What Are Anderson Waves in Composite Ball Bats?

Hitting a homer is a very violent event not just for the ball, but also for the bat. Ball bats suffer structural trauma every time they are used. At a certain point, structural fatigue sets in, and the grains of the wood separate, cracking and breaking the bat. Wood grains run roughly longitudinally along a bat made of solid wood. But composite material bats suffer an injury called an "Anderson wave," instead, because their structure is different.

  1. Definition of Anderson Wave and Anisotropy

    • Composite materials are fibers woven and compressed in an epoxy resin. Combinations of high-strength fiberglass, carbon fiber and Kevlar fiber are layered, spun and woven in ways that shape and maximize their effect on ball delivery. Anisotropic design seeks to shape most of the energy in one direction. Anderson waves are a phenomenon that localizes energy due to random interference in propagation between complex wavelets of sound and vibration. In composite bat matrices, a bat-ball collision produces a shock that does not disperse along the length of the bat but instead stays within a small area. The internal layer-to-layer friction damps propagation, but develops so much local heat and stress that a spider web-like concentric micro fracture shows up. Bat aficionados call this an "Anderson wave."

    Glass/Carbon/Kevlar Composites

    • Composite bats made purely of resin-impregnated fiber composites seem to suffer Anderson wave dings more than other types of bats employing fiber composites as part of their design. The lower temperature limit above which one of these bats should be used is strictly defined and best adhered to because the resin medium becomes more brittle at low temperatures. Using a bat like this in cold weather increases likelihood of Anderson wave dings.

    Aluminum Skin/Woven Fiber Composites

    • Composites with an aluminum skin can ding below the skin if the skin dents, but that is rare. However, aluminum-skinned bats are not sanctioned in all baseball or softball ruling organizations.

    Foam-core, Wood and Synthetic Composite Bats

    • Bats manufactured with a traditional ash wood skin over layers of synthetic matrix and a foam core do not seem to suffer damage as easily as any other design. The wooden skin is resilient enough to provide proper trampoline effect while resisting permanent dings. The sub-layers provide long-term structural strength without localized fracturing because they are not expected to take direct surface impact.