Contact between deformable bodies is a dif- cult problem in the analysis of engineering systems A new approach to contact has been implemented us- ing the Material Point Method for solid mechanics, Bar- denhagen, Brackbill, and Sulsky (2000a) Here two im- provements to the algorithm are described The rst is to include the normal traction in the contact logic to more appropriately determine the free separation crite- rion The second is to provide numerical stability by scaling the contact impulse when computational grid in- formation is suspect, a condition which can be expected to occur occasionally as material bodies move through the computational grid The modications described preserve important properties of the original algorithm, namely conservation of momentum, and the use of global quantities which obviate the need for neighbor searches and result in the computational cost scaling linearly with the number of contacting bodies The algorithm is demonstrated on several examples Deformable body so- lutions compare favorably with several problems which, for rigid bodies, have analytical solutions A much more demanding simulation of stress propagation through ide- alized granular material, for which high delity data has been obtained, is examined in detail Excellent quali- tative agreement is found for a variety of contact con- ditions Important material parameters needed for more quantitative comparisons are identied

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An Improved Contact Algorithm for the Material Point Method and Application to Stress Propagation in Granular Material

Summary The paper considers the application of theoretical contact mechanics to computer simulation of dissipative solid particle systems. Theoretical and computational requirements are discussed, and results obtained from simulated impact experiments are presented.

Applications of Theoretical Contact Mechanics to Solid Particle System Simulation

Force Transmission in Granular Media

Through numerical experiments we investigate stress localization in granular material with application to plastic-bonded explosives. The results shed light on static versus dynamic loading, and on the role of an interstitial material between grains. Under static loading, we observe stress localization and bridging in a lattice of polydisperse cylinders in two dimensions. Under dynamic loading, we observe a two wave structure with stress fingers propagating ahead of a normal compaction wave. When an interstitial material is added (a polymeric binder), force fluctuations are substantially reduced under both static and dynamic loading. Under dynamic loading, the structure of the stress wave depends upon the material properties of the binder. As the binder stiffness increases, stress fingering decreases and is replaced by a planar compaction wave.

Dynamic stress bridging in granular material

An implicit particle-in-cell method for granular materials

Dynamic photoelasticity in conjunction with high-speed photography is utilized to study impact wave propagation and dynamic load transfer in granular soil. Series of sequentially recorded isochromatic fringe patterns provide full field information of the dynamic event. Experimental results show that the wave propagation process is governed by a contact wave which increases the density of contacts in propagation direction. The study of dynamic load transfer along specific representative load chains provides basic information about wave velocities, contact duration, and directional stability necessary for a rigorous analysis of the general complex dynamic wave-soil interaction problem.

Photoelastic Investigation of Dynamic Load Transfer in Granular Media

Transient phenomena of reflection and diffraction of explosively-generated plane and cylindrical elastic waves at the tips of a finite crack buried at some depth below a free surface are investigated. Dynamic photoelasticity has been used as a means for visualizing the highly complex interaction process between stress waves and cracks. Primary and secondary diffraction are studied and sequences of isochromatic fringe patterns and their associated wave front reconstruction patterns are presented. Fracture mechanics aspects of dynamic crack initiation under stress wave loading are discussed.

Photoelastic investigation of stress wave diffraction about stationary crack-tips

This paper deals with the dynamic contact of an explosively excited disc with another disc or a half-plane. Dynamic photoelastic recordings show the development of the time-dependent contact area and the formation of the highly complex diffraction pattern.

Dynamic photoelastic investigation of wave propagation and energy transfer across contacts

Dynamic Photoelastic Study of Crack-Wave Interaction in Thick-Walled Rings

Dynamic photoelasticity in conjunction with linear elastic fracture mechanics was utilized to study the dynamic behavior of imperfectly bonded single lap joints. Transient phenomena of propagation, reflection and diffraction of explosively generated plane elastic stress field disturbances about the tips of a crack located at the interface between the two adherends are investigated in detail. Fracture mechanics aspects of dynamic initiation under stress wave loading in similar and dissimilar lap joints are discussed.

H. P. Rossmanith

Papers

Photoelastic Investigation of Dynamic Load Transfer in Granular Media

Photoelastic investigation of stress wave diffraction about stationary crack-tips

Dynamic photoelastic investigation of wave propagation and energy transfer across contacts

Dynamic Photoelastic Study of Crack-Wave Interaction in Thick-Walled Rings

Dynamic Fracture of Imperfectly Bonded Lap Joints