Versatile projects

Sample research projects

Phase-field modeling of damage and fracture in fiber reinforced composites

Despite the relevant development of PF methods within the last decade, a careful revisitation of the State of the Art shreds of evidence that these numerical techniques have been developed for their application for a limited type of engineering materials, with major attention for brittle fracture. However, PF methods possess enormous potential for the inclusion of phenomenological or physically-motivated failure criteria for brittle or ductile failure in a modular form, which can widen its range of application. Within this context, in this research, I developed sophisticated phenomenological material models based on the PF approach to fracture that can be employed into Finite Element Analysis (FEA) packages for virtual testing of damage and fracture in FRPs. A central aspect of this investigation is the development of a comprehensive theoretical and numerical study of PF methods for polymeric-based fiber-reinforced composites, namely Short Fiber Reinforced Polymers (SFRPs) and Long Fiber Reinforced Polymers (LFRPs).

Crashworthiness analysis and design optimization of energy absorption devices

Nowadays, researchers and engineers tend to develop protective structures to prevent damages and injuries resulted from high-velocity impacts and automotive crushes. Energy-absorbing devices provide the safety of high priority systems like vehicles and blast protection structures by protecting them from damages resulted from kinetic energy and converting this energy into plastic and fracture deformation. Most of these energy-absorbing devices are considered as thin-walled tubes with various geometries, dimensions, and material properties, their high strength-to-weight ratio, and energy-absorbing capability make it suitable for impact resistance. For this purpose, many new techniques are applied or under development. One of the most popular techniques used is installing energy absorption devices in ballistic protection products. This technique can provide well prevention criteria from sudden impacts. In this project, we study the effect of geometry, material type, and loading direction on the behavior of different energy absorption devices.

Multi-scale modelling of static failure and fatigue damage in fiber reinforced polymers

There are different types of damage that can develop during the static and fatigue failure of laminated Fiber Reinforced Polymers (FRPs). The main types of these damages can be classified as matrix cracks, delamination, interface failure, and fiber fracture. Although each of the aforementioned failure mechanisms can initiate and evolve independently, in practice they act synergistically and appear simultaneously at different locations of the loaded materials. Given that experimental investigations can be limited, very expensive, and time-consuming, in this project we develop a reliable multi-scale based virtual test environment for thorough studies of the static and fatigue damage in FRPs. The need for a deeper understanding of fatigue failure mechanisms interactions is important for the development of physically consistent predictive models and to improve the fatigue properties of composites materials. Moreover, the virtual test environment is to also be used as a virtual calibration platform.

Global-local thermomechanical analysis of fracture events in photo-voltaic module

The existing works in the literature addressing damage events in Photo-Voltaic (PV)-Modules have different drawbacks and needs for improvements. On the one hand, the lack of a computationally efficient multiscale-based framework to model progressive failure in Polycrystalline Silicon Wafers (PSWs) is observed. Furthermore, a coupled thermo-mechanical phase-field modeling framework for shells based on the geometrically nonlinear theory which takes into account the anisotropy effects as well as the presence of residual stresses is not yet available. In this project, we aim to cover these shortcomings in a unified way and at modeling progressive failure at both the micro- and macro-scale by developing a theoretically robust and computationally efficient framework.

Computational modeling and simulation of delamination migration in multi-layered long fiber reinforced polymers​​

Failure processes in Long Fiber Reinforced Polymers (LFRPs) entail the development and progression of different physical mechanisms and in particular the interaction between inter-laminar and intra-laminar cracking. Reliable modeling of such complex scenarios can be achieved through the development of robust numerical predictive tools that allow for the interaction of both failure modes. In this project, a novel multi Phase-Field (PF) model relying on the Puck theory of failure for intra-laminar failure at ply level is efficiently coupled with a cohesive zone model for inter-laminar cracking, in order to simulate delamination migration cracking events in multi-layered LFRPs. The computational method is numerically implemented as a system of non-linear partially coupled equations using the finite element method.

Computational fracture modeling of functionally graded materials

In this project, we developed a Phase-Field (PF) approximation of fracture for functionally graded materials (FGM) using a diffusive crack approach incorporating the characteristic length scale as a material parameter. A rule of the mixture is employed to estimate the material properties, according to the volume fractions of the constituent materials, which have been varied according to given grading profiles. In addition to the previous aspects, the current development includes the internal length scale of the PF approach variable from point to point, to model a spatial variation of the material strength. Based on the ideas stemming from the study of size-scale effects, Gamma-convergence for the approximation is proved when the internal length scale is either constant or a bounded function. 

Non-linear thermo-mechanical analysis of thin-walled structures

This project was about developing a thermodynamically consistent framework for coupled thermo-mechanical simulations for thin-walled structures with the presence of cohesive interfaces. Regarding the shell formulation, a solid shell parametrization scheme is adopted, which is equipped with the mixed Enhanced Assumed Strain (EAS) method to alleviate Poisson and volumetric locking pathologies. It is further combined with the Assumed Natural Strain (ANS) method leading to a locking-free thermo-mechanical solid shell element using a fully integrated interpolation scheme. In order to model thermo-mechanical decohesion events in thin-walled structures with imperfect internal boundaries, an interface finite element for geometrical nonlinearities is extended to account for the thermal field and thermo-elastic coupling.

Computational modeling of low-cycle fatigue damage in short fiber reinforced composites​

For fatigue life prediction, it is critical to model the damage evolution accurately since fatigue analysis puts great demand on model accuracy. Nevertheless, the fatigue damage model cannot be too complex since the analysis is time-consuming. In this project, we consistently extended and coupled the Fatigue Damage Models (FDM) of Nouri and Ladeveze with an invariant-based plasticity model for the numerical prediction of low-cycle fatigue damage in Short Fiber Reinforced Polymers (SFRPs).

Computational modeling and simulation of the failure of fiber reinforced polymers and metal sheets by clinching