As per Modi on Medical Jurisprudence and Toxicology, normally the hymen is ruptured by the first act of coitus, though it may persists even after several act of s*xula intercourse if it happens to be loose,folded and elastic or thick, tough and fleshy. It further says that if in a woman with an intact hymen, the edge of the membrane are distinct and regular, with an orifice of small dimension, which allows the terminal phalanx of a finger to penetrate and the hymen is well stretched, all the persumption are in favour of true virginity or in other words, all the persumption are in favour of non penetration of the penis into the v**gina. See at page 355-356.
See Section 12(1) (a) of the Hindu Marriage act also read with section 25(i) Special marriage Act which provide for ground of avoiding marriage for non consumation of marriage.