Pick two materials and a temperature swing to see the thermal-mismatch strain and stress in the joint, its galvanic corrosion risk, and whether the pair can be fusion-welded at all, with practical ways to make the joint work.
Stress-free temperature is where the joint carries no thermal stress: room temperature for a bolted or bonded assembly, but close to the solidus or braze temperature for a welded or brazed joint. Use the service extreme farthest from it.
Highest stress as a fraction of allowable: yield for metals, design tensile strength for glass and ceramic.
Two failure mechanisms dominate dissimilar-metal joints. When the temperature changes, the materials try to grow by different amounts and fight each other. When the joint gets wet, the more active metal becomes an anode and corrodes.
Galvanically the pair is borderline: 200 mV is fine indoors but over the 150 mV marine limit.
A long, narrow bonded strip is stressed in one direction, so the plain modulus E applies. A bonded plate is restrained both ways, which raises stress by 1/(1−ν), about 40%. Held flat, all the mismatch becomes stress. Left free, the pair curls like a bimetallic strip and some of the stress turns into bow, which the tool reports from Timoshenko's solution. Free edges of any bonded joint carry extra peel and shear stress that this simple model doesn't capture.
A welded or brazed joint locks together at high temperature, so its biggest mismatch strain comes from cooling to room temperature, before service even starts. For a 900 °C braze, enter 900 as the stress-free temperature and the coldest service temperature as the extreme. Yielding during that cooldown is common in metal-to-metal braze joints; for glass and ceramics it means fracture.
| Group | Index (V) |
|---|---|
| Nickel, titanium | 0.30 |
| Copper, Ni-Cr alloys | 0.35 |
| 18% Cr stainless | 0.50 |
| 2000-series aluminum | 0.75 |
| Carbon and low-alloy steel | 0.85 |
| Other wrought aluminum | 0.90 |
| Galvanized steel | 1.20 |
| Magnesium | 1.75 |
Couples are typically acceptable within 0.15 V in harsh environments, 0.25 V in normal indoor conditions, and 0.50 V in controlled environments. A large cathode coupled to a small anode makes any couple worse.
Jeffrium designs dissimilar joints for aerospace and energy hardware: transition joints, buttering and interlayer strategies, braze and seal design, and thermal-cycling analysis, backed by metallurgical testing.