A Novel Design of Guiding Stress Wave Propagation
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RESEARCH PAPER
A Novel Design of Guiding Stress Wave Propagation Y. Li1 · E. Ngo2 · B. Song3 Received: 13 February 2020 / Accepted: 18 June 2020 © Sandia National Laboratories 2020
Abstract Impact loads can induce a series of undesirable physical phenomena including vibration, acoustical shock, perforation, fracture and fragmentation, etc. The energy associated with the impact loads can lead to severe structure damage and human injuries. A design approach which effectively reduces these negative impacts through shock/stress wave diversion is highly needed. In this paper, a computational model which predicts stress wave propagation by considering different beam geometries and configurations is developed. A novel concept of wave guide design which modifies the stress wave propagation path without disturbance is also presented. This design approach is not only useful for material property characterization particularly at intermediate or high strain rates, but also allows stress wave propagation in a desired direction as the shock/ impact energy can be redistributed in controllable paths. The numerical results are experimentally verified through a DropHopkinson bar apparatus at Sandia National Laboratories. Keywords Stress wave propagation · Finite element method · Wave diversion · Kolsky bar · Drop-Hopkinson bar · Intermediate strain rate
Introduction Blast and impact loadings are associated with shock or stress wave initiation and propagation in solids and structures. When a stress wave propagates in a solid, it can lead to different types of stress states, such as compression, tension, shear, or any combination [1]. The stress wave propagation may be disturbed when the stress wave propagates from one solid to another in a structure due to mechanical impedance mismatch between the solids. Based on such wave propagation theory, the split Hopkinson pressure bar, also called the Kolsky bar was successfully developed in 1949 to dynamically characterize the material response at high strain rates [2]. A conventional Kolsky bar consists of a striker and two long rods (known as the incident bar and the transmission bar). The specimen is sandwiched between the incident and * Y. Li [email protected] 1
Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA
2
Department of Mechanical and Aerospace Engineering, California State University, Long Beach, CA 90840, USA
3
Sandia National Laboratories, 1515 Eubank SE, Albuquerque, NM 87185, USA
transmission bars. The striker is usually launched with a gas gun to impact the incident bar to generate a stress wave (“incident wave”) that propagates along the incident bar. When the stress wave propagates to the incident bar/specimen interface, part of the stress wave is reflected back as a “reflected wave” due to the mismatched impedance between the pressure bars and the test specimen. The rest of the stress wave transmits into the transmission bar as a “transmitted wave” while the specimen is deformed at high rates. A typical Kolsky bar can achieve
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