Fatigue characterization of Poly Vinyl Chloride (PVC) foam core sandwich composite using the G-control method

This paper presents experimental results from cyclic crack propagation tests performed on sandwich specimens with glass/epoxy face sheets and Poly Vinyl Chloride (PVC) foam cores using the G-controlled cyclic energy release rate (ΔG) test procedure. The face material was tested in tension, compression and shear to determine in-plane and out-of-plane mechanical properties, such as Young’s modulus, Poisson’s ratio and shear modulus. These properties were then used in an analytical model of the mixed-mode bending sandwich specimen to calculate compliance and energy release rate. Finite element analysis was used to determine the mode-mixity of the crack loading. Experimental crack growth cyclic tests were carried out on pre-cracked mixed-mode bending sandwich specimens with H45, H100 and H160 PVC foam cores under two mode-mixities (mode I and mode II dominant). Post-mortem analysis was performed on tested specimens, highlighting the influence of mode mixity and foam density on the crack path. Crack propagation diagrams showing da/dN versus ΔG curves were obtained to establish the Paris-Erdogan relation for each material combination tested at the two mode-mixities. Results showed constant crack growth rates for all the materials tested and revealed the influence on mode-mixity on crack propagation speed and foam density (higher foam density, slower crack propagation). </jats:p

James Watson, Maclyn McCarty, and Torsten Wiesel

Torsten Wiesel (right) with Professor Emeritus Maclyn McCarty (center), co-author of the paper with Oswald Avery and Colin MacLeod, and James D. Watson, director of Cold Spring Harbor Laboratory, 1994 Photo by Leif Carlsson To commemorate the fiftieth anniversary of the discovery at The Rockefeller University that genes are made of DNA - considered by many to be the single most important biological discovery of the twentieth century - the university has kicked off a year-long series of events that were running through May 1994. The celebration was formally inaugurated in November 1993 with a lec­ture by Nobel laureate James D. Watson, best known for discovering the double-helical structure of DNA. See also Search Winter 1994, vol. 4, no. 1https://digitalcommons.rockefeller.edu/group-portraits/1013/thumbnail.jp

Kvalitet och publikationsdatabaser

Forum för bibliotekschefer inom SUHF (Sveriges universitets- och högskoleförbund) tillsatte hösten 2009 en arbetsgrupp med uppdraget att ta fram riktlinjer för kvalitetssäkring av publikationsdatabaser vid svenska universitet och högskolor. Arbetsgruppen konstaterar i denna rapport att de lokala publikationsdatabaserna, genom sin bredare täckning av framför allt de humanistiska och samhällsvetenskapliga forskningsområdena och genom sitt större spektrum av dokumenttyper, kan utvecklas till att ge analys- och medelsfördelningsmöjligheter utöver vad de idag använda internationella databaserna ger. För att förverkliga detta krävs ett kvalitetsarbete inriktat både på åtgärder lokalt vid lärosätena och på justeringar i det nationella överföringsformatet, med vilket data förs till centrala samlingsdatabaser. Denna rapport innehåller rekommendationer inriktade på ökad kvalitet i lokal täckning och bibliografisk standard, verifikation och nationell överföring. Arbetsgruppen föreslår att SUHF: • arbetar för att de lokala databaserna skall utgöra underlag för analys och medelsfördelning på nationell nivå, • rekommenderar sina medlemmar att anpassa sina publikationstjänster enligt denna rapports rekommendationer, • initierar en vidareutveckling av formatspecifikationen för SwePub MODS på nationell nivå genom att en nationell samordningsgrupp utses.SUHF - Sveriges universitets- och högskoleförbun

Implementation of a Plastically Dissipated Energy Criterion for Three Dimensional Modeling of Fatigue Crack Growth

Fatigue crack growth is simulated using three dimensional elastic-plastic finite element analysis. The crack extension per load cycle, da/dN, as well as crack front profile changes (crack tunneling) under cyclic loading is not specified as an input but evaluated based on a condition that relates plastically dissipated energy to a critical value. Simulation of cyclic crack propagation in a middle-crack tension M(T) specimen using this implementation captures the well established, experimentally obtained crack growth rate reduction accompanying a single overload event. The analysis predicts that the single overload also affects the crack front profile, where a tunneling crack propagates with a flatter crack front in the overload affected zone

Numerical Evaluation of Paris-Regime Crack Growth Rate Based on Plastically Dissipated Energy

The crack growth rate during cyclic loading is investigated via numerical simulations. The crack advancement is governed by a propagation criterion that relates the increment in plastically dissipated energy ahead of the crack tip to a critical value. Once this critical value is satisfied, crack propagation is modeled via a node release scheme. Thus, the crack growth rate is an output from the numerical simulation. The crack growth rate predicted by the proposed scheme is compared with published experimental crack growth data in the Paris-regime for selected metals. A good match is found between the experimentally observed crack growth rates and the numerically obtained results. The Paris coefficients are subsequently evaluated from the numerically obtained crack growth rates