Tensile Test on Steel — Transcript

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1. 0:00gurney assistant professor Watson
2. 0:01Institute of Technology Sala poor I am
3. 0:04here to discuss with you on topic
4. 0:06tensile test on steel today learning
5. 0:11outcomes of today's session at the end
6. 0:13of this session students will be able to
7. 0:15explain procedure of tensile test on
8. 0:17steel they will be able to perform
9. 0:20tensile tests on steel in laboratory
10. 0:25introduction as we know still is an
11. 0:29important construction material mainly
12. 0:31used as a reinforcement in the form of
13. 0:34round bars in concrete and also at
14. 0:36different places like groups frames form
15. 0:38in doors and so on
16. 0:39now quality of this steel bars is very
17. 0:44important mainly they have to carry
18. 0:46tensile load so they are tested for
19. 0:49tensile strength in laboratory by using
20. 0:53relevant ice core so the ice cores for
21. 0:56testing of Steel are listed here you can
22. 0:59see is 432 1982 is the core for mild
23. 1:03steel and medium tensile steel bars and
24. 1:05hardened steel wires for concrete
25. 1:07reinforcement today we are dealing with
26. 1:09is this particular ice core as we are
27. 1:13studying tensile test on mild steel bars
28. 1:16today so let us see test procedure this
29. 1:21particular test procedure is according
30. 1:23to ice for 32 1982 now aim of today's
31. 1:28experiment to study tensile strength of
32. 1:30mild steel bar specimen this is the aim
33. 1:33equipments used universal testing
34. 1:36machine universal testing machine you
35. 1:39can see here this is the machine which
36. 1:41is used for this particular test app
37. 1:45artists used vernier calliper test
38. 1:48specimens etcetera then procedure mild
39. 1:52steel specimen of say 20 mm diameter is
40. 1:54say it is to be tested
41. 1:56then diameter of this bar is measured
42. 1:59with vernier caliper accurately remember
43. 2:01so measurement of diameter of the
44. 2:04specimen is important standard gauge
45. 2:07length is marked on the specimen this is
46. 2:10next important step I scored you
47. 2:12standard gauge
48. 2:13length and accordingly the gaze length
49. 2:15should be marked and it is by 0.65 under
50. 2:19cross section area of bar accordingly
51. 2:22this particular gauge length is marked
52. 2:24and bar is held in the jaws of the
53. 2:27middle cross head and upper cross here
54. 2:30so firstly it is held in the middle
55. 2:32cross head of the eutteum firmly then
56. 2:35middle cross head is taken up and the
57. 2:37other end of the bar is fixed in the
58. 2:39jaws of the top cross head of the UTM
59. 2:43remember see the specimen is prepared
60. 2:46like this
61. 2:47it's part on two ends is having more
62. 2:51diameter and the gauge length part is
63. 2:54reduced in diameter so that we can get
64. 2:57the results for this particular part we
65. 3:00are testing the bar for this particular
66. 3:02gauge length or which diameter is
67. 3:04reduced so that we can come and confirm
68. 3:06the failure of bar in this particular
69. 3:09region only okay now for taking strain
70. 3:14readings and elongation readings
71. 3:16extensometer is also fixed or the gauge
72. 3:20length while testing is being performed
73. 3:22and loading is given gradually gradual
74. 3:26loading is given to the bar tensile
75. 3:29loading and for every fix the time
76. 3:31interval of loading say 20 kilo Newton
77. 3:33or so extension of the bar is measured
78. 3:36with the help of extensometer
79. 3:38it is recorded from the external
80. 3:40extensometer the extension for each load
81. 3:45interval so that we can draw stress
82. 3:48strain graph or load versus elongation
83. 3:50graph and graph is directly available on
84. 3:53UTM also which we can validate the
85. 3:56results with then before actual failure
86. 3:59of the specimen takes place remember
87. 4:02extensometer has to be taken out so as
88. 4:05to avoid its damage and then yield point
89. 4:08is noted down load at yield point is
90. 4:11recorded then ultimate load is recorded
91. 4:15breaking load is also recorded these
92. 4:18silent points we will see soon necking
93. 4:21can be seen clearly before failure in
94. 4:24the mild steel as it is a ductile
95. 4:26material
96. 4:26Kingman's reduction in diameter is
97. 4:28clearly seen and before this you have to
98. 4:31take out the extensor meter and avoid
99. 4:36the damage of the extensometer
100. 4:37now after failure of the specimen two
101. 4:40parts are brought together and their
102. 4:43extension in length or the gauge length
103. 4:46and reduction in diameter at the failure
104. 4:50point is matured so these are the
105. 4:53readings taken now we will discuss about
106. 4:56these different readings in this
107. 4:59particular part of slide now reduction
108. 5:03in diameter of the specimen is measured
109. 5:05now percent elog inch elongation of the
110. 5:08bar is calculated how will be the
111. 5:11percent elongation calculated final
112. 5:13gauge length minus initial gauge length
113. 5:16divided or final gauge length in 200
114. 5:18this will give us the percentage
115. 5:21elongation of the steel bar remember and
116. 5:24percentage reduction in diameter how it
117. 5:27is to be measured initial diameter minus
