Wayne Hall

Modulus and Strength Prediction for Natural Fibre Composites

Abstract This paper presents a new micromechanical model for the prediction of the tensile modulus and strength of natural fibre reinforced polymer matrix composites. The model addresses issues linked to the statistical variation inherent in fibre reinforcements extracted from plants. The new model introduces a fibre area correction factor (FACF). Modulus and strength are estimated and compared to experimental data for a jute–epoxy composite. The predictions of tensile modulus and strength using the FACF show improvements over those from other micromechanical models presented in the literature.

An Evaluation of a Project-Based Learning Initiative in Engineering Education

Project-based learning (PBL) is a well-known methodology for engineering design education due to a number of benefits it is claimed to offer. This paper presents the initial offering of a first-year engineering PBL unit at Griffith University in Australia. An evaluation of student perceptions of the unit revealed that students generally enjoyed the experience, with the oral presentation aspect receiving the lowest satisfaction rating. There was no significant difference in the ratings between any demographic grouping, suggesting that all students were able to participate in, and experience, the unit in essentially the same way. The best aspects of the unit and those aspects needing improvement were similar to the findings of other investigations documented in the literature. It is proposed that future offerings of the unit will reduce the number of design projects from three to two per semester and will attempt more sophisticated individualisation of marks for group work activities.

Tensile properties of jute fibres

Abstract One hundred tensile tests were undertaken at each of five distinct fibre lengths (6, 10, 20, 30 and 50 mm) on a single batch of jute fibres from South Asia. The Youngs moduli were found to be independent of length. The ultimate stress (fracture strength) and fracture strains were found to decrease with increasing fibre length. The variation in mechanical properties at each fibre length was characterised using Weibull statistics based on a maximum likelihood estimate; referred to as point estimates. Two empirical based models (a linear and a natural logarithmic interpolation model) have been developed to estimate the fracture properties at any length between 6 and 50 mm. These two interpolation models were also developed based on maximum likelihood estimates. The point estimates were used to benchmark the performance of the two models. The natural logarithmic model was found to be superior to the linear model.

On the Anisotropic Mechanical Properties of Selective Laser Melted Stainless Steel

The thorough description of the peculiarities of additively manufactured (AM) structures represents a current challenge for aspiring freeform fabrication methods, such as selective laser melting (SLM). These methods have an immense advantage in the fast fabrication (no special tooling or moulds required) of components, geometrical flexibility in their design, and efficiency when only small quantities are required. However, designs demand precise knowledge of the material properties, which in the case of additively manufactured structures are anisotropic and, under certain circumstances, inhomogeneous in nature. Furthermore, these characteristics are highly dependent on the fabrication settings. In this study, the anisotropic tensile properties of selective laser-melted stainless steel (1.4404, 316L) are investigated: the Young’s modulus ranged from 148 to 227 GPa, the ultimate tensile strength from 512 to 699 MPa, and the breaking elongation ranged, respectively, from 12% to 43%. The results were compared to related studies in order to classify the influence of the fabrication settings. Furthermore, the influence of the chosen raw material was addressed by comparing deviations on the directional dependencies reasoned from differing microstructural developments during manufacture. Stainless steel was found to possess its maximum strength at a 45° layer versus loading offset, which is precisely where AlSi10Mg was previously reported to be at its weakest.

A longitudinal evaluation of a project-based learning initiative in an engineering undergraduate programme

Project-based learning (PBL) is a well-known student-centred methodology for engineering design education. The methodology claims to offer a number of educational benefits. This paper evaluates the student perceptions of the initial and second offering of a first-year design unit at Griffith University in Australia. It builds on an earlier evaluation conducted after the initial offering of the unit. It considers the implementation of the recommended changes. Evaluations of the two offerings reveal that students (in both the initial and second offering) generally enjoyed the experience, but that the second offering was found to be a significantly more enjoyable learning experience. Students in the second offering also reported a significantly better understanding of what they needed to do for the design projects and where to find the requisite information. The oral presentation aspect of the initial and second offerings received the lowest satisfaction rating. The inclusion (and delivery) of the computer-aided drawing component of the unit is seen as a positive aspect by some students, but many others comment on it negatively. The best aspects of the PBL unit and those aspects needing further improvement were similar to the findings of other investigations documented in the literature.

Physical Characterization of Jute Technical Fibers: Fiber Dimensions

Natural fibers are characterized by large variation in their cross-section, both between fibers and along the length in any single “technical” fiber. This short communication describes an attempt to fully characterize the fiber cross-sectional area using single sample measurements from several fibers. This should enable an improved determination of mechanical properties of natural fibers.

Modelling tensile properties of jute fibres

Abstract This short communication extends earlier modelling of the tensile strength and failure strain of jute technical fibres. A maximum likelihood estimate (MLE) model, a linear model and a natural logarithmic interpolation model (NLIM) are compared. The NLIM model is found to give superior predictions.

Microstructural Characterisation of Jute/Epoxy Quasi-Unidirectional Composites

The elastic properties of a composite can be predicted by micromechanical models based on the properties of the individual constituent materials of the composite and their geometrical characteristics. This paper presents a novel methodology using image analysis to determine (a) the fibre volume fraction and (b) the fibre orientation distribution factor of quasi-unidirectional jute fibre reinforced epoxy resin composites. For fibre volume fraction, digital micrographs were smoothed to reduce noise in the image, an intensity histogram informed selection of the threshold intensity for conversion to a binary image, the image was morphologically closed and opened to remove internal voids and small features respectively and the fibre volume fraction was calculated as the ratio of the detected fibre area to the total image area. For fibre orientation, the image was sharpened with Contrast-Limited Adaptive Histogram Equalisation, a threshold was set for conversion to binary and then a masking image was rotated at a number of seed points over the image to find the angles with the minimum sum of intensity at each point. The data generated was then used to validate new rules-of-mixture equations for natural fibre composites.

An evaluation of an online student portfolio for the development of engineering graduate attributes

An online student portfolio was evaluated as a means for engaging students with the concept of graduate attributes, and for documenting student attainment of graduate attributes. Students rated the portfolio system as easy to use, and indicated that it helped them to appreciate the skills and knowledge they had developed.

Automatized Estimation of the Effective Thermal Conductivity of Carbon Fiber Reinforced Composite Materials

In the current study, the representative volume element (RVE) is used to model randomly generated nanocomposite structures consisting of carbon nanotubes (CNTs) embedded in an epoxy resin matrix. The finite element Method is utilized for numerical simulations and investigation of the influential parameters on the generated RVEs. In order to automatize the whole procedure - fromgenerating the finite element models to conducting the analyses - a subroutine-based programming approach is adopted using the MSC Marc finite element package and Fortran programming language. The simulations can successfully predict the increase in thermal conductivity of CNT-reinforced nanocomposites by increasing the fiber volume fraction.