This post has been updated since the original publish date by including videos that demonstrate the tapping test described below.
In several previous articles (“Thermoformed Paddle Delamination” and “Jansen vs Devidze Revisited”), we discussed a potential damage mechanism for delaminated paddles. In our analysis, we determined that delamination likely reduces the bending stiffness of the inner area of the paddle face, where the outer edge remains stiff. This makes the paddle face behave like a conventional tennis racquet, resulting in a trampoline effect that provides more “pop” to the ball at impact.
In our analysis, we also suggested that the USAPA methodology for testing the delaminated paddles may not be adequate, as it focuses on measuring the stiffness through the thickness of the paddles. This essentially measures the paddle core stiffness and not the paddle bending stiffness. We also recommended use of an alternative three-point test apparatus (described in our article, “Paddle Power vs Control Comparison”) that is capable of measuring the true bending stiffness of the paddle face about its lateral and longitudinal axes.
Since publishing our article, we have been contacted by several paddle manufacturers and readers who mentioned that the fundamental cause of paddle delamination was found to be crushed cores. These cores were likely damaged during the thermoforming process, where the paddles are subjected to high temperatures and pressures. During use, the paddle cores can be further damaged by impact loads, resulting in delamination of the face sheets from the cores.
One of the limitations of our previous analysis is that we did not have delaminated paddles to test. Pickleball Central has graciously sent us some damaged paddles that were returned as part of their warranty program. In this article we will perform tests of these paddles to ascertain the root cause of the delamination problem.
Tap Test
We received six damaged paddles for evaluation: two Ronbus R1 Pulsar’s, a Legacy Pro, an Electrum Elite, a ProKennex Black Ace, and a Vatic Pro (Figure 1). Visual inspection of the paddles found no obvious damage to the outside of the face sheets. Bending of the paddles by hand found a “crunchy” sound in isolated areas for one of the Ronbus paddles and the Electrum Elite paddle. The crunchy sound was especially pronounced at the end furthest away from the handle for the Legacy Pro paddle. The crunchy sound was not detected on the other Ronbus paddle or the ProKennex and Vatic Pro paddles.
By tapping on the face of a paddle with the hard plastic end of a screwdriver handle, it is possible to identify damaged areas by listening for changes in pitch of the tapping noise (try it yourself with one of your paddles). An undamaged paddle will emit a high frequency “ping” uniformly across the paddle face. Damaged areas will emit a low frequency “thud”. Figures 2a and 2b show an undamaged and a damaged ProKennex Black Ace paddle, and Figures 3a and 3b show the undamaged and damaged Electrum Elite paddle.
The tapping test found a few isolated areas of damage on the Electrum Elite paddle. The damage to both of the Ronbus paddles and the Vatic Pro paddles were concentrated at the top edges of the paddles, furthest away from the handle. Damage to the ProKennex and Legacy Pro paddles was found over the entire the paddle face.
Figures 2a and 2b. Undamaged and Damaged ProKennex Black Ace Paddles
Figures 3a and 3b. Undamaged and Damaged Electrum Elite Paddles
Core Stiffness Test
The stiffness of the paddle core can be measured by applying a load directly through the thickness of the paddle and measuring the deformation at the point of load application (Figure 4). This is essentially the USAPA test, where the paddle face is not allowed to bend under application of load.
Using our force / displacement gauge, we measured the core stiffness of several damaged paddles (Figure 5). These paddles were supported directly through the thickness and loads of 10, 20, 30, 40 and 50 lbs were applied at two locations on the front and rear faces near the paddle center. As a “control”, an undamaged CRBN 1X paddle was also tested so that comparisons can be made between undamaged and damaged paddles.
Core stiffness results are shown in Table 1 below. These results come at a bit of a surprise. As indicated, the undamaged CRBN 1X paddle ranks among the lowest in core stiffness! All other paddles (except for the Electrum Elite) have a core stiffness that is greater than 800 lb/in. If crushed cores are supposed to reduce the stiffness of the paddle face to exacerbate the trampoline effect, we would expect the core stiffness to reduce not increase.
