Strain rate and tempertaure effects on the mechanical properties and tensile stress-strain behavior of a nanocomposite with functionalized carbon nanofibers

The effects of functionalized carbon nanofiber addition on mechanical properties and behavior of vinyl ester polymer composites under tensile loading are discussed. Temperature and strain rate effects on tensile properties of these nanocomposites are also discussed. Tensile strength and modulus were found to increase linearly with the log of strain rate, and decrease linearly with increasing temperature. Addition of 0.5 wt% functionalized carbon nanofibers did not significantly increase tensile strength and ductility of the material; however, there was a maximum increase of 19% in tensile modulus of elasticity. Ramberg-Osgood and Menges models were used and extended to describe the strain rate and temperature dependency of the stress-strain behavior. The extended Menges model provided better representation of the observed behavior compared to the Ramberg-Osgood model, for a wide range of temperatures and strain rates. Mechanical properties obtained from flexure tests are also presented and compared to tensile data

Fatigue behavior of vinyl ester polymer and effects of carbon nanofiber reinforcement

Fatigue and cyclic deformation behaviors of vinyl ester and its nanocomposite with 0.5 wt% functionalized carbon nanofiber were obtained by performing tension-tension cyclic tests at different constant stress amplitude levels. Strains were predominantly elastic for both materials, even at high strain amplitudes. There was a small decrease in the cyclic modulus of elasticity of both materials with increasing fatigue cycles, possibly due to the breaking of some polymer chains during the cycling process. Considerable scatter was observed in the fatigue data because of the materials brittleness, necessitating the use of a large number of tests and statistical analysis. Comparisons between vinyl ester and nanocomposite for different probabilities of survival based on log-normal distribution of life showed that the nanocomposite had shorter life than vinyl-ester at higher stress amplitudes, while it had higher life than vinyl ester at lower stress amplitudes. Fracture surfaces observed by SEM consisted of a crack initiation region followed by a smooth region leading to steps or river-like pattern. The fatigue fracture surfaces also contained a series of concentric crack growth bands surrounding the surface source. Cracks initiated subsurface in the nanocomposite specimens and small patches of nanofibers and nanofiber pullouts were observed in the crack initiation area

Strain rate and temperature effects on tensile properties and their representation in deformation modeling of vinyl ester polymer

This paper discusses the effects of strain rate and temperature on tensile properties and stress-strain behavior of vinyl ester polymer. Tensile strength and modulus were found to increase linearly with the log of strain rate, and decrease linearly with increasing temperature. Ramberg-Osgood and Menges models were used and extended to describe the strain rate and temperature dependency of the stress-strain behavior. The extended Menges model provided better representation of the observed behavior compared to the Ramberg-Osgood model for a wide range of temperatures and strain rates. Mechanical properties obtained from flexure tests are also presented and compared to tensile data

Tensile creep and deformation modeling of vinyl ester polymer and its nanocomposite

This article discusses tensile creep behavior of vinyl ester polymer and its nanocomposite with 0.5 wt% functionalized carbon nanofibers. It is shown that for a constant temperature the creep resistance decreases with increasing stress. At lower temperature, higher creep compliance was observed for vinyl ester as compared to nanocomposite, while at temperatures close to Tg of vinyl ester creep compliance in nanocomposite was higher than that for vinyl ester. An analytical power-law relationship was used to predict the creep deformation behavior of both vinyl ester and its nanocomposite which showed good prediction of creep strain versus time, especially at lower temperatures and for lower applied stresses. A three-parameter Findley-type creep law for the compliance was also used. Good correlations between experimental data and the predictive model were obtained for both materials

Influence of carbon nanofiber content and surface treatment on mechanical properties of vinyl ester

This paper discusses the effects of carbon nanofiber surface treatment (purification and chemical functionalization) and carbon nanofiber volume fraction on mechanical properties of thermoset vinyl ester polymer nanocomposites under tensile and flexural loadings. Highly graphitic carbon nanofibers were surface treated by addition of functional groups to their surface, which provided a stronger composite as compared to conventional composites due to better bonding of the fibers to the polymer matrix. It was found that addition of up to 1 wt.% functionalized carbon nanofibers provided increases in mechanical properties over the addition of higher volume fraction of carbon nanofibers. © Smithers Rapra Technology, 2008

Fatigue behavior and life predictions of notched specimens made of QT and forged microalloyed steels

Fatigue behavior of notched specimens was investigated using circumferentially notched round bar and double-notched flat plate geometries, each with different stress concentration factors. Specimens were made of a commonly used vanadium-based microalloyed forging steel, in both the as-forged and quenched and tempered (QT) conditions. The effects of different notch severities and constraint conditions (i.e. plane stress versus plane strain) on fatigue behavior, and the ability of S-N and strain-life approaches to correlate and predict the experimental data are examined. Notched fatigue behavior of the microalloyed steel is evaluated and compared with its QT counterpart. © 2003 Elsevier Ltd. All rights reserved

Application of bi-linear log-log S-N model to strain-controlled fatigue data of aluminum alloys and its effect on life predictions

Bi-linear log-log model is applied to stress amplitude versus fatigue life data of 14 aluminum alloys. It is shown that the bi-linear S-N model provides a much better representation of the data than the commonly used linear model for Al alloys. The effects of bi-linear model on stress-strain, stress-life, and strain-life curves are discussed. Life predictions of aluminum alloys based on linear and bi-linear models are also compared and discussed. Estimations of the bi-linear fit constants from the linear fit constants are then presented. © 2005 Elsevier Ltd. All rights reserved