Lifetime prediction in creep-fatigue environment
The creep-fatigue interaction has been studied and innovative mathematical models are proposed to predict the operating life of aircraft components, specifically gas turbine blades subject to creep-fatigue at high temperatures. The historical evolution of the creep-fatigue lifetime prediction is given in order to place the present study in the context. A literature review of the life estimation under creep-fatigue environment is presented.
SERVICE-LIKE THERMO-MECHANICAL FATIGUE TESTS FOR THE LIFETIME ASSESSMENT OF TURBINE COMPONENTS
A key requirement for modern power generation turbines is a flexible operating capability. One of the main objectives in the design optimization of modern plant is to reduce the time required to reach rated values of power generation during turbine start-up. Significant transient thermal stresses can lead to a complex creep-fatigue damage condition, which has to be evaluated in the lifetime assessment of modern turbine components. Thermo-mechanical fatigue (TMF) tests have been performed in order to characterize the constitutive behaviour and the endurance characteristics of a 1%CrMoV rotor steel. The temperature and mechanical strain control profiles adopted during test were selected to represent conditions which could occur at critical locations in a high temperature turbine rotor. Specific features of the service-like TMF cycles were low strain rates (in the range of 10 /s) and significant hold periods at the peak cycle temperature. The results of the TMF tests are presented with particular attention to the endurance characteristics of the material. In all the tests performed, a local amplification of the strain range accompanied by ratcheting occurred in the central portion of the specimen gauge length, leading to a progressive section reduction (necking). The causes of this phenomenon are explored and the consequences on the endurance characteristics are analyzed. The endurances measured in the TMF tests are rationalised on the basis of (i) the results of the post-test metallurgical analysis and (ii) the calculation of fatigue and creep damage components. Different methods of damage calculation for creep-fatigue interaction are applied and compared in their predictive capabilities. Based on this analysis, recommendations for turbine component lifetime calculation are proposed.
Impact of cancer-related fatigue on the lives of patients: new findings from the Fatigue Coalition.
PURPOSE
This survey was designed to confirm the prevalence and duration of fatigue in the cancer population and to assess its physical, mental, social, and economic impacts on the lives of patients and caregivers. Patients and Methods. A 25-minute telephone interview was completed with 379 cancer patients having a prior history of chemotherapy. Patients were recruited from a sample of 6, 125 households in the United States identified as having a member with cancer. The median patient age was 62 years, and 79% of respondents were women. Patients reporting fatigue at least a few times a month were asked a series of questions to better describe their fatigue and its impact on quality of life.


RESULTS
Seventy-six percent of patients experienced fatigue at least a few days each month during their most recent chemotherapy; 30% experienced fatigue on a daily basis. Ninety-one percent of those who experienced fatigue reported that it prevented a "normal" life, and 88% indicated that fatigue caused an alteration in their daily routine. Fatigue made it more difficult to participate in social activities and perform typical cognitive tasks. Of the 177 patients who were employed, 75% changed their employment status as a result of fatigue. Furthermore, 65% of patients indicated that their fatigue resulted in their caregivers taking at least one day (mean, 4.5 days) off work in a typical month. Physicians were the health care professionals most commonly consulted (79%) to discuss fatigue. Bed rest/ relaxation was the most common treatment recommendation (37%); 40% of patients were not offered any recommendations.


CONCLUSIONS
Cancer-related fatigue is common among cancer patients who have received chemotherapy and results in substantial adverse physical, psychosocial, and economic consequences for both patients and caregivers. Given the impact of fatigue, treatment options should be routinely considered in the care of patients with cancer.