| 1. |
- Bellm, Eric C., et al.
(författare)
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The Zwicky Transient Facility : System Overview, Performance, and First Results
- 2019
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:995
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Tidskriftsartikel (refereegranskat)abstract
- The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg(2) field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.
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| 2. |
- Kao-Walter, Sharon, et al.
(författare)
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Acoustic imaging internal microstructure of a packaging material
- 2008
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Konferensbidrag (refereegranskat)abstract
- Microstructure of a paper-based packaging material was studied by acoustic microscopy method. The laminate structure of the packaging material contains paperboard, polymer and aluminium, which are widely used for aseptic liquid food package. The method has also been used to detect delaminations inside the material. The results show the possibility to study the micro structural features of paperboard, polymer and aluminium foil layered materials by applying the high-resolution ultrasonic acoustic microscopy. The potential for visualization defects in the body of this kind of materials is discussed in order to further develop the Non-Destructive Testing (NDT) method in food packaging industries.
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| 3. |
- Chen, S.H., et al.
(författare)
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A crack perpendicular to a bimaterial interface an interface in finite solid
- 2003
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Ingår i: International Journal of Solids and Structures. - : Elsevier, UK. - 0020-7683. ; 40:11, s. 2731-55
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Tidskriftsartikel (refereegranskat)abstract
- The dislocation simulation method is used in this paper to derive the basic equations for a crack perpendicular to the bimaterial interface in a finite solid. The complete solutions to the problem, including the T stress and the stress intensity factors are obtained. The stress field characteristics are investigated in detail. It is found that when the crack is within a weaker material, the stress intensity factor is smaller than that in a homogeneous material and it decreases when the distance between the crack tip and interface decreases. When the crack is within a stiffer material, the stress intensity factor is larger than that in a homogeneous material and it increases when the distance between the crack tip and interface decreases. In both cases, the stress intensity factor will increase when the ratio of the size of a sample to the crack length decreases. A comparison of stress intensity factors between a finite problem and an infinite problem has been given also. The stress distribution ahead of the crack tip, which is near the interface, is shown in details and the T stress effect is considered.
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| 4. |
- Chen, S.H., et al.
(författare)
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Finite boundary effects in problem of a crack perpendicular to and terminating at a bimaterial interface
- 2005
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Ingår i: Acta Mechanica Sinica. - Heidelberg : Springer Berlin. - 0567-7718. ; 21:1, s. 56-64
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Tidskriftsartikel (refereegranskat)abstract
- The problem of a crack perpendicular to and terminating at an interface in bimaterial structure with finite boundaries is investigated. The dislocation simulation method and boundary collocation approach are used to derive and solve the basic equations.Two kinds of loading form are considered when the crack lies in a softer or a stiffer material, one is an ideal loading and the other one fits to the practical experiment loading. Complete solutions of the stress field including the T stress are obtained as well as the stress intensity factors. Influences of T stress on the stress field ahead of the crack tip are studied. Finite boundary effects on the stress intensity factors are emphasized. Comparisons with the probled presented by Chen et al. (int. J. Solids and Structure, 2003,40, 2731-2755) are discussed also.
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| 5. |
- Kao-Walter, Sharon, et al.
(författare)
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A Finite Element Analysis of a Crack Penetrating or Deflecting into an Interface in a Thin Laminate
- 2006
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Ingår i: Key Engineering Materials. - Switzerland : Trans. Tech. Publications. - 1013-9826 .- 1662-9795. ; 312, s. 173-178
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Tidskriftsartikel (refereegranskat)abstract
- The crack tip driving force of a crack growing from a pre-crack that is perpendicular to and terminating at an interface between two materials is investigated using a linear fracture mechanics theory. The analysis is performed both for a crack penetrating the interface, growing straight ahead, and for a crack deflecting into the interface. The results from finite element calculations are compared with asymptotic solutions for infinitesimally small crack extensions. The solution is found to be accurate even for fairly large amounts of crack growth. Further, by comparing the crack tip driving force of the deflected crack with that of the penetrating crack, it is shown how to control the path of the crack by choosing the adhesion of the interface relative to the material toughness.
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| 6. |
- Mfoumou, Etienne, et al.
(författare)
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A New Method of Acoustical Remote Evaluation of Defective Structures and Material Characterization
- 2007
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Konferensbidrag (refereegranskat)abstract
- The feasibility of a remote monitoring of structures for a progressive damage assessment as well as material characterization using a simple and inexpensive experimental setup is discussed. The method is based on a remote acoustic excitation of transverse vibrations on a membrane using an ordinary broadband low frequency loudspeaker, and the measurement of the response using a Laser Doppler Vibrometer (LDV). Theoretical modeling is also developed to correlate the experimental results obtained, and this yields a new method for Non Destructive Testing (NDT) of sheet-like materials. The function generator provides an input voltage of a sine signal to the loudspeaker, and laser detection of the surface vibrational response of the sample is accomplished with the laser vibrometer.
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| 7. |
- Ståhle, P., et al.
(författare)
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Fracture of a Thin Laminated Foil
- 2014
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Ingår i: Procedia Materials Science : 20th European Conference on Fracture (ECF20) - 20th European Conference on Fracture (ECF20).
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Konferensbidrag (refereegranskat)abstract
- The micro-mechanisms of fracture in a laminate composed of an aluminium foil and a polyethene film are considered. Thelaminate as well as the freestanding layers were fracture mechanically tested. Inspection of the broken cross-sections shows thatfracture occurs through necking, i.e., localised plastic deformation leading to a decreasing and eventually vanishing cross-section.This occurs ahead of the crack tip for both freestanding layers and the laminate. The plastic properties and a slip-line theory aresuccessfully used to derive the work of failure. An accurate prediction of the fracture toughness is made for the aluminium foil andthe laminate. Even though the toughness of the freestanding polyethene film could not be accurately determined by the theory, itsrole as a member of the laminate is predicted by the theory with great accuracy. It is shown that the load carrying capacity of thelaminate is many times larger than the added load carried by the freestanding layers. The study further indicates that necking maybe impeded which may increase the toughness several times. It is also shown how the laminate may be forced to produce multiplenecking with a significantly improved toughness as a result.
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