Search results for "Toughness"
showing 10 items of 105 documents
Interlaminar fracture toughness behavior of electron-beam cured carbon-fiber reinforced epoxy-resin composites
2013
The work describes the preparation and physical-mechanical characterization of unidirectional CFRP panels manufactured by an electron beam curing technique. Delamination fracture toughness in Mode I and II is investigated in order to evaluate the influence of fiber–matrix adhesion strength, matrix toughness and matrix crosslinking density as determined by the radiation curing process. A matrix system comprising a DGEBA epoxy monomer and an initiator of cationic polymerization have been used, with one batch of resin mixed with a PES monomer in order to enhance matrix toughness. Curing was achieved with a pulsed 10 MeV Electron Beam accelerator. Thermally cured composite systems have also bee…
Anionic Copolymerization Enables the Scalable Synthesis of Alternating (AB)n Multiblock Copolymers with High Molecular Weight in n/2 Steps
2018
Based on the highly disparate reactivities of isoprene (I, rI = 25.4) and 4-methylstyrene (4MS, r4MS = 0.007) in the anionic copolymerization in nonpolar media, a general strategy for the rapid and scalable synthesis of tapered multiblock copolymers with an extremely steep gradient has been developed. A repetitive addition strategy of a mixture of isoprene and 4MS leads to a tapered diblock in each case, giving access to linear alternating multiblock copolymers of the (AB)n type with up to 10 blocks. All multiblock copolymers showed narrow molecular weight distributions (dispersity Đ = 1.04–1.12). High molecular weights in the range of 80 to 400 kg mol–1 were achieved. Due to the incompatib…
Micromechanics of “raspberry” morphology in PPE/SAN polymer blends compatibilized with linear ABC triblock terpolymers
2015
Abstract The effect of compatibilization with a symmetrical polystyrene- block -polybutadiene- block -poly(methyl methacrylate) (SBM) triblock terpolymer on the morphological and mechanical properties (specifically toughness) of immiscible poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene- co -acrylonitrile) (PPE/SAN) blends with different blend (w/w) ratios is investigated. We study the effect of blend viscosity on the localization of the compatibilizer at the blend interface, influencing the mechanical properties of the macroscopic material. The impact of the specific morphology of the blends, known as “raspberry morphology”, on the final material will be explained using thermomechanica…
Tapered Multiblock Star Copolymers: Synthesis, Selective Hydrogenation, and Properties
2020
Two series of well-defined multiblock four-arm tapered star copolymers with “arms” of the type poly(styrene)-block-poly(isoprene-grad-styrene), (SI/S)₄, were synthesized on a multigram scale with short reaction times. Targeted molecular weight (M) values ranged from 80 to 240 kg mol–¹ with polystyrene (PS) compositions of 40 and 60 wt %. Narrowly distributed (Đ = 1.04–1.12) copolymers were obtained regardless of M and without additional purification beyond precipitation. At sufficiently high M, members of the 40 wt % PS series possessed either a cylindrical or bicontinuous morphology, whereas the 60 wt % PS series yielded lamellae. The star copolymers outperformed their corresponding linear…
Estimation of interfacial fracture toughness based on progressive edge delamination of a thin transparent coating on a polymer substrate
2010
Evaluation of interfacial toughness of sub-micron-thickness layers deposited on a ductile substrate is a challenging task which has motivated different experimental approaches Fragmentation testing was used in the present study as a means of interface characterization of a silicon-nitride-coated polyimide substrate. During the test, after an initial rapid segmentation-cracking phase, the coating fragments developed edge delaminations which propagated in a stable manner with further increase in the applied strain The debonding process was modelled by the finite element method Incorporating a cohesive zone at the front of the interfacial crack The edge cracks were found to be dominated by mod…
Synergistic effects of Janus particles and triblock terpolymers on toughness of immiscible polymer blends
2017
Abstract By influencing both the interfacial adhesion and the morphology, compatibilizers determine the mechanical properties of polymer blends. Here, we study the mechanical properties, in particular the fatigue crack propagation (FCP) of immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene- co -acrylonitrile) (PPE/SAN), compatibilized with Janus nanoparticles (JPs) and linear polystyrene- block -polybutadiene- block -poly(methyl methacrylate) (SBM) triblock terpolymers. Synergistic effects of a mixture of both compatibilizers improve the FCP behavior and reveal the important role of interface stiffness and flexibility on the mechanical properties of polymer blends. The…
Effects of fiber orientation of adjacent plies on the mode I crack propagation in a carbon-epoxy laminates
2011
Abstract The influence of ply orientation on the resistance to mode I delamination of multidirectional composite laminates can be assessed by Double Cantilever Beam (DCB) tests. However, one of the difficulties associated with such a study is the change in overall elastic parameters occurring when modifying local ply orientations. The present work uses laminates with special stacking sequences allowing for isolating the orientation parameter. Multidirectional DCB specimens were designed so as to obtain an uncoupled quasi isotropic and quasi-homogeneous elastic behavior, with the same properties for the entire laminate and the two sub laminates separated by the pre crack at mid-plane. The re…
Mechanical, thermal and electrical properties of nanostructured CNTs/SiC composites
2018
International audience; Dense SiC-based nanostructured composites reinforced by well-distributed carbon nanotubes (CNTs) were elaborated for the first time by spark plasma sintering (SPS) without sintering additive. Microstructures of materials containing different amounts of CNTs – up to 8.0 vol% – were correlated with their mechanical, electrical and thermal properties. A continuous decrease of the SiC grain size was observed when the amount of CNT was increased, while the evolution of density showed a different behavior that could be explained by the particular combination of SPS technique with the electrical resistivity evolution of the green bodies. Optimal effect of CNTs addition on h…
Evaluation of toughness by finite fracture mechanics from crack onset strain of brittle coatings on polymers
2008
Crack onset strain measurements of a confined layer in tension provide the means for layer toughness estimation. The procedure can be simplified if steady-state conditions prevail starting from the commencement of crack propagation, an assumption frequently employed in energy release rate evaluation. It is demonstrated, by numerical analysis of experimental data, that an estimate of the defect size in the film is needed in order to reliably evaluate its fracture toughness from the crack onset strain. Only if microcracks of sufficient size are present in the brittle layer, the steady-state energy release rate at the crack onset strain can be identified with layer toughness. Otherwise, the to…
Siliceous spicules enhance fracture-resistance and stiffness of pre-colonial Amazonian ceramics
2015
AbstractPottery was a traditional art and technology form in pre-colonial Amazonian civilizations, widely used for cultural expression objects, utensils and as cooking vessels. Abundance and workability of clay made it an excellent choice. However, inferior mechanical properties constrained their functionality and durability. The inclusion of reinforcement particles is a possible route to improve its resistance to mechanical and thermal damage. The Amazonian civilizations incorporated freshwater tree sponge spicules (cauixí) into the clay presumably to prevent shrinkage and crack propagation during drying, firing and cooking. Here we show that isolated siliceous spicules are almost defect-f…