October_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 0 1 1 include nondestructive testing, eval- uation, and inspections for structural health monitoring. ncsu.edu . MEASURING GRANULAR PROPERTIES A team of researchers from Law- rence Livermore National Laboratory, Calif., used x-ray measurements and analyses to show that velocity scaling and dispersion in wave transmission is based on grainy particle arrange- ments and chains of force between them, while reduction of wave intensity is caused mainly from grainy particle arrangements alone. Stress wave prop- agation through granular material is important for detecting the magnitude of earthquakes, locating oil and gas res- ervoirs, designing acoustic insulation, and designing materials for compacting powders. Two sets of data from x-ray scans of single crystal sapphire spheres are shown here with colorization representing the distribution of stresses for each grain under load. Structure-property relations of granular materials are governed by the arrangement of particles and the chains of forces between them. These relations enable design of wave damping mate- rials and nondestructive testing tech- nologies. “The novel experimental as- pect of this work is the use of in-situ x-ray measurements to obtain packing structure, particle stress, and inter- particle forces throughout a granular material during the simultaneous measure- ment of ultrasound trans- mission,” the researchers say. “These measurements are the highest fidelity dataset to date investi- gating ultrasound, forces, and structure in granular materials.” The research provides new insight into time and frequency-domain features of wave propagation in randomly packed grainy materials, shedding light on the funda- mental mechanisms controlling wave velocities, dispersion, and attenuation in these systems. llnl.gov.