Showing papers by "Michael May published in 2020"
TL;DR: In this paper, the Transverse Crack Tension test has been identified as a promising approach to measure the high-rate mode II fracture toughness of composites under high rates of loading.
Abstract: Composite materials are often subjected to mechanical impact causing delamination. For quasi-static loading, measuring the mode II fracture toughness has been standardized. However, for high-rate loading, additional challenges arise. Consequently, no standard test has yet been defined for measuring the mode II fracture toughness under high rates of loading. This article therefore reviews candidate tests for measuring the high-rate mode II fracture toughness. Strength and weaknesses of different specimen designs and test setups are shown. The different approaches are compared and recommendations are provided for measuring the mode II fracture toughness of composites under high rates of loading. The Transverse Crack Tension test has been identified as a promising approach to measure the high-rate mode II fracture toughness.
17 citations
TL;DR: In this paper, a sandwich panel based on upcycled bottle caps core and sustainable components is investigated to contribute to advances in lightweight and environmentally friendly structural solutions, where low-cost reinforcement (Portland cement) is added to adhesives to enhance the mechanical behaviour of the panel.
Abstract: A sandwich panel based on upcycled bottle caps core and sustainable components is investigated to contribute to advances in lightweight and environmentally friendly structural solutions. Ecological alternatives to the panel skin and adhesive, such as a recycled PET-bottle foil and a castor oil bio-polyurethane, respectively, are tested and compared to commercial components (aluminium skin and epoxy polymer). Bottle caps are characterised using a small punch test specially developed to obtain the properties of the bottle caps. Additionally, low-cost reinforcement (Portland cement) is added to adhesives to enhance the mechanical behaviour of the panel. The sustainable panels achieve enhanced efficiency compared to aluminium-based panels for core shear strength and stiffness, besides having similar specific flexural properties compared to those of epoxy-based PET panels. Despite their higher strength and stiffness, epoxy polymer-based panels show visible adhesive peeling off to bottle caps core and aluminium skin. In contrast, the biopolymer exhibits larger deformation and debonding of both substrates, indicating a progressive and ductile failure. The satisfactory efficiency of sustainable panels confirms the promising reuse of recycled bottle caps in structural applications.
16 citations
TL;DR: In this article, a bio-polyurethane (bio-PU) adhesive made from castor oil plant is used in sustainable (eco-friendly) sandwich panels made from recycled plastic waste.
15 citations
TL;DR: In this paper, the authors performed transverse compression tests on a unidirectional composite under quasi-static and high-rate loading conditions using servo-hydraulic machines as well as a direct impact Hopkinson bar.
Abstract: Transverse compression tests on a unidirectional composite were performed under quasi-static and high-rate loading conditions using servo-hydraulic machines as well as a direct impact Hopkinson bar. Aside the expected increase of compressive strength with increasing loading rate, a change of fracture plane orientation was observed. For quasi-static loading conditions, the fracture angle was 54.5°, for high rate-loading conditions this increased to 65°. Assuming a Mohr-Coulomb type of fracture for unidirectional composites under transverse compression loading, the change of fracture plane orientation indicates a rate dependency of the internal friction angle ϕ , which has not previously been reported for composite materials.
6 citations
15 Apr 2020
TL;DR: In this paper, the joint failure plays a key role in determining structural stability and crash or impact response, and characterizing the joints at high loading rates is challenging as oscillations are often overlaid on...
Abstract: Joint failure plays a key role in determining structural stability and crash or impact response. Characterizing the joints at high loading rates is challenging as oscillations are often overlaid on...
5 citations
TL;DR: In this paper, the photoelastic effect was used to visualize and quantify stresses at the end of fibers embedded in birefringent epoxy resin, and a method was proposed allowing not only quantifying the differences in main principal stress for a single loading state, but also monitoring the evolution of local stress throughout the micro-mechanical experiment.
Abstract: The photoelastic effect was used to visualize and quantify stresses at the end of fibers embedded in birefringent epoxy resin. A method was proposed allowing not to only quantify the differences in main principal stress for a single loading state, but to allow monitoring the evolution of local stress throughout the micro-mechanical experiment. It was found that the ends of fibers foster the formation of shear stresses which influence the principal stress distribution. Typically, star-shaped principal stress distributions were found at the ends of fibers. Finite Element simulations of the tests were in good agreement with the experimental evidence.
1 citations