High Temperature Epoxy Composites for Material Extrusion Additive Manufacturing

The geometric design freedom, short lead time, and customization make additive manufacturing (AM) increasingly popular. In addition to rapid prototyping and three-dimensional molds, additive manufacturing has created wind turbine blades, robotic arms, and custom medical implants. Major manufacturing companies such as Porsche and Aetrex are utilizing AM to customize automotive seats and orthopedic footwear. However, available materials limit AM applications. Currently, the high-temperature requirements from the aerospace and automotive industries provide additional, unmet challenges. Many high-temperature epoxies have high pre-polymer viscosities and produce highly exothermic cure reactions, which limits volumetric scaling. Traditionally, fast, high-temperature processing reduces the viscosity, filling a mold before crosslinking initiation; however, this is not possible for AM. Currently, epoxy-fiber composites replace many traditional materials, such as aluminum, in applications where their high strength-to-weight ratios reduce lifetime energy costs. Fiber composites are limited by current fabrication methods, which can be expensive with limited geometric adaptability. Direct ink write (DIW) AM extrudes viscoelastic feedstock, creating parts layer-by-layer. The ink feedstock can readily incorporate fibers while AM produces parts without a mold reducing start-up requirements. This work develops a high temperature, heated cure epoxy feedstock for DIW applications achieving strength and modulus values of 145 MPa and 4.9 GPa, respectively. Two pre-polymers are combined, to maintain a glass transition temperature upwards of 285°C while reducing the viscosity. A heated deposition system requires understanding the thermal viscosity and cure profiles. With a viscosity of 5.4 Pa.s and an 18-hour pot life, 70°C allows for shear flow without premature cure during extrusion. An upper loading limit of 30 vol% glass fibers was determined. The fibers improve the heat deflection temperature by 100°C to 320°C and yield a 160% increase in flexure modulus; however, a 34% reduction in strength occurs. While processing did not decrease the fiber length as observed with carbon, the initial distribution contained 15% of fibers shorter than the critical length. The short fibers and pores that arose from both processing and dissimilar fiber-matrix expansion can account for the reduction. This work aims to develop a hightemperature fiber-filled feedstock while broadly considering print and extrusion parameters of viscous inks

Search for high-energy neutrinos from gravitational wave event GW151226 and candidate LVT151012 with ANTARES and IceCube

The Advanced LIGO observatories detected gravitational waves from two binary black hole mergers during their first observation run (O1). We present a high-energy neutrino follow-up search for the second gravitational wave event, GW151226, as well as for gravitational wave candidate LVT151012. We find two and four neutrino candidates detected by IceCube, and one and zero detected by Antares, within �500s around the respective gravitational wave signals, consistent with the expected background rate. None of these neutrino candidates are found to be directionally coincident with GW151226 or LVT151012. We use nondetection to constrain isotropic-equivalent high-energy neutrino emission from GW151226, adopting the GW event�s 3D localization, to less than 2�10^51�2�10^54??ergby Anand Sengupta et al

Search for intermediate mass black hole binaries in the first observing run of Advanced LIGO

International audienceDuring their first observational run, the two Advanced LIGO detectors attained an unprecedented sensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-mass binary black hole systems. This paper reports on an all-sky search for gravitational waves (GWs) from merging intermediate mass black hole binaries (IMBHBs). The combined results from two independent search techniques were used in this study: the first employs a matched-filter algorithm that uses a bank of filters covering the GW signal parameter space, while the second is a generic search for GW transients (bursts). No GWs from IMBHBs were detected; therefore, we constrain the rate of several classes of IMBHB mergers. The most stringent limit is obtained for black holes of individual mass 100  M⊙, with spins aligned with the binary orbital angular momentum. For such systems, the merger rate is constrained to be less than 0.93  Gpc−3 yr−1 in comoving units at the 90% confidence level, an improvement of nearly 2 orders of magnitude over previous upper limits

First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

International audienceSpinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signal-to-noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far

First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data

International audienceWe report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the first Advanced LIGO observing run. This search investigates the low frequency range of Advanced LIGO data, between 20 and 100 Hz, much of which was not explored in initial LIGO. The search was made possible by the computing power provided by the volunteers of the Einstein@Home project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population, corresponding to a sensitivity depth of 48.7  [1/Hz]. At the frequency of best strain sensitivity, near 100 Hz, we set 90% confidence upper limits of 1.8×10-25. At the low end of our frequency range, 20 Hz, we achieve upper limits of 3.9×10-24. At 55 Hz we can exclude sources with ellipticities greater than 10-5 within 100 pc of Earth with fiducial value of the principal moment of inertia of 1038  kg m2