Fully recyclable corrugated sandwich beams made from self-reinforced poly(ethylene terephthalate) SrPET are manufactured and tested in quasi-static three-point bending. For a constant areal mass, the influence of mass distribution on peak load and energy absorption is investigated. Beams with a higher proportion of their mass distributed in the core generally show higher peak loads and energy absorption. A finite element (FE) model was developed using an anisotropic visco-plastic constitutive material law. The FE predictions are in excellent agreement with the measurements. When comparing to sandwich beams with similar weight and geometry of different materials, the SrPET sandwich beams outperform corrugated sandwich beams made from aluminium in terms of peak load and energy absorption.

Corrugated sandwich beams made entirely from self-reinforced poly (ethylene terephthalate) SrPET are manufactured and tested dynamically. The beams are subjected to impact loading at the mid-span using a metal foam projectile and the beam deflection is measured. For sandwich beams with a constant areal mass, beams with a high mass portion in the core webs outperform configurations with a high mass portion in the face sheets (given that the face sheets are thick enough to carry the transversal loads induced by the core webs). Reinforcing the face sheet - core web interface further improves the impact response. The strain rate sensitivity of SrPET has also been investigated. A three-dimensional finite element (FE) model has been developed to simulate the impact event and a good agreement is found with the measured response. It is found that corrugated sandwich beams made from SrPET has competitive impact performance compared to similar sandwich beams with equal mass and geometry out of aerospace grade aluminium and carbon fiber/high performance foam sandwich.

One typical way to obtain higher stiffness and strength to weight ratios within structural applications is to use sandwich structures containing lightweight cellular cores. In this study a novel second order hierarchical sandwich structure and its manufacturing principle are described. The whole hierarchical structure is made of a fully recyclable material - different forms of poly-ethylene terephthalate (PET): PET matrix, reinforced with PET fibres (Self reinforced - SrPET) and PET foam resulting in a recyclable structure. The manufacturing path is developed such that it can be implemented within a continuous production line. Out-of-plane compression test are carried out in order to determine the stiffness and strength properties of the proposed structure. An analytical model is developed for evaluating the out-of-plane stiffness and strength properties and used for investigating the influence of the geometric parameters on the structural performance of the proposed hierarchical sandwich structure. (C) 2016 Elsevier Ltd. All rights reserved.

Self-reinforced polymer composites are gaining increasing interest due to their higher ductility compared to traditional glass and carbon fibre composites. Here we consider a class of PET composites comprising woven PET fibres in a PET matrix. While there is a significant literature on the development of these materials and their mechanical properties, little progress has been reported on constitutive models for these composites. Here we report the development of an anisotropic visco-plastic constitutive model for PET composites that captures the measured anisotropy, tension/compression asymmetry and ductility. This model is implemented in a commercial finite element package and shown to capture the measured response of PET composite plates and beams in different orientations to a high degree of accuracy.

Weight reduction is commonly adopted in vehicle design as a means for energy and emissions savings. However, selection of lightweight materials is often focused on performance characteristics, which may lead to sub optimizations of life cycle environmental impact. Therefore systematic material selection processes are needed that integrate weight optimization and environmental life cycle assessment. This paper presents such an approach and its application to design of an automotive component. Materials from the metal, hybrid and polymer families were assessed, along with a novel self-reinforced composite material that is a potential lightweight alternative to non-recyclable composites. It was shown that materials offering the highest weight saving potential offer limited life cycle environmental benefit due to energy demanding manufacturing. Selection of the preferable alternative is not a straightforward process since results may be sensitive to critical but uncertain aspects of the life cycle. Such aspects need to be evaluated to determine the actual benefits of lightweight design and to base material selection on more informed choices.

