Strength properties and density of SO2 polluted spruce wood

Spruce wood from two sites in the East Ore mountains in Germany with more a nd less strong SO2 pollution during approximately 1935 and 1992 respectivel y, was studied as to its mechanical properties (fracture toughness, acousti c emission (AE)) as well as its density and annual ring width changes. Earl ywood and latewood width and density were measured with X-ray densitometry equipment. The mechanical tests were performed with specimens taken from th e same trees using the wedge splitting technique. Using notched, rectangula rly shaped specimens, the experiments allowed to determine the notch-tensil e strength sigma(NTS) Of each yearring in RL orientation separately by diff erentiating earlywood and latewood. The results show clear correlations bet ween earlywood density and notch-tensile strength, good, inverse correlatio n to some extent between ring width and sigma(NTS) and also between AE emis sion activity and earlywood width for the less polluted trees. Data scatter ing with resulting less pronounced trends was found for all parameters meas ured for the more severely polluted trees. The results and correlations all ow assuming that sigma(NTS) is influenced by the SO2 pollution to some exte nt via treering growth (ring width) and density. The results point to a mor e pronounced influence of SO2 pollution between approximately 1970 and 1985 than before that time, and a subsequent recovery of the tested wood proper ties in the trees that had survived this period.