Bulk fatigue damage evolution in polyamide-6 and in a polyamide-6 nanocomposite

Polymer Composites, 2004

Materials Science and Engineering: A, 2011

Imbibed moisture affects the mechanical properties of polymers and influences the performance of products made out of them during service. Flexural fatigue tests were conducted under deflection control mode using a custom built, table-top flexural fatigue test rig at laboratory condition on PA66/hectorite nanocomposites (PA66CN). Dynamic mechanical analysis studies of PA66CN revealed significant plasticization effect of water on moduli and damping factor with increase in imbibed moisture content. A decrease in induced flexural stress amplitude and rise in temperature of specimen with increase in moisture content result in increased fatigue life at a constant cyclic end deflection. The microstructure of failed flexural fatigue specimens manifested a rubbery behavior. The extent of rubberiness is directly related to the difference between specimen temperature at cyclic steady state and glass transition temperature.

Journal of Materials Science, 2003

In this paper, yield and fatigue behavior of a polypropylene nanocomposite and a polyamide-6 nanocomposite has been studied. The Eyring equation was used to model the temperature and strain rate sensitivity of the yield strengths of these two nanocomposites. Both activation volume and activation energy of the polypropylene nanocomposite were higher than those of the polyamide-6 nanocomposite. The fatigue strength

Materials Science and Engineering: A, 2008

Limits of linear viscoelastic behaviour of TiO 2 nanoparticle-filled polyamides are estimated quantitatively by the results of uniaxial tension tests. The stress limit of the filled polymer is higher than that of the unfilled one. Their values are the lower, the higher the temperature and moisture content of test specimens, and the lower, the lower the strain rate. The concept of an energy threshold for the linear viscoelastic behaviour is used to comprehensively characterize the limits over a wide range of test conditions. The energy limit is not affected by the strain rate, temperature, or moisture, and its value for the filled polymer is higher than that for the un-filled one. When plotted in the stress-strain axes, the data for different test conditions fall on a common curve described by a quasi-linear energy function. The higher the energy, the wider the region of the linear viscoelastic behaviour.

Journal of Materials Science, 2006

The tensile and fatigue behaviours of two types of high performance polyamide 66 fibres have been studied. Marked differences have been found in their fatigue behaviours although their simple tensile behaviours were almost identical. The fibres have been analysed by DSC, X-ray diffraction and by Raman spectroscopy. The fibres have been seen to possess different microstructures with different percentages of ordered regions. In addition the compressive stresses in the regions near the surfaces of the fibres have been found to differ markedly, which may explain the existence of a minimum cyclic load threshold for fatigue failure and suggest a method for improving fatigue resistance.

Materials Science and Engineering: A, 2010

Humidity affects the mechanical properties of polymers and their composites. Understanding the influence of humidity on the strength, stiffness and fatigue characteristics will aid in better product design. The effect of relative humidity (RH) on indentation hardness and flexural fatigue behavior of polyamide 6 nanocomposites is reported. Indentation hardness and indentation modulus of the material reduces up to ∼50% in the samples conditioned in water due to the plasticization and associated increased polymer chain mobility. Cantilever bending fatigue tests conducted at different relative humidity levels at constant displacement amplitude revealed increased fatigue life for polyamide 6 nanocomposites at high humidity. Hysteresis heating and molecular reorientation lowers the modulus during fatigue process and causes a reduction in the force amplitude at high humidity levels. The failure mechanisms at different humidity levels are discussed.

Polymer Testing, 2020

Tensile, fatigue and thermomechanical properties of poly(ethylene-co-vinyl acetate) nanocomposites incorporating low and high loadings of pre-swelled organically modified montmorillonite, Polymer Testing (2020), doi:

International Journal of Fatigue, 2019

Understanding fatigue damage mechanisms in short fiber reinforced thermoplastics is a key issue in order to optimize material processing and propose physically based multiscale fatigue damage models. The present work aims at further understanding observations of fatigue damage in the polyamide 6.6 matrix with respect to its semi-crystalline structure. In this paper the polymer and associated composite are tested in their ductile regime i.e. above the glass transition temperature. Tomographic and SEM observations are used in order to establish a damage scenario at the spherulitic scale. These observations prove that fatigue damage progresses by intra-spherulitic failure in their equatorial plane. Observations of the spherulite nuclei also evidence the oriented structure of the semi-crystalline polymer induced by the injection-molding manufacturing process.

Composites Science and Technology, 2007

The long-term tensile creep of polyamide 66 and its nanocomposites filled with 1 vol.% TiO 2 nanoparticles 21 and 300 nm in diameter is studied. It is assumed that the dominant mechanisms of creep deformation are of viscoelastic nature, while the contribution of plastic strains is not essential in the stress (< 0.6 of the ultimate stress) and time (about 100 h) ranges considered. The creep isochrones obtained show that the materials exhibit a nonlinear viscoelastic behaviour and the degree of nonlinearity is reduced significantly by incorporation of the nanoparticles. The evolution of viscoelastic strains is less pronounced for the nanocomposite filled with smaller nanoparticles. Smooth master curves are constructed by applying the Time-Stress Superposition (TSS). The Boltzmann-Volterra hereditary theory is used for the creep modeling. The nonlinearity of viscoelastic behaviour is taken into account by using the TSS principles and introducing a stress reduction function into an exponential creep kernel. The master curves are employed to predict the creep for time periods more than 60 times exceeding the test time. A comparison of relaxation spectra of the polymers shows that the incorporation of nanoparticles restricts the mobility of polymer chains.

Journal of Applied Polymer Science, 2012

The relative amounts of amorphous and crystalline cand a-phases in polyamide-6 nanocomposites, estimated from the deconvolution of X-ray diffraction peaks using Gaussian functions, correlates with their mechanical, thermomechanical, and barrier properties. The incorporation of organoclay platelets (Cloisite 15A and 30B) induced the crystallization of the polymer in the c form at expense of the amorphous phase, such that 1-2 wt % of Cloisite is enough to enhance the mechanical and the thermomechanical properties. However, higher nanofiller loads were necessary to achieve good barrier effects, because this property is mainly dependent on the tortuous path permeation mechanism of the gas molecules through the nanocomposite films. V