Modelling the permeability of random discontinuous carbon fibre preforms

A force-directed algorithm was developed to create representative geometrical models of fibre distributions in directed carbon fibre preforms. Local permeability values were calculated for the preform models depending on the local fibre orientation, distribution and volume fraction. The effect of binder content was incorporated by adjusting the principal permeability values of the meso-scale discontinuous fibre bundles, using corresponding experimental data obtained for unidirectional non-crimp fabrics. The model provides an upper boundary for the permeability of directed carbon fibre preform architectures, where predictions are within one standard deviation of the experimental mean for all architectures studied

Simulation of the forming process for curved composite sandwich panels

© 2019, The Author(s). For affordable high-volume manufacture of sandwich panels with complex curvature and varying thickness, fabric skins and a core structure are simultaneously press-formed using a set of matched tools. A finite-element-based process simulation was developed, which takes into account shearing of the reinforcement skins, multi-axial deformation of the core structure, and friction at the interfaces. Meso-scale sandwich models, based on measured properties of the honeycomb cell walls, indicate that panels deform primarily in bending if out-of-plane movement of the core is unconstrained, while local through-thickness crushing of the core is more important in the presence of stronger constraints. As computational costs for meso-scale models are high, a complementary macro-scale model was developed for simulation of larger components. This is based on experimentally determined homogenised properties of the honeycomb core. The macro-scale model was employed to analyse forming of a generic component. Simulations predicted the poor localised conformity of the sandwich to the tool, as observed on a physical component. It was also predicted accurately that fibre shear angles in the skins are below the critical angle for onset of fabric wrinkling

Design guidelines for hybrid continuous/discontinuous carbon fibre laminates

Combining discontinuous carbon fibre moulding compounds with unidirectional (UD) non-crimp fabric has been studied as a potential solution for producing cost effective composite structures, with short cycle times via compression moulding. The tensile stiffness and strength of a composite with a hybrid fibre architecture were found to be up to 60% and 110% higher, respectively, than the baseline discontinuous fibre moulding compound, when 20% (by vol.) of UD fibres were aligned in the primary loading direction. However, stress concentrations arising from the dissimilar material properties can result in the strength of the hybrid architecture being reduced to below that of the baseline composite if the UD fibres are not incorporated effectively. This paper focusses on optimising the stress transfer within the transition zone (inter-material interface) between the UD material and the discontinuous fibre moulding compound, when local isolated patches of continuous fibre are used rather than full coverage plies. This is key if hybrid architectures are to be adopted for structural applications, minimising the stress concentration effects from the UD ply ends, whilst maintaining the low cycle times and costs associated with compression moulding. Following aerospace laminate design guidelines, a range of step sizes and joint configurations have been considered for different ply drop strategies, minimising the magnitude of the stress concentration at the UD ply ends. Results indicate that the step length must be at least 20 times the thickness of the UD ply to ensure the bending strength at the joint is the same as the baseline discontinuous fibre material. An ‘alternating joint' yields 18% higher bending strengths than a conventional ‘stepped joint’ design, as the stress concentrations at the dropped ply ends are reduced in comparison to the inherent stress concentrations within the discontinuous fibre material

3D geometric modelling of discontinuous fibre composites using a force-directed algorithm

A geometrical modelling scheme is presented to produce representative architectures for discontinuous fibre composites, enabling downstream modelling of mechanical properties. The model generates realistic random fibre architectures containing high filament count bundles (>3k) and high (~50%) fibre volume fractions. Fibre bundles are modelled as thin shells using a multi-dimension modelling strategy, in which fibre bundles are distributed and compacted to simulate pressure being applied from a matched mould tool. FE simulations are performed to benchmark the in-plane mechanical properties obtained from the numerical model against experimental data, with a detailed study presented to evaluate the tensile properties at various fibre volume fractions and specimen thicknesses. Tensile modulus predictions are in close agreement (less than 5% error) with experimental data at volume fractions below 45%. Ultimate tensile strength predictions are within 4.2% of the experimental data at volume fractions between 40%-55%. This is a significant improvement over existing 2D modelling approaches, as the current model offers increased levels of fidelity, capturing dominant failure mechanisms and the influence of out-of-plane fibres

Optimisation of intra-ply stitch removal for improved formability of biaxial non-crimp fabrics

