>>11367315
The action that would be referred to as "rape" in the case of a free woman would, for a slave, be much more accurately characterized as "vandalism" (or even "plunder" - which is what the latin word "rapere" translates to). As someone else said, it's a crime against a master, not against a slave.
It should go without saying that masters may freely use their slaves. It would be odd for a slave owner to ask the slave for their permission at all. However, slaves are property that are, by default, for the exclusive use of their owner. Violating a free person's property, whether that be his car or his house or his slave, is a serious crime.