Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

http://wwwcourses.sens.buffalo.edu/ce435/StewardHearnWilkinson2000.pdf

An overview of polymer latex film formation and properties.

We present chain structure, phase morphology, and toughness relationships in thermoplastic polymers and polymer/rubber blends. In neat polymers, molecular aspects of craze/yield behavior are controlled by two chain parameters: entanglement density ν e and characteristic ratio C ∞ . The crazing stress is proportional to ν e 1/2 , and the yield stress is proportional to C ∞ . The dispersed rubber toughens a polymer/rubber blend mainly by promoting energy dissipation of the matrix. The toughening efficiency correlates with the rubber phase morphology and the chain structure of the matrix

Chain structure, phase morphology, and toughness relationships in polymers and blends

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Sliding Friction-Physical Principles and Applications

Dendritic hyperbranched polymers as tougheners for epoxy resins

Elastic recovery of a scratch in a polymeric surface: experiments and analysis

Most existing models describing the scratch properties of materials take into account forces acting at the interface between the material and a grooving tip, but do not consider the stress and strain properties of the material far beneath or ahead of the tip. In the case of polymer scratches, there are no models at all which take into account the viscoelastic viscoplastic behaviour of the material. In standard indentation tests with a non moving tip, the elastic plastic boundary and the limits of the region subjected to hydrostatic pressure beneath the tip are known. These models were used to analyse the geometry of the grooves left on the surface of a viscoelastic viscoplastic body by a moving cone-shaped diamond tip having a radius of about 40 μm. A new apparatus was built to control the velocity of the tip over the range 1 to 104 μm/s, at several different temperatures from −10°C to 100°C. The material was a commercial grade of cast poly(methylmethacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress and temperature activated process. Values of the activation energy and volume of the dynamic hardness and of the interfacial shear stress were in good agreement with those usually attributed to the mechanical properties of PMMA.

Time and temperature dependence of the scratch properties of poly(methylmethacrylate) surfaces

The influence of strain hardening of polymers on the piling-up phenomenon in scratch tests: Experiments and numerical modelling

A surface flow line model of a scratching tip: apparent and true local friction coefficients

The current analytical models are insufficient to describe the ploughing part of the friction coefficient when there is elastic recovery at the rear part of the contact after passage of a moving tip. A solution for the case of a perfectly conical tip was proposed recently. This paper presents a model to describe the ploughing friction for a perfectly spherical tip and then develops this analysis for the case of a conical tip with a blunted spherical extremity. The major difficulty resides in taking into account the shape of the contact area in relation to the elastic, elastoplastic or plastic behaviour of the contact.

Robert Schirrer

Papers

Elastic recovery of a scratch in a polymeric surface: experiments and analysis

Time and temperature dependence of the scratch properties of poly(methylmethacrylate) surfaces

The influence of strain hardening of polymers on the piling-up phenomenon in scratch tests: Experiments and numerical modelling

A surface flow line model of a scratching tip: apparent and true local friction coefficients

The ploughing friction: analytical model with elastic recovery for a conical tip with a blunted spherical extremity