TAILIEUCHUNG - High Cycle Fatigue: A Mechanics of Materials Perspective part 61

High Cycle Fatigue: A Mechanics of Materials Perspective part 61. The nomenclature used in this book may differ somewhat from what is considered standard or common usage. In such instances, this has been noted in a footnote. Additionally, units of measurement are not standard in many cases. While technical publications typically adhere to SI units these days, much of the work published by the engine manufacturers in the United States is presented using English units (pounds, inches, for example), because these are the units used as standard practice in that industry. The graphs and calculations came in those units and no attempt was made to convert. | 586 Appendix G In-plane view Out-of-plane view Test result Fine mesh prediction Figure . Comparison of various mesh refinements to experimental damage. The failure of the fine mesh to better predict material failure indicates that advanced codes such as hydrocodes and Particle-In-Cell PIC methods require significant expertise in order to be used correctly. In this case the poor predictions may be due to mesh size or they may well be due to the shortcomings in the deformation failure constitutive model. In fact the failure to arrive at a converged solution indicates that there may be competing shortcomings in various features of the model that may be offsetting each other. Because of this these tools require expert users in order to predict damage prior to the impact event. Even without expert users hydrocodes and PIC methods can be Appendix G 587 033 VALUE 04 04 04 04 01 04 10 -INFINITY INFINITY 0 15 30 45 Figure . Comparison of residual stress fields for different impact angles. used to parametrically evaluate different facets of blade design. In this role they can be useful design tools that can supplement experimental data in order to eliminate designs that are FOD intolerant. An additional benefit of hydrocode modeling is that the output of these models can be used to determine the relative magnitudes of residual stresses due to impact. For example if a mesh refinement is chosen based on its correlation with impact damage size that mesh could be used to predict residual stresses. An example of a parametric residual stress study based on an experimentally correlated mesh and a varying impact angle is shown in Figure . Once the residual stresses are calculated they can be superimposed over cyclic stresses in order to predict life with greater accuracy. Numerical modeling of FOD is similar to modeling of all other ballistic impact events. Accurate predictions require physically realistic deformation and .

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