Temperature dependent stress distribution in steel sheet around active NiTi inserts

This paper reports selected results of the research motivated by SMA application development in frame of European research project PROSTONE aimed at innovation in stone processing equipment. In many devices used in the stone sector, stress inhomogeneity in machine parts and tools seems to cause problems.

There is an idea to solve the problem of stress concentrations in metallic sheets occurring during operation through the insertion of small prestrained elliptical NiTi elements into elliptical holes in locations of maximum stress concentration which would counteract these stress concentrations.

In order to evaluate the effect of the temperature, compression force and on the stress distribution in the steel plate, three different neutrons strain scanning experiments have been carried out.

1. the effect of a prestrain insert at room temperature,

2. the effect of the temperature with in-situ heating experiment at 3 different temperature (25°C, 50°C, 70°C),

3. the effect of stress and temperature with in-situ compression up to 300MPa at temperature 70°C,

The deep penetration of the thermal neutrons in steel provides average data in the thickness with a gauge volume of about 1 to 8mm³. In the futur a complementary experiment using synchrotron x-ray radiation will performe to achieve high enough spatial resolution necessary for reliable evaluation of the internal stress gradient.