NASA Scientific and Technical Aerospace Reports

This paper describes a new approach for severing or weakening a variety of materials. The technique employs embedding
explosive cords into parallel grooves that are cut into a surface of a material. The cords are initiated simultaneously to produce
shock waves that progress toward the centerline between the cords and the lower surface of the material. Intersecting incident
and reflected waves augment at the centerline to fail or weaken the material in tension. No harmful debris is produced on the
opposite side of the material from the explosive cords. The primary focus of the effort described in this paper was to fracture
the F-16 aircraft trilaminate canopy. Also, complete severance was achieved in 2024-T4 aluminum plate stock. Possible
applications are through canopy egress and crew module severance from military aircraft and separation of rocket vehicle
stages and payloads. This approach offers important advantages over explosive methods currently in use.
Author
F-16 Aircraft; Shock Waves; Augmentation; Fracturing; Aircraft Construction Materials; Aircraft Structures
20040111320 NASA Langley Research Center, Hampton, VA, USA
Waveform Based Acoustic Emission Detection and Location of Matrix Cracking in Composites
Prosser, W. H.; [1995]; 2 pp.; In English; No Copyright; Avail: CASI; A01, Hardcopy
The operation of damage mechanisms in a material or structure under load produces transient acoustic waves. These
acoustic waves are known as acoustic emission (AE). In composites they can be caused by a variety of sources including
matrix cracking, fiber breakage, and delamination. AE signals can be detected and analyzed to determine the location of the
acoustic source by triangulation. Attempts are also made to analyze the signals to determine the type and severity of the
damage mechanism. AE monitoring has been widely used for both laboratory studies of materials, and for testing the integrity
of structures in the field. In this work, an advanced, waveform based AE system was used in a study of transverse matrix
cracking in cross-ply graphite/epoxy laminates. This AE system featured broad band, high fidelity sensors, and high capture
rate digital acquisition and storage of acoustic signals. In addition, analysis techniques based on plate wave propagation
models were employed. These features provided superior source location and noise rejection capabilities.
Derived from text
Acoustic Emission; Delaminating; Detection; Graphite-Epoxy Composites; Cracks; Matrix Materials
20040111373 Arizona State Univ., Tempe, AZ, USA
A Nonlinear Theory for Smart Composite Structures
Chattopadhyay, Aditi; [2002]; 5 pp.; In English
Contract(s)/Grant(s): NAG1-2283; No Copyright; Avail: CASI; A01, Hardcopy
The paper discusses the following: (1) Development of a completely coupled thermo-piezoelectric-mechanical theory for
the analysis of composite shells with segmented and distributed piezoelectric sensor/actuators and shape memory alloys. The
higher order displacement theory will be used to capture the transverse shear effects in anisotropic composites. The original
theory will be modified to satisfy the stress continuity at ply interfaces. (2) Development of a finite element technique to
implement the mathematical model. (3) Investigation of the coupled structures/controls interaction problem to study the
complex trade-offs associated with the coupled problem.
Author
Nonlinearity; Mathematical Models; Composite Structures; Piezoelectric Actuators; Finite Element Method
20040111384 NASA Glenn Research Center, Cleveland, OH, USA
SiC/SiC Composites for Applications Above 2600 F
DiCarlo, James A.; Bhatt, R. T.; [2004]; 10 pp.; In English; 28th Annual Conference on Composites, Materials and Structures,
26-30 Jan. 2004, Cape Canaveral, FL, USA
Contract(s)/Grant(s): 22-274-00-02-02; No Copyright; Avail: CASI; A02, Hardcopy
Using data from panels with 2D woven architectures,t his presentation describes progress in identifying advanced
constituent materials and processes for achieving a high conductivity SiC/SiC composite system with long-term structural life
under oxidizing conditions at 2600 degrees F. A key factor for this progress is the development of approaches at NASA GRC
that allow the constituent SiC fiber and SiC matrix to display high thermal conductivity, high creep-rupture resistance and high
microstructural stability at temperatures above 3000 degree F. Another important factor is the avoidance of free silicon in the
SiC matrix, thereby providing the composites with the capability for extended service above the silicon melting point (2550
degrees F). The effects of utilizing various materials and processes for the SiC matrix are presented and discussed.
Author
Identifying; Silicon Carbides; Materials; Materials Selection; High Temperature
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