Investigation of the strain-rate-dependent mechanical behavior of a photopolymer matrix composite with fumed nano-silica filler

With the evolution of additive manufacturing, there is an increasing demand to produce high strength and stiffness polymers. Photopolymers are very commonly used in stereolithography and fused deposition modeling processes, but their application is limited due to their low strength and stiffness values. Nano‐sized fibers or particles are generally embedded in the polymer matrix to enhance their properties. In this study, we have studied the effect of fumed nano‐sized silica filler on the elastic and viscoelastic properties of the photopolymer. The uniaxial testing coupons with different concentrations of silica filler have been fabricated via casting. We observed improvement in mechanical properties by the addition of the nano‐sized filler. As polymers exhibit time‐dependent mechanical response, we have conducted tensile tests at different strain rates as it is one of the most common modes of deformation, and is commonly used to characterize the parameters of the rate‐dependent material. We noticed significant dependence of the mechanical properties on the strain rate. quasi‐linear viscoelastic (QLV) model, which combines hyperelastic and viscoelastic phenomena, has been employed to capture the response of the material at different strain rates. We found out that the QLV model with Yeoh strain energy density function adequately describes the rate‐dependent behavior of the material and has reasonable agreement with the experimental results

Association between statin use after diagnosis of esophageal cancer and survival: a population-based cohort study

Background & Aims: Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors), commonly prescribed to prevent cardiovascular disease, promote apoptosis and limit proliferation of esophageal cancer cell lines. We investigated whether statin use following diagnosis of esophageal cancer is associated with reduced esophageal cancer-specific and all-cause mortality.  Methods: We identified a cohort of 4445 men and women in the United Kingdom diagnosed with esophageal cancer from January 2000 through November 2009 using the General Practice Research Database. The National Cancer Registry and Office of National Statistics datasets respectively established the histologic subtype and cancer-specific mortality. Cox proportional hazard regression analysis with time-dependent exposures estimated the association between statin use after diagnosis and esophageal cancer-specific and all-cause mortality.  Results: The median survival time of the entire cohort was 9.2 months (inter-quartile range [IQR], 3.7–23.2 months). Among subjects who used statins after diagnosis of esophageal cancer, the median survival time was 14.9 months (IQR, 7.1–52.3) compared to 8.1 months for non-users (IQR, 3.3–20). In the entire cohort, statin use after diagnosis was associated with a decreased risk of esophageal cancer-specific mortality (adjusted hazard ratio [HR], 0.62; 95% confidence interval [CI], 0.44–0.86) and all-cause mortality (HR, 0.67; 95% CI, 0.58–0.77). In patients with esophageal adenocarcinoma, statin use after diagnosis was associated with decreased risk of esophageal cancer-specific mortality (HR, 0.61; 95% CI 0.38–0.96) and all-cause mortality (HR, 0.63; 95% 0.43–0.92). This effect was not observed in patients with esophageal squamous cell carcinoma. There was no evidence for effect modification of these associations with statin use before cancer diagnosis.  Conclusions: In a large population-based cohort, statin use after diagnosis of esophageal adenocarcinoma, but not esophageal squamous cell carcinoma, was associated with reduced esophageal cancer-specific and all-cause mortality

Novel Loci for Adiponectin Levels and Their Influence on Type 2 Diabetes and Metabolic Traits : A Multi-Ethnic Meta-Analysis of 45,891 Individuals

J. Kaprio, S. Ripatti ja M.-L. Lokki työryhmien jäseniä.Peer reviewe

A comparison of the quasistatic and dynamic compressibilities of wet and dry vermiculite

Wet and dry vermiculite granules were compressed both dynamically and quasistatically in a steel powder-compression cell. The compressibility was found to depend both on strain rate and water content. The wet vermiculite was less compressible than the dry. Vermiculite (both wet and dry) was also less compressible under dynamic loading. The stress supported by discs of vermiculite pre-compressed to a density of 2445 kg m−3 was found to be around 90 MPa at a strain rate of around 4000 s−1 using a split Hopkinson pressure bar

The effect of aspect ratio on the compressive high rate deformation of three metallic alloys

