Carpenter, acquired in exchange for prospect Tony Renda, has an 11-11 record and a 3.79 ERA in 210 appearances in the Major Leagues. The 29-year-old appeared in 22 games for the Yankees and logged a 4.82 ERA before being designated for assignment by New York on June 3.
"He's been throwing regular bullpen [sessions]," Nationals manager Matt Williams said before Friday's game. "Of course, he hasn't had regular game competition in quite some time, but he threw a touch-and-feel bullpen today. He's fully healthy and ready to go."
Carpenter spent two seasons with the Braves in 2013 and '14, and he registered a 10-5 record with a 2.63 ERA in 121 games with Atlanta. The Yankees acquired him from Atlanta in January. Carpenter and Chasen Shreve went to the Yankees in exchange for Manny Banuelos.
Carpenter believes his experience pitching in the National League East will only aid his cause.
"It will definitely help getting to face guys I'm familiar with," Carpenter said. "They're also familiar with me, but getting back to a familiar setting is kind of nice."
The Nationals have struggled to keep arms in the bullpen healthy this season and Barrett joins that list. The right-hander has appeared in 30 of the Nats' 60 games and over the past week, he's pitched five times.
With Carpenter's appearance on Friday, the Nationals have used 16 relievers this season. They used 13 in all of 2014.
Barrett, who was injured while throwing a pitch in the eighth inning, will head back to see the club's doctor and undergo further tests.
"Preliminary [report] is that he's got a biceps strain," Williams said. "He'll get back and see the doctor, see what the diagnosis is and what the program would be from there."
Barrett has pitched to a 3-2 record and a 4.64 ERA this season.
Brandon Curry is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.