A novel manufacturing route to efficiently produce fibre composite lattice structures has been developed. By using thermoplastic composite materials, flat sheets have been continuously folded, cut into a lattice shape and joined into a sandwich structure. Carbon fibre reinforced poly-ethylene terephthalate (CPET) and poly-ethylene terephthalate fibre reinforced poly-ethylene terephthalate (SrPET) materials have been used to explore two different core options; a carbon fibre option which gives high performance but low recyclability and a single polymer PET option which gives lower performance but full recyclability. Parametric numerical simulations have been used to investigate how the various manufacturing parameters affect the mechanical performance of the core. The carbon fibre composite cores have mechanical performance on-par or better than existing metallic and composite lattice cores presented in literature. Single polymer PET cores show better performance compared to high-end foam cores but have considerable lower performance than carbon fibre lattice cores.

A novel manufacturing route for fully recyclable corrugated sandwich structures made from self-reinforced poly(ethylene terephthalate) SrPET composites is developed. The dynamic compression properties of the SrPET material and the out-of-plane compression properties of the sandwich core structure are investigated over a strain rate range 10(-4)-10(3) s(-1). Although the SrPET material shows limited rate dependence, the corrugated. core structures show significant rate dependence mainly attributed to micro-inertial stabilisation of the core struts and increased plastic tangent stiffness of the SrPE"T material. The corrugated SrPET cores have similar quasi-static performance as commercial polymeric foams but the SrPET cores have superior dynamic compression properties.

Lightweight structures in vehicles are a proven way to reduce fuel consumption and the environmental impact during the use. Lower structural weight can be achieved by using high performance materials such as composites or using the material efficiently as a sandwich structure. Traditional composite materials such as carbon or glass fiber reinforced polymers have high weight specific mechanical properties but are inherently brittle and expensive. They consist of at least two different materials making recycling a difficult endeavor.The best composite material would have good weight specific properties and is ductile, cheap and comprises of a reinforcement and matrix material based on the same recyclable material making recycling easy. In self-reinforced polymer (SrP) composite materials, reinforcing fibers and matrix material are based on the same recyclable thermoplastic polymer making recycling to a straightforward process. SrP composite materials are ductile, inexpensive and have a high energy absorption potential. The aim of this thesis is to investigate the potential of SrP composites in structural applications. Firstly, the quasi-static and dynamic tensile and compression properties of a self-reinforced poly(ethylene terephthalate) (SrPET) composite material are investigated confirming the high energy absorption potential. Sandwich structures out of only SrPET with a lattice core are manufactured and tested in quasi-static out-of-plane compression showing the potential of SrPET as core material. Corrugated sandwich structured out of only SrPET are manufactured and tested in out-of-plane compression over a strain rate range10⁻⁴ s⁻¹ - 10³ s⁻¹. The corrugated SrPET core has similar quasi-static properties as commercial polymeric foams but superior dynamic compression properties. Corrugated sandwich beams out of only SrPET are manufactured and tested in quasi-static three-point bending confirming the high energy absorption potential of SrPET structures. When comparing the SrPET beams to aluminum beams with identical geometry and weight, the SrPET beams shows higher energy absorption and peak load. The experimental results show excellent agreement with finite element predictions. The impact behaviorof corrugated SrPET sandwich beams during three-point bending is investigated. When comparing SrPET sandwich beams to sandwich beams with carbon fiber face sheets and high performance thermoset polymeric foam with the same areal weight, for the same impact impulse per area, the SrPET shows less mid-span deflection.

Tensile and compression properties of self-reinforced poly(ethylene terephthalate) (SrPET) composites has been investigated. SrPET composites or all-polymer composites have improved mechanical properties compared to the bulk polymer but with maintained recyclability. In contrast to traditional carbon/glass fibre reinforced composites, SrPET composites are very ductile, resulting in high failure strains without softening or catastrophic failure. In tension, the SrPET composites behave linear elastically until the fibre-matrix interface fails, at which point the stiffness starts decreasing. As the material is further strained, strain hardening occurs and the specimen finally fails at a global strain above 10%. In compression, the composite initially fails through fibre yielding, and at higher strains through fibre bending. The stress-strain response is reminiscent of an elastic-perfectly plastic material with a high strain to failure (typically over 10%). This indicates that SrPET composites are not only candidates as semi-structural composites but also as highly efficient energy absorbing materials.