Intensity is % of 1RM, not perceived effort as some like to think it is.
Volume is intensity times number of lifts (which is sets times reps).
Failure is typically not considered to be needed to induce hypertrophy. Some studies indicate that failure makes your recovery longer without any hypertrophy benefits in relation to leaving reps in the tank. So if you train a muscle infrequently and very hard, you will have a high muscle protein breakdown, with no extra muscle protein synthesis, but you can't train it as soon as the MPS is back down at base levels (48 hours at most) since you are still sore and not recovered from doing all that training to failure.
That 85% of 1RM gives max hypertrophy stimuli thing I talked about was just for one rep in isolation. It showed precisely that when doing single reps, you won't get a higher hypertrophy response by going heavier than 85% of 1RM, since that's where max hypertrophy stimuli has reached 100% already. Now, I interpret this as that you do not have to go "as heavy as you can" for whatever rep range you do. Anyone can do 90% for 1 rep almost any day, but it will not give more growth than 85% for one rep.
Similarily, you may be able to just bust out 12 reps at 70% with no reps left, but I don't think that results in more hypertrophy than stopping at 10 reps, or doing 12 reps with 65% instead.
About appropriate intensities:
80% of 1RM is most often considered to be a great balance of pure strength and hypertrophy, if maximum strength is your end goal.
For pure hypertrophy goals, that video I linked shows that 60-70% can be more appropriate, since that is the range where the hypertrophy stimuli increases the most per additional 1% increase in intensity. In other words, the curve of the relationship between hypertrophy response and intensity is at its steepest in te 60-70% range of 1RM.
For example: 3x3 at 80% of 1RM might give you 90% of max hypertrophy stimuli. If 3x3 at 65% of 1RM would give you 85% of max hypertrophy stimuli (almost the same response with a lot less effort), that would be a better choice since you can easier increase the remaining number of lifts to reach 100% hypertrophy stimuli.
But then again, that video also says that occlusion training, using 1 set of 30% of 1RM to failure gives the same hypertrophy response as 5 reps at 90% of 1RM. So maybe you could just do occlusion training all the time, if you go closer to failure. However, although that will give the same hypertrophy, it might have longer recovery. I have not seen any studies on recovery times for occlusion training. Speaking of it, I actually have occlusion training in my current program.
But to give you some real world examples of intensities and NL (number of lifts):
- in a high frequency powerlifting program of 6 days per week with squats, bench, and deadlifts every session, the usual reps and sets are: pyramid style warmup with declining amount of reps with each heavier set, to 3-5 work sets of 3-5 reps, at 60-75% of 1RM. The volume per session is low since they will train the muscle 5 more days that week.
The bodybuilder might want to trade some of that intensity (lower weights) for more reps and sets.