High strain-rate testing of parachute materials

Abstract

Research at Sandia National Laboratories has shown a strain rate dependence of many materials used in the production of parachutes. Differences in strength of 30% have been found between strain rates of 12 sec-' and slow rates normally used to define material properties for lightweight nylon cloth. These structures are sometimes deployed in a rapid fashion and the loading is experienced in milliseconds; the production of material data in the same loading regime is required for full understanding of material response. Also, material behavior suitable for structural analysis of these structures is required for successful analysis. This is especially important when different materials are used in the same fabric structure. Determining the distribution of load to various portions of a nylon and Kevlar parachute requires the correct moduli and material behavior in the analytical model.The effect of strain rate on the material properties of nylon and Kevlar components commonly used in parachute construction are reported in this paper. These properties are suitable for use in analytical models of these fabric structures. TntroductioqUsing analysis tools of structural mechanics on high performance fabric structures is a new area of research at Sandia National Laboratories. Several successful examples have included studies of cross parachutes, analyses of the Jet Propulsion Laboratory Mars Pathfinder Airbag System, and, most recently, the design and analysis of a new generation automobile airbag [1,2,3]. Supplying the correct material behavior is of prime importance to the successful analysis and design of *This work was performed at Sandia National Laboratories, Albuquerque, New Mexico, supported by the United States Department of Energy under Contract DE-ACO4-94AL85000. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.these structures. The behavior of the materials under representative rates of loadiig must also be provided because many of these structures are used in dynamic environments. The high strain-rate measurement of fabric behavior at cold, ambient, and high temperatures is even more challenging, but necessary, as differences of 30% are found for various environmental combinations.The purpose of this paper is to provide the basis of high strain rate material properties for the engineering of parachute systems and other high performance fabric structures. A description of the test method is given along with results from representative materials. The difficulties of adapting equipment normally used to test metals for the testing of fabrics is also discussed. Additionally, high speed photography was necessary for the measurement of strain and strain rate of the fabric. All of these complicating factors are necessary for the measurement of fabric high strain rate material behavior.

Structural Analyses of the JPL Mars Pathfinder Impacts

“…The data used to define the material behavior was determined from high strain-rate testing of parachute materials [3]. For Kevlar, the airbag and tether construction materials, the strain-rate sensitivity is not very great, so little deviation from static data occurs.…”

Structural analyses of the JPL Mars Pathfinder impact

“…The data used to defhe the material.behavior was determined from high strain-rate testing of parachute materials [3]. For Kevlar, the airbag and tether construction materials, the strain rate sensitivity is not very great.…”