118. 5:29final diameter divided by initial
119. 5:31diameter in 100 so this will give us
120. 5:34percentage reduction in diameter
121. 5:37apart from this calculate in apart from
122. 5:40these two calculations stresses are also
123. 5:42measured ultimate stress yield stress
124. 5:44etcetera from the loads which you have
125. 5:47obtained in the test now there are
126. 5:50certain specifications given bias for 32
127. 5:54part 1 1982 regarding the ultimate
128. 5:58stress in distress and percent
129. 6:00elongation for mild steel of grade 1
130. 6:04this particular code use specifications
131. 6:07for bars less than 20 mm and bars more
132. 6:12than 20 mm differently little different
133. 6:14is there when bars are less than 20 mm
134. 6:16ultimate tensile stress should minimum
135. 6:20tensile stress should be 4 1 0 410
136. 6:23Newton per mm square yield stress should
137. 6:26be minimum 250 Newton per mm square and
138. 6:29percent elongation minimum should be 23
139. 6:32so these are the specifications given by
140. 6:35is 432 if bars are more than 20 mm up to
141. 6:3950 mm
142. 6:40the ultimate tensile stress should be
143. 6:43minimum 410 CM yield stress minimum
144. 6:46should be 240 little less to 40 Newton
145. 6:51per mm square and percent elongation is
146. 6:54same 23% now let us see some silent
147. 6:58points on this stress-strain curve so
148. 7:01stress-strain curve is very important
149. 7:03curve which is drawn after every tensile
150. 7:05test and you will see that for initial
151. 7:08portion this particular curve is
152. 7:11straight one which shows that stress is
153. 7:15proportional to strain up to certain
154. 7:17limit say up to point a so this
155. 7:19particular point a is known as
156. 7:21proportional limit right up to
157. 7:25proportional limit the material obeys
158. 7:27Hookes law we know stress is
159. 7:29proportional to strain up to
160. 7:31proportional limit
161. 7:32now beyond proportional limit this point
162. 7:36B is there which is elastic limit and up
163. 7:40to elastic limit materially said to be
164. 7:42elastic that means if you unload the
165. 7:45material here it will regain its
166. 7:46original shape and size immediately
167. 7:49right so point B here is elastic limit
168. 7:54now once this elastic limit passes here
169. 7:58Point C and D these are the two points
170. 8:02which are called yield points C's the
171. 8:04upper end point D is the lower yield
172. 8:07point in this region what happens load
173. 8:11practically remains constant and strain
174. 8:14increases continuously so here you can
175. 8:17see the most part of this curve between
176. 8:21C to D is horizontal 1 so at the same
177. 8:25loading at the same loading the strain
178. 8:29in crippe increases considerably so it
179. 8:32is called yield stress and when a higher
180. 8:35point at higher point C this particular
181. 8:39point is called higher yield point upper
182. 8:43yield point and lower point say higher
183. 8:46say higher point is C and lower point is
184. 8:49D right so C is the upper yield point
185. 8:53is the lower intimate then thereafter
186. 8:56again stress increases a little till
187. 8:59ultimate point is reached and here
188. 9:02ultimate stress is obtained so maximum
189. 9:05stress this is point a where stress
190. 9:08taken by the specimen is maximum right
191. 9:12and after this certain drop again occurs
192. 9:17in the stress and breaking stresses of
193. 9:20tamer
194. 9:20remember after ultimate stress what
195. 9:24happens Nichkhun starts as soon as
196. 9:27necking start sneaking means reduction
197. 9:28in diameter at the weakest point what
198. 9:30happens load decreases a little than the
199. 9:33ultimate and this particular breaking
200. 9:36load is lower than the ultimate load so
201. 9:38breaking stress at Point F is also found
202. 9:42out so here is one exercise for you
203. 9:46students let us pause the video we hear
204. 9:48a little and solve this particular
205. 9:50problem in a tensile test and mild steel
206. 9:53specimen of diameter 12 mm over a gauge
207. 9:56length of 100 mm following observations
208. 9:58are taken ill load twenty eight point
209. 10:01three kilo Newton ultimate load 47 kilo
210. 10:04Newton find yield and ultimate stresses
211. 10:06these are the this is the exercise now
212. 10:13here we can see the solution cross
213. 10:16sectional area of specimen can be found
214. 10:18by by four PI d square because it is
215. 10:21ground specimen and in the stress is
216. 10:24equal to e load divided by cross section
217. 10:26area so it is 250 point 35 Newton per mm
218. 10:30square ultimate stresses ultimate load
219. 10:32by cross section area and you will tell
220. 10:34for one 5.78 Newton per mm square simple
221. 10:37is the solution
222. 10:38so here are two rib equations for you
223. 10:41solve them as pariahs 432 1982 to mild
224. 10:46steel grade one bar of diameter less
225. 10:47than 20 mm should have minimum will
226. 10:49strength off - Newton per mm square pick
227. 10:52up the correct answer and as per eyes
228. 10:55432 mile slope grade one should have
229. 10:57minimum percent elongation of - become
230. 11:00the correct answer write your answers
231. 11:05answers question number one a250
232. 11:08questionable to d23 these are the
233. 11:14references for precision thank you