Monitoring Dynamic Recrystallisation in Bioresorbable Alloy Mg-1Zn-0.2Ca by Means of an In Situ Acoustic Emission Technique

The tensile behaviour of the biocompatible alloy Mg-1Zn-0.2Ca (in wt.%) in the fine-grained state, obtained by severe plastic deformation via multiaxial isothermal forging, has been investigated in a wide range of temperatures (20 ÷ 300) °C and strain rates (5 × 10−4 ÷ 2 × 10−2) s−1 with the measurements of acoustic emission (AE). The dependences of mechanical properties, including the yield stress, ultimate strength, ductility, and the strain-hardening rate, on the test temperature and strain rate, were obtained and discussed. It is shown for the first time that an acoustic emission method is an effective tool for in situ monitoring of the dynamic recrystallisation (DRX) process. The specific behaviour of the acoustic emission spectral density reflected by its median frequency as a function of strain at various temperatures can serve as an indicator of the DRX process’s completeness.

Tensile Behaviour of Slag-based Engineered Cementitious Composit

Engineered Cementitious Composites (ECC) have become another alternative in the concrete industry due to their excellent strain capacity under uniaxial tension. Research and development for new ECC mix incorporating wastes remain open to fulfil the industrial needs to produce green and sustainable ECCs. This paper presents the experimental work on the tensile and cracking behaviour of ECCs utilising industrial waste, namely ground granulated blast-furnace slag (GGBS), to replace cement. A total of four slag-based ECC mixes containing 2%–2.5% of PVA fibres and 50%-60% GGBS were investigated under uniaxial compressive and tensile tests. Compressive strength, tensile strength and the crack behaviours of the slag-based ECCs were evaluated and compared with a control mix. The experimental results show that the slag-based ECCs can achieve tensile strain capacity 2.6 %–2.75 % and ultimate tensile strength 1.43 MPa–2.82 MPa at 28 days. It was also found that the ECCs with GGBS and fibres formed few hairline cracks at the gage of the dog bone compared to brittle fracture in the control specimens.

Effect of the Fibre Orientation Distribution on the Mechanical and Preforming Behaviour of Nonwoven Preform Made of Recycled Carbon Fibres

Recycling carbon-fibre-reinforced plastic (CFRP) and recovering high-cost carbon fibre (CF) is a preoccupation of scientific and industrial committees due to the environmental and economic concerns. A commercialised nonwoven mat, made of recycled carbon fibre and manufactured using carding and needle-punching technology, can promote second-life opportunities for carbon fibre. This paper aims to evaluate the mechanical and preforming behaviour of this nonwoven material. We focus on the influence that the fibre orientation distribution in the nonwoven material has on its mechanical and preforming behaviour at the preform scale, as well as the tensile properties at composite scale. The anisotropy index induced by fibre orientation is evaluated by analysing SEM micrographs using the fast Fourier transform (FFT) method. Then, the anisotropy in the tensile, bending, and preforming behaviour of the preform is inspected, as well as in the tensile behaviour of the composite. Additionally, we evaluate the impact of the stacking order of multi-layers of the nonwoven material, associated with its preferred fibre orientation (nonwoven anisotropy), on its compaction behaviour. The nonwoven anisotropy, in terms of fibre orientation, induces a strong effect on the preform mechanical and preforming behaviour, as well as the tensile behaviour of the composite. The tensile behaviour of the nonwoven material is governed by the inter-fibre cohesion, which depends on the fibre orientation. The low inter-fibre cohesion, which characterises this nonwoven material, leads to poor resistance to tearing. This type of defect rapidly occurs during preforming, even at too-low membrane tension. Otherwise, the increase in nonwoven layer numbers leads to a decrease in the impact of the nonwoven anisotropy behaviour under compaction load.

Novel Tough and Transparent Ultra-Extensible Nanocomposite Elastomers Based on Poly(2-methoxyethylacrylate) and Their Switching between Plasto-Elasticity and Viscoelasticity

Novel stiff, tough, highly transparent and ultra-extensible self-assembled nanocomposite elastomers based on poly(2-methoxyethylacrylate) (polyMEA) were synthesized. The materials are physically crosslinked by small in-situ-formed silica nanospheres, sized 3–5 nm, which proved to be a very efficient macro-crosslinker in the self-assembled network architecture. Very high values of yield stress (2.3 MPa), tensile strength (3.0 MPa), and modulus (typically 10 MPa), were achieved in combination with ultra-extensibility: the stiffest sample was breaking at 1610% of elongation. Related nanocomposites doubly filled with nano-silica and clay nano-platelets were also prepared, which displayed interesting synergy effects of the fillers at some compositions. All the nanocomposites exhibit ‘plasto-elastic’ tensile behaviour in the ‘as prepared’ state: they display considerable energy absorption (and also ‘necking’ like plastics), but at the same time a large but not complete (50%) retraction of deformation. However, after the first large tensile deformation, the materials irreversibly switch to ‘real elastomeric’ tensile behaviour (with some creep). The initial ‘plasto-elastic’ stretching thus causes an internal rearrangement. The studied materials, which additionally are valuable due to their high transparency, could be of application interest as advanced structural materials in soft robotics, in implant technology, or in regenerative medicine. The presented study focuses on structure-property relationships, and on their effects on physical properties, especially on the complex tensile, elastic and viscoelastic behaviour of the polyMEA nanocomposites.

Microstructure Evolution and Tensile Behaviour of a Cold Rolled 8 Wt Pct Mn Medium Manganese Steel

A novel medium manganese steel with composition Fe–8.3Mn–3.8Al–1.8Si–0.5C–0.06V–0.05Sn was developed and thermomechanically processed through hot rolling and intercritical annealing. The steel possessed a yield strength of 1 GPa, tensile strength of 1.13 GPa and ductility of 41 pct. In order to study the effect of cold rolling after intercritical annealing on subsequent tensile properties, the steel was further cold rolled up to 20 pct reduction. After cold rolling, it was observed that the strain hardening rate increased continuously with increasing cold rolling reduction but without a significant drop in ductility during subsequent tensile tests. The microstructural evolution with cold rolling reduction was analysed to understand the mechanisms behind this phenomena. It was found that cold rolling activated additional twinning systems which provided a large number of potent nucleation sites for strain induced martensite to form during subsequent tensile tests in what can be described as an enhanced TRIP effect.