Department of Aerospace, Physics and Space Sciences AEE 4261 Aerospace Experimentation Fatigue Lab Rotating Bending Fatigue Test Overview Lab 4.1 - Notched aluminum (5 tests per section) Lab 4.2 - Brass (1 ea.) Lab 4.3 - Brass with defect (1 ea.) Note – these instructions supersede those provided by the manufacturer. Also, we are not testing steel, despite the picture above showing a steel test article YouTube Video Links - YouTube video links are provided to help you get up to speed: https://youtu.be/o-6V_JoRX1g https://youtu.be/XkJ_VyLEcps https://www.youtube.com/watch?v=ZsIwEp574ho 3 Student Lab Report - Generic lab report expectations that apply to all labs is here: - https://fit.instructure.com/files/45856245/download?download_frd=1 - Stress Concentrations Lab Report Guidance - “fatigue lab report guidelines.doc” 4 Rotating beam test set-up - Test specimen is clamped in the middles of the loading arm, and a point force F is applied near the left side - Relevant moment arm L is defined as the distance from the applied force F to the middle of the test section - Some relevant theory of operation of this machine and data analysis is given by the P.A. Hilton company’s manual for this device. Extracts of the manual are included in a separate file 5 Aluminum Test Article Note – test results in the instructions is for a different grade of aluminum and test cross section w d Note – d is not the standard diameter discussed in the instructions. It was increased to support a broader range of test loads s 6 CZ121 Brass Test Article Information CZ121 Brass Properties | Technical Information | metals4U - Ideas & Advice | metals4U r L1 d Brass Alloy CZ121 (CW614N) (smithmetal.com) s Lab Procedures (applies to all test articles) 4.x.1 Students measure test article as shown on previous slides and evaluate surface conditions (roughness, damage, 4.x.2 Every student shall calculate and discuss the following before starting the lab: - Max and min bending stress in SI units - Stress amplitude, mean stress, and stress range - Calculate the percentage yield (or proof) and ultimate as a function of max applied bending stress - Estimate time to failure from existing data (see instructions) to ensure all tests can be completed in lab period - Students shall evaluate previous section’s load cases to work towards having at least 3 tests across 11 total load cases Ref [2] Lab Procedures (applies to all test articles) 4.x.3 GSAs guide and students install specimen by following procedures in separate document “rotating fatigue manual – including data.pdf” 4.x.4 Student roles during test: a) Test article geometric measurements b) Test setup c) Oversight to ensure instructions are being followed d) Apply test load and measure moment arm e) Observe test article during test f) Record time to failure and test speed g) Collect test specimen cross section failure images from microscope 4.x.5 Students examine, photograph, and sketch in their lab notebooks to include applied load, number of cycles to failure, cantilever length, test speed, and time to failure 4.x.6 GSAs work with students to ensure all data is shared between sections in CANVAS AEE 3261 Aerospace Structures Laboratory Fatigue Experiments Report Guidelines - This laboratory report, covering fatigue experiments is due on the date specified in Canvas, and turned in through TurnItIn. - It is explicitly forbidden for you to access lab reports from previous years for any purpose whatsoever. They may not be used ‘as a template.’ They are not a valid resource to help you if you feel you don’t understand what to do. Do not download an old lab report. Do not look at one. Don’t even think about doing it – use the previous data provided with this lab. If you have questions or are unclear what to do, the proper course of action is contact your GSA or Dr. Swenson. - This laboratory requires a full, formal laboratory report (unlike the Exercise Reports, which permitted a briefer format.) - General guidelines for report formatting are in Canvas. In particular, please observe the standards described for the presentation of graphs and tables. When in conflict, this document supersedes the general guidance - This document provides specific directions for the Fatigue Lab Introduction (10%): Describe the purpose of the experiments conducted. Include paragraphs on each of the following: • Fatigue theory as relevant to the various tests conducted • Find and describe at least two engineering examples where fatigue was a significant factor in an aerospace engineering failure. Provide technical detail about each case and provide citations to external sources. • Explain what is a S-N diagram, and what is its purpose. Procedure (15%): • Describe the test specimens that were used in the testing program, and what one hopes to learn by testing them. • Show a “test matrix” (i.e. a listing of what specimens were made of what materials and tested under what conditions) in a concise, easy-to-understand table. (This is in addition to describing the various test specimens and test types the written text.) • Discuss the instrumentation of your test specimens. What data were collected. • Describe the equipment and explain their basic operating principle (not the step-by-step operating procedure) • Summarize the testing and data acquisition procedures (two to three paragraphs) • Note: the procedure should be written in narrative form (i.e. paragraphs), not a bullet point list or a numbered step-by-step set of instructions. Results (25%): All significant results should be summarized in a clear tables in addition to being described in the body of the report. 1 • Summarize the physical measurements of your specimens in a table – here is an example • • • • • Provide the Excel spreadsheets created in lab showing the test cases Plot stress amplitude (Units: MPa), S (y-axis) against number of test cycles N (x-axis) For each value of S and N, calculate the Log10 value Plot Log10 S (y-axis) against Log10 N (x-axis) Make the graphs look good. Properly label axes and lines. The aesthetics of the graphs will be a graded part of this assignment. For example, make the axes of the semi-log graph look good. Axes like the following: • For the aluminum case only, do a mathematical curve fit to obtain the parameters A and B such that the high cycle fatigue response can be modeled as 𝑆𝑎 = 𝐴𝑁𝑓𝐵 . Include some explanation and justification of how you did it. Your results should look similar to those found in the instructions For both the brass and aluminum samples, add the data sets provided at the end of the instructions to compare your data against • • Discussion (30%): • Write a discussion (2 paragraphs) about the role of stress concentrations in fatigue life of structures • Discuss fatigue life characteristics you can interpret from the data • Discuss sources of error in fatigue life measurements including the following points. Be as quantitative as possible. Please take this section seriously! Don’t just make vague statements like “there was human error”: 2  Influence on the results due to test setup and test article misalignment  Other effects that may influence the results Conclusions (10%): • Describe what was learned from the experiment. o Give key points in a bullet-point format o Address the topic of your fatigue results and its relevance in static failure and fatigue life o Describe what design practices you would apply knowing what you learned from this lab Recommendations (10%): • How could the experiment be improved? • What feedback do you have to offer? References: • Cite appropriate references using AIAA citation format. 3
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