Search results for "Toughness"
showing 10 items of 105 documents
The durability of carbon fiber/epoxy composites under hydrothermal ageing
2011
Studies on fibre reinforced composites are now receiving greater attention. Industrial applications have been successful in areas like aerospace, automobile, marine, construction and sporting goods. The first generation of epoxy resins for use in carbon fibre composites are able to achieve optimized high stiffness modules and high heat resistance by a high crosslink density, reached through thermal curing. However, these formulations can be very toxic and brittle with low crack resistance, which was a major disadvantage for structural applications. In the last years the use of ionizing radiation as alternative to thermal curing has been proposed as an environmentally friendly process. Furth…
The effect of the through-the-thickness compressive stress on mode II interlaminar fracture toughness
2017
The effect of through-the-thickness compressive stress on the mode II interlaminar fracture toughness is investigated experimentally and replicated numerically. The modified Transverse Crack Tensile specimen recently proposed by the authors is used, together with an experimental device designed to apply a constant transverse compressive stress on the surface of the specimen. Experiments are conducted using IM7/8552 specimens for different compressive stresses, ranging from 0 to 100 MPa, covering all the practical applications commonly encountered in the aeronautical industry (e.g., tightened filled holes or bolted joints). It is shown that the mode II interlaminar fracture toughness increas…
Mode I fracture toughness behaviour of epoxy resincarbon fiber composites cured by ionising radiation
2012
In this work Mode I fracture toughness behavior of Electron Beam cured unidirectional CFRP laminates is investigated by means of standardized Double Cantilever Beam (DCB) tests. A matrix system, comprising a DGEBA epoxy monomer and a typical initiator of cationic polymerization, was used and panel samples assembled by hand lay-up. Curing was achieved by 20 to 40 minutes irradiation on a pulsed 10 MeV Electron Beam accelerator. One batch of resin was also mixed with 10 phr of a PES thermoplastic monomer in order to enhance the matrix toughness. The influence of fibre-matrix adhesion, matrix toughening and matrix crosslinking density on the mode I delamination behavior have been investigated …
Experimental evaluation of through-the-thickness stress distribution in transverse crack tension test samples
2015
Transverse Crack Tension (TCT) samples represent an alternative to End Notched Flexure configurations for the characterization of pure mode II fracture toughness of Fibre Reinforced Polymer composites. TCT is supposed to reproduce a pure Mode II failure mechanism while avoiding the frictional energy dissipation between the flanks of a starter crack. The TCT geometry is that of a unidirectional tensile sample where a number of embedded plies, centered on the middle plane, are cut in the transverse fibres direction. The tensile loading should then activate four symmetric fronts of mode II delamination from the transverse cut tips. The present work describes the implementation of two full fiel…
Sub-micron structured Polymethyl Methacrylate/Acrylonitrile-Butadiene rubber blends obtained via gamma radiation induced “in situ” polymerisation
2004
The morphology and properties of PMMA/rubber blends, obtained through gamma radiation induced “in situ” polymerization of methyl methacrylate (MMA) in the presence of small quantities of an acrylonitrile–butadiene based rubber (ABN), are presented. Different systems have been obtained by irradiating at a fixed irradiation dose rate and temperature, varying the integrated dose. All the blends obtained were characterized with respect to their melt state and solid state dynamic-mechanical response and mechanical tensile properties. In particular, the effect on the blend properties of prolonging the irradiation time was investigated. Furthermore, a morphological characterization through atomic …
Interfacial fracture toughness of universal adhesive systems treated with an antioxidant
2017
Background Secondary caries, degradation of the dentin-resin interface and fracture of the restoration are the most common forms of failure. The aim of this study was to assess the interfacial fracture toughness of three different adhesive approaches and to compare their fracture toughness after surface treatment with antioxidant. Material and methods Seventy two dentin blocks with 3×4mm dimension and 3mm thickness were prepared and attached to precured 3×4×12mm composite blocks from both sides. Six adhesive groups (N=12), All-bond universal, Scotchbond universal and Clearfil SE bond with or without antioxidant treatment (Sodium Ascorbate 10% )were applied to dentin surfaces, a 160µ polyeth…
Thermodynamics and continuum fracture mechanics for nonlocal-elastic plastic materials
2002
Nonlocal elasticity is used as an improved elasticity model which engenders no crack-tip stress singularities and thus makes applicable the classical stress-based failure criteria. Considering nonlocal-elastic plastic materials exposed to softening by particle decohesion in a process surface and to subsequent surface separation by fracture, fracture mechanics is addressed within the framework of irreversible internal-variable thermodynamics in the hypothesis of small strains and arbitrary (but sufficiently regular) fracture surface (crack surface plus process surface). The state equations and the energy dissipation densities are derived for the bulk material and for the process surface, for…
Finite fracture mechanics analysis of crack onset at a stress concentration in a UD glass/epoxy composite in off-axis tension
2010
The presence of stress concentrations at holes and notches is known to reduce the strength of composite materials. Due to complexity of the damage processes at a stress raiser in a composite, different modeling approaches have been developed, ranging from empirical point and average stress criteria to involved damage mechanics or cohesive zone-based models of failure. Finite fracture mechanics approach with a coupled stress and energy failure criterion, recently developed and applied mainly to cracking in homogeneous isotropic materials, allows predicting the appearance and propagation of a crack using material strength and toughness characteristics obtained from independent tests. The pres…
MoSi2 laser cladding—a comparison between two experimental procedures: Mo–Si online combination and direct use of MoSi2
2001
International audience; There are very strong interests in developing low density advanced material systems for service at temperatures up to 1300°C. These materials should mainly have moderate fracture toughness at low and intermediate temperatures and should exhibit oxidation resistant behaviour. The intermetallic compound, MoSi2 has been considered to be an attractive candidate due to its melting point (2030°C) and excellent oxidation resistance at high temperatures. In this paper, we compare the results obtained with two different techniques for laser cladding, one using an online combination between Mo and Si powders, the second using direct injection of the MoSi2 powder.
High-Performance TiO2 Nanoparticle/DOPA-Polymer Composites
2014
Many natural materials are complex composites whose mechanical properties are often outstanding considering the weak constituents from which they are assembled. Nacre, made of inorganic (CaCO 3 ) and organic constituents, is a textbook example because of its strength and toughness, which are related to its hierarchical structure and its well-defi ned organic–inorganic interface. Emulating the construction principles of nacre using simple inorganic materials and polymers is essential for understanding how chemical composition and structure determine biomaterial functions. A hard multilayered nanocomposite is assembled based on alternating layers of TiO 2 nanoparticles and a 3-hydroxytyramine…