Lab report Essay Example | Topics and Well Written Essays - 1000 words

Lab report - Essay ExampleThe method of tensile tasteing is conducted by a tensile testor in which the test specimen is clamped and loaded and subjected to a tensile force until the show up of failure. Stress-strain curves are an extremely important graphical measure of a materials mechanically skillful properties (Roylance, 2001). Stress is defined as the force of resistance offered against the deformation and Strain is defined as the ratio of the change in continuance to the original length of the member (Ramamrutham, 2003). The stress-strain curve for the specimen is an important method of characterizing the demea noner of the material and adjudging its suitability as a material for any function. Almost all the materials, chase Hookes law in the early portion of the curve i.e. at low strain which states that stress is proportional to strain with the constant of proportionality existence the Youngs modulus, E Stress = Strain ? Youngs Modulus. As the strain increases, the line ar proportionality comes to an end at a point termed as the proportional limit and marks the beginning of the plastic phase rearrangement of the specimen. Plasticity requires molecular mobility and materials lacking this mobility are usually brittle rather than ductile. polymeric materials behave both as viscous fluids as well as elastic solids. They are viscoelastic materials (Koustos, 2002). The stress-strain curve of a polymer is different from those of other materials. The deprecative point in the stress-strain curve is the yield point beyond which the material enters the plastic deformation state. Experimentation The experiment was conducted to obtain the stress-strain curve of polymer judges and study their behavior under the application of tensile force. For this test, polymer samples were loaded and clamped in the tensile testing machine. The tensile testing machine that was used was Instron 1026. The tensile testing machine pulls the sample from both ends and measures the force required to pull the specimen apart and how much the sample stretches before breaking. The testing was done on four different specimens PE (polyethylene from a shopping bag), PP (polypropylene from plastic folder), Rubber (natural rubber from a rubber band) and Acetate (cellulose acetate from an overhead transparency). The specimens were obtained by cutting the polymer samples into appropriate lengths. The thickness and width of the samples were metric before stretching each one of them and putting them in the tensile tester. The dimensions of the specimens are taken with the aid of calipers for precision. Results and Discussion The stress-strain curves for the various test specimens are as follows Figure 1 Stress-Strain Curve of Rubber (Poly-Isoprene) Figure 2 Stress-Strain Curve of Acetate (Cellulose Acetate) Figure 3 Stress-Strain Curve of PE (Polyethylene) Figure 4 Stress-Strain Curve of PP (Polypropylene) S. no. Test name Tensile Strength (MPa) Elongation at failure 1 PE 11.1 26% 2 PP 23.5 738% 3 Rubber 4.1 575% 4 Acetate 1 181.9 131% 5 Acetate 2 297.3 114% 6 Acetate 3 166.9 93% It goat be observed from the graphs that the stress-strain curve of acetate was obtained thrice. The possible explanation for this can be that cellulose acetate exhibits different tensile strengths at different states dry, wet & after being boiled (Stadlinger). The difference in