Publications

Abstract not provided.

Abstract not provided.

The effect of spatial nonlocality on the decay of waves in a dissipative material is investigated. The propagation and decay of waves in a one-dimensional, viscoelastic peridynamic medium is analyzed. Both the elastic and damping terms in the material model are nonlocal. Waves produced by a source with constant amplitude applied at one end of a semi-infinite bar decay exponentially with distance from the source. The model predicts a cutoff frequency that is influenced by the nonlocal parameters. A method for computing the attenuation coefficient explicitly as a function of material properties and source frequency is presented. Here, the theoretical results are compared with direct numerical simulations in the time domain. The relationship between the attenuation coefficient and the group velocity is derived. It is shown that in the limit of long waves (or small peridynamic horizon), Stokes’ law of sound attenuation is recovered.

The dynamic behavior of an elastic peridynamic material with a nonconvex bond potential is studied. In spite of the material's inherently unstable nature, initial value problems can be solved using essentially the same techniques as with conventional materials. In a suitably constructed material model, small perturbations grow exponentially over time until the material fails. The time for this growth is computed explicitly for a stretching bar that passes from the stable to the unstable phase of the material model. This time to failure represents an incubation time for the nucleation of a crack. The finiteness of the failure time in effect creates a rate dependence in the failure properties of the material. Thus, the unstable nature of the elastic material leads to a rate effect even though it does not contain any terms that explicitly include a strain rate dependence.

Abstract not provided.

Abstract not provided.

Nonlocal modeling has come a long way. Researchers in the continuum mechanics and computational mechanics communities increasingly recognize that nonlocality is critical in realistic mathematical models of many aspects of the physical world. Physical interaction over a finite distance is fundamental at the atomic and nanoscale level, in which atoms and molecules interact through multibody potentials. Long-range forces partially determine the mechanics of surfaces and the behavior of dissolved molecules and suspended particles in a fluid. Nonlocality is therefore a vital feature of any continuum model that represents these physical systems at small length scales.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Significant testing is required to design and certify primary aircraft structures subject to High Energy Dynamic Impact (HEDI) events; current work under the NASA Advanced Composites Consortium (ACC) HEDI Project seeks to determine the state-of-the-art of dynamic fracture simulations for composite structures in these events. This paper discusses one of three Progressive Damage Analysis (PDA) methods selected for the second phase of the NASA ACC project: peridynamics, through its implementation in EMU. A brief discussion of peridynamic theory is provided, including the effects of nonlinearity and strain rate dependence of the matrix followed by a blind prediction and test-analysis correlation for ballistic impact testing performed for configured skin-stringer panels.

The propagation and decay of waves in a nonlocal, one-dimensional, viscoelastic medium is analyzed. Waves emanating from a source with constant amplitude applied at one end of a semi-infinite bar decay exponentially with distance from the source. A method for computing the attenuation coefficient explicitly as a function of material properties and source frequency is presented. The results are compared with direct numerical simulations. The relationship between the attenuation coefficient and the group velocity is investigated. It is shown that in the limit of long waves (or small peridynamic horizon), Stokes' law of sound attenuation is recovered.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.