Staff

Abstract:
This paper evaluates the efficacy of a patented grip for high-temperature fatigue testing by establishing the S-N curve for full-scale nickel-based turbine blades under simulated environmental conditions. Initially, a bending test assessed the stress-displacement characteristics of the component. This was followed by a series of fatigue tests at 950°C, using cyclic bending with force amplitudes from 5.2 kN to 6.6 kN and a constant frequency of 10 Hz. The setup, integrating the grip into a standard testing machine,
proved effective for high-temperature tests and successfully determined the service life of full-scale components.

Keywords:
fatigue,high temperature,turbine blade,full-scale fatigue test

Abstract:
Nonlinear properties of metal matrix composites (MMCs) are studied. The research combines results of loading-unloading tensile tests, microstructural observations and numerical predictions by means of micromechanical mean-field models. AA2124/SiC metal matrix composites with SiC particles, produced by the Aerospace Metal Composites Ltd. (AMC) are investigated. The aluminum matrix is reinforced with 17% and 25% of SiC particles. The best conditions to evaluate the current elastic stiffness modulus have been assessed. Tensile tests were carried out with consecutive unloading loops to obtain actual tensile modulus and study degradation of elastic properties of the composites. The microstructure examination by scanning electron microscopy (SEM) showed a variety of phenomena occurring during composite deformation and possible sources of elastic stiffness reduction and damage evolution have been indicated. Two micromechanical approaches, the incremental Mori–Tanaka (MT) and self-consistent (SC) schemes, are applied to estimate effective properties of the composites. The standard formulations are extended to take into account elasto-plasticity and damage development in the metal phase. The method of direct linearization performed for the tangent or secant stiffness moduli is formulated. Predictions of both approaches are compared with experimental results of tensile tests in the elastic–plastic regime. The question is addressed how to perform the micromechanical modelling if the actual stress–strain curve of metal matrix is unknown.

Keywords:
metal matrix composites, tension with unloadings, damage, microstructure, non-linear effective properties

Abstract:
Praca dotyczy oceny możliwości identyfikacji zmian twardości warstw nawęglanych i hartowanych indukcyjnie z wykorzystaniem metody prądów wirowych. Badania przeprowadzono na trzech zestawach próbek ze stali AMS 6414 o różnej grubości warstwy, poddanych hartowaniu indukcyjnemu oraz odpuszczaniu w szerokim zakresie temperatury, w celu uzyskania różnic w twardości warstwy dla każdego zestawu. Próbki każdego zestawu, z warstwami o twardości w zakresie 760-920 HV, poddano badaniom z zastosowaniem prądów wirowych, polegających na ocenie zmian kąta fazowego uzyskanego w efekcie oddalenia (lift - off). Przeprowadzono także standardowe pomiary twardości na powierzchniach warstw hartowanych oraz wykonano profile mikrotwardości na przekrojach próbek. Wyniki pomiarów twardości poddano analizie porównawczej z wynikami badań nieniszczących i na tej podstawie stwierdzono możliwość identyfikacji zmian twardości warstw.

Keywords:
nawęglanie i hartowanie indukcyjne, prądy wirowe, nieniszcząca ocena zmian twardości