Browsing by Author "Sandesh, S."

Now showing 1 - 4 of 4

Bending strength of cenosphere foam cored jute/glass skin sandwiches
(2004) Kulkarni, S.M.; Sandesh, S.; Sharnappa
Sandwich construction is widely used in structural application because of its high bending stiffness coupled with lightweight. In design of sandwiches, skin made of high modulus of elasticity is used with core of high shear modulus. This balance is important so that neither material fails long before the other is stressed to accepted level. In the present study, experiments have been carried out on polymeric foam core sandwich beams with jute/epoxy faces. Syntactic polymeric foam cores, which have high compressive strength compared to open cell foams are made by mixing hollow fly-ash particles called cenospheres in a matrix material. The variable considered is the density of the core varied by differing the volume fraction of cenospheres. Cenospheres used in the present study are obtained from flyash, a waste byproduct of thermal power plants using a low cost separation process. Cores with four different volume fractions are prepared and sandwiched between a set of jute fabric layers. It is noticed that as volume fraction of cenospheres increased density is decreasing (1.12 to 0.98 g/cm3). The sandwich beams cut from the samples are tested using standard three-point bending procedure and the results obtained are compared with the results of glass skin sandwich with similar cores. Results showed a large difference in specific strengths of glass and jute skin sandwiches, which could be attributed to high tensile strength of glass fiber compared to jute fiber. There is a decrease of about 13% and 8% from the maximum specific strength for glass skin and jute skin sandwiches respectively at higher volume fractions of cenospheres. This could be traced to the failure of core well before the skin is stressed to accepted level in case of glass skin sandwiches. The jute skin sandwiches exhibited a little flatter specific strength response with respect to volume fraction of cenospheres indicating matching of the features pertaining to jute skin and the core properties. As the specific strength per unit cost of jute approaches that of glass, jute may be used to replace glass fiber with a significant cost advantage for less demanding applications.
Bending strength of cenosphere foam cored jute/glass skin sandwiches
(2004) Kulkarni, S.M.; Sandesh, S.; Sharnappa
Sandwich construction is widely used in structural application because of its high bending stiffness coupled with lightweight. In design of sandwiches, skin made of high modulus of elasticity is used with core of high shear modulus. This balance is important so that neither material fails long before the other is stressed to accepted level. In the present study, experiments have been carried out on polymeric foam core sandwich beams with jute/epoxy faces. Syntactic polymeric foam cores, which have high compressive strength compared to open cell foams are made by mixing hollow fly-ash particles called cenospheres in a matrix material. The variable considered is the density of the core varied by differing the volume fraction of cenospheres. Cenospheres used in the present study are obtained from flyash, a waste byproduct of thermal power plants using a low cost separation process. Cores with four different volume fractions are prepared and sandwiched between a set of jute fabric layers. It is noticed that as volume fraction of cenospheres increased density is decreasing (1.12 to 0.98 g/cm3). The sandwich beams cut from the samples are tested using standard three-point bending procedure and the results obtained are compared with the results of glass skin sandwich with similar cores. Results showed a large difference in specific strengths of glass and jute skin sandwiches, which could be attributed to high tensile strength of glass fiber compared to jute fiber. There is a decrease of about 13% and 8% from the maximum specific strength for glass skin and jute skin sandwiches respectively at higher volume fractions of cenospheres. This could be traced to the failure of core well before the skin is stressed to accepted level in case of glass skin sandwiches. The jute skin sandwiches exhibited a little flatter specific strength response with respect to volume fraction of cenospheres indicating matching of the features pertaining to jute skin and the core properties. As the specific strength per unit cost of jute approaches that of glass, jute may be used to replace glass fiber with a significant cost advantage for less demanding applications.
Strength and failure analysis of cenosphere foam cored glass skin sandwiches
(2004) Kulkarni, S.M.; Sharnappa; Sandesh, S.
In weight specific applications, sandwich structures provide a better solution as they can withstand larger bending loads with a lesser net weight of the structure. These structural members consist of two stiff and strong skins and a light weight core. In this case E-glass bidirectional woven fabric as skin and cores made of cenospheres filled in epoxy matrix. Cenospheres used are hollow spherical particles of fly ash separated using a low cost procedure. The size of these particles is in the range 20-200 ?m with an average size of 108 ?m. The cenosphere concentrations are varied from 25-58%, 58% being the maximum that could be filled in epoxy with dough flowing just enough to fill the mould. The standard three-point bend test was performed on the sandwich samples. Specific strength in bending of sandwiches increased about 17% with an increase in volume fraction initially (35%) and then it declined. This could be attributed to occurrence of debonds in larger particles and poor wetting of the particles by the resin especially at higher volume fractions. In order to reduce the severity of debonds and improve the compatibility, a surface treatment involving coating of a silane agent on the filler is attempted. The effect of the treatment reflected in the improvement of sandwich properties such as maximum increase in specific strength of about 26% is noticed at lower volume fractions. But at higher volume fraction agglomeration of the particles and the resulting poor wetting could have been a dominant phenomenon for reduction in strength. The samples tested under bending were observed in SEM to analyze and account for failure modes. Chiefly, two types of failures could be observed in the samples. Firstly, core failing well before the skin, implying a significant difference in the modulii of skin and core materials. Secondly, delamination observed at the skin-core interface, which could be due to reduced wetting on account of smooth surfaces of skin and core in contact. With compatible values achieved for core properties and with proper sanding of the cores, cenosphere foam cores can be used for realizing a significant cost reduction.
Strength and failure analysis of cenosphere foam cored glass skin sandwiches
(2004) Kulkarni, S.M.; Sharnappa; Sandesh, S.
In weight specific applications, sandwich structures provide a better solution as they can withstand larger bending loads with a lesser net weight of the structure. These structural members consist of two stiff and strong skins and a light weight core. In this case E-glass bidirectional woven fabric as skin and cores made of cenospheres filled in epoxy matrix. Cenospheres used are hollow spherical particles of fly ash separated using a low cost procedure. The size of these particles is in the range 20-200 Î¼m with an average size of 108 Î¼m. The cenosphere concentrations are varied from 25-58%, 58% being the maximum that could be filled in epoxy with dough flowing just enough to fill the mould. The standard three-point bend test was performed on the sandwich samples. Specific strength in bending of sandwiches increased about 17% with an increase in volume fraction initially (35%) and then it declined. This could be attributed to occurrence of debonds in larger particles and poor wetting of the particles by the resin especially at higher volume fractions. In order to reduce the severity of debonds and improve the compatibility, a surface treatment involving coating of a silane agent on the filler is attempted. The effect of the treatment reflected in the improvement of sandwich properties such as maximum increase in specific strength of about 26% is noticed at lower volume fractions. But at higher volume fraction agglomeration of the particles and the resulting poor wetting could have been a dominant phenomenon for reduction in strength. The samples tested under bending were observed in SEM to analyze and account for failure modes. Chiefly, two types of failures could be observed in the samples. Firstly, core failing well before the skin, implying a significant difference in the modulii of skin and core materials. Secondly, delamination observed at the skin-core interface, which could be due to reduced wetting on account of smooth surfaces of skin and core in contact. With compatible values achieved for core properties and with proper sanding of the cores, cenosphere foam cores can be used for realizing a significant cost reduction.