plastic smile

a plastic smile (looking artificial) — деланная улыбка; натужная, неискренняя, неестественная улыбка

Example: She gave me a wide, plastic smile.

wear a plastic smile
When someone is wearing a plastic smile, they are appear to be happier with a situation or events than they actually are. This is actually a description of the forced smile you might see in many photographs. (usingenglish.com)

Related vocabulary:
[crack a smile]
Син.:
улыбаться через силу
натужно улыбнуться
улыбаться деланно