To open up to someone; to become unreserved or relaxed; to become friendly and comfortable with others.
初対面の人ともすぐに打ち解けるタイプだ。
He's the type who quickly warms up even to people he meets for the first time.
会議の雰囲気が和らいで、皆が打ち解けて話し始めた。
The meeting's atmosphere softened and everyone started talking more openly.
子供たちが先生に打ち解けるのに時間がかかった。
It took time for the children to become comfortable with the teacher.
彼女が冗談を言ったことで、相手も打ち解けた。
Because she made a joke, the other person relaxed and opened up.