1) Piezoelectric Stack Actuators (Group: Analyse)
Previous Answer
In current work, piezoelectric stack actuators (PSA) have been studied as an alternatice solution to allow for satisfying all desirable characteristics without compromising between them. The main motivation for such study is actuator not only demonstrates all properties (advantages) of a single piezoceramic actuator, but it also provides a high actuation force partially by accumulating the produced force of each single piezoceramic in one unit. Other contributing factor of producing large actuation force in a piezoelectric stack lies in the large actuation force in a piezoelectric stack lies in the utilization of direct direction of polarization.
(Mehrdad R. Kermani,Mehrdad Moallem,Rajni V. Patel, Applied vibration suppression using piezoelectric materials, 2008, p. 90)
In current work, piezoelectric stack actuators (PSA) have been studied as an alternatice solution to allow for satisfying all desirable characteristics without compromising between them. The main motivation for such study is actuator not only demonstrates all properties (advantages) of a single piezoceramic actuator, but it also provides a high actuation force partially by accumulating the produced force of each single piezoceramic in one unit. Other contributing factor of producing large actuation force in a piezoelectric stack lies in the large actuation force in a piezoelectric stack lies in the utilization of direct direction of polarization.
(Mehrdad R. Kermani,Mehrdad Moallem,Rajni V. Patel, Applied vibration suppression using piezoelectric materials, 2008, p. 90)
New/Better Answer
The following analysis of the actuation of elastic
structures is based upon what is known as the static approach. The static
response of an interaction between a piezoelectric element and a structure is
first determined by coupling the constitutive relations of the piezoelectric
element and structure with their equilibrium and compatibility equations. Once
the equivalent static force or moment due to the actuator is obtained it is
then used as a frequency-independent amplitude for a harmonically varying input
to the system. This approximate approach has been found to provide reasonable
results for relatively lightweight piezoelectric elements driven well below
their internal resonance frequency. Most importantly, the static approach
includes the distributed forcing function effects of the piezoelectric elements
which will be shown to be a very important attribute for selective control of
the states of the structural system.
The first configuration of piezoelectric material we
consider is the stack arrangement shown in Fig. 5.2 which is working against an
applied external force F and an external stiffness represented by a spring. A
stack is defined to be a single or multi-layered piezoelectric element which is
relatively long in the z direction. This configuration is intended to induce
motion in the 3 direction by applying voltages over electrodes at the top and
bottom of the element. Two configurations of the actuator are shown. In Fig.
5.2(a) the actuator is working against an external spring stiffness arranged in
parallel with the actuator while in Fig. 5.2(b) the stiffness is positioned in
series. In both cases for zero voltage the external spring is in equilibrium
and applies no stiffness force. Note that the actuator also has an internal
stiffness associated with its material Young's modulus of elasticity. The
objective is to find the resultant displacement of the actuator and thus the
effective stiffness when a voltage is applied to the actuator. The following
static analysis of the parallel configuration of Fig. 5.2(a), although simple,
does illustrate the basic technique for solving for coupled response of
piezoelectric-structural systems.
(C. R. Fuller,S. J. Elliott,P. A.
Nelson,
Active Control of Vibration, p.118)
2) Quickstep Molding (Group: Manufacturing Process)
Previous Answer
Process works by rapidly
appliying heat to the laminate trapped between a rigid (or a semi-rigid) mold
that floats in a heat transfer fluid. (Pascault J.P.,Williams R.J.J.,Epoxy
Polymers:New Materials and İnnovation,p. 278) Hot Press Matched Metal Molding (18:10 13.04) Process
is similar to cold press molding except that heated matched metal is used.The
reaction is faster and therefore more pressure is required to force resin to
fill the tool before it becomes too viscous.This process has some limits due to
press size and availability.(ASM International, Characterization and Failure
Analysis of Plastics, p. 85)
New/Better Answer
The Quickstep process works
by rapidly applying heat to the laminate, trapped between a rigid (or
semi-rigid) mold that floats in a heat transfer fluid (HTF). The mold and
laminate are separated from the circulating HTF by a flexible membrane
fiber-metal laminates. It can be combined with resin film infusion or vacuum-assisted
RTM.
The processing machine is
composed of a curing chamber, three Ear containers at different temperatures
(cold, warm and hot), and a control unit. Thanks to the HTF heat capacity,
heating rates as high as 22 °C min are achievable. That leads to several
consequences: the viscosity of the resin decreases to lower minimum values
compared to conventional processes, enabling a better impregnation: energy
consumption is decreased by 70% compared to the cure in an autoclave: and the
cycle times are reduced by 50% or more. The molds that "float" in the
curing chambers do not need to be stiff. The cost for tooling can be lowered by
60%. The HFT enables an efficient heat transfer, decreasing the maximum
temperature produced by the reaction. This contributes to a better quality of
the parts, decreasing the risk of thermal degradation.
The low pressure (0.8 bar)
applied in the chamber, combined with vibration, results in the production of
high quality parts comparable to autoclave-cured parts. Some properties such as
the interlaminar shear strength or the adhesion to foam-cores and honeycombs
are increased.
As the curing chamber is composed
of separated compartments, HTF from different containers can be circulated in selected
places permitting local cure. This so-called "melding process" allows
the manufacture of stiffeners. T junctions or complex shapes without bonding
with an adhesive. Indeed it is possible to co-cure the uncured areas to make a
perfect bond.
