A multiaxial prediction equation of low/medium/high cycle fatigue life of metallic materials for plain and notch components

In this paper, it is important to illustrate that, for the LCF of metallic materials, a “stress quantity” calculated based on the linear-elastic analysis of the studied component is taken to be a mechanical quantity, S, to establish a relation of the mechanical quantity, S, to the fatigue life, N, is practicable. Based on the practicability, a prediction equation, for a low/medium/high cycle fatigue life assessment of metallic materials, is proposed. The prediction equation is a stress invariant based one, in which the computation of stress invariant is on the basis of the linear-elastic analysis of the studied component. Using experimental data of plain specimens reported in literature, it is proved that the prediction equation is both accurate and high efficient. In addition, the prediction equation in conjunction with the Theory of Critical Distances and linear-elastic notch mechanics are combined to establish the fatigue life estimation equation of the notched components. Finally, using experimental data of the fatigue life of 16MnR steel, validation verification of the notch fatigue life prediction equation is given.

Novel Method of Contactless Sensing of Mechanical Quantities

This article addresses the method of sensing mechanical quantities, in particular force and pressure, without the electrical connection of the sensing element and the electronics. The information about the mechanical quantity is transmitted only by evaluating the changes in the electromagnetic field created around the sensor. The sensor is designed on the basis of a flexible micro-electro-mechanical element (MEMS), the resonance of which carries the information about the measured quantity.

Electrostatic Potential at Nuclei

The chapter surveys mostly original work of the authors on the application of the electrostatic potential at nuclei (EPN) as a reactivity index in quantifying hydrogen bonding as well as different reactions of organic compounds. The EPN index was defined and introduced by E. B. Wilson (1962). However, it was first applied as a reactivity index much later in works from our laboratory (Bobadova-Parvanova & Galabov, 1998; Galabov & Bobadova-Parvanova, 1999; Dimitrova, Ilieva, & Galabov, 2002; Cheshmedzhieva, Ilieva, Hadjieva, Trayanova, & Galabov, 2009; Galabov, Cheshmedzhieva, Ilieva, & Hadjieva, 2004; Galabov, Ileiva, & Schaefer, 2006; Galabov, Nikolova, Wilke, Schaefer, & Allen, 2008; Galabov, Ilieva, Hadjieva, Atanasov, & Schaefer, 2008; Koleva, Galabov, Wu, Schaefer, & Schleyer, 2009). Numerous applications showed that the EPN index, an accurate quantum mechanical quantity, predicts with remarkable accuracy the energy shifts accompanying hydrogen bonding. The theoretically evaluated EPN descriptor correlates also excellently with experimental and theoretically evaluated kinetic parameters for a number of important organic reactions. Based on these findings an efficient computational approach for the evaluation of substituent constants was developed.

Electrostatic Potential at Nuclei

Numerous applications showed that the EPN index, an accurate quantum mechanical quantity, predicts with remarkable accuracy the energy shifts accompanying hydrogen bonding. The theoretically evaluated EPN descriptor correlates also excellently with experimental and theoretically evaluated kinetic parameters for a number of important organic reactions. Based on these findings an efficient computational approach for the evaluation of substituent constants was developed.

Testing Different Hypotheses of Vascular Homeostasis Based on Mechanical Stress or Strain in Image-Based Models Using an Inverse Method

Various hypotheses are previously suggested to describe the tendency of vascular tissue to adapt in response to alterations in mechanical stimuli. It is still a matter of controversy which mechanical quantity governs or correlates well with the adaptation, contributing to the mechanical homeostasis. A computational tool that can distinguish between different hypotheses under various physiological conditions may help better understanding of the governing rules. Recently, an inverse optimization method has been developed to estimate the optimal spatial distributions of arterial wall thickness and material anisotropy of image-based models while satisfying a homeostatic condition assumed [1]. The same numerical method can be utilized to investigate the consequent optimal structures resulting from different hypotheses for the mechanical homeostasis. We consider three hypotheses for a homeostatic state based on intramural stress or cyclic stretch and examine their effects on the optimized distributions of thickness and anisotropy. The results show the capability of the presented method in discriminating different hypotheses of vascular homeostasis with image-based models, the validity of which requires more experimental data.

A REVIEW OF VOLUME CHANGES IN RUBBERS: THE EFFECT OF STRETCHING

Elastomeric materials are subjected to significant change in volume during their deformation. This paper proposes to review the change in volume of stretched rubber and to highlight why volume change can be considered as a relevant mechanical quantity to characterize rubbery materials in terms of microstructure evolution. The first part of the present review examines experimental measurements of volume change reported from the end of the 19th century until now. The second part reports the models proposed to predict the change in volume of stretched rubbers. These are formulated for small deformations. Some of them account for the decrease in volume due to crystallization.