with parallel adaptive analysis. One of the most prominent meshless method, The element-free Galerkin method (EFGM) [1] is u...

Efficient computational modelling of problems with material and geometric nonlinearities is very challenging. These problems are often solved with the adaptive finite element method (FEM), which involves error estimation coupled with refinement strategies to automatically find regions for fine and coarse discretization. For these problems meshless...

The element-free Galerkin method (EFGM) is superior to its counterpart the finite element method (FEM) in terms of accuracy and convergence but is computationally expensive. Therefore it is more practical to use the EFGM only in a region, which is difficult to model using the FEM, while the FEM can be used in the remaining part of the problem domai...

The element free Galerkin method (EFGM) [1] is one of the most robust meshless methods for the solution of elasto-statics problems. In the EFGM, moving least squares (MLS) shape functions are used for the approximation of the field variable. The essential boundary conditions cannot be implemented directly as in the case of Finite Element Method (FE...