Search results for "Fracture toughness"
showing 10 items of 67 documents
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…
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…
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…
Statistical model of the transverse ply cracking in cross-ply laminates by strength and fracture toughness based failure criteria
2008
Cross-ply laminate subjected to tensile loading provides a relatively well understood and widely used model system for studying progressive cracking of the transverse ply. This test allows to identify material strength and/or toughness characteristics as well as to establish relation between damage level and the composite stiffness reduction. The transverse ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. The variability affects both crack initiation (governed by the local strength) and propagation (governed by the local fracture toughness). The primary aim of the present study is elucidation of the relative importance…
Influence of preheating on mechanical and surface properties of nanofilled resin composites
2019
Background Resin composite preheating is an innovative method that could be clinically beneficial by improving the handling properties, marginal adaptation, and surface properties of uncured nanofilled resin composite materials. There is conflict and unclear information regarding the effect of preheating on the microhardness, fracture toughness and surface roughness of nanofilled resin composites. Thus, it is important to assess whether dental clinicians can adopt preheating procedures without compromising composite mechanical strength. Objective: The purpose of this study was to evaluate the effect of preheating on microhardness, fracture toughness and surface roughness of nanofilled resin…
R-Curve Modelling of Mode I Delamination in Multidirectional Carbon/Epoxy Composite Laminates
2014
In the present work, the mode I delamination behaviour of a quasi-isotropic quasi-homogeneous carbon/epoxy composite laminate with adjacent plies of 0o//45o is studied numerically. To describe the R-curve behaviour observed during crack propagation, a linear-exponential traction-separation law is proposed, where the fracture toughness and the increment in the fracture energy could be considered separately in the model. This model is then implemented in the finite element simulation of the delamination process in the composite laminate. Numerical results indicate that with the incorporation of the fibre bridging effect leads to a well-predicted force-displacement response of the composite la…
Hydrothermal ageing of radiation cured epoxy resin-polyether sulfone blends as matrices for structural composites
2010
Abstract The hydrothermal ageing of epoxy–thermoplastic blends, used as matrices for carbon fibre composites, cured by electron beam, has been studied. Two different thermoplastic percentages have been adopted. A suitable choice of both curing process and formulation parameters allows to carry out irradiation at mild temperature with several advantages, coming from a “non thermal” process, for both the final properties of the materials and the environment. Nevertheless the occurring of vitrification phenomena needs the use of a short thermal treatment after irradiation on the already solid materials, in order to complete the cure reactions. Radiation cured epoxy based matrices have been sub…
Electrospun rubber/thermoplastic hybrid nanofibers for localized toughening effects in epoxy resins
2020
Synthetic rubber/thermoplastic blends were electrospun from their solutions. The rubber was a solid acrylonitrile/butadiene/acrylic acid copolymer and the thermoplastic was polyacrylonitrile. The aims of this study were to identify suitable systems and processing conditions for obtaining rubber-based electrospun nanofibers, to investigate the ability of an epoxy resin system to impregnate and swell selected hybrid rubber/thermoplastic mats, and to assess the impact of the nanofibers on the resin morphology and curing behavior. In particular, electrospinning trials were carried out varying the composition of the feed solution and process parameters, such as the applied voltage, the flow rate…