Fatigue crack growth in an aluminum alloy

| openaire: EC/H2020/857470/EU//NOMATENIn fatigue fracture the crack growth is slow and in many materials exhibits apparent self-similarity as expressed by the dependence of the growth velocity on a stress intensity factor that grows with the crack size. We study the intermittency of fatigue crack dynamics in aluminium alloys by optical tracking. A power-law distribution of crack tip jumps is found with an exponent close to two and a cutoff which increases with time or crack propagation. The cutoff is related to the crack velocity. We show how such a distribution evolves or coarse grains with the scale of observation or time window. The correlations of the crack propagation imply short-range memory effects in the underlying dynamics. Our results show universal features of fatigue cracks and how these lead to the crack growth and failure in material samples.Peer reviewe

Cellulose foams as scalable templates for phase change materials

Funding Information: M. Alava and J. Koivisto acknowledge support from FinnCERES flagship [ 151830423 ] and Business Finland [ 211835 ]. M. Alava, T. Mäkinen and I. Y. Miranda-Valdez acknowledge support from Business Finland [ 211909 ]. M. R. Yazdani acknowledges financial support from the Academy of Finland [ 343192 ]. I. Y. Miranda-Valdez acknowledges financial support from the Finnish Ministry of Education and Culture via its Finland Fellowship scholarship program. The funding sources had no role in any activity related to this manuscript. Publisher Copyright: © 2023 The Author(s)Cellulose foams produced by wet-templating fibers and surfactants offer an unlimited creative space for the design of green functional materials with a wide range of energy-related applications. Aiming to reduce plastic pollution, cellulose foams promise to replace plastic foams after tailoring physical functionalities into their structures. Here, this work demonstrates that cellulose foams made of methylcellulose and cellulose fibers can exhibit a solid–liquid phase change functionality by adding a phase change material (PCM) during the foam-forming process. The resulting foam composites, termed cellulose phase change foams (PCFs), exhibit a tenth of cellulose's density (134.7 kg m−3) yet a high Young's modulus (0.42MPa). They are also dimensionally stable over a wide range of temperatures while absorbing up to 108 kJ kg−1 as latent heat when the PCM confined to the foam experiences a solid-to-liquid transition at ∼60 °C, and releasing 108 kJ kg−1 as latent heat when changing from liquid to solid at ∼40 °C. Such phase change transition opens up broad applications for the PCFs as thermal insulators. For example, by further tuning the transition temperature, the PCFs can exploit their phase change and reduce the heat flow rate through their radial direction at specified temperatures. This article showcases the versatility of the foam-forming process of cellulose to accommodate physical functionalities in materials with complex architectures. Furthermore, thanks to the advances in cellulose foam-forming, such foams are recyclable, industrially scalable, and can be exploited as heat storage materials.Peer reviewe

Scalable method for bio-based solid foams that mimic wood

| openaire: EC/H2020/857470/EU//NOMATENMimicking natural structures allows the exploitation of proven design concepts for advanced material solutions. Here, our inspiration comes from the anisotropic closed cell structure of wood. The bubbles in our fiber reinforced foam are elongated using temperature dependent viscosity of methylcellulose and constricted drying. The oriented structures lead to high yield stress in the primary direction; 64 times larger than compared to the cross direction. The closed cells of the foam also result in excellent thermal insulation. The proposed novel foam manufacturing process is trivial to up-scale from the laboratory trial scale towards production volumes on industrial scales.Peer reviewe

Foam-formed biocomposites based on cellulose products and lignin

Funding Information: M.A., L.J., J.K., T.M. and A.P. acknowledge support from FinnCERES flagship (151830423) and Business Finland (211835). L.V. acknowledges funding from the Vilho, Yrjö, and Kalle Väisälä Foundation via personal grants. Publisher Copyright: © 2023, The Author(s).Abstract: Foam-formed cellulose biocomposites are a promising technology for developing lightweight and sustainable packaging materials. In this work, we produce and characterize biocomposite foams based on methylcellulose (MC), cellulose fibers (CF), and lignin (LN). The results indicate that adding organosolv lignin to a foam prepared using MC and CF moderately increases Young’s modulus, protects the foam from the growth of Escherichia coli bacteria, and improves the hydrophobicity of the foam surface. This article concludes that organosolv lignin enhances many properties of cellulose biocomposite foams that are required in applications such as insulation, packaging, and cushioning. The optimization of the foam composition offers research directions toward the upscaling of the material solution to the industrial scale. Graphical abstract: [Figure not available: see fulltext.].Peer reviewe