Damage progression in compressively loaded laminates containing a circular cutout

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76038/1/AIAA-10597-113.pd

Determination of Short Crack Depth with an Acoustic Microphone

For the prediction of the lifetime of any component, subjected to alternating stresses, the knowledge of the growth behavior of defects is essential. Most methods of monitoring the propagation of short cracks are confined to measuring the length of the crack on the surface [1]. The depth of the crack must be determined indirectly, assuming the shape of the crack. Acoustic waves, on the other hand, offer the possibility of measuring the depth directly, since acoustic waves can penetrate into the material. This allows the measurement not only of the growth behavior of fatigue cracks on the surface, but also changes of the crack geometry inside the specimen. Current applications of direct acoustic monitoring of crack growth have been developed for cracks of the order of millimeters. One acoustic depth measurement technique is the Time-of-Flight-Diffraction (TOFD) technique [2–4], which is based on timing measurements of the scattered signals from the defect. Our investigations are concerned with the application of TOFD technique for the depth measurement of short cracks (70–200 μm in surface length) using a scanning acoustic microscope (SAM) [5–6]. Depth measurements were first carried out on cracks in the transparent material polystyrene. This allows a direct comparison between acoustic and optical depth measurements. Subsequently, the depth of fatigue cracks in an A1 alloy were measured, and the acoustic measurements were compared with direct measurements of the crack geometry by sectioning the crack

Hydrothermal interaction of solid wafers of Topopah Spring Tuff with J-13 water and distilled water at 90, 150, and 250{sup 0}C, using Dickson-type, gold-bag rocking autoclaves

The Nevada Nuclear Waste Storage Investigations Project has conducted experiments to study the hydrothermal interaction of rock and water representative of a potential high-level waste repository at Yucca Mountain, Nevada. The results of these experiments help define the near-field repository environment during and shortly after the thermal period that results from the emplacement of nuclear waste. When considered in conjunction with results contained in companion reports, these results can be used to assess our ability to accelerate tests using the surface area/volume parameter and/or temperature. These rock-water interaction experiments were conducted with solid polished wafers cut from both drillcore and outcrop samples of Topopah tuff, using both a natural ground water and distilled water as the reacting fluid. Pre- and post-test characterization of the reacting materials was extensive. Post-test identification and chemical analysis of secondary phases resulting from the hydrothermal interactions were aided by using monoliths of tuff rather than crushed material. All experiments were run in Dickson-type, gold-bag rocking autoclaves that were periodically sampled at in situ conditions. A total of nine short-term (up to 66-day) experiments were run in this series; these experiments covered the range from 90 to 250{sup 0}C and from 50 to 100 bar. The results obtained from the experiments have been used to evaluate the modeled results produced by calculations using the geochemical reaction process code EQ3/6. 31 refs., 37 figs., 7 tabs

Fundamental Studies Relating to Systems Analysis of Solid Propellants : Progress Report No. 6 - GALCIT 101, Subcontract No. R 69752, January 1, 1960-May 31, 1960

Previous reports of this series have attempted to define some of the important parameters affecting structural integrity of solid propellant rocket grains. Three general areas have been discussed, namely material properties, analytical procedures, and criteria for mechanical failure. This particular report is devoted to failure criteria, including both limiting deformation and fracture. First of all, the characteristic material properties of filled and unfilled elastomers are described, followed by a brief description of current and proposed tests which can be conducted to obtain experimental information relating to these characteristics in such a form that they can be incorporated in structural integrity analyses. In particular, the necessity for multi-axial tests is stressed in conjunction with minor requirements for new experimental equipment. The selection of appropriate fracture criteria is discussed. Most progress, however, can be reported only in criteria for unfilled elastomers for small and large strains where it appears a distortion strain energy density may be used. It is necessary to delay any really definitive remarks upon filled elastomers or actual grain composites, and subsequent use with cumulative damage analyses, until additional experimental data for propellants is forthcoming

Small deformations of supersymmetric Wilson loops and open spin-chains

We study insertions of composite operators into Wilson loops in N=4 supersymmetric Yang-Mills theory in four dimensions. The loops follow a circular or straight path and the composite insertions transform in the adjoint representation of the gauge group. This provides a gauge invariant way to define the correlator of non-singlet operators. Since the basic loop preserves an SL(2,R) subgroup of the conformal group, we can assign a conformal dimension to those insertions and calculate the corrections to the classical dimension in perturbation theory. The calculation turns out to be very similar to that of single-trace local operators and may also be expressed in terms of a spin-chain. In this case the spin-chain is open and at one-loop order has Neumann boundary conditions on the type of scalar insertions that we consider. This system is integrable and we write the Bethe ansatz describing it. We compare the spectrum in the limit of large angular momentum both in the dilute gas approximation and the thermodynamic limit to the relevant string solution in the BMN limit and in the full AdS_5 x S^5 metric and find agreement.Comment: 40 pages, amstex, 4 figures. V2: Corrected eqn (2.14) and some equations in section 5. Version to appear in JHE

Fundamental Studies Relating to Systems Analysis of Solid Propellants : Progress Report No. 5 - GALCIT 101, Subcontract No. RU- 293, October l, 1959-December 31, 1959

Previous reports of this series have attempted to define some of the important parameters affecting the structural integrity of solid propellant rocket grains. Three general areas have been discussed, namely material properties, analytical procedures, and criteria for mechanical failure. This particular report is devoted to a more detailed examination of the properties of a filled viscoelastic resin, and their representation by appropriate mechanical models. In addition, a comparison of two methods of computing viscoelastic strains in a pressurized cylinder is presented. In the category of material properties, linear viscoelastic model theory is reviewed, and certain important relations among sets of experimental data are deduced. A justification for the application of this theory is provided by the analytic representation of available dynamic data in terms of a well-known distribution function. Since the inception of this work additional experimental data on propellants has become available. In the category of analytical procedures, the usual approach of representing material properties by a four-element model, as determined from the dynamic data in a limited frequency range, is compared with the more sophisticated Fourier transform method in which the entire frequency range is utilized. The two approaches are applied to calculate the viscoelastic hoop strain at the inner boundary of an internally pressurized infinitely long hollow cylinder subjected to a ramp-type pressure pulse. In this example, the dilatation is assumed elastic or frequency independent and the distortion viscoelastic. In the following quarter, primary effort will be devoted to the determination of a criterion for mechanical failure of propellants. Two steps are involved. One is the analytical representation of ultimate strain as a function of temperature on strain rate by means of a mechanical model. In addition to the usual distribution of relaxation (or retardation) times, this model will be supplied with a distribution of ultimate strain. Step two involves the choice of a suitable criterion for compounding ultimate strain or ultimate stress components into a single parameter, which, when exceeded at a given rate and temperature, denotes the onset of fracture or mechanical failure

Viscoelastic hinge formation in beams

A constitutive equation for nonlinear viscoelasticity is used to model the mechanical response of solid polymers such as polycarbonate. The nonlinearity arises from a reduced time variable which causes stress relaxation to occur faster as strain increases. This constitutive equation is used to study the consequences of the interaction of the acceleration of stress relaxation with strain and the spatial variation of strain within the context of the structural theory of beams undergoing small displacements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41706/1/707_2005_Article_BF01182510.pd