Probabilistic fatigue methodology for six nines reliability

Fleet readiness and flight safety strongly depend on the degree of reliability that can be designed into rotorcraft flight critical components. The current U.S. Army fatigue life specification for new rotorcraft is the so-called six nines reliability, or a probability of failure of one in a million. The progress of a round robin which was established by the American Helicopter Society (AHS) Subcommittee for Fatigue and Damage Tolerance is reviewed to investigate reliability-based fatigue methodology. The participants in this cooperative effort are in the U.S. Army Aviation Systems Command (AVSCOM) and the rotorcraft industry. One phase of the joint activity examined fatigue reliability under uniquely defined conditions for which only one answer was correct. The other phases were set up to learn how the different industry methods in defining fatigue strength affected the mean fatigue life and reliability calculations. Hence, constant amplitude and spectrum fatigue test data were provided so that each participant could perform their standard fatigue life analysis. As a result of this round robin, the probabilistic logic which includes both fatigue strength and spectrum loading variability in developing a consistant reliability analysis was established. In this first study, the reliability analysis was limited to the linear cumulative damage approach. However, it is expected that superior fatigue life prediction methods will ultimately be developed through this open AHS forum. To that end, these preliminary results were useful in identifying some topics for additional study

Loading rate sensitivity of open hole composites in compression

The results are reported of an experimental study on the compressive, time-dependent behavior of graphite fiber reinforced polymer composite laminates with open holes. The effect of loading rate on compressive strength was determined for six material systems ranging from brittle epoxies to thermoplastics at both 75 F and 220 F. Specimens were loaded to failure using different loading rates. The slope of the strength versus elapsed time-to-failure curve was used to rank the materials' loading rate sensitivity. All of the materials had greater strength at 75 F than at 220 F. All the materials showed loading rate effects in the form of reduced failure strength for longer elapsed-time-to-failure. Loading rate sensitivity was less at 220 F than the same material at 70 F. However, C12000/ULTEM and IM7/8551-7 were more sensitive to loading rate than the other materials at 220 F. AS4/APC2 laminates with 24, 32, and 48 plies and 1/16 and 1/4 inch diameter holes were tested. The sensitivity to loading rate was less for either increasing number of plies or larger hole size. The failure of the specimens made from brittle resins was accompanied by extensive delaminations while the failure of the roughened systems was predominantly by shear crippling. Fewer delamination failures were observed at the higher temperature

Extended follow-up of a phase 2 trial of bortezomib alone and in combination with dexamethasone for the frontline treatment of multiple myeloma

P>High-quality response to multiple myeloma (MM) therapy can be predictive for improved outcomes. Novel agents may improve the depth of responses and therefore prolong survival. We report on the extended follow-up of a phase II study in frontline MM of bortezomib alone and in combination with dexamethasone. Forty-nine previously untreated, symptomatic MM patients received bortezomib 1 center dot 3 mg/m(2), days 1, 4, 8, 11, for up to six 3-week cycles. High-dose dexamethasone was added for patients not reaching either a partial response after cycle 2 or a complete response (CR) after cycle 4. The overall response rate in 48 evaluable patients was 90%, with 42% achieving at least a very good partial response, of which 19% were CR/near CR. Thirty-six patients received high-dose dexamethasone with 28 (77%) showing improved response. Twenty-seven patients have undergone successful stem-cell transplantation (SCT). After median follow-up of 49 months, 15 patients have died; median overall survival has still not been reached, with an estimated survival at 4 years of 67%. Overall survival with and without SCT was not different (P = 0 center dot 54). Grade 3/4 adverse events included neutropenia (10%), sensory neuropathy (6% grade 3), neuropathic pain (4% grade 3), and diarrhoea (4% grade 3). Bortezomib +/- dexamethasone is an effective and well-tolerated induction regimen for the frontline treatment of MM