Rodney J. Clifton Rush C. Hawkins University Professor Emeritus of Engineering, Professor of Engineering (Research)

Brown Affiliations

Research Areas

research overview

Professor Clifton's primary research is on the mechanical response of materials at very high loading rates. Applications include: high speed machining, armor penetration, shear band formation, martensitic phase transformations, elastohydrodynamic lubrication, and dynamic fracture. Principal experimental approach is pressure-shear plate impact. A second research focus involves the measurement of the high frequency, viscoelastic response of soft, biological tissues, especially vocal folds.

research statement

Beginning with Harry Kolsky (deceased) and continuing with Jacques Duffy (deceased) and Rod Clifton, Brown investigators have led the development of the experimental methodologies for studying the mechanical behavior of materials at high strain rates. The torsional Kolsky bar and the pressure-shear plate impact experiment developed at Brown are widely used to study the deformation and failure of materials at the high strain rates that occur in high speed machining, terminal ballistics, and explosive loading. Professor Clifton's group conducts research on the mechanical response of materials subjected to very high loading rates. This research is motivated by the need for better understanding of such processes as high speed machining, armor penetration, shear band formation, martensitic phase transformations, elastohydrodynamic lubrication, and dynamic fracture. The research involves combined experimental and computational investigations in which the experimental component makes use of plane wave loading to provide the most direct interpretation of the experimental results in terms of the response of the material.
Pressure shear plate impact: Plane waves are generated in a plate impact facility, which is designed to produce the impact of parallel plates. In order to subject the impacting plates to combined pressure and shear loading, the impacting plates are inclined relative to the direction of approach. The motion of the rear surface of the impacted plate is recorded using a variety of laser interferometers. Computer simulation of the experiment is used to relate the recorded velocity-time profiles to the response of the material being studied. Scope: Studies have been conducted on a wide variety of materials including metals, metal alloys, glasses, ceramics, ceramic powders, lubricants, and shape memory alloys. In addition, studies have been conducted on the dynamic friction of sliding interfaces, such as the interface between a machine tool and the stock being machined. Recently, an induction heater has been added that makes it possible to conduct the experiments at temperatures up to 700 degrees C. Experiments can also be conducted in a so-called "soft recovery" configuration in which the specimen is recovered after being subjected to a single plane pulse -- thereby making it possible to relate the dislocation motion or microcracking that occurred to the action of a known stress pulse.

Current projects: Current research projects are concerned with the modeling of martensitic phase transformation, dynamics failure of steel welds, dynamics plasticity of refractory metals, dislocation mobility in Ni 3 Al, and the competition between shear banding and shear fracture in the dynamic failure of materials.

funded research

Externally Supported Research (Since l973)

Brown Materials Research Laboratory, "Anelastic Waves in Metals and Polymers" (July l, l973 - June 30, l974). Amount: $l9,000

Brown Materials Research Laboratory, "Plate Impact Experiments on LiF" (July l, l976 - June 30, l977). Amount: $22,974

National Science Foundation, "Fundamental Studies in Dynamic Plasticity by Means of Plane Wave Experiment" (February l, l976 - January 3l, l979) Amount: $200,348

Army Research Office, "Plastic Deformation and Fracture of Steel Under Dynamic Loading" (Co-P.I. with J. Duffy) (December l5, l976 - February l5, l980). Amount $l44,000

National Science Foundation Energy Related Traineeships (Participating faculty: B. Caswell, L.B. Freund, J. Rice, D. Simons, T. Tullis (2 three-year traineeships - l976-79). Amount: $42,000

Brown Materials Research Laboratory, "Plate Impact Experiments on LiF" (July l, l977 - June 30, l978). Amount: $25,000

Terra Tek, Inc., "Computer Time for Generating Time Dependent Solutions of Hydraulic Fracture Propagation" (February l, l977- ). Amount: $3,000

Brown Materials Research Laboratory, "Dislocation Dynamics and Plate Impact Experiments," (July l, l978 - June 30, l980). Amount: $40,000

National Science Foundation, "Fundamental Studies in Dynamic Plasticity by means of Plane Wave Experiments," (October l, l979 - April 30, l983). Amount: $282,569

Army Research Office, "An Investigation of Inhomogeneous Inelastic Deformations through Plate Impact Experiments and Mathematical Modelling of Propagating Localized Deformations," (October l, l980 - September 30, l983). Amount: $l65,000

Brown Materials Research Laboratory, "Dislocation Dynamics in Plate Impact Experiments," (July l, l980 - June 30, l98l). Amount: $36,000

Army Research Office, "Critical Conditions for Failure in Materials Subjected to High Rates of Loading," (August l5, l98l - October l5, l984). (Co-investigators: R.J. Asaro, J. Duffy, L.B. Freund, A. Needleman). Amount: $l,l00,000

Brown Materials Research Laboratory, "Dislocation Dynamics and Shear Strain Localization," (July l, l982 - June 30, l983). Amount: $45,000

National Science Foundation, "Time Dependent Plasticity: Theory, Experiment and Computation," (May l, l983 - October 3l, l985). Amount: $199,999

Brown Materials Research Laboratory, "Dynamic Plastic Deformation of Crystals," (July l, l983 - June 30, l984). Amount: $49,397

Army Research Office, "Critical Conditions for Failure in Materials Subjected to High Rates of Loading," (December l, l984 - October 3l, l987). (Co-investigators: R.J. Asaro, J. Duffy, L.B. Freund, A. Needleman). Amount $1,140,000.

