Sean Carey Tafe No. 366851615 Lab Report: Hounsfield Tension Test August 2012
The Hounsfield Tester The Hounsfield Tester can do a variety of tests on a small test-piece. It is mostly used for tensile testing. It doesn't measure elasticity very well. In this lab we are measuring the UTS - Ultimate Tensile Strength. This is the highest stress a material can take before it breaks. We will also analyse the test to determine the material stiffness E, called Modulus of Elasticity. (Also called Young's Modulus) Lab Procedure: 1. Take measurements of the specimen. Diameter, Length etc. Ascertain the material as best you can. 2. Then calculate the maximum load that can be applied to the specimen, assuming a sensible UTS of the material. We must also calculate an expected yield point. See http://www.matweb.com/ for a material data list. 3. Load the correct beam into the Hounsfield (to suit the expected loading at UTS + 10%). 4. Zero Mercury indicator 5. Apply load to about 70% of Yield by rotating the handwheel and watching the mercury indicator to ensure the specimen it fully seated in the jaws. 6. Release the load and reset the mercury indicator.
7. Add paper to the chart roller and begin the test (Usually recording the load by depressing the pin of the Mercury indicator lever onto the graph paper every 2x rotations of the handwheel) until the specimen breaks. By recording the force as we increase the load on the specimen, the highest force is used to determine UTS. 8. Remove paper, measure the % elongation of the specimen. 9. Attempt to record all sources of error relevant to the measurements taken (Force, Extension) Calculate approximate Yield point & UTS Force for sample Material: Brass
Material: Brass Description Units Formula Results Length (L) mm 27.3mm Diameter (d) mm 5mm Radius ( r ) mm 2.5mm Cross Section Area mm² π r² 19.635mm² Yield Point Mpa Data Sheet 247Mpa 70% Yield Point Mpa Data Sheet Newtons @ Yield Point N Mpa xcsa (mm²) 4849.845N kn 4.85kN Newtons @ 70% Yield Point N 3394.8915N kn 3.395kN Ultimate Tensile Strength Mpa Data Sheet 440 Mpa Newtons @ U.T.S. N Mpa xcsa (mm²) 8639.4N kn 8.639kN Lab Results:
Sample Results From Graph Description Units Formula Results Guage Length (L) mm 27.3mm Diameter (d) mm 5mm Radius ( r ) mm 2.5mm Cross Section Area mm² π r² 19.635mm² Yield Point (actual) Mpa N / mm² 150.24Mpa Newtons @ Yield Point N Graph 2950.00N Ultimate Tensile Strength (actual) Mpa N / mm² 188.439Mpa Newtons @ U.T.S. N Graph 3700.00N Axial Stress ( σ ) ( @ 70% yield point) Mpa σ = F / A Axial Strain ( ε ) no units ε = x / L 0.2527 Guage Extension (x) mm 6.9mm Modulus Of Elasticity ( E ) Mpa E = σ / ε Note: If initial calculated settings were used for setup, the yield point would have already been exceeded and false results obtained. The test sample was not as Strong as the average Brass figures on the data sheet. 1. Ultimate Tensile Stress = 188.439Mpa 2. Yield Stress = 150.240Mpa 3. % Elongation = Stretch / Original Length x 100 = 25.27% 4. It is not possible to get a reliable Strain or Modulus of Elasticity (E) in this testing apparatus as (1) the material also tends to deform in the jaws of the tester giving an error in the results and (2) Especially in more tensile materials which have a tendency to compress (pull against) the tester which is not very rigid above certain forces Again giving false results 5. Method :1 Set up a spring as a testpiece. Test this spring to several values in a tension tester that is known to be accurate, record these results. Set up spring in Hounsfield tester (in the same ambient conditions) and use the correct results from the previous machine as a reference to calibrate the Hounsfield unit. Method :2 Set up a dial guage in the Hounsfield tester Use it to check in several points if the distance travelled corresponds with the reading on the graph ( this method does not allow for the compression forces in the actual tester itself when it is performing a test).
Monday Night Class. Aug 6 2012. The Specimen reached limit of machine and did not break. Please make comments about what this test can tell us.. In this test an unknown Steel sample was being tested. A number of faults could have occurred. One possibly being that the incorrect mercury indicator was used with the 10 kn scale, another was that the steel may just well have been outside this particular testers capabilities However when the tester was released it was noticed that the final point was not on the set zero point. So assuming the the testpiece was correctly seated prior to this pull we can assume that the yield point / elastic limit had been exceeded.