Geometry-Sensitive Fatigue Behavior of Ultra-Thin Copper-Brazed 316 L STS Joints: Experimental Characterization and Stress-Life Analysis
摘要
The fatigue reliability of plate heat exchangers (PHEs) is increasingly governed by brazed joints as ultra-thin stainless steel (STS) plates are adopted to enhance efficiency. However, the peel-mode fatigue behavior of copper-brazed joints, particularly under conditions combining ultra-thin geometry, micro-scale fillet features, and Mode-I loading, remains largely unexplored. This study presents a systematic characterization of peel fatigue in 316 L (50 μm)–Cu (12 μm)–316 L (50 μm) brazed joints through an integrated experimental and finite element framework. Two distinct fatigue regimes were identified: high-cycle fatigue (50–100 N; 104-105 cycles) characterized by stable crack growth within the copper layer, and low-cycle fatigue (150–200 N; 103-104 cycles) dominated by plastic deformation and accelerated crack initiation. Three crack propagation modes were observed, with copper-confined propagation dominating at lower loads. Finite element analysis considering fillet radii of 4–9 μm revealed a strong geometry-dependent stress response, where local stress increased from 205 to 217 MPa (6%) near yield conditions and from 448 to 580 MPa (30%) in the plastic regime as fillet radius decreased. A geometry-sensitive stress–life framework was developed by combining finite element stress mapping with experimental force–life data, demonstrating that stress-based evaluation captures fillet effects not evident in force-based analysis. These results provide quantitative design guidance by linking fillet geometry control to fatigue reliability of ultra-thin brazed joints in lightweight thermal systems.