Experiment V The Charpy Impact Test OBJECTIVES The objectives of this experiment are (a) to investigate and determine the ductile to brittle transition temperature for annealed low carbon steel, and (b) to become acquainted with the notched bar impact test (Charpy test). THEORY Materials that fracture with little or no plastic deformation are said to be brittle. One set of materials that have a microscopic structure known as body-centered cubic (BCC) become brittle at low temperatures or at extremely high rates of strain. Many metals with a microscopic structure known as face-centered cubic (FCC), on the other hand, remain ductile even at very low temperatures. Still, there is another group of metals and alloys with a microstructure known as hexagonal closed-packed (HCP). When in the form of single crystals and under favorable orientation for basal slip, metals/alloys with HCP structure are ductile, but may be brittle in polycrystalline form. In most BCC metals, the stress that is required to cause plastic flow increases rapidly with decreasing temperature. The decreased thermal energy at low temperatures makes it difficult for the thermally activated dislocation processes to operate. The stress needed to propagate a crack does not increase as rapidly with decreasing temperature and so brittle failure by crack propagation becomes the favored process at low temperatures. Also, at very high rates of strain, even at ambient temperatures, the activated dislocation processes have insufficient time to operate, and, therefore, the tendency for brittle failure increases with increasing rates of strain. Figure VII-1 Standard Specimen for Charpy Impact Test V-1 Thus a material may be ductile in a slow tension test, but brittle in an impact test where the rates of strain are faster by orders of magnitude. The introduction of a notch in the specimen that will be impact tested, as shown in Fig. V-1, increases the tendency for brittle failure, due to the stress concentration at the notch. Brittle behavior in some BCC metals may also arise as a consequence of a change in slip character rather than a change in yield stress. PROCEDURE WARNING: Use extreme caution when performing this experiment. Be sure no one is in the front or in the back of the pendulum when it is in the raised position. Also, liquid nitrogen is at T = -320°F, so handle the specimens with asbestos gloves, and be careful. Wear safety glasses throughout this experiment. 1. Twelve specimens made of two types (compositions) of steel will be tested during this experiment. Place one steel specimen of each type (composition) in liquid nitrogen, dry ice, wet ice, an oven at 120°F and boiling water; retain 1 of each for room temperature testing. For safety reasons, the impact tester is set at Izod test standards. For this set up the hammer of the impact tester is raised to the maximum height which is lower than that of the standard Charpy test. 2. Raise the hammer of the impact tester to its maximum height. Set the pointer at the maximum capacity (usually 240 ft-lb on the Izod scale). Release the hammer first to record any zero error in the machine. To avoid accidents, always make sure that the hammer can swing to the other side without hindrance to its full height. 3. When the sample has been at room temperature for at least ½ hour, place the Charpy specimen in position as shown in Figure V-2. Raise and release the hammer and record the energy consumed in breaking the specimen, as indicated by the pointer. Examine and record the appearance of the fracture. Figure V-2 Position of Charpy Specimen in the Testing Machine V-2 REPORT REQUIREMENTS 1. Report the data as follows: Specimen: (identification) Temp. (°F) Charpy Impact (ft.-lb) Appearance of Fracture Surface 2. Plot impact strength vs. temperature for each group of samples. 3. From the curves, estimate the transition temperature of each heat-treated group and compare with the published data. 4. Discuss the fracture surface appearance as related to test temperature, heat treatment and impact strength. 5. The following items should be discussed pertaining to the results: a. effects of temperature on fracture b. types of fracture that may occur in a metallic material REFERENCES [1] Cottrell, A.H., The Mechanical Properties of Matter. John Wiley and Sons. [2] Wertzberg, R. W., Deformation and Fracture, Mechanics of Engineering Materials, John Wiley and Sons. [3] Reed-Hill, R.E., Physical Metallurgy Principles, Van Nostrand. [4] Stadelmaier, H. H., and W. W. Austin, Materials Science Research, Vol. I, Plenum Press. [5] Van Vlack, L. H., Materials for Engineering, Addison-Wesley, Reading, Mass. V-3 EGME 306 A Charpy Impact Test Data Sh 1018 Steel (Blue) Set Temeperature Boiling Water (212 oF) Temperature 4140 Steel (Red) Asorbed Engergy Temperature 206 97 206 100,6 85 104,4 Room Temperature (72 oF) 73,7 28 73,5 Ice Water (32 oF) 42,8 4,5 43,6 Dry Ice(-109 F) -110,9 5 -110,9 Liquid Nitrogen (-321 oF) -284,8 