On July 2, 2012, at 1745 eastern daylight time, an experimental amateur-built Velocity XL RG airplane, N224SM, experienced a separation of the nose landing gear strut on landing roll out at Thomson-McDuffie County Airport (HQU), Thomson, Georgia. The airplane was registered to a private owner and was operating as a 14 Code of Federal Regulations Part 91 personal flight. The airplane sustained substantial damage. Visual meteorological conditions prevailed and no flight plan was filed. The private pilot reported no injuries. The flight originated from Elkins-Randolph County Airport,(EKN), Elkins, West Virginia, at 1535. The pilot stated he landed on the main landing gear and lowered the nose landing gear on the runway. The nose wheel started to shimmy and he applied aft pressure on the control yoke with negative results. The nose of the airplane pitched down on the runway centerline. He steered the airplane off the right side of the runway into the grass and performed an emergency shutdown. When he exited the airplane he observed the nose landing gear yoke and strut had separated and was on the runway. The pilot further stated that he had experienced a shimmy event about 50 hours prior to the accident, and he decided to install the shimmy dampener on the airplane. The nose landing gear strut assembly fractured into two pieces. The pieces were sent to the NTSB Materials Laboratory, Washington, DC, for metallurgical examination. Examination of the components revealed the nose landing gear collapsed due to a preexisting fatigue crack, consistent with a prior shimmy event and incorrect installation of the shimmy dampener. Specifically, there was no evidence that the shimmy dampener alignment pin was installed. There were no signs of mechanical deformation in the pinhole where the dampener shaft and the fork are coupled by the alignment pin that passes through the pinhole and engages a slot in the fork. Without the alignment pin installed, the rotations of the fork and the dampener shaft were not coupled and the shimmy was not dampened out.