Structural damage identification based on self-fitting ARMAX model and multi-sensor data fusion

Statistical time series methods have proven to be a promising technique in structural health monitoring, since it provides a direct form of data analysis and eliminates the requirement for domain transformation. Latest research in structural health monitoring presents a number of statistical models that have been successfully used to construct quantified models of vibration response signals. Although a majority of these studies present viable results, the aspects of practical implementation, statistical model construction and decision-making procedures are often vaguely defined or omitted from presented work. In this article, a comprehensive methodology is developed, which essentially utilizes an auto-regressive moving average with exogenous input model to create quantified model estimates of experimentally acquired response signals. An iterative self-fitting algorithm is proposed to construct and fit the auto-regressive moving average with exogenous input model, which is capable of integrally finding an optimum set of auto-regressive moving average with exogenous input model parameters. After creating a dataset of quantified response signals, an unlabelled response signal can be identified according to a 'closest-fit' available in the dataset. A unique averaging method is proposed and implemented for multi-sensor data fusion to decrease the margin of error with sensors, thus increasing the reliability of global damage identification. To demonstrate the effectiveness of the developed methodology, a steel frame structure subjected to various bolt-connection damage scenarios is tested. Damage identification results from the experimental study suggest that the proposed methodology can be employed as an efficient and functional damage identification tool. © The Author(s) 2014.

Toughening of a carbon-fibre composite using electrospun poly(Hydroxyether of Bisphenol A) nanofibrous membranes through inverse phase separation and inter-domain etherification

The interlaminar toughening of a carbon fibre reinforced composite by interleaving a thin layer (~20 microns) of poly(hydroxyether of bisphenol A) (phenoxy) nanofibres was explored in this work. Nanofibres, free of defect and averaging several hundred nanometres, were produced by electrospinning directly onto a pre-impregnated carbon fibre material (Toray G83C) at various concentrations between 0.5 wt % and 2 wt %. During curing at 150 °C, phenoxy diffuses through the epoxy resin to form a semi interpenetrating network with an inverse phase type of morphology where the epoxy became the co-continuous phase with a nodular morphology. This type of morphology improved the fracture toughness in mode I (opening failure) and mode II (in-plane shear failure) by up to 150% and 30%, respectively. Interlaminar shear stress test results showed that the interleaving did not negatively affect the effective in-plane strength of the composites. Furthermore, there was some evidence from DMTA and FT-IR analysis to suggest that inter-domain etherification between the residual epoxide groups with the pendant hydroxyl groups of the phenoxy occurred, also leading to an increase in glass transition temperature (~7.5 °C).

New results in robust functional state estimation using two sliding mode observers in cascade

 This paper presents a functional observer scheme using two sliding mode observers in cascade. A coordinate transformation is performed on the system such that existing sliding mode observer theory can be directly applied to achieve functional state estimation. The necessary and sufficient existence conditions for the scheme (in terms of the original system matrices) are also investigated, and they are found to be less stringent than earlier work on functional state estimation using one sliding mode observer; this could have benefits in terms of cost and simplicity. A numerical example verifies the effectiveness of the scheme.

Firsts: performing ways first year teachers experience identity transformation

This thesis reports on research showing the survival discourse of beginning teaching has shifted from sink or swim metaphors to describe surviving transition shock and classroom management concerns to surviving contract employment. Beginning teachers are neither sinking nor swimming in this liminal state. Rather, it is as though they are on a lifeboat where they cannot feel like a ‘real’ teacher until they can operate with certainty.

Interrogating the experiences of beginning teachers, and the transformation of their identity in their first year (1yr) of teaching, the thesis explores research participants’ firsts as epiphanic or revelatory moments of identity transformation. Participants were followed for three years from upon completion of their teacher education, through their first year of teaching, up to the beginning of their third year in the profession. The major finding was that while contemporary understandings of professional identity highlight the transformative nature of the phenomenon,  contract employment had the most impact on these teachers’ identity transformation.

Teachers’ perceptions of their own professional identity affect their efficacy and professional development as well as their ability and willingness to cope with educational change (Beijaard, Verloop & Vermunt 2000). It has been reported by the Australian Education Union (AEU) and in the Victorian media in recent years that up to 50% of beginning teachers are leaving the profession within their first five years. The reasons given for this level of
attrition include workload, pay, and behaviour management, among the top concerns of beginning teachers. These categories have positioned beginning teachers in a survival discourse for many years, yet there is more to beginning teachers’ intentions to leave than their struggles to survive in the classroom. More recently in Victoria what it means to ‘survive’ has shifted to surviving the pervasive contractual nature of beginning teachers’
employment conditions.