0,1 -283,9 Oven ( 120 oF ) mpact Test Data Sheet 4140 Steel (Red) Al 6061-T6 (Green) Asorbed Engergy Temperature Asorbed Engergy 35 206 18 28,5 106,2 6 28 74 18 14 43,4 0 4,5 -110,9 20 5 -284,3 20 EGME 306 A Charpy Impact Test Data Sh 1018 Steel (Blue) Set Temeperature Boiling Water (212 oF) Temperature 4140 Steel (Red) Asorbed Engergy Temperature 208 95 208 119.3 103 119.3 Room Temperature (72 oF) 75.8 20 75.8 Ice Water (32 oF) 42.1 8 42.1 Dry Ice (-109.3 oF) -110.9 2 -110.9 Liquid Nitrogen (-321 oF) -287.4 4 -287.4 Oven ( 120 oF ) mpact Test Data Sheet 4140 Steel (Red) Al 6061-T6 (Green) Asorbed Engergy Temperature Asorbed Engergy 38 208 17 34 119.3 16 39 75.8 18 43 42.1 14 -110.9 16 -287.4 22 X 4 APPENDIX C TECHNICAL WRITING STYLE In experimental reports, the most important factors are the actions performed, the results obtained, and their meaning. The person or persons doing the experiment are of secondary importance. Therefore, it has become standard practice to write technical reports in an “impersonal” style. Impersonal Writing Style How does one write impersonally? There are several techniques, not usually emphasized in English courses, which help the student to develop an impersonal “scientific or technical” style to his or her writing. The following guidelines will help you: a) Personal Pronouns Omitted The personal pronouns: I, you, he, she, they, and who, should never be used in scientific writing. For example: Incorrect We set the dial to zero. Correct The dial was set to zero. “It” (a neutral pronoun) can be used occasionally when following a short sentence. However, if the previous sentence is long or involved, restate the subject under discussion. Ex: The measuring apparatus was adjusted. It was then set to zero. The pronoun “one” (General for ‘A Person’) may be used occasionally. Ex: One needs to consider alternative theories. b) Passive instead of Active Voice The most commonly used method of making writing appear more impersonal is to change the sentence from the active to the passive voice. This is done by inverting the word order so that the noun which was the direct object becomes the subject. A form of the verb to be is added to the past participle of the verb. The sentence on the next page shows the preferred form. In the following examples, an “S” above the word denotes the subject, “V” the verb, and “D.O.” the direct object. The verb is also underlined to show the transformation from active to passive voice. (Active) Ex: S V D.O. He found a direct correlation as shown in …… C-1 (Passive) Ex: S V A direct correlation was found as shown in…… S V D.O. Ex: The assistant gave Dr. Wizard the readout. Inverted Word Order Difficulties In writing an experimental report, many of the sentences are inverted word order, that is, the verb appears before the subject. One must be careful to make the verb agree with the subject, and not some other word in the sentence: Ex: V. S. Is any one (subject) of the gyroscopes available for use? Ex: V. S. Throughout the manual appear frequent references (subject) to the J. of Mech. Engr. Ex: Accompanying the report were the index and two S. appendices (compound subject) Economy of Expression Technical or scientific style is short and direct. This style can be achieved by the following: a) Word Selection Generally, short words are easier to understand than long words. Only occasionally is a long technical term more precise and therefore to be preferred over short ones. b) Sentence Structure A Sentence is a group of words which expresses a complete thought. Long, involved sentences with many clauses are difficult to comprehend, while short single sentences, one after another, tend to be choppy. The solution is to alternate long and short sentences. This gives relief and variety to the reader while retaining comprehension. (Note: If this structuring is difficult for you in the beginning, then you should write many short sentences; include some longer sentences later as your skill develops). C-2 c) Paragraph Length A Paragraph is a group of sentences which expresses the development of one idea or subject. They are like punctuation. When the idea you are writing about changes, start a new paragraph. Many students tend to write all of their paragraphs the same length, either filling up the whole page, or changing topics with each sentence. Both are difficult for the reader to digest. Such writing takes away from the “flow” of the report. In general, paragraphs should vary from three to ten typewritten lines covering one idea. If they are longer or shorter, they may need to be rewritten to provide clarity. What Questions Should You Ask? Technical writing needs to be concrete and give the answers to several important questions. Basically in writing a report the writer should briefly answer the following questions: What object was experimented on? How many things were involved? (number) How long (or What size) were they? (measurements) What happened to the