R. Ramesh Kumar

Intralaminar fracture toughness of a cross-ply laminate and its constituent sub-laminates

Abstract The intralaminar mode I fracture toughness values for a M55J/M18 carbon/epoxy cross-ply laminate [0°/90°]15 (alternate 0 and 90° layers) and its constituent sub-laminates, namely the [0°]30 and [90°]30 laminates are theoretically evaluated on the basis of a modified crack-closure integral (MCCI) method corresponding to the fracture loads obtained by testing C(T) specimens. A simple relationship between the intralaminar fracture toughness at the specimen level of a cross ply and its constituent sub-laminates is presented. Test data for fracture loads and crack-opening displacements at the opposite end (far end) to the crack tip of the three types of C(T) specimens are obtained. A comparison of fracture toughness values KIc and crack-opening displacements obtained from tests with theoretical predictions by finite-element analysis shows good agreement for the type of laminates considered. Comparison of the analytically determined KIc of the cross-ply C(T) specimen based on the new relationship using the respective values of KIc of its constituent C(T) specimens shows good agreement with test data.

Free vibrations of multilayered thick composite shells

Abstract Free vibration characteristics of a multi layered graphite/epoxy circular cylindrical shell are presented using an eight-noded isoparametric quadrilateral shear flexible shell element. The effects of rotary inertia are considered in the formulation of the mass matrix. Variations of length to radius and radius to thickness ratios of the shell, and different fibre orientations such as (0/90°), (0/90/0/90°), (0/90°) s and (0/90/0/90°) s with respect to the frequency parameter, K ω are studied. The influence of the ratio of major to minor Youngs moduli on frequency parameter is also shown. Comparison of numerical results with those available in the literature shows a good agreement.

Normal stress distribution adjacent to optimum holes in composite plates

An approximate solution in the form of a polynomial is presented for the normal stress distribution adjacent to a class of optimum holes in symmetrically laminated infinite composite plates under uniaxial loading. Comparison of the present approximate solution with that of the finite element method shows good agreement. The approximate solution is useful in assessing the strength of the laminated composite plates with holes. The present simple solution will be of immense use to design engineers who are interested in obtaining quick and reliable solutions for circular and optimized holes in symmetrically laminated composite plates.

Accurate evaluation of strain-energy release rate in unidirectional FRP compact-tension specimen

Strain-energy release rate of a standard compact-tension unidirectional C(T) specimen of S-glass-epoxy Scotchply 1002 is evaluated using a finite element method (FEM). Initially failure mode (cracking direction) is theoretically predicted and the strain-energy release rate is estimated using a crack-closure integral approach where branch-crack is modelled along the cracking direction instead of fibre orientation. The strain-energy release rate is evaluated for fibre orientations of 0°, 45°, 60°, 75° and 85° and compared with the fracture toughness (available in literature) and thus the fracture loads (crack initition loads) obtained. The results are found to be in very good agreement with the test data. This approach is simple and accurate for the evaluation of strain-energy release rate of the unidirectional fibre reinforced composite C(T) specimen.

Cohesive zone modeling of coupled buckling – Debond growth in metallic honeycomb sandwich structure:

Buckling-induced skin–core debond growth in honeycomb sandwich cantilever beam is demonstrated using a cohesive zone model. The input parameters for the analysis are interfacial bond strength, mode I and mode II interfacial fracture toughness values, obtained from flatwise tension tests, drum-peel tests and three-point end notch flexure tests, respectively. Debonded honeycomb specimens are tested and the acoustic emission technique was used to observe the initiation of the debond growth. The load-displacement response from the cohesive zone model model shows a good agreement with the experimental results. The conventional analysis without cohesive zone model overestimates failure load by 56%. Cohesive zone model is able to predict the coupled debond growth and buckling failure in honeycomb sandwich structures.

