why not incorporate shocking methods like supersets, drop-sets etc.
For me i always use shocking methods as the bicep are used alot of the time. As the bicep is a pulling muscle you tend to use them a lot of the time in the day i.e opening doors, jars, so when you come to do your workout i.e 3 sets of curls, 3 sets of seated incline curls then really they aren't gona get shocked enough due to you using them a lot of the time.
I had the same problem as you and the way to get those arms sore is the blast them with shocking methods like i said above.
For instance if your workout was 3 sets of standing dumbells curl and 3 sets of seated incline dumbell curls then why not add the two together in which you would be performing a superset.
E.g 1 set would be 10 reps of standing dumbell curl then as soon as you finished the set, straight away you perform the seated dumbell incline curl and do about 8 0r 10 reps, the weight for the incline won't be as much as the first exercise because your muscles are pre-fatigued so by doing the next exercise you will be shocking your muscles into growth which will be hitting several fibres in that muscle.
But you are right in going to failure which is good, but always change your routines each week as i find this with biceps that they recover very quickly and have a good memory, so by changing your routines weekly then hopefully those biceps should get sore.
I hope that helps and i hope i didn't go on too much.