The only sure way to find out is simply to ask Apple whether or not they'll cover your specific cables under warranty.
There's no general rule that frayed cabled must be under warranty - on the other hands, there's also no general rule that they are not under warranty.
Depending on the laws in your particular country, it is often so that if the frayed ...
According to Apple One (1) Year Limited Warranty – Accessory:
This warranty excludes normal depletion of consumable parts such as
batteries unless failure has occurred due to a defect in materials or
workmanship and, damage resulting from abuse, accident, modifications,
unauthorized repairs or other causes that are not defects in materials