The effect of silica (SiO2) nanoparticles and ammonia/ethylene plasma treatment on the interfacial and mechanical properties of carbon-fiber-reinforced epoxy composites

A nanoparticle dispersion is known to enhance the mechanical properties of a variety of polymers and resins. In this work, the effects of silica (SiO₂) nanoparticle loading (0–2 wt%) and ammonia/ethylene plasma-treated fibers on the interfacial and mechanical properties of carbon fiber–epoxy composites were characterized. Single fiber composite (SFC) tests were performed to determine the fiber/resin interfacial shear strength (IFSS). Tensile tests on pure epoxy resin specimens were also performed to quantify mechanical property changes with silica content. The results indicated that up to 2% SiO₂ nanoparticle loading had only a little effect on the mechanical properties. For untreated fibers, the IFSS was comparable for all epoxy resins. With ethylene/ammonia plasma treated fibers, specimens exhibited a substantial increase in IFSS by 2 to 3 times, independent of SiO₂ loading. The highest IFSS value obtained was 146 MPa for plasma-treated fibers. Interaction between the fiber sizing and plasma treatment may be a critical factor in this IFSS increase. The results suggest that the fiber/epoxy interface is not affected by the incorporation of up to 2% SiO₂ nanoparticles. Furthermore, the fiber surface modification through plasma treatment is an effective method to improve and control adhesion between fiber and resin.     

Geometrical range of microscopic stress distribution change due to fibre array irregularities for thermally and transversely loaded CF/epoxy composites

Abstract

A detailed numerical investigation has been carried out to investigate the effect of local fibre array irregularities on microscopic interfacial normal stress for transversely loaded unidirectional carbon fibre/epoxy composites with random fibre arrangement. Linear elastic finite element analyses were carried out for a two-dimensional image based model composed of 70 fibres. One fibre in this image based model is replaced with resin as the resin equivalent fibre, and the resulting change in microscopic interfacial normal stress distribution is investigated. Three fibres are selected for the resin equivalent fibres to clarify the individual local geometrical irregularity. Calculations were carried out for three loading conditions: case A, cooling of –155 K from the curing temperature; case B, transverse loading of 75 MPa chosen as an example of macroscopic transverse fracture strength and case C, both cooling from the curing temperature and transverse loading of 75 MPa. The effect of fibre array irregularities on the interfacial stress state is limited to the region between the resin equivalent fibre and its first neighbouring fibres. The contribution of the second neighbouring fibre is small and that of further fibres is negligible.     

Ultraviolet surface treatment for adhesion strength improvement of carbon/epoxy composite

—As the applications of composite structures have increased, various techniques to join composite parts to the structures have been developed in order to meet the required adhesion strength. In this work, surface modification of carbon/epoxy composites was investigated using ultraviolet (UV) surface treatment to increase the adhesion strength between the carbon/epoxy composite and the epoxy adhesive. After UV surface treatment, X-ray photoelectron spectroscopy (XPS) analysis and contact angle measurements were performed to analyze the surface characteristics of the carbon/epoxy composites. From the results of XPS analyses and adhesion strength tests, it was found that the increase of C O bond density on the surface of carbon/epoxy composite caused the enhancement of adhesion strength. Also it was found that the UV-B (wavelength 280–315 nm) surface treatment resulted in a superior adhesion strength compared to the UV-A (wavelength 315–400 nm) surface treatment.     

The Effect of Variability of Fibre Diameter on Worsted Processing

An examination of the effect of a range of cationic surfactants on the bending properties of a woven wool fabric is reported. The changes in fabric properties caused by the surfactant differed considerably from those observed on cotton fabric. Factors affecting the fabric properties included the distribution of the surfactant on wool fibres, the nature of the surfactant, the method, time, and temperature of application, and the nature of any modification to the wool fibres.     

22—THE PATTERN OF VARIABILITY OF YIELD,VEGETABLE-MATTER CONTENT,AND FINENESS IN THE AUSTRALIAN WOOL CLIP

A survey is presented of measurements of the variability of yield, vegetable-matter content, and fineness between core samples within growers' or auction lots representing a variety of types of wool from the Australian clip.

The pattern can be represented, in part, by a linear relationship between the within-bale standard deviation of a particular characteristic and the mean value of that characteristic for the lot.

The data presented do not suggest that a change from the present sampling schedule is necessary.     

30—HEAT AND MOISTURE EXCHANGE IN WOOL BEDS: EQUILIBRIUM THEORY IN THE HYGROSCOPIC RANGE

Cassie's theory of propagation of heat and moisture changes in beds of wool fibres is re-examined by means of the method of characteristics. Substantial differences result in the predictions of the theory by treating the coefficients of the pertinent differential equations as functions of the dependent variables rather than as constants.     

31—THE EFFECT OF VARIABILITY OF FIBRE DIAMETER ON WORSTED PROCESSING. PART II. THE USE OF COMPARISON SAMPLES OF COMMERCIAL TOPS AND THEIR BLENDS

Changes in the coefficient of variation of fibre diameter (V _d ) were made by blending top qualities (a) 70s and 56s, and (b) 60s and 56s, and comparing these with a 58s. In this way, a range of values of V _d from 21.4 to 24.9% was obtained over three top samples whose mean fibre diameters and fibre lengths were closely similar. These tops were worsted-spun to determine their performance at the spinning limit and other yarn counts and to measure the yarn properties. The three samples did not give any important differences in chemical composition or in spinning limit, but did show a trend to significant differences in yarn breaking strength and elongation, the lower-V _d sample being favoured. Over this range of values of V _d at mean diameters of 25–26 μm, although there are hints of slight differences in spinning and in the product, the trend is not important. The range of V _d values for European tops of mean fibre diameter 25.3 μm appears to lie between 22 and 28%. The Australian tops investigated gave V _d values over the lower half of this range.