Mithila Achintha

An experimentally validated contour method/eigenstrains hybrid model to incorporate residual stresses in glass structural designs

Contour method–based finite element models together with knowledge of the surface deformation resulted from the stress relaxation along a newly cut-plane were used to construct the residual stresses in commercially available float glass. The results show that the residual stress depth profile of float glass is parabolic. The constructed residual stress profiles, validated to some extent against results of scattered light polariscope experiments, were then used to establish the misfit strains (i.e. eigenstrains) existed in the original glass specimens. It is shown that despite the modelling uncertainty of the contour method and the limitations associated with the scattered light polariscope measurements, the eigenstrain depth profile in a given float glass specimen can be determined to an acceptable accuracy. The article shows that once the underlying eigenstrain distribution in a given thickness of glass has been determined, the complete residual stress distribution can simply be determined by incorporating the eigenstrain profile as a misfit strain in an appropriate finite element model. It is also shown that the hybrid contour method/eigenstrain model enables modelling the residual stress around stress concentration features such as holes and/or stress evolution during subsequent applied loadings, by simply using the knowledge of eigenstrains.

Sustainability of glass in construction

This chapter discusses the potential applications of glass to deliver dynamic design solutions that enable buildings to be more energy efficient by making use of the most of daylight and solar gain whilst protecting the environment and conserving energy. The article also provides an overview of recent advances in modern glass products, and their potential applications in building envelops that can engineer reductions in the operational carbon. Glass is a brittle material, and its structural behaviour poses greater challenges when designing load-bearing structural members in buildings envelops. An overview of existing design guidelines of structural glass together with the need for detailed finite element analyses in accurate designs are briefly presented. The sustainability of glass as a construction material, including methods of recycle and reuse, is discussed. An outline of possible future developments in the use of glass in buildings is also presented.

Parametric study of FRP plate debonding using global energy balance

Fiber-reinforced polymer (FRP) plate debonding is commonly caused by the fracturing of concrete, but few studies of fracture debonding models exist, from which the failure load of the concrete cover layer can be evaluated. This paper presents a parametric study for plate end debonding using the global energy balance approach (GEBA), which has been proposed recently for determining the structure-debonding load. GEBA determines the debonding load using moment-curvature (M-?) models, and can thus be used to determine how debonding is affected by the beam’s flexural design. This paper presents parametric results using debonding contours on plots of moment capacity against the plate curtailment locations, and shows that beams with the same depth-to-fracture energy ratio give virtually the same debonding contour. This helps to generalize debonding determination for beams with different depths, and can be conveniently used for design. The parametric study lays a foundation for the application of fracture mechanics in FRP-plate retrofitting design using conventional M-? models to cover a wide range of flexural retrofitting situations.

Data for figures in "A numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests"

This dataset reports data for the figures published in: You, C. et al. (2017). A numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests. International Journal of Fatigue.

Using TSA to Identify Regions Having Developed Plastic Strain during Welding

Residual stress can be related to plastic strain experienced by a component; therefore the measurement of plastic strain presents the potential for residual stress to be investigated. Previous work has shown that Thermoelastic Stress Analysis (TSA) can identify regions that have undergone plastic strain. To do this, it was necessary to manufacture a test specimen of identical geometry containing zero plastic strain known as a reference specimen. Identifying the regions that have undergone plastic strain is then a simple matter of subtracting two data sets. This approach assumes there is always a reference specimen available, which in an industrial context is not the case. To make the work applicable to in-service components it is necessary to create a simulated reference specimen. The paper presents a means of establishing the simulated TSA reference specimen using Finite Element (FE) modelling through building a linear, elastic model and then including effects of nonlinear plasticity. To validate the idea a welded mock-up is used that contains a known level of plastic strain alongside a strain free specimen of identical material and geometry to the mock-up that has been manufactured to shape using water jet cutting. The work in the paper describes the outcome of using both the experimental and simulated reference specimens and considers the effect of varying material properties.

A novel design concept for connections in glass: structural Integrity of glass reinforced with externally–bonded GFRP laminates

The paper reports experimental results of the load response and failure behaviour of open-hole annealed glass tensile test specimens reinforced with adhesively-bonded GFRP laminates. The results show that the bonded GFRP has potential to strengthen stress concentration features in glass by either arresting the cracks developed in the critical zone or eliminating the failure from the vicinity of the critical area. It is anticipated that the findings of this research could be effectively used to develop reinforcement strategies for critical joints in glass structures.

Residual stress in geometric features subjected to laser shock peening

This article reports selected findings from a collaborative research study into the fundamental understanding of laser shock peening (LSP), when applied to key airframe and aero-engine alloys. The analyses developed include explicit simulations of the peening process together with a simpler eigenstrain approach, which may be used to provide an approximation to the residual stress field in a number of geometries. These are chosen to represent parts of structural components under conditions relevant to service applications. The article shows that the eigenstrain approach can provide good approximations to the stress field in most circumstances and may provide a computationally efficient tool for exploring different peening strategies. Both explicit and eigenstrain results demonstrate that the interaction between the LSP process and geometric features is important for understanding the subsequent performance of components. Particularly relevant for engineering applications is that not all instances of LSP application may provide an improvement in structural integrity.

A stress-free model for residual stress assessment using thermoelastic stress analysis

Thermoelastic Stress Analysis (TSA) has been proposed as a method of obtaining residual stresses. The results of a preliminary study demonstrated that when Al-2024 plate containing holes that were plastically deformed by cold expansion process to 2% and 4% strain the thermoelastic response in the material around the hole was different to that obtained from a plate that had not experienced any plastic cold expansion (i.e. a reference specimen). This observation provides an opportunity for obtaining residual stresses based on TSA data. In many applications a reference specimen (i.e. residual stress free specimen) may not be available for comparison, so a synthetic, digital bitmap has been proposed as an alternative. An elastic finite element model is created using commercially available software Abaqus/Standard and the resultant stress field is extracted. The simulated stress field from the model is mapped onto a grid that matches the TSA pixel data from a physical reference specimen. This stress field is then converted to a ?T/T field that can be compared to the full-field TSA data. When the reference experimental data is subtracted from the, bitmap dataset the resultant ?T/T field is approximately zero. Further work proposes replacing the experimental reference data with that from specimens that have undergone cold expansion with the aim of revealing the regions affected by residual stress through a departure from zero in the resultant stress field. The paper demonstrates the first steps necessary for deriving the residual stresses from a general specimen using TSA.