We have methods in Chen Taijiquan which are called seizing methods 拿法 nafa or capturing and seizing 擒拿 qinna, which also contain a range of techniques from catching sinews 抓筋 zhua jin or turning bones 反骨 fan gu among others. Often we refer to these methods simply as joint locks though their usage differs somewhat. All methods contain a range of great applications for practical usage. They can also be trained in a pretty safe environment if taught in a reasonable manner.
Training opportunities
Besides being a practical and fun exercise (at least for one person) qinna in Chen Taijiquan is also a great tool to generally understand lines and angles better, finding the weak spots in your opponent's body structure, and thus to comprehend entry maneuvers for techniques. Also they help to work on our own body mechanics, as the lock should be applied after neutralizing incoming forces first and then it should be driven by our own internal body method. Both require interconnected and differentiated movements of the whole body. The locking techniques should exhibit strategies and concepts of "not going against your opponent's power", "don't lose contact", "using your opponent's point of force" and such things. Our seizing and capturing methods should train to cope correctly with our opponent's power and his body mechanics in general.
Here is a short video, though it's in German I think the body actions are visible and quite understandable. It doesn't necessarily show what one should do in a "self defense scenario" (whatever that specifically means anyway). Rather it shows how we can generally use joint locks to stay connected to our opponent, to use his force and to disconnect in the right moment to follow the locking techniques up with punches or the like.
Body locks
A related, but somewhat different way to train qinna is to learn how to absorb your opponent's power with your own shenfa (body method), to stick and adhere and then to follow up with a precise technique. Basically this body method should be underlying all the other techniques as well, powering them from the inside (as you can see in the above video). This short excerpt from Chen Yu shows a very high-level way of using your own body method in this kind of way:
Martial body method
Martially speaking joint locks offer a great opportunity to better understand power lines and to learn how to connect the locks with other close range techniques like throws, short-distance punches and similar apps. But I thought it is also interesting to think of joint locking not only as a pragmatic set of applications and techniques, but rather to understand the versatile training opportunities you can create using the seizing methods, including honing your own body method. I understood how integrated these methods were into the overall bodywork of the style when I started to learn from my shifu. They truly are a means to train a myriad of different things, whether working with our opponent's structure or our own as both structures should be linked anyway.