Three piece wheels are very light, being friction-spun on a big lathe; the inner and outer rim halves are only 0.040" (1.0 mm)-or so thick. Most are made exclusively for racing and yes- they DO occasionally fail, both on racers and the street. The alloys and heat treats used are unknown but the ones I'm sort-of familiar with have proven not weld-repairable. You should simply replace any damaged rim-half. The problem is, fabricators or shops that make such rims often do not last very long, so after they depart the scene, sourcing replacements is extremely expensive. It entails finding a shop that can duplicate your damaged rim-half as a one-off part. One such shop in CA does this and their rim-halves WILL be stamped 'FOR RACING ONLY', with zero guarantees.
Race cars that use such things often weigh at most 1800-2000 lbs; a street Pantera weights 3500, or 75% more. Giant sticky tires and public road bumps only make things worse IMHO. In addition, a popular 3 piece wheel- Centerline- is designed for drag racing, not high-load cornering. So with these wheels on a street car, the centers sometimes fatigue-crack around the bolt circles. The highest loaded part of a street driven Pantera suspension has proven to be circumferentially at the rear inner rim-halfs right at the point where the tire bead contacts the rim. Explosive deflation occurs. See attached photo-
I have seen cracks up to 18" long. Periodic visual inspection is prudent, as is the torque of any fastening bolts.