Calculation of fatigue limits of case-hardened specimens with consideration of mean stresses and residual stresses

 The strength of case-hardened parts under cyclic loading can be determined in an experimental manner, but this can produce a large amount of costs due to the expenditure of material and testing time. Therefore, a calculation method is developed, that strongly reduces the number of experiments. The presented model is based on Weibull's weakest-link concept and allows to compute the survival probability of a case-hardened part which is loaded close to the fatigue limit. The essential quantities in this model are the distribution of Vicker's hardness of the material, the exponents of the Weibull distribution of the volume and the surface, the residual stress state, the surface roughness and the surface oxidation depth. By integrating the survival probabilities of the surface and the volume, the survival probability of the entire specimen or part can be calculated, which allows to compute the fatigue limit. The necessary parameters have to be determined from reference specimens. The model is successfully examined by comparing experimental and calculated results of smooth and notched case-hardened specimens under alternating torsion, rotating bending, repeated tension and tension-compression. Received 20 August 2001 / Accepted 11 November 2001     

A Multicriteria Approach to Data Summarization Using Concept Ontologies

This paper describes a conceptual and theoretical framework to allow better user control over data summarization for knowledge discovery. Basic to the approach is a measure of quality of summarization of data using categories provided by the hierarchical structure of concept ontology. This involves the modeling, using a fuzzy sets approach, of the four criteria implicit in a summarization imperative: minimum coverage, minimum relevance, succinctness, and usefulness. With these criteria modeled, a multicriteria approach is presented, using a decision function aggregating these criteria that provides an overall quality measure to guide the summarization of the data. The development of the theory is first presented for the simple case of a single attribute to clearly delineate the basic issues and approach and then extended to multiple attributes. Finally, approaches to provide a more user-oriented presentation of the summarized data are considered     

Relationship between platelet cyclooxygenase pathway and plasma malondialdehyde-like material

Thrombin-induced platelet malondialdehyde (MDA) formation and plasma malondialdehyde-like material (MDA-LM) were evaluated in 12 healthy subjects before and after 1 and 7 days from aspirin (1 g) ingestion. 24 hr after aspirin administration, platelet MDA was almost abolished while MDA-LM showed a 23% decrease. Platelet MDA and plasma MDA-LM returned to baseline values 7 days after aspirin ingestion. These data suggest that platelet cyclooxygenase pathway affects only in part plasma MDA-LM. The evaluation of plasma MDA-LM before and after aspirin could be useful for evaluating in vivo platelet cyclooxygenase activation.     

Further studies on elastic-plastic stable fracture utilizing the T integral

Herein, the T^* fracture parameter is shown to have relevance to the mechanics of elastic-plastic fracture. Specifically, it is shown to have certain advantages over the currently established plastic fracture parameters such as J and CTOA. Finite element analyses of experimental data were carried out as a means to obtain a comparison of the effectiveness of the plastic fracture parameters. T^* is clearly superior. A note on problems associated with satisfying the plastic incompressibility constraint is also included.     

A novel system for mammary epithelial cell culture

A method is described for the isolation and density gradient enrichment of mammary epithelial fragments from pregnant, nonlactating bovine tissue. Immunocytochemical analysis prior to and following culture revealed specific staining with antibodies to keratin, indicating that these cells are epithelial in nature. Fragments enriched for epithelium could be stored in liquid nitrogen for extended periods prior to culture. When cast within a three-dimensional matrix of collagen gel, the mammary fragments grew as branching, duct-like structures and displayed a 4-fold increase in cell number during 10 to 12 d of culture.     

The automated simulation of dynamic non-linearity to shot-peening mechanics

This paper gives an automated simulation of dynamic non-linearity to shot-peening mechanics. Three-dimensional constitutive material law expressed in the stress invariants is used along with the nonlinear analysis based on the concept of initial stress. Residual stresses, strains, displacements and plasticity can be calculated using information in Gauss integration points. The ultimate load is reached when the algorithm does not converge. The corresponding failure modes can be interpreted as those for which as state of equilibrium is no longer possible. The final results obtained the shakedown diagrams plotted in three dimensions. The history of these diagrams is self-explanatory.     

A new technique for on-line and off-line high speed computation

A novel technique for both online and offline computation is presented. With this technique, a reconstruction analysis in elementary particle physics, otherwise prohibitively long, has been accomplished. It will be used online in an upcoming Fermilab experiment to reconstruct more than 100000 events per second and to trigger on the basis of that information. The technique delivers 40 gigaoperations per second, has a bandwidth on the order of gigabytes per second, and has a modest cost. An overview of the program, details of the system, and performance measurements are presented