My needles have been bending a little while I’ve been using them and I wasn’t sure if its normal or not. 
Is it normal for aluminum needles to bend?
Mine are all bent. I think it came from me being really tense when I first started knitting. I noticed that right where I hold my needles over time they would start to bend just a little. So I think it came from constant pressure from being so tense. I don’t think that I am quite that tense anymore so I think its better now. But it definately happened.
It also has to do with the heat from your hands and aluminum being incredibly maliable… think of crinkling up an aluminum can or wadding up the foil that covers a meal.
As you get better at knitting, less tense and tend to work faster you will notice they don’t do it as much. Good luck on your latest project.
I’ve bent metal needles too, usually the thinner ones.
I warped my bamboo sock needles too, skinny and I knit really tight to avoid ladders.
The only needles I’ve ever bent were these 2.5mm needles I had when I was still knitting on straight needles. They were ridiculously thin, but they weren’t bent from use-someone sat on them >: (
Tension in your hands and the weight of the fabric will bend very thin aluminum needles, but not affect thicker sizes (US 4 and above), as long as they are solid and not hollow (there have been a few of those manufactured over the years). This is especially true of the longer straight needles. The heat of your hands won’t affect it-- try passing a needle through a flame: it won’t bend in the heat alone. If you have thicker needles and are still bending them, then you must be pressing on them, somewhere, some how.
Combine 5 children running around a living room (playing that game where you try not to touch the floor), dpns on the back of a couch - and yes, you can definitely bend your aluminum needles quite a bit! Beyond that, the only needles I’ve bent are bamboo needles.