Showing papers on "Durability published in 1983"

Probabilistic Fracture Mechanics Analysis Methods for Structural Durability

Abstract: : The United States Air Force requires that Air Force aircraft be designed to be durable. This requirement necessitates an analytical demonstration that excessive cracking within the airframe will not occur during the aircraft's design service life. In order to predict the time at which excessive cracking occurs, an analysis is needed which is capable of predicting the distribution of crack sizes within the airframe at any point in time. Such an analysis was recently developed and is presented in this paper. The durability analysis is based on a fracture mechanics philosophy, combining a probabilistic format with a deterministic crack growth rate relationship. Essential elements of the methodology are presented, with emphasis on the statistical representation of the initial fatigue quality of the structure. The accuracy of the durability analysis is demonstrated by correlating analytical predictions with experimental results of a fighter full-scale test article as well as complex-splice specimens subjected to a bomber load spectrum.

Durability of Some Glass Fiber Reinforced Cement Composites

Abstract: A number of glass fiber reinforced cement composites currently on the market were investigated with regard to the alteration of mechanical properties over time. Among these were several so-called alkali-resistant glass fibers (AR-GFRC) and a system consisting of E-glass fibers with a polymer-modified cement matrix (Forton (P)GFRC) . Properties such as strain at ultimate tensile stress, bending strength, and impact strength were initially higher for the AR-GRFC than for the (P)GFRC. However, the AR-GFRC system showed a considerable decrease of these properties over time, resulting over the long term in a lower level than for (P)GFRC.

Dielectric switch arrangement

Abstract: At the boundary area of a dielectric waveguide, the total reflection of an electromagnetic wave is disturbed by contact with an object (e.g. a finger). A switching function is triggered by the concomitant drop in intensity of the electromagnetic wave. The dielectric switch arrangement has several advantages over conventional switch arrangements: greater durability, low-cost basic materials, few manufacturing stages, possibility of use even under difficult environmental conditions. A transparent design of the switch arrangement opens up new application possibilities.

Methanol Engine Durability

Abstract: Engine durability refers to the ability of an engine to function properly and reliably over an extended period of time. Engine durability is a major remaining technical hurdle prior to expanding the use of methanol fuel. This paper will present engine durability data derived from the California Energy Commission's continuing Alcohol Fleet Test Program, review this data in relationship to previously reported engine durability information, discuss some of the possible reasons for observed effects, and suggest design considerations for further improvement in methanol engine durability.

Three decades of durability

Abstract: Correlation between small-scale, comparatively short term, static, non-interactive, laboratory investigations into concrete weathering characteristics and the durability of large-scale, dynamically loaded structures is discussed.

Engine cyclic durability by analysis and material testing

Abstract: The problem of calculating turbine engine component durability is addressed. Nonlinear, finite-element structural analyses, cyclic constitutive behavior models, and an advanced creep-fatigue life prediction method called strainrange partitioning were assessed for their applicability to the solution of durability problems in hot-section components of gas turbine engines. Three different component or subcomponent geometries are examined: a stress concentration in a turbine disk; a louver lip of a half-scale combustor liner; and a squealer tip of a first-stage high-pressure turbine blade. Cyclic structural analyses were performed for all three problems. The computed strain-temperature histories at the critical locations of the combustor linear and turbine blade components were imposed on smooth specimens in uniaxial, strain-controlled, thermomechanical fatigue tests of evaluate the structural and life analysis methods.

Adhesive bonding of aluminium

Abstract: Adhesive bonding of aluminium is widely used in the aerospace industry. High initial bood strengths can be obtained, but bond failure occurs atter prolonged exposure to humid enviroments. The thesis contains details ot a test procedure which has been designed and developed for the assessment of different alloys, pretreatments, and adhesives, which will give adhesively bonded aluminium joints of high strength coupled with long term durability. The test involves assembly of lap shear specimens in a precision jig using 250 ballotini spacers in the adhesive to control the bond line thickness. The test is modified by drilling three accurately located holes through the bonded area after assembly of the joint and curing of the adhesive. Further important features at the test, such as fillet control, are detailed. The test was assessed, modified and developed to give a reliable and reproducible method which would discriminate amongst different bonding systems after exposure to humid test environments. This is the first test to have achieved the discrimination necessary for short term assessment of bond systems where long term durability is required. Even better discrimination has been obtained by applying stress in a stress humidity test. Having established accurate, reliable and discriminating test methods they were used to study the durability of structural epoxy adhesive bonds to aluminium as a function of alloy, pretreatment, adhesive and environment. It was established that the long term durability or adhesively bonded aluminium was directly related to the infulence of water migrating within the adhesive. Pretreatments differed in their ability to prevent hydration of the aluminium oxide by the water absorbed within the adhesive.