HOUNSFIELD TEST

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.

Finding UTS using the Hounsfield  Tensometer

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 YS - Yield Strength.

Notes: Hounsfield Tensometer Guide:  Hounsfield_Notes.pdf Hounsfield Contents.pdf

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Axial Stress Theory

Axial stress acts along an axis, which is really just a shorthand way of saying Tensile or Compressive Stress.

Axial Stress:  s = F /A	s = Axial Stress (MPa) A = Cross-sectional Area (mm2) F = Force (N) e = Axial strain (no units) L = Gauge length - originally (mm) x  = extension (mm) E = Modulus of Elasticity (MPa)
Axial Strain:  e = x / L
Modulus of Elasticity: E = ss / e s

By recording the force as we increase the load on the specimen, the highest force is used to determine UTS.

Hounsfield Laboratory Procedure

Before starting the lab, you must calculate the maximum load that can be applied to the specimen, assuming a sensible UTS of the material. Note that in practice, the UTS is nearly always higher than the published values. This is because the published data is usually a 'guaranteed' value, or the lowest value you would rarely, if ever, encounter. See Materials.htm for our list of  material data. 

1. Take measurements of the specimen. Diameter, Length etc. Ascertain the material as best you can.
2. Load the correct beam into the Hounsfield (to suit the expected loading at UTS).
3. Apply load to about 75% of Yield to ensure the specimen it fully seated in the jaws.
4. Release the load and set the mercury indicator. 
5. Add paper to the chart roller and begin the test (recording the load as you go) until the specimen breaks. Blank graph paper is here: High quality (1MB), Low quality (0.3MB).
6. Remove paper, measure the % elongation of the specimen.
7. Attempt to record all sources of error relevant to the measurements taken (Force, Extension)

Laboratory Report

Determine the following:

1. Ultimate Tensile Stress (UTS), MPa
2. Yield Stress (YS), MPa
3. % elongation
4. Discuss the issues regarding the horizontal axis of the graph plot (elongation) and why it is not possible to get a reliable Strain or Modulus of Elasticity (E).
5. Explain two possible ways to (approximately) calibrate the elongation axis.

The report should follow the Laboratory Report guide. Include an approximate error analysis.

Results

The following images show plots of Houndsfield tests. Choose the appropriate test for your class (or as instructed).

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Thurs night Class. Nov 2015

Larger Image | Full Size

 

Larger Image | Full Size

 

Mon Night Class. Sep 8 2014.

 

Mon Night Class. Sep 9 2013.

 

Thurs Day Class. Feb 21 2013. Larger Image here.

 

Monday Night Class. Aug 6 2012. Larger Image here.

Note: Specimen reached limit of machine and did not break. Please make comments about what this test can tell us, but complete your lab assignment using this specimen here.

Thursday Day Class July 26 2012. Larger image here

 

Thurs Class June 14 2012

 

Mon night class: Sep 05, 2011 (larger image here)

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Monday PM class October 26, 2010 Original Diam 5.05mm Original Length ID = 27 Original Length OD = 36.6 Final Length ID = 30.89 Final Length OD = 40.03 Final Diam 4.5mm

Final Length = 34.7mm    
Break Diameter (necking) = 3.8mm

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The vertical axis is calibrated as 5kN on the mercury scale = 8cm on the graph paper.

Test 1: Monday night class: Oct 27
Parallel red curves have been superimposed to estimate the contraction after breakage, from which the x axis (extension) can be calibrated.

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Test 2: Tuesday night class: Oct 28

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Test 3: Wed day class: Oct 29

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Questions:

Assignment: