Effect of strain rate on the yielding mechanism of amorphous metal foam

Stochastic amorphous Pd_(43)Ni_(10)Cu_(27)P_(20) foams were tested in quasistatic and dynamic loading. The strength/porosity relations show distinct slopes for the two loading conditions, suggesting a strain-rate-induced change in the foam yielding mechanism. The strength/porosity correlation of the dynamic test data along with microscopy assessments support that dynamic foam yielding is dominated by plasticity rather than elastic buckling, the mechanism previously identified to control quasistatic yielding. The strain-rate-induced shift in the foam yielding mechanism is attributed to the rate of loading approaching the rate of sound wave propagation across intracellular membranes, thereby suppressing elastic buckling and promoting plastic yielding

Loading rate sensitivity of open hole composites in compression

The results are reported of an experimental study on the compressive, time-dependent behavior of graphite fiber reinforced polymer composite laminates with open holes. The effect of loading rate on compressive strength was determined for six material systems ranging from brittle epoxies to thermoplastics at both 75 F and 220 F. Specimens were loaded to failure using different loading rates. The slope of the strength versus elapsed time-to-failure curve was used to rank the materials' loading rate sensitivity. All of the materials had greater strength at 75 F than at 220 F. All the materials showed loading rate effects in the form of reduced failure strength for longer elapsed-time-to-failure. Loading rate sensitivity was less at 220 F than the same material at 70 F. However, C12000/ULTEM and IM7/8551-7 were more sensitive to loading rate than the other materials at 220 F. AS4/APC2 laminates with 24, 32, and 48 plies and 1/16 and 1/4 inch diameter holes were tested. The sensitivity to loading rate was less for either increasing number of plies or larger hole size. The failure of the specimens made from brittle resins was accompanied by extensive delaminations while the failure of the roughened systems was predominantly by shear crippling. Fewer delamination failures were observed at the higher temperature

Dynamic wrinkling and strengthening of a filament in a viscous fluid

We investigate the wrinkling dynamics of an elastic filament immersed in a viscous fluid submitted to compression at a finite rate with experiments and by combining geometric nonlinearities, elasticity, and slender body theory. The drag induces a dynamic lateral reinforcement of the filament leading to growth of wrinkles that coarsen over time. We discover a new dynamical regime characterized by a timescale with a non-trivial dependence on the loading rate, where the growth of the instability is super-exponential and the wavenumber is an increasing function of the loading rate. We find that this timescale can be interpreted as the characteristic time over which the filament transitions from the extensible to the inextensible regime. In contrast with our analysis with moving boundary conditions, Biot's analysis in the limit of infinitely fast loading leads to rate independent exponential growth and wavelength

Fatigue life prediction of z-fibre pinned composite laminate under mode I loading

A hybrid method is presented combining linear elastic fracture mechanics with nonlinear damage mechanics that can predict the fatigue crack growth rate in z-fibre pinned composites under mode I loading. The strain energy release rate is evaluated using the virtual crack closure technique via finite element analysis. Cohesive elements are used in the pinned region to represent the crack bridging force generated by the pins. The reduction of the pins' bridging force under the fatigue loading is accommodated by applying a degradation law, based on damage mechanics with empirical fitting parameters. A modified degradation law is proposed which is capable of accumulating fatigue damage under varying crack opening displacement ranges experienced by the pins during fatigue loading. Fatigue testing was performed with a z-pinned double cantilever beam at two different values of applied displacement amplitude. The predictions show reasonably good agreement with the test results in terms of the fatigue crack propagation rate and fatigue life

High Strain Rate Response of Adhesively Bonded Fiber-Reinforced Composite Joints A Computational Study to Guide Experimental Design

Adhesively bonded carbon fiber-reinforced epoxy composite laminates are widely used in aerospace applications. During a high energy impact event, these laminates are often subjected to high strain rate loading. However, the influence of high strain rate loading on the response of these composite joints is not well understood. Computational finite element (FE) modeling and simulations are conducted to guide the design of high strain rate experiments. Two different experimental designs based on split Hopkinson bar were numerically modeled to simulate Mode I and Mode II types loading in the composite. In addition, the computational approach adopted in this study helps in understanding the high strain rate response of adhesively bonded composite joints subjected to nominally Mode I and Mode II loading. The modeling approach consists of a ply-level 3D FE model, a progressive damage constitutive model for the composite material behavior and a cohesive tie-break contact element for interlaminar delamination

A high flux source of cold strontium atoms

We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms in a magneto-optical trap operating in a high vacuum environment. A key innovation of this setup is a two dimensional magneto-optical trap deflector located after a Zeeman slower. We find a loading rate of 6x10^9/s whereas the lifetime of the magnetically trapped atoms in the 3P2 state is 54s.Comment: 12 pages, 16 figure

Pengaruh Hydraulic Loading Rate (Hlr) Dan Konsentrasi Influen Terhadap Penyisihan Parameter Bod, Cod Dan Nitrat Pada Pengolahan Air Limbah Domestik Campuran (Grey Water Dan Black Water) Menggunakan Reaktor Uasb

In this study using a mixture of domestic wastewater. Parameters to be researched is the Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD) and nitrate-nitrogen (NO3-N). Alternative anaerobic treatment is to use UASB (upflow Anaerobic Sludge Blanket) . This study performed a variation of Hydraulic Loading Rate (HLR) and the influent concentration to obtain the optimum conditions on an UASB reactor laboratory scale for removal BOD5, COD and NO3-N in a mixture of domestic waste water (grey water and black water). Pollutant removal efficiency by varying the influent concentration and HLR for BOD5 was about 57% -76%, for COD was about 59% -69% and NO3-N was about 75% -98%. The results is the lower influent concentration will decrease removal efficiency that occurred on the parameters of BOD5, COD and NO3-N. The maximum removal efficiency on the parameters BOD5 and COD occurs when HLR low at 0.025 m3/m2/hour or 6.94 x 10-6 m / s. While the maximum removal efficiency of NO3-N occurred when HLR high 0.05 m3/m2/hour or 1.4 x10-5 m / s. Removal for BOD5 optimum occurs at low concentrations are 419 mg / l with a variation HLR of 0.05 m3/m2/hour or 1.4 x10-5 m / s, for COD occurred at low concentrations are 878 mg / l with a variation HLR of 0.025 m3/m2/hour or 6.9 x10-6 m / s, and NO3-N concentration was occur in the 36 mg / l with a variation HLR of 0.033 m3/m2/hour or 9.2 x10-6 m / s. The results of treatment using UASB still above the standards that should UASB be used as a secondary treatment to obtain the effluent below quality standart

Baryonic loading and e^+e^- rate equation in GRB sources

The expansion of the electron-positron plasma in the GRB phenomenon is compared and contrasted in the treatments of Meszaros, Laguna and Rees, of Shemi, Piran and Narayan, and of Ruffini et al. The role of the correct numerical integration of the hydrodynamical equations, as well as of the rate equation for the electron-positron plasma loaded with a baryonic mass, are outlined and confronted for crucial differences.Comment: 5 pages, 3 figures, to appear in the proceedings of "Relativistic Astrophysics and Cosmology - Einstein's Legacy" meeting, November 7-11, 2005, Munich, Germany, edited by B. Aschenbach, V. Burwitz, G. Hasinger, and B. Leibundgu