40K isnt an awful lot in Norway.
I earnt a bit less than that when I worked there for 4 years and paid 36% tax (which is a very normal tax rate there). You will pay a bit more. Your first 6 months of work are charged only 15% tax though, think that is still the case. Dunno about yuour PhD situation though, the institution will have that info for you.
Standard of living is high, but so is the cost of EVERYTHING so dont kid yourself, you wont be buying up luxury goods!
I found I learnt to spend less whimsically but bought what I needed and spent wisely on great quality stuff, especially cycling and skiing gear. You have to eat though so make it good food.
People have lots of nice stuff there cos they dont just mortgage houses, they have hefty loans for big cars and goodness what else you care to mention. money does go around there, but it doesnt come back at you!
Beautiful country and I'd recommend anyone to take a chance such as yours to live there. Nice folk, if conservative and over democratic, but they love a good old time.
GO FOR IT!