Thomas G. Came, Randy L. Mayas and Vesta I. Bateman .... _ i_ _ :!_ Sandia NationalLaboratories _. .... Albuquerque, NewMexico87185, USA ' _ i_ _ / ABSTRACT important design consideration. This would include payloador satelliteloads duringrocket launches[3]. Force reconstruction is a procedure in which the externally applied force is inferred from measured An applicationthat will be discussed as part of this structuralresponse ratherthan directlymeasured. In paper is the impact into a rigid barrier of a weapon a recently developed technique, the response system with an energy-absorbing nose. The nose acceleration time-histories are multiplied by scalar had been designed to absorb the energy of impact weights and summed to produce the reconstructed and to mitigate the shock to the interiorcomponents. force. This reconstruction is called the Sum of To evaluate the crush capabilityof the nose, impact Weighted Accelerations Technique (SWAT). One tests were performed, and the measured forcestep in the application of this technique is the displacement curve was compared to the design calculationof the appropriatescalar weights. In this objective. Figure 1 shows the weapon mass-mockup paper a new methodof estimatingthe weights, using with the energy absorbing nose hung from its launch measured frequency response function data, is rail and fixture. The mass-mockup was designed to developed and contrasted with the traditional SWAT have the same mass, center-of-mass, and momentmethod of inverting the mode-shape matrix. The of-inertia as the real weapon. Both axial and diagonal techniqueuses frequency responsefunctiondata, but impact tests of the nose were plannedso the mockis not based on deconvolution, up needed to possess the correct rigid-bodyinertiaas well as mass. Figure2 showsthe plasticdeformation This work was supported by the U. S. Department of '_ _,. Energy under contract No. DE-AC04-94AL85000. _,t _ ]L. __ c_ .Olr. _P_[J'i ;_; '} :" "H]_; D0/CUt_.Ft'4T J:_i.JIYLI,_ITF._ DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer er, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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A new technique for force reconstruction is developed. To estimate the externally applied force, this technique sums the weight-scaled acceleration signals, and is referred to as the Sum of Weighted Accelerations Technique (SWAT). To obtain the scalar weights the inverse of the mode shape matrix is used. Application of this technique is illustrated with both numerical calculations using a mass-spring model and experimental data from a structure impacting a rigid barrier.

Two force reconstruction techniques were used to evaluate the impact test of a scale model nuclear transportation cask dropped 30 ft. onto an unyielding target. The two techniques are: the sum of weighted acceleration technique (SWAT) and the deconvolution technique (DECON). A brief description and the calibration of the techniques as applied to the cask are presented. For the impact test, both techniques yielded very similar resultant forces and provided more accurate definition of the force-time history for the cask than is available from conventional data reduction methods. An applied moment, measurement previously unobtainable from conventional accelerometer data reduction techniques, was determined with SWAT. The angular velocity calculated with SWAT was verified with photometric measurements.

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Issued by Sandia National Laboratories, operated for the United States. Department of Energy by Sandia Corporation. NOTICE This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereoc nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not i&inge privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessady constitute or imply its endorsement, recommendation, or favoring by the United States Government, any agency thereof, or any of their contractors or subcontractors. The views and opinions expressed herein do not nekessarily state or reflect those of the United States Government, any agency thereof, or any of their contractors.

This article comprises a comprehensive description of pyroshock, the interpretation of pyroshock data, and the validation of pyroshock data. Recent events in the pyroshock testing community show that corrupted pyroshock data are still being taken at both government agencies and private companies. A large part of this article is devoted to the acquisition and analysis of pyroshock data because proper time-history data acquisition and, consequently, test specification development are common industry problems. To avoid corrupted pyroshock data and resulting corrupted pyroshock specifications, recommended practices for instrumentation and data acquisition systems as well as data analyses are given. Causes of corrupted pyroshock data are explored, and recommendations for avoiding corrupted pyroshock data are provided. Pyroshock was once considered a relatively mild environment due to its low-velocity change and high-frequency content. Pyroshock rarely damages structural members, but can easily cause failures in electronic components that are sensitive to high-frequency pyroshock energy. In the near field, pyroshock acceleration is a high-frequency, high-amplitude shock wave that may have transients with a duration of microseconds. 1,2,3,4,5 In the mid field and the far field, the pyroshock acceleration time history approximates a combination of decayed sinusoids with one or more dominant frequencies. 2,3,4,5 Pyroshock or pyrotechnic shock originates from point sources (explosive nuts and bolts), line sources or flexible linear shaped charges (FLSC), mild detonating fuses (MDF), and combined sources (V-band/Marmon clamps). Types of failures caused by pyroshock commonly include relay chatter, separation of small-circuit test items, and dislodging of contaminants (e.g. solder balls) that cause short circuits. 2,3,4,5 Definitions for pyroshock are now uniform in all major documents, as shown in Table 1; this was accomplished during the last four years. 2,3,4,5 These definitions are only guidelines. The most important aspect of these definitions is the frequency specification, because frequency content determines the pyroshock test or simulation. A near-field pyroshock test requires frequency control up to and above 10,000 Hz for amplitudes greater than 10,000 g. A pyrotechnically excited simulation technique is usually appropriate, although in some cases, a mechanically excited simulation technique may be used for small components. 6 A mid-field pyroshock test requires frequency control from 3,000 to 10,000 Hz for amplitudes less than 10,000 g. A mechanically excited simulation technique other that shaker shock is usually required. A far-field pyroshock test requires frequency control no higher than 3,000 Hz for amplitudes less than 1,000 g. A shaker shock or a mechanically excited simulation technique is appropriate. Recent events show that sources of pyroshock data contamination appear to be the usual culprits that have been known for some time-electromagnetic noise (or other noise sources), digital aliasing and offsets...

This paper describes the design and implementation of a surface micromachined accelerometer for measuring very high levels of acceleration (up to 50,000 G). Both the mechanical and electronic portions of the sensor were integrated on a single substrate using a process developed at Sandia National Laboratories. In this process, the mechanical components of the sensor were first fabricated at the bottom of a trench etched into the wafer substrate. The trench was then filled with oxide and sealed to protect the mechanical components during subsequent microelectronics processing. The wafer surface was then planarized in preparation for CMOS processing using Chemical Mechanical Polishing (CMP). Next, the CMOS electronics were fabricated on areas of the wafer adjacent to the embedded structures. Finally, the mechanical structures were released and the sensor tested.The mechanical structure of the sensor consisted of two polysilicon plate masses suspended by multiple springs (cantilevered beam structures) over corresponding polysilicon plates fixed to the substrate to form two parallel plate capacitors. The first polysilicon plate mass was suspended using compliant springs (cantilever beams) and acted as a variable capacitor during sensor acceleration. The second polysilicon plate mass was suspended using very stiff springs and acted as a fixed capacitor during acceleration. Acceleration was measured by comparing the capacitance of the variable capacitor (compliant suspension) with the fixed capacitance (stiff suspension).