Validation Of Structural Dynamics Models At Los Alamos National Laboratory

This publication proposes a discussion of the general problem of validating numerical models for nonlinear, transient dynamics. The predictive quality of a numerical model is generally assessed by comparing the computed response to test data. If the correlation is not satisfactory, an inverse problem must be formulated and solved to identify the sources of discrepancy between test and analysis data. Some of the most recent work summarized in this publication has focused on developing test-analysis correlation and inverse problem solving capabilities for nonlinear vibrations. Among the difficulties encountered, we cite the necessity to satisfy continuity of the response when several finite element optimizations are successively carried out and the need to propagate variability throughout the optimization of the model's parameters. After a brief discussion of the formulation of inverse problems for nonlinear dynamics, the general principles which, we believe, should guide future developments of inverse problem solving are discussed. In particular, it is proposed to replace the resolution of an inverse problem with multiple forward, stochastic problems. The issue of defining an adequate metrics for test-analysis correlation is also addressed. Our approach is illustrated using data from a nonlinear vibration testbed and an impact experiment both conducted at Los Alamos National Laboratory in support of the advanced strategic computing initiative and our code validation and verification program

Toughened ceramics in the system Al2O3:Cr2O3/ZrO2:HfO2

Composites of Al2O3:Cr2O3 solid solution matrix with ZrO2:HfO2 solid solution dispersed particles were prepared and their properties studied. Thermal conductivity of compositions containing 20 mol% or more of chromia was found to be lower than that of partially stabilized zirconia at temperatures above 700[deg]C. Specimens in this system were annealed at 1000[deg]C for longer than 500 h and no mechanical property degradation was observed. Modulus of elasticity, bend strength and fracture toughness of these composites depend strongly on composition, volume fraction, size and the crystallographic modification of the dispersed particles. Best average bend strength of the composites is 490 MPa and the best average fracture toughness observed for these composites was 7[middle dot]4 MPa m1/2. It was found that the fracture toughness of some of the compositions increased with increasing temperature reaching a maximum of 300-500[deg]C, and returned to the room temperature value at 1000[deg]C. From the results obtained these composites can be considered as a potential candidate for advanced heat engine applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26372/1/0000459.pd