(Jean-Pierre
Pascault, R. J. J. Williams, Epoxy Polymers: New Materials and
Innovations, pp.280-281)
3) Hot Press Matched
Metal Molding (Group: Manufacturing Process)
Previous Answer
Process
is similar to cold press molding except that heated matched metal is used.The
reaction is faster and therefore more pressure is required to force resin to
fill the tool before it becomes too viscous.This process has some limits due to
press size and availability.(ASM International, Characterization and Failure
Analysis of Plastics, p. 85)
New/Better Answer
In hot-press molding,
matched metal dies are used and a hot curing polyester resin. Pressures arc 1 MPa
and temperatures in the range 100-130 `C, with a mold cycle time of 2-5min. Because
of the higher pressures, entrapped air is forced out of the mold giving lower void
content than with cold-press molding. In conventional hot-press molding, the
operator must still handle the glass fibers and the liquid resin, but the
process can be made cleaner by using molding com-pounds. These have a high
viscosity and thus require higher molding pressure, typically 1-7 MPa, with
temperatures in the range 120-170°C. Prepregs are cut accurately and each ply
is positioned in the mold to have the required orientation. Because of the
short fibers, SMC, and more particularly DMC, arc able to now into the mold.
With these materials, a weighed charge is positioned by hand centrally in the
mold and on closing flows into the mold causing significant fiber
reorientation.
(Fred Moavenzadeh, Concise
Encyclopedia of Building and Construction Materials, p. 318)
4) Electro-magnetic Clutches (Group: Mechanical Component)
Previous Answer
The rear axle differential,
center differential, and transfer case ( Figure 10-42) on some vehichles are
equipped with electromagnetic clutches for lockup of the differential. The
clutch may be controlled by a switch ar by a traction control computer. When
one wheel or axle loses traction and speeds up, the computer energizes the
clutch, which locks up the differential and provides equal power to both wheels
or axles. The electromagnetic clutch consist of an actuator coil, an armature,
an a stack of steel clutch plates. When the clutch is energized, a magnetic
field is produced to compress the clutches, thereby locking the differential. (
Manual transmission and transaxles - Jack Erjavec - page 470)
New/Better Answer
Due to their ease of control,
electromagnetically operated clutches are predominantly used in mechanical
engineering applications. The torque is transmitted without backlash through
the use of friction or positive fits, similarly to electromagnetic brakes
(chapter 3.3.5), with the exception that both the drive and the output can move
freely.
The method of functioning
generally follows the open circuit principle. When de-energised, the clutch is
open. Prestressed flat springs ensure disengagement free of residual torque.
When the coil of the stator is supplied with DC voltage, a magnetic field is
created. The magnetic pull causes the armature plate to be drawn against the
force of the springs across the air gap and toward the friction surface of the
rotor. The torque is transmitted. There are also clutches which work to the
closed-circuit principle and are therefore closed when no voltage is applied.
When disengaging, the force of the electromagnet works against the force of the
springs.
(Edwin Kiel, Drive Solutions: Mechatronics for Production and
Logistics, p.215)
5) Prepregs (Group: Material)
Previous Answer
Prepregs another prefabricated form for FRP shaping operation is prepreg, which consist of fibers impregnated with partially cured thermosetting resins to faciliate shape processing. Completion of curing must be accomplished during and/or after shaping. Prepregs are available in the form of tapes or cross-plied sheets or fabrics.The adventage of prepregs is that they are fabricated with continious filaments rather than chopped random fibers, thus increasing strength and modulus of the final product.Prepreg tapes and sheets are associated with advanced composites (reinforced with boron, carbon/graphite and kevlar as well as fiberglass.
(Mikell P. Groover,Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, p.331)
Prepregs another prefabricated form for FRP shaping operation is prepreg, which consist of fibers impregnated with partially cured thermosetting resins to faciliate shape processing. Completion of curing must be accomplished during and/or after shaping. Prepregs are available in the form of tapes or cross-plied sheets or fabrics.The adventage of prepregs is that they are fabricated with continious filaments rather than chopped random fibers, thus increasing strength and modulus of the final product.Prepreg tapes and sheets are associated with advanced composites (reinforced with boron, carbon/graphite and kevlar as well as fiberglass.
(Mikell P. Groover,Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, p.331)
New/Better Answer
The term prepreg stands for
pre-impregnated. Prepregs are made by running fibers that are uniformly
separated by tows into a resin bath for wetting. The wetted fibers are then
conditioned so that a small portion optic bonds in the resin is formed. In this
state, the resin is a viscous liquid. This makes the prepreg a flexible sheet
of fibers and resin. The resin is neither liquid nor solid. This state allows
the prepregs to be rigid enough to he handled and yet liquid enough so that
they can be draped onto a complex shaped mold and he bondable. One analogy to
the prepregs is wet wallpaper, except that prepregs are sticky on both sides.
In order to provide handlability, usually a piece of non-stick paper is placed
on one side of the prepregs to prevent them front sticking to each other. As
such, prepregs can be provided in roll form. Usually prepregs are shipped in
refrigerated bags to slow down the reaction. Under storage, the resin in the
prepregs may continue to crosslink. As such prepregs should be stored at low
temperature (about -3°C). If enough bonding has occurred in the resin in the
prepreg, the prepreg becomes too stiff for forming, and also the tackiness
(stickiness) of the prepreg is no longer sufficient for further processing. The
time that the prepregs can stay in storage before becoming stiff or non-sticky
is called the shelf life.
(Suong V. Hoa, Principles of
the Manufacturing of Composite Materials, p.78)
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