IUL - The Tensile Test — Transcript

Full transcript

1. 0:00[Music]
2. 0:17so hey everyone my name is Josh welcome
3. 0:21to section three the tensile test of our
4. 0:25chapter 3 the tensile test ok let's get
5. 0:29started in this section we will take a
6. 0:33look at the general experimental setup
7. 0:36of a standard tensile test we'll talk
8. 0:39about the important aspects of the
9. 0:41standards according to which such tests
10. 0:45are or at least should be performed and
11. 0:48we will take a closer look at some
12. 0:51details of the specimen characteristic
13. 0:54that have to be obeyed in order to make
14. 0:57all the results be comparable alright so
15. 1:02I have to point out that my colleagues
16. 1:05from the WPT will later talk about in
17. 1:09more detail about the general set up
18. 1:11different machines the technologies and
19. 1:15they will show you also how to actually
20. 1:18perform a test tensile test which is why
21. 1:22this shall be only brief overview on the
22. 1:26concept and principles of a standard
23. 1:29tensile test so many of the modern
24. 1:32testing machines basically all they work
25. 1:35the same way that includes not only
26. 1:38tensile test machines but most of the
27. 1:40so-called general purpose machines like
28. 1:43the one you can see here which is
29. 1:47obviously also capable of performing
30. 1:50compression tests instead of not only
31. 1:54tensile tests but I would say that's a
32. 1:56different story for later so we have
33. 1:59that massive machine frame left and
34. 2:03right that is often fixated on the
35. 2:06ground sometimes even using a foundation
36. 2:09if necessary in that machine frame is
37. 2:13usually a spiral spindle so inside here
38. 2:20on each side moves the typically the
39. 2:23lower platform
40. 2:25up and down and the specimen which would
41. 2:30be placed somewhere here as kept in
42. 2:36place by our to clamping drawers or
43. 2:41specimen grips which are often powered
44. 2:46by a hydraulic unit so we see down here
45. 2:50in this case the load cell on top of the
46. 2:53machine is usually placed above the
47. 2:56upper gripper let's say the fixed one
48. 3:01provides the data of the force which is
49. 3:04currently acting on the grips and thus
50. 3:09the specimen for modern machines the
51. 3:14measurement and control electronics are
52. 3:16very important thing because everything
53. 3:22is controlled and recorded by that unit
54. 3:25nowadays it is furthermore the
55. 3:27connection to the computer on which the
56. 3:30actual testing software is running
57. 3:33though there is also a manual control
58. 3:36panel still existing most of the
59. 3:39operations are executed via the testing
60. 3:43software on the computer this comprises
61. 3:47the entire testing protocol including
62. 3:49forces velocities positioning
63. 3:53measurement details and for example also
64. 3:56stopping criteria so we can maybe stop
65. 3:59the test before the entire specimen
66. 4:02cracks but only when you have a small
67. 4:05drop in the force indicating that there
68. 4:08is a small crack just being initiated
69. 4:11and also in many cases the user can
70. 4:15select predefined test procedures which
71. 4:18execute the tests based on a chosen
72. 4:21standard for example or other special
73. 4:24regulations if you have for example some
74. 4:28special in-house procedures that you
75. 4:30have to follow and because material
76. 4:33tests should usually be performed
77. 4:35according to specific standards
78. 4:38this is exactly what we're gonna talk
79. 4:41about next when it comes to standards
80. 4:45that define how to perform a t-test
81. 4:48in order to get comparable and reliable
82. 4:51results it's absolutely no surprise that
83. 4:54the most general distinguishing feature
84. 4:58is the material itself of course like
85. 5:02metals plastics forms rubbers and so on
86. 5:06and so on so because everybody has quite
87. 5:09a natural understanding of how
88. 5:10differently these different materials
89. 5:13behave and thus it's only logical
90. 5:18in a sense that different standards were
91. 5:20developed for these different classes of
92. 5:22materials in many cases there is often
93. 5:26more than one standard available for a
94. 5:28specific class often standards from the
95. 5:31ISO nore ayahs or the International
96. 5:35Organization for Standardization or the
97. 5:37ASTM the American Society of testing and
98. 5:41material they exist parallel so you
99. 5:44should always declare according to which
100. 5:48standard the test was performed in some
101. 5:51cases different standards exist even for
102. 5:54the very same specific material and
103. 5:59because the standards can and are
104. 6:03actually showing some differences always
