No abstract

The effect of porosity on the elastic behavior of cast steel is investigated experimentally, and an approach for including porosity effects in finite element analysis (FEA) simulations is presented. Porous cast steel specimens are mechanically tested having apparent elastic moduli reduced between 17 and 61 pct. Analysis of radiographs and tomography is used to measure and reconstruct the porosity distribution in these test specimens. The porosity distribution is incorporated into FEA simulations, where elastic mechanical properties are dependent on the locally varying porosity. A relationship between elastic modulus and porosity E(/) is determined by minimizing the difference between the simulations and the measurements: E(/) ¼ E 0 1 À /=0:5 ð Þ 2:5 , where E 0 is the elastic modulus of the sound material and / is the porosity volume fraction. It is found that the elastic modulus decreases nonlinearly with porosity and that the steel exhibits a critical porosity level above which it loses all stiffness. This study shows that the stiffness of porous materials depends not only on the amount of porosity, but on how it is distributed and other characteristics such as pore shape and size. By modeling the effect of the porosity distribution in the simulations, the measured strain is predicted within ±10 pct agreement.

Despite the potential of silver to mediate synthetically valuable cross-coupling reactions, the operating mechanisms have remained unknown. Here, we use a combination of rapid-injection NMR spectroscopy, electrospray-ionization mass spectrometry, and quantum chemical calculations to demonstrate that these transformations involve argentate(i) and (iii) complexes as key intermediates.

Fatigue and monotonic test specimens having porosity ranging from micro-to macroscopic levels were cast from 8630 steel. Monotonic and fatigue properties were obtained to determine the effect of porosity on the mechanical performance of the cast steel. Axial fatigue tests were conducted under fully reversed conditions in both strain and load control on specimens containing microporosity, and in load control for specimens containing macropores. Monotonic tests revealed that specimens containing microporosity had strength properties comparable to sound material, but with substantially reduced ductility (76% less reduction in area). At stress amplitudes of 126 MPa, microporosity specimens were found to have lives greater than 5 million cycles (run-out) whereas macroporosity specimens had fatigue lives in the 10 2 -10 4 cycle range at the same stress level. Fatigue lives for macroporosity specimens were in a range from 10 4 to 10 6 cycles when tested at the lowest stress amplitude, 53 MPa. The measured specimen elastic modulus was found to vary with porosity volume. Specimens with higher measured modulus outperformed the lower modulus specimens. Fatigue lives of the cast steel specimens were calculated using conventional models of fatigue behaviour, the strain-life and linear elastic fracture mechanics (LEFM) approaches. Life calculations made using the strain-life approach gave good agreement with measurements for specimens having microporosity, but this approach gave non-conservative results for macroporosity. LEFM modelling gave non-conservative results for both micro-and macroporosity specimens. For specimens with macroporosity, the calculations are difficult because of the porosity's complex shape and large size relative to the specimen, and the inability to determine the specific macropores responsible for fatigue failure of the specimens which is necessary for direct model-measurement comparisons. IJCMR/514