This qualitative study seeks to question what remains concealed with regard to beginning teachers’ experiences through an investigation of the differences between and within individuals, allowing categories of description to emerge from the data rather than pre-determining categories of investigation. Data was collected from twelve participants through individual semi-structured interviews and written communication. A theatre-based research approach to representing the participants’ experiences was employed, culminating in a performance titled ‘The First Time’. The processes of scripting, rehearsing, and performing, were utilised to analyse and represent the data to expert audiences. In an aim to uncover questions that have been buried by answers, the research is oriented as a
phenomenographic inquiry. This mode of inquiry seeks to describe, analyse, and understand (Marton 1981) the qualitatively different experiences 1yr teachers undergo in their identity formation and transformation.

The results of this research reveal the destabilising effect of short-term contracts so prevalent in the current context; that status and belonging are central to 1yr teachers’ identity work. Status and belonging are positioned within survival, liminal, and hegemonic discourses; and expressed through artefacts as symbols of belonging. The low status ascribed to contractual work has a clear impact on beginning teachers’ commitment to the profession.

Exploring first year teachers’ identity transformation through theatre-based research

Why are beginning teachers leaving the profession in large numbers? Are they leaving because of their dissatisfaction with teaching? Are they leaving because of the conditions of their work that shape their identity? Teacher identity work emphasises it is important beginning teachers understand their professional identity as something shifting, fluid and emerging – not fixed. These and other water metaphors – such as ‘washout’, ‘sink or swim’, and ‘thrown in the deep end’ – are often used to describe beginning teachers’ experiences. Such words and metaphors assist to portray the fluid and unpredictable nature of identity transformation. However, these survival terms also influence beginning teachers to believe that their transition to teaching will be difficult. Recently there has been an increased concern over beginning teacher attrition linked to the difficulties they encounter in their early years of teaching. Yet the conditions of beginning teachers’ work in Victorian schools in Australia – including the contractual nature of employment of first year (1yr) teachers – encourage these 1yr practitioners to view their work as semi-permanent. As a result these 1yr teachers do not see themselves as teaching for extended periods of time, as was once the case. Throughout 2011 twelve 1yr teachers shared their experiences of identity transformation in semi-structured interviews with the researcher. Their interview data was analysed through a theatre-based research method, examining how first experiences shape teachers’ future practice and identity. This presentation includes excerpts from the theatre-based research performance ‘The First Time’, and expands on the methodological approaches taken to analyse the data in a way that reflects the fluid and unpredictable nature of teachers’ identity formation and transformation. This qualitative study allows categories of description to emerge from the data rather than pre-determining categories of investigation. As such the processes of scripting, rehearsing, and performing, were utilised to analyse and re-present the data. In an aim to uncover questions that have been buried by answers, the research is oriented as a phenomenographic inquiry. This mode of inquiry seeks to describe, analyse, and understand the qualitatively different experiences 1yr teachers undergo in their identity formation and transformation. The results of this research reveal that beginning teachers’ identity transformation through their first experiences have both individual features specific to each teacher’s roles and aspirations, and extra-individual factors such as interactions, affiliations, and status, which shape their identity. Categories of description that have emerged from the analysis include survival, liminal, and hegemonic discourses, artifacts as symbols of belonging, and the impact of the contractual nature of teaching. Implications of this research focus on the importance for beginning teachers to develop an understanding of the transformative nature of identity in relation to the practice of teaching, to counter the negative preconceptions beginning teachers are told to expect as rites of passage upon entering the profession. The research outcomes have implications for teacher educators and in-service teachers negotiating the waters of an ever-changing profession.

Structural transformation of polyacrylonitrile fibers during stabilization and low temperature carbonization

The effect of oxidative stabilization and carbonization processes on the structure, mass and mechanical properties of polyacrylonitrile (PAN) precursor fibers was analyzed. A gradual densification of the fibers occurring from mass loss, decrease in fiber diameter and increase in density were observed after stabilization at a maximum temperature of 255 °C and carbonization at a maximum temperature of 800 °C. The tensile strength and modulus of the fibers were found to decrease after stabilization but then increased after low temperature carbonization. The thermal processing of the precursor fibers affected their mode of failure after tensile loading, changing from a ductile type of failure to a brittle type. The type of failure correlated well with the crystal structure changes in the fibers. Whilst the PAN precursor fiber started to exotherm above 225 °C in air, no prominent exothermic reaction was measured in the carbonized fibers in air up to 430 °C. The aromatization index of stabilized fiber was calculated to be ∼66%, and that of carbonized fiber was ∼99%. FTIR studies indicated that the variation in the chemical structure of the fibers with the stabilization of the fibers. Radial heterogeneity in the stabilized fibers was observed however it was not promoted to the carbonized fibers. Finally, a method to calculate mass retention of PAN precursor fiber after heat treatment was developed, and the calculated percentage mass retained of the precursor fiber after oxidation and carbonization were found to be 81% and 51%, respectively. . This study proposes an effective method to calculate the percentage of mass retained by precursor fibers after stabilization and low temperature carbonization to provide a model for evaluating carbon fiber yield from a given amount of fibers.