Report and Guidelines for Data Evaluation - E Portfolio Assessment Answers

Data Evaluation E Portfolio Writing

Introduction Defining an appropriate material model and appropriate representative properties is key to obtaining accurate results in FEA. Even though for a preliminary analysis it may be sufficient to use one of the materials available in ANSYS library, as we move forward in our project design and look at our final design specifications it is important that we include the properties of the specific material we will be analysing. For that, experimental tests that allows to describe the behaviour (elastic and/or plastic regimes) are required. Four different materials were tested in a tensile testing machine: balsa wood, acrylic and two metals that you are supposed to identify after analysing the experimental data. The purpose of having four different materials was to give you an idea of the different material behaviours (ductile vs brittle). In the case of balsa wood, the samples broke very early during the tensile test. This suggests that it may be required to prepare the surface of the samples before running the tensile tests.

Tensile Testing

We started by measuring the dimensions of the flat dogbone shaped specimens using callipers. Three specimens were used for each material. The dimensions measured include thickness, width and gage length as illustrated in Figure 1. These dimensions are required for both determining the setup of the tensile test (the test rate) and for post-processing the data extracted (stress and strain data). The samples are clamped in within the grips of the tester, and the setup is input into the tester’s software. Test rate, thickness, width and gage length are input, and the software will return a report which will include these in addition to load-extension values registered. During the test the upper crosshead moves upwards deforming the sample in tension and the sample is pulled until necking and fracture occur in the reduced section. See refer to Annex A for photographs of specimens and testing equipment. Some of the samples may exhibit fracture somewhere other than the middle section of the gage length, e.g., near the shoulder of the specimen (shoulder is illustrated in Figure 1). For these tests we are not able to determine the total elongation. Note: The tensile test generally leads to Young’s Modulus values that are too low. You still need to analyse the Young’s Modulus using the recorded data. However, to enable you to identify the material type tested the typical values are given in the corresponding data files(use these typical values for your ePortfolio tasks).

Test Data Analysis

After testing all four materials, based on the load-extension data extracted we calculated and plotted for one of the tests: ? Engineering Stress-Strain curves ? True Stress-Strain curves ? Yield strength and corresponding strain ? Hardening curve based on a Power law

In ANSYS we are able to add user defined Material Libraries and Materials. During this Practical Class we created one Material Library and added two metals to this library: 4340 High Tensile Steel and Aluminium 7075-T6. The FEA of a connecting rod loaded in compression at the power stroke of a piston was carried out using both materials and the results were compared. See “SED302 - Practical Class 1_ANSYS Instructions.pdf” for reference.

ePortfolio Tasks

The results from the tensile testing run during the Practical Class of two different metals are provided to you in the files: ? Metal 1.csv ? Metal 2.csv These files include: ? Load and extension values measured ? Specimen dimensions: gage length, width and thickness You are expected to obtain from the data above, for both metals, the following: ? Young’s Modulus (?) ? Yield Strength, YP0.2% ? Engineering Stress-Strain Curve ? True Stress-Strain Curve ? Ultimate Tensile Stress (UTS) ? Total Elongation (?????) ? Hardening coefficient, ? Note: The tensile test generally leads to Young’s Modulus values that are too low. You still need to analyse the Young’s Modulus using the recorded data. However, to enable you to identify the material type tested the typical values are given below: Metal 1: ?=200 GPa Metal 2: ?=70 GPa You should then create a Material Library in ANSYS to which you will add both metals’ material properties and run two Static Structural Analyses for the connecting rod (as described in “SED302 - Practical Class 1_ANSYS Instructions.pdf”): (i) using Metal 1 and (ii) using Metal 2 (use the typical values given above for the Young’s modulus). Finally, in your ePortfolio, answer the following questions based on your data analysis for Metals 1 and 2 and based on your FE Analyses results: ? What types of metals have been tested in the Practical Class? Justify your answer. ? Which metal out of the two tested in the PracClass would be the best material to achieve the best safety factor for the connecting rod? Why? ? Which metal out of the two tested in the PracClass would be the best material to achieve the lowest possible weight? Why?