105. 6:05named standard according to which it was
106. 6:08before though metals and I would say
107. 6:12more specifically the ductile metals are
108. 6:15the most important material usually used
109. 6:19in mechanical engineering it's also
110. 6:21important to know about some other
111. 6:25standards like the one on plastic or the
112. 6:28emerging class of fiber reinforced
113. 6:31composite materials and the remaining
114. 6:35classes are generally of minor
115. 6:38importance and are used only usually for
116. 6:43special applications okay so once the
117. 6:46correct standard for the material of
118. 6:49interest is chosen it is important to
119. 6:52understand what is actually defined by
120. 6:56that standard and this is what we see
121. 6:59now so if we look for example at the
122. 7:03standard Dean and is oh six eight nine
123. 7:07two one which is based on the
124. 7:11international version is EO as oh six
125. 7:15eight nine two one that's a very easy to
126. 7:19remember you are usually first presented
127. 7:22with a detailed nomenclature that
128. 7:25includes can also country specific
129. 7:28symbols as well as the corresponding
130. 7:30international Simmons symbols for
131. 7:33example a very good example is in this
132. 7:35chapter we have presented you the I
133. 7:39would say the German perspective so for
134. 7:42true strains we use the word fine odd or
135. 7:46the symbol file but in many
136. 7:49international literature you will see
137. 7:51still something like the engineering
138. 7:53strain symbol may be used with the with
139. 7:59a dash a bar or a head on top to
140. 8:03indicate that now you're doing a
141. 8:06logarithmic strain analysis some other
142. 8:11informative country specific and axis
143. 8:14are usually also present as well here so
144. 8:18the standard usually then continues with
145. 8:22the definitions of the symbols and terms
146. 8:25used throughout the standard itself and
147. 8:28this is very important to read these
148. 8:30definitions so read the beep
149. 8:38instructions so that everybody is on the
150. 8:41same page here it's very important and
151. 8:43this also includes the dimension and
152. 8:46unit of the variables which are measured
153. 8:50so for example especially if you switch
154. 8:52between us and basically the rest of the
155. 8:56world it's very important to always
156. 8:59check the unit system later on the
157. 9:03standard deals with the
158. 9:05general test requirements including
159. 9:08stuff like preparation of the test and
160. 9:11determining the initial starting values
161. 9:14to environment and so on
162. 9:16since for example the rate of elongation
163. 9:20can be based upon different methods the
164. 9:25different strategies are described
165. 9:28explicitly in most of the standards the
166. 9:32analysis of the data which you get out
167. 9:35of the machine and I would say here
168. 9:37especially the deformation the
169. 9:41determination of the characteristic
170. 9:43values such as ultimately strings and so
171. 9:47on is discussed in detail and usually
172. 9:52final comments are given on the
173. 9:54measurement uncertainties which can
174. 9:58heavily depend on the type of material
175. 10:01being tested being tested so one more
176. 10:04important aspect that we will now talk
177. 10:06about is that a standard has to define
178. 10:10specimen characteristic such that
179. 10:13comparability between measurements is
180. 10:15ensured so the specimen characteristic
181. 10:22is among the most important aspects of a
182. 10:25standard and this is where we'll talk
183. 10:28about this now first of all the
184. 10:31manufacturing method of a specimen is to
185. 10:35be mine it in this standard for example
186. 10:38as cast or machine tests piece pieces
187. 10:42are allowed so on the other hand for
188. 10:46example laser cutting which is very
189. 10:48popular nowadays especially for flat
190. 10:51specimen is technically not a confirming
191. 10:56a way to manufacture the specimen
192. 10:59according to the standard so it's
193. 11:02important to understand that the
194. 11:04manufacturing method has a high
195. 11:06influence on the surface of a specimen
196. 11:09and this is the vital thing to
197. 11:11understand think for example about
198. 11:13differences of machined and form parts
199. 11:16the effect on the surface has
200. 11:19wider implications for instance because
201. 11:22the damage and later stuff like the
202. 11:26crack evolution which eventually causes
203. 11:29the test to be stopped influence or are
204. 11:34influenced by this very surface
205. 11:36structure which in turn itself is
206. 11:39heavily dependent on the manufacturing
207. 11:41method this ultimately also determines
208. 11:45when the specimen fails which define
