Experimental characterisation of rate-dependent compression behaviour of fibre reinforced composites

Fibre reinforced polymers (FRP) materials are being increasingly used for aerospace and automotive structural applications. One of the critical loading conditions for such applications is impact, consequently, understanding of the composite behavior under such loads becomes critical for structural design. The analysis and design process for achieving impact-resistant composite structures requires rate-dependent constitutive models, which, in turn, requires material properties of the composite over a range of strain rates. It is, therefore, the objective of the research to investigate the strain rate-dependent behavior of fiber reinforced composites under compressive loads for a wide range of fiber orientations. Quasi-static (≈ 1e-3 s-1) and high loading (≈ 200 s-1) rates are considered for the experimental study. Accordingly, two different test setups are utilized, a screw-driven universal testing machine for quasi-static tests and a Split Hopkinson Pressure Bar (SHPB) system for dynamic tests. The stress-strain response of the composite is reported for the different fiber orientations and the strain rates, revealing the rate-dependent characteristics of the carbon fiber reinforced composite. From the test results, it is observed that, the dependency of the fracture strength on the loading rate is significant. The results are summarised in terms of the failure envelope in the transverse compression-in-plane shear σ22-σ12 plane for the two strain rates

A Wedge-DCB Test Methodology to Characterise High Rate Mode-I Interlaminar Fracture Properties of Fibre Composites

A combined numerical-experimental methodology is presented to measure dynamic Mode-I fracture properties of fiber reinforced composites. A modified wedge-DCB test using a Split-Hopkinson Bar technique along with cohesive zone modelling is utilised for this purpose. Three different comparison metrics, namely, strain-displacement response, crack propagation history and crack opening history are employed in order to extract unique values for the cohesive fracture properties of the delaminating interface. More importantly, the complexity of dealing with the frictional effects between the wedge and the DCB specimen is effectively circumvented by utilising right acquisition techniques combined with an inverse numerical modelling procedure. The proposed methodology is applied to extract the high rate interlaminar fracture properties of carbon fiber reinforced epoxy composites and it is further shown that a high level of confidence in the calibrated data can be established by adopting the proposed methodology

On the Rate-dependent Plasticity Modelling of Unidirectional Fibre-reinforced Polymeric Matrix Composites

Three different approaches to plasticity are investigated to model the experimentally-observed non-linear behaviour of unidirectional fibre-reinforced polymeric matrix materials. The first and simplest approach consists on assuming independent one-dimensional rate-dependent plasticity on in-plane (12) and through-thickness longitudinal (13) shear components of the Cauchy stress tensor. The second, employs a 3D extension of the plane stress Hill'48 anisotropic plastic surface. The third and the last is formulated as a quadratic yield function inspired by Puck's fracture initiation criterion. It searches for a plastic localisation plane in which a certain combination of normal and shear stresses is maximum. Numerical simulations are conducted to analyse the off-axis compression behaviour of carbon fibre reinforced epoxy composite under varying loading rates. The afore-mentioned three different approaches are explored with an aim to predict the experimentally-observed non-linear response of such composites. The model parameters are determined using a deterministic inverse modelling strategy employing an iterative domain reduction optimisation technique. As far as the experiments are concerned, the quasi-static and medium rate tests were carried out in universal testing machines, while the experiments at high rate were conducted in a Split Hopkinson Pressure Bar system. The effectiveness in terms of accuracy and robustness of the three approaches are discussed

Institutional investors’ horizons and bank transparency

\ua9 2023 The Authors. Journal of Business Finance & Accounting published by John Wiley & Sons Ltd. We examine the relation between institutional investors’ horizons and bank transparency. The novelty of this research is to consider three important aspects of transparency: disclosure quality, private information gathering and auditor fees. We find strong evidence indicating that banks dominated by long-term (short-term [ST]) institutional shareholders exhibit higher (lower) levels of disclosure quality. However, there is no evidence that investor horizon has a differential effect on private information gathering and audit pricing. The study employs alternative proxies and estimations such as two-stage least squares and propensity score matching to address endogeneity. We also document that banks with higher ST institutional shareholding are associated with lower crash risk. These findings are particularly significant because poor bank transparency has been identified as a contributing factor to the 2007–2009 financial crisis

