Mixed-mode cyclic debonding of adhesively bonded composite joints

A combined experimental-analytical investigation to characterize the cyclic failure mechanism of a simple composite-to-composite bonded joint is conducted. The cracked lap shear (CLS) specimens of graphite/epoxy adherend bonded with EC-3445 adhesive are tested under combined mode 1 and 2 loading. In all specimens tested, fatigue failure occurs in the form of cyclic debonding. The cyclic debond growth rates are measured. The finite element analysis is employed to compute the mode 1, mode 2, and total strain energy release rates (i.e., GI, GII, and GT). A wide range of mixed-mode loading, i.e., GI/GII ranging from 0.03 to 0.38, is obtained. The total strain energy release rate, G sub T, appeared to be the driving parameter for cyclic debonding in the tested composite bonded system

Interaction of mixed mode loading on cyclic debonding in adhesively bonded composite joints

A combined experimental and analytical investigation of an adhesively-bonded composite joint was conducted to characterize the fracture mode dependence of cyclic debonding. The system studied consisted of graphite/epoxy adherends bonded with EC 3445 adhesive. Several types of specimens are tested which provide the cyclic debond growth rate measurements under various load conditions: mode 1, mixed mode 1 to 2, and mostly mode 2. This study shows that the total strain-energy-release rate is the governing factor for cyclic debonding

Abundances of Suprathermal Heavy Ions in CIRs during the Minimum of Solar Cycle 23

In this paper we examine the elemental composition of the 0.1-1 MeV/nucleon interplanetary heavy ions from H to Fe in corotating interaction regions (CIRs) measured by the SIT (Suprathermal Ion Telescope) instrument. We use observations taken on board the STEREO spacecraft from January 2007 through December 2010, which included the unusually long solar minimum following solar cycle 23. During this period instruments on STEREO observed more than 50 CIR events making it possible to investigate CIR ion abundances during solar minimum conditions with unprecedented high statistics. The observations reveal annual variations of relative ion abundances in the CIRs during the 2007-2008 period as indicated by the He/H, He/O and Fe/O elemental ratios. We discuss possible causes of the variability in terms of the helium focusing cone passage and heliolatitude dependence. The year 2009 was very quiet in CIR event activity. In 2010 the elemental composition in CIRs were influenced by sporadic solar energetic particle (SEP) events. The 2010 He/H and He/O abundance ratios in CIRs show large event to event variations with values resembling the SEP-like composition. This finding points out that the suprathermal SEPs could be the source population for CIR acceleration.Comment: accepted for publication in Solar Physic

3He-rich SEP Events Observed by STEREO-A

Using the SIT (Suprathermal Ion Telescope) instrument on STEREO-A we have examined the abundance of the rare isotope 3He during the rising activity phase of solar cycle 24 between January 2010 and December 2011. We have identified six solar energetic particle (SEP) events with enormous abundance enhancements of 3He (3He/4He >1). The events were short lasting, typically ~0.5-1 day and most of them occurred in association with high-speed solar wind streams and corotating interaction regions. With one exception the events were not associated with ~100 keV solar electron intensity increases. The events showed also enhanced NeS/O and Fe/O ratios. The solar images indicate that the events were generally associated with the active regions located near a coronal hole.Comment: accepted for publication in AIP Conference Proceedings for 'Thirteenth International Solar Wind Conference

Multi-Spacecraft Observations of Recurrent 3He-Rich Solar Energetic Particles

We study the origin of 3He-rich solar energetic particles (<1 MeV/nucleon) that are observed consecutively on STEREO-B, ACE, and STEREO-A spacecraft when they are separated in heliolongitude by more than 90{\deg}. The 3He-rich period on STEREO-B and STEREO-A commences on 2011 July 1 and 2011 July 16, respectively. The ACE 3He-rich period consists of two sub-events starting on 2011 July 7 and 2011 July 9. We associate the STEREO-B July 1 and ACE July 7 3He-rich events with the same sizeable active region producing X-ray flares accompanied by prompt electron events, when it was near the west solar limb as seen from the respective spacecraft. The ACE July 9 and STEREO-A July 16 events were dispersionless with enormous 3He enrichment, lacking solar energetic electrons and occurring in corotating interaction regions. We associate these events with a small, recently emerged active region near the border of a low-latitude coronal hole that produced numerous jet-like emissions temporally correlated with type III radio bursts. For the first time we present observations of 1) solar regions with long-lasting conditions for 3He acceleration and 2) solar energetic 3He that is temporary confined/re-accelerated in interplanetary space.Comment: accepted for publication in The Astrophysical Journa

In a pig model ePTFE grafts will sustain for 6 weeks a confluent endothelial cell layer formed in vitro under shear stress conditions

AbstractObjective: to investigate in a pig model whether small diameter ePTFE grafts will sustain a confluent endothelial cell layer formed in vitro under shear stress conditions. Material and Methods: thirteen ePTFE (4 mm) grafts were implanted end to end in the right femoral artery of; 8 grafts had been endothelialized in vitro. Grafts were left in situ for 6 weeks then evaluated with ultrasound and histology. Results: seven endothelialized graft were patent with confluent endothelial cell lining. None of the control grafts were patent or showed evidence of an endothelial lining. Conclusion: in this pig model ePTFE grafts sustained for 6 weeks a confluent endothelial cell layer formed in vitro under shear stress.Eur J Vasc Endovasc Surg 26, 156-160 (2003