A multiscale Meshless Method for Brittle Fracture
Brittle fracture is one of the main failure mechanisms pertaining to materials and structural components.
Although a common phenomenon in many natural and engineering processes, robust and accurate simulation of the evolution of brittle fracture, from crack initiation and crack propagation and crack branching has been proven to be a challenging task.
In this project, the efficiency of implementing a novel multiscale meshless method alongside proper mathematical descriptions of crack surfaces is examined in terms of numerical efficiency, source code implementation and accuracy.
Bond Between Cement-Based Textile Composites and Concrete Substrates
The use of Fiber Reinforced Polymers (FRPs) as externally bonded reinforcement for retrofitting existing concrete and masonry structures has become very popular technique over the last two decades, thanks to the favourable properties offered by these materials.
However, FRPs entails a few drawbacks which are associated with the epoxy resins used to bind the fibers, i.e. poor behaviour of at high temperature; high costs; incompatibility with substrate materials.
To address such problems, a new structural material, the so-called Textile Reinforced Mortar (TRM) has been recently developed.
TRM combines advanced fibers in form of textiles (with open-mesh configuration) with inorganic matrices, such as cement-based mortars. Nevertheless, due to granularity of cement used, the bond between TRM and concrete has become an issue. This PhD study aims to investigate the bond between TRM and concrete substrates using double lap shear test.
Key investigated parameters include:
- the number of layers,
- the bond length
- the concrete surface preparation
- the concrete compressive strength
- the textile surface condition (i.e. coated and uncoated)
- the anchoring of TRM through wrapping
- Raoof, Saad Mahmood Raoof
Confinement of Masonry Columns with Textile-Reinforced Mortar (TRM) Jackets
Jacketing of masonry columns in order to enhance their axial capacity and improve their performance under earthquakes, is a popular retrofitting solution.
The conventional strengthening technique though, which comprise the use of shotcrete layers, entails few drawbacks such as the corrosion of the steel reinforcement and the significant increase of the column thickness (up to 50%). To overcome these drawbacks the use of textile-reinforced mortar jackets is suggested.
The result is a very thin (up to 10 mm) jacket with non-corrosive high-strength fibers (i.e. carbon, AR-glass or basalt), which effectively contribute to the load-carrying capacity of the columns.
A broad experimental campaign is currently under investigation, with the main parameters being the number of textile layers and the column dimensions.
Deformation and Collapse of 3D Woven Composites Under Quasi-Static and Dynamic Impact Loading
An experimental and numerical investigation was undertaken in order to develop the understanding of the behaviour of orthogonal 3D woven composites under quasi-static tension/compression, out-of-plane bending and dynamic soft and multi-hit impact load cases.
A pressurised gas gun system was designed and developed at the University of Nottingham in order to conduct dynamic impact experiments on composite beam and circular plate samples.
A numerical modelling strategy based on an established continuum damage mechanics framework was also developed and validated with experimental tests, providing further insights into the results. The through-thickness reinforcement of the 3D weave was shown to provide reductions in the propagation of damage throughout the material.
Flexural Strengthening of Reinforced Concrete Slabs with Textile-Reinforced Mortar (TRM)
The aim of this project is to investigate the effectiveness of a new strengthening technique in increasing the flexural capacity of reinforced concrete slabs. The need for enhancing their strength comes from poor initial design or deterioration due to aging.
By bonding thin layers of high-strength, lightweight textiles (i.e. carbon or glass) on the bottom of the slabs with the use of cement mortars, the flexural capacity significantly increases.
The project includes testing of large-scale square slabs (1.8 m side length) under two-way bending. Key parameters of the study are:
- the number of textile layers,
- the material of the textile fibers
- the presence of a cut-opening at the centre of the slab.
Innovative Shear Strengthening of existing Concrete Members with Textile-Based Composite Materials
Structural retrofitting of existing reinforced concrete (RC) structures is a constantly growing need due to their deterioration. One of the most common structural deficiencies is the poor shear capacity of RC beams or bridge girders.
The use of fiber reinforced polymers (FRP) as externally bonded (EB) reinforcement in shear strengthening of RC members has become very popular over the last two decades. However, the FRP strengthening technique has a few drawbacks mainly associated with the use of epoxy resins (i.e. high cost, poor performance in high temperatures, inability to apply on wet surfaces).
In an attempt to alleviate the problems arising from the use of epoxies, researchers have introduced a novel composite material, namely textile-reinforced mortar (TRM), which combines advanced fibers in form of textiles (with open-mesh configuration) with inorganic matrices, such as cement-based mortars. This project studies the efficiency of TRM jackets in shear strengthening of RC members. Key parameters of this study include:
- the use of textile-based anchors as end-anchorage system of the U-jacket
- the effect of number of layers
- the use of different textile material or geometry
- the comparison of the performance of TRM jacketing versus equivalent Fiber-Reinforced Polymer (FRP) system
Modelling of Dyneemma
Dyneema is an ultra-high molecular weight polyethylene fiber manufactured by Dutch company DSM Dyneema.
The properties of Dyneema, which include high tensile strength, allow it to be one of the best performing reinforcements for composite materials under intensive dynamic loadings. However, the failure mechanism of Dyneema composite is poorly understood. Nonlinear finite element method, employed by Commercial FE codes, cannot give accurate prediction as local failure mode governs the damage initiation and evolution of the composite materials.
In this project, the pyrodynamics based method in conjunction with well-defined experimental methods will be employed to explore the failure mechanism. It is expected high quality technical publications and advanced modelling methods would be achieved at the end of the project.