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.
On improvement of cast iron brake discs for heavy vehicles
Disc brakes are commonly used in motorcycles, passenger cars, commercial vehicles, heavy-duty vehicles, passenger trains and landing gears of airplanes. Depending on the application, a wide variety of brake discs have been developed, with a multitude of designs, geometries and materials. The brake disc materials used for heavy-duty vehicles are still mostly based on traditional grey cast iron, due to its favourable performance and low cost. Gradual improvements of the thermal and mechanical properties of grey cast iron for production of brake discs have been introduced over the years through fine-tuning of the alloying elements. Nevertheless, because of a material behaviour that comprises non-linear elasticity and non-symmetric yield stress in tension and compression, the mechanical properties of grey cast iron are not as well established as those of steel or aluminium alloys.

The subject of the present work is a better understanding of the mechanisms that control the life of cast iron brake discs. In the end, the aim is an enhanced vehicle performance and reduced maintenance costs of heavy-duty vehicles. First, a state of the art survey has been carried out with a review of brake disc technology and mechanisms related to brake disc life. Second, full-scale brake dynamometer experiments have been carried out and analysed, with brake discs made from eight different grey cast iron alloys, at controlled torque, speed and cooling conditions. Crack propagation and disc temperatures have been studied. Disc temperatures were recorded by use of a thermocamera and embedded thermocouples. Detailed analyses were performed on temperature data to clarify characteristics of the tested brake discs. The main phenomena influencing the life of brake discs were identified, and the spatial fixation of bands and/or hot spots was found to have a major impact on disc life.

Third, a constitutive model useful for grey cast iron was implemented for use with a commercial finite element software. The model was calibrated for temperatures relevant for braking applications using dedicated isothermal tests and, finally, validated against monotonic tensile tests, isothermal fatigue tests and thermomechanical fatigue tests. Fourth, a parametric study was performed to explore potential improvements of the cooling channels of a brake disc design when considering an established fatigue criterion. The thermal loading of the brake discs was chosen to represent the full-scale experiments. In the end, a response surface methodology was applied to optimize six types of cooling arrangements (one with straight vanes and five with different numbers of pillar rows) in order to minimize brake disc mass and/or maximize fatigue life.

Finally, fifth, some fatigue life models useful for grey cast iron were calibrated and used to assess brake disc design. In the calibration process, results from both isothermal and thermomechanical experiments were exploited. The life models were used to study the reference brake disc.
The influence of daytime inactivity and nighttime restlessness on cancer-related fatigue.
PURPOSE/OBJECTIVES
To identify indicators involving circadian activity/rest cycles associated with higher levels of cancer-related fatigue (CRF) during the first three chemotherapy cycles after surgery for stage I/II breast cancer.


DESIGN
Prospective, descriptive, repeated measures.


SETTING
Midwestern oncology clinics and subjects' homes.


SAMPLE
72 women, ages 33-69 and free of unstable chronic illnesses, entered the study. Complete data were obtained from 30-47 subjects at each time.


METHODS
CRF was measured using the Piper Fatigue Scale at the start and midpoint of each chemotherapy cycle. Circadian activity/rest indicators were obtained using Mini-Motionlogger wrist actigraphs for 96 hours at the start of each treatment and for 72 hours at the midpoint of each chemotherapy cycle.


MAIN RESEARCH VARIABLES
Fatigue and circadian activity/rest indicators.


FINDINGS
Women who were less active and had increased night awakenings reported higher CRF levels at all three cycle midpoints, with the strongest association being number of night awakenings. During the third chemotherapy cycle, women who were less active during the day, took more naps, and spent more time resting during a 24-hour period experienced higher CRF.


CONCLUSIONS
Women whose sleep is disrupted at cycle midpoints are at risk for CRF. The cumulative effects of less daytime activity, more daytime sleep, and night awakenings are associated with higher CRF levels.


IMPLICATIONS FOR NURSING PRACTICE
Assessment of CRF and night awakenings at the midpoints of each chemotherapy cycle and development of nursing interventions to promote daytime activity and nighttime rest are key to managing fatigue and preventing loss of biologic rhythmicity.