Tensile Deformation and Fracture of Brazed Joints - AF - 1961
1961-- MIT/USAF study: silver-brazed steel joints achieve very high strength via triaxial constraint—showing meniscus-driven thickening, >50% joint strain, ~35–40% apparent volume rise (not porosity) and cleavage-facet initiation—key for aerospace brazing reliability
Summary:
Silver is the primary filler metal studied in this 1961 USAF–MIT report on the tensile deformation and fracture of brazed joints. Silver-brazed steel specimens showed very high apparent strength driven by a triaxial stress state from base-metal constraint, with strength tied to joint geometry (thickness/diameter) and pronounced meniscus formation at the periphery under load.
Engineers measured large apparent mean joint strains (>50%) and ~35–40% apparent volume increase as load approached failure—effects traced mainly to non-uniform joint thickening and meniscus shape rather than porosity (radiography found few voids; density stayed ~full). Example data include meniscus formation near 47,000 psi, failure around 58,700 psi in mild steel, and 82–84 ksi in higher-strength 1075 steel, with joints often comprising only 2–3 large grains.
Fractography of silver joints revealed small brittle “cleavage facets” with river markings at the bottoms of plug-pullout holes—localized features inside the silver (not at the interface) that likely nucleate under the high hydrostatic component of stress. Overall, silver’s work-hardening resists cavity growth (unlike lead), enabling high-strength, reliable brazed joints while flagging facet initiation as a failure risk to monitor.