Designing to distribute stress.

When you design a brazed joint, obviously you aim to provide at least minimum adequate strength for the given application. But in some joints, maximum mechanical strength may be your overriding concern. You can help insure this degree of strength by designing the joint to pre- vent concentration of stress from weakening the joint. Motto – spread the stress. Figure out where the greatest stress falls. Then impart flexibility to the heavier member at this point, or add strength to the weaker member. The illustrations below suggest a number of ways to spread the stress in a brazed joint.

To sum it up – when you're designing a joint for maximum strength, use a lap or scarf design (to increase joint area) rather than a butt, and design the parts to prevent stress from being concentrated at a single point. There is one other technique for increasing the strength of a brazed joint, frequently effective in brazing small-part assemblies. You can create a stress-distribution fillet, simply by using a little more brazing filler metal than you normally would, or by using a more "sluggish" alloy. Usually you don't want or need a fillet in a brazed joint, as it doesn't add materially to joint strength. But where it contributes to spreading joint stresses, it pays to create the fillet.