Piper won the race in 4 minutes, 11.05 seconds, squeaking by her nearest competitor, Kelsey Ditto, who finished in 4:11.62.
"We are so proud of Carly, she has done such a good job," head coach Eric Hansen said. "Carly representing the USA for the second time is a great feat."
Piper, who is also competing in the 200-, 800- and 1500-meter freestyles, received an automatic invite to the World Championships in Montreal this summer. She joins Badger senior Adam Mania, who will compete with the Polish team at the World Championships.
Wisconsin senior Tim Liebhold placed fifth in the 400-meter individual medley in 4:22.03. With his finish, he could advance to the World University Games, another meet that serves as a qualifying opportunity for the World Championships. Liebhold will also compete in the 200 IM and 100 and 200 backstrokes.
Wisconsin sophomore Susan Johnson competed in the 100-meter butterfly and finished 35th in the preliminaries in 1:02.93. She did not advance to the finals. She will compete in the 100- and 200-meter backstrokes later in the meet.
Bethany Pendleton and Dale Rodgers, former Badgers, also competed Friday at the World Championship Trials. Pendleton placed 16th in the finals of the 200 IM in 2:19.82 and Rodgers took 23rd in the preliminaries of the 100-meter breaststroke in 1:05.37; the latter did not qualify for the finals.
Women's tennis: Badgers sneak past Nittany Lions
The No. 35 Wisconsin women's tennis team earned its third straight 4-3 win by defeating Penn State (5-8 overall, 0-4 Big Ten) 4-3 Friday on Nittany Lion turf.
Wisconsin (11-4, 3-1) took the doubles point 2-1, with wins from the duo of seniors Katie McGaffigan and Lindsay Martin and the duet of redshirt freshman Nicole Beck and true freshman Chelsea Nusslock.
McGaffigan, who moved down to the No. 2 spot after playing at No. 1 singles throughout her senior year, defeated Sarah Spence 4-6, 7-5, 6-2 to win a point for Wisconsin. Sophomore Kaylan Caiati and freshman Nicole Beck posted Wisconsin's other wins.
Sophomore Caitlin Burke, playing at No. 1 for the first time this season, fell to Maaria Husain 7-5, 7-5. Martin and Nusslock also fell to their opponents.
Wisconsin will face Indiana in Bloomington on Sunday.
Sixth inning homer propels UW to win
Senior shortstop Kris Zacher broke a 1-1 tie and gave the Badger softball team a win in its Big Ten opener with a sixth inning leadoff home run as Wisconsin (10-11 overall, 1-0 Big Ten) topped Ohio State (16-9, 0-1) 2-1 at Goodman Diamond Friday.
Sophomore Eden Brock pitched a complete game seven-hitter for UW, allowing just two base runners after the third inning. Brock (8-4) walked none and struck out seven, including five straight between the third and fifth innings.
Sophomore first baseman Christina Douglas gave OSU a 1-0 lead in the top of the first with a two-out RBI single to center, but the Badgers tied it on senior catcher Boo Gillette's two-out RBI single in the bottom of the first.
The game remained tied until Zacher's blast to left to open the sixth, her team leading fifth round tripper of the season and school record 16th of her career.
Sophomore hurler Jamee Juarez (12-7) took a hard-luck loss for the Buckeyes, allowing just six hits and two runs in six innings.