Predictions of the mechanical properties of unidirectional fibre composites by supervised machine learning

We present an application of data analytics and supervised machine learning to allow accurate predictions of the macroscopic stiffness and yield strength of a unidirectional composite loaded in the transverse plane. Predictions are obtained from the analysis of an image of the material microstructure, as well as knowledge of the constitutive models for fibres and matrix, without performing physically-based calculations. The computational framework is based on evaluating the 2-point correlation function of the images of 1800 microstructures, followed by dimensionality reduction via principal component analysis. Finite element (FE) simulations are performed on 1800 corresponding statistical volume elements (SVEs) representing cylindrical fibres in a continuous matrix, loaded in the transverse plane. A supervised machine learning (ML) exercise is performed, employing a gradient-boosted tree regression model with 10-fold cross-validation strategy. The model obtained is able to accurately predict the homogenized properties of arbitrary microstructures

Understanding the Complexity of Motivational Orientations towards Learning English among Pakistani Female University Students

The present study goal is to investigate female university students’ motivation toward learning English as Second Language (ESL) studying at the University of Sindh, Pakistan. Two main objectives of the study were to evaluate the motivational orientation of the female learners in terms of integrativeness or instrumentality. Second, to study the factors that affect the learners motivation towards learning English. A mixed-method approach was employed with descriptive and inferential statistics were performed on the data to evaluate the data. A number of 158 female students from both the Science and Arts faculties at the English and Chemistry departments filled the structured questionnaire. Additionally, to gain a deeper understanding of the researched phenomenon, the semi-structured interviews were conducted with 20 students. The findings revealed a complex portrait of the target population, with the most prominent motivational factors being integrative motive, classroom environment, and instrumental motive. Besides, the influence of teachers was found to induce behavioral changes, while gender did not appear to significantly impact the learning process

Technological Developments and the Role of L2 Motivation in University English Language Teaching Education

The 21st century is the era of technology and digitalization in teaching and learning dynamics., The present study explores the function of L2 motivation in university-based English language teaching (ELT) education. It also seeks to comprehend how technological developments are changing L2 motivation and examines teachers coping mechanisms in this changing educational environment. This study employs a qualitative research approach to explore the university teachers choices of technology instruments and pedagogical choices for enhancing students’ L2 motivation. Thus, the study uses semi-structured interviews to collect data from the 15 university teachers, (8 from Pakistan and 7 from Russia). Moreover, the secondary aim of the study is to comprehend the variables influencing L2 teacher motivation, and pedagogical approaches. This study adds to the body of information on language teaching by emphasizing the necessity for university teachers to adapt to changes in L2 motivation by utilizing technology, developing cutting-edge resources, and creating motivating learning settings

Clinical evaluation of diaphyseal femoral fractures operated in lateral decubitus position with interlocking nail

Background: The diaphyseal fractures of femur in adults are conventionally treated in supine position on traction table, which carries risk of compartment syndrome, pudendal nerve palsy, whereas in lateral decubitus position these complications can be avoided with additional advantage of easy access to greater trochanter particularly in obese patients. The aim of this study is to evaluate outcomes of femur diaphyseal fractures treated with intramedullary interlocking nail in lateral decubitus position.Methods: In this study 40 patients with femur diaphysea fractures were treated with intramedullary interlocking nail in lateral decubitus position, were studied for a period of 9 months from September 2019 to May 2020.Results: At the end of our study of 40 patients, outcome is graded according Thoresen’s criteria where 22 (55%) patients had excellent results with full, pain-free, function of the extremity and 11 (27.5%) patients had good result; 10 patients had range of motion 1200 and shortening of femur by 1.5 was observed in 1 patient. There were 6 (15%) patients with fair result; with range of motion 900 and 1 poor result (2.5%) had non-union with range of motion <900.Conclusions: Fixation of femur diaphyseal fracture in lateral decubitus position leads to easy access to the proximal femur making it easy to establish an entry point for an intramedullary device and it significantly eliminates the complications caused by other conventionally used methods