National Science Foundation, "Rheology of Lubricants at High Pressures and High Shear Rates," (November l, l985 - April 30, l986). Amount: $34,448.

Brown Materials Research Laboratory, "Plastic Deformation and Fracture at High Strain Rates," (July l, l985 - April 30, l987). Amount: $97,438.

National Science Foundation, "Theoretical and Experimental Investigation of the Inelasticity and Failure of Ceramics," (with M. Ortiz) (March 15, 1987 - March 14, 1990) Amount: $368,026.

Office of Naval Research, "Fundamental Studies in Dynamic Plasticity," (February 1, 1987 - January 31, 1990) Amount: $424,255.

Army Research Office, "Microstructural Mechanisms of Dynamic Ductile Fracture and Implications for Structural Failure," (with R.J. Asaro, J. Blume, J. Duffy, L.B. Freund, and S. Nutt) (December 1, 1987 - November 30, 1990) Amount: $1,122,767.

Brown Materials Research Group, "Viscoplastic Response at High Strain Rates," (May 1, 1987 - April 30, 1988) Amount: $47,205.

Office of Naval Research, "Kinetics of Stress-Induced Phase Transformations," 9/1/91 - 9/1/94, $368.830.

Army Research Office, "Investigation of Dynamic Material Response for Model Development," 1/15/91 - 01/14/94, $323,173.

National Science Foundation, "Development of Computational and Experimental Capability for the Simulation of High Speed Machining," 10/15/90-09/30/94, $1,053,692. (with J. Duffy, A. Needleman, and M. Ortiz).

National Science Foundation, "Micro-Mechanics of Failure Resistant Materials," 3/1/90 -2/28/93, $2,634,600. (P.I., with 10 faculty from Solid Mechanics and Material Science.)

National Science Foundation, "Micro- and Nano-Mechanics of Failure Resistant Materials" 7/1/93-3/30/96, $2,557,000. (P.I., with 10 faculty from solid Mechanics and Material Science).

Army Research Office, "Dynamic Behavior of Brittle Materials," (with L.B. Freund, K.S. Kim, S. Nutt, M. Ortiz and S. Suresh) 8/1/92-7/31/97, $2,000,000.

Army Research Office, "Research Training in Dynamic Response of Materials," 6/93 - 5/96, $120,000.

Army Research Office, "Plastic Flow and Shear Banding in Refractory Metals and Martensitic Steels at Very High Shearing Rates," 8/1/94 - 7/31/97, $452,078.

Sumitomo, "Research on High Rate Deformation of Metals (Gift) $20,000.

National Science Foundation, MRSEC on "Micro- and Nano-Mechanics of Materials," 9/1/96 - 4/30/2001, at $1,150,000 per year (P.I., with 11 faculty from Solid Mechanics and Materials Science.

Office of Naval Research, "Kinetics of High Rate Martensitic Tranformations in Ni-Ti," 6/1/96 - 8/31/96 $20,000.

Office of Naval Research, "Characterization of High Strain Rate Response of Steel Welds," 6/1/97 - 9/30/03, $736,475.

Army Research Office(DURIP), "High-Speed, Real-Time Measurement Instrumentation for High-Strain-Rate Behavior of Brittle Ceramics Subjected to High Velocity Impact," 6/1/95 - 11/30/97, $150,000 (with K.-S. Kim).

National Science Foundation, Infrastructure Award (with Clyde Briant and K. Sharvan Kumar).

Army Research Office, "High Rate Deformation of Metals at High Temperatures," 8/01/98 - 11/30/01, $414,000.

Alcoa, Unrestricted grant for research on the dynamic plastic response of metals (1999-2000), $20,000.

Amorphous Technologies, INC. Subcontract on ARO/SBIR on "Development of Highly Reinforced Amorphous Metal Matrix Composites," 6/1/99 - 5/31/01, $75,000.

Amorphous Technologies, INC. Subcontract of DARPA award on "Bulk Amorphous Metals," 9/12/01 - 4/30/04, $105,000.

Office of Naval Research, "High Strain Rate Properties of Elastomers," 10/1/03 – 2/28/06, $444,674.

Massachusetts General Hospital, "Vocal Fold Tissues," 3/01/05 – 8/31/05, $42,000.

Office of Naval Research/DURIP, "A Scanning White Light Interference Microscope to Study Adhesion at Metal-Polymer Interfaces," 5/15/04 – 5/14/06, $128,432, (w/ P. Guduru)