Nripati Ranjan Bose

The mechanical properties of vinylester resin matrix composites reinforced with alkali-treated jute fibres

Jute fibres were subjected to alkali treatment with 5% NaOH solution for 0, 2, 4, 6 and 8 h at 30°C. The modulus of the jute fibres improved by 12, 68 and 79% after 4, 6 and 8 h of treatment, respectively. The tenacity of the fibres improved by 46% after 6 and 8 h treatment and the % breaking strain was reduced by 23% after 8 h treatment. For 35% composites with 4 h-treated fibres, the flexural strength improved from 199.1 to 238.9 MPa by 20%, modulus improved from 11.89 to 14.69 GPa by 23% and laminar shear strength increased from 0.238 to 0.283 MPa by 19%. On plotting different values of slopes obtained from the rates of improvement of flexural strength and modulus, against NaOH treatment time, two different failure modes were apparent before and after 4 h of NaOH treatment. In the first region between 0 and 4 h, fibre pull out was predominant whereas in the second region between 6 and 8 h, transverse fracture occurred with minimum fibre pull out. This observation was well supported by the SEM investigations of the fracture surfaces.

Dynamic mechanical analysis of FRP composites based on different fiber reinforcements and epoxy resin as the matrix material

Three-ply composite laminates prepared from E-glass or N-glass chopped strand mats (CSMs) and jute (J) fabrics as reinforcing agents and amine-cured epoxy resin as the matrix material were subjected to dynamic mechanical thermal analysis at a fixed frequency of 1 Hz over a temperature range of 30–180°C. The volume fraction of fibers ranged between 0.21 and 0.25. The reinforcing effect for the three fibers is in the order E-glass > N-glass ≫ jute. Glass-reinforced composites show a higher storage modulus (E′) than that of jute-reinforced composites. The E′ values of glass-jute hybrid composites lie between those of glass-reinforced and jute-reinforced composites. Odd trends in temperature variability of the loss modulus (E′) and the damping parameter, tan δ, and in the glass transition temperature (Tg) for the three different unitary and four different hybrid composites are interpreted and understood on the basis of odd differences in (1) the chemical nature and physical properties of the three different fibers (E-glass, N-glass, and jute), (2) the void content and distribution, (3) the thermal expansion coefficients of the main phases in the composites, (4) the degree of matrix stiffening at or near the fiber-matrix interface, and (5) the extents of matrix softening in the zone next to the interface.

Temperature dependence of hydrothermal ageing of CSM-laminate during water immersion

Abstract Random glass fibre reinforced polyester resin specimens were exposed to hot water at different temperatures. Effects of the environmental history on strength characteristics of the composite were investigated using the three-point bend tests. The study shows that reduction of the strength of random-fibre composites due to hydrothermal effects is a rate process for which the temperature influences only the rate constant. The rate constant follows the Arrhenius equation 1/τ = 1/τ 0 exp [−E/RT], where 1/τ is the rate constant, E and R are activation energy and gas constant respectively; τ 0 is a constant and T is absolute temperature. The time/temperature superposition principle is applicable for the degradation process and a master curve for strength can be obtained by shifting the data along the logarithmic time scale by a shift distance, ln a D . This allows the estimation of strength at any temperture from experiments conducted only at one temperature.

Hydrothermal ageing of CSM-laminate during water immersion — an acousto-ultrasonic study

Acousto-ultrasonics represents a very attractive and promising technique for detecting flaws and studying degradation of composite material. Studies of damage under hydrothermal ageing incurred by random fibre-reinforced laminates have been carried out with this technique. It is shown that the “stress wave factor” is a sensitive indicator of random fibre composite strength reduction due to a hydrothermal effect. The same study can be used for the estimation of strength from the data generated under accelerated conditions.

Hydrothermal ageing of jute-glass fibre hybrid composites: an acousto-ultrasonic study

Studies of damage under hydrothermal ageing incurred by random fibre glass-reinforced laminates and jute-glass fibre hybrid composites have been carried out using an acoustoultrasonic technique. It is shown that the “stress wave factor” is a sensitive indicator of flexural strength reduction due to hydrothermal effects in both these composites. The incorporation of jute into glass fibre composites brings about a reduction in the rate of degradation of these composites. The treatment of jute with a silane coupling agent marginally improves the strength properties of the hybrids.