experimental sample? How was the change measured? (apparatus and units) Where is the experimental change most evident? (location) When did the sample alter? (time) Why are the experimental results important? How do these results relate to the presently held theory or theories? As you can see, the most important questions to answer in technical and scientific writing are: What, How, How long, or How many, Where, When, and Why. By contrast, who is not an important question. Notice how many of these important questions are answered in this one brief sentence. (How many?) (What?) (How long?) Four samples of iron, varying in length from 2” to 10” were (What happened?) (What was done?) subjected to compressive axial loading while measurements (What change?) (Where located?) were made of the deflection at the midpoint of the metal bar. C-3 Common Pitfalls or Which Way is Up? The student who has finished an experiment has the tendency to talk to the reader as if he or she were in the room: “First we did this and then we walked over there to the apparatus which was held up by clamps. We wrote down the data from these dials which were compared to those theoretical results.” As you can see, it’s difficult for someone not looking over the experimenter’s shoulder to know what is going on. It is best to use such “pointer” words as first, then, this, that, there, which, up, down, etc., sparingly. Remember, in writing your report, write as though the reader (a manager or another engineer) was not in the room and has not seen the experiment. Agreement of Noun and Verb in a sentence S. V. Ex: Our chief trouble (subject) was (not were) the black flies that swarmed about us during the experiment. S. Ex: The black flies (subject) that swarmed about us V. during the experiment were (not was) our chief trouble. Ex: S. The material (subject) that was most interesting to me V. when I worked on my research paper was (not were) the books that included graphs and diagrams. When part of the sentence is singular and part plural, as in the first two examples,, the sentence usually sounds less awkward if the subject and verb are plural, as in the example #2. Singular and Plural Nouns A “singular” noun refers to one item, object or person only when used as the subject in a sentence, and takes a singular form of the verb in every tense; e.g., present, past, future perfect. C-4 The woman is at work; The teacher gave out the equations; The student will be graduating in a few years. A “plural noun refers to two or more items, objects or persons and takes a plural form of the verb to match it in number regardless of the tense of the verb. Regular nouns are made plural by adding “s” or “es” to the singular form. The students studied hard. Quarks have yet to be seen by experimenters. Irregular Singular and Plural Nouns Many foreign words coming into the English language, especially technical and scientific terms, are made plural in a manner other than adding “s” or “es”. Below are some of the common rules for forming plurals of these irregular nouns: General Rules. To form the plural from the Singular Foreign nouns ending in: “us” change to an “i” Ex: alumnus changes to alumni “um” or “on” generally change to an “a” Ex: stratum changes to strata; phenomenon alters to phenomena “a” change to “ae” Ex: alga becomes algae “x” or “ex” usually alter to “ces” or “ices” Ex: appendix changes to appendices vortex becomes vortices “eau” generally add “x” for the plural form Ex: the tableau changes to tableaux “is” alter to “es” or “ides” Ex: analysis becomes analyses C-5 iris changes to irides In table C-1 are listed frequently misspelled and misused scientific and technical words of use to engineering students. The first column lists the singular form of the noun and the second column presents the foreign or the original plural. The third column gives the American plural form to which many of these words are slowly changing. However, the foreign (original) plural form is generally preferred, except for those words in the table noted by an asterisk. Table C-1. Irregular Singular and Plural Nouns (Including Frequently used Technical and Scientific Terms) _________________________________________________________ Foreign Singular Foreign Plural American Plural alumna (f) alumnus (m) analysis apex apparatus appendix axis basis criterion datum erratum focus formula gauge hypothesis matrix maximum medium memorandum minimum momentum parenthesis phenomenon radius spectrum syllabus symposium synopsis synthesis thesis vortex alumnae alumni analyses apices apparati appendices axes bases criteria data errata foci formulae gauges hypotheses matrices maxima media memoranda minima momenta parentheses phenomena radii spectra syllabi symposia synopses syntheses theses vortices alumni* alumni apexes apparatus* appendixes criterions focuses formulas* gage(s) matrixes maximums mediums memorandums minimums momentums radiuses spectrums syllabuses symposiums vortexes In