Analytical approach for modal characteristics of honeycomb sandwich beams with multiple debond

An analytical formulation for the evaluation of vibration characteristics of sandwich beams with multiple debond at the interface between the carbon fiber reinforced plastic (CFRP) face sheets and honeycomb core is obtained and verified through test. The well-known split theory is modified considering the core stiffness of sandwich beam model and accordingly the equations of motion are set up for both the undebonded and the debond regions to solve the Eigenvalue problem. Honeycomb sandwich beams with aluminium as well as quasi-isotropic carbon epoxy laminate face sheets of same thickness and core height are fabricated and tested. In the case of cantilever beam with single debond, the region of validity of the analytical solution for natural frequencies and mode shapes are found to be within a debond size of 12% of the beam length for sandwich beams with either CFRP or aluminium skin. Studies on multiple debond reveal that a single long debond can result in significant reduction in the frequencies of the beam than multiple debond of comparable length located along the same axial direction compared to intact beam.

Enhancing blooming period and propagation coefficient of tulip ( Tulipa gesneriana L.) using growth regulators

A study was carried out to evaluate the effect of plant growth regulators on growth, flowering and bulb production of tulip under Karewa conditions of Kashmir Himalaya during 2009 to 2011. The three different growth regulators; gibberellic acid (GA 3 ) at 100, 200, and 400 ppm, 2-chloroethyl trimethyl ammonium chloride (CCC) and maleic hydrazide (MH) each at 100, 200 and 500 ppm along with control were applied as dip treatment and foliar spray. Plant height was recorded maximum with 400 ppm GA 3 (37.32 cm) followed by 200 ppm GA 3 (34.13 cm). GA 3 at 400 ppm significantly caused earliest flowering (141.30 days) followed by 200 ppm GA 3 (142.43 days) as compared to the control (148.93 days), while delayed flowering were observed by 500 ppm MH (152.96 days) followed by 200 ppm MH (151.93 days). The longest blooming period was recorded in 200 ppm GA 3 (28.46 days) followed by 400 ppm GA 3 (27.76 days) in comparison to the control (21.59 days). The maximum vase life was obtained with 400 ppm GA 3 (11.26 days) followed by 200 ppm GA 3 (10.43 days) over the control (7.30 days). The maximum number of bulbs and daughter bulbs per plant were recorded with 400 ppm GA 3 (1.43 and 3.03) followed by 500 ppm CCC (1.41 and 2.65) over the control (1.07 and 1.72), respectively and thereby enhanced propagation coefficient was obtained in 400 ppm GA 3 (258.66%) followed by 500 ppm CCC (237.73%) as against the control (170.00%). Keywords: Tulipa gesneriana , gibberellic acid, 2-chloroethyl trimethyl ammonium chloride, maleic hydrazide, blooming period, propagation coefficient African Journal of Biotechnology Vol. 12(2), pp. 168-174

Influence of Mineral Admixtures on Fracture Energy of Refractory Cement at Elevated Temperatures

The influence of three mineral admixtures, Silica Fume (SF), Fly Ash (FA), and Rice Husk Ash (RHA) on the fracture energy of Refractory Cement (RC) over a wide range of temperature from 300K to 1173K is studied. The optimum percentage replacement of RC by these admixtures is found to be around 0.5 for all the temperatures considered but for FA. Fracture energy of control (0% admixture) and blended RC (with 0.5% admixture) are determined by three point bending of notched beam specimens. Fracture energy of RC blended with the three mineral admixtures is lower than that of control RC for temperature range of 300K to 873K. But at elevated temperature of 1173K, blending plays its role as an admixture. Experimental results are corroborating with XRD. It is observed that phenomenon of pseudo dryness of Gismondine in the blended RC causes higher fracture energy which is double that of RC only at 1173K.

Stresses and deformations due to flow past a circular cylinder

Abstract An analysis has been presented to calculate the stresses and deformations in the cylinder due to flow past a stationary circular cylinder by adopting a numerical technique. The flow has been considered at Reynolds number 3.32 × 105 and the cylinder has been considered to be a thick cylinder under plane strain loading conditions. The pressure distribution on the cylinder surface has been approximated by Fourier series. The solution has been obtained by using Airys stress function approach. It has been observed that the values for maximum and minimum stresses and deformations are quite remote from those for a cylinder having uniform pressure.