I managed to force a smile as they were leaving. 他们离开时，我强装笑颜。
"No, no, it didn't worry me at all," he said, forcing a laugh.
It was a pretty lame joke, to be honest, but I managed to force a laugh.
I remember forcing a smile when all I wanted to do was cry.
Eventually she forced a smile for the cameras and was helped into the car.
See also: force verb (GIVE NO CHOICE)