How to take the effect Poisson value of foam in impact application

Well, you are trying to do an impact analysis on foam and dont know if it has a poisson ratio? Pretty ambitious. Is the foam a blown foam, a syntactic. Yes it has a poisson ratio, pretty much as every material in existance. If you find what type of foam you are using, you can use a vendor datasheet to assist you. "low density foam" can mean a lot of things, I find it hard to believe you will get any kind of decent results if you dont know what foam properties really are and your just picking something out a generic list. In fact, I would even go to the extent of testing the foam for its properties independently.

If you read the LSdyna manual it says this is a highly compressible low density foam. It has unidirectional properties and hence no poission's ratio is considered. I don't know where you are using this material. It is generally used to represent seat cushions and padding on side impact dummies. Depending upon where you are using it might be appropriate.

regards