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The Leaky Lamb wave (LLW) technique is approaching a maturity level that is making it an attractive quantitative NDE tool for composites and bonded joints.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Robotic exploration of the Martian surface will provide important scientific data on planetary climate, life history, and geologic resources.
We report a significant advance in space robotics design based on innovation of 3D composite structures and piezoelectronic actuation.
The leaky Lamb waves (LLW) technique is approaching a maturity level that is making it attractive quantitative NDE tool for composites and bonded joints.
Explore the source record for details and available documents.
Composite materials are used in aerospace, automotive, and underwater applications.
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This paper presents the structural and mechanical development of a 7-meter inflatable/self-rigidizable reflectarray antenna that is intended for space communication applications.
Increasingly, electroactive materials are used to produce acutators, sensors, displays and other elements of mechanisms and devices. In recognition of the potential of these materials, research at the JPL's NDEAA Lab have led to many novel space and terrestrial applications. This effort involves mostly the use of piezoelectric and electroactive polymers (EAP).
The study of membrane behavior is one of the areas of interest in the development of ultralightweight and lightweight structures for space applications. Utilization of membranes as loadcarrying components or support structure for antenna patch-arrays, collectors, sun-shades and solar-sail reflective surfaces brings about a variety of challenges that require understanding of the ripple-formation phenomenology, development of reliable test and analysis techniques, and solution methods for challenges related to the intended applications. This paper presents interim results from a study on the behavior of unidirectionally tensioned flat and singly-curved membranes. It focuses on preliminary experimental work to explore formation of ripples' and on finite element analysis (FEA) to correlate and predict their formation on thin polyimide membrane models.
This paper presents the analysis and test results related to buckling capability, modal characteristics, and thermal expansion coefficient of STR aluminum laminate inflatable/self-rigidizable booms with lengths up to 10 metes. STR booms are fundamental building blocks of space inflatable/self-rigidizable reflectarray antennas. These boom characteristics are essential for analyzing structural integrity, in orbit dynamic response, and in orbit thermal distortion of the 8-mter reflectarray antenna. Distinct advantages of the STR booms will also be identified and presented by this paper.
Electroactive polymers (EAP) are an emerging class of actuation materials. Their large electrically induced strains (longitudinal or bending), low density, mechanical flexibility, and ease of processing offer advantages over traditional electroactive materials. However, before the capability of these materials can be exploited, their electrical and mechanical behavior must be properly quantified. Two general types of EAP can be identified. The first type is ionic EAP, which requires relatively low voltages (<10V) to achieve large bending deflections. This class usually needs to be hydrated and electrochemical reactions may occur. The second type is Electronic-EAP and it involves electrostrictive and/or Maxwell stresses. This type of materials requires large electric fields (>100MV/m) to achieve longitudinal deformations at the range from 4 - 360%. Some of the difficulties in characterizing EAP include: nonlinear properties, large compliance (large mismatch with metal electrodes), nonhomogeneity resulting from processing, etc. To support the need for reliable data, the authors are developing characterization techniques to quantify the electroactive responses and material properties of EAP materials. The emphasis of the current study is on addressing electromechanical issues related to the ion-exchange type EAP also known as IPMC. The analysis, experiments and test results are discussed in this paper.
Two documents present updates on thin-shell, adjustable, curved mirrors now being developed for use in spaceborne imaging systems. These mirrors at an earlier stage of development were reported in Nanolaminate Mirrors With Integral Figure-Control Actuators (NPO-30221), NASA Tech Briefs, Vol. 26, No. 5 (May 2002), page 80. To recapitulate: These mirrors comprise metallic film reflectors on nanolaminate substrates that contain "in-plane" actuators for controlling surface figures with micron-level precision. The actuators are integral parts of the mirror structures, typically fabricated as patches that are bonded onto the rear (nonreflective) surfaces of the mirror shells. The current documents discuss mathematical modeling of mirror deflections caused by actuators arranged in unit cells distributed across the rear mirror surfaces. One of the documents emphasizes an actuator configuration in which a mirror surface is divided into hexagonal unit cells. Each unit cell contains four rectangular actuator patches in an off-axis cruciform pattern to induce a combination of bending and twisting. For deflections to reduce certain optical aberrations, it is found that, relative to other configurations, this configuration involves a smaller areal density of actuators.
An experimental miniature peristaltic pump exploits piezoelectrically excited flexural waves that travel around a ring: A fluid is carried in the containers formed in the valleys between the peaks of the flexural waves, What sets the present pump apart from other pumps that exploit piezoelectrically excited flexural waves is the ring shape, which makes it possible to take advantage of some of the desirable characteristics of previously developed piezoelectric rotary motors. A major advantage of the circular (in contradistinction to a straight-line) wave path is that the flexural waves do not come to a stop and, instead, keep propagating around the ring. Hence, a significant portion of the excitation energy supplied during each cycle is reused during the next cycle, with the result that the pump operates more effectively than it otherwise would.
Efforts are under way to develop a special class of thin-shell curved mirrors for high-resolution imaging in visible and infrared light in a variety of terrestrial or extraterrestrial applications. These mirrors can have diameters of the order of a meter and include metallic film reflectors on nanolaminate substrates supported by multiple distributed piezoceramic gpiston h-type actuators for micron-level figure control. Whereas conventional glass mirrors of equivalent size and precision have areal mass densities between 50 and 150 kg/sq m, the nanolaminate mirrors, including not only the reflector/ shell portions but also the actuators and the backing structures needed to react the actuation forces, would have areal mass densities that may approach .5 kg/m2. Moreover, whereas fabrication of a conventional glass mirror of equivalent precision takes several years, the reflector/shell portion of a nanolaminate mirror can be fabricated in less than a week, and its actuation system can be fabricated in 1 to 2 months. The engineering of these mirrors involves a fusion of the technological heritage of multisegmented adaptive optics and deformable mirrors with more recent advances in metallic nanolaminates and in mathematical modeling of the deflections of thin, curved shells in response to displacements by multiple, distributed actuators. Because a nanolaminate shell is of the order of 10 times as strong as an otherwise identical shell made of a single, high-strength, non-nanolaminate metal suitable for mirror use, a nanolaminate mirror can be made very thin (typically between 100 and 150 m from the back of the nanolaminate substrate to the front reflecting surface). The thinness and strength of the nanolaminate are what make it possible to use distributed gpiston h-type actuators for surface figure control with minimal local concentrated distortion (called print-through in the art) at the actuation points.