A Study on Effect of Residual Stress on Crack Growth of Aluminum Plate
One technique used to enhance the fatigue strength of a fastener hole is to introduce a compressive residual stress field around the hole. An applied load must overcome this residual stress before the crack can grow, thus leading to a longer fatigue life. The cold expansion of the holes is largely employed to obtain improvement in fatigue performance of structures with initially uncracked holes. In this research, considered is a fatigue crack growth from a hole under the influence of residual stress. The entire cold working processing- including hole expansion, elastic recovery, and finish reaming of two aluminum alloys 2024-T351 and 7075-T6 is simulated. This method of fatigue life prediction is compared with a superposition technique and experimental data. The crack closure level is computed from a finite element simulation and a fatigue life is predicted. The conclusions obtained here are beneficial to the understanding of the phenomenon of fatigue crack initiation and growth at the perimeter of cold worked holes.
Method of Laurent series expansion for internal crack problems
This paper presents a general method of analysis of internal cracks in isotropic homogeneous elastic media. The proposed method is based on the Laurent series expansions of the complex potentials which are consistent with the singlevaluedness of displacements as well as stresses and strains. It applies to the problems of longitudinal shear, plane stress or plane strain and classical plate bending in which the stress state is completely characterized by one or two complex potentials.
Inequality trends in health and future health risk among English children and young people, 1999–2009
Objective To investigate trends in health inequality among children and young people between 1999 and 2009, using outcomes consistent with the current NHS reforms. Design/data Secondary analysis of participants aged 0–24 in the Health Surveys for England (HSE) undertaken in 1999, 2004, 2006 and 2009. Main outcome measures Changes in the absolute and relative risks of four health outcomes by deprivation tertiles, based on occupation of the head of household ▸ self/parent-reported general health, ▸ presence of a long-standing illness (LSI), ▸ obesity ▸ smoking. Results No indicator showed a reduction in relative or absolute inequality between 1999 and 2009. For children (0–12 years), the relative risk comparing the most and least deprived tertiles increased significantly for poor general health (1999:1.6 (95% CI 1.2 to 2.2); 2009:3.9 (2.4 to 6.2), while the absolute difference in LSI prevalence(%) increased from 1.3 (−2.9 to 5.5) to 7.4 (3.6 to 11.4). Among young people (13–24 years), the absolute difference in LSI prevalence increased from −5.9 (−10.9 to −1.1) to 3.1 (−4.1 to 10.7). Absolute inequality in having tried smoking among children aged 8–15(%) increased significantly in the first half of the decade before decreasing in the second half (1999:3.3 (−1.1 to 7.7); 2004:14.1 (9.6 to 18.8); 2009:4.1 (0.1 to 8.8)). However, the increase in absolute inequality for smoking prevalence among young adults (16–24 years) was maintained throughout the decade (1999:−7.0 (−15.6 to 1.3); 2004:11.6 (3.7 to 20.0); 2009:8.2 (−0.3 to 16.9)). Conclusions The national programme between 1999 and 2009 was not successful in reducing inequality in four key indicators of health status and future health risk among children and young people. Some inequality measures for general health, LSI prevalence and smoking increased over this time.