Automated fabric forming solutions are required to meet the demand of liquid moulding processes, but wrinkling is a common problem for double-curvature parts due to a combination of the reinforcement type, manufacturing parameters and the part geometry. Local intra-ply stitch removal is introduced in the current work to improve the formability of a pillar-stitched biaxial NCF. An optimisation method is developed to remove stitches selectively, using a genetic algorithm coupled with a finite element model. Two criteria are defined to reduce the occurrence of forming defects whilst maintaining the integrity of the fabric. The first is to minimise the local shear angle across the surface of the ply and the second is to minimise the total stitch removal area. These criteria are combined into a single objective function and validated using a hemisphere forming case study. Experimental results confirm that macro-scale wrinkling can be successfully eliminated when intra-ply stitches are removed according to the optimised pattern. The stitch removal regions are distributed across both the positive and negative shear areas of the optimised NCF blank, indicating that local stitch removal can have a global effect on the formability. Perimeter shapes show that the optimum local stitch removal pattern enables a more balanced global material draw-in, demonstrating that the effect of stitch removal is not limited to the high shear regions. Removing stitches from just the over-sheared regions is therefore insufficient to fully mitigate wrinkles, justifying the need for the optimisation algorithm, as the optimised stitch removal pattern appears to be non-intuitive

Thermoplastic composite injection-overmoulding with indirectly-loaded reinforcement: Design for manufacture

Thermoplastic Overmoulding is an emerging manufacturing method combining low-cost, high-rate injection moulding with continuous fibre composite elements. The combination of materials with dissimilar stiffnesses can create stress concentrations and warpage, with further complications caused by high injection pressures distorting the continuous fibre elements (wash). This study uses a numerical model to consider a particular overmoulding approach that utilises a strategically positioned local reinforcing element (an insert) that is loaded indirectly via stresses transferred from the surrounding overmoulding material. This offers a low-cost solution by minimising use of continuous fibre material, but has a higher likelihood of the aforementioned problems. A geometrical solution (a waffle-type structure) is used to address these manufacturing challenges without compromising the primary stiffening role of the continuous fibre element. An insert efficiency factor is proposed to describe the tensile behaviour and the diminishing returns on peak load in the insert when embedding increasingly higher stiffness inserts into moderate stiffness overmoulding materials containing short fibres. According to the simulation results, the proposed Waffle structure should provide stiffness commensurate with the conventional configuration; however, the experimental coupons highlight the complexities of injection moulding short fibres and indicate the detrimental effect of anisotropic fibre distributions within the overmoulded sections

Participatory Action Research-Dadirri-Ganma, using Yarning: methodology co-design with Aboriginal community members

Background: Appropriate choice of research design is essential to rightly understand the research problem and derive optimal solutions. The Comorbidity Action in the North project sought to better meet the needs of local people affected by drug, alcohol and mental health comorbidity. The aim of the study focused on the needs of Aboriginal peoples and on developing a truly representative research process. A methodology evolved that best suited working with members of a marginalised Aboriginal community. This paper discusses the process of co-design of a Western methodology (participatory action research) in conjunction with the Indigenous methodologies Dadirri and Ganma. This co-design enabled an international PhD student to work respectfully with Aboriginal community members and Elders, health professionals and consumers, and non-Indigenous service providers in a drug and alcohol and mental health comorbidity project in Adelaide, South Australia. Methods The PhD student, Aboriginal Elder mentor, Aboriginal Working Party, and supervisors (the research team) sought to co-design a methodology and applied it to address the following challenges: the PhD student was an international student with no existing relationship with local Aboriginal community members; many Aboriginal people deeply distrust Western research due to past poor practices and a lack of implementation of findings into practice; Aboriginal people often remain unheard, unacknowledged and unrecognised in research projects; drug and alcohol and mental health comorbidity experiences are often distressing for Aboriginal community members and their families; attempts to access comorbidity care often result in limited or no access; and Aboriginal community members experience acts of racism and discrimination as health professionals and consumers of health and support services. The research team considered deeply how knowledge is shared, interpreted, owned and controlled, by whom and how, within research, co-morbidity care and community settings. The PhD student was supported to co-design a methodology that was equitable, democratic, liberating and life-enhancing, with real potential to develop feasible solutions.Results The resulting combined Participatory Action Research (PAR)-Dadirri-Ganma methodology sought to create a bridge across Western and Aboriginal knowledges, understanding and experiences. Foundation pillars of this bridge were mentoring of the PhD student by senior Elders, who explained and demonstrated the critical importance of Yarning (consulting) and Indigenous methodologies of Dadirri (deep listening) and Ganma (two-way knowledge sharing), and discussions among all involved about the principles of Western PAR.. Conclusions Concepts within this paper are shared from the perspective of the PhD student with the permission and support of local Elders and Working Group members. The intention is to share what was learned for the benefit of other students, research projects and community members who are beginning a similar journey.Hepsibah Sharmil, Janet Kelly, Margaret Bowden, Cherrie Galletly, Imelda Cairney, Coral Wilso