Table 1. Core Stiffness of Various Paddles
These results suggest that crushed cores (by themselves) do not directly contribute to the paddle trampoline effect. Furthermore, these results also suggest that the USAPA methodology for identifying delaminated paddles by measuring the core stiffness is not adequate or reliable. A better testing methodology might involve the measurement of the paddle bending stiffness.
Bending Stiffness Test
The bending stiffness of a paddle can be measured by applying a load at the center of the paddle and supporting it at the edges. For our tests, we developed an apparatus that used and described in our article, “Paddle Power vs Control Comparison” (Figures 6 & 7). This apparatus supports the paddle face on three ball bearings, with the force applied at the paddle center. This allows the paddle face to bending freely about its lateral and longitudinal axes. The applied force divided by the displacement at the center of the paddle then defines the paddle bending stiffness.
Paddle bending stiffness results (Table 2) are quite revealing. The three undamaged paddles each have a face bending stiffness greater than 800 lb/in. The Electrum Elite, Vatic Pro, and Ronbus #1 paddles had a face bending stiffness in the 500 – 800 lb/in range. The ProKennex and Legacy Pro paddles, which were identified as especially bad in the tapping test, each had a face bending stiffness less than 500 lb/in. Because its bending stiffness exceeds 800 lbs/in, it is unlikely that the Ronbus paddle #2 is delaminated and might instead have smaller regions of delamination or “dead spots” that do not yet affect the paddle’s overall bending stiffness.
Table 2. Bending Stiffness of Various Paddles
Conclusions and Recommendations
Testing of the damaged and undamaged paddles indicate the following:
- Crushed cores may be one of several potential causes of the thermoformed paddle delamination problem. Other failure mechanisms could involve failure of the face sheets near the edges of the paddle, failure of the adhesive that bonds the face sheets to the core, or failure of the cores to provide adequate shear stiffness.
- Crushed cores by themselves do not necessarily create a more pronounced trampoline effect as it was shown that the core stiffness of the damaged paddles was actually higher than the core stiffness of undamaged paddles.
- The higher measured core stiffness of the damaged paddles could be an indicator of crushed cores. However, it is not completely clear why a paddle with a crushed core would have a higher core stiffness than an undamaged paddle.
- The USAPA core stiffness test will not adequately identify damaged or delaminated paddles. As described above, these tests cannot be used to identify paddles with a lower stiffness and a more pronounced trampoline effect. Consequently, USAPA should discontinue using the core stiffness test to identify damaged paddles.
- The three-point bending stiffness test as described in our article, “Paddle Power vs Control Comparison”, has been demonstrated to effectively and reliably differentiate damaged paddles from undamaged paddles. Undamaged paddles will have a face bending stiffness greater than 800 lb/in and damaged paddles will have a face bending stiffness less than 800 lb/in. Paddles that have excessive delamination will have a face bending stiffness less than 500 lb/in.
- It is recommended that the USAPA adopt the three-point bending stiffness test to qualify new paddles for approval and to screen paddles for excessive trampoline effect if they are damaged during play.
- The tap test may be used as an effective initial screening for damaged and undamaged paddles in the field for tournament play. Undamaged paddles will emit a high frequency “ping” when tapped with a hard plastic object, whereas damaged paddles will emit a lower frequency “thud”. Players should routinely perform the tap test on their paddles to identify “dead spots” and potential areas of damage and delamination.
- Paddle manufacturers and pickleball equipment suppliers might consider use of the three-point bending test and the tap test to determine the likelihood of paddle damage for warranty and return purposes.
Pickleball Science is in the process of developing a simplified “go / no-go” test that can be used by the general public to determine the paddle bending stiffness and whether paddle delamination is providing an unfair advantage to players by developing more “pop” through an enhanced trampoline effect.
