Accession Number : ADA210989


Title :   Porosity and Crack Initiation During Low Cycle Fatigue


Descriptive Note : Technical rept. no.13


Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEERING


Personal Author(s) : Gerard, D. A. ; Koss, D. A.


Report Date : JUL 1989


Pagination or Media Count : 25


Abstract : The influence of porosity on crack initiation during low cycle fatigue LCF has been examined by both experimental observations and theoretical modeling. Experimental data based on powder-processed titanium indicate a porosity-induced enhancement of crack initiation, which contributes to significant reductions in low cycle fatigue life. All of the levels of porosity examined, which range from 0.4 to 6 volume percent, cause an order of magnitude or greater decrease in the number of cycles to initiate a 15 micron crack. Based on a modification of a Neuber analysis, local strain profiles which develop adjacent to holes in uniaxial tension and large-strain amplitude fatigue testing have also been predicted and experimentally verified. Modeling porosity located at a surface as a through-thickness hole deforming under plane-stress conditions, adapting a Coffin-Manson law as a failure criterion and using cumulative damage theory, a theoretical analysis has been developed for predicting the number of cycles for microcrack initiation in the presence of porosity. The predictions, which rely on pore shapes and the low cycle fatigue response of the fully dense matrix, accurately predict the number of cycles necessary to initiate a 15 micron crack adjacent to both isolated and interconnected pores during low cycle fatigue.


Descriptors :   *POROSITY , *LIFE CYCLES , *FATIGUE LIFE , *CRACKING(FRACTURING) , VOIDS , CYCLES , DEFECTS(MATERIALS) , HOLES(OPENINGS) , RESPONSE , TENSION , AXES , FATIGUE , UNIDIRECTIONAL , THEORY , MODELS , MICROCRACKING , EXPERIMENTAL DATA , DAMAGE


Subject Categories : PROPERTIES OF METALS AND ALLOYS
      MECHANICS


Distribution Statement : APPROVED FOR PUBLIC RELEASE