Created on 10/19/04
Four-Point Bending Test Protocol
I. Materials
A. B. C. D.
A. Base (Support Points)
B. Base Clamp
C. Load-Cell Attachment (Load Points)
D. Instron Attachment Insert
E. Allen Wrenches (2 sizes: one for base clamp and one for the load-cell attachment to secure movable loading point)
F. Tweezers
G. Petri Dish
H. Bottle of PBS
I. Femur bones
** Keep Specimen in hydrated (in vile) until ready to test **
II. Setting Up
1. Log onto the computer located to the right of the Instron Machine.
2. Turn on the Instron by flipping the switch, located on the right side of the base of the Instron, upward.
3. Go to Start Programs Instron Merlin
4. Click on the genipin button directly below Method.
~ Note: This will take a few seconds to load and the download progress will scan twice. There is no need to click OK.
III. Calibration of the Instron
***Remove all attachments from the load cell***
1. Click on the icon on the top right of the computer screen, second from the right.
2. Click on Calibrate
3. Double-check to make sure there is no load attached. Once no load is verified, click OK.
4. When the calibration is complete, click Done.
IV. Specimen Preparation
1. Remove the bone from the vile and unwrap the gauze.
2. Tweezers are recommended for use when handling the bone.
3. Measure the width and the depth of the bone with a vernier caliper. The depth measurement, d, is the distance from the anterior to the posterior surface of the bone at the mid-diaphysis. The width, w, is the medial to lateral surface distance. Take 3 measurements of each and then take the average value. Record these numbers on the measurement input sheet.
V. Attaching the Testing Materials
1. Place the base and base clamp below the load cell.
2. Lightly screw in the base clamp to hold down the base, allowing the base to move slightly.
3. Take the load cell attachment and tighten the bolt at the bottom of the screw shaft as tightly as possible.
4. Attach this piece to the Instron with the movable load point on the right, by inserting the tip and sliding in the Instron attachment insert.
5. Tighten the top bolt as tightly as possible, making sure that the whole piece is straight and securely fastened.
6. Lower the load cell of the Instron until it is approximately 5 mm above the base support points. Position the base support as close to centered as possible, i.e. that the distance between the load point and support point is the same on both the left and the right.
7. Once centered, secure the base clamp with an allen wench so that neither piece moves.
8. Double check that both bolts and the base support is secure and as straight as possible.
VI. Beginning the Test
1. Click on the “Stoplight” button on the right side of the screen.
2. Located on the left of the command window, click on Test
3. Browse to find and select C:\INSTRON\TEMPLATE\Femur.twf
4. Select and close out of the command box.
5. Reset the Balance and Gauge Load.
6. Place the bone onto the support points as pictured here:
6. Lower the Instron using the quick motion control until within 5 mm above the bone and then use the slow incremental scroll until the movable point is touching the bone.
7. While watching the load value on the computer screen, continue lowering the load cell with the slow incremental scroll.
8. Once there is a considerable change in load (typically a jump ~ >0), scroll back a notch toward 0 and secure the movable load point with an allen wrench to hold it into place. The load measured should be as close to 0 as possible at this point.
~ Note: This can also be done visually. One can often see when both
load points are touching the bone. Using both methods simultaneously
can also be done for more accuracy.
VII. Testing
1. Click on the Play button on the right of the screen.
The test will run and it typically takes about 30-45 seconds. The load typically causes fracture at approximately -17 N.
2. Once the bone fractures, you can push the “Stop” button on the right side of the screen below the “Play” button.
3. To save the data, go to the upper command File Data End&Save.
4. Save the File to whatever name you choose (e.g. femur1.raw), with a *.raw extension. It should be saved under D:\femur-bend04. You must chose the Set Default button each time you save to this directory.
VIII. Finishing-up
1. Exit out of Merlin.
2. Measure the distance between the load points, L, and the support points, X. To get the value of a, Subtract X from L and divide by 2. Take 3 measurements and average the values. Record the results on the measurement input sheet. The distance between the loading points is ‘a’ and ‘L’ is the distance between the support points.
3. Remove attachments and place them in the set storage place.
4. Save the broken bone by putting it into a vile with a small piece of gauze and some PBS. Label the specimen and put it into the freezer.
IX. Transferring of Data
1. Open up D:\femur-bend04 on the computer in Windows Explorer.
2. Copy the recently collected data file to S:\Common\4-Point Femur Bending.
3. Log-off of the computer and move to a computer with MATLAB.
4. Once stationed at another computer, open the data file you just copied in Notepad.
5. Delete all of text which appears at the beginning of the *.raw file.
6. Re-save with the same file name.
X. Analyzing the Data
1. Open up MATLAB.
2. Set the directory to S:\Common\4-Point Femur Bending.
3. To begin the data analysis, type “fanalysis”.
4. Input the measurements.
5. When the graph loads, the first click should be made where the data reaches a maximum value on the y-axis.
6. The second click should be made where the secant modulus line (blue) intersects with the experimental data (green).
7. Open up the *.dat file found in the S:\Common\4-Point Femur Bending directory in Excel and import the given values into the Data Chart file. The most recent analysis done in MATLAB will appear at the end of the *.dat file.
8. When open, chose Column A. Go to Data à Text to Columns à Delimited à Check Tab and Space à Finish. This allows the data to be directly copied to the Experimental Results spreadsheet. This spreadsheet contains all results from previous experiments.
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