All-cellulose composites (ACCs) were prepared from filter paper via partial dissolution in the ionic liquid 1-ethyl-3-methylimidazolium acetate, and material tensile properties were investigated ...using various approaches. One is based on data directly taken from a tensile testing machine, and the other uses two-cameras stereovision with digital image correlation (DIC) technique. In the latter case, virtual extensometer with different locations on the sample and averaging over sample surface were tested. Nominal and true stress–strain dependences were built and Young's modulus, tensile strength, elongation at maximal stress and toughness were evaluated as a function of ACC density. A minor difference was observed for the stress–strain dependences derived from different approaches which use the DIC technique, most probably because of low ACC deformation. However, the results reveal that the nominal stress–strain curve from DIC is significantly different from that which is directly derived from the data provided by machine sensors thus strongly impacting Young’s modulus and elongation at break values. This study provides an insight into the evaluation of the mechanical properties of ACCs.
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Poly(ethylene 2,5-furandicarboxylate), PEF and poly(ethylene terephthalate), PET, are two polyesters with close chemical structures. It leads to similar thermal, mechanical and barrier properties. In ...order to optimize their stretching, a strategy based on the time/temperature principle is used. The building of master curves, in the linear visco-elastic domain, allows the identification of the experimental conditions for which the two materials are in the same physical state. The initial physical state of the materials is important as, to fit with the industrial constrains, the polymers must reach high level of deformation, and develop strain induced crystallization (SIC). In this paper, the screening of the forming range is described, as well as the mechanical response depending on the stretching settings. Moreover, the same mechanical response can exist for PEF and PET if the same gap from the α-relaxation exists.
The effect of the strain rate on damage in carbon black filled Ethylene Propylene Diene Monomer rubber (EPDM)stretched during single and multiple uniaxial loading is investigated. This has been ...performed by analyzing the stress-strain response, the evolution of damage by Digital Image Correlation (DIC), the associated dissipative heat source by InfraRed thermography (IR), and the chains network damage by swelling. The strain rates were selected to cover the transition from quasi-static to medium strain rate conditions. In single loading conditions, the increase of the strain rate yields in a preferential damage of the filler network while the rubber network is preserved. Such damage is accompanied by a stress softening and an adiabatic heat source rise. Conversely, increasing the strain rate in cyclic loading conditions yields in a filler network accommodation and a high self-heating whose combined effect is proposed as a possible cause of the ability of filled EPDM to limit damage by reducing cavities opening during loading, and favoring cavities closing upon unloading.
The ideal artificial heart valve does not exist yet. Understanding of mechanical and structural properties of natural tissues is necessary to improve the design of biomimetic aortic valve. Besides ...these properties are needed for the finite element modeling as input parameters. In this study we propose a new method combining biaxial tests and digital image correlation. These tests are carried out on porcine aortic valves. In this work, we use a modified version of the HGO (Holzapfel-Gasser-Ogden) model which is classically used for hyper-elastic and anisotropic soft tissues. This model can include fiber orientation. The identification of HGO model parameters can be determined using experimental data and two different protocols. One protocol is based on the identification of collagen fibers orientation as well as the mechanical parameters. The second one, is based on a complementary experiment to determine orientation (confocal laser scanning microscope). Both lead to determine different sets of material parameters. We show that the model is more likely to reproduce the actual mechanical behavior of the heart valves in the second case and that a minimum of three different loading conditions for the biaxial tensile tests is required to obtain a relevant set of parameters.
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•Several loading protocols are necessary to measure aortic valves mechanical behavior.•A modified version of the HGO model gives relevant results.•Both biaxial tensile test data and confocal structural information are required.•Our set of model parameters allows to model every loading conditions.
Powder metallurgy stands out as a highly promising and versatile method for manufacturing particle-reinforced metal matrix composite (MMCs) as compared to other fabrication processes. This method ...ensures excellent binding between the matrix and reinforcement, uniform microstructure, and effectively prevents the formation of undesirable phases. In this study, magnesium alloy (AZ91) metal matrix composites (MMCs) reinforced with 0–30 vol% of Ti3AlC2 MAX phase were prepared by Spark Plasma Sintering (SPS) from powders at temperature close to the solidus. Ti3AlC2 is a member of the MAX phases which are known for their layered structure, machinability and being ternary carbides. The latter was synthetized from pure components (Ti, TiC and Al) using insulated SPS technology at high temperature. Sintered composites reached quasi-full density, as measured by Archimedes’ method. Their microstructure has been assessed by SEM and X-ray diffraction (XRD) respectively. Mechanical properties in relationship with the microstructure of all composites were carefully investigated. The experimental compressive tests data were extracted to obtain true strain-true stress curves. Vickers hardness (HV1), ultimate compressive strength (UCS) and conventional yield strength (0.2%YCS) increase with an increasing fraction of Ti3AlC2 in the composites and compare favorably with literature. SEM observations of fracture surfaces after compression tests seem to show that cracks initiate in both Ti3AlC2 clusters and α-Mg/MAX interfaces.
•For the first time, fully dense Ti3AlC2/AZ91 composites are manufactured by SPS powder metallurgy method.•These composites, exhibited a uniform distribution of the MAX phase into the AZ91 powder matrix.•An increase in Ti3AlC2 vol% in AZ91 improved hardness and the compressive strength.•The Ti3AlC2/AZ91 composites, in comparison to others MMCs exhibited superior strength and elasticity.
Ice-templated waxy maize starch.
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•Neat anisotropic waxy maize starch cryogels were made via ice-templating method.•The morphology varied from lamellar to sponge-like, controlled by ...starch concentration.•Cryogels possess anisotropic mechanical and thermal conductivity properties.•Cryogel compression in the transverse direction leads to thermal conductivity decrease.
Biodegradable anisotropic neat porous starch materials without any additional cross-linking, plasticizer or any extra matter have been fabricated via facile ice-templating method. Waxy maize was dissolved in water followed by unidirectional freezing and ice sublimation. The influence of process parameters (starch concentration and retrogradation time) on the morphology, density, mechanical properties under the uniaxial compression and thermal conductivity were investigated. The internal morphology and the shape of the pores, from lamellar to sponge-like, was shown to be governed by starch concentration. All porous starches have very low density (0.07–0.15 g/cm3), anisotropic mechanical properties and low thermal conductivity, in particular in transverse direction (0.037–0.048 W/(m·K)). Interestingly, when compressing the ice-templated starches in the transverse direction, the thermal conductivity was further decreased reaching the values of 0.033 W/(m·K). This work provides the guidelines for making fully biobased porous starch materials with controlled morphology and properties.
Aerogels are highly porous nanostructured materials with a high specific surface area, a very low density and a low thermal conductivity. Bio-aerogels, prepared from biopolymers, have gained interest ...for biomedical applications. While most bio-aerogels are polysaccharide-based, protein-based aerogels using silk fibroin (SF) from Bombyx mori cocoons remain underexplored. Our study delved into the impact of coagulation methods on SF aerogel properties, specifically, comparing ethanol treatment (Method 1) and sodium dihydrogen phosphate (NaH 2 PO 4) (Method 2). Aerogels obtained through Method 1 exhibited a volume shrinkage of approximately 12-22 % and a density of about 0.06-0.07 g cm-3 , while those obtained via Method 2 demonstrated a more substantial volume shrinkage of approximately 60-70 % and a higher density of around 0.2 g cm-3. These differences significantly influenced the internal structure of the aerogels, manifesting distinct morphological features of the materials. Mechanical tests revealed that SF aerogels derived from Method 2 displayed superior stress resistance at 80 % strain and higher elastic recovery when compared to samples of Method 1. In conclusion, the choice in coagulation methods broadens the mechanical property and density window for this type of aerogel which offers opportunities for a wide range of biomedical applications.
Chains and filler network damage were investigated during single and multiple cycles on a series of vulcanized EPDM containing various filler contents. In both series of experiments, a strain and a ...filler ratio transitions for damage mechanisms were identified. For low filler content (≤40 phr), damage mechanisms mostly occur in the elastically active rubber network consistent with the chains network alteration theory associated with irreversible chains scission/bond breakage. For high filler content (>40 phr), a strain transition occurs with damage initially located in the elastically active rubber network, but subsequently localizes in the vicinity of the filler-filler network. This is ascribed to filler re-aggregation with strain, improving its load-bearing capacity, that may release the immobilized rubber formed by the chains that are occluded and bonded to fillers. During cyclic experiments, such reversible release involving loss of weak physical bonds and chains slippage yields in a progressive cavity closing with cyclic accumulation that prevents further irreversible damage of the elastically active rubber network.
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•Mechanical damage of EPDM with various CB fillers content (ϕ) were studied.•For ϕ ≤ 40 phr, irreversible damage of the rubber network occurs.•For ϕ > 40 phr, a strain transition to a reversible filler network damage occurs.•For ϕ > 40 phr, cyclic accumulation favours voids closing.
This paper presents an experimental method to follow in-situ the chains network alteration of filled vulcanized rubbers induced by deformation. Macroscopic damage is first investigated on a series of ...EPDM by quantifying void fraction via Digital Image Correlation (DIC). In-situ DIC void fraction and the swollen pore fraction measured ex situ, i.e. on mechanically tested specimen, show analogous dependence on applied deformation. From such observation, Flory-Rehner equation is used by substituting fraction of swollen specimen by DIC void fraction to access to in-situ changes in network chains density, ν. Below the stretching ratio λ = 3, reversible voids and accompanied by slight decrease of ν. Above λ = 3, irreversible voids are associated with significant decrease of ν. Transition from reversible to irreversible voiding is finally ascribed to increased pore size of damaged elastically active chains network domains, as revealed by ex situ thermoporosimetry.
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•DIC-based method provides access to in-situ alteration of rubber chains network.•For λ < 3, reversible voids are related to slight decrease of ν•For λ > 3, irreversible voids are related to large decrease of ν•Transition at λ = 3 is due to increased size of damaged network chains domains.
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