14-3-3ε Is Required for Germ Cell Migration in Drosophila

Although 14-3-3 proteins participate in multiple biological processes, isoform-specific specialized functions, as well as functional redundancy are emerging with tissue and developmental stage-specificity. Accordingly, the two 14-3-3ε proteins in Drosophila exhibit functional specificity and redundancy. Homozygotes for loss of function alleles of D14-3-3ε contain significantly fewer germ line cells (pole cells) in their gonads, a phenotype not shared by mutants in the other 14-3-3 gene leo. We show that although D14-3-3ε is enriched within pole cells it is required in mesodermal somatic gonad precursor cells which guide pole cells in their migration through the mesoderm and coalesce with them to form the embryonic gonad. Loss of D14-3-3ε results in defective pole cell migration, reduced pole cell number. We present evidence that D14-3-3ε loss results in reduction or loss of the transcription factor Zfh-1, one of the main regulatory molecules of the pole cell migration, from the somatic gonad precursor cells

Exploring self-determined solutions to service and system challenges to promote social and emotional wellbeing in Aboriginal and Torres Strait Islander people: a qualitative study

PUBLISHED 22 September 2023Introduction: Many Aboriginal and Torres Strait Islander people living on Kaurna Country in northern Adelaide experience adverse health and social circumstances. The Taingiwilta Pirku Kawantila study sought to understand challenges facing Aboriginal and Torres Strait Islander communities and identify solutions for the health and social service system to promote social and emotional wellbeing. Methods: This qualitative study applied Indigenous methodologies undertaken with Aboriginal and Torres Strait Islander governance and leadership. A respected local Aboriginal person engaged with Aboriginal and Torres Strait Islander community members and service providers through semi-structured interviews and yarning circles that explored community needs and challenges, service gaps, access barriers, success stories, proposed strategies to address service and system challenges, and principles and values for service design. A content analysis identified the breadth of challenges in addition to describing key targets to empower and connect communities and optimize health and social services to strengthen individual and collective social and emotional wellbeing. Results: Eighty-three participants contributed to interviews and yarning circles including 17 Aboriginal community members, 38 Aboriginal and Torres Strait Islander service providers, and 28 non-Indigenous service providers. They expressed the need for codesigned, strengths-based, accessible and flexible services delivered by Aboriginal and Torres Strait Islander workers with lived experience employed in organisations with Aboriginal and Torres Strait Islander leadership and governance. Community hubs and cultural events in addition to one-stop-shop service centres and pre-crisis mental health, drug and alcohol and homelessness services were among many strategies identified. Conclusion: Holistic approaches to the promotion of social and emotional wellbeing are critical. Aboriginal and Torres Strait Islander people are calling for places in the community to connect and practice culture. They seek culturally safe systems that enable equitable access to and navigation of health and social services. Aboriginal and Torres Strait Islander workforce leading engagement with clients is seen to safeguard against judgement and discrimination, rebuild community trust in the service system and promote streamlined access to crucial services.Anna P. Dawson, Eugene Warrior, Odette Pearson, Mark A. Boyd, Judith Dwyer, Kim Morey, Tina Brodie, Kurt Towers, Sonia Waters, Cynthia Avila, Courtney Hammond, Katherine J. Lake, Uncle, Frank Lampard, Uncle, Frank Wanganeen, Olive Bennell, Darrien Bromley, Toni Shearing, Nathan Rigney, Schania Czygan, Nikki Clinch, Andrea Pitson, Alex Brown and Natasha J. Howar