209. 11:50certain material properties such as the
210. 11:53AAT value which is the elongation at
211. 11:56fracture
212. 11:58I hope it's now easier to understand for
213. 12:01example why laser cutting which melts
214. 12:06the material in the cutting zone which
215. 12:09will later then be the lateral surface
216. 12:11of the specimen is not allowed as a
217. 12:14manufacturing method so it actually
218. 12:16makes sense
219. 12:16so always keep in mind that standards
220. 12:19want to create comparable conditions
221. 12:22according to which the tests have to be
222. 12:25performed that is the overall mission I
223. 12:28would say so if we now look at the
224. 12:33specimen shapes we find I would say
225. 12:36variety of admissible shapes such as
226. 12:40circular square rectangular annular and
227. 12:45so on for each shape specifications on
228. 12:49the dimension are usually also given the
229. 12:52user can find further information on the
230. 12:56different sizes in the corresponding
231. 12:59annexes for these specific shapes if for
232. 13:04special reason an on standardized shape
233. 13:07has to be used this shape has to at
234. 13:12least comply with the uniform
235. 13:15cross-section requirement if for a
236. 13:18special reason however an on
237. 13:20standardized shape is desired or to be
238. 13:24used or has to be used it has to at
239. 13:26least comply with the uniform
240. 13:31cross-section requirement
241. 13:32if it is if it does not fit in one of
242. 13:35the categories defined by the specific
243. 13:38shapes transition radius is also to be
244. 13:45incorporated in any case either for
245. 13:49standard shapes or are also non-standard
246. 13:52shapes also the end of each specimen can
247. 13:58be designed in order to fit the
248. 14:00corresponding grip that I used for the
249. 14:04test in the example displaced here which
250. 14:07is a standard flat tensile specimen we
251. 14:11find both aspects included correctly we
252. 14:15can clearly see the transition readyyy
253. 14:20here that marks the end of the so-called
254. 14:25gauge length and the beginning of the
255. 14:31ends suited for the grips so the gauge
256. 14:35length is actually the testing area and
257. 14:40the ends themselves are designed so that
258. 14:44the grips have higher contact surface
259. 14:47which ensures no deformation in that
260. 14:52part of the specimen so here's where the
261. 14:58grips will be positioned so the same
262. 15:05aspects are even more visible I would
263. 15:08say for cylindrical specimens the
264. 15:11transition radius here increases the
265. 15:16diameter of the specimen and the ends
266. 15:20are even threaded in order to maximize
267. 15:24the contact between the specimen and
268. 15:27grips so one can clearly see that the
269. 15:30design of the ends follows the grips
270. 15:33because the ends have the same size and
271. 15:37geometry independent of the specimen so
272. 15:40we can see that is basically the same
273. 15:43because we use the same machine
274. 15:45whereas the testing lengths can change
275. 15:49according to whatever you want to do so
276. 15:54in order to avoid so-called scaling
277. 15:57effects and ensure controlled handling
278. 16:00of the specimen there is a minimum gauge
279. 16:02length defined by the standard such a
280. 16:05length is hoped to cancel out any
281. 16:09microscopic inhomogeneities
282. 16:11such that the tensile test delivers
283. 16:13results which are in term valid on the
284. 16:17macroscopic level in relation to that
285. 16:21gauge length the initial cross-section
286. 16:24area is also specified by the standard
287. 16:27pretty much for the same reason the
288. 16:30specimen shall neither be too thin not
289. 16:34too thick
290. 16:34in both cases undesired effects are to
291. 16:39be expected if it's too thin or too
292. 16:42thick so the very 4k presented here is
293. 16:48quite a strong suggestion by the
294. 16:50standard but if the cross section area
295. 16:53and the length are of such dimensions
296. 16:58that the value K is slightly different
297. 17:01it is typically not so much of a big
298. 17:05deal
299. 17:08what's definitely even more important is
300. 17:10that during a tensile test the force
301. 17:13applied by the testing machine goes
302. 17:16straight through the specimen that means
303. 17:20also that the direction of testing shall
304. 17:23or must coincide with the main axis of
305. 17:27the specimen and also coincide with the
306. 17:31main testing direction of the machine
307. 17:34itself in short don't clamp your
308. 17:37specimen skew all right that was the end
309. 17:42of chapter 3 I hope you guys enjoyed it
310. 17:46learned a bit and good luck with the
311. 17:48questions and I'm looking forward to see
312. 17:52you again in chapter 5 bye bye