Abstract
Materials exhibit different chemical and mechanical properties such as strength and durability. Combining different materials to form a material composite enhances their individual properties in different measures. In this experiment, the mechanical strength of composite sandwich structures was investigated through bending. Four samples were investigated for their properties on bending and strength. Three of the four polystyrene beams were reinforced with paper while the fourth beam was investigated without paper reinforcement. One of the beams was bonded with construction paper on one side; the next bema was bonded with construction paper on both sides while the third beam was bonded with construction paper on both sides with an additional gap in the glue at the midpoint. According to the results of the experiment, the sample beam with paper bonded on both sides and a gap in the glue reported the highest strength while the beam without paper bonding reported the lowest strength.
Introduction
The mechanical properties of materials vary with the internal composition and structure of the materials. While some materials, like metals, exhibit high strength, other materials are highly ductile and brittle. Some materials easily break under high tensile and compressive force while other materials sustain the force exerted on them under the same condition. A beam is regarded as any structural material subjected to bending (Dahshan, 2002). As opposed to a material under pure tensile force, the deformation of a beam does not entirely rely on the cross-sectional area. Instead, the deformation of a beam is dependent on the cross-sectional shape and the cross-sectional area in equal measure.
It is imperative to note that bending of a beam does not occur uniformly. The bending of a beam occurs around the central axis. The neutral axis or the central plain of the beam is located at 90 degrees to the applied loads. Materials that are far away from the neutral axis exhibit high efficiency in preventing bending for an applied force. For this reason, box-sections and I-beams are preferred over other cross-sections. Materials in these cross sections are displaced further away from the central axis thus provide high efficiency in preventing bending.
While the ideal theoretical structure would require two planks distinct further away from the central axis as possible by nothing, the practical structure requires a material to detach the planks and to contain the shear loads (Dahshan, 2002). As a consequence, a practical structure is made up a sandwich where the skins are used to contain most of the force. When a beam is subjected to a bending deflection, the lower section will extend while the top section would contract. This profile behaviour is because the top section of the beam is subjected to a compressive load while the bottom section is subjected to tensile load.
Experimental procedure
The following material and equipment were used to perform the experiment; polystyrene, construction paper, rapid cure epoxy, weights and a simple testing device.
Four beams were constructed using the construction paper, and the polystyrene provides. One of the beams was left unaltered. It was constructed to measure 1.704cm thick. The second beam was constructed by bonding construction paper on one of its sides. It measured 1.758 cm thick. The third beam was constructed by bonding construction paper on both of its sides. It measured 1.784 cm thick. The fourth beam was constructed by bonding construction paper on both of its sides. A 3cm by 6 cm gap in the glue at the midsection of the beam was generated between the construction paper and the beam on one side. It measured 1.758cm thick. All the four beams were weighed and their weights recorded.
The gains in the stiffness of the beams were measured using a simple testing device to assess the deflection of the beams. The beam to be tested was inserted into the two trucks and secured firmly using bolts. The two trucks were placed on top of the tray with the indenter in the midsection of the beam. After positioning the trucks, the dial indicator was set up to ensure that its point was resting against the lower section of the beam and directly below the indenter. The weights were placed on top of the indenter platform, and the deflection of the beam was measured using the dial indicator. Care was taken in placing the weights in regular intervals of 15 seconds. The beam deflection for a given weight was recorded and their Young’s modulus calculated. The process was repeated for the rest of the three beams are their results tabulated as follows.
Results
Data for graph
Discussion
It is apparent that the stiffness of the beam is increased with facing of the material with construction paper. The stiffness of the beam is highest in the beams faced with construction paper on both sides while lowest in the beam without facing. The beam that was not bonded with construction paper exhibited the lowest stiffness given that it broke at the smallest force as compared to the other beams (Dahshan, 2002). Additionally, the beam bonded with construction paper on one of its sides recorded extra stiffness as compared to the beam without construction paper. Bonding the beam with construction paper on one of its sides increased its stiffness given that it had an increased capacity to bear the force exerted on it. On the other hand, the beams bonded with construction paper on both sides were stiff and did not break.
Conclusion
It is apparent that facing increases the mechanical property of the material since it bears the force exerted on the beam. Bonding the beams with construction paper enhanced their mechanical property of stiffness. The construction paper used for facing contained the compressive forces and the tensile force exerted on the beam at the bottom and the top sections. The stiffness of the beam can be enhanced by bonding it with material that has advanced mechanical properties. Additionally, the stiffness of the beam can be increased by increasing the height; the space between the material and the neutral axis.
References
Dahshan, M. (2002). Introduction to Material Science and Engineering.2nd 2002.
