J. Setién

Automated measurement of magnesium/calcium ratios in gastropod shells using laser-induced breakdown spectroscopy for paleoclimatic applications

The chemical composition of mollusk shells offers information about environmental conditions present during the lifespan of the organism. Shells found in geological deposits and in many archeological sites can help to reconstruct past climatic conditions. For example, a correlation has been found between seawater temperature and the amount of some substituent elements (e.g., magnesium, strontium) in the biogenerated calcium carbonate matrix of the shell, although it is very species-specific. Here we propose the use laser-induced breakdown spectroscopy (LIBS) to estimate Mg/Ca ratios in modern specimens of the common limpet Patella vulgata. An automated setup was used to obtain a sequence of Mg/Ca ratios across a sampling path that could be compared with the seawater temperatures recorded during the organism’s lifespan. Results using four shells collected in different months of the year showed a direct relationship between the Mg/Ca ratios and the seawater temperature, although the sequences also revealed small-scale (short-term) variability and an irregular growth rate. Nevertheless, it was possible to infer the season of capture and the minimum and maximum seawater temperatures from the LIBS sequences. This fact, along with the reduction in sampling and measurement time compared with other spectrometric techniques (such as inductively coupled plasma mass spectrometry [ICP-MS]), makes LIBS useful in paleoclimatic studies.

Evolution of mechanical behaviour in a structural steel subjected to high temperatures

Abstract In this work a study of how exposure to high temperatures can affect the mechanical properties of a structural steel is presented. To this end, several mechanical tests such as tensile, impact and microhardness tests have been carried out in order to compare the properties of the heat-exposed steel with those of an unaffected reference steel. Complementary compositional, metallographic and fractographic analyses have also been performed to try to cast some light on the problem. The results obtained allow us to extract some conclusions on the reutilization of the steel for structural applications.

Cracking diagnostics of brake pedals during press forming operations

Abstract In this work a study of the cracking problems arising in manufacturing of steel brake pedals by press forming is presented. Cracks were detected in critical zones of the part revealing a possible lack of ductility in the constitutive material. In order to overcome this problem, a detailed study of the behaviour of the steel used has been carried out. In this way, mechanical characterization as well as microstructural analysis were performed over both cracked and uncracked pedals. The results obtained from this comparative analysis showed different microstructural features and, consequently, the dissimilar mechanical behaviour can be justified.