Abstract
The aim of the research was to investigate the effect of impact damage on the fatigue life of steel using both experimental and finite element methods. Any component that is subjected to a single impact may have not only noticeable surface damage, but also residual stresses in its surface and subsurface layers. These residual stresses may reduce or possibly improve the fatigue life of the component. The objectives of the research were, therefore, to investigate what effect the size of an impacting object has on the fatigue life of a specimen and also to evaluate experimentally how the amount of single impact energy affects the fatigue life of specimens. Furthermore, three dimensional, non-linear transient numerical models were developed, which were used to show the surface and subsurface residual stresses produced as a result of the impact.The specimens used in the experimental programme were made from two different types of cold-rolled, mild steel strip; namely Bending Quality Bright Steel (BS1449), and '070M20' Carbon Steel (BS970). To investigate what effect the size of an impacting object has on the fatigue life of a specimen, the impactors were produced in six sizes; 10mm, 11mm, 12mm, 18mm, 25mm and 40mm radii, and in order to determine how the amount of impact energy affects the fatigue life of a specimen, the height of the impactor hammer head was adjusted to impact heights of 410mm, 276mm, 163mm and 87mm, thus altering the amount of impact energy imparted into the specimen.
The current study found that the fatigue life of a specimen is greatly reduced due to a single impact and that the greater the height of the impact, and consequently the higher the impact energy, then the lower the fatigue life of the specimen becomes. It was also noted that the reduction in fatigue life due to the single impact is not affected by the size of impactor but by the energy of the impact, as a single impact at the chosen impact energy for this study will impart residual stresses in the specimen which causes a normalisation in the reduction in the fatigue life of the specimen.
| Date of Award | Oct 2008 |
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| Original language | English |
| Supervisor | Kathryn Franklin (Supervisor) & Steven Wilcox (Supervisor) |