Determination of Yield Point of Structural Materials With Using the Metric Entropy

Abstract

The yield point is one of the basic characteristics of construction materials, which are used in the design engineering calculations. The methods used to determine the yield point is based on the interpretation of the geometric shape of the curve uniaxial tension. This shape is specific for different construction materials and depends among others to the conditions carrying trials. Specific guidelines for determining the yield point were included in the standards specification. The conventionality of procedure concerns especially materials, which, in their deformation characteristic do not have a distinct top of knee. The authors propose an alternative method based on the use of the concept of the metric entropy by Kolmogorov-Sinai. The metric entropy by Kolmogorov-Sinai is used to study the phenomena about a dynamic character. Therefore, this method requires the recording of more number of measuring points: from a few hundred to a dozen thousand, depending on the type of research of constructional materials. A dynamic character of measurement data results from their scatter, which consists of local, non-linear disturbances occurring during deformation of the material and the noise, associated from the action of acquisition path. The aim of the study is to present a more objective method of determining the yield point structural materials, which do not require the use of conventional procedures. The paper presents the results determining of this constant material on the basis of data records monoaxially stretching of tests for metals used in shipbuilding.

Acoustic Emission and K-S Metric Entropy as Methods for Determining Mechanical Properties of Composite Materials

“…Earlier tests carried out on materials showing a clear yield point showed a high agreement of the yield strength values obtained in accordance with the standard and the specified K-S entropy method [ 18 , 19 , 20 , 21 , 22 , 23 ]. On the basis of a series of laboratory tests carried out by the authors of the study for isotropic and anisotropic materials, it was assumed that the application of the K-S method allows to determine the transition of the material from the elastic to the plastic phase.…”

“…Works [ 18 , 19 , 20 , 21 , 22 , 23 ] present an overview of a measurement collection and a diagram for calculating K-S entropy for successive positions of measurement collections containing an n number of items, relative to measurement data.…”

“…The minimum value of metric entropy in the vicinity of the passage from elastic to plastic state is marked by the point that separates individual states of the process. The value of stress corresponding to the passage of the tested material from its elastic to its plastic state is determined on the basis of the “critical” point [ 18 , 19 , 20 , 21 , 22 , 23 ].…”

“…Examples are the graphs of the static tensile test, on the basis of which the internal dynamics of the material deformation process cannot be observed. The dynamics of the tensile deformation process of the sample in the form of chaotically arranged measurement points (especially in the elastic range of the material) can only be observed by significantly enlarging a part of the graph [ 18 , 19 , 20 , 21 , 22 ].…”

Application of metric entropy to determine properties of structural materials

“…The calculations included data sets consisting of several hundred to over a dozen thousand measurement points. Based on the K-S entropy calculations, the report [10] includes determining material constants for metals and the report [11] for composites. Both analyses involved stretching samples, controlled by extensometer signal.…”