Analysis of Multiple Sight Damage with Implications for Nondestructive Evaluation

Multiple-Site Damage (MSD) in aging aircraft has motivated analysis of the fatigue life of a panel containing a row of cracked holes [1–3]. Given the initial MSD configuration and loading conditions, individual cracks are grown incrementally until link-up or the panel failes. First, stress intensity factors are calculated for all cracks. One crack tip is then assumed to advance a small amount, and the cycles for this increment of growth are calculated. The remaining cracks are then grown a distance corresponding to this cyclic interval by employing a fatigue crack growth model to relate the cyclic stress intensity factor and fatigue crack growth rate. After each incremental growth the current crack geometry is compared to one of several failure criteria [3] to determine whether the panel fails. For holes which are initially uncracked, cumulative damage is summed at these locations in conjunction with a Neuber notch analysis. When this strain-life analysis determines that “crack initiation” has occurred at a given hole, crack growth calculations continue at that location, and the routine is repeated until the failure criterion is satisfied

Fatigue analysis of multiple site damage at a row of holes in a wide panel

This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging

Reclaiming Illinois strip coal land with legumes and grasses

MAKING AGRONOMIC SPECIES GROW where none grew before is an accomplishment worthy of man's efforts. The challenge presents itself on many thousands of acres of what was good corn belt land, where the "stripping" method of mining coal has replaced the original land surface with a new mass of varying soil materials. Barren parallel ridges, left by stripping practices, temporarily disturb the social and economic aspects of a community. The disturbance can be overcome in whole or in part by making the new lands produce agronomic species or trees, or by developing chosen sites for recreational facilities.This report was made possible by the cooperation of the Illinois Coal Strippers Association and the Illinois Agricultural Experiment Station. It complements a previous study, "Reclaiming Illinois Strip Coal Lands by Forest Planting," published as Bulletin 547 by the University of Illinois Agricultural Experiment Station in cooperation with the Central States Forest Experiment Station, Forest Service, U. S. Department of Agriculture

One small step : the history of aerospace engineering at Purdue University

The history of aerospace engineering at Purdue University by A.F. Grandt Jr., W.A. Gustafson, L.T. Cargnin

Semielliptical cracks along holes in plates and lugs /

This report summarizes a basic research effort directed at characterizing the growth of semielliptical surface cracks embedded along the bore of a hole in a large plate or an attachment lug. Fatigue cracks are grown in transparent polymer test specimens which allow in situ observation of the crack plane. Crack growth was recorded by time lapse photography. Subsequent measurement of the crack photographs gave crack size and shape changes as a function of elapsed cycles. A multidegree of freedom fracture mechanics model was developed to predict the growth of embedded surface and corner cracks located at open holes in plates loaded in remote tension. Crack growth predictions gave excellent agreement for the embedded surface crack plate results obtained under the current effort and also gave good results for corner cracked hole tests conducted under an earlier program."Final Report for Period 5 January 1981 - 30 November 1982.""May 1983."Includes bibliographical references (pages 124-125).This report summarizes a basic research effort directed at characterizing the growth of semielliptical surface cracks embedded along the bore of a hole in a large plate or an attachment lug. Fatigue cracks are grown in transparent polymer test specimens which allow in situ observation of the crack plane. Crack growth was recorded by time lapse photography. Subsequent measurement of the crack photographs gave crack size and shape changes as a function of elapsed cycles. A multidegree of freedom fracture mechanics model was developed to predict the growth of embedded surface and corner cracks located at open holes in plates loaded in remote tension. Crack growth predictions gave excellent agreement for the embedded surface crack plate results obtained under the current effort and also gave good results for corner cracked hole tests conducted under an earlier program.Research supported by the United States Air Force Wright Aeronautical Laboratories, and performed by Purdue University, School of Aeronautics and Astronautics, West Lafayette, Indiana, under contract no.Mode of access: Internet