the above table, words designated by an asterisk “*” are preferred in current usage; otherwise, the foreign plural form is preferred. C-6 Two Plurals Some words have two plurals with different meaning. The one technical term you are likely to use is: Singular Plural #1 Plural #2 index indexes (in books) indices (in mathematics) One Item, Plural Meaning Nouns which describe a pair of things, such as a pair of pants, are usually treated as plural. Common words and engineering terms are: calipers scales tongs dividers pliers tweezers pincers scissors shears Plural Form - singular Meaning Other nouns are plural in form, that is, they end in an “s” but are used as a singular word with a singular verb in a sentence. Ex: Aeronautics is studied by a large number of engineers. Scientific terms ending with “ics” are the most common type in this group. acoustics economics hydrostatics optics statics aeronautics electronics mathematics physics statistics dynamics harmonics mechanics pyrotechnics tactics Singular Words That May Fool You When words like series, portion, part, type are used as the subject of a sentence, they take a singular verb even when followed by a phrase with a plural noun. Ex: A series of panel discussions is scheduled for the conference. Ex: A large portion of the references is missing. Ex: The most interesting part of the expeditions was the discovery and identification of the prehistoric fossils. Ex: One type of management options includes participant teamwork in problem solving. C-7 LABORATORY REPORT CONTENT For almost all of the experiments, the laboratory reports should include the following (total of 20 points): • Title Page (0.5 points) • Table of Content (0.5 points) • Abstract (2 points) • List of Symbols and Units (2 points) • Theory (3 points) • Procedures and Experimental Setup (2 points, with colored pictures) • Sample Calculation and Error Analysis (3 points, Error Analysis may not exist for some experiments) • Results (2 points with Table of Results and/or Figures) • Discussion and Conclusion (4 points) • References (0.5 points, e.g. textbooks, journal papers. Do NOT reference Wikipedia.) • Appendix (0.5 points, raw data sheet and hand calculation) LABORATORY REPORT FORMAT • Use 1 ½ spacing for texts and equations. • For all texts and equations, you must use the font Times New Roman, font size 12. • For section titles, use Times New Roman, size 14 with boldface. • Use 1 inch left margin, and ¾ margin on all other sides (right, top, and bottom). • Use justification on both left and right margins. • All equations must be centered with equations number: (1), (2), (3) with right justification • Try to use present tense in writing your report. • For all pages, you should have headers/footers such that: o Upper left corner: EGME 306A o Upper right corner: Experiment name o Lower left corner: Your name o Lower right corner: Page # /Total pages • • • • • Title Page: o Please include: course number, course title, name of the experiment, your name, Group name, your lab partner’s names, date the report due date, submission date Abstract: o Abstract should be between ½ pages to ¾ pages. You should clearly state the objective of the experiment in the very first sentence. You must also briefly answer a) What was done? b) How was it done? c) What were your basic results? d) How is your result compare to that of theory and/or other sources? List of Symbols and Units: o You should clearly write variables, name of the variables, and units in three column format. Theory: o With books and other sources, you must provide background information that helps in analyzing your data. You should include theoretical information for all of the equations that you used in analyzing your data. Procedures and Experimental Setup: o Concisely describe procedures and setup in your own words (do not copy from lab 1 • • • • handouts). Number the procedure in chronological order. Please place a couple of colored photos to better illustrate your procedure of the experiment. Sample Calculations and Error Analysis: o “Number” the sample calculation that you are analyzing in chronological order. o This number should correspond to the number in the error analysis. Results: o Make sure you have titles, axis labels with units in all tables and figures. Discussion: o Explain how your results relate to the theory. Similarities and differences between your results and that of others can be used to confirm your conclusions. You must explain in detail some sources of error. If your result disagrees with the published source, try to explain possible sources of error. If it agrees, you must also explain how you obtained the accurate results. Conclusion: o For the concluding paragraph, you must discuss the most important overall result and explain what you have accomplished. Remember, this “Discussion and Conclusion” section weighs more than any other section for a good reason (4 points). 2
Purchase answer to see full attachment