Mechanical properties of glass polymer multilayer composite

The preliminary experimental studies on the comparative behaviour of the deformation processes involved in the failure of a commercial, 0.3 mm thick, 18 mm diameter soda-lime-silica glass disks (G) and multilayered glass disk-epoxy (GE) as well as glass disk-epoxy-E-glass fabric (GEF) composite structures are reported. The failure tests were conducted in a biaxial flexure at room temperature. The epoxy was a commercial resin and theE-glass fabric was also commercially obtained as a two-dimensional weave ofE-glass fibres to an area density of about 242 g m−2. The multilayered structures were developed by alternate placement of the glass and reinforcing layers by a hand lay-up technique followed by lamination at an appropriate temperature and pressure. Depending on the number of layers the volume fraction of reinforcement could be varied from about 0.20 for the GE system to about 0.50 for the GEF system. It was observed that the specific failure load (load per unit thickness) was enhanced from a value of about 60 N/mm obtained for the glass to a maximum value of about 100 N/mm for the GE composites and to a maximum of about 70 N/mm for the GEF composite system. Similarly, the displacements at failure (δ) measured with a linear variable differential transformer (LVDT) were also found to be a strongly sensitive function of the type of reinforcement (GE or GEF) as well as the number of layers.

Comparative evaluation of N-glass and E-glass fibres with special reference to their use in FRP composites

The abilities of E-glass and N-glass fibres and of composites based on them to withstand degradative effects in boiling water or in boiling aqueous solutions of HCl (10%), NaOH (0.5%) and NaCl (10%) have been evaluated on a comparative basis by following the loss or retention of strength properties (tensile/flexural) with the time of the respective degradative exposure. The degradative effects under different chemical environments for the composites were also analysed with the help of SEM micrographs of the composites before and after the specific degradative treatments. Analysis of strength properties and retention of strength and of the micrographs clearly indicates that N glass is highly superior to E glass, and the former imparts a much higher order of stability to composites in different chemical environments despite substantial initial advantages in the strength properties for E-glass fibre and composites based on this fibre.

Fibre-reinforced glass/glass-ceramic matrix composites

Publisher Summary Traditional or conventional ceramics are generally in monolithic form. However, ceramic materials are lacking energy-dissipating phenomenon, which causes them to fail in a catastrophic fashion, i.e. makes them unforgiving. Therefore, a critical need exists for increasing the toughness of ceramic materials. With a view to achieving high fracture toughness of ceramic materials, the major effort of the materials community in the field of structural materials has been directed toward incorporating a variety of energy-dissipating phenomena in the fracture process of ceramics, i.e. imparting damage-tolerant behavior. To improve the toughness and in-service reliability of ceramic materials is thus the major objective. One of the important approaches to attaining these goals is through composite and glass/glass- Ceramics Matrix Composites (CMCs) and these are among the materials attracting major attention today. In the past, designers worked with data on the properties of homogeneous, isotropic materials and designed their components to fit the ranges of design allowances by using fiber-reinforced polymer matrix and metal–matrix composites for structural applications. The use of such composites increased to the point where boronand graphite-fiber reinforced epoxy resin and boron-reinforced aluminum were restricted to applications up to 300°C. However, recently, the concept of composite materials has permitted almost limitless tailoring of composites to create entirely new designs never previously possible. The quest for excellent environmental aspects and improved characteristics of materials prompted the development of fiber-reinforced glass/glass-ceramic matrix composite. The fibers should not be greatly degraded during processing either by handling or by chemical reaction and the resultant fiber–matrix interface must have the characteristics necessary to prevent excess fiber–matrix bonding.

Tensile failure of unidirectional carbon fibre reinforced polypropylene composite: an acoustic-ultrasonic study

The potential of the acoustic-ultrasonic stress-wave factor as a non-destructive testing technique for unidirectional carbon-fibre-reinforced polypropylene composite laminates has been investigated. The stress-wave factor is found to be a sensitive indicator of strength variation in these composites, and increases in proportion to fractional powers of the ultimate tensile strength. The lowest value of the stress-wave factor also correlates well with the fracture on the specimen. This method is also sensitive to strength variations associated with porosity and differences in the fibre: resin ratio.