I apologize if this subject has been covered.  I think most will agree that no lock on any folding knife should be considered strong enough for the knife to be considered as strong as a fixed blade.  Given that assumption I think we can continue with lock strength requirements.

A few companies who have high claims to their lock strength have videos (or just claims) that a lock will hold up to 500lbs of force is applied to it.  One company goes up to 1000lbs.  I'm not really interested in this amount of strength.  I'm never going to apply that much force to even a fixed blade.  I would need to clamp the blade in a vise and get 5 of me to stand on the handle.

My expectation of a lock is very high.  This is due to the fact that I have mainly been using knives that lock and the design expectations from the company are also high and their products live up to these expectations.  Even in the less expensive models.  The cost reduction is based on materials, fit & finish, etc. not the quality of the performance IMO.  There are also lots of lock types with different reasons for possible failures.  For the purposes of this discussion I'm thinking of a backlock since it is one of the most common knife locks.

In my opinion a lock should NEVER release accidentally.  NEVER!  The only way a locking folder lock should release without it being released by the user is for one or more parts in the knife to break.  How much force it takes to break the knife is my concern.  But if the lock releases under a lot more pressure than it takes to close a slip joint without breaking something, is that ok?   Example:  In a lockback knife if the angle of the lockbar sitting in the blade tang is not 90° there may be a problem.  If the angle is 89° I'm sure it's ok but if it's 50° (estimate) the lockbar could be forced up just by putting force on the blade spine causing the lock to release as if you pressed on the lock button.  So this would be considered a design flaw IMO.  I recently purchased a knife where this would happen.  It was replaced because the companie's opinion was the knife was flawed.  I got another one and it seems fine for now.   But maybe for some people this is "good enough" for a knife to be called a locking knife.  Compared to a slip joint I mean.  I still feel the knife lock will fail if I put a lot of pressure on the spine.  I mean more force than you would ever apply during normal use.  So, this lock I'm considering strong enough even though I don't feel it's as strong as other knives of the same size with the same lock that I own.

If someone buys a locking folder and feels it WILL STAY LOCKED NO MATTER WHAT, using a knife with that assumption may be less safe than using a slip joint that you know isn't supposed to stay locked.  I think most locking folders come with a safety warning not to count on the lock 100%.  Even though this is 100% true I feel sometimes warnings like this are to protect themselves from lawsuites when a lock fails and someone looses a couple of fingers. :)

Getting long winded.  Summary:  I think when a lock fails it should be because a part breaks or at least is rounded off drastically.  On a lockback knife a lockbar of steel that is too soft might allow this over time.  That's another thing.  I don't mean when you test a knife once when you first buy it.  I mean a knife that is still working after years of "normal" use.  Of course the knife that is abused dramatically should not be required or expected to work for years.

I am wondering how other user's feel and ESPECIALLY how a manufacturer feels, resulting in the strength of their locks on knives that are supposed to LOCK.