Effects of Processing Residual Stresses on Fatigue Crack Growth Behavior of Structural Materials: Experimental Approaches and Microstructural Mechanisms

Fatigue crack growth mechanisms of long cracks through fields with low and high residual stresses were investigated for a common structural aluminum alloy, 6061-T61. Bulk processing residual stresses were introduced in the material by quenching during heat treatment. Compact tension (CT) specimens were fatigue crack growth (FCG) tested at varying stress ratios to capture the closure and Kmax effects. The changes in fatigue crack growth mechanisms at the microstructural scale are correlated to closure, stress ratio, and plasticity, which are all dependent on residual stress. A dual-parameter ΔK-Kmax approach, which includes corrections for crack closure and residual stresses, is used uniquely to connect fatigue crack growth mechanisms at the microstructural scale with changes in crack growth rates at various stress ratios for low- and high-residual-stress conditions. The methods and tools proposed in this study can be used to optimize existing materials and processes as well as to develop new materials and processes for FCG limited structural applications

VIPER: an industrially scalable high-current high-temperature superconductor cable

High-temperature superconductors (HTS) promise to revolutionize high-power applications like wind generators, DC power cables, particle accelerators, and fusion energy devices. A practical HTS cable must not degrade under severe mechanical, electrical, and thermal conditions; have simple, low-resistance, and manufacturable electrical joints; high thermal stability; and rapid detection of thermal runaway quench events. We have designed and experimentally qualified a vacuum pressure impregnated, insulated, partially transposed, extruded, and roll-formed (VIPER) cable that simultaneously satisfies all of these requirements for the first time. VIPER cable critical currents are stable over thousands of mechanical cycles at extreme electromechanical force levels, multiple cryogenic thermal cycles, and dozens of quench-like transient events. Electrical joints between VIPER cables are simple, robust, and demountable. Two independent, integrated fiber-optic quench detectors outperform standard quench detection approaches. VIPER cable represents a key milestone in next-step energy generation and transmission technologies and in the maturity of HTS as a technology

Major lung complications of systemic sclerosis

Systemic sclerosis (SSc) is associated with high mortality owing to internal organ complications, and lung disease is the leading cause of SSc-associated death. The most notable lung complications in SSc are fibrosis and pulmonary arterial hypertension (PAH). A major challenge for the management of lung disease in SSc is detecting those patients with severe pathology and those patients who are likely to benefit from available treatments. In the past few years, strategies for managing lung fibrosis and pulmonary hypertension, including PAH, have greatly progressed. For lung fibrosis, the tools to assess risk of progression and severity of the disease have been refined. Clinical trial results support the use of immunosuppression, including high-intensity regimens with autologous stem cell transplantation. New trials are underway to test other potential therapies including treatments that are approved for use in idiopathic lung fibrosis. For PAH, identifying individuals at high risk of disease development is critical. In addition, individuals who have borderline elevation of pulmonary arterial pressure need to be appropriately managed and followed up. Many approved drugs targeting PAH are now available, and results from large-scale clinical trials provide robust evidence that various treatments for SSc-associated PAH are associated with good long-term outcomes