Metallic cylinders of rolled homogeneous armour (RHA) steel, Ti6Al4V, and FNC tungsten alloy of four different length $l$ to diameter $d$ ratios (dimensions in mm): 8/4, 4/8, 10/8, 8/10) were deformed at high rates of deformation using a direct impact Hopkinson pressure bar. Highspeed photographic sequences of the deformation were taken using a Hadland Imacon 790 imageconverter camera working at either 1 or 2 x 10$^{4}$ frames/s. It was found that titanium alloy cylinders of all four aspect ratios shear-banded and fractured, but that cylinders made from RHA steel and FNC tungsten behaved in a ductile manner when $l$/$d$ $<$ 1 but in a brittle manner when $l$/$d$ $>$ 1. We conclude that adiabatic shear banding is not just an inherent material property but that in some materials size effects/geometry can trigger this phenomenon

A COMPARISON OF THE HIGH STRAIN RATE BEHAVIOUR IN COMPRESSION OF POLYMERS AT 300K AND 100K

La réponse mécanique de plusieurs polymères ductiles d'utilisation courante a été étudiée en compression à des vitesses de déformation de 2,5 x 103 s-1, à température ambiante et dans l'azote liquide (100 K). Une barre d'Hopkinson à impact direct (BHID) est utilisée pour déterminer les courbes contrainte-déformation dans ces conditions d'expérimentation. La cinématographie ultra-rapide (7 µs entre images) est l'outil majeur pour déterminer la déformation à rupture, en particulier pour les polymères ayant une grande déformation à rupture, pour lesquels celles-ci n'apparaît pas dans la fenêtre de temps imposée par la BHID (285 µs).The mechanical response of a number of widely used ductile polymers has been investigated in compression at strain rates of ca. 2.5x103s-1, both at room temperature (ca. 300K) and at liquid nitrogen temperatures (ca. 100K). A direct impact Hopkinson bar (DIHB) was used to measure the polymer stress-strain curves at this strain rate at both temperatures. High-speed photography (interframe time 7 µs) was a major tool in determining the fracture strain at both temperatures, particularly for those polymers that had such large failure strains that they did not fail within the time window of the DIHB (285µs)

Erosion of polyethylene by solid particle impact

SIGLEAvailable from British Library Lending Division - LD:D52843/84 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

A novel technique for performing symmetric Taylor impact

A novel spring tensioned wire cradle arrangement has been developed to hold the target rod lightly but firmly in place when performing rod-on-rod (symmetric Taylor) impact in a vacuum. In addition, a soft capture system has been designed and used to decelerate both rods while reducing the chance of them colliding a second time. High-speed photography was used to obtain the profile of a pure aluminium target rod as a function of time. Photon Doppler Velocimetry (PDV) was also deployed to record the velocity of the rear of the target rod as a function of time. Voiding in the interior of recovered rods was investigated non-destructively using X-ray tomography. The data provides comprehensive validation information for predictive constitutive models

Validation of a path-dependent constitutive model for FCC and BCC metals using "symmetric" Taylor impact

In this study, the rod-on-rod impact geometry was used at impact speeds of ca. 200 m s-1. This is widely believed to be equivalent to the impact of a single rod on an infinitely rigid target and hence an ideal form of the Taylor test as no real target is infinitely rigid. However, our modelling studies showed that the two rods do not behave symmetrically. Two metals were studied : AQ85 iron and XM copper. These were machined into cylinders 15mm long and 5.35mm in diameter. High-speed photographic sequences of the impacts were taken with an interframe time of 5 µs. These pictures were then digitised to obtain profiles as a function of time. The bcc material (iron) exhibited the classic "mushroom" shaped profile which was relatively easy to model as a function of time using existing constitutive models. However, the fcc material (copper) exhibited an additional bulge a few millimetres from the impact face. This behaviour proved impossible to simulate using path-independent models. It proved, however, possible to simulate the behaviour of fcc copper in the "symmetric" Taylor impact configuration using a newly-developed path-dependent constitutive model. The paper contains the results of this comparison between experiment, theory and modelling