Situation arises in some christian homes were the man is incapable to do his duty sexually, using the bible as the authority of christians; is it permissible for the woman to have another(either from the family or outside) man take the place of the man, if the woman decides not to adopts.

Some women nowadays do insemination if their husband is infertile, and in this case it involves that of another man, is this permissible for christians?