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

Lab report - Essay ExampleThe method of m botheable testing is conducted by a bendable testor in which the test specimen is clamped and smashed and subjected to a tensile force until the point of failure. express- wrinkle curves are an extremely Copernican graphical measure of a materials mechanical properties (Roylance, 2001). Stress is defined as the force of resistance offered against the overrefinement and Strain is defined as the ratio of the change in length to the original length of the member (Ramamrutham, 2003). The stress-strain curve for the specimen is an important method of characterizing the behavior of the material and adjudging its suitability as a material for any function. Almost all the materials, obey 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 be the Youngs modulus, E Stress = Strain ? Youngs Modulus. As the strain increases, the linear proportionali ty 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(a) mobility and materials lacking this mobility are usually brittle rather than ductile. Polymeric materials behave both as syrupy fluids as well as elastic solids. They are viscoelastic materials (Koustos, 2002). The stress-strain curve of a polymer is different from those of separate materials. The critical 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 samples and study their behavior under the application of tensile force. For this test, polymer samples were loaded and clamped in the tensile testing mold. 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 beforehand breaking. The testing was done on four different specimens PE (polyethylene from a shopping bag), PP (polypropylene from plastic folder), gum elastic (natural arctic 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 comprehensiveness of the samples were measured before stretching each one of them and putting them in the tensile tester. The dimensions of the specimens are interpreted 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 meander 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) E longation 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 can be observed from the graphs that the stress-strain curve of acetate was obtained thrice. The possible commentary for this can be that cellulose acetate exhibits different tensile strengths at different states dry, wet & after being boiled (Stadlinger). The difference in