The foam material of interest in this investigation is a rigid closed-cell polyurethane foam PMDI with a nominal density of 20 pcf (320 kg/m 3 ). Three separate types of compression experiments were conducted on foam specimens. The heterogeneous deformation of foam specimens and strain concentration at the foam-steel interface were obtained using the 3-dimensional digital image correlation (3D-DIC) technique. These experiments demonstrated that the 3D-DIC technique is able to obtain accurate and full-field large deformation of foam specimens, including strain concentrations. The experiments also showed the effects of loading configurations on deformation and strain concentration in foam specimens. These DIC results provided experimental data to validate the previously developed viscoplastic foam model (VFM). In the first experiment, cubic foam specimens were compressed uniaxially up to 60%. The full-field surface displacement and strain distributions obtained using the 3D-DIC technique provided detailed information about the inhomogeneous deformation over the area of interest during compression. In the second experiment, compression tests were conducted for cubic foam specimens with a steel cylinder inclusion, which imitate the deformation of foam components in a package under crush conditions. The strain concentration at the interface between the steel cylinder and the foam specimen was studied in detail. In the third experiment, the foam specimens were loaded by a steel cylinder passing through the center of the specimens rather than from its end surface, which created a loading condition of the foam components similar to a package that has been dropped. To study the effects of confinement, the strain concentration and displacement distribution over the defined sections were compared for cases with and without a confinement fixture. Published by Elsevier Ltd.
This report documents how active structural control was used to significantly enhance the metal removal rate of a milling machine. An active structural control system integrates actuators, sensors, a control law and a processor into a structure for the purpose of improving the dynamic characteristics of the structure. Sensors measure motion, and the control law, implemented in the processor, relates this motion to actuator forces. Closed-loop dynamics can be enhanced by proper control law design. Actuators and sensors were imbedded within a milling machine for the purpose of modifying dynamics in such a way that mechanical energy, produced during cutting, was absorbed. This limited the on-set of instabilities and allowed for greater depths of cut. Up to an order of magnitude improvement in metal removal rate was achieved using this system. Although demonstrations were very successful, the development of an industrial prototype awaits improvements in the technology. In particular, simpler system designs that assure controllability and observability and control algorithms that allow for adaptability need to be developed.
This report documents how active structural control was used to significantly enhance the metal removal rate of a milling machine. An active structural control system integrates actuators, sensors, a control law and a processor into a structure for the purpose of improving the dynamic characteristics of the structure. Sensors measure motion, and the control law, implemented in the processor, relates this motion to actuator forces. Closed-loop dynamics can be enhanced by proper control law design. Actuators and sensors were imbedded within a milling machine for the purpose of modifying dynamics in such a way that mechanical energy, produced during cutting, was absorbed. This limited the on-set of instabilities and allowed for greater depths of cut. Up to an order of magnitude improvement in metal removal rate was achieved using this system. Although demonstrations were very successful, the development of an industrial prototype awaits improvements in the technology. In particular, simpler system designs that assure controllability and observability and control algorithms that allow for adaptability need to be developed.
In the stereolithography process, three dimensional parts are built layer by layer using a laser to selectively cure slices of a photocurable resin, one on top of another. As the laser spot passes over the surface of the resin, the ensuing chemical reaction causes the resin to shrink and stiffen during solidification. When laser paths cross or when new layers are cured on top of existing layers, residual stresses are generated as the cure shrinkage of the freshly gelled resin is constrained by the adjoining previously-cured material. These internal stresses can cause curling in the compliant material. tion to R. P. Chartoff, J. S. Ullett, and A. J. Lightman at the University of Dayton for their assistance in making propem measurements and for their SLA software which allowed us to create our own build styles. Manfred Hofman at Ciba-Geigy and Paul Jacobs at 3D Systems were helpful in discussing issues and reviewing the technology. D. B. Adolf and W. R. Witkowski graciously agreed to review this report.
ABSTRACTreasonable stroke limits, all of which can be used to increase performance levels in precision manufacturing systems. This paper describes two examples of embedding piezoelectric actuators in structural components for vibration control. One example involves suppressing the self excited chatter phenomenon in the metal cutting process of a milling machine and the other involves damping vibrations induced by rigid body stepping of a photolithography platen. Finite element modeling and analyses are essential for locating and sizing the actuators and permit further simulation studies of the response of the dynamic system. Experimental results are given for embedding piezoelectric actuators in a cantilevered bar configuration, which was used as a surrogate machine tool structure. These results are incorporated into a previously developed milling process simulation and the effect of the control on the cutting process stability diagram is quantified. Experimental results are also given for embedding three piezoelectric actuators in a surrogate photolithography platen to suppress vibrations. These results demonstrate the potential benefit that can be realized by applying advances from the field of adaptive structures to problems in precision manufacturing.Piezoelectric actuators provide high frequency, force, and stiffness capabilities along with
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