Adhesive Bond Line Tester USU Composites
Team: Cambria Cannon, Jameson Bullen, Taylir Nagel, and Canon Breckenridge
Sponsor: USU COE
Project Description
Traditional adhesive bond shear tests using tensile testers introduce peel stresses that prevent accurate measurement of shear strength. To address this, our team created a device that enables pure shear testing of adhesive bonds using a Tinius Olsen tensile tester. We also created a data analysis method to convert the raw data into engineering data.
This solution provides a cost-effective alternative to torsional testing and expands accessibility for educational and industrial labs seeking accurate bond strength data without investing in new equipment.
Design Description
Apparatus
Apparatus Setup
Apparatus Top View
Apparatus Side View
The pictures on the left show the setup of the apparatus in the tensile tester. The apparatus is placed onto the tensile tester and a wooden board. Next, it is secured to the tensile tester with a bolt and straps to prevent bending. The new load cell is attached to the existing load cell on one end and an eyelet hook with a metal rope on the other end. Bonded adherends are loaded into the apparatus. The metal rope is attached to the lever arm with a shear pin.
The apparatus works by transforming the linear motion of the tensile tester to rotational motion. This is accomplished by fixing one adherend to the side wall and the other to the lever arm. As the lever arm is pulled up by the tensile tester, the adherend fixed to it rotates. This loads the bond line in pure and uniform shear stress.
Data Acquisition/Collection
DAQ Setup
Amplifier Setup
A new load cell was purchased to improve data collection accuracy. The pictures on the left show the amplifier and data acquisition (DAQ) system setup. This setup is needed to measure and display force data from the load cell. The load cell is first connected to an amplifier, then the amplifier is connected to a DAQ device. A LabVIEW Load Cell program is used to collect the data. The data is displayed as a force vs. time plot.
An alternate method is using the data that is outputted directly from the tensile tester. During testing, we found that the results using the new load cell setup, and the tensile tester are the same. Therefore, either method can be used to collect data.
Adherend Design and Bonding
To ensure strong bonds, the bond surfaces on each adherend are prepared with 30 grit sandpaper and saline primer. Next, a thin layer of adhesive is forced into the bond surfaces with a scraper. A spacer is used to separate the adherends and create and uniform bond line thickness. The bond is allowed to partially cure for 2-3 hours before being transferred to the oven. The oven is set to 120˚C for 3-9 hours to achieve full cure, after which the adherends are removed to prevent burning. Once the adherends are tested and the bond is broken, they need to be cleaned for reuse. This is done by hitting the adhesive with a hammer until it breaks off the adherend. Then the adherends can be lathed to make a smooth, level surface.
Performance Review
The following table compares the customer requirements to the apparatus’ performance. The apparatus meets or exceeds all requirements..
| Requirement/Constraint | Target | Threshold | Actual Performance |
|---|---|---|---|
| Maximum Width of Apparatus | 10 in | 16 in | 11 in |
| Maximum Height of Apparatus | 8 in | 2 ft | 5 in |
| Maximum Depth of Apparatus | 9 in | 20 in | 9 in |
| Weight of Apparatus | 25 lbs | 40 lbs | 28 lbs |
| Uncertainty of Shear Strength Data Collection Software | ±5% | ±10% | ±0.5% |
| Number of Times the Adherends Can Be Reused | 3 tests | 1 test | 37 tests |
| Cost Per Adherend | $10 | $20 | $5.49 |
The plot below compares the results for six tests. The coefficient of variation between trials is 29%, which is relatively high but expected due to poor bonding conditions. In an ideal bonding environment, lower variation would be achieved. Despite this, the results fall within the anticipated range for bond line shear strength given the quality of the bonds.
The maximum tensile strength of the adhesive is listedas 4600 psi in the material specification sheet. Assuming the maximum shear strength is approximately 80% of the tensile strength, the theoretical shear strength is 3680 psi.The experimental values fall within ±21% of the theoretical value. This variation is higher than ideal but still consistent with expectations given the poor bonding conditions.
Conclusion
Our design meets every requirement and is within all constraints. This project highlighted the importance of designing for manufacturing. Tight fits and bonding issues emphasized a need for better alignment, surface preparation, and tolerance control. Hand calculations proved more effective than simulations, and earlier LabVIEW integration would have saved time. Logistical improvements include tighter scheduling and batch ordering. Future revisions should focus on alignment aids, improved bonding, and usability enhancements like an extended lever arm and added handles.