A. Del Puglia

A mathematical model of heat transfer processes in hardening high vacuum furnaces

Abstract The present work illustrates the scheme adopted as well as its consequent calculation process to stimulate the behaviour of samples of different steels (AISI 316, X210 Cr 13 KU, 88 MnV 8 KU) during a complete thermal cycle carried out in high vacuum furnaces. The results which were obtained by numerical simulation are compared with the corresponding experimental data.

Bithermal Fatigue Testing: Experimental and Prediction Problems

The need of thermomechanical fatigue testing is strongly indicated by the actual working conditions of various machine components used at high temperatures. In many cases, temperature is not uniformly distributed on a component and it also changes over the course of time. In these conditions, isothermal testing has been shown to be unsuitable and life prediction must be based on more complex testing procedures.

Fatigue maps and multistage life prediction methods

Abstract Various methods have been recently developed for life prediction under creep-fatigue conditions. This study is concerned with continuous damage models. In particular, a model developed at ONERA, which evaluates the creep and fatigue contributions separately and which sums the corresponding differential damage, has been used for fitting the high-temperature experimental data for IN 738 test bars. The data were taken both from the literature and from our own tests. In addition, it was found that the model can also be used to derive schematic fatigue maps. Following the introduction of Ashby maps for creep, several other maps have been proposed for fatigue. However, the task for fatigue maps is more difficult to define. This work presents a discussion of the whole problem, a review of existing proposals, and some indicative maps that have been obtained for IN 100. Even though the approach appears to be promising for outlining approximate fatigue maps, metallographic observations are still a necessary complement for mapping single domains where given microstructural mechanisms are predominant.

Fatigue Maps and Mean Load Dependences

The influence of mean stress on fatigue life has been investigated for IN 792 at 800° C The results and their interpretation are reported. For the application of a life prediction model, a suitable input parameter has been determined on the basis of the experimental results obtained. Lastly, a creep-fatigue map is illustrated for IN 792 at 800° C.

Mathematical models of phase transformations and shape variations in a mechanical component during high vacuum hardening

Abstract The present paper deals with the mathematical models defined and adopted tostimulate the phase transformation processes and the shape variations in samples of different tool steels subjected to hardening in high vacuum furnaces. The results, which are obtained by numerical simulation, are compared with the corresponding experimental data.