Characterization of a Crack by the Acoustic Emission Signal Generated During Propagation

AbstractAcoustic Emission (AE) generates at different space and time scales ranging from the rupture of atomic bonds to seismic failure. Seismic and AE information are complementary concerning their application and their theoretical grounds. Following previous work we simulate the AE generated at a crack propagating in a bulk material by means of a model coming from Geophysics. The duration, the rise time and the relative amplitude of the AE burst are estimated with the model, and they are related to characteristics of the source. The crack length is estimated by means of the Fourier spectrum of the signal. The objective of the present paper was to apply the model to laboratory fragile samples in order to verify its validity at very different scales. The selected fragile material was methyl methacrylate because the length of fractures could be obtained with high precision. Different tests were performed varying the applied tensile stress. Experimental and modeled AE spectra due to fracture were quite similar. Modeled and measured crack length values were of the same order of magnitude

Authentication and Authorization of Users and Services in Dynamic Military SOA Environments

The problem of user authentication and authorization is usually being solved in a single system. Federated environment assumes heterogeneity of systems, which brings the problem of mutual users and services authentication and authorization. In this article the authors presented security requirements for cross domain information exchange in federated environments and a method of secure access to information resources on the basis of web services. Special attentionwas paid to authentication and authorization of users and services. As opportunities, there were presented solutions verified in multinational experimentations and exercises