End Notch Flexure Test(Previous)
GROUP: Fracture Mechanics test
The End Notch Flexure test is based in the flexure of
a beam with an initial crack in one of its ends. The test has been applied to a
composite made of carbon fibers with an epoxy polymeric matrix. Fibers are
oriented in the longitudinal direction of the beam and initial crack is created
introducing an insert in the laminate during its fabrication. The width of the
gap generated by this insert must be smaller than 50µm. The span of the beam is
100 mm and it is loaded with a concentrated load at its mid-span. The test is
made with a displacement controlled mechanism. Three different series (GRIN006,
GRIN015, GRIN024), each one containing five different samples, where tested
during the experimental campaign. To perform the numerical simulation, the
first sample of serie GRIN006 has been considered (beam 3M101, according to the
notation used in the test). The dimensions of this sample, as well as the
dimensions considered for the numerical simulation, are shown in Fig.6.3.
The experimental test applies a vertical displacement
to the beam, as shown in Fig.6.3, until the initial crack starts its
propagation. The imposed displacement is applied until the crack propagation
stops and the beam recovers its linear behavior. At this point, the sample is
unloaded. Main results obtained from this test are two: The force-displacement
graph, which shows the structural performance of the composite beam, and the
final length of the initial crack. These two results are the ones that will be
compared with the numerical model developed. The exact properties of the
composite material used in the experimental simulation were unknown when the
experimental tests were performed. However, the composite is known to be
made of carbon fibers and an epoxy polymeric matrix from Hexcel composites. For
the numerical simulation, the mechanical values considered to define the
composite are the ones described in Table 6.1, obtained from Hexcel Product
data description. The fiber (AS4) and matrix considered are the ones found in
Hex Ply 8552 UD prepegs.
End Notch Flexure Test(New)(Better)
The end notch flexure test (ENF)
is the most common Mode-II interlaminar fracture toughness test, likely to be
standardized hy ASTM in near future. The geometry of the ENF test is shown in Fig.
6.8(a). The specimen is placed on top of two supporting rollers with span of
2L. The bending load P is applied via a loading roller located in the mid-span.
The crack tip is aligned such (hat it falls between the loading and supporting
rollers, in the area of constant internal shear force. The shear force results
in longitudinal sliding of the crack faces, resulting in pure mode II loading.
Because of the unstable nature of
the test, upon fracture the crack tip travels and arrests underneath the
loading roller. If one wishes to obtain an additional toughness value from the
same specimen, the crack front must he non-destructively examined, and
straightened if necessary. Prior to the fracture test, it is recommended to
obtain a specimen's compliance as a function of crack length, such that it can
be used in the compliance calibration method of data reduction.
(Alan T. Zehnder, Fracture Mechanics, pages 118-119)
Diecast Alloys (Previous) GROUP: Material
The four major types of alloys that are die cast are zinc, aluminum, magnesium, and copper-based alloys. The die casting process was developed in the nineteenth century for the manufacture of lead/tin alloy parts. However, lead and tin are now very rarely die cast because of their poor mechanical properties.
The four major types of alloys that are die cast are zinc, aluminum, magnesium, and copper-based alloys. The die casting process was developed in the nineteenth century for the manufacture of lead/tin alloy parts. However, lead and tin are now very rarely die cast because of their poor mechanical properties.
The most common die-casting alloys are the aluminum
alloys. They have low density, have good corrosion resistance, are relatively
easy to cast, and have good mechanical properties and dimensional stability.
Aluminum alloys have the disadvantage of requiring the use of cold-chamber
machines, used for zinc alloys, owing to the need for a seperate molten metal
ladling operation.
(Product Design for Manufacture and Assembly, Third
Edition, Yazar Geoffrey Boothroyd, Peter Dewhurst, Winston A. Knight, Page 424)
Diecast
Alloys (New)(Better)
The die casting
process consists of forcing the molten metal into closed metal die. This
process is used for metals with low melting point. The advantages of the die
casting process arc as follows:
(i) Small parts can be made economically in
large quantities.
(ii) Surface finish obtained by this method
is excellent and requires no further finishing.
(iii) Very thin section or complex shapes can
be obtained easily.
Die casting alloys are made from zinc, aluminum
and magnesium. Brass can be die cast but its casting temperature is high.
Zinc die castings are more popular due to their high strength, long die life
and moderate casting temperature. Aluminum and magnesium die-castings are light
weight but their casting temperature is higher than that of zinc die castings.
(Bhandari, Design of Machine
Elements, page 49)
Breadboard
(Previous) GROUP: Electronic
The term
breadboard is used for a variety of experimenter wired circuit products. In this
book, the term will be used to describe the
temporary prototyping circuit platform shown
in Fig. 7-3 in which the holes are connected to
adjacent ones by a spring-loaded connector. The typical arrangement is to have
the interior holes connected outward while the outside rows of holes are
connected together to provide a bus structure for power and common signals.
Wire (typically 22 gauge) and most electronic components can be pushed into the
circuit to make connections and, when the application is finished, to pull out
for reuse.
Breadboards are engineered to enable you to
experiment with a circuit, without the trouble
of soldering. When you are assured that the
circuit works, you may use one of the other
four construction techniques described in this
chapter to make the design permanent. A
typical solderless breadboard mounted on a metal
carrier is shown in Fig. 7-4. Breadboards are available in many different sizes
and styles, but most provide rows of common tie points that are suitable for
testing ICs, resistors, capacitors, and most other components that have
standard lead diameters.
(G. McCOMB, M. PREDKO, ROBOT BUILDER’S BONANZA 3th ed., pg. 84)
Breadboard
(New)(Better)
Breadboards are plastic blocks with arrays
of electrically connected holes (figure6-I6). They are designed to hold DIP
(Dual Inline Package) integrated circuits and discrete components. The term
"breadboard" dates back to the olden days when valve radios were
constructed on a base of solid wood (a cutting board for bread). The term has
stuck, and the modern breadboard can still he found in electronics hobbyist
stores, and even the occasional university teaching lab.
As a general rule, breadboards are bud
news, and their use should be avoided at all costs. (Think of them as the
hardware equivalent of COBOL.) They suffer from excessive capacitance,
crosstalk, and noise susceptibility and, as such, are completely inappropriate
for microprocessor system construction. It's hard enough trying to debug
microprocessor hardware and software (together) without the additional
complications that breadboards can add. Breadboards can also suffer from
mechanical failure after extended use, leading to short circuits. Circuit
interconnections on a breadboard are done with small sections of wire. These
make great little antennas and will pick up every scrap of stray
electromagnetic radiation, channeling it straight into your circuit!
Microprocessors don't, as a rule, like "Classic Ruck FM* modulated onto
their data bus.
Using a breadboard is not the way to
construct a robust and reliable system. Breadboards
are used for their internal RC oscillators. But I'd advise against using
breadboards for anything that uses a crystal or that has any last-switching
digital signals. While it is possible to build very low-speed microprocessor
systems and general digital circuits on breadboards, try not to.
(John Catsoulis, Designing Embedded
Hardware, page 137)
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