Friction Shim Coefficient of Friction Test: Diamond Claw® 40µm vs. 35µm Diamond Shims On 6061-T6 Aluminum
Diamond Claw® Delivers 37% Higher Coefficient of Friction Than Competitor Shims
As-Received Aluminum Coupon Information
The test coupons were manufactured from 6061-T6 aluminum. Each sample was milled and shot-blasted to replicate the surface conditions of the intended application.
Shim Comparison Pre-Test
| DC40 | Competitor | |
| Shim Base Material | AISI 1095 (1095 Spring Steel) | AISI 1060 or similar |
| Substrate Thickness | .254mm ± .007mm | 0.1mm ± 0.01mm |
| Particle Size | 40 µm | 35 µm |
| EN Coating Thickness | 25 µm | 10 µm |
| Total Shim Thickness | 0.344 mm ± 0.02mm | 0.19mm |
The two shims were placed side by side and photographed for comparison. As shown in the 200× image below, the Diamond Claw® shim exhibited a considerably higher diamond density than the competitor shim.
35µm Competitor Shim Diamond Claw® 40µ Shim
Test Method
The diamond shims were placed between the aluminum coupons, as shown below, and subjected to a normal force. Shear force was then increased until the shim began to slip. The coefficient of friction was calculated from the resulting load-versus-displacement data.
- Back-to-back testing was performed using identically sized M12 bolt shims.
- Test loads and shim placement were kept identical for both shim types.
- Coefficient of friction values were calculated at zero deflection using the linear portion of the test curve.
Some testing methods use an offset value to calculate COF, which can produce a higher reported result. The zero-deflection method used here provides a more representative measure of performance at the true point of initial slip.
Test Results
A total of 15 tests were completed: eight using Diamond Claw® shims and seven using competitor shims. The resulting load-versus-displacement curves are shown below, with individual COF values provided in the legend.
- Average Diamond Claw Linear-COF: 0.546
- Average Competitor Linear-COF: 0.400
- Diamond Claw® performance improvement: approximately 37% higher COF than the competitor shim.
- The Diamond Claw® shims also demonstrated a substantially higher post-slip COF advantage.
Post Test Shim Analysis
The images below show the aluminum material transferred to the shims during a typical test.
- More aluminum material was transferred to the Diamond Claw® shim than to the competitor shim.
- The greater material transfer appears to be associated with the Diamond Claw® shim’s higher diamond density.
- A relatively small force is sufficient to plow an individual diamond through a soft material such as aluminum.
- Because the Diamond Claw® shim has a greater number of diamond contact points, the combined force required to move the shim is substantially higher.
Post-Test Competitor Shim Post-Test Diamond Claw® Shim
Post-Test Aluminum Coupon Analysis
The figure below shows the plow patterns created by individual diamonds on the aluminum surface. The image was taken from a competitor shim sample tested slightly beyond the linear portion of the load-versus-displacement curve. One diamond plow mark, the direction of diamond travel, and the displaced aluminum have been highlighted. The image’s z-axis was amplified to improve visual clarity.
The following observations were made:
- The lower diamond density of the competitor shim made individual plow marks easier to identify.
- Each diamond produced a furrow in the aluminum surface after the shim slipped.
- A mound of displaced aluminum identified the final location of each diamond at the end of the test.
Conclusions
- The Diamond Claw® 40 µm shims achieved an average coefficient of friction of 0.546.
- The competitor 35 µm shims achieved an average coefficient of friction of 0.400.
- Under the conditions tested, the Diamond Claw® shims produced an approximately 37% higher COF than the competitor shims.
- The higher diamond concentration of the Diamond Claw® shim appears to be the primary factor contributing to its increased resistance to slip.