We did fracture analysis in uni (engineering) and what i took away from it is that basically any metal under load (especially fatigue load) is susceptible to cracking, but the crack needs somewhere to start. The start is usually a microscopic defect buried deep in the grain structure and over time it gets bigger and bigger. You can minimize the likely hood of the defects using various post processing techniques (heat treatment), but for a subframe i highly doudt this is done. The part is just stamped out, welded up and sent on its way.
Gotta remember we are coming up on 30+ years of these steel items being in use, potentially millions if not billions of load cycles. Its no wonder cracks are starting to show, but similarly its no wonder there doesn't seem to be any method to whether it will crack or not, luck of the draw really. not to mention possible "high load incidents" (ie crashes) over the life of the car potentially causing cracks.
I must admit i've never had any of my cars subframes cracked, but then again i've never really looked to hard either. Mate with a JZA70 supra found a few cracks in his front subframe, simliar to the photos above showing cracks around mounting holes etc.
Gotta remember we are coming up on 30+ years of these steel items being in use, potentially millions if not billions of load cycles. Its no wonder cracks are starting to show, but similarly its no wonder there doesn't seem to be any method to whether it will crack or not, luck of the draw really. not to mention possible "high load incidents" (ie crashes) over the life of the car potentially causing cracks.
I must admit i've never had any of my cars subframes cracked, but then again i've never really looked to hard either. Mate with a JZA70 supra found a few cracks in his front subframe, simliar to the photos above showing cracks around mounting holes etc.
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