Laboratory Report Format for ME354: Formal Laboratory Report Instructions, Lecture notes of Engineering

Download Laboratory Report Format for ME354: Formal Laboratory Report Instructions and more Lecture notes Engineering in PDF only on Docsity! Appendix A: Laboratory Report Format This appendix contains details on the format for formal written laboratory reports in the form of author's instructions. 01 Jan 2000 mgj Author's Instructions for ME354 Formal Lababoratory Report by Author's Name Author's Laboratory Section, Day, Time, Date of this Laboratory Excercise Author's LaboratoryTA Date of Laboratory Report: (usually the official due date) Report submitted to: Instructor of the course Executive Summary: The executive summary should provide a brief description of the objectives, procedure, results and conclusions of the laboratory excercise. Total verbiage should be ~300 to 500 words. Quantitative results (e.g., % of error) should be given to add credibility to conclusions. RESULTS The Results section contains calculated results, graphs, tables, and final equations in a coherent and understandable manner. Explanations must be given to provide the reader with an understanding of how reduced results were obtained. Each graph, table, etc. must have a figure caption or table heading and must be referred to the text in support of the presented results. Place raw data (such as strip chart plots and data sheets) in an Appendix. Just showing a large number of graphs and tables without supporting text is not coherent and understandable!! However, the Results section should not contain excessive verbiage since detailed explanations and interpretation are best left to the Discussion section. For example: The primary test results from the room-temperature creep tests of the lead-tin solder are in the form of relative displacement versus time data sets (See Appendix A for raw data sets). However, these raw data were reduced to more meaningful engineering results by calculating the engineering strain, ε, such that: ε = ∆L Lo (1) where ∆L is the relative displacement and Lo is the initial gage length. (See Appendix B for sample calculations). The resulting strain versus time plots are shown in Fig. 3 for four different pan masses (4, 6, 7, and 8 lb) corresponding to four different stresses (σ=4.48, 6.64, 7.89 and 8.90 MPa). Note that as expected, as the stress increased, both the levels and shape of the strain- time curves changed. The strain-time results were further reduced by calculating the creep strain rate (i.e., the derivative, dε/dt) as a function of time, t. The minimum creep strain rate, ε̇min , was then found or each applied stress as shown in Table 1. A power law relation between minimum strain rate and applied stress was assumed such that: ε̇min = Bσn (2) where B is the pre-exponential coefficient and n is the creep stress exponent. The data was linearized by taking logarithms of both sides of Eq. 2. These results are plotted in Fig. 4. A least squares, linear regression of data was then used to determine A and n as shown in Table 1. Finally, long-term test results obtained previously are compared in Fig. 4 to the short-term results determined in this exercise. Note that when B and n determined from the short- term tests were substituted into Eq. 2 to predict ε̇min from the stresses of the long-term tests, errors of 17 to 80% resulted (See Table 1 and Fig. 4). Graphically, this prediction is shown by the solid line in Fig. 4. 0 0.005 0.01 0.015 0.02 0.025 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 TIME (s) S T R A IN (m /m ) m=4 lbfm=6 lbfm=7 lbfm=8 lbf Figure 3 - Creep strain versus time for four different applied masses on a lead-tin solder at room temperature. Table 1 Creep test results of solder for short and long-term tests Short-term tests ε̇min ( s-1) Force #1, σ = 4.48 MPa 7.8 x 10-6 Force #2, σ = 6.64 MPa 1.5 x 10-5 Force #3, σ = 7.89 MPa 2.5 x 10-5 Force#4, σ = 8.90 MPa 7.6 x 10-6 Short-term test results Parameters for ε̇min = Bσn B (MPa-n /s) 7.84 x 10-8 n 2.97 Long term tests ε̇min ( s-1) σ = 1.32 MPa, ε̇min measured 9.5 x 10-8 σ = 1.32 MPa, ε̇min = Bσn 1.7 x 10-7 % difference 80% σ = 1.82 MPa, ε̇min measured 3.8 x 10-7 σ = 1.82 MPa, ε̇min = Bσn 4.4 x 10-7 % difference 17% - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 0 0 0.2 0 .4 0 .6 0 .8 1 log σ lo g εm in Long-term tests Short-term tests Figure 4 - Log creep strain rate versus log stress for a lead-tin solder at room temperature. DISCUSSION / CONCLUSIONS In the Discussion / Conclusions section, discuss the results of the experiment or test through interpretation of data , error analysis (i.e. include all sources and discuss relative magnitude, probability, how ([quantitative ±] the error would affect the experimental results), etc. (Note: Answer the question - Did I get the results I expected? If not, why not?) If obtaining material properties, compare your experimental results to published data. In this section, the results which are merely presented in the Results section are discussed in more detail. For example: Use of Eq. 2 to fit the creep results was fairly successful. Comparison of the A and n values obtained for the short term tests of this 60-40 lead-tin solder showed the A value to be in reasonable agreement (A=7.4 x 10-8 for this experiment and A=2.6x10-7 from the text, Mechanical Behavior of Material, N.E. Dowling, 1993, Prentice Hall). Similarly the n value was in reasonable agreement (n=2.9 for this experiment and n=2.2 from Dowling) Although Eq. 2 can be used to obtain fairly good descriptions of the creep test results for the short term tests (see Fig. 4), use of the A and n values obtained from the short term tests to predict the long-term strain rates gave poor agreement (17-80% error). This poor agreement could be attributed to several factors. For example, the alloys from the long and short term tests may not have been the same, or the temperatures between the two tests may not have been the same, or the data was not recorded correctly for the two tests, or there is a change of creep mechanism between low and high stress tests. However, the more plausible explanation is that the rule-of-thumb for predicting long-term creep from short-term test results was violated (i.e., test results should be at least 10% of the required prediction). In this case, the short term results were less than 3 hr whereas the long-term results extended to over 500 h. Thus, it seems reasonable that the so- called "minimum" strain rate for the short-term tests was actually still a transient strain rate rather than a steady-state strain rate (See Fig 5). The errors in predicting the minimum strain rates of the long-term tests are therefor due to the A and n values determined from the short-term tests not being representative of the steady-state strain rate behavior.