In order to test two standard tensile specimens, one metal (aluminum 2011-23) and one non-metal (polypropylene), we used a computer-controlled universal testing machine (UTM) that operates by the rotation of two power»screws. The UMT moves a cross member attached to the end of the specimen away from the other end. Using MATLAB R2014a, we determined the modulus of resilience and toughness. The aluminum was determined to have a modulus of elasticity 7.6767e+06 psi, a modulus of resilience of 2091605 psi, and a final elongation of 213850 %. The purpose of this experiment is to determine the modulus of resilience and toughness of two “505” specimens, one metal and one non-metal. By observing the behavior of a particular substance under stress with a specimen of known dimensions, we can extrapolate its behavior under stress in other situations.
Specifically, while subjecting a specimen to greater and greater normal stress via applied loading on either end (tensile loading), we can measure its deformation and determine the relationship of applied stress vs. strain for any given load. Graphing this relationship lets us determine the Elastic Modulus of the sample, i.e. the initial linear stress-strain relationship before the sample passes the “yield stress,” after which its deformations are permanent. Using this point, we can integrate the curve to measure the amount of energy (due to strain) that a material can absorb before permanently deforming, called the modulus of resilience for the material We can also determine the ultimate tensile strength of the material from the highest point on the graph, where the material bears the greatest stress with the least deformation and the maximum load/stress it can bear without rupture.
As with the modulus of resilience, we can determine the modulus of rupture or “toughness“ of the material by integrating over the entire stress-strain curve (from zero to strain at failure) to find the energy due to strain required to break it completely. The machine consisted of a universal testing machine hooked up a to a computer. The UTM had two long power»screws to fit the two opposite ends of the specimens. The UTM rotated its two power-screws, moving the cross member attached to one end away from the other end, simulating the specimens under both elastic and post-yield conditions. We observed the tensile tests for two “505” specimens, one metal (aluminum 2011-23) and one non-metal. We measured the diameters of the specimens, while the UTM created ASCII files with the columns of time, force, and displacement data. We also recorded the observed changes in geometry of the specimens, as the test progressed to destructively strain the specimens.
Using the data produced by the UTM, we confirmed the elastic modulus, 0.2% offset yield strength, ultimate tensile strength, and percent elongation at failure for the specimens, We then used MATLAB to determine the modulus of resilience and the toughness of the specimens. The modulus of elasticity is the term given for the tendency of a material to deform elastically (not permanently), and is given by the stress upon an object divided by the strain for the first part of the stretch of a material. The elastic modulus for the aluminum sample was 7.6767e+06 psi. Which is 77.9% of the true value of the elastic modulus of aluminum . 9860 ksi – as recorded on http://www.matweb.com/index.aspx. The yield strength of the aluminum was 4,358*10M psi, which is the amount of stress at which aluminum 2011-13 begins to deform permanently.
The tensile strength of the aluminum was S3720 psi, which denotes the maximum stress (force per area) aluminum 2011-13 can receive before breaking Its modulus of resilience was 209.1605 psi, which is the required strain to stress the material to the yield point, at which the material begins to permanently deform. The modulus of rupture was 8.0057e+03 psi, which refers to the material’s capacity to resist deformation due to a load, The measuring error in these calculations is low, due to the use of an electronic caliper. The modulus of elasticity of the polypropylene sample could not be easily calculated, as we did not receive strain readings for the sample This was caused by the weaker nature of the material, and possibly by a weakness or defect in the particular 505 sample we used in the UTM. The load was increased very quickly, too fast to get enough clear data to be run in the Matlab program, and the sample ruptured earlier than expected along an almost perfectly horizontal line near its midpoint.
Though we were unable to get proper strain readings, the data we did obtain shows a nonlinear relationship between the distance spanning the UTM’s screws and the load applied to the sample, further suggesting that the sample contained a defect or impurity that ruptured more easily and behaved differently under stress than the rest of the material. Despite this issue, the data suggests that the aluminum is significantly more sturdy than the polypropylene; even if our sample was slightly defective it deformed much more easily than the aluminum, and endured a much lower ultimate tension than aluminum did. As such it is a better choice of materials for building stronger simple rigid structures.
The modulus of elasticity for the aluminum “505” specimen was 7.6767e+06 psi, and its modulus of resistance was 209.1605 psi. The aluminum sample was much more capable of handling a high load, and was able to its previous state under a moderate load. in the future, a slower rate of load increase could be used when testing the polypropylene so that a clearer pattern can be observed in its stress and strain. Due to the rapidly increased load, and a possible deformity in the material, the polypropylene quickly broke, giving us a small sample of data that could not be processed by the Matlab script.
It is clear from the reaction of the material, however, that it would have a significantly smaller modulus of resistance. Our results demonstrate the vital importance of the careful selection of materials to be used in structures. Different materials can have very different properties, even within subtypes of aluminum for example, and a designer must be aware of the strength and properties required in the specific situation to properly select the right material for the job. Sloppy selection of materials and preparation could have catastrophic results, leading to disasters such as building or bridge collapses, and vehicle malfunctions (eg, the 2007 I-35W